I am asked this question by a customer: How much more efficient is a water-air system versus air to air when you have to run your well pump.  5.2 cop versus 3.88 cop.,  or is it any more efficient?

Does the efficiency take in to consideration of the pump?

The COPs published are without the circulation or well pumps. AIR to AIR systems really drop in performance due to cooler air now, the benefit of the geo systems come in because the ground is much warmer right now as a heat source. Same is true for the summer, where the ground is colder than the air.

Posted By How on 21 Jan 2011 12:39 AM 
How much more efficient is a water-air system versus air to air when you have to run your well pump.  5.2 cop versus 3.88 cop.,  or is it any more efficient?

Your COPs are likely only for snapshots in the season. Geo average (generally) COP will be in the 3.5 to 4 range. Air source less.

Now closed loop does not require the well pump cost but has a higher starting price. Open loop however can actually have a higher average COP due to higher EWTs and may also occasionally permit the use of a smaller unit.

Air source can't be beat in some applications, but that is seldom true in my AO. That is why every project is designed on a case by case basis, not by rules of thumb.

Joe

Posted By joe.ami on 21 Jan 2011 09:07 AM
Open loop however can actually have a higher average COP due to higher EWTs...

True. OTOH, open loop might have a lower overall COP due to
higher pumping costs -- especially if the well is deep.

Posted By Looby on 21 Jan 2011 11:23 AM

Posted By joe.ami on 21 Jan 2011 09:07 AM
Open loop however can actually have a higher average COP due to higher EWTs...

True. OTOH, open loop might have a lower overall COP due to
higher pumping costs -- especially if the well is deep.

Of course. I should have qualified; higher average COP "without factoring pump cost".
To an unscientific guy like myself I look at these things as the law of "no free lunch" which is no less firm than the law of gravity.
Open loop = higher COP (sans pumping cost), has more btu's available (requiring less aux contribution) and cheaper installation but costs as much to operate (or more) and more maintenance.....meanwhile closed loop costs more to install and may have lower average COP it also requires more auxiliary contribution but it costs about the same or less to operate and requires less auxiliary contribution.
The only thing that really cheeses me about any of these conversations is when people use the term "more efficient" as though it is a universal fact for one system or another. Each is best designed job by job- budget by budget.

j

An artesian well with sufficient pressure and volume of quality water with an open loop system would be the way to go.  I mention this obvious fact because artesian wells are available in some areas.  Along this same line of thinking one should consider using a closed loop system when the building is located close to a large deep pond.  I have a client now that I could not convince to use this setup five years ago but now is wondering why he did not.

I have another client that already has a well and pump that produces enough water to fill a pond that I could not convince to install geothermal.

A lot of potential new homeowners read this forum but some may not realize they should use available resources that can lower initial and future operating cost.  I agree with Joe that each application should be considered on its own merits.