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1、Results from measurements onthe PV-VENT systems atSundevedsgade/TndergadeSolar Energy Centre DenmarkDanish Technological InstituteSEC-R-15DraftSolar Energy Centre DenmarkDanish Technological Institute SEC-R-15Results from measurements onthe PV-VENT systems atSundevedsgade/TndergadeSren stergaard Jen
2、senSolar Energy Centre DenmarkDanish Technological InstituteApril 2001PrefaceThe present report concludes together with (Jensen, 2001) Solar Energy Centre Denmarks(Danish Technological Institute) measuring work in the PV-VENT project. The measuringproject was partly financed by EU via the JOULE proj
3、ect “PV-VENT Low cost energy effi-cient PV-ventilation in retrofit housing”, contract no. JOR3-CT97-0160 and partly by theDanish Ministry of Environment and Energy via the project “PV-VENT”, journal no.51181/97-0021.The project group behind the project was:Cenergia Energy Consultants, DKFortum Energ
4、y (former NESTE-NAPS), SFAirVex Danmark (former Temovex Denmark), DKFSB, DKDanish Technological Institute, DKEcofys, NLPA-Energy, DKNTNU, NCopenhagen Energy, DKThe following persons have participated in the measuring project:Sren stergaard Jensen. M.Sc., Solar Energy Centre DenmarkWilliam Otto, labo
5、ratory technician, Solar Energy Centre DenmarkOle Larsen, laboratory technician, Solar Energy Centre DenmarkLars Molnit, student (B.Sc.), Solar Energy Centre DenmarkBertel Jensen, B.Sc., Solar Energy Centre DenmarkUlrik Mehr, M.Sc., Solar Energy Centre DenmarkHans Olsen. B.Sc., Ventilation and Envir
6、onment, Technological Institute of DenmarkJens Heidelbach Andersen, B.Sc., Cenergia Energy ConsultantsLisbet Michaelsen, B.Sc., Cenergia Energy ConsultantsResults from measurements on the PV-Vent systems at Sundevedsgade/Tndergade1st printing, 1st edition Danish Technological InstituteEnergy divisio
7、nISBN: 87-7756-614-9ISSN: 1600-37802List of content1.Introduction . 31.1.The PV-VENT systems . 61.1.1.Control of the systems . 131.1.2. PV-mixer . 152.Measuring system . 172.1.Air temperature measurements in the solar wall . 172.2.Weather measurements . 192.3.Temperature and flow measurements in the
8、 ventilation system . 192.4.Electrical measurements . 202.5.Data collection . 232.6.Treatment of measured data . 243.Measurements . 253.1.Measurements from week 5 and 6, 2001 . 253.1.1.Thermal part of the system . 253.1.2.PV-part of the system . 273.2.Measurements from specific weeks . 383.2.1.Air f
9、lows . 383.2.2.PV-mixer . 383.3.Calculations based on the measurements and more general conclusions . 403.3.1.The efficiency of the air to air heat exchanger . 403.3.2.Fan power . 513.3.3.Temperatures in the solar wall . 523.3.4.The PV-mixer . 573.4.Obtained and obtainable savings of the system . 60
10、3.4.1.Obtained savings . 603.4.2.Obtainable savings . 644.Conclusions . 704.1.Aims of the PV-VENT project . 704.2.Results from the PV-VENT project . 704.2.1.Architectural results . 704.2.2.Pre-heating of fresh air cooling of PV-panels . 714.2.3.Air to air heat exchanger . 724.2.4.Low fan power . 724
11、.2.5.Direct coupling of PV-panels and fans . 724.2.6.Total systems . 734.2.7.General conclusions . 735.References . 74Appendix A Data sheets for the heat exchangers and fans . 75Appendix BData sheets for the PV-panels . 7831. IntroductionThe objective of the project was to research, develop and test
12、 low cost, high efficiency PV-powered ventilation systems for retrofitting of apartment blocks. Systems where the fans arepowered directly by the PV-panels and where the waste heat from the PV-panels is utilized topre-heat fresh air to the apartments.The present report describes the obtained experie
13、nce from measurements on the PV-VENTsystems installed in an apartment building in the area Vesterbro of Copenhagen, Denmark.The building is situated Sundevedsgade 14/Tndergade 1. The building is part of the Hede-bygade block a site plan of this block is shown in figure 1.1. The Hedebygade block hasd
14、uring the late 90ies been exposed to a major renovation project including extensive utilisa-tion of solar energy.Sundevedsgade 14/Tndergade 1Figure 1.1. The site plan for the Hedebygade block and the location of Sundevedsgade14/Tndergade 1.The five-storied building was erected in 1884 and is typical
15、 for that period. The buildingcontains 20 apartments and has a net floor area of 1137 m. Figure 1.2 shows the facades ofthe building facing the streets after the renovation. The original appearance of the facade hasnot been changed.4Figure 1.2. The facades of the building after the renovation.The dw
16、ellings had before the renovation no bathrooms or central heating, and the piping sys-tem for domestic water and the sewer system were of a poor quality. The flats were poorlyinsulated and the heating system was old-fashioned e.g. wood-burning stoves, electricheating panels or gas heating furnaces.
17、The windows where not tight and there was no venti-lation system in the building. A renovation of the building was thus badly needed.The renovation contained the following items:- total renovation of the interior including new kitchens and bathrooms,- new piping and pluming,- low-energy windows,- in
18、sulation especially against the attic and roof,- new heating system with radiators,- sun spaces in 8 of the dwellings,- balanced ventilation system including the PV-VENT systems with solar walls,- solar air heating system for pre-heating domestic hot water and space heatingFigure 1.3 shows the facad
19、es of the building facing the courtyard after the renovation. Theappearance of these facades is changed considerably compared to the facades facing thestreets. The photo shows the solar walls with PV-panels and the sun spaces.5Figure 1.3. The facades facing the courtyard after renovation.A more deta
20、iled description of the ideas behind the renovation may be found in (Lien andHestness, 1999 and Cenergia, 1999). Here will only the PV-VENT systems briefly be de-scribed.61.1. The PV-VENT systemsFigure 1.4 gives a schematically overview of the ventilation system in the building.Type 1Type 1Type 1Typ
21、e 1Type 1Type 1Type 1Type 1Type 1Type 1Type 1Type 1Type 2Type 2Type 2Type 2Type 2Type 2Type 2Type 2Figure 1.4. Principle of the ventilation system in the building.The ventilation system consists basically of two types of ventilation systems:Type 1: Individual PV-VENT systems with a heat exchanger Jo
22、Vex 175 and fans type 175(56 V dc) (developed by AirVex as part of the project (Jensen and Pedersen, 1999)and appendix A) in each apartment are installed in 12 dwellings: the 8 lowest dwell-ings in Sundevedsgade 14 and the 4 lowest apartment to the right in Tndergade 1.The heat exchangers are locate
23、d on the outside of the exterior wall behind the glazingof the solar walls the spacing between the exterior walls and the cover of the solarwalls is 40 cm. The area of the solar wall per dwelling is 3 1 m in Tndergade 1and 3 1.25 m in Sundevedsgade 14 (height width). In Sundevedsgade 14 two heatexch
24、angers are located site by site at each floor (see figure 1.8), while in Tndergade1 only one heat exchanger is located at each floor (see figure 1.9). The fresh air to theheat exchangers is taken from the solar wall. The fresh air is thus pre-heated by thesolar wall/excess heat from the PV-panels an
25、d by the heat loss through the walls ofthe building. The fresh air to the solar wall is drawn in through a grill at the bottomof the solar wall as shown in figure 1.4-5. The cover of the solar wall consist partlyof the PV-panels and partly of opal glazing (as seen in figure 1.3) in order to hide the
26、heat exchangers behind the glazing and still let solar radiation into the solar walls.During warm days the solar walls may be vented by opening dampers in the solarwalls.heat exchangersolar wall7Figure 1.5. The inlet to one of the solar walls.Figures 1.6-7 show drawings of the solar walls and the su
27、n spaces, while figures 1.8-9 show the location of the heat exchangers in the solar walls. Figure 1.10 shows aphoto of one of the heat exchangers in the solar wall and an entrance door to one ofthe solar walls. Figure 1.11 shows the floor plans before and after the renovation.The total ventilation s
28、ystem of Tndergade 1 to the right is shown in figure 2.5.The ventilation system consists of efficient counter flow heat exchangers and DCfans with a very low electricity demand developed within the project by AirVex(Jensen and Pedersen, 1999) (see also appendix A).The PV-array for each dwelling cons
29、ists of three PV-panels of two different sizes(A1 and A2) in the front of the solar walls as shown in figures 1.3, 1.12 and Appen-dix B and two other sizes (B1 and B2) in the gable of the solar wall on Sundeveds-gade 14 as seen in figure 1.13 (Leppnen, 2000). The dimensions of the panels areA1: 490
30、x 723 mm, A2: 490 x 1122 mm, B1: 907 x 723 mm and B2: 907 x 1122mm (see appendix B). The total peak power per three panels (ie per PV-mixer seelater) is either 121 or 242 Wp. The polycrystalline (c-Si) cells of the PV-panels arelocated with an spacing of 3-4 mm with a translucent lamination film in-
31、between thecells allowing solar radiation to penetrate into the solar wall. The PV-panels weredeveloped by Fortum Energy as part of the project (Leppnen, 1999). The electricityproduced by the PV- panels is directly used to power the fans. However, the PV-panels are not able to power the fans all 24
32、hours of the day, so a so-called PV-mixeris installed to mix PV-power with grid power in order to maintain the necessarypower level for the fans. The PV-mixer is further described in section 1.1.2.Three of the top floor apartments are not as shown in figure 1.4 connected to the so-lar air collector
33、at the roof but obtain the fresh air from the solar walls. Apart fromthis the ventilation systems are type 2 as described below. The three apartments are:the two top floor dwellings in Sundevedsgade 14 and the top floor to the right inTndergade 1.8Figure 1.6. Drawing of the solar wall and sun spaces
34、 at Sundevedsgade 14.Figure 1.7. Drawing of the solar wall and sun spaces at Tndergade 1.9Figure 1.8. Location of the heat exchangers in the solar wall at Sundevedsgade 14.The solar wall of Sundevedsgade 14 has mainly a westerly orientation (20 from west towardssouth), while the solar wall of Tnderg
35、ade 1 has an orientation of 20 from south towardseast.heat exchangerPV panel10Figure 1.9. Location of the heat exchangers in the solar wall at Tndergade 1.heat exchangerPV panelOrbesen damperfor overheatingprotectionOrbesen damperfor overheatingprotection11Figure 1.10. Photo of one of the heat excha
36、ngers in the solar walls and an entrance door to asolar wall.Figure 1.11. Typical floor plan before (to the left) and after (to the right) the renovation.glazing of thesolar wallheatexchangerentrance doorto the solarwall12Figure 1.12. Close up of the PV-panels for one dwelling.Type 2: The ventilatio
37、n systems of the remaining 8 dwellings have also individual heat ex-changers JoVex H300 and fans type 175 (56 V dc) from AirVex (Jensen and Peder-sen, 1999) see also appendix A. These system is not part of the PV-VENT project.The efficiency of the heat exchanger in the type 2 systems has been evalua
38、ted in theproject at Lundebjerg (Jensen, 2001). The heat exchangers are situated inside thedwellings except for the top floor apartments where the heat exchangers are locatedin the attic. These three dwellings are as earlier mentioned connected to the solarwalls.Solar air collector: A solar air coll
39、ector of 19 m is located on the roof of Tndergade 1 asseen in figure 1.13. The solar air collector covers via an air to water heat exchangerpart of the domestic hot water and space heating of the building.This system is nor part of the PV-VENT project.Damper for over-heating protection13solar air co
40、llectorgridconnectedPV-panelsFigure 1.13. The grid connected PV-panels on the south gable of the solar wall on Sunde-vedsgade 14 and the solar air collector array on the roof of Tndergade 1.1.1.1. Control of the systemsThe occupants of the apartments are able to control their ventilation systems via
41、 a controlpanel located in the dwelling figure 1.14 shows a photo of the control panel. According tothe Danish building code the flow rate of exhaust air from a dwelling should be 126 m/h. Thetenants may, however, choose between normal, max and min flow rate and between winterand summer mode as show
