IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at
IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at
IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask A Report, Date:… In order to operate a latent heat storage as efficient part of a heating or cooling system, precise information about the actual energy content of the storage is essential. Due to the fact that a metering method for the thermal content of a latent heat storage is still a matter of development, up to now the potential for efficient charging and discharging of the storage could not be fully exploited. As a first attempt, different approaches using a heat meter to indicate the actual state of charge had only little success due to the small temperature difference of the heat carrier between storage inlet and outlet and the resulting inaccuracy of the control. To integrate the storage into the solar heating and cooling system despite the missing charge control, for the moment different temperature criteria are used to achieve a rough estimate of the actual state of charge. The development of a more precise metering procedure is ongoing. Figure 8 shows the transferred heat for a series of loading and unloading cycles of the mentioned latent heat storage during solar cooling operation in summer 2008 an 2009, respectively. In cooling mode complete discharge of the accumulated heat during the following night is strived for. Yet , due to the imperfect charge control a substantial mismatch between loading and unloading of the storage occurred in 2008. Finally, by improving the control strategy in 2009 the daily disbalance of the heat storage has been minimized. As a second conclusion from Figure 8, it can be stated that the storage allows for efficient mid-term storage, e.g. storage periods of some days, without substantial heat loss: A proof is given by the period May 23 to 30, 2008, when the solar gain accumulated during 8 days is almost completely extracted on two days only. Heat / kWh 120 100 80 60 40 20 0 -20 -40 -60 -80 -100 -120 charge discharge 2008 21.05.08 22.05.08 23.05.08 24.05.08 25.05.08 26.05.08 27.05.08 28.05.08 29.05.08 30.05.08 31.05.08 Heat / kWh 2009 120 100 loading 80 60 40 20 0 -20 -40 -60 -80 -100 unloading -120 11.08.2009 12.08.2009 13.08.2009 14.08.2009 15.08.2009 16.08.2009 17.08.2009 18.08.2009 19.08.2009 20.08.2009 21.08.2009 Fig. 8. Loading / unloading cycles of the PCM Storage 2008 / 2009
IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask A Report, Date:… In 2008 a substantially higher level of insolation compared to 2009 allowed for a higher solar heat accumulation accompanied by a lower building heat demand. Consequently, a monthly solar fraction of 24 % to 85 % was reached in the period Jan – March 2008, whereas under severe winter condition in January and February 2009 the solar coverage was limited to 15 to 18 % only. In the transitional period March/April 2008 and April/May 2009 almost fully solar coverage has been reached. For the whole winter periods 2008 and 2009 solar fractions of 48 % and 33 % have been achieved, as shown in Fig. 9. January solar fraction 23 % (LT) 24 % (total) Februrary solar fraction 50% (LT) 73% (total) March solar fraction 50% (LT) 85% (total) April solar fraction 72% (LT) 98% (total) Mai cooling kWh 200 150 100 50 0 kWh 400 350 300 250 200 150 100 50 0 missing data missing data missing data High Temperature >50°C Low Temperature (LT) 50°C Low Temperature (LT)
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<strong>IEA</strong> SHC Task 38 <strong>Solar</strong> Air Conditioning <strong>and</strong> Refriger<strong>at</strong>ion<br />
Subtask A Report, D<strong>at</strong>e:…<br />
In order to oper<strong>at</strong>e a l<strong>at</strong>ent he<strong>at</strong> storage as efficient part of a he<strong>at</strong>ing or cooling system,<br />
precise inform<strong>at</strong>ion about the actual energy content of the storage is essential. Due to the<br />
fact th<strong>at</strong> a metering method for the thermal content of a l<strong>at</strong>ent he<strong>at</strong> storage is still a m<strong>at</strong>ter of<br />
development, up to now the potential for efficient charging <strong>and</strong> discharging of the storage<br />
could not be fully exploited. As a first <strong>at</strong>tempt, different approaches using a he<strong>at</strong> meter to<br />
indic<strong>at</strong>e the actual st<strong>at</strong>e of charge had only little success due to the small temper<strong>at</strong>ure<br />
difference of the he<strong>at</strong> carrier between storage inlet <strong>and</strong> outlet <strong>and</strong> the resulting inaccuracy of<br />
the control. To integr<strong>at</strong>e the storage into the solar he<strong>at</strong>ing <strong>and</strong> cooling system despite the<br />
missing charge control, for the moment different temper<strong>at</strong>ure criteria are used to achieve a<br />
rough estim<strong>at</strong>e of the actual st<strong>at</strong>e of charge. The development of a more precise metering<br />
procedure is ongoing.<br />
Figure 8 shows the transferred he<strong>at</strong> for a series of loading <strong>and</strong> unloading cycles of the<br />
mentioned l<strong>at</strong>ent he<strong>at</strong> storage during solar cooling oper<strong>at</strong>ion in summer 2008 an 2009,<br />
respectively. In cooling mode complete discharge of the accumul<strong>at</strong>ed he<strong>at</strong> during the<br />
following night is strived for. Yet , due to the imperfect charge control a substantial mism<strong>at</strong>ch<br />
between loading <strong>and</strong> unloading of the storage occurred in 2008. Finally, by improving the<br />
control str<strong>at</strong>egy in 2009 the daily disbalance of the he<strong>at</strong> storage has been minimized.<br />
As a second conclusion from Figure 8, it can be st<strong>at</strong>ed th<strong>at</strong> the storage allows for efficient<br />
mid-term storage, e.g. storage periods of some days, without substantial he<strong>at</strong> loss: A proof<br />
is given by the period May 23 to 30, 2008, when the solar gain accumul<strong>at</strong>ed during 8 days is<br />
almost completely extracted on two days only.<br />
He<strong>at</strong> / kWh<br />
120<br />
100<br />
80<br />
60<br />
40<br />
20<br />
0<br />
-20<br />
-40<br />
-60<br />
-80<br />
-100<br />
-120<br />
charge<br />
discharge<br />
2008<br />
21.05.08<br />
22.05.08<br />
23.05.08<br />
24.05.08<br />
25.05.08<br />
26.05.08<br />
27.05.08<br />
28.05.08<br />
29.05.08<br />
30.05.08<br />
31.05.08<br />
He<strong>at</strong> / kWh 2009<br />
120<br />
100<br />
loading<br />
80<br />
60<br />
40<br />
20<br />
0<br />
-20<br />
-40<br />
-60<br />
-80<br />
-100<br />
unloading<br />
-120<br />
11.08.2009<br />
12.08.2009<br />
13.08.2009<br />
14.08.2009<br />
15.08.2009<br />
16.08.2009<br />
17.08.2009<br />
18.08.2009<br />
19.08.2009<br />
20.08.2009<br />
21.08.2009<br />
Fig. 8. Loading / unloading cycles of the PCM Storage 2008 / 2009
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