I am trying to find the right well pump for my heat pump application. Currently, I have a 120' closed loop of copper in my well, but it is old and I want to replace with with an open loop system, where I pump from the bottom of the well and return to near the water table (always 20' from surface). Looking as the curves for Gundfos pumps, it looks like a high volume pump like a Grundfos 22 SQ05-80 (22 gpm at 75') would cycle on only briefly every 10 min or so, with a 20 gal pressure tank; I was advised by and "expert" that the lower volume, higher head pump, 5 SQ05-90 (4.4 gal at 112') would be a better solution, but this makes no sense to me---using 3 gpm through the heat pump would result in the well pump being on most of the time, using far more electricity. Am I over-looking something?XXX@XXXXXX.XXX
Brand: Florida Heat Pump
Type of HVAC: Other
I am using a closed vertical loop right now.
All work to be done by licensed professional. WE KEEP GOING UNTIL YOU HAVE THE INFORMATION YOU NEED, I come and go. This is step ONE.
Hello, welcome to Just Answer !
Summary: The larger pump will draw more current than the smaller pump when its running, and on a 20 gallon tank it will cycle a lot, that's hard on the pump and its switching mechanism... beyond that the pump draws 300% of full load amps for 2 or 3 seconds each time it starts.
The net energy aside from the extra starting current as the larger pump cycles will be about the same with either pump.
Regarding an open loop system, if the water is pristine, and not particularly laden with minerals (hard water) then an open loop system is workable. Otherwise a closed loop system is the way to go.
Regarding the 4.4 gpm / 112' of head pump.. the gpm is in range but the head pressure is higher than required... it could tend to cavitate.. if you can send me a link to the pump curve that would save me some time.
If you are returning the water to the well, *below the water table* so that the the siphon effect eliminates the lift. then the only resistance to flow you have is in through the heat exchanger with is generally less than 10 psig, or 4 feet of head..
Even with the 20 feet of head lift required for self priming on start up, a pump in the range of 5 or 6 gpm at 40 or 50 feet of head would be more than sufficient... it would need to be a *self priming* pump however at 20' lift... not a circulating pump as you most likely have in place now...
Your existing closed loop circulating pump will be less expensive to operate than any open loop pump system for those reasons... however at those low flow rates, the cost of running the pump are *minimal compared to the cost of running the rest of the heat pump.
This is step one of our discussion.. and opener more or less. Give these issues some consideration... we can go from there, there are no time limits.
Use the reply button to get back to me, not one of the two lower ratings, each of those put a negative on my stats.
Water is NOT hard, but does have small amount of sodium; that's why I'm concerned that the copper loop will not last that much longer. Also, in the very coldest weather (like -10F), the well gets a little too cold and the heat pump sometimes will not operate (I have a thermostat that shuts it down below 39F); but I have a pond I can dump some of the water into, in those really cold conditions that might help out if I were to go to an open loop system. Here is information about the the Grundfos pump rated at 4.4 gpm at 112' head.
...sorry, didn't finish that first message: Grundfos 5SQ-90: this pump also has a slow start mechanism, so draws only slightly more than rated amps on start-up, as do all of the Grundfos SQ pumps. Yes, my present closed loop system produces the 3gpm at only 150 watts!, and the heat pump is only about 1 ton. What I DON'T want to do is select a pump that is going to use a large fraction of what the heat pump uses; so given the slow start protection of these Grundfos pumps, wouldn't you WANT a pump that pumps a large volume in a minute or so, then can shut down for 10 min while pressure tank continues to supply the 3 gpm?
I know what you mean about the fact that when system is running, the return pipe into the well makes this a zero lift system. I had that arguemt with an "expert" at Worldwide Power and Pump systems http://www.wwpp.co/ He kept trying to tell me that had no effect because I was pumping into a pressure tank. Pump should be drawing much less amps under these conditions; does that make cavitation more likely?
I will try to attach the pump sheet here http://www1.union.edu/willingp/5SQ_90spec.pdf
Hello, indeed if you are pumping into a pressure tank, then you need to meet that pressure output.... if the tank is to be operated at say 40 psig, then multiply that by 2.3 to get the feet of head required to pressurize the tank. and add that to the pressure loss through the piping and heat exchanger.
a column of water 2.3 feet high exerts 1 psig at the base.
..and here is the higher volume pump that I though would be better because it would only be on a fraction of the time. http://www1.union.edu/willingp/22SQ_80spec.pdf
I psig of pressure will push a 2.3 foot tall column of water
You are caught up this operating *time issue.... it IS a factor... it is just much less of a factor than the feet of head required to pressurize the tank.
Volume and pressure ratings are two *different aspecs of the *same equation.
If you use a high pressure tank then its its going cost a lot more to operate than if you use no tank and stay with a much lower pressure rated pump...
You need the 4 gpm volume in either of those two cases.
but you will pay exponentially more to move that 4 gpm at 120' feet of head than at 30 feet of heat if its no siphoning, or 10 feet of head if it is siphoning.
Since i can presently circulate my 3 gpm using only a 150 watt pump, I was thinking I could use a really LOW pressure setting, like 15 to 24 psi.
You can determine that empiracly by looking at the horse power or amperage ratings of the various pumps in question
yes you could indeed do that... but the savings in less run time will be dramatically less than the added cost of pumping into a pressure tank..
You will most likely find that your current pump rated at 150 watts is actually drawing less, mabye as little as 75 to 100 watts.
both of those Grundfos pumps are the same: 1/2 HP, 5.2A the difference is that one is 4.4 gpm at 112' and the other is 22 gpm at 72' Do I understand correctly: I would be using the pressure tank in either case, but the cost of pumping into it is much higher for the lower heat, higher flow pump?