42、n in table 1.1. Table 1.1 shows the intended/pre-set air flow ratesin the apartments. The flow rate of exhaust air should always be higher than the flow rate offresh air in order to create a small under pressure in the apartments, which will prevent humidair in being forced into the constructions. I
43、t is as shown in table 1.1 possible to run the venti-lation systems as purely exhaust ventilation (summer mode) in order to prevent pre-heated airfrom the solar wall to enter the dwellings diring periods with no heat demand.The max power consumption of the two fans per dwelling is 45 W each.14Figure
44、 1.14. The control panel from which the occupants of the dwellings may control theirventilation systems.ModeWinterSummerExhaustm/hFresh airm/hExhaustm/hFresh airm/hMax1981161980Normal1261161260Min45-85*40-77*45-85*0Table 1.1. Ventilation modes, which can be chosen via the control panel in the apartm
45、ents.* the minimum ventilation is not identical for the apartments.The systems can during warm periods be run in summer mode which means that no air will bedrawn from the solar walls to the dwellings. The air gap behind the PV-panels may, therefore,overheat which will reduce the electricity producti
46、on of the PV-panels. So in order to cool thePV-panels during these periods Orbesen dampers driven by wax motors are installed in thetop of each of the two solar walls. One damper is further installed at each floor as seen in fig-ure 1.3, 1.9 and 1.12. The dampers start to open at a temperature of 23
47、C and is fully open ata temperature of 27C the dampers starts to close again at a temperature of 24C and areclosed a 21C. When the dampers start to open the PV-panels will be cooled by a buoyancydriven air stream in the air gab.151.1.2. PV-mixerThe dc fans of the ventilation systems are directly con
48、nected to the PV-panels. However, thePV-panels are not during the night and during overcast conditions able to run the fans at therequired speed. A so-called PV-mixer has, therefore, been developed as part of the project.The function of the PV-mixer is to ensure that as much electricity from the PV-
49、panels as pos-sible is used for running the fans. If the PV-power is too low to run the fans the PV-mixer topup with electricity from the grid via a transformer.The development of the PV-mixer was unfortunately delayed. The first company chosen forthe development came up with a solution as late as i
50、n January 2000. The Danish Technologi-cal Institute obtained one sample for evaluation (Mehr, 2000). It was judged that the principlechosen for controlling the power from the PV-panels and the grid didnt give enough credit tothe PV-panels leading to too high power consumption from the grid even if e
51、nough powercould be delivered by the PV-panels. The PV-mixers was further of a very poor quality. Thesoldering of the components looked to be made by a plumber rather than by a electrotechni-cian.The PV-mixer was, therefore, rejected and a new firm for developing the PV-mixer wasfound. They came up
52、with a new design in August 2000 which also was evaluated and furthertested by the Danish Technological Institute (Jensen, 2000). This concept was approved. Thetest results are shown in tables 1.2-4.Supply from PV and gridtest 1test 2test 3unitMeasuredU pv12.1112.2048.10 VoltI pv5.008.003.50 AmpereU
53、 grid54.6054.7055.20 VoltI grid4.103.552.35 AmpereU consumption fans53.4053.7054.20 VoltI consumption fans5.105.155.10 AmpereCalculatedP1 pv + grid284.4291.8298.1 WattP2 consumption fans272.3276.6276.4 WattEfficiency95.894.892.7 %PV ratio22.235.360.9 %Table 1.2. Results from tests of the PV-mixer in
54、 mixed mode.Only supply from gridtest 1unitMeasuredU grid56.10 VoltI grid5.20 AmpereU consumption fans54.90 VoltI consumption fans5.10 AmpereCalculatedP1 grid291.7 WattP2 consumption fans280.0 WattEfficiency96.0 %Table 1.3. Results from tests of the PV-mixer in grid mode.16Only supply from PVtest 1t
55、est 2test 3unitMeasuredU pv12.2412.3047.90 VoltI pv7.9710.057.08 AmpereU consumption fans25.3527.8057.80 VoltI consumption fans3.103.495.30 AmpereCalculatedP1 pv97.6123.6339.1 WattP2 consumption fans78.697.0306.3 WattEfficiency80.678.590.3 %Table 1.4. Results from tests of the PV-mixer in PV mode.Th
56、e tests showed an efficiency of the PV-mixer of between 93 and 96% for mixed PV andgrid mode, which is in the same area of the efficiency of inverters. In purely grid mode theefficiency of the PV-mixer is 96% which is the max efficiency that can be expected for thisconcept based on the switch mode t
57、echnology. For the purely PV mode the efficiency lay inthe tests between 81 and 90% depending on the power needed for the fans. Table 1.4 indicatesthat the efficiency of the PV-mixer in only PV mode may get lower at lower fan power thanshown in table 1.4.The first PV-mixers of the final concept were
58、 delivered and installed in December 2000.172. Measuring systemThe PV-VENT system in Sundevedsgade/Tndergade consists of several ventilation systemswhere most are more or less identical consisting of individual heat exchanger units for eachdwelling located in common solar walls. Main difference is t
59、he orientation of the solar walland if there is one or two heat exchanger units per floor in the solar wall.For this reason measurements have only been performed for one of the solar walls and de-tailed measurements for one apartment.The chosen solar wall is the most south facing solar wall located
60、on the wall of Tndergade 1.The apartment for detailed measurements was chosen to be the dwelling on the fourth floor tothe right as pointed out on figure 2.1.Figure 2.1. The solar wall and apartment where the measurements have been carried out on.2.1. Temperature measurements in the solar wallFigure
61、 2.2 shows the location of the air temperature sensors in the solar wall together with thelocation of the sensor for surface temperature on one of the PV-panels. Figure 2.2 furthershows the location of the sensors for measuring the solar radiation and ambient temperature.The used air temperature sen
62、sors were PT100 class A sensors. The air temperature sensors inthe solar wall were located at the fresh air inlet to the heat exchangers as shown in figure 2.3.The sensors were thus well vented and shielded from direct sun light.The sensor in the fresh air inlet to the fifth floor was located about
63、20 cm inside the fresh airduct to this system in order to shield it from the sun as seen on figure 2.5.4th floorsolar wallmeasured onpyranometer18T5ToutTcellT4T3T2T1Figure 2.2. The location of temperature sensors in the solar wall and location of pyranometerand ambient temperature sensor.One more ai
64、r temperature sensor (also a PT100 class A sensor) was located at the top of thesolar wall (Tout in figure 2.2) at the outlet for summer venting of the solar wall.Tambsolarradiation19Figure 2.3. The location of the air temperature sensor in the solar wall mounted at the gridof the fresh air inlet to
65、 the heat exchanger units.The surface temperature sensor at the back of the PV-panel at the fourth floor was located inthe middle of the middle panel behind a solar cell. This sensor was a PT100 class A sensormounted by means of aluminium tape. Thermo pasta was located between the PV-panel andthe se
66、nsor in order to obtain a good thermal connection.2.2. Weather measurementsThe used pyranometer was a calibrated SolData Pyranometer type 80-HD for measuring oftotal radiation. The instrument for measuring of ambient temperature was a PT100 class Atemperature sensor located in a shield consisting of
67、 two concentric tubes in order to screen itfrom the sun. Figure 2.1 shows the location of the pyranometer while figure 2.4. shows theambient temperature sensor and the back of the pyranometer.2.3. Temperature and flow measurements in the ventilation systemFigure 2.5 shows the ventilation system of T
68、ndergade 1. The figure further shows the loca-tion of the air temperature sensors and air flow measuring devices in the ventilation system inthe apartment at the fourth floor.Besides the temperature of the fresh air (figure 2.2) three other air temperatures were meas-ured in the ventilation system o
69、f the apartment at the fourth floor to the right as seen in fig-ure 2.5: the temperature of the outlet from the apartment, the exhaust air from the heat ex-changer and the inlet air to the apartment from the heat exchanger. The sensors were PT100class A sensors.The air flow rate of fresh air and exh
70、aust air was determined by measuring the pressure dropacross a calibrated orifice or a calibrated bending. For the fresh air a calibrated bending(Lindab MBU 90-100) was used while the exhaust air was measured using a calibrated ori-20fice (Lindab FMU-100). The pressure drops were measured using cali
71、brated pressure trans-mitters (Huba Control type 694) see figure 2.9.Figure 2.4. The shielded ambient temperature sensor and the back of the pyranometer.The calibrated orifice was located in a small shaft between the solar wall and the bathroom asshown on figure 2.6 while the calibrated bending was
72、located above the suspended ceiling ofthe bathroom. The calibrated orifice and calibrated bending are shown in figures 2.7-8. In or-der to determine any heat losses from the ventilation ducts in the shaft a PT100 class A tem-perature sensor was located in the shaft to measure the air temperature see
73、 figure 2.6.2.4. Electrical measurementsThe fans of the system are partly powered by the PV-panels in the solar wall. At low or noPV-power the fans run partly or only on power from the grid. A PV-mixer is in charge of as-suring that the fans are supplied with as much PV-power as possible.The PV-mixe
74、r is one of the new parts developed in the project. It is, therefore, important toestablish knowledge of the function of the PV-mixer.It is, however, a non-trivial task to determine the performance of the PV-mixer as it has twopower inputs and one power output. Especially the inputs may change rapid
75、ly over time e.g. ifa cloud gets in front of the sun. It is, thus, extremely important that the voltage and current ismeasured at the same time even a small time shift between the measuring of the two valuesfor all in and outputs may lead to a wrong picture of the performance of the PV-mixer and the
76、PV-panels.21air temperature sensorFigure 2.5. The ventilation system of Tndergade 1 to the right.solar wallheat exchanger unitshaftbathroomTshaftFigure 2.6. The installation shaft.22Figure 2.7. The calibrated orifice.Figure 2.8. The calibrated bending.At first it was tried to find an existing sensor
77、/meter that was able to perform the measure-ments with the necessary accuracy on the first version of the PV-mixer. However, no suchwas found as it was very difficult to measure connected values of voltage and current to andfrom the PV-mixer in order to get a true picture of the power to and from th
78、e first version of23the PV-mixer. Finally Solar Energy Centre Denmark decided to develop the sensor. The sen-sor consisted basically of a 4-quadrant analogue multiplier, which at a high frequency meas-ure the voltage and current going either in or out of the PV-mixer and multiply the two valuesin or
79、der to obtain the power. The measuring frequency is higher than the fastest variation ofeither in or output of the PV-mixer this ensures precise and correct measurements of thepower. This design of the sensor was maintained although the new version of the PV-mixermade it much easier to measure conne
80、cted values of voltage and current to and from the PV-mixer. The developed sensors was installed and calibrated by the end of 2000. However, itwas discovered that the readings from the sensors unfortunately didnt give much meaning.After a careful investigation it was discovered that the 4-quadrant a
81、nalogue multiplier israther temperature dependent (not mentioned in the data sheet for the chip). This means thatthe calibration equation changes with the temperature meaning that the readings cannot betransferred to meaningful measurements.The new version of the PV-mixer makes it fortunately easier
82、 to measure connected values ofvoltage and current to and from the PV-mixer. A new marked survey showed that signal cal-culators from PRelectronics type 2289 could measure connected voltage and current to andfrom the PV-mixers. The new sensors were installed and calibrated by the end of January2001.
