Quote:
Originally Posted by randen
If I could ask AC Hacker; do you run your GSHP continually? and what performance do you see.
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Good question... Just about every aspect of my setup is different than yours (except for the propane), so it's definitely comparing apples to oranges.
Last winter I did a test run, to see how the heat pump and the loop field were working together. I didn't have any kind of thermostat for most of the run, so I left it on, 24/7. I used an automobile radiator for an air handler, because that was all I had, and I put a box fan behind it, blowing on 'medium' speed. I ran the test in my basement which is pretty small, 24 x 15, and the basement has no insulation at all, I haven't done any rigorous air sealing, and there was an opening in the basement to a crawl space that was 16 x 16, no insulation. I would say that only 180 square feet of the 616 square feet of the ceiling in the basement (and crawl space) had directly heated space (70F) above it. The rest of the cieling space was only heated by the heat that leaked out of the heated space (37F to 55F). I was using a loop pump that was moving about 2.3 gallons per minute. My compressor is really miniature, it came out of a 25 pint per day de-humidifier, it draws somewhere in the neighborhood of 400 watts. My conservative guess is that it was putting out around 4000 BTU/hr.
Having said all that, it took about three days for my basement to go from it's usual low 40s temperature (for that time of year) to around 60F degrees... which I felt was not an unreasonable temperature for a shop. There was a lot of variation in my basement temperature during that time, partly due to ambient air temperature (I think because the space is almost all underground, this was not so important), and partly due to the effects of the loop field temperature during this test. Because I live in the Pacific Northwest, rain that has come off the Pacific ocean has a major effect on local weather. I noticed that rainfalls carried a lot of heat, and when the rain fell on the ground, that heat passed into the ground, and therefore affected my loop filed temperature in a positive way, and had a noticeable effect on the performance of my heat pump and on the basement temperature. I also learned that a warmish rain would not register in the loop field temperature for maybe three days, but then as it worked it's way down through the ground, I would see an up-tick in loop temperatures and also basement temperatures. an up-tick in loop temperatures might be in the neighborhood of 1 or 2 tenths of a degree, but that would mean an up-tick of maybe 4 to 6 degrees in the basement. At one point, the basement hit 73 degrees and felt uncomfortably warm.
(* It was about this time that I broke my arm quite badly, so not much has been done since then. *)
So, I don't know if this is what you wanted, but this was how it was. Because I was using air out, I wasn't sure how to measure performance quantitatively... I just went for experiential knowledge.
Regarding your system, I would suspect that your air handler is on the small size... this kind of gets back to my rant about low temperature heating and hydronic floors and how low temp heating needs optimized floors and large radiating areas, and all that...
I forget exactly what you said about your air handler, I seem to recall that you may have said that you converted it from another type of fuel source to what you are presently using.
At any rate, I have read quite a few accounts about people who have plumbed a heat pump into an air handler that was originally meant for fossil fuel, and were disappointed by the results. The reason in that situation is that fossil fuel yields much higher temperatures, so an air handler with a smaller area will work, but if you try to use the same air handler with a lower temperature heat source, it will not put out heat at the same rate.
I think it should be pretty easy to see if this could be a remedy for you, you could hook up a few car radiators with fans, in-line with your regular air handler to see if it made any improvement.
Another thing to look at is testing and tweaking your heat pump to get maximum performance. Have you looked into subcooling & superheat?
Here's a document on it...
Another approach would be to run a series of your COP test like you did before, and try tweaking your TXV and also refrigerant pressure level to get maximum heat output... which might be a different 'tuning' than what you'd get with a maximum COP 'tuning'...
And, lastly, you may be right, you just might need a bigger compressor.
I hope this has been of some help...
-AC_Hacker