I've heard that measured performance of actual, installed geoexchange systems can be much lower than advertized COP numbers.

Is anyone aware of any accessible, reliable reports about real-world performance of these systems?

If not an academic-level paper, anyone have any good anecdotal information?

Thanks in advance,


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Residential Ground-Source Heat Pumps: In-Field System Performance and Energy Modeling

by Srikanth Puttagunta, Robb A. Aldrich, Douglas Owens, and Pallavi Mantha

Steven Winter Associates, Inc., Norwalk, CT

GRC Transactions, Vol. 34, 2010


This page has a link to a Manitoba Hydro study, as well as the Steven Winter study:


The Feb. 2013 issue of Energy Design Update has an interview w/ Steve Kavanaugh, ASHRAE fellow and heat pump guru. He's calling out the industry on misleading ratings, and he's a long-time GSHP researcher (literally, wrote the book on GSHPs).


This page allows you to compare heating costs using different heating systems. As always, choose your assumptions carefully:


Thanks Danny Parker, for the link to the study.


Natural gas is hard to beat for fuel cost, it's the deliver/meter charges that get you. Gas is only 50 cents per therm in our area but the meter fees add up to $360/yr. For people with well insulated homes the meter fee doesn't justify having gas installed in the home. If you have a gas meter installed, make ALL appliances natural gas. Based on our local electric/gas price structure if your house is well insulated going all electric with a standard heat pump will be the most economical operation. Our local electric company has about 1/2 price power for use over 600KWH in winter. For the most part Geothermal makes no economic sense in our area, but I see a few systems installed. Over half of all electric homes use RESISTANCE HEAT as the primary heating method. They won't pay $800 for a normal heat pump, much less $10K+ for geo.

"Why is further geothermal heat pump research needed in cold climates?

The measured performance of geothermal heat pumps in cold climates in studies that we are aware of suggests that heat pump systems don't work as efficiently as people would expect. We also have heard from customers who have geothermal heat pumps and are unhappy because they see higher heating costs than they expected."


I have a Water Furnace Envision V in my own home. Open vaulted environment with 23' ceilings. 2000 square feet. North wall is 75% glass with Low-E, low-U and low SHGC. Demilac SealEction 500 foam encapsulation of vault, walls, floor. The Envision has the domestic hot water/desuper heater feature. I DO NOT have any electric resistance back-up strips. Winter heating mode daily average consumption is 10-15 kilowatts. Purrs like a kitten...  Average year-round daily consumption is 9-kilowatts. Again...no back-up heat strips or dual fuel. 

This gets me to thinking about the installation cost of Geo. I'm thinking if your unit can do the job w/o any heat strips it's on the large side relative to the load in your home. With Geo, a lot of the installation cost is the ground loop. If the Units were sized for cooling load the downsizing may make the installation practical where it may otherwise not be. Running heat strips for a few of the coldest winter nights could be cheaper than installing another ton or 2 of ground loop and ductwork.

"I'm thinking if your unit can do the job w/o any heat strips it's on the large side relative to the load in your home."

Could be...could be not. Much depends on the climate. In some areas (south) cooling load exceeds heating load. In north Florida that is often the case. We do incorporate heat strips with air source heat pumps, mostly for defrost cycles, but we do not include heat strips with geo systems.

My bad, I wasn't considering the deep south.

Following Curt's comment - a house this well insulated and air tight, & possibly with thermal mass, may not really experience the "peak" load you think about with a leaky house in Upstate NY (or anywhere else)...  Mass, and insulation thermal inertia, can really flatten out cold spikes.  

 At 2000 sf, might be hard to find a Geo system that would be "undersized" and require supplemental heat.  

Thermal inertia is NOT considered in Manual J calculations!! Equiptment can be sized a bit smaller once inertia is considered, just don't expect quick recovery times.

Strip heat will be a requirement mostly north of NC. The amount it requires is a fraction of an air source unit. The amount of EH is so small it could cost $10 or less per year, the max I've seen is about $100/yr.

Geo outperforms every other option I've modeled. The real difference is the disparity at how they are rated. A 19 SEER HP actually Is only 12 SEER at 95 degrees. The variation in efficiency along its glide of operation could be up to 70% range, Geo is about 13%. NG is still priced without tax and regulation, and because of the lack of infrastructure to export it is keeping price based on it not being globally priced, US about $4, UK about $10/mill btu's. when our NG it will be priced globally like oil is. Payments on a Geo system usually is less than the amount saved each month giving positive cash flow from day one. Also when doing economic modeling make sure you utilize fuel escalation rate, I conservatively use 8%. Good luck, live and breathe Geo, if you don't believe how can you expect a customer to????

Bob P

With NG at current prices, no way Geo will ever have a reasonable payback time. Geo's real market is all electric homes, or those on oil/propane.


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