In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
probably restarting an obvious thread here although i ran back through the last couple months and didn't see anything that jumped out. i apologize if my search wasn't exhaustive enough.
The thing that chased me over to the heat pump forum was actually the EIA price/btu comparison chart posted on a propane vs. oil thread (where i normally troll - well hopefully not)
I'm glad i clicked on it, although i don't need the help for conventional fuels, I noticed the efficiencies for heat pumps. now i had never thought of it this way, but of course they would enter in a table like this with efficiencies greater than 100% because they deliver more btu's per kwh than direct 100% conversion of kwh to btus through resistance heating.
so to develop a comparison model you look at how many more btu's and that becomes an efficiency greate than 100%.
and i was long aware that ground source heat exchange could keep heat pumps producing when outdoor temps dropped below operating parameters for airsource.
The thing I hadn't wrapped my mind around was whether ground source was actually more efficient than airsource. you figure you got a fan moving air or a pump moving water. maybe i can see moving the amount of air involved as more power consumptive and the heat exchanger as larger so there is a little bit more load on the refrigeration compressor from the head loss across the heat exchanger. But i hadn't considered that to be such a significant source of savings.
well, according to the EIA worksheet, an 8.3 HSPF airsource is 240% efficient while a 3.3. COP groundsource is 330%. If i read the fine print these differences are not related to temperature zone and percentage of time running on backup assumed not to affect groundsource. They have a separate chart below that calculates operating efficiency in certain geographies from the HSPF although i guess there must be some allowance for an avg. ambient in the HSPF because in a very few, very warm locations, e.g. Miami, the corrected HSPF is actually higher than the nameplate HSPF.
So as best I can tell, the 90% difference between groundsource and airsource is related to the efficiencies of heat transfer. I wouldn't have guessed it was that high.
you learn something new everyday.
so I missed my opportunity to caress a bunch of these babies at AHRExpo because I was so busy chasing down hydronic control and pumping strategies and i have to start from scratch.
While the minisplit airsource is a fairly robust approach, one other thing that attracts me about a groundsource approach water to water is that it will retrofit into most any radiant hydronic application and it isn't a split unit. rather you get groundwater feed and return in one side and system feed and return in the other. so that seems to me like it should be a cheaper unit to design and manufacture than a mini-split with the exception that you just aren't going to see as many units esp. early in market adoption but there are always going to be less situations you can use water to water.
And where do i go for entry level primer like converting tons to btus for comparison to boiler capacities. how one calibrates for higher desired water temp. in that equation and what are the highest water temps available. what do horizontal field sizes look like in terms of pipe length and dsq. or cubic area of ground most appropriate to those pipe lengths. and what manfuacturers and distributors are big in these so I can look for actual unit costs. Because getting stoked on all the energy savings can be dashed by the infrastructure investment.
After all wind and solar are free, so we would all have them but for the cost of the infrastructure (and those fussy reliability problems so add storage or grid back-up to those infrastructure costs).
And one thing occurs to me which is not specified in the EIA worksheet. I'm going to assume that their 'typical' efficiencies might be calculated with condensor temps around 140. am i right about that and how much do higher or lower design water temps affect the efficiency?
Pointers appreciated so i can learn enough to ask some real questions.