[Bldg-sim] Geo-thermal Heat Pump (UNCLASSIFIED)

[Fred Betz]

John,

eQuest can model a geoexchange field but there are a lot of limitations. There is an upper limit on field size and there are limitations on the plant side as well. You can use a single zone heat pump configuration or try to setup a loop-to-loop heat pump, but that can get nasty. 

To do an accurate model of a geoexchange system you'd probably be best off using TRNSYS and/or a manufacturer's software. TRNSYS has a steep learning curve and the manufacturer's software can be a bit of a black box with hidden factors of safety, etc. Also TRNSYS can only do cylindrical fields, which can be a significant limitation in some instances.

I've never tried a geoexchange model in Trace.

Getting an accurate heat pump performance curve can be challenging. To make a good performance map in TRNSYS takes about 50 selections at varying inlet temperatures on both evaporator and condenser sides. Then there is a whole other ball of wax called controls. 

What we typically do is model the building and get hourly loads in eQuest. And then transfer the loads to TRNSYS to be modeled there with a field sized using manufacturer software. It's unfortunately a bit of a convoluted process to right size a field, but it is worth it as design costs are much less than construction costs for large fields. 

If you have a small field you probably could get away with getting loads out of Trace or eQuest and placing it in the manufacturer's software. 

Sorry for the long convoluted answer. 

Good luck!


Fred


FRED BETZ  PhD., LEED AP 
SUSTAINABLE SYSTEMS ANALYST
 
AEI | AFFILIATED ENGINEERS, INC.  
5802 Research Park Blvd. | Madison, WI  53719

P: 608.236.1175 | F: 608.238.2614  
fbetz at aeieng.com  |  www.aeieng.com  



-----Original Message-----
From: Eurek, John S NWO [mailto:John.S.Eurek at usace.army.mil] 
Sent: Tuesday, February 22, 2011 10:28 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Geo-thermal Heat Pump (UNCLASSIFIED)

Classification: UNCLASSIFIED
Caveats: NONE

The EER of WWHP can vary from 11.8 to 23.3 depending on the water temperature
returning from the well field.  Can Trace or Equest model this?

I'm starting to design a lot of geo-thermal systems, but I can't model the
well field performance, my models accuracy will be greatly affected. 

Classification: UNCLASSIFIED
Caveats: NONE