Heat pipe sensible heat transfer effectiveness in energyplus

asked 2016-08-03 15:36:45 -0500

812 ●2 ●12

I am going to use series heat pipes for cooling coils in a model that I´m doing. Energyplus has an object called CoilSystem:CoolingWater:HeatExchangerAssisted to do this. I would like to know what is the average sensible heat transfer effectiveness in energyplus. I know that typical sensible heat transfer effectiveness for this kind of application is 32%. But I did not find a specific value in the engineering reference manual. I will appreciate your help. Thank you.

answered 2016-08-04 07:45:21 -0500

rraustad

13599 ●72 ●12 http://www.fsec.ucf.edu/

Carlos, the 2 HXs used in this object define the effectiveness used in the simulation. The HeatExchanger:AirToAir:FlatPlate uses the NTU method where design effectiveness is derived from user inputs. The other HX is HeatExchanger:AirToAir:SensibleAndLatent where effectiveness is a user input. Since the SensibleAndLatent model does have report variables for effectiveness while the FlatPlate model does not I assume you are asking about the FlatPlate model and what the effectiveness is during your simulation. You can post process this information using the T and w node reports at the inlet/outlet of the HX.

Using node reporting: Output:Variable,,System Node Temperature,hourly; !- HVAC Average [C] Output:Variable,,System Node Humidity Ratio,hourly; !- HVAC Average [kgWater/kgDryAir]

The temperature effectiveness is:

Eps = ( Tsup,out - Tsup,in ) / ( Texh,in - T sup,in ) pg. 179 Engineering Reference, Eq 15.1139

Same equation for w effectiveness.

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Thank you for the clarification. I revised the manual again and the objects in my idf editor. For my case I realized that I have to use the CoilSystem:CoolingWater:HeatExchangerAssisted object together with another object HeatExchanger:AirtoAirSensibleAndLatent. For heat pipes in series with a cooling coil then I have to enter user inputs of effectiveness for sensible heat transfer only.