Quote:
Originally Posted by jeff5may
... I probably need to do the math that AC_Hacker had suggested as to the COP and raw btu output of the unit as the temps drop off. Can someone lead me in the right direction here?
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Doing a COP analysis for a water-in-water-out heat pump is pretty straight forward, since you can work with a known volume of water and measure the before & after difference. You can also work with measured flow rates of water and do the same thing.
But with an ASHP, calculating COP is not such an easy matter, since air, a gaseous mixture, diffuses out into the environment.
However, I did see a university doing it though... by capturing air output in a very large plastic bag (yes, really), they were able to measure the volumetric rate of the output... I think they did something similar for the input, too. Then measure the entire heat content (sensible and latent), of the input air stream and the output air stream, to find out the work done on the air to change its temperature & humidity, etc. Then divide by the electrical power required (Kill-a-Watt used here) to do that work.
To build the 'COP vs. Ambient Temperature' curve, several of these tests would need to be done with various incoming air temperatures, to establish enough data points for the curve to be reliably created.
That's the best I can come up with.
With a water-in-water-out heat pump, it is really easy, just run a data logger with a temperature probe in each water container, and periodically measure the power consumed. Since there is no change of state, and the effect of heat on water is linear, the process is very straight forward.
Best,
-AC