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IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

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<strong>IEA</strong> SHC Task 38 <strong>Solar</strong> Air Conditioning <strong>and</strong> Refriger<strong>at</strong>ion Subtask A Report, D<strong>at</strong>e: November 2010<br />

4.2.2 Free cooling<br />

The CoolCabin is equipped with a special hydraulic design in order to run on a free cooling<br />

mode. This fe<strong>at</strong>ure is included to ensure the cooling of the office rooms also on days without<br />

sunshine. Therefore the chiller is bypassed so th<strong>at</strong> the cooling tower is able to run on wet<br />

mode <strong>and</strong> can serve the cooling load directly. The mode is activ<strong>at</strong>ed if the outside<br />

temper<strong>at</strong>ure is falling below 21.5°C <strong>and</strong> the office still has a cooling dem<strong>and</strong>.<br />

Similar to the absorption chiller above a day in August was picked out in order to evalu<strong>at</strong>e<br />

the oper<strong>at</strong>ion behavior of the free cooling mode. In Figure 10 the free cooling power, the<br />

solar yield <strong>and</strong> four temper<strong>at</strong>ures are drafted in a diagram. To be able to compare the solar<br />

yield to a st<strong>and</strong>ard sunny summer day the solar radi<strong>at</strong>ion of the August 25, 2009 is added.<br />

It can be seen th<strong>at</strong> the free cooling mode started three times th<strong>at</strong> day, always switching on<br />

when the outside temper<strong>at</strong>ure falls under 21.5°C <strong>and</strong> stopping when the outside temper<strong>at</strong>ure<br />

exceeds the 22°C level. The room temper<strong>at</strong>ure stays quite stable throughout the day<br />

showing a slight downtrend in a b<strong>and</strong>width between 25°C-23°C. Furthermore the flow <strong>and</strong><br />

return temper<strong>at</strong>ure to the radiant ceiling of the office shows values between 18-16°C/19-<br />

17°C (flow/return). The realized temper<strong>at</strong>ure differ ence between flow <strong>and</strong> return temper<strong>at</strong>ure<br />

is very small. In total 71 kWh cold were delivered to the office rooms on th<strong>at</strong> day.<br />

Figure 10: Free cooling oper<strong>at</strong>ion performance of the CoolCabin on the Aug. 29, 2009<br />

The cooling power revealed a saw tooth tread design which can also be seen in the<br />

developing of the radiant ceiling flow temper<strong>at</strong>ure. In Figure 11 the practical oper<strong>at</strong>ion<br />

experience of the August 23, 2009 is marked in a diagram. The room temper<strong>at</strong>ure stays<br />

stable between 25°C <strong>and</strong> 23°C. In night times the fr ee cooling mode is activ<strong>at</strong>ed <strong>and</strong> running<br />

on a poor power level. On the day the chiller is oper<strong>at</strong>ing <strong>at</strong> an average power level of 10<br />

kW. The room temper<strong>at</strong>ure in this time declines only slightly.<br />

page 12

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