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Old 08-12-13, 07:25 PM   #1
Robaroni
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Default Mini Split COP?

Hi,
A few years ago I built a new garage so that I could convert the garage part of my house to a work room, new kitchen, etc.(depending on who you talk to here!)
The room is about 225 sq/ft and I'm thinking about the mini split system. I know how heat pumps work but I'm not sure how much energy I'm saving with these heat pumps as compared to, say, a ceramic heater.
I don't really need cooling in the summer, just a little extra heat in the winter. I have radiant tubes in the floor but I'm trying to get away from the high cost of #2 oil and my house oil burner.

Thanks for the help,
Rob

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Old 08-13-13, 07:32 AM   #2
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much energy I'm saving with these heat pumps as compared to, say, a ceramic heater.

Inverter nimi splits have COP in the 2X to 5X region (2x when it is -5 outside, up to 5x or better when it is 60F) so even at -5 F outside you use only 1/2 the power a ceramic heater uses for the same BTU dumped into the room. At -5F though, an 18000 BTU minisplit will deliver only about 8000 BTU/hr, or less depending on the model and rating.

Should be lots of other threads nearby on DIY proceedure for mini split installation. Pretty easy, but you do need a vacuum pump and micron gauge to do it right.
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Old 08-13-13, 09:35 AM   #3
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If you are considering a heat pump solution, I would suggest doing a decent amount of research before installing a system. The performance is all over the place, depending mainly on the technology and engineering put into the unit.

Cheaper units are usually labeled "10 SEER" and have performance comparable to a window air conditioner at 40 degF. As the outdoor temps drop, so does the energy efficiency. They are mainly built with capillary tube metering devices, so their heating capacity falls off rather quickly at lower temps.

More robust units have a higher price tag, but their performance improvement over the "basic" models translates directly into energy savings. They have features built in such as: variable speed fans/compressors, electronic metering devices, heat transfer and defrost optimization software/firmware, domestic hot water preheat, hardwired thermostat connection, and more. They generally will produce generous heat down to around 5-10 degF before losing capacity. Depending on your current energy source and demand, these units can pay for themselves in energy savings rather quickly.

Regardless of price, most all of these mini-split units will provide 3X or more heat per watt than a ceramic heater above 30 degF.
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Old 08-14-13, 10:37 PM   #4
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The minimum SEER (not to be confused with EER) has been 13 for some time now.
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Old 08-15-13, 08:56 AM   #5
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Quote:
Originally Posted by jeff5may View Post
If you are considering a heat pump solution, I would suggest doing a decent amount of research before installing a system. The performance is all over the place, depending mainly on the technology and engineering put into the unit.

Cheaper units are usually labeled "10 SEER" and have performance comparable to a window air conditioner at 40 degF. As the outdoor temps drop, so does the energy efficiency. They are mainly built with capillary tube metering devices, so their heating capacity falls off rather quickly at lower temps.

More robust units have a higher price tag, but their performance improvement over the "basic" models translates directly into energy savings. They have features built in such as: variable speed fans/compressors, electronic metering devices, heat transfer and defrost optimization software/firmware, domestic hot water preheat, hardwired thermostat connection, and more. They generally will produce generous heat down to around 5-10 degF before losing capacity. Depending on your current energy source and demand, these units can pay for themselves in energy savings rather quickly.

Regardless of price, most all of these mini-split units will provide 3X or more heat per watt than a ceramic heater above 30 degF.
Those temps are great for more moderate climates but we see 20 below here in the mountains and a month of 0F is not uncommon so I'm wondering if these might be inadequate for us.
I looked into heat pumps using deep well tubing a couple of years ago. The cost is relatively high but the payback, as oil prices keep going up, could pay back in a few years but then there is the issue of added complexity with motors, compressors, etc.
Last winter I ran an oil filled heater in my great room for a month or so and the PV covered it. It did take a couple of months to catch back up to net zero and now I'm making money again because the added off grid/intertie system with 4.2Kw from this summer is doing better than I expected, in fact, I saw over 4.5Kw out of it the other day.
Now I'm getting ready to add micro-hydro and wind. I might look back into a whole house heat pump again and bite the bullet for the $15k it will cost me. I think I'll stick a temperature sensor in my 12 ft. deep pond and see what the temps drop to this winter. Running spiral tubes might be cheaper than the $7,500 cost of the deep well tubing system. It's not a big pond but it does have several springs in it. Trouble is I don't like upsetting the ecosystem and once you stick tubes in a pond it's a pain to back track.