83、Figure 2.9.The pressure transducers for measuring the pressure drop across a claibrated ori-fice and a calibrated bending.2.5. Data collectionAll sensors were connected to a data logger system with modules from Analog Devices. Eachsensor were scanned each 10th second and averaged into 10 minutes mea
84、n values and storedon the hard disk of a PC.24The PC via the software Labteck Control controlled the data logger system. Spot values of thesensor readings were continuously shown on the screen of the PC. The PC/data logger systemwas located in the attic at Tndergade 1 as shown in figure 2.10.Figure
85、2.10. The attic at Tndergade 1 with the PC/data logger system located at the backwall.2.6. Treatment of measured data Using the data logger system/PC the measured values were directly translated into physicalunderstandable values like temperatures and solar radiation.Using the calibration equations
86、other measured values were later transformed to air flow ratesand power. The thermal performance of the heat exchanger and solar wall were likewise latercalculated using the measured temperatures and air flow rates.253. MeasurementsMeasurements have been carried out at Sundevedsgade/Tndergade for mo
87、re than on yearfrom the beginning of February 2000 to end March 2001. Some sensors have, however, notbeen in place for the whole period e.g. the measurements on the PV-mixer were first startedon February 1, 2001 as mentioned earlier. One other sensor the pressure transducer for de-termination of the
88、 air flow rate of exhaust air was malfunctioning until March 15, 2000 andthe temperature sensor for measuring the air temperature in the shaft was first installed onMarch 15, 2000.Data has unfortunately been lost due to what is believed to be power cuts to the measuringPC. These holes in the measure
89、ments are mainly a few hours to one day. However, 18 dayswas unfortunately lost in May 2000 (May 8-26).The first section of this chapter contains graphs showing the measurements from two weeks inorder to illustrate the function of the PV-VENT system the two chosen weeks are week 5and 6 of 2001 (Janu
90、ary 29 February 11), after this is a section with graphs showing differentdetails from the one year of measurements. The third section contains more general conclu-sions on the different components of the system, while in the fourth section the savings of thesystem is calculated.3.1. Measurements fr
91、om week 5 and 6, 2001Figures 3.1-2 show the weather conditions during these specific weeks i.e. total solar radia-tion on the wall at the fourth floor see figure 2.1 and ambient temperature at the same lo-cation. The two weeks are characterised by days with clear sky conditions and days withcloudy c
92、onditions. The ambient temperature was between 9 and 12C.3.1.1. Thermal part of the systemFigures 3.3-4 show the temperatures in the solar wall at the points shown in figure 2.2 in-cluding the ambient temperature. The figures show an increase of the fresh air temperature tothe ventilation system at
93、Tndergade 1, 4, to the right (T4) of up to 20 K, while the tempera-ture at the top of the solar wall (Tout) is up to 28 K higher than the ambient temperature. Astrange phoneme is seen for the fresh air temperature to the fifth floor (T5) regularly thetemperature at this point doesnt follow the behav
94、iour of the other temperatures. This is be-cause the temperature sensor as seen in figure 2.5 is located 20 cm inside the duct in order toavoid the solar radiation hitting the sensor. However, when the fresh air fan to the fifth flooris stopped, the temperature at this point will as seen increase du
95、e to the heat gain from theshaft at the fourth floor, where this duct is situated see figure 2.5. The temperature of theshaft is as seen in figure 3.9-10 rather high.Figures 3.5-6 show the temperature of the PV-panel together with the ambient temperatureand the temperature at the top of the solar wa
96、ll (Tout). The temperature of the PV-panel is ofcourse lower than Tout during periods without solar radiation, but during clear sky conditionsthe temperature of the PV-panel obtain during the two weeks an excess temperature comparedto ambient of up to 37 K, while this temperature difference is 28 K
97、at the top of the solar wall.26Figures 3.7-8 show the air flow rates of fresh air to and exhaust air from the apartment(Tndergade 1, 4 to the right). The occupant operates the ventilation system in order to run itat normal mode during the day and at min. mode during the night. This is because althou
98、ghrather silent the noise from the system still irritates the occupants during the night. The flowrate during normal mode is: exhaust 113 m/h and fresh air 107 m/h which is close to thevalues given by the Danish building code (126 and 113 m/h). During min. mode the flowrates are: exhaust air 76 and
99、fresh air 80 m/h. During year 2000 the flow rate of fresh airand exhaust air at min. flow rate has further been almost identical see section 3.2.1. Theshift to a higher air flow rate of fresh air is because only the filter for the fresh air has beenchanged prior to figures 3.7-8. The peak values of
100、exhaust air of op to 170 m/h are created bythe kitchen hood which on/off contact control the max. mode of the ventilation system. By thestart of the measurements the max. air flow rate of exhaust air was 190 m/h. This illustratethe influence of a dirty filter in the system. Figures 3.7-8 show a well
101、 operated ventilationsystem. However, during most of year 2000 the system was only run in min. mode (and max.mode when cooking) see section 3.2.1.Figures 3.9-10 show the temperatures around the air to air heat exchanger located in the solarwall and the air temperature in the shaft. The fresh air tem
102、perature shown in figures 3.9-10 isidentical to T4 in figures 3.3-4. Solar radiation at clear conditions brings the fresh air tem-perature to the heat exchanger above the exhaust temperature. Figure 3.9-10 further show thatthe air temperature of the shaft is rather high 23-24C. This is because the t
103、ubing of the heat-ing system is located here and further not insulated as seen at the lover left corner of figure2.7.Figures 3.9-10 give together with figures 3.7-8 the efficiency of the heat exchanger. Figures3.11-12 show the efficiency of the heat exchanger calculated in the following way: = qin /
104、 qout(3.1)where: qin is the heat transferred to the fresh air in the heat exchangerqout is the energy in the exhaust air calculated based on the temperature of the exhaustair from the apartment and the temperature of the fresh air to the heat exchangerHowever, the efficiency shown in figures 3.11-12
105、 is not the real efficiency for the heat ex-changer as the heat from the fans are not considered. Figure 3.21 shows the principle of theheat exchanger incl. fans and the locations of the temperature measurements. If the efficiencyfrom figures 3.11-12 is compensated for the energy to the fans figures
106、 3.13-14 appears. Thecompensation for the fan energy is based on the measured fan power see figures 3.42.The peak values in figures 3.11-14 are created by the excess exhaust by the kitchen hood andby solar radiation. Two levels of efficiencies appear. One for min. flow rates and one fornormal flow r
107、ates. It would be expected, that the efficiency increases with increasing air flowrates. But figures 3.13-14 show the opposite situation around 80 % at min. flow rate andaround 70 % at normal flow rate. This is because the air flow rate of fresh air at min. flow rateis higher than the flow rate of e
108、xhaust air. A more thorough investigation of the efficiency ofthe heat exchanger is carried out in section 3.3 also including condensation and heat losses please see this.273.1.2. PV part of the systemFigures 3.15-16 show the electrical power to and from the PV-mixer. From the figures is seenthat wh
109、en solar power is available an immediate drop occurs in the power consumption fromthe grid. When the PV-panels can supply all the power to the fan no power is taken from thegrid i.e. the power demand of the PV-mixer itself is in these situations taken from the PV-panel. The difference between fan an
110、d grid power at no solar power gives the efficiency of thePV-mixer in grid mode, which according to table 1.3 should be 96 %. In pure PV mode thenecessary PV power is higher than the fan power the difference gives the efficiency of thePV-mixer in pure PV mode. From figures 3.15-16 it is seen that th
111、e efficiency in pure PVmode is lower than in pure grid mode. This is dealt with in table 1.4 and further in section 3.3.Figures 3.17-18 show the utilized PV power and the potential power from the PV-panels (theloss in the wiring is not considered as it is in the order of 2-3% and thus far less than
112、the un-certainty of the measurements). The potential power from the PV-panel is the power the PV-panel would have been able to deliver, if a higher demand had been present. The potentialpower is calculated in the following way:Ppotential = Pp Euseful / Ep (1 (Tactual - Tp) 0.004) W(3.2)where Pp is t
113、he peak power found with a solar radiation Ep of 1000 W/m and a cell tem-perature Tp of 25CEuseful is the useful solar radiation calculated as described belowTactual is the temperature measured at the backside of the PV-panel see figures 3.5-6.0.004 is the temperature dependence of the PV-panels-The
114、 total radiation on the PV-panel is transformed to useful radiation by taking into ac-count the reflection of the solar radiation in the glazing of the PV-panels at periods with anon zero incidence angle for the solar radiation. In order to correct for the reflections it isnecessary to calculate the
115、 split between direct and diffuse radiation based on the measuredtotal radiation. This was done using the equations in (Duffie and Beckman, 1991). The cal-culated split introduces a small uncertainty compared to a case where both total and diffuseradiation are measured. The following correction fact
116、or has been applied to account for thereflection in the cover:k = 1- tana(/2)(3.3)where is the incidence angle for the radiation: the actual incidence angle for thedirect radiation and 60 for the diffuse radiation. a is 3.7 (Nielsen, 1995).Figures 3.17-18 show that the utilazation of the potential P
117、V power is very dependent on theactual demand as seen when comparing figures 3.17-18 with figures 3.15-16. How large afraction - that actually is utilized - is shown in figures 3.19-20. Between 30 and 90 % (30 %on day 33 with a very low power demand of the fans) has been utilized during the shown pe
118、-riod. At low radiation levels the utilization should have been 100 % as the potential powerfrom the PV-panels is lower than the demand of the fans. The reason for not being 100 % isthe large uncertainty of the model (3.2) at low radiation levels and the uncertainty of themeasuring equipment - 1 W,
119、which at low power leads to high uncertainties. The yearlysaving and waste are dealt with in section 3.4. However, from figures 3.17-20 it can be stated28that the peak power of the PV-panels should not be higher that the demand divided with theefficiency of the PV-mixer at that specific demand.Tnder
120、gade/Sundevedsgadeweather data-10001002003004005006007008002930313233343536time Julian day, 2001solar radiation W/m-10-8-6-4-202468ambient temperature Csolar radiationTambFigure 3.1. The weather conditions during week 5, 2001 (January 29 February 4).Tndergade/Sundevedsgadeweather data-10001002003004
121、005006007008003637383940414243time Julian day, 2001solar radiation W/m-6-4-202468101214ambient temperature Csolar radiationTambFigure 3.2. The weather conditions during week 6, 2001 (February 5 February 11).29Tndergade/Sundevedsgadetemperatures in the solar wall-10-5051015202530352930313233343536tim
122、e Julian day, 2001temperature CT1T2T3T4T5ToutTambFigure 3.3. Temperatures in the solar wall during week 5, 2001 (January 29 February 4).Tndergade/Sundevedsgadetemperatures in the solar wall-505101520253035403637383940414243time Julian day, 2001temperature CT1T2T3T4T5ToutTambFigure 3.4. Temperatures
123、in the solar wall during week 6, 2001 (February 5 February 11).30Tndergade/Sundevedsgadetemperature of solar cell-10-50510152025303540452930313233343536time Julian day 2001temperature CTambTpvToutFigure 3.5. Temperatures of the PV-panel during week 5, 2001 (January 29 February 4).Tndergade/Sundeveds
124、gadetemperature of solar cell-10010203040503637383940414243time Julian day 2001temperature CTambTpvToutFigure 3.6. Temperatures of the PV-panel during week 6, 2001 (February 5 February 11).31Tndergade/Sundevedsgadeair flows in the heat exchanger0204060801001201401601802930313233343536time Julian day
