Hello all, I am thinking of ways to improve the efficiency of an open loop pump and dump system What I am thinking is to find a pump that can fill up a 200 gallon tank as fast as possible with the greatest motor + pump efficiency. Then allow the heat pump to feed off that tank So if the tank is 200 gallons and the pump runs at 30 gallons per minute it would fill the tank in 6.6 minutes Say the heatpump needs 10 gpm to operate.. that tank would last for 20 mins before it starts to refill again My well is 80' down.. trying to find a pump to match what the heat pump needs is very hard But say this 30 gallon per minute pump uses 1200 watts 60 mins / 20 mins = 3 cycles 3 X 6.6 pump minutes = 19.8 mins 1200 / 60 = 20 20 * 19.8 = 396 / 1000 = 0.396 Kwh It would be approx the same as running a 400 watt pump at 10 gpm My premise is to find a pump / GPM ratio that is most efficient and buffer it with a temp storage tank What do you think of my math / idea? Thanks John
Math-wise, you are basing the two pumps being able to more closely match the demands of your system vs. one pump that doesn't quite fit and has an inefficiency penalty for that. This really is specific to your exact needs. Plumbing-wise you have more moving parts your system is dependent on.
My main focus is energy efficiency since I am off grid My current pump uses 760 watts at 10 GPM With my above math I save 300 watts.. which does not seem like much but on a day where the heat pump needs to run for a long time it could save me over 8 Kwh per day Every little Kwh helps!
I like this idea. I had the same one. did you try it? did you like it? I have a couple of existing old dug wells on my property. I was thinking to use one instead of a tank. on the bright side, they are usually filled with ground water in the winter so perhaps my float switch wouldn't ask the potable pump to kick in as often, on the other hand when the groundwater is low i could be pumping just to let it leach into the ground...
farmerjohn hasn't been heard from since he made this post two and a half years ago. I'd think if he was off grid and his main focus was energy efficiency then he should have installed a closed loop system with a variable speed pump. Mine averages about 60W, which is 700W less than his.
It is all about the lift. To get 20 PSI to the heat pump the storage tank would need to be 46' high above the ground. If you have water in tanks at the surface you should be able to use a little 5 GPM pump that delivers 20'-40' of head and use the same size pump as with a closed loop system.
