Hi Chuck,
I was under the impression, and could be wrong, that each heat pump
manufacturer will provide specified COP values for each model of heat-pump they
manufacture. The COP values vary over temperature, and decrease as
temperatures get lower. As the temperature gets lower, eventually the heat
pump yields a COP value of 1, which is essentially similar in performance as a
full electric furnace. I viewed this number (COP ~1.0) as the point at which
your heat pump is essentially running as efficient as if it was an all electric
furnace.
I was curious what the specified COP values are for your unit, and if they're
close to the values you calculated?
I'm a huge fan of my heat pumps and always feel good when I hear them turn-on
on cold days. However, at some point it becomes just to expensive to run them
and they're too inefficient. That's when I'm happy to have my Propane furnace
turn on and quickly heat up the house. As I said earlier, if I could find a
much more efficient heat pump that held a COP value above even 2.5 at extreme
cold temps, I'd probably find it cost effective to swap mine out.
Thanks for the info.
Best,Scott
On Monday, 6 February 2023 at 10:27:45 pm GMT-5, Cj Sizer
<[email protected]> wrote:
Hi Scott,
Your comments are very relevant. The COP calculated was the theoretical
number based on the R410A refrigerant temperatures from actual measurements.
It was not based on the EER taking into account the electrical and mechanical
losses of energy. At the coldest time, the compressed refrigerant was 41.7
degrees Celsius and the refrigerant under vacuum was at a temperature of -30
Celsius. The COP was calculated to be about 4.4. I included these
calculations in the spreadsheet so that I could compare them to the actual
hourly energy usage of the heat pump (which was measured with an Emporia Energy
System).
The very low temperatures that we experienced had more of an effect on the heat
loss through the walls than it did on the efficiency of the heat pump. I was
very skeptical of air source heat pumps initially. After this brief study, I
think that they are an economical solution that is sustainable. I considered
the cost of drilling two 750 feet deep geothermal wells. This is more easily
offset by adding two more solar panels to make up for the reduced efficiency of
air source heat pumps.
Chuck Sizer
On Mon, Feb 6, 2023 at 5:57 PM Scott Stewart <[email protected]> wrote:
Hi Collette,Thanks for sharing this info... Do you have the model of the heat
pump you're running at your house? I find it very interesting that it can hold
a COP so steady around 5 with such a wide outdoor temperature swing. Is it
underground?
My heat pump is ~5 years old, and not by any means the most expensive. It's
specs between 10F and -5F go from 2.06 to 1.24.
Are you sure you're getting a COP of around 5 from 10F to -13F?
I plug my cost for electricity and propane into a DOE calculator each year to
figure out when to set my heat-pump to turn-off and the propane furnace to kick
on. If I could get a COP of 5... I'd never need propane. :-)
Just curious.
Thanks,Scott
On Monday, 6 February 2023 at 08:46:01 am GMT-5, Cj Sizer
<[email protected]> wrote:
Hi Rich,
My husband kept data on our system through the bitter weather. He made a ppt
for CFREE (working group of the Green Energy Committee). You might find it
interesting, Our heat pump is located in a nook on the southeast side of the
house. The area warms when the sun comes up. We added insulation when we
replaced our roof last year. We also replaced many of our single-pane windows
with triple pane. These things surely helped keep our energy usage down through
the cold wave. In the coldest hours of the early morning, the heat pump held
the temperature 1° below the thermostat setting.
Best regards,Collette
On Sun, Feb 5, 2023 at 11:42 AM Rich Rosenbaum <[email protected]> wrote:
I was wondering how people with air-to-air heat exchangers managed during our
very cold night.
Rich
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