125、 2001air flow rate m/hfresh airexhaustFigure 3.7. Air flow rates in the system during week 5, 2001 (January 29 February 4).Tndergade/Sundevedsgadeair flows in the heat exchanger0204060801001201401601803637383940414243time Julian day 2001air flow rate m/hfresh airexhaustFigure 3.8. Air flow rates in
126、the system during week 6, 2001 (February 5 February 11).32Tndergade/Sundevedsgadetemperatures around heat exchanger05101520252930313233343536time Julian day, 2001temperature Cto appartmentfresh airfrom appartmentexhaustshaftFigure 3.9. Temperatures of air to and from the heat exchanger during week 5
127、, 2001 (January29 February 4).Tndergade/Sundevedsgadetemperatures around heat exchanger0510152025303637383940414243time Julian day, 2001temperature Cto appartmentfresh airfrom appartmentexhaustshaftFigure 3.10. Temperatures of air to and from the heat exchanger during week 6, 2001 (Febru-ary 5 Febru
128、ary 11).33Tndergade/Sundevedsgadeefficiency of heat exchanger00.10.20.30.40.50.60.70.80.912930313233343536time Julian day 2001efficiencyFigure 3.11. The efficiency of the heat exchanger incl. fans during week 5, 2001 (January 29 February 4).Tndergade/Sundevedsgadeefficiency of heat exchanger00.10.20
129、.30.40.50.60.70.80.913637383940414243time Julian day 2001efficiencyFigure 3.12. The efficiency of the heat exchanger incl. fans during week 6, 2001 (February 5 February 11).34Tndergade/Sundevedsgadeefficiency of heat exchanger00.10.20.30.40.50.60.70.80.912930313233343536time Julian day 2001efficienc
130、yFigure 3.13. The efficiency of the heat exchanger excl. fans during week 5, 2001 (January 29 February 4).Tndergade/Sundevedsgadeefficiency of heat exchanger00.10.20.30.40.50.60.70.80.913637383940414243time Julian day 2001efficiencyFigure 3.14. The efficiency of the heat exchanger excl. fans during
131、week 6, 2001 (February 5 February 11).35Tndergade/Sundevedsgadepower to and from PV-mixer0102030405060702930313233343536time Julian day 2001power WgridPVfansFigure 3.15. Power to and from the PV-mixer during week 5, 2001 (January 29 February4).Tndergade/Sundevedsgadepower to and from PV-mixer0102030
132、405060703637383940414243time Julian day 2001power WgridPVfansFigure 3.16. Power to and from the PV-mixer during week 6, 2001 (February 5 February11).36Tndergade/Sundevedsgadepower from PV-panels01020304050607080902930313233343536time Julian day 2001power Wpossible PVmeasuredFigure 3.17. Actual power
133、 and potential power from the PV-panel during week 5, 2001(January 29 February 4).Tndergade/Sundevedsgadepower from PV-panels01020304050607080903637383940414243time Julian day 2001power Wpossible PVmeasuredFigure 3.18. Actual power and potential power from the PV-panel during week 6, 2001 (Feb-ruary
134、 5 February 11).37Tndergade/Sundevedsgademeasured power from PV vs possible00.10.20.30.40.50.60.70.80.912930313233343536time Julian day 2001ratioFigure 3.19. Actual power divided with potential power from the PV-panel during week 5,2001 (January 29 February 4).Tndergade/Sundevedsgademeasured power f
135、rom PV vs possible00.10.20.30.40.50.60.70.80.913637383940414243time Julian day 2001ratioFigure 3.20. Actual power divided with potential power from the PV-panel during week 6,2001 (February 5 February 11).38exhaustfresh airapartmenttemperature sensorFigure 3.21. The principle of the air to air heat
136、exchanger and the location of the temperaturessensors.When comparing figures 3.7-8 with 3.15-16 it is seen that the air flow rates increase when thePV-panels are able to cover the demand. This is because the voltage to the fans increases.3.2. Measurements from specific weeksIn this section graphs ar
137、e shown for specific weeks in order to show features/problems notshown in the graphs in section 3.1.3.2.1. AirflowsFigures 3.7-8 show a very well controlled system with respect to the air flow rate. However,the figures also show the risk of this way of manually controlling the system. The system was
138、not switched to normal mode on day number 30 and 33 even if it can be seen that the occu-pants were at home i.e. the max. flow rate created by the kitchen hood.During main part of year 2000 the system was run at min. mode as e.g. seen in figure 3.22.The efficiency of the heat exchanger and the utili
139、zed PV-power are lower in this mode andthere is a risk of getting a too humid indoor climate in the apartment. The latter is the reasonfor the “better” operation of the system in year 2001 because the occupants got aware thatdrying of cloth in the living room leads to high relative humidity in the d
140、welling if not venti-lated well.The reason for the min. mode during year 2000 and during the nights of year 2001 is as al-ready mentioned the noise from the system during the night.Figure 3.22 further shows that the two air flows by the start of the system was almost identi-cal.From end of April 200
141、0 to beginning of October 2000 the ventilation system was mainly runin summer mode - i.e. the fresh air fan was switched off. The exhaust was run in min. flowrate mode.3.2.2. PV-mixerIt was in chapter 2 mentioned that the first PV-mixer installed in the system didnt work. Thisis shown in figures 3.2
142、3-24, where it is seen that although able to maintain the power to thefresh air fan the air flow of exhaust air fluctuated extremely much. Figure 3.24 shows that af-ter installing the new PV-mixer everything functioned again. The figure further shows that the39PV-mixer was installed on December 13 l
143、eaving very little time to perform measurements onthe system with all components working.Tndergade/Sundevedsgadeair flows in the heat exchanger0204060801001201401601802008788899091929394time Julian day 2000air flow rate m/hfresh airexhaustFigure 3.22. Air flow rates during the week March 28 April 2,
144、 2000.Tndergade/Sundevedsgadeair flows in the heat exchanger050100150200250332333334335336337338339time Julian day 2000air flow rate m/hfresh airexhaustFigure 3.23. Air flow rates during the week November 27 December 3, 2000.40Tndergade/Sundevedsgadeair flows in the heat exchanger0501001502002503463
145、47348349350351352353time Julian day 2000air flow rate m/hfresh airexhaustnew PV-mixerFigure 3.24. Air flow rates during the week December 11 December 17, 2000.3.3. Calculations based on the measurements and more general conclusionsThe section deals with the function of the air to air heat exchanger,
146、 the fan power, the tem-peratures in the solar wall and the PV-mixer, while the next section deals with the actual sav-ings due to these components.3.3.1. The efficiency of the air to air heat exchangerFigures 3.11-14 show the efficiency of the heat exchanger incl./excl. fan power for two weeksin th
147、e beginning of year 2001. The shown efficiencies dont necessarily show a correct pictureof the efficiency of the heat exchanger. In the following the efficiency is evaluated based onthe whole set of data rather than on only two weeks.Determination of the efficiency of the heat exchanger is not an ea
148、sy task as condensation mayoccur and as the heat exchanger is located outside the heated indoor space the heat loss furtherplays a role.First of all is determined if the calculations of the heat flows (based on dry temperatures) onboth sides of the heat exchanger are correct they should be identical
149、 when no condensationoccurs. Figures 3.25-28 show the calculated heating of the fresh air divided with the calcu-lated cooling (based on dry temperatures) of the exhaust air in the heat exchanger for year2000 and January-March 2001 respectively and further for min. and normal mode. The ratio isshown
150、 as a function of the inlet temperature to the heat exchanger, however, only for inlettemperatures below 17C in order to avoid periods with high inlet temperatures due to the41sun, as the function of the heat exchanger here is opposite when the inlet temperature getshigher than the exhaust temperatu
151、re. High inlet temperatures further leads to small tempera-ture differences across the heat exchanger, which again increase the uncertainty of the calcu-lations.Be aware of different y-axises in figures 3.25-28.Figures 3.25-28 show not as expected an increase in the ratio between the two heat flowsw
152、hen going towards lower inlet temperatures to the heat exchanger. At low inlet temperaturesto the heat exchanger condensation should occur in the heat exchanger leading to a higherheating of the fresh air than cooling of the exhaust air when the heat flows are calculatedbased on dry temperatures. A
153、reason for this has not been found. It could be that the heat ex-changer couldnt get rid of the water from the condensation leading to a decrease in heattransfer area. But the heat exchanger is vertical as seen in figure 1.10 and even if the wateroutlet is blocked, the water will just drain down the
154、 exhaust duct. Another reason, whichseams more likely, is that the heat loss of the heat exchanger has a major influence of the effi-ciency of the heat exchanger. The increase of the efficiency due to condensation at decreasinginlet temperature is compensated due to an equal increase in the heat los
155、s, as the inlet tem-perature to the heat exchanger also is the surrounding temperature for the heat exchanger.This may also be the reason why the ration in figures 3.26-27 increases going towards higherinlet temperatures. The increase may be due to solar radiation actually hitting the surface ofthe
156、heat exchanger leading to a surface temperature above the inlet temperature.Figures 3.29-36 show the calculated “dry” efficiencies for normal and min. flow mode, withand without the fan power included and for the year 2000 and January-March 2001.Most parts for the values in 3.29-36 lay nicely togeth
157、er on a line.The heat exchanger has hardly been run in normal flow mode during year 2000. The valuesare thus limited here, which makes figures 3.29-3.30 less conclusive.In order to compensate for condensation and the heat loss the efficiency of the heat exchangershould be found at the axis to the ri
158、ght in the graphs. However, figures 3.31 and 3.33 show anunrealistic increase of the efficiency at inlet temperatures above 13C. The efficiencies areinstead found by extrapolation a regression line for the values between inlet temperatures of 6and 13C to the axis to the right of the graphs. Doing th
159、is the following information are ob-tained however, the stated efficiencies are rather uncertain do to the way they are deter-mined:Yearventilation modeapprox. flow ratem/hefficiency%2000normal120692001normal120702000min.80772001min.8083Table 3.1. The efficiency of the heat exchanger found from figu
160、res 3.29, 3.31, 3.33 and 3.35.42Tndergade/Sundevedsgadepower diff (qin/qout) vs inlet temp to exchanger00.10.20.30.40.50.60.70.80.911.11.21.31.41.50246810121416inlet temperture Crationorm modeFigure 3.25. The calculated heating of the fresh air divided with the calculated cooling of theexhaust air (
161、based on dry temperatures) in the heat exchanger for year 2000 atnormal flow rate.Tndergade/Sundevedsgadepower diff (qin/qout) vs inlet temp to exchanger00.10.20.30.40.50.60.70.80.911.11.21.31.41.50246810121416inlet temperture Crationorm modeFigure 3.26. The calculated heating of the fresh air divid
162、ed with the calculated cooling of theexhaust air (based on dry temperatures) in the heat exchanger for January-March2001 at normal flow rate.43Tndergade/Sundevedsgadepower diff (qin/qout) vs inlet temp to exchanger00.20.40.60.811.21.41.61.822.20246810121416inlet temperture Cratiomin modeFigure 3.27.
163、 The calculated heating of the fresh air divided with the calculated cooling of theexhaust air (based on dry temperatures) in the heat exchanger for year 2000 atmin. flow rate.Tndergade/Sundevedsgadepower diff (qin/qout) vs inlet temp to exchanger00.20.40.60.811.21.41.61.822.20246810121416inlet temp
164、erture Cratiomin modeFigure 3.28. The calculated heating of the fresh air divided with the calculated cooling of theexhaust air (based on dry temperatures) in the heat exchanger for January-March2001 at min. flow rate.44Normal flow modeTndergade/Sundevedsgadeexchanger eff vs inlet temp to exchanger0
165、0.10.20.30.40.50.60.70.80.910246810121416inlet temperture Cefficiencynorm modeFigure 3.29. The calculated efficiency of the heat exchanger excl. the fan power (the “real”efficiency) for year 2000 at normal flow rate.Tndergade/Sundevedsgadeexchanger eff vs inlet temp to exchanger00.10.20.30.40.50.60.