Just thinking out loud, all comments welcomed.
Rob
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Old 08-15-13, 11:37 AM   #6
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The cost of heating oil isn't likely to go down any time soon.
I know from our experience with Sanyo Inverter Mini-split, the savings are in the 75% range.
The only time I run my oil burner nowadays is a 10 or 15 minute test each Sunday.
Check out my posts about the Sanyo 24KHS72 (an older high SEER model).
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Old 08-19-13, 03:19 PM   #7
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Rob,

Pardon the tons of questions I'm about to ask, just trying to help.

How much, if any, of the heating solution are you planning on DIY?

How many BTU of heat will you need, especially at sub-zero ambient temperatures?

Is this thread about a small, supplemental heater, or the whole house?

Have you considered a water-to-water setup to heat your floor?

Do you have any kind of thermal store for your radiant floor?

Do you want to maximize energy savings, or just meet your (10% or less) demand on those extremely cold days?

Your answers to these questions will lead you in different directions. To provide heat to a 225 ft2 room at -20degF can be done with the right air-source minisplit at roughly 2/3 the electricity per BTU as an electric resistance heater. However, to maximize your energy savings year-round for the whole house, a completely different system would save you gobs more energy, yet may or may not cost a whole lot more. Better off is a matter of opinion.
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Old 08-19-13, 04:23 PM   #8
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It doesn't look extra cold in Delhi NY.. It's about the same as around here.

Delhi, New York (NY 13753) profile: population, maps, real estate, averages, homes, statistics, relocation, travel, jobs, hospitals, schools, crime, moving, houses, news

Average climate in Delhi, New York

It does get down under 5 deg F around here, but it's so rare, and has such a short duration,
I'm calling it 20deg F average during the cold winter months.
Easy for an inverter model 19-22 SEER Mini-Split to handle.

If extreme cold did hit us for a long duration, that's what back-up heat is for..
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Old 08-19-13, 06:42 PM   #9
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Quote:
Originally Posted by Xringer View Post
It doesn't look extra cold in Delhi NY.. It's about the same as around here.

Delhi, New York (NY 13753) profile: population, maps, real estate, averages, homes, statistics, relocation, travel, jobs, hospitals, schools, crime, moving, houses, news

Average climate in Delhi, New York

It does get down under 5 deg F around here, but it's so rare, and has such a short duration,
I'm calling it 20deg F average during the cold winter months.
Easy for an inverter model 19-22 SEER Mini-Split to handle.

If extreme cold did hit us for a long duration, that's what back-up heat is for..
Xringer,
The last few years the winters seem to have been a bit milder but I've seen 40 below and even last year we had single digits for three or four weeks straight. I remember February's with 20 below for two weeks. I'd love a mean temp of 30F in the winter! The last week or so the temps at night have been in the low 40's, in fact if you talk to the farmers they will tell you that they have seen frost, at one time or another, every month of the year. This is the mountains and we're up a couple of thousand feet. In town they get about three weeks longer growing season. I get 6" of snow and they get a dusting.
The real killer is the wind. I put up a row of Colorado Blue Spruce when I built the house and they are starting to cut some of the shear winds down that come across my 4 acre front field. I'd plow my driveway and an hour later you couldn't get up it with a car, the tree line helped that. Thinking of the wind here makes me anxious to put up a couple of windmills!
The worst part is I'm an ocean person who used to live in Hawaii! Wasn't it John Lennon who said," Life is what happens to you while you're making other plans!"
Rob
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Old 08-19-13, 07:29 PM   #10
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I just looked at the underground weather data for Meredith, NY and does get a lot colder up in the hills around there!
Around here, the coldest temps are very early in the AM..
But when the sun comes out, it's back up into the teens and twenties.
One of the advantages of living near the sea, I guess.

Even with your excessive cold stretches, if your average cold season temp is in the teens,
you still might find a good mini-split useful.. Ours does the job 99.4% of the time.
So, maybe up in those hills, it might be useful 80% of the time.?.
They work pretty well above 5F.. The new models do better..
http://i46.photobucket.com/albums/f1...CL/heatcap.jpg

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