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 11 Humidity distribution 54 Temperature distribution 10.5 52 10 50 Humidity ratio [g.kg -1 ] 9.5 9 8.5 8 7.5 7 Temperature [ C] 48 46 44 42 40 6.5 model experimental 6 0 20 40 60 80 100 120 140 160 180 Angular position [ ] 38 36 0 20 40 60 80 100 120 140 160 180 Angular position [ ] model experimental Figure 26: Comparison of the predicted and measured temperature and humidity distribution at the outlet of the desiccant wheel The profiles obtained numerically are coherent with the measured profiles and we notice 0.3 g/kg error in the humidity ratio while an error of 2°C in the temperature. The outlet conditions of the desiccant wheel depend on the temperature and humidity at both inlets of the wheel. In order to validate the detailed and the simplified models of the wheel were considered. Different inlet conditions were considered: the inlet temperature of the process stream varies between 25 and 35°C while the humidity ratio varies between 10 and 15 g/kg and the regeneration temperature was considered varying from 60 to 80°C. Humidity ratio deviation [g.kg -1 ] 2 1.75 1.5 1.25 1 0.75 0.5 0.25 0 -0.25 -0.5 -0.75 -1 -1.25 -1.5 -1.75 -2 Detailed model T reg =80 T reg =70 T reg =65 T reg =60 measurement accuracy -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 Temperature deviation [ C] Figure 27: Comparison of the predicted and measured mean outlet temperature and humidity at the outlet of the desiccant wheel. page 54
IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C2-A, November 9, 2009 Figure 27 gives the temperature and humidity ratio deviations at the outlet of the desiccant wheel for the detailed. The maximum humidity ratio deviation of the detailed model is 0.4 g/kg and the maximum temperature deviation is 2°C. The uncertainty of the mean temperature at the outlet of the wheel is in the order of 1 to 1.5°C (inhomogeneous outlet with 10°C gradient) and the uncertainty of the humi dity ratio is 0.35 g/kg. The uncertainty of the humidity is evaluated by comparing the mean humidity at the outlet of the wheel (position 2) with the absolute humidity at points 3, 4 and 5 (with reference to figure 1) while turning off the supply humidifier. In these conditions the humidity must be constant. We notice that the humidity ratio deviations are in the domain of the validity of the measurements. The detailed model established of the physical description shows the same accuracy independently of the regeneration temperature. Conclusion In this chapter a model of the solar desiccant installation is developed and validated experimentally. First the components model considered solely showed acceptable accuracy and low errors under different operating conditions. Then the overall model of the air handling unit coupled with the solar installation gave satisfactory results for the considered day and predicts accurately the supply air conditions. For the developed solar collector model it showed a good accuracy in predicting the outlet temperature under transient operating conditions and permits a good estimation of the potential of the collectors in transient conditions. This model was used to elaborate control strategies and to optimize the operations of the installation in function of outside and load conditions. The developed detailed transient model of the desiccant wheel showed a good accuracy in predicting the temperature and humidity distribution at the outlet of the wheel as well as the mean outlet temperature and mean outlet humidity ratio. This detailed model is not suited for seasonal simulation but it is very useful to elaborate control strategy and to study transient behaviour of the desiccant air handling unit. The model can be used to study different desiccant materials. page 55
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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 />
Figure 27 gives the temper<strong>at</strong>ure <strong>and</strong> humidity r<strong>at</strong>io devi<strong>at</strong>ions <strong>at</strong> the outlet of the desiccant<br />
wheel for the detailed. The maximum humidity r<strong>at</strong>io devi<strong>at</strong>ion of the detailed model is 0.4<br />
g/kg <strong>and</strong> the maximum temper<strong>at</strong>ure devi<strong>at</strong>ion is 2°C. The uncertainty of the mean<br />
temper<strong>at</strong>ure <strong>at</strong> the outlet of the wheel is in the order of 1 to 1.5°C (inhomogeneous outlet<br />
with 10°C gradient) <strong>and</strong> the uncertainty of the humi dity r<strong>at</strong>io is 0.35 g/kg. The uncertainty of<br />
the humidity is evalu<strong>at</strong>ed by comparing the mean humidity <strong>at</strong> the outlet of the wheel (position<br />
2) with the absolute humidity <strong>at</strong> points 3, 4 <strong>and</strong> 5 (with reference to figure 1) while turning off<br />
the supply humidifier. In these conditions the humidity must be constant. We notice th<strong>at</strong> the<br />
humidity r<strong>at</strong>io devi<strong>at</strong>ions are in the domain of the validity of the measurements. The detailed<br />
model established of the physical description shows the same accuracy independently of the<br />
regener<strong>at</strong>ion temper<strong>at</strong>ure.<br />
Conclusion<br />
In this chapter a model of the solar desiccant install<strong>at</strong>ion is developed <strong>and</strong> valid<strong>at</strong>ed<br />
experimentally. First the components model considered solely showed acceptable accuracy<br />
<strong>and</strong> low errors under different oper<strong>at</strong>ing conditions. Then the overall model of the air<br />
h<strong>and</strong>ling unit coupled with the solar install<strong>at</strong>ion gave s<strong>at</strong>isfactory results for the considered<br />
day <strong>and</strong> predicts accur<strong>at</strong>ely the supply air conditions. For the developed solar collector<br />
model it showed a good accuracy in predicting the outlet temper<strong>at</strong>ure under transient<br />
oper<strong>at</strong>ing conditions <strong>and</strong> permits a good estim<strong>at</strong>ion of the potential of the collectors in<br />
transient conditions. This model was used to elabor<strong>at</strong>e control str<strong>at</strong>egies <strong>and</strong> to optimize the<br />
oper<strong>at</strong>ions of the install<strong>at</strong>ion in function of outside <strong>and</strong> load conditions.<br />
The developed detailed transient model of the desiccant wheel showed a good accuracy in<br />
predicting the temper<strong>at</strong>ure <strong>and</strong> humidity distribution <strong>at</strong> the outlet of the wheel as well as the<br />
mean outlet temper<strong>at</strong>ure <strong>and</strong> mean outlet humidity r<strong>at</strong>io. This detailed model is not suited for<br />
seasonal simul<strong>at</strong>ion but it is very useful to elabor<strong>at</strong>e control str<strong>at</strong>egy <strong>and</strong> to study transient<br />
behaviour of the desiccant air h<strong>and</strong>ling unit. The model can be used to study different<br />
desiccant m<strong>at</strong>erials.<br />
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