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 C2-A, November 9, 2009 Error propagation For the solar installation the maximum error in the temperature prediction was that of the tank with a maximum error of 1°C which yields an er ror in the prediction of the regeneration temperature. Or the experimental results showed that 1°C difference in the regeneration temperature does not have any practical impact on the performance of the desiccant wheel and thus on the supply conditions. For the air handling unit the evaporative cooler model and the sensible regenerator models has shown negligible errors. In reversal the desiccant wheel model has shown simultaneous error in temperature and humidity. Let us consider an error α in the prediction of the outlet temperature T 2 of the desiccant wheel. The temperature T 3 at the outlet of the sensible regenerator in function the inlet temperature T 2 and T 6 of the regenerator and its efficiency η: T = ( −η + ηT (24) 3 T2 1 ) 6 With the error α in the prediction of the temperature T 2 the temperature T 3 is now: ' T = T + α(1 − ) (25) 3 3 η This means that an error α in the prediction of the T 2 will yield an error (1-α) in the prediction of T 3 . Now considering an error β in the prediction of the humidity ratio at the outlet of the wheel, this will yield an error at the outlet temperature of the evaporator cooler in the order of: h fgβ ∆ T = (26) c pa h fg is the latent heat of vaporization of water. With a maximum deviation of 2°C and 0.4 g/kg in the temperature and humidity prediction at the outlet of the desiccant wheel and appropriately combining the impact of the errors we have a maximum error of 1.3°C in the prediction of the supply temperature. This is the maximum error in the supply temperature that can be committed by the model. Finlay we will compare the overall model prediction for the air handling unit coupled with the solar installation for day under typical desiccant operations. page 42
IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C2-A, November 9, 2009 Overall performance of the model A day under desiccant operation is selected to validate the overall model. The response of the model will be compared with the measured performance for the most important components and especially for the supply conditions. Figure 14 below shows the outside conditions. Temperature [ C] Outside conditions 40 35 30 25 20 15 10 5 w ext 20 1000 T ext 18 900 16 800 14 700 12 600 10 500 8 400 6 300 4 200 2 100 0 Humidity ratio [g.kg -1 ] Radiation [W.m -2 ] Solar global radiation 0 0 9 10 11 12 13 14 15 16 17 18 19 Time [hours] 9 10 11 12 13 14 15 16 17 18 19 Time [hours] Figure 14: Outside temperature and humidity ratio (left) and solar global radiation for the considered day The outlet temperature of the collectors, the temperature at the bottom and the top the storage tank as well as the regeneration temperature are shown on the figures below. We notice that the error is below 1°C in all the cases . page 43
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<strong>IEA</strong> SHC Task 38 <strong>Solar</strong> Air Conditioning <strong>and</strong> Refriger<strong>at</strong>ion Subtask C2-A, November 9, 2009<br />
Overall performance of the model<br />
A day under desiccant oper<strong>at</strong>ion is selected to valid<strong>at</strong>e the overall model. The response of<br />
the model will be compared with the measured performance for the most important<br />
components <strong>and</strong> especially for the supply conditions. Figure 14 below shows the outside<br />
conditions.<br />
Temper<strong>at</strong>ure [ C]<br />
Outside conditions<br />
40<br />
35<br />
30<br />
25<br />
20<br />
15<br />
10<br />
5<br />
w ext<br />
20<br />
1000<br />
T ext 18<br />
900<br />
16<br />
800<br />
14<br />
700<br />
12<br />
600<br />
10<br />
500<br />
8<br />
400<br />
6<br />
300<br />
4<br />
200<br />
2<br />
100<br />
0<br />
Humidity r<strong>at</strong>io [g.kg -1 ]<br />
Radi<strong>at</strong>ion [W.m -2 ]<br />
<strong>Solar</strong> global radi<strong>at</strong>ion<br />
0<br />
0<br />
9 10 11 12 13 14 15 16 17 18 19<br />
Time [hours]<br />
9 10 11 12 13 14 15 16 17 18 19<br />
Time [hours]<br />
Figure 14: Outside temper<strong>at</strong>ure <strong>and</strong> humidity r<strong>at</strong>io (left) <strong>and</strong> solar global radi<strong>at</strong>ion for the<br />
considered day<br />
The outlet temper<strong>at</strong>ure of the collectors, the temper<strong>at</strong>ure <strong>at</strong> the bottom <strong>and</strong> the top the<br />
storage tank as well as the regener<strong>at</strong>ion temper<strong>at</strong>ure are shown on the figures below. We<br />
notice th<strong>at</strong> the error is below 1°C in all the cases .<br />
page 43
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