Dear Equesters,
We have one building where we are proposing to
cool the condenser of chiller by Ground sourse heat pump(Geothermal
system) rather than cooling by cooling tower. As i have studied the
literature about GSHP it says that since earth tempearture remains constant
through out the year and hence the COP of chiller will be better as
condenser entering temperature is reduced but how can i model the increase
of COP due to this ,should i reduce this value directly in chiller EIR or
there is some indirect method.
Regards
Sambhav
The performance map in the heat pump should account for this when you?re connected to the Lake/Well circulation loop. You can plot the hourly EIR from the heat pump to confirm this.
That said, the ground temperature in the Earth is relatively constant if you go deep enough. Surface temperatures will fluctuate to a depth of about 2-3m. However, if you only plan on rejecting heat to the ground, the temperature of the ground will increase unless you?re in a highly conductive area such as a swamp.
In a typical geoexchange field with a starting temperature of 50F (10C), the ground temperature will vary between 40F (4C) and 85F(29C) over the course of a year as heat is rejected to the ground in the summer, and removed from the ground over the winter.
I would caution against solely rejecting heat to the ground from your heat pump unless your conductivity is sufficiently high and/or your geoexchange system is sufficiently large to let the heat bleed away during the winter.
The real value in a geoexchange system comes from recovering this heat in the winter so you?re heating your building from a relatively warm source rather than from a fossil fuel or electrical resistance. Often geoexchange systems use more energy than a high performance chiller with open cooling tower for cooling, but make that up by being a very efficient heat source. If you have no need for heat, a centrifugal chiller with an open tower might be a better solution.
Hope that makes sense,
Fred
Fred Betz PhD., LEED AP