I'm working on the design for a GSHP system. I'm wondering how flow effects a heat pump eff%? Does more flow mean better efficiency like it does in a boiler or does it have other effect?

I'll be using either the waterfurnace NSW025 or NSW040 but lets just use the 2 ton for this question.

I'm trying to better understand the performance charts. They are a little daunting. it looks like for a Source flow of 7GPM and a Load flow of 7GPM that I get the best COP for a given ELT/LLT, is this correct?

On top of that what happens if the flow envelope is excited? lets say I can push 8GPM but the envelope listed in the performance chart only goes to 7gpm?

With my current design a simple UPS 15-58FC on high will push 10GPM through the heat pump

Going "off the chart" by 10-15% probably has little effect other than wasting power via overpumping. Efficiency increases through higher flow rates are subject to diminishing returns

Going too far off the chart subjects heat exchangers to faster flow rates than they may be able to stand, long term. Erosion of the metal may result, decreasing life.

Can you downsize the pump so as to fall into the upper middle of the chart, likely benefiting from decreased pumping power? Fractional HP pumps are notoriously inefficient.

Posted By engineer on 16 Feb 2013 10:38 PM
Going "off the chart" by 10-15% probably has little effect other than wasting power via overpumping. Efficiency increases through higher flow rates are subject to diminishing returns

Going too far off the chart subjects heat exchangers to faster flow rates than they may be able to stand, long term. Erosion of the metal may result, decreasing life.

Can you downsize the pump so as to fall into the upper middle of the chart, likely benefiting from decreased pumping power? Fractional HP pumps are notoriously inefficient.

Yeah I know but no way around the poor eff as the pump clearances are crap.

heres the same system with the 15-58's on low