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
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 Evans, PE, LEED AP