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Old 10-05-09, 02:48 PM   #14
AC_Hacker
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Default Declining temperature, declining COP...

Quote:
Originally Posted by Xringer View Post

According to what I've found, the COP is 3.4 when you are running it full bore.

29,000 BTUh, burning 2,490 watts gives you a 3.4 COP.
But, after things have warmed up and the unit is just coasting along at, say,
4,400 BTU, only burning 290 watts, you get a COP of 4.4

Maybe it's good this thing is a tad over-sided.?.

We have added a bunch of insulation in the past year, and I'm really looking
forward to seeing if I can actually heat my home using 290 watts!! LOL!!
At least on the mild days..
Hey Rich,

I built a small water-in, water-out heat pump and did various test, with this one being a good example: (full thread here)


The light blue line that jumps all over the place is the COP for the five minute period just measured. To make it fit on the graph, I multiplied COP time 10, so if it says that cop is 35, it's actually 3.5.

I'm not exactly sure why it's so jumpy, but there is a definite trendline that can be drawn through the COP values, that is very close to parallel to the temperature of the water coming into the system. Which makes sense when you think of it.

So, when as the outside air temperature gets colder, the COP of our Air-Source Heat Pumps will most surely, also decline.

So this all tells me that there's a point, when another system, like in you case, a hydronic heating system, will be cheaper to operate.

I don't know if you're set up to be able to measure the power that is being drawn by your heat pump, but it would be interesting to know that information.

Best Regards,

-AC_Hacker

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