[Bldg-sim] Central Ground Source Heat Pump

[Jon Evans]

Raj,

You can simulate a ground loop as a lake/well loop by applying a temperature schedule to the lake/well loop.  Your annual schedule will have 12 weekly schedules set for each month of the year.  Then each weekly schedule will have a daily schedule.  Each daily schedule will have all 24 hours at the same temperature. I typically make weekly (monthly) schedules that follow the anticipated loop temperatures (heating design temp in March and cooling design temp in September and average ground temperature in shoulder months).  Your geothermal sizing software can give you this temperature profile for your particular situation. If you don't do this, then the program assumes you have water available at the average ground temperature all year from the lake/well loop.

The bigger issue is that the loop-to-loop heat pump library part load curves are not correct and WAY overestimate cooling/heating savings.  For example, using the same size/efficiency water-source chiller will use ~5 times more cooling energy than a loop-to-loop heat pump, mostly independent, of the condenser temperatures.  Try it out and let me know if you see the same thing in your model as it probably depends on how much simultaneous heat/cool you have.  You need to develop your own equipment part load curves/curves that are a stronger function of condenser temperature and not rely on the ones provided with eQUEST for loop-to-loop heat pumps connected to a geothermal field.

Best of luck... -Jon


Jon Evans, PE, LEED AP

Senior Mechanical Engineer | jevans at sustaineng.com

Sustainable Engineering Group LLC

901 Deming Way, Suite 201 | Madison, Wisconsin 53717

608.836.4488 ext. 13 | Fax: 608.836.4477
www.sustaineng.com<http://www.sustaineng.com/>

________________________________
From: Kris Raj [mailto:kris_raj at rocketmail.com]
Sent: Saturday, April 09, 2011 6:13 PM
To: Bldg-sim
Subject: [Bldg-sim] Central Ground Source Heat Pump

Hello,
I am trying to simulate a ground source heat pump system where the ground loop is attached to a central water source four pipe heat pump system. The heat pump provides both chilled and hot water simultaneously to the air handling units in the building as required.

The chiller type loop to loop heat pump serves my purpose well. However the condenser loop of this system can only be connected to a lake/Well. I need to connect this system to a closed ground loop which I am unable to do so.

The chiller type Heat Pump allows connection to the ground loop. But, unfortunately this is only a two pipe system and does not allow simultaneous heating and cooling.

Could any one one please advice me on how to model this.

raj

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