Unexpected electricity use with heat pump

willi1972

Hi,
we have an air source heat pump for all of our domestic heating and hot water. We also have an additional solar panel for water heating. We recently had a very large electricity bill - almost twice what it has been for the last 3 years. This is the electricity just for the heating. We have a different tariff for the heating, so it is on a separate meter.

I decided to do some investigating. I have been monitoring the electricity use for a few days. At the moment, the heating is switched off, and it is sunny all day, so I would not expect the heat pump to be doing much. However, the electricity meter says that we used 6kWh. When I checked the control panel for the heating, there is a section where you can find values for the "heat quantity" used. This says for the past 2 days, we have used 0.4 kWh. How can there be such a difference? Am I missing something obvious here? What exactly is heat quantity? I assume it is a calculated value based on the temperature and volume of water returned from the heat pump.

Any thoughts would be much appreciated.
Richard

Jamie Hall

My first thought is is there any reason why the heat pump would be kicking on the backup electric resistance heating? An unusual hot water draw, for instance?

JUGHNE

It has happened that some resistance element heating is energized due to failed controls or the element shorting to ground in the middle of the coil. All of your "heat quantity" monitors might be fooled. It may only sense the pilot circuit of heat relays.

However the utility meter (cash register for them) will catch anything they pass.

HVAC tech or electrician may catch phantom current flow.

Leonard

I know in a restaurant in old large Carrier roof top HVACs there was a heater wrapped around compressor base that was factory wired DIRECTLY across 240 V power inlet. NO switching at all. On 24/7/365 for 30 years. Glad I wasn't paying for that......

Guessing it was to make sure oil in pump wasn't too cold and thick on start up, helped keep motor windings from burning up when started with cold THICK VISCOUS oil.

Anarchist01

They use the heater to prevent migration of the refrigerant to the cold outdoor units compressor where the refrigerant will condense to liquid and if you turn on the a/c liquid refrigerant will boil off rapidly taking(pumping) the oil with it. Not good for moving parts. It is usually wired to come on when contactor is off, so on the load side.

pecmsg

Leonard said:

I know in a restaurant in old large Carrier roof top HVACs there was a heater wrapped around compressor base that was factory wired DIRECTLY across 240 V power inlet. NO switching at all. On 24/7/365 for 30 years. Glad I wasn't paying for that......

Guessing it was to make sure oil in pump wasn't too cold and thick on start up, helped keep motor windings from burning up when started with cold THICK VISCOUS oil.

What does it cost to run a small 30 - 45 Watt heater ?
What does it cost to replace the compressor?

Newer heaters are self regulating!

Leonard

The Carrier one was OLD, installed ~1984.
Watlo type "rod" heater ~ 50 watts wrapped around compressor, no thermostat.

Noticed it when I was doing repair work.
24/7/365 was an issue when bulding was vacant for 3 years, and HVAC would never be on. Only left utility power on for ice melt cable in roof drain, and lighting when potential tenants came in.

willi1972

As far as I can tell (I'm no heating expert), there is no resistive element. The only cables I can see going into the tanks are thin ones that I assume are for temperature sensors. The aperture that, according to the diagram on the tank, should be for the resistive element is blanked off.

Leonard

50 watts continuous 24/7 for 1 month would be 36 KWH

$6.84 ..... @ 19 cents/KWH

hot_rod

Air to water HL? Does it have a defrost mode if it freezes up under high loads

The Soltice brand uses heat from the buffer tank to defrost, to avoid using resistance heat to defrost