Author Topic: Advice for New Open Loop System  (Read 225 times)

JSDrummer1

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Advice for New Open Loop System
« on: July 13, 2017, 11:30:29 PM »
I'm getting ready to build a house in a few months and I am determined to have a "pump and dump" open loop geothermal heat pump installed. I also have to have a water well for domestic water anyway, so I'm planning to use the same well for both. I was looking at variable speed pumps, but based on the reviews on this site and others, it sounds like that would be a big mistake.

The CSVs with a pressure tank definitely seem like the way to go, but I'm concerned about the efficiency loss of the heat pump getting water from the pressure tank that would either be in the garage, or outside in a pump house. In the summer, both the garage and a pump house would be hot in the summer and cold in the winter, so drawing water from the pressure tank will be hot during the cooling season, and cold during the heating season. Won't that cause the heat pump to lose efficiency? I realize that eventually, it would be fresh, cool groundwater that's running through the system once the pressure drops enough, but the time it takes to get to that point seems like a problem to me. Is there anything I can do about this?

Cary Austin

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Re: Advice for New Open Loop System
« Reply #1 on: July 14, 2017, 07:44:11 AM »
Even big pressure tanks like an 86 gallon size tank only holds 25 gallons of water.  25 gallons won't last long for a 6-9-12 GPM heat pump.  But with a CSV you only need a 4.5 gallon size tank, which only holds 1 gallon of water.  So worrying about the temp of the water coming out of the tank is a moot point.  I sort of have the same problem with my geo system.  The underground lines coming to the house are not deep enough, so I get hotter water coming in the summer and cooler water in the winter.  But it still works fine.

The trick to efficiency for a pump and dump system is using the smallest well pump possible.  It sometimes pays to have a 2 pump system.  This way the well pump can be smaller because it only supplies 20 PSI to the heat pump.  Then you have an additional jet pump booster that only comes on when needing water in the house.  The booster pump comes on and boost the 20 PSI to 50 PSI when the house needs water.  The majority of the time the well pump is the only one running, and feeding the geo 20 PSI is more efficient that feeding it 50 PSI.

See this thread.  http://www.cyclestopvalves.com/smf/index.php?topic=2093.0
« Last Edit: July 14, 2017, 07:46:02 AM by Cary Austin »

JSDrummer1

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Re: Advice for New Open Loop System
« Reply #2 on: July 15, 2017, 04:23:46 PM »
Very helpful. Thank you. One follow-up.

In the forum post you referenced, the original solution was to use a 2 HP pump and replaced with a 1 HP and a 3/4 HP pump.

In my situation, the well contractor recommended a 1 HP 25 gpm pump for both the house water and my single, 4 ton geothermal heat pump. Would the 2 pump solution still provide energy savings in my scenario?

Cary Austin

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Re: Advice for New Open Loop System
« Reply #3 on: July 16, 2017, 06:32:49 PM »
Even better!  You just need a 1/2HP, 25 GPM well pump, and a 1/2HP jet pump to boost pressure when the house needs water.