Will the extra power required to run the larger pump for an open loop geothermal system be offset by the power saved by using a constant Entering Water Temperature from a deep well?  For the same size geo system, how much more electricity will a larger pump for the open loop system use?

I hope I'm not taking your thread to a place you don't want it to go... Speaking of open loop costs, wouldn't periodic heat exchanger flushing maintenance costs and the initial purchase of a more resilient heat exchanger (if needed depending on water quality) add to costs? I'm not suggesting that open loop isn't worth it, but these may be factors to consider. To me, it's worth somewhat more than the cost of the additional maintenance to have a system that doesn't require as much maintenance (within reason.)

Alton,

the answer to your questions depends a lot on how deep the water level is in the well. I installed a open loop heat pump for a guy who had an artesian well and a pump was not needed.

The biggest savings on an open loop come from not having to drill or excavate in order to install a closed loop.

Condition must be very favorable for me to go with an open system. We just did a 30 ton system for a house which was sitting right on an aquafier. One supply well, one discharge well, good water (both flow and quality), 66ft deep. Equipment was $5K more due to NiCo coils and variable speed well pump. The alternative would have been 10 bores, 400ft each, overall $20K more. For 20K you can do a lot of maintenance. I think the increased operating costs for the well pump equal more than out with the higher COP and lesser equipment needs for larger systems, since now the units make more BTUs at constant 50 degrees F. For smaller, single unit systems, I still need the same amount of drilling, same 2 wells, smaller well pump. Then I need the excavator for the header trench anyway. By that time we have a horizontal loopfield installed for lessser money and never look back ....

It's not hard to run all the numbers. Water quality is a big question although it is much more of an issue with cooling than with heating. Variable speed pumps help although not by much. Keeping pressure low and using a booster pump for domestic water helps - you might even be able to avoid getting a larger pump.

Open loop is still the most common system in operation in my neighborhood. As Doc points out, on smaller applications installation may be just a couple thousand apart (there's about a thousand bucks in controls on a 2 ton or 3k in loops).
As Dewayne mentioned, pumping cost varies.
Water quality is an issue as is maintenance.
If I had to guess why there is such an explosion in closed loop systems here, I'd have to say it's a change in buyers.
Geo isn't just for engineers and gadget guys anymore....
Joe

In our area, open loop is almost unheard of. Some of the municipalities don't even allow it for fear of aquifer contamination. The installers avoid it like the plague because of the claimed maintenance issues.

Posted By tinoue on 22 Aug 2010 10:03 PM
In our area, open loop is almost unheard of. Some of the municipalities don't even allow it for fear of aquifer contamination. The installers avoid it like the plague because of the claimed maintenance issues.

Some companies sell on fear (of what the other guy is offering). Some sell on the merits of their offerings.
I am an advocate of what is best for my customer and am indifferent to what that is (open loop, closed loop, gas furnace.....).
j

As has been said, much depends on local conditions. A careful analysis of expected compressor power vs pump power tailored to the specifics of the site should indicate the right road to take.

We're about to embark on a dual well open loop system for a new beachfront house. Prior practice was 300' of closed loop bore per ton owing to relatively high ground temps. That has been pricey and is getting more so; also difficult to place multiple bores on very tight beach lots.

Interestingly, the water regulators are swinging away from favoring closed loop for coastal projects - they are worried about salt water intrusion into shallow aquifers occasioned by poorly grouted bores.

The driller will case through the upper aquifers and provide two 500' bores to the deep and high quality Floridan aquifer - though deep pressure is high - static head is expected to be just a few feet below grade, so I expect minimal pumping power and am hunting the correct pump.

I'm curious - with the discharge well level a few feet below grade, how will you apply enough pressure to get the well to accept the discharge water without overflowing?

Standing column wells have shown that a large percentage (90-100%) of the water can be returned to the same well. This might help.

Don't have to apply any pressure...the local highly porous deep aquifer both easily giveth and taketh away.

I'm aware of and curious about the applicability of an SCW to our deep aquifer. My concern is that such a lengthy section of the upper part of the bore has to be cased to isolate it from the lower quality upper aquifers that a thermal short circuit would result, rendering ineffective an SCW. This concern is unsupported by rigorous design calculation or field experience, a shortcoming I hope to remedy some day soon.

Technically, water never moves without pressure and the water level in a discharge well will always rise (and a supply well will always have some drawdown). But it is possible that the few psi created before it overflows will be enough to push the water back into the aquifer.

A long casing will reduce SCW performance but never render it completely ineffective.

Scott, an example of the crossover point where open loop is more efficient is less than 200' of head.

I expect you have data or example design calculations that you will shortly share with us to support these statements.