166、70.80.910246810121416inlet temperture Cefficiencynorm modeincl. power to the fansFigure 3.30. The calculated efficiency of the heat exchanger incl. the fan power for year 2000at normal flow rate.45Tndergade/Sundevedsgadeexchanger eff vs inlet temp to exchanger00.10.20.30.40.50.60.70.80.911.11.202468
167、10121416inlet temperture Cefficiencynorm modeFigure 3.31. The calculated efficiency of the heat exchanger excl. the fan power (the “real”efficiency) for January-March 2001 at normal flow rate.Tndergade/Sundevedsgadeexchanger eff vs inlet temp to exchanger00.10.20.30.40.50.60.70.80.911.11.20246810121
168、416inlet temperture Cefficiencynorm modeincl. power to the fansFigure 3.32. The calculated efficiency of the heat exchanger incl. the fan power for January-March 2001 at normal flow rate.46Min. flow modeTndergade/Sundevedsgadeexchanger eff vs inlet temp to exchanger00.10.20.30.40.50.60.70.80.911.102
169、46810121416inlet temperture Cefficiencymin modeFigure 3.33. The calculated efficiency of the heat exchanger excl. the fan power (the “real”efficiency) for year 2000 at min. flow rate.Tndergade/Sundevedsgadeexchanger eff vs inlet temp to exchanger00.10.20.30.40.50.60.70.80.911.10246810121416inlet tem
170、perture Cefficiencymin modeincl. power to the fansFigure 3.34. The calculated efficiency of the heat exchanger incl. the fan power for year 2000at min. flow rate.47Tndergade/Sundevedsgadeexchanger eff vs inlet temp to exchanger00.10.20.30.40.50.60.70.80.911.11.20246810121416inlet temperture Cefficie
171、ncymin modeFigure 3.35. The calculated efficiency of the heat exchanger excl. the fan power (the “real”efficiency) for January-March 2001 at min. flow rate.Tndergade/Sundevedsgadeexchanger eff vs inlet temp to exchanger00.10.20.30.40.50.60.70.80.911.11.20246810121416inlet temperture Cefficiencymin m
172、odeincl. power to the fansFigure 3.36. The calculated efficiency of the heat exchanger incl. the fan power for January-March 2001 at min. flow rate.48Table 3.1 shows a strange pattern the efficiency increases with decreasing air flow rate itshould be opposite. However, the values in table 3.1 cannot
173、 be compared directly, as the twoflow rates are different except for min. mode 2000, where the two air flow rates were almostidentical. The efficiency at min. mode 2001 is quite much higher than min. mode 2000, be-cause the flow rate of fresh air here was higher than the flow rate of exhaust air.In
174、order to compare the efficiencies it is necessary to bring them on a form where the two airflow rates are identical, as this is the way which normally is used when comparing efficien-cies of air to air heat exchangers.Normalized efficiency of the heat exchangerIt can be shown (Hansen, Kjerulf-Jensen
175、 and Stampe, 1997) that the exchanger efficiency atidentical flow rates equal to the lowest flow rate is identical to the temperature efficiency forthe smallest flow rate. The temperature efficiency is calculated based on the actual measuredtemperatures in the system.1t = (T1o T1i) / (T2i T1i) (3.4)
176、where: 1t is the temperature efficiency at the smallest flow rateT1i is the inlet temperature to the exchanger for the air with the smallest flow rateT1o is the outlet temperature from the exchanger for the air with the smallest flow rateT2i is the inlet temperature to the exchanger for the air with
177、 the largest flow rateFigures 3.37-3.40 shows the result from applying equation 3.4 on the values from normal andmin air flow rates for 2000 and 2001, while excluding the power from the fans i.e. the effi-ciency of the heat exchanger alone.In order to compensate for condensation and the heat loss th
178、e efficiency of the heat exchangershould be found at the axis to the right in the graphs. Figure 3.38 shows an unrealistic in-crease of the efficiency at inlet temperatures above 13C, however, not as much as figure 3.31and the values in figures 3.37 and 3.39-40 dont go as far as 17C. Further figure
179、3.39 con-tains less values as figure 3.34 this is because values where the flow rate of fresh air ishigher than the flow rate of exhaust air have been rejected (although the difference betweenthe two flow rates is small). The efficiencies and flow rates are found by extrapolation a re-gression lines
180、 for the values between inlet temperatures of 6 and 13C to the axis to the rightof the graphs. Doing this the figure 3.41 is obtained however, the shown efficiencies are al-though less uncertain than the efficiencies in table 3.1 still a bit uncertain.Figure 3.41 shows that the efficiency of this ty
181、pe of heat exchanger is between 75 and 77 %and that this efficiency is higher than measured in laboratory. The exchangers in Sundeveds-gade/Tndergade have been changed a bit compared to the exchanger tested in laboratory inorder to increase the efficiency (Pedersen, 2001). The measured efficiency is
182、 rather high but abit lower than the aim of the project an efficiency between 80 and 90 %. This is because theheat transferring area of the heat exchangers is less than optimal in order to obtain a slim heatexchanger, which may fit into the solar walls. The heat exchangers in the type 2 systems has
183、alarger heat transferring area and has in the Lundebjerg project (Jensen, 2001) been measuredto have an efficiency of between 75 and 85%.49Tndergade/Sundevedsgadeefficiency of heat exchanger00.10.20.30.40.50.60.70.80.9101234567891011121314151617temperature of fresh air to the heat exchanger Cefficie
184、ncy020406080100120140160180200flow rate m/hefficiencyflow rate of fresh airnorm modeFigure 3.37. The calculated (normalized) efficiency of the heat exchanger excl. the fan powerfor 2000 at normal flow rate.Tndergade/Sundevedsgadeefficiency of heat exchanger00.10.20.30.40.50.60.70.80.9101234567891011
185、121314151617temperature of fresh air to the heat exchanger Cefficiency020406080100120140160180200flow rate m/hefficiencyflow rate of fresh airnorm modeFigure 3.38. The calculated (normalized) efficiency of the heat exchanger excl. the fan powerfor January-March 2001 at normal flow rate.50Tndergade/S
186、undevedsgadeefficiency of heat exchanger00.10.20.30.40.50.60.70.80.9101234567891011121314151617temperature of fresh air to the heat exchanger Cefficiency020406080100120140160180200flow rate m/hefficiencyflow rate of fresh airmin modeFigure 3.39. The calculated (normalized) efficiency of the heat exc
187、hanger excl. the fan powerfor 2000 at min. flow rate.Tndergade/Sundevedsgadeefficiency of heat exchanger00.10.20.30.40.50.60.70.80.9101234567891011121314151617temperature of fresh air to the heat exchanger Cefficiency020406080100120140160180200flow rate m/hefficiencyflow rate of fresh airmin modeFig
188、ure 3.40. The calculated (normalized) efficiency of the heat exchanger excl. the fan powerfor January-March 2001 at min. flow rate.51Tndergade/Sundevedsgadeefficiency of the heat exchanger00.10.20.30.40.50.60.70.80.91020406080100120140air flow rate m/hefficiencyTndergadelaboratoryFigure 3.41.The cal
189、culated temperature efficiency found at an inlet temperature of 17Cdifferent flow rates together with the efficiencies measured in laboratory on anearlier version of the exchanger.3.3.2. Fan powerThe power to the fans of the ventilation system was measured during February and March2001. Figure 3.42
190、shows the dependency of the fan power on the total flow rate through thesystem. The total flow rate is the sum of the flow rate of fresh air and exhaust air.The equation for the regression line shown in figure 3.42 to witch the values fits very nicelyis:fan power = 0.00000223 flow + 0.000169 flow +
191、0.0213 flow W(3.5)where flow is the total flow rate i.e. the sum of fresh air and exhaust airFrom figure 3.42 and equation (3.5) it is seen that the fan power at the flow rates given in theDanish building code (126 + 113 = 239 m/h) is 45 W. This is very much lower than the max.power given in the Dan
192、ish building code 87 W. However, to the 45 W the power loss of theac/dc converter has to been added. The power loss of the ac/dc converter is:power loss = 5.6 + 0.0278 P W(3.6)where P is the total power consumption from the grid of the fans incl. the loss of the ac/dcconverterThe total power consump
193、tion of the ventilation system at a flow rate of in total 239 m/h isthen 45 + 7 = 52 W, which still is 40 % lower than required by the Danish Building code. The52fan powers in figures 3.42 should be divided with 0.96 (efficiency of the PV-mixer in gridmode see later) when then the power is delivered
194、 entirely from the grid.Tndergade/Sundevedsgadepower to fans vs flow rates010203040506070050100150200250300total flow rate m/hfan power WFigure 3.42. The dependency of the fan power on the total flow rate.3.3.3. Temperatures in the solar wallThe evaluation of the temperatures in the solar wall durin
195、g sunshine is rather difficult as thesolar walls are situated on the walls facing a courtyard as seen in figure 1.1. The sun will es-pecially during winter time first hit the solar wall at Tndergade just before noon and thenat full power, while the sun will start to shine on the solar wall on Sundev
196、edsgade also aroundnoon. It is further not possible to characterize the solar wall in the same way as solar air col-lectors as done for Lundebjerg (Jensen, 2001) as only one flow rate has been measures. Evenif all flow rates had been measured the characterization as solar air collector would still h
197、avebeen very difficult at the air leaves the solar wall at different levels/floors.Figures 3.43-45 show an evaluation of the temperatures in the solar wall at Tndergade usingdata from 2000 and January-March 2001. Figure 3.43 shows the temperature increase com-pared to ambient when air is taken from
198、the solar wall to the apartment Tndergade 1, 4 to theright, while figure 3.44 shows values during situations without this air flow rate. Only datafrom after 12:00 has been used in order to give a clearer picture of the pattern of the tem-perature i.e. the rapid heating up as seen in figure 3.46 has
199、been excluded. In this way it willfurther be possible to transfer the findings to other situations without shading. Figures 3.43-45show the inlet temperature (T4 in figure 2.2) minus ambient temperature and PV-panel tem-perature minus ambient temperature at the fourth floor the inlet temperatures at
200、 the lowerfloors will be lower as seen in figures 3.47, while the PV-temperature of the lower panelswont be very different from the PV-temperature shown in figure 3.43-45 due to the very lowair speed in the solar wall below 0.5 m/s, which is in the same order of magnitude as forbuoyancy driven air f
201、lows. The equations for the regression lines are enclosed in the figures.53Tndergade/SundevedsgadePV panel temperature and inlet temperaturey = 0.0473x + 1.3979R2 = 0.9184y = 0.0107x + 4.1957R2 = 0.43530510152025303540450100200300400500600700800900useful radiation W/mtemperature increase KTpvT4Figur
202、e 3.43. The dependency of the temperatures in the solar wall on the useful solar radia-tion during periods in 2000 with air flow to the apartment Tndergade 1, 4 to theright. The shown temperature differences are T4 and Tpv minus the ambienttemperature.Tndergade/SundevedsgadePV panel temperature and
203、inlet temperaturey = 0.0454x + 2.1376R2 = 0.9153y = 0.0129x + 4.3265R2 = 0.61780510152025303540450100200300400500600700800900useful radiation W/mtemperature increase KTpvT4Figure 3.44. The dependency of the temperatures in the solar wall on the useful solar radia-tion during periods in 2000 without
204、air flow to the apartment Tndergade 1, 4 tothe right. The shown temperature differences are T4 and Tpv minus the ambienttemperature.54Tndergade/SundevedsgadePV panel temperature and inlet temperaturey = 0.0482x + 3.4547R2 = 0.9175y = 0.0173x + 6.9514R2 = 0.6488051015202530354045010020030040050060070
205、0800900useful radiation W/mtemperature increase KTpvT4Figure 3.45. The dependency of the temperatures in the solar wall on the useful solar radia-tion during January-March 2001 with air flow to the apartment Tndergade 1, 4to the right. The shown temperature differences are T4 and Tpv minus the ambi-
206、ent temperature.Tndergade/SundevedsgadePV panel temperature and inlet temperature05101520253035400100200300400500600700800useful radiation W/mtemperature increase KTpvT4Figure 3.46. The progress during daytime of the temperature difference at T4 and the PV-panel for February 3, 2001.noon55The scatte
207、ring of the values in figure 3.43-45 is partly due to the wind and partly due to thethermal capacity of the solar wall. The wind induces different heat losses depending on thewind speed, while the thermal mass brings the temperatures out of phase with the sun atchanging radiation levels.Figures 3.43
208、-35 show as expected that the temperature of the PV-panel is lower than the airtemperature in the solar wall during low or no solar radiation while being increasingly higherat increasing solar radiation ending at being more than 20 K higher than the air temperature inthe solar wall. This indicates t
209、hat the cooling of the PV-panel by the air flow in the solar wallis not efficient, which is explained by the very low air speed of the air in the solar wall inthe same order of magnitude as for buoyancy driven air flows.Figures 3.43-45 shows identical pattern during summer and winter (2000 covers bo