I meant: electrical use would be higher for high flow, lower head pump (22 gal/min) than for the higher head lower flow (4.4 gal, 112')?
....or are you saying that with the 4.4 gpm pump I actually don't even need a pressure tank?
Cost would be the same, you are simply trading less flow rate for higher head pressure. the pump efficience drops though with higher lift, so you loose a bit there, it will draw a bit more amperage per gallon.
The amperage ratings given are peak ratings, unless they include an amperage curve and most do not (site, wire size and local power factor conditions vary0
Yes, no pressure tank needed at 4.4 gpm flow, the pump would run whenever the heat pump was running... your closed loop uses no pressure thank but will include and Expansion Tank if its designed properly and run the system at 15 psig or so... but thats not head pressure, because the pump suction runs at 15 psig as well in that example.
None the less I recommend over sizing the pump by 50% or so, especially in these low flow rate conditions... thats because all pumps are rated under ideal inlet and impeller fit conditions.. and what gets manufactured and sold is not quite as well built or fit. although grundfos (and goulds for that matter) come pretty close to the performance ratings.
In an open loop, over sizing is never a bad idea, in order to compensate for scale build up in the heat heat pumps ground water coil.
(that will have to be acid cleaned periodically depending on the ground water chemistry0
Ok, now I think I understand: I use the 4.4 gal pump, with just a rather small expansion tank, like I have now with closed loop, set at 15 psi or so. Then that Grundfos pump will draw really only enough current to push the water through the pipes, since it's not really lifting, just as with my closed loop system. So instead of 5.5A , the pump might draw only 1A or something? I think the 4.4 gpm pump is already over-sized, since my heat pump can actually get by with 2 gpm. Yes, I could acid clean the system the heat pump, since I got the cupronickel type. Shouldn't be much scale build-up, but might be bacterial slime (when we briefly used this well for the house, inside of toilet would get black slime). Wouldn't be a problem to run acid through once a year, and/or dump a few gallons of bleach into the well.
I appologize for the typo's, in chat mode its not easy to edit them
You do not want to have an expansion tank in an open loop
You *could use a pressurized storage tank, but it runs up your operating costs.
If you oversize the pump a bit, and fit a tee with a valve on the side branch, you could always add a pressurized storage tank later.
... then adjust the pressure switch setting low enough that the pump can meet that pressure and cycle off.
water scale issues
Ok--what I'm shooting for is absolute lowest electrical use, as long as maintenance is not too high. Optional pressure tank sounds like a good idea; might actually use this system for watering garden in summer. I'm thinking early washing with acid and bleach in the well a few times a year would keep down deposits; not worried about calcium or magnesium deposits.
When water scale builds up in the heat pumps ground source heat exchanger, the refrigerant pressure goes up... and the compressor costs more to operate.
...mean YEARLY washing, not early
acid and bleach in the well will not affect mineralization of the ongoing water flow.. it will keep the well flowing better in some cases though.
I did not mean acid in the well. Bleach in well for bacteria, and acid was the heat pump. sorry
acid wash. can't type
you might end up flushing the condenser coil with the propertly inhibited acid occasionally however... maybe only once every 5 years if the water is not heavily mineralized (hard water)
In selecting a pump you want to pick it in the mid section of the pump curve..being sure that the worse case conditions do not run off either end of the pump curve.
Put a good, expensive, soft seated, spring loaded check valve in the pump discharge line, about 2 feet from the pump.
Ok, every 5 years is easy! Your advice has been fantastic. Now you have me thinking: maybe I don't even need an expensive well pump with this system! Just calculate roughly the frictional head loss, plus just enough to get the water up into my heat pump, and use a REALLY small lightweight, easily replaceable little submersible pump. If I get it wrong the first time, I just buy another, and still come out WAY cheaper than Grundfos pump. why the check valve near the heat pump? (I assume you meant 2 feet from heat pump).
Lets make that 10 feet away from the pump and put a good removeable cartridge type water filter just ahead of the check valve.. and fit full port size ball valves on either side of the pump so you don't loose the pump prime each time you change the the water filters.
Check valve is to prevent back flow down the well on the off cycle and loss of prime, and subsequent air pumped into the heat exchanger...causing you to have to air bleed it, or fit an automatic air bleed on its high point.
thats a point well worth mulling over.
air in the heat exchanger 'vapor locks' it.
the air stays at the high point of the heat exchanger.. odds are in the 99% range it has at least a manual air bleed fit.
Various types of air bleeds.
filter in FRONT of heat pump, I assume. ya, have that same type of ball valve system in front of my hot water heater.
If you put the water filter ahead of the check valve, you keep grit out of the valve seat, so it keep sealing tightly..and not cause the water too fall back down well, filling the line with air.
If the water filter arrangement is not entirely air tight however, it will leak air, and let the water fall back down the well... you need a non vented water filter arrangement (most are).
yes, I have those types of air bleeds on my homemade solar hot water collector and storage tank. pretty sure my heat pump does not have one, but is easy to add just outside. Oh. I see the point of filter. So the check valve has to be really weak spring type, weak enough to open with flow, but strong enough to not open when flow stops.
a submersible pump should be installed with a check valve in its water discharge as well.
Yes, weak spring type.
'swing' check valves close regardless but when worn not perfectly in all cases, so a weak spring and a soft seat works better over the long term... most of the more expensive check valves are built that way... the cheap ones, are brass swing checks.. they work too.. but are not as reliable with potentially dirty water.
ok. You have been tremendous help. Will give you highest rating.
If you feel like giving me one of the top two ratings, you can still follow up regardless of the tag that says it closes the question... JA is having programming issues with that
Retired HVAC/ Electrical & Boiler contractor. Industrial