Heat pump efficiencies seem to go to pot in colder weather

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davidmcbeth3
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Post by davidmcbeth3 » Sat. Feb. 11, 2023 3:38 pm

https://learnmetrics.com/heat-pump-efficiency-vs- ... ure-graph/

I would guess that cost to operate about doubles from 60F outside to 10F outside

Am I right ?

 
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Post by hotblast1357 » Sat. Feb. 11, 2023 4:33 pm

My 18,000 BTU heat pump uses 800-900 watts per hour at 25 degrees OAT with a indoor temperature setting of 73.

 
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Post by davidmcbeth3 » Sat. Feb. 11, 2023 4:44 pm

hotblast1357 wrote:
Sat. Feb. 11, 2023 4:33 pm
My 18,000 BTU heat pump uses 800-900 watts per hour at 25 degrees OAT with a indoor temperature setting of 73.
What model is that Hotblast ?

900w * 24 hrs/day * 30 days/month * 0.00035 $/kwh = $226 /month

Also, how did you measure the wattage used ?

Interesting


 
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Post by hotblast1357 » Sat. Feb. 11, 2023 4:49 pm

I have a cooper and hunter, it has one 18,000 BTU unit outside and two 12,000 btu indoor units. I have a whole house energy monitor system so I have an amp clamp on the heat pump circuit and it records the usage. I only pay .15 per KW here in upstate NY.

 
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Post by gardener » Mon. Mar. 13, 2023 9:34 am

That learnmetrics only references a latest study of 2013. I bought our heat pump that year, it was advertised to continual heating down to 5 degrees with auto shutoff, and down to 0 degrees if fitted with the optional baffle. It worked well even below 10 degrees but less heat output and with the inverter you can recognize it working at full speed at those outdoor temps. I bought the baffle a few years later and it continued to work past 5 degrees outside, as I recall that day I paid attention it was 3 degrees out.

I noticed back when I was shopping for a heat pump that there were a few offered that would operate down to -13 degrees outside, and since then more manufacturers are offering a line of those. The times I have looked at literature directed at Canadians they are often advertising these product lines. I don't know what that means for efficiency, but my guess would be COP charts are shifting down the temperature scale. The 0 degree units I shopped included efficiency charts, I assume it could looked up in the product literature for those units that operate down to -13.

 
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Post by Lightning » Mon. Mar. 13, 2023 1:18 pm

Does the heat pump still deliver the full 18,000 BTU as outdoor temperature falls?

Also, is that 800-900 watts per hour an average or is the mini split running constantly?


 
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Post by hotblast1357 » Mon. Mar. 13, 2023 3:43 pm

Lightning wrote:
Mon. Mar. 13, 2023 1:18 pm
Does the heat pump still deliver the full 18,000 BTU as outdoor temperature falls?

Also, is that 800-900 watts per hour an average or is the mini split running constantly?
No obviously it falls as outdoor temps fall. There’s no easy way to know what the actual BTU output is, as it modulates. As long as it keeps my house warm I don’t really care what the btu output actually is lol I don’t plan on using this for cold weather, if it’s below 20 degrees, I’ll use coal.

The mini split is running constantly, but it does modulate, today for instance, up till right now at 3:30 I’ve used 13.2 KW, it is currently using 854 watts, and if you do the math, 13.2kws in 15.5 hours happens to be 851 watts per hour, but I’ve seen as low as 600 watts and as high as 1200 today. I had a low of 26 this morning and it’s 38 right now.

 
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Post by mozz » Mon. Mar. 13, 2023 8:49 pm

I thought heat pumps were known to not work well when it gets below 32? I'd probably move south before i would ever heat my house with elec.

 
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Post by hotblast1357 » Mon. Mar. 13, 2023 9:36 pm

mozz wrote:
Mon. Mar. 13, 2023 8:49 pm
I thought heat pumps were known to not work well when it gets below 32? I'd probably move south before i would ever heat my house with elec.
They work good below 32, just not as good as above 32.

It’s not heating with electric resistance heat, you’re only using electricity to power the compressor and fans, whole different machine.

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