210、th summerand winter) and with and without air flow in the solar wall (well actually only with and with-out air flow to Tndergade 1, 4 to the right). This indicates that the regression lines may beused more general to evaluate the savings of the solar wall on a more general basis this willbe done in
211、section 3.4.Figure 3,47 shows the inlet temperatures to the heat exchangers minus the ambient tempera-ture at all floors. The figure shows only little difference in the inlet temperature to the 2nd, 3rdand 4th floor, while the inlet temperature to the 1st floor is considerably lower due to the close
212、location to the air inlet to the solar wall as shown in figure 2.2.Tndergade/Sundevedsgadeinlettemperatures to the heat exchangers05101520250100200300400500600700800useful radiation W/mtemperature increase K1st floor2nd floor3rd floor4th floorFigure 3.47.The inlet temperature to the heat exchangers
213、in the solar wall minus the ambi-ent temperature at different floor levels dependent on the useful radiation.Figures 3.43-45 indicate that the temperature of the air at no solar radiation stays 5-7 K abovethe ambient temperature. This is further evaluated in figures 3.48-49. These figures show the56
214、absolute temperature at T4 and the temperature difference between T4 and ambient as a func-tion of the ambient temperature. The temperatures are found during night-time and are fromOctober-November 2000 and January-February 2001. The equations for the regression linesas given in the figures. The sca
215、ttering of the values in figure 3.48-49 is partly due to the windand partly due to different air flows through the solar wall. The wind induces different heatlosses depending on the wind speed, while the temperature difference between the air in thesolar wall and the ambient is directly dependent on
216、 the air flow rate of fresh air to the solarwall.Figures 3.48-49 show that the temperature difference between the air in the solar wall andambient increases with decreasing ambient temperature. This is due to the heat loss from theshaft behind the solar wall which as seen in figures 3.9-10 is held a
217、t a rather high temperaturelevel. The wall between the shaft and the solar wall is further a non insulated half stone brickwall with an U-value of approx. 4 W/Km. The area of this wall is about 3 m. The mainte-nance door (see figure 1.10) to the solar wall is also facing heated floor area. The U-val
218、ue ofthis door is estimated to be about 3 W/Km and has an area of approx. 0.4 m. The heat lossfrom the dwelling is thus considerable. It is, therefore, no wonder that the air temperature inthe solar wall is so high during periods with no solar radiation. Part of the heat loss is recov-ered due to th
219、e intake of fresh air from the solar wall. However, it is only a smaller part whichis recovered due to the low air flow rates which especially occurs during the night as the ten-ants tends to run the ventilation systems at min. mode or shut down the fresh air fan com-pletely. This will further be ev
220、aluated in section 3.4.Tndergade/Sundevedsgadenight temperature in the solar wally = 0.7451x + 6.3743R2 = 0.7038y = -0.2549x + 6.3743R2 = 0.2176024681012140246810121416ambient temperature Ctemperature difference K02468101214161820temperatur CT4-TambT4Figure 3.48.Nighttime temperatures in the solar w
221、all from October-November 2000.57Tndergade/Sundevedsgadenight temperature in the solar wally = 0.5029x + 7.5224R2 = 0.5557y = -0.4971x + 7.5224R2 = 0.5502468101214-10-8-6-4-20246810ambient temperature Ctemperature difference K02468101214161820temperatur CT4-TambT4Figure 3.49.Nighttime temperatures i
222、n the solar wall from January-February 2001.3.3.4. The PV-mixerThe PV-mixer was one of the new features of the PV-VENT systems. It is therefore of specialinterest to evaluate this component. The objective of the PV-mixer is that it should be able tomaintain the desired power to the fans while utiliz
223、ing as much PV-power as possible.The actual operation is shown in figures 3.15-20. The chosen concept of the PV-mixer doesthat it cannot utilize excess power from the PV-panel above the actual demand. The size ofthe PV-panel should therefore carefully be dimensioned in accordance with the actual pow
224、erdemand in order not to waste PV-power. If the power from the PV-panel is larger than thedemand an inverter feeding the grid with the PV-power will most properly be a better solu-tion.The efficiency of the PV-mixer is evaluated in the following.Grid modeTable 1.3 shows the efficiency of the PV-mixe
225、r in pure grid mode. As the switch mode tech-nology is utilized in the PV-mixer the shown efficiency of the PV-mixer of 96 % is constant.PV modeTable 1.4 shows the efficiency of the PV-mixer in pure PV mode. Table 1.4 indicates that theefficiency in pure PV mode is dependent on the actually power de
226、mand. Figure 3.50 showsthe measured efficiency of the PV-mixer in the systems at pure PV-mode. In figure 3.51 these58values are shown together with the values from table 1.4 and values from Lundebjerg (Jensen,2001). The equation for the regression line is further shown in the figure.Tndergade/Sundev
227、edsgadeefficiency of the PV-mixer at purely PV00.10.20.30.40.50.60.70.80.910102030405060fan power WefficiencyFigure 3.50. The efficiency of the PV-mixer at pure PV-mode as a function of the demandmeasured in Sundevedsgade/Tndergade.Efficiency fo the PV-mixer in pure PV-modefrom in-situ and laborator
228、y measurementsy = 8.5113Ln(x) + 43.358R2 = 0.63760102030405060708090100050100150200250300350fan power Wefficiency %table 1.4Sundevedsgade/TndergadeLundebjergFigure 3.51. The efficiency of the PV-mixer at pure PV-mode as a function of the demandmeasured in Sundevedsgade/Tndergade, Lundebjerg (Jensen,
229、 2001) and inlaboratory (table 1.4).59The max. power which the PV-mixer can deliver to the fans is 300 W. This means that themax. efficiency of the PV-mixer in pure PV-mode is 90 %, while slowly decreasing to 80 %at a demand of about 50 W. At lower demands figure 3.51 indicates that the decrease of
230、theefficiency will be much faster however, the measured values are rather scattered in this areaindicating a large uncertainty.Mixed PV and grid modeThe efficiency of the PV-mixer in mixed mode is rather difficult to obtain. The efficiency ofthe grid part will always be 96 %. Based on this the effic
231、iency can be found based on themeasured inputs from the grid and the PV-panels and the measured output to the fans. How-ever, the measured values are too scattered to give an answer. In order to give an impressionof the efficiency of the PV part during mixed mode operation the values from table 1.2
232、andtest 3 from table 1.3 has been used in the following way:PV = (Pfan Pgrid * 0.96) / PPV(3.7)where PV is the efficiency of the PV part in mixed modePfan is the measured consumption of the fanPgrid is the measured power from the grid: U grid * I gridPPV is the measured power form PV: U pv * I pv0.9
233、6 is the efficiency of the grid part of the PV-mixerThe results are shown in figure 3.52. The values are for a demand of about 276 W and thevalue on the x-axis is the PV-power divided with the demand in order to obtain a normalizedexpression which may be used in other situation e.g. the simulations
234、in the next section.Figure 3.52 indicate that the efficiency of the PV-mixer is linear dependent on the ratio be-tween the power for PV and the power demand of the fans. At zero PV power the efficiency isabout the efficiency of the PV-mixer at pure grid mode 0.96, while it when going towardspure PV-
235、mode decreases linearly towards the efficiency in pure PV-mode as shown in figure3.51.This means that the efficiency for the PV part of the PV-mixer for other fan powers may befound as a linearly function based on two points: 0.96 at no PV-power and a value found infigure 3.51 for pure PV-mode depen
236、dent on the actual power demand of the fans. When com-bining the information from figures 3.50 and 3.51 the following equation appears: = a*(PV power / fan power) + 0.96(3.8)where: is the efficiency of the PV-part at mixed PV/grid modea = (b + c*fan power + d*fan power)/(1 + e*fan power + f*fan powe
237、r+g*fan power)b = -0.2405c = -0.00593d = 1.36*10-5e = 0.04232f = 1.1646*10-4g = -1.1374*10-70.96 is the efficiency of the grid part60Efficiency of the PV-mixer in mixed PV and grid modefrom laboratorie testsy = -0.0499x + 0.9464R2 = 0.735100.10.20.30.40.50.60.70.80.9100.20.40.60.811.2PV power / fan
238、powerefficiencyFigure 3.52.The efficiency of the PV-mixer at mixed PV and grid mode as a function of thePV power divided with the fan power - measured in laboratory (table 1.2).It is not possible to prove that the above conclusion is correct, however, it is believed that therelationship is sufficien
239、tly correct in order to allow for the calculations in the next section.3.4. Obtained and obtainable savings of the systemThis section deals with the actual savings from the system as it has been run during the meas-uring period. The section further contains calculations regarding the savings if the
240、system hasbeen more optimal i.e. being run in normal flow mode, no shading on the solar wall, etc.For both sub-sections the following has been calculated:- saving in ventilation losses due to the heat exchanger- savings due to the pre-heating of the air in the solar wall- heat loss from the apartmen
241、t to the solar wall- savings in electricity consumption due to the PV-panels- waste of PV-energy due to a lower demand than the peak power of the PV-panels3.4.1. Obtained savingsUsing the measurements it is possible to calculate the yearly performance of the system fromApril 1, 2000 March 31, 2001 f
242、or the actual running of the system. It is further possible toestimate the savings of the heat exchanger if the fresh air had not been taken from the solarwall but directly from ambient. Measurements for the PV part of the system are only available61for part of the year the energy flows thus have to
243、 be calculated based on the findings in sec-tion 3.3.4.A computer program, which partly calculates the energy flows directly based on the meas-urements partly, simulated the PV performance and thermal performance of the heat ex-changer without the solar wall has been created. The features of the pro
244、gram are listed below.Computer programThe thermal calculations have only been carried out if the fresh air fan had been switched onand when the ambient temperature was below 17C in order to exclude periods without heat-ing demand. The model does not include a thermal model of the building i.e. calcu
245、lations ofthe actual heating demand of the building. This is why the above restrictions have been ap-plied.Pre-heatingThe actual heat flow from the apartment due to the exhaust and the pre-heating of the fresh airin the solar wall and heat exchanger has been calculated directly based on the measured
246、 airflow rates and temperatures in the system.The performance of the heat exchanger without pre-heating in the solar wall has been calcu-lated/simulated in the following way:The actual efficiency of the heat exchanger has been calculated using equation 3.1 (page26). The temperature of the fresh air
247、after the heat exchanger has been calculated in thefollowing way:T = Tamb + (Texh Tamb) exh/ fr cpexh/cpfr Vexh/Vfr (3.9)where is the actual efficiency of the heat exchanger incl. the fan power (figures 3.30,3.32, 3.34 and 3.36) in order to account for the heat delivered to the air from thefans is t
248、he density of aircp is the heat capacity of airV is the flow rates of air subscript amb indicate ambientsubscript exh indicate exhaust air subscript fr indicate fresh airWhen the temperature for the fresh air after the heat exchanger (for the case of no pre-heating) has been found the pre-heating in
249、 the heat exchanger can be found. One prob-lem with equation 3.9 is that the efficiency of the heat exchanger as shown in figures3.29-36 is dependent on the inlet temperature. The ambient temperature has been lowerthan the actual inlet temperature to the heat exchanger. This means that 3.9 leads to
250、a bittoo high inlet temperature of fresh air to the dwelling, which again favour the case of nopre-heating in the solar wall a bitWhen having the savings of the system with and without pre-heating of the fresh air in thesolar wall the benefit of the solar wall may be evaluated.62The energy transferr
251、ed to the fresh air in the solar wall has been calculated based on the actualflow rate of fresh air, the ambient temperature and the temperature in the solar wall. The cal-culations have been divided in day and night in order to be able to evaluate the effect the pre-heating due to the sun and due t
252、o the heat loss from the building to the solar wall.Heat loss from the apartment to the solar wallThe wall between the shaft and the solar wall is as mentioned earlier a non insulated halfstone brick wall with an U-value of approx. 4 W/Km. The area of this wall is about 3 m. Themaintenance door (see
253、 figure 1.10) to the solar wall is also facing heated floor area. The U-value of this door is estimated to be about 3 W/Km and has an area of approx. 0.4 m.The heat loss to the solar wall per dwelling may be calculated in the following way:Q = (Uw Aw + Ud Ad) (Tshaft Tsolarwall) (3.10)where U is the
254、 heat loss coefficientA is the area of the construction facing the wallsubscript w stands for wallsubscript d stands for maintenance doorThe calculations have as for the pre-heating in the solar wall been divided in day and night inorder to be able to compare the losses with the pre-heating for the
