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Frequently Asked Questions / Re: Number of Cycles, Large Tank verses CSV

« on: October 24, 2020, 04:07:22 PM »

Friction losses noted - I hadn't taken that into account, and at the flow rates the HVAC needs, they would be significant.  I did think about doing a two pump system, but that requires that I run a high-flow submersible at low flow a lot of the time, and the efficiency drops off a lot at lower flows.  I still like the idea of an unpressured storage tank for the HVAC.

I'm thinking of putting a small high-flow, low-pressure DC pump at the outlet of the tank, together with a Hall-effect flowmeter to do closed-control of the flow through the heat pump.  If I do that, then maybe I could get away with just one well pump that would be able to supply the house at 50 psi and send the excess to the tank. 

Can you put two CSVs in parallel?  One 50 psi for the house and another one for the tank?  I'm thinking that if the one for the tank was set just a notch above 50, then it would open any time the pump was capable of producing more water than the house required and send the excess to the tank, and close if the demand was high enough that the house pressure fell below 50.  Am I thinking clearly?  Thanks for your patience in answering my questions.

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Frequently Asked Questions / Re: Number of Cycles, Large Tank verses CSV

« on: October 22, 2020, 01:13:53 PM »

Hi Cary,

Thanks for the quick response!  I'm putting in a Tetco TY-036, two-stage, 3 tons.  The spec sheet gives the pressure drop across the heat exchanger as 1.0 psi at 4.5 GPM and 2.8 psi at 9 GPM.  I'm in PA, with 50F ground water.  The COP increases by about 10% for the higher flow rate, so I'd rather err on the side of higher flow.  I was thinking that a plastic tank, couple hundred gallons maybe, mounted on a platform, would give me at least 2-3 psi.  Maybe that's not enough?  20 psi seems like overkill, but it probably would be a simpler setup.

Don

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Frequently Asked Questions / Re: Number of Cycles, Large Tank verses CSV

« on: October 22, 2020, 12:02:36 PM »

Hello - thanks for all the good info on this forum!  I get that a small tank is all you need for the house, but I'm wondering if a large low-pressure tank might work well for a geothermal HP? I'm building a new home and just drilled the well - 175 GPM with a 20' static head. My two-stage geo needs between 4.5 and 8 GPM (at just a couple of psi), and I'm estimating the house at 14 GPM (2.5 baths, DW, front-load washer, just the two of us).  I'm thinking about putting in a 1/2 HP 25 GPM submersible to fill a large unpressurized tank to supply the geo, and a 1/2 HP booster with a CSV to supply the house at 50 psi. 

My thinking is that when the house isn't using water, the well pump will fill the large tank, running at its pressure/flow efficiency sweet spot.  When the geo comes on, it gravity feeds from the large tank.  If someone opens a tap, the booster kicks on.  If the well pump is currently filling the big tank, it just reduces the flow into the big tank to meet the house demand.  If the well pump is off, it comes on with the booster, again running at its sweet spot, since whatever excess the house doesn't need goes into the big tank.

I think the big tank needs to be big enough to supply the geo for at least one complete heating/cooling cycle, and should only call for water when it's empty.  That would minimize cycling while supplying the geo.  And, any time the house calls for water when the big tank is less than full, the well pump would run at peak efficiency even if it's just supplying one sink in the house, because it's filling the large tank with the excess.  If the geo empties the big tank, the well would kick on and refill it, again running at optimum efficiency.  The only time the well pump isn't running at peak efficiency is when the geo tank is full and the house calls for water, at which point the CSV throttles the flow, reducing the power consumption of the well pump (although at a significantly reduced efficiency).

Am I thinking clearly?  Not pretending to be any kind of expert, but trained as an electrical engineer and like to learn new things.  Having a lot of fun designing this system for our new house.  Thanks.