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