255、two periods.Fan power and savings due to the PV-panelsThe actual fan power has been calculated using equation 3.5 (page 51).The losses due to the transformer has been calculated using equation 3.6 (page 51). Losses inthe wiring are not considered, as these should be as low as 2-3% and thus far less
256、than the un-certainty of the calculations.The potential power from the PV-panels has been calculated using equation 3.2 (page 27).The method described on page 27 for calculating the useful radiation has also been applied.How large part of the fan power which actually can been covered by PV has been
257、calculatedusing the equation in figure 3.51 (page 58) and equation 3.7 (page 59).Based on the above the following energy flows has been calculated: Energy to fans with andwithout PV, energy delivered to the PV-mixer from the PV-panels and PV energy not utilizeddue to too low demands.Calculated energ
258、y flowsThe calculations have been divided in 2000 and 2001, because the system was run rather wellin 2001 while it in 2000 was run improperly. Table 3.2 shows the results from the calcula-tions.63Table 3.2 shows major differences between the two years, which of course is caused by theimproper runnin
259、g of the system in 2000.20002001yearkWhkWhkWhHeat exchangerEnergy in the exhaust air 164012172857Energy in the inlet air incl. pre-heating in the solar wall 76811001868Energy in the inlet air exc. pre-heating in the solar wall 713 9931706Benefit of pre-heating in the solar wall 1) 55 107 162Solar wa
260、llEnergy to the air from the solar wall day 129 246 375Energy to the air from the solar wall night 149 230 379Total energy to the air from the solar wall 2) 278 476 754Losses to the solar wall day 143 139 282Losses to the solar wall night 212 221 433Total losses to the solar wall 3) 355 360 715Fans
261、and PVEnergy to the fans from the grid - without PV 159 68 227Energy to the fans from the grid - with PV 146 60 206Benefit of PV 4) 13 8 21PV energy delivered to the PV-mixer 18 9 27Not utilized PV energy 23 2 25Table 3.2. Yearly measured (and calculated) energy flows in the ventilation system.1) en
262、ergy in the inlet air with pre-heating in the solar wall minus without pre-heating.2) energy to the air from the solar wall for both day and night3) losses to the solar wall for both day and night4) energy to the fans from the grid without PV minus with PVThe benefit of the pre-heating in the solar
263、wall was for the whole year 162 kWh, which corre-spond to 5.7 % of the energy in the exhaust air. This percentage was 3.4 and 8.8 % for 2000and 2001 respectively. In all (for 2000/2001) 1868 kWh was saved due to the heat exchangerand solar wall corresponding to 65 % of the energy in the exhaust air,
264、 while this was 47 %and 90 % for 2000 and 2001 respectively. The very low amount of recovered heat in 2000 isdue to the malfunction of the first version of the PV-mixer as shown in figure 3.23-24. Theflow rate of exhaust air was here up to three times the flow rate of fresh air leading to a verylow
265、efficiency of the heat exchanger (down to 25 %).The pre-heating (day and night) of the fresh air was for 2000/2001 in the same order of mag-nitude as the losses from the apartment to the solar wall. Due to the better running of the sys-tem in 2001 the fresh air was pre-heated more than was lost to t
266、he solar wall. However, thebenefit of the pre-heating of the fresh air after the heat exchanger was only 30 % (107/360 100) of what was lost to the solar wall. Based on this it can be stated that the wall and door64facing the solar wall should have been insulated better in fact it could also be stat
267、ed that itwould have been better to insulate the installation shaft better rather than installing the solarwall.The benefit of the PV-panels was for 2000/2001 21 kWh equal to about 9 % of the requiredenergy to the fans. This value was 8 and 12 % for 2000 and 2001 respectively. Due to the im-proper r
268、unning of the system 56 % of the potential PV power was not utilized during 2000,while only 18 % was not utilized during 2001. It should be remembered though that the sys-tem was not run in summer mode i.e. only the exhaust fan running during 2001.The above results were obtained from the actual meas
269、urements on the system. The systemwas during main part of the measuring period run improperly, so in order to evaluate the sys-tem under more ideal conditions a simulation program was created. This is described in thenext section.3.4.2. Obtainable savingsA simulation program has been developed in or
270、der to be able to evaluate the intended per-formance of the systems in Tndergade 1. The program is based on the findings in section3.3.Simulation programThe simulation program is based on the Danish Test Reference Year (TRY) (SBI, 1982) andthe applied solar processor (for calculation of solar incide
271、nce angle, direct and diffuse solarradiation) is the one from (Dutr, 1985).No thermal model of the building i.e. calculations of the actual heating demand of thebuilding has been includes. However, in order to exclude periods without heating demandthe calculations on the thermal part of the system h
272、as been skipped outside the Danish heatingseason (September 22 May 8) and when the ambient temperature was above 17C.A more favourable location of the building is assumed in the program: the solar wall is southfacing and no obstructions cause shading on the solar wall.Pre-heatingThe flow rates of th
273、e system are day and night as defined in the Danish building code: exhaust126 m/h and fresh air 126 0.9 =113.4 m/h.The inlet temperature of fresh air to the heat exchanger is either the ambient temperature (i.e.no pre-heating before the heat exchanger) or (in the case of pre-heating in a solar wall)
274、 calcu-lated based on figures 3.43-45 (page 53-54) as a mean value of the three figures for T4 (+ theambient temperature) during daytime and figure 3.48 (page 56) during the night.The efficiency of the heat exchanger for the two cases is found using a regression equation forthe values in figure 3.32
275、 (page 45). The efficiency incl. fan power has been used as the fanpower transferred to the air thus already will be included.The inlet temperature of fresh air to the apartment from the heat exchanger is calculated usingequation 3.9 (page 61). As it is on page 61 for no pre-heating in a solar wall
276、and with Tamb65replaced with the above air temperature (T4) in case of pre-heating in a solar wall. Texh (tem-perature of the exhaust air from the dwelling) is in the simulation program (based on themeasurements) set to 22C.Based on the above the energy transferred to the fresh air in the heat excha
277、nger and solar wallcan be calculated. In this case opposite the former calculations - the efficiency of the heatexchanger for the two cases: with and without pre-heating in a solar wall will be different asthey should.The energy transferred to the fresh air in the solar wall has been calculated base
278、d on the flowrate of fresh air, the ambient temperature and the temperature in the solar wall. The calcula-tions have been divided in day and night in order to be able to see the effect of the pre-heatingdue to the sun and due to the heat loss from the building to the solar wall. The air temperature
279、in the solar wall has been calculated based on figures 3.43-45 (page 53-54) as a mean value ofthe three figures for T4 (+ the ambient temperature) during daytime and figure 3.48 (page 56)during the night.Heat loss from the apartment to the solar wallThe heat loss from the apartment to the solar wall
280、 has been calculated as described under theformer computer program i.e. using equation 3.10 (page 62). The air temperature in the so-lar wall was found in the same way as described in the above paragraph. The temperature ofthe shaft Tshaft was (based on the measurements) set to 24C.The calculations
281、have as for the pre-heating in the solar wall been divided in day and night inorder to be able to compare the losses with the pre-heating for these two periods.Fan power and savings due to the PV-panelsThe fan power and savings due to the PV-panels were calculated in the same way as describedfor the
282、 former program see page 62. The temperature of the PV-panels was found using fig-ures 3.43-45 (page 53-54) where Tpv was found as a mean value of the three figures for Tpv(+ the ambient temperature).Calculated energy flowsTable 3.3 shows the base case results from the above-described simulation mod
283、el. The peakpower of the PV-panels were as in Tndergade 1 121 W.Table 3.3 shows far better results than table 3.2. The ventilation loss is of course higher thanfor 2000/2001 due to the higher constant flow rate of exhaust air.The pre-heating in the heat exchanger and solar wall amounts to 84 % of th
284、e mechanical ven-tilation loss, while the benefit of the solar wall is 452 or 11 % of the mechanical ventilationloss. The benefit of the solar wall is now quite good.The pre-heating in the solar wall is now 43 % higher than the losses from the apartment to thesolar wall. However, the beneficial part
285、 of the pre-heating in the solar wall (after the heat ex-changer) is only 46 % of the losses to the solar wall. This again illustrates that the wall anddoor facing the solar wall should have been insulated better. Better insulation of these con-structions will, however, decrease the pre-heating in t
286、he solar wall i.e. the pre-heating dur-66ing the night is in the same order of magnitude as the pre-heating during the day. Part of thepre-heating during the day is also due to the losses from the building to the solar wall. Sobetter insulated constructions facing the solar wall will considerably de
287、crease the pre-heatingof the fresh air in the solar wall. It is judged that the benefit of the solar wall in this case willbe reduced from 452 to 100-200 kWh i.e. to below 5 % of the mechanical ventilation loss.yearkWhHeat exchangerEnergy in the exhaust air 4129Energy in the inlet air incl. pre-heat
288、ing in the solar wall3462Energy in the inlet air exc. pre-heating in the solar wall3010Benefit of pre-heating in the solar wall 1) 452Solar wallEnergy to the air from the solar wall day 712Energy to the air from the solar wall night 688Total energy to the air from the solar wall 2)1400Losses to the
289、solar wall day 359Losses to the solar wall night 618Total losses to the solar wall 3) 977Fans and PVEnergy to the fans from the grid - without PV 314Energy to the fans from the grid - with PV 268Benefit of PV 4) 46PV energy delivered to the PV-mixer 55Not utilized PV energy 13Table 3.3. Yearly calcu
290、lated energy flows in the ventilation system.1) energy in the inlet air with pre-heating in the solar wall minus without pre-heating.2) energy to the air from the solar wall for both day and night3) losses to the solar wall for both day and night4) energy to the fans from the grid without PV minus w
291、ith PVThe benefit of the PV-panels is 46 kWh equal to 15 % of the required energy to the fans andas only 19 % of the PV power is not utilized this is satisfactory. So the PV-system is thusrather well dimensioned. The reason for the low part not utilized (although the peak power ofthe PV-panels is mo
292、re than twice as high as the required fan power) is of course that the ra-diation level at vertical south seldom is 1000 W/m and the temperature of the PV-panels sel-dom is 25C or below.Parameter variationsThe above simulation model is rather general, which means that it is possible to perform pa-ra
293、meter variations for some of the main parameters of the system. Parameter variations are in67the following carried out for the efficiency of the heat exchanger and the peak power of thePV-panels.Efficiency of the heat exchangerThe efficiency of the heat exchanger is in the following fixed values i.e
294、. not dependent onthe inlet temperature of fresh air as this makes it much easier to display the results graphicallywithout loosing too much of the realism. The simulations are carried out in order to evaluatethe influence of the efficiency of the heat exchanger on the utilized fraction of the pre-h
295、eatingin the solar wall. Figure 3.53 shows the results from the simulations.Tndergade/Sundevedsgadesaved ventilation loss00.10.20.30.40.50.60.70.80.9100.10.20.30.40.50.60.70.80.91efficiency of the heat exchangerpart saved of the ventilation lossrecovered by the heatexchangerbenifit of the pre-heatin
296、gin the solar wallFigure 3.53. The recovered fraction of the mechanical ventilation loss and the utilized frac-tion of the pre-heating in the solar wall dependent on the efficiency of the heatexchanger.Figure 3.53 shows as expected a decreasing utilization of the pre-heating in the solar wallwith in
297、creasing efficiency of the heat exchanger. Due to the rather simple model without abuilding part, the utilized part of the pre-heating in the solar wall is at low exchanger efficien-cies a bit too high, as it here compete with the direct solar gains through the windows. On theother hand - the utiliz
298、ed part of the pre-heating in the solar wall is a bit too low at high ex-changer efficiencies as the solar energy also may cover a part of the transmission loss of theapartment.The utilization of the pre-heating of the fresh air in the solar wall is low at high heat ex-changer efficiencies and shoul
