Heat Pump Operating Wattage
I’m going crazy… My 3 ton heat pump is only drawing 2.1 kW and blowing 80 degree air. Is this normal?
So, per its matchup chart, the best it can be paired with would give it 9.6 HSPF. I state that because it should indicate its lowest operating wattage. It is also sticker for 14.7 A at the outdoor unit, “running amps”.
I watch major circuits in my house and this one has always troubled me. I ran a test this morning.
It’s currently 21 degrees outside, and approximately 63 degrees nominal at the return vents for this unit. At the nearest vent right off the air handler, it blew 80 degree air fresh off a defrost with 5 minutes additional to stabilize. To make that temp it pulled 2050-2100 watts at the outdoor unit.
Now when I do the quick math for 14.7A * 240V I get 3528W. For the 9.6 HSPF math for a 3 ton unit (this one is rated for 34,000 BTU) I get 3541W. BOTH of those numbers seem to tell me that it should be pulling significantly more power (and thus making more heat, I would hope!)
I have recently had a guy out to look at it but of course the day he arrived was 62 degrees, and he said that makes his pressure checks useless.
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Replies
Which heat pump is it? If it’s a variable speed unit, 2kw is fine. In the 20Fs, mine only pulls 1kw. The temp is an issue though. Is it maintaining the setpoint? What’s the blower speed set to?
"The temp is an issue though."
Is the temp really an issue? If return is 63 F at the return vent it's probably even a degree or two lower right before the coil. And if supply is 80 F at the supply vents it's probably at least a degree or two higher right off the coil. If the airhandler + any of the ductwork is in an unconditioned attic or crawl space, the return and supply temps at the coil could be several degrees off from what's being measured at the vents.
So we are probably looking at a delta-T of ~20 degrees, which is within the realm of normal for many standard split system heat pumps.
But yeah, definitely need to know which heat pump it is and whether it's maintaining the setpoint or not.
You're supposed to complain when your equipment draws TOO MUCH power, not when it uses TOO LITTLE :-D
Chances are you'll see some increased power consumption by the outdoor unit when temperatures drop, and possibly also if it has a defrost setting. Note that in the world of AC power, volts times amps DOES NOT equal watts, at least not all the time. You have to include power factor in there too, which is probably going to be in the 0.8-0.95 range or so. That would mean that your 14.7A at 240V would be closer to 3kw or so than the number you calculated. Power factor is also likely to be lower (worse) at lighter loads, which would mean you'd see even lower actual wattage compared to calculated wattage in this case.
If your unit is keeping you comfy, you're probably OK, but it would be worth checking those pressures once it's more consistently cold outside.
Bill
Correct. In heating mode with fan on high you should see 400-425 psi on the high side.