Quote:
Originally Posted by RB855
Pulled some new numbers. Using an open loop (read, city water)...
1 gpm flow
Water entering 85.8*f
Water leaving 103.5*f
~8900btu hr
Liquid temp 87.3*f
Hot gas 121.8*f
Ambient 86.8*f 54%
Evap discharge air 74*f
Draw 2.4amps ~550w @ 220v (1725 btu equiv)
Est Gain 5.2:1
Using very inaccurate amp clamp, total system current is 2.4amps @ 220v
So, say 550w. Pump not included as I'm using city atm for steady state testing.
----+edit
Lowered the gpm to get it closer to intended operating conditions
0.62 gpm
Water entering 88.7*f
Water leaving 115.7*f
~8500 Btu/hr
Liquid temp 92.7*f
Hot gas temp 134.5*f
Ambient 94.5*f 45%
Evap air 74.9*f
Draw 2.9amp 640watt @ 220v (2180btu equiv)
Est Gain 3.9:1
There seems to be a pretty significant efficiency hit with the temperature increase, Even though the liquid temp only went up a couple degrees. I didnt have gauges on it at the time so don't know what the pressures were running. About a 400btu/hr loss, and almost 100watts more power. Granted the incoming water temp had risen, as well as the ambient. But, it looks like I can go with significantly less water flow than I originally imagined. Seems 1gpm is more than suitable, vs the 5+gpm I thought I needed. Suppose the oversize BPHE are paying for themselves in this respect since the delta is reduced to 2* at 1gpm.
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Good information, very useful.
Curious thing with pump velocity... when the volume goes up, you may notice a reduction in temperature, but because you're moving more water, you may be transferring more heat (more BTUs/sec) even though the outgoing temp is lower.
Also, when you connect your unit to a water tank, and the heat pump is circulating water in the tank, instead of heating constant temp city water, your delta-T will gradually go down, and your efficiency will also decline, similar to this graph:
It will be interesting how it all plays out.
But your initial tests look very promising!
-AC