299、d in such cases carefully be evaluated before chosen.68Utilized and not utilized PV powerFigure 3.54 shows the results from simulations where the peak power of the PV-panels hasbeen varied. The necessary fan power during the heating season is in the simulations 45 W as were the case in the former si
300、mulations.Sundevedsgade/Tndergadeutilized and not utilized PV power010203040506070050100150200250300350400450500peak power of PV-panels Wpcovered by PV - not utilizedt PV power %fan power coveredby PVnot utilized PVpowerFigure 3.54.Utilized and not utilized PV power dependent on the peak power of th
301、e PV-panels.Figure 3.54 may be used for other fan powers if the x-axis is replaced with the peak powerdivided with 45 (fan power in figure 3.54) as done in figure 3.55. However, the efficiency ofthe PV-mixer is dependent on the fan power as shown in figure 3.51 and equation 3.7. So thefound values i
302、n figure 3.55 should be multiplied with the following factor:f = / 75.75(3.11)where is the efficiency of the PV-mixer at the actual fan power found in figure 3.51 75.75 is the efficiency at a fan power of 45 W as used in figures 3.53-54Figures 3.54-55 show that a considerable area of PV-panels is ne
303、cessary to cover e.g. 25 % ofthe necessary fan power. The problem is, however, that the not utilized PV power increasesmore rapidly than the utilized part of the PV power. So if the aim is to cover a large fractionof the necessary energy to the fans it would be wise to apply an inverter rather than
304、a PV-mixer.69Sundevedsgade/Tndergadeutilized and not utilized PV power010203040506070024681012peak power of PV-panels / fan powercovered by PV - not utilizedt PV power %fan power coveredby PVnot utilized PVpowerFigure 3.55.Utilized and not utilized PV power dependent on the ration between the peakpo
305、wer of the PV-panels and the actual fan power.704. ConclusionsThe following conclusions are common for both measuring projects under PV-VENT: Lun-debjerg (Jensen, 2001) and Sundevedsgade/Tndergade.4.1. Aims of the PV-VENT projectThe aims of the projects was research, development and tests in the fol
306、lowing areas:-develop and illustrate different ways of architectural integration of solar energy systemswith combined PV power production and pre-heating of ventilation air in buildings-investigate the potential in pre-heating fresh air to the building by cooling the PV-panelswith the fresh air and
307、further to determine how much this cooling will increase the elec-trical performance of the PV-panels-develop and test air to air heat exchangers with an efficiency of 80 % or above-develop and test fans and ventilation systems with an overall fan power demand ofabout 35 W-develop and test a direct
308、coupling of the PV-panels to the fans in order to avoid thelosses in an inverter-develop and test different ventilation systems utilizing the above-mentioned features4.2. Results from the PV-VENT project4.2.1. Architectural resultsDifferent ways of integrating PV-VENT systems in the building envelop
309、e has been developedand tested:LundebjergThree different ways of integrating PV-panels with pre-heating of fresh air to the buildinghave been demonstrated in Lundebjerg: a large PV-gable with amorphous PV-panels, a PV-facade with polycrystaline (c-Si) PV-panels and solar ventilation chimneys with po
310、lycrysta-line (c-Si) PV-panels. Especially the latter feature the solar ventilation chimney is a newand interesting concept as it allows for increased PV areas although the orientation of thebuilding is not optimal for utilization of solar energy - as was the case in Lundebjerg.However, the Lundebje
311、rg project is not only interesting due to the demonstrated methods forarchitectural integration of PV systems in buildings. As a part of the project an architecturalcompetition on the renovation of the building including PV-VENT systems was held in 1998with five well known Danish architect firms. Th
312、e result of the competition is seen at Lun-debjerg today, but many other ways of introducing PV-VENT systems was proposed in the71not winning contributions way of introducing PV-VENT systems that may be utilized byothers in future projects.Sundevedsgade/TndergadeIn this building only on way of integ
313、rating PV-VENT systems is tested. The integration tech-nique is, however, very interesting as the PV-panels is integrated in a solar wall also contain-ing the heat exchangers. The solar wall is further integrated with a new sun space for eachdwelling.General conclusions on architectureSeveral new an
314、d interesting way of solving building integration of PV-VENT systems hasbeen developed. Several of these have further been demonstrated in the project. It is believedthat the results from the project will influence future projects in this field.4.2.2. Pre-heating of fresh air cooling of PV-panelsThe
315、 aim of pre-heating fresh air by cooling the PV-panels is twofold: reduce the ventilationlosses of the building while increasing the performance of the PV-panels.The actual benefit of the pre-heating of the fresh air to the buildings has been low. The rea-sons for this are several:-The absorber of t
316、he “solar air collectors” is the PV-panels. There is no cover in front ofthe absorbers as cooling of the PV-panels with ambient air is desirable in order to keepthe cell temperature down and thereby the efficiency of the PV-panels up. This de-creases the efficiency of the system as solar air collect
317、or the efficiency is less thanhalf of the efficiency of a good traditional solar air collector-The very high efficiency of the heat exchangers in the system see later decreases theutilizable part of the pre-heating in the solar wall, PV-facade and solar ventilationchimneys. The projects showed that
318、only about one third of the pre-heating by the sunactually was utilized-It was decided that the PV-panels should be cooled on the backside by natural ventila-tion during the summer in order to save fan power. This means that the air cap behindthe PV-panels has to be rather wide in order to decrease
319、the pressure loss across the PV“solar air collectors”. The air speed in forced air flow mode will then be low leading toa low heat transfer coefficient between the backside of the PV-panels and the air. Thisagain results in a low efficiency of the solar air collectorsThe solar wall at Sundevedsgade/
320、Tndergade showed a higher benefit of the pre-heating inthe solar wall than shown at Lundebjerg. The reason for this is the high heat loss from thebuilding to the solar wall rather than utilization of solar radiation.The measured temperature of the PV-panels was often rather high 50C due to the low a
321、irspeeds behind the PV-panels. The benefit of the cooling of the PV-panels was therefore low.72Due to the low benefit of the pre-heating by the sun this feature should carefully be evaluatedbefore chosen in future projects.4.2.3. Air to air heat exchangersBased on the measurements in the two project
322、s the normalized efficiency of the air to air heatexchangers has been found. The normalized efficiency is when the two air flow rates areidentical this is the normal way to state the efficiency of air to air heat exchangers. Thenormalized efficiency was found to lay around 80 %. The actual efficienc
323、y was shown to beboth much below or much above 80 % due to too large differences between the two air flowsand due to condensation in the heat exchangers.The aim of the project regarding efficient heat exchangers was thus fulfilled.4.2.4. Low fan powerThe necessary fan power in the balanced ventilati
324、on systems with heat recovery was shown tobe 38 W per dwelling for Lundebjerg and 52 W per dwelling for Sundevedsgade/Tndergade.The higher fan power at Sundevedsgade/Tndergade is caused by the higher pressure loss inthe heat exchanger arrangement. The high pressure loss of the heat exchangers at Sun
325、deveds-gade/Tndergade is due to the many bendings in the duct works necessary due to the locationin the solar wall.38 W is very close to the aim of 35 W. If further the contribution from the PV-panels is sub-tracted (10-15 % of the necessary fan energy) the average necessary fan power is 32-34 W.4.2
326、.5. Direct coupling of PV-panels to fansElectricity from PV-panels cannot be the only supply to the fans as the fans run day and nightand because hardly any solar radiation is available during large part of the winter meaningthat a battery bank and the area of PV-panels should be large.Instead it wa
327、s decided to develop a so-called PV-mixer, which is in charge of utilizing asmuch as possible of the available PV power while topping up with power from the grid whenthe PV power is too low or not present.The measurements show that the developed PV-mixer works as intended. The efficiency ingrid mode
328、 is 96 % but below 90 % is pure PV mode. The latter efficiency can maybe be in-creased by further development of the concept.The main problem with the concept of coupling of the PV-panels to the fans via a PV-mixerrather than an inverter is that excess power from the PV-panels is not utilized i.e. i
329、f the PV-panels are able to supply more power than the demand of the fans this excess power is lost.For this reason one should not aim at cowering more than 15 % of the energy to the fans byPV via a PV-mixer. Below 15 % the waste of PV energy will stay below 20 %. If the wish isto cover a larger fra
330、ction of the energy to the fans by PV it may be wiser to apply an inverterrather than a PV-mixer.734.2.6. Total systemsSeveral total ventilation system utilizing the above described features and techniques has beendeveloped and tested in the project both individual and common ventilation systems.The
331、 individual systems were all equipped with a control panel in the dwellings. The tenantsare thus able to change the way the systems run. The tenants are happy that they themselvescan decide how the systems should run. But there is a high risk that the systems are run im-properly i.e. at too low air
332、flow rates because e.g. the noise from the fans (although very si-lent) annoys the tenants.The tenants are not allowed to control the common ventilation systems one ventilation sys-tem per three dwelling. This has, however, not lead to a more proper running of these systemsthan the individual system
333、s. Due to the low pressure drops in the systems and the thereby lowspeed of the fans, the systems has been very difficult to balance. There has for that reasonbeen several complaints. This illustrates that special care should be taken when dimensioningthis type of systems with low pressure losses es
334、pecially the fans should fit the actual de-mands.The testing of the complete systems rather than components has revealed much valuable in-formation on the influence of one component on the other components of the systems whichin the future may lead to better systems.4.2.7. General conclusionsIt is b
335、elieved that the PV-VENT project has added important information and experience tothe field of combining PV and ventilation systems. Information and experience that futuresystems of this type may benefit from. Several of the components from the project are be-lieved to be able to contribute to set t
336、he standards for future PV and ventilation systems. Sev-eral of the components from the project is today commercial available and are used in ordi-nary building projects.745. ReferencesDuffie, J.A. and Beckman, W.A., 1991. Solar Engineering of Thermal Processes. John Wiley& Sons, New York. ISBN 0-47
337、-51056-4.Dutr W.L., 1985. A Thermal Transient Simulation Model for Thermal Solar Systems EMGP2. Solar Energy R&D in the European Community, series A, volume 5. D. ReidelPublishing Company. ISBN 90-277-2051-7.Cenergia, 1999. Technical report on renovation project in Sundevedsgade 14, Tndergade 1,Cope
338、nhagen. Cenergia Energy Consultants.Hansen, H.E., Kjerulf, P. and Stampe, O.B. (ed), 1997. Heating and climate technology (inDanish). Danvak Aps. ISBN 87-982652-8-8.Jensen and Pedersen, 1999. PV-VENT, Technical Progress Report, first two years Te-moVex Denmark.Jensen, 2000. Measuring report PV-mixer
339、 (in Danish). Solar Energy Centre Denmark, Dan-ish Technological Institute. August 2000.Jensen, 2001. Results from measurements on the PV-VENT systems at Lundebjerg. Solar En-ergy Centre Denmark, Danish Technological Institute. SEC-R-14. ISBN 87-7756-611-0.Leppnen, 1999. PV-VENT, Technical Progress
340、Report, first two years Neste/NAPS.Leppnen, 2000. Solar panels Maintenance and Operation Guide. Sundevedsgade/Tonder-gade, Copenhagen, Denmark. Fortum.Lien, A.G. and Hestness, A.G., 1999. Architectural Integration of PV for ventilation in threebuildings in Denmark PV-VENT, Low cost energy efficient
341、PV-Ventilation in retrofithousing. Department of Building Technology, Norwegian University of Science andTechnology.Mehr, 2000, Evaluation report PV-mixer. (in Danish). Solar Energy Centre Denmark, Dan-ish Technological Institute. January 2000.Nielsen, J.E., 1995. Documentation of KVIKSOL a program
342、for simulation of solar heatingsystems (in Danish). Version 5.0. Solar Energy Laboratory, Danish Technological In-stitute Energy.Olsen, H., 1998. Measuring report for heat exchangers from Temovex (in Danish). DanishTechnological Institute.SBI, 1982. Weather Data for HVAC and Energy Danish Test Reference Year. DanishBuilding Research Establishment. SBI Report no. 135.75Appendix ADrawings of theheat exchanger with fans(unfortunately only available in Danish)78Appendix BData sheets forthe PV-panels
