Questions about heat pump for my shop

woodgeek

Minister of Fire
Jan 27, 2008
4,277
SE PA
I have a 5600 watt heater that can raise the temp about 10 degrees in an hour. Yesterday it was 23 outside and the heater brought the temp up from 34 degrees to 48 degrees in a little more than an hour. 5600 watts is 19K BTU so I was thinking something around that rating or slightly lower might be good.
I was thinking a little different....if you turned on a heater at fixed power, and then let it run until you reached a steady temperature increase relative to the outside.

I would expect that if you left that 5600W heater on, with no thermostat, it would heat the space well above +10°F. But if your goal was to turn on a mini in the AM to use the shop later in the day, then you would want to upsize the unit relative to what is needed to just barely heat it all the time.

And the COP is higher when these run at lower throttle, so upsizing the BTUs of the unit is an upfront cost that pays back later in higher efficiency (contrary to other kinds of heaters where too big lowers eff).

The higher BTU rating would, as above, also get you warmer faster, which is an advantage if you are not leaving it on 24/7.
 

JRP3

Member
Sep 17, 2007
215
No my intent is to keep it on so the temp never drops below 50F, I was just using the heater example to give an idea of what 19K BTU can do in an hour of use. I'd also get the wifi option so I could boost the temp from the house before I go out if I want to.
 
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begreen

Mooderator
Staff member
Nov 18, 2005
85,854
South Puget Sound, WA
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woodgeek

Minister of Fire
Jan 27, 2008
4,277
SE PA
Does that translate to about a 20% efficiency improvement?
On a seasonable basis in some simulated reference climate. Last time I checked, HSPF was computed for a climate like Atlanta, Ga.
 
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semipro

Minister of Fire
Jan 12, 2009
3,932
SW Virginia
It really is as simple as connecting 4 flare fittings and vacuuming the lineset.

All the big manufacturers insist on using a torque wrench on the nuts. I did and everything I read says this assures an extremely reliable flare. Nylog on the flares is also recommended.
It surprises me that they use flares rather than o-rings. I wonder why. The Nylog makes sense but you'd need to make sure no errant bits end up floating around in the refrigerant.
 

Brian26

Minister of Fire
Sep 20, 2013
550
Branford, CT
It surprises me that they use flares rather than o-rings. I wonder why. The Nylog makes sense but you'd need to make sure no errant bits end up floating around in the refrigerant.
The use of flares I heard is because of the massive fire risk of brazing pipes with open flame in Asia where these units are from. The flare fitting are actually extremely reliable simple connections. It was found the main issue with flares was from over tightening the nuts. Torque wrenches are specd now by almost every mini split manufacturer. Using a torque wrench to properly torque the nut with a good flare has an extremely low failure rate.

Nylog is actually made of refrigerant oil so is totally safe if it gets in the system. This stuff has stellar reputation in the HVAC field.
 
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Brian26

Minister of Fire
Sep 20, 2013
550
Branford, CT
HSPF is 10.0 which is ok, but not extraordinary. A really good unit is going to be up around 12.0.
Yeah. Most of the lower end Chinese units seem to not go much about 10-11 HSPF and don't have the best cold weather heating specs. Though for costing a fraction of the high end name brands they aren't terrible.

I am doing some research in adding another unit at my house with better cold weather performance. Right now Gree has the best cold weather mini split out there according to the AHRI tested ratings with a HSPF of 15. The specs on them are pretty incredible.

Here is the heating capacity chart on the 18k Gree Sapphire. It actually puts out almost 24k in the 20-50 outside air temp range. The cold weather output is pretty impressive as well.
Capture.JPG
 
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begreen

Mooderator
Staff member
Nov 18, 2005
85,854
South Puget Sound, WA
That is definitely impressive. Who makes Gree? What is their history?
 

JRP3

Member
Sep 17, 2007
215
This site seems to imply there is a warranty of 5 years for the Mitsubishi if there is "proof of proper installation", whatever that is.

All parts are warranted for a period of five (5) years to the original registered end-user with proof of proper installation. The compressor is warranted for a period of seven (7) years to the original registered end-user with proof of proper installation. Ten (10) year parts and ten (10) year compressor coverage is offered when your system is installed by a licensed contractor and registered with Mitsubishi in 90 days from the date of installation. Twelve (12) year parts and twelve (12) year compressor coverage is offered when your system is installed by a Diamond Contractor and registered within 90 days of installation.
https://customercare.comfortup.com/post-purchase-faqs/what-is-the-mitsubishi-warranty
Similar wording for the Gree but doesn't mention longer warranty for professional installation.
The Gree Manufacturer's Warranty has recently updated. For systems sold before 2017, all parts are warranted for a period of five (5) years and the compressor is warranted for a period of five (5) years to the original registered end-user with proof of proper installation. As with all ductless mini split warranties in the industry, labor costs are not covered under the manufacturer’s warranty – extended warranties can be offered to cover that additional expense.
https://customercare.comfortup.com/post-purchase-faqs/what-is-the-gree-warranty

Edit: I guess not https://customercare.comfortup.com/post-purchase-faqs/can-i-install-a-ductless-mini-split-myself
Your new cooling and heating system will only perform at optimal efficiency, comfort and safety levels if it is well installed. In fact, an improperly installed system could reduce the system’s efficiency by as much as 50%. In addition, any applicable warranties will only be valid if properly installed by a licensed contractor.
 

begreen

Mooderator
Staff member
Nov 18, 2005
85,854
South Puget Sound, WA

begreen

Mooderator
Staff member
Nov 18, 2005
85,854
South Puget Sound, WA
For certain it does. Though the quality and lifespan are good, defects and human error in assembly can still happen.
 

semipro

Minister of Fire
Jan 12, 2009
3,932
SW Virginia
The prices on the Gree units are really competitive.
From reading reviews though it seems their documentation and support may be lacking.
 

CaptSpiff

Minister of Fire
Jan 13, 2014
527
Long Island, NY
Back to the OP's use plan, and probably a question I asked before and can't remember the answer: What is the minimum operating temperature setting for these newer units?

I never did get one installed in my vacation cabin, but I still want to. Presently I use electric baseboard with a typical winter heating use between 9000-9500 kwh. At about 12 cents per kwh, that's about $1100 for the heating season, and we keep the place at 55 degF except for one weekend a month.
 

DBoon

Minister of Fire
Jan 14, 2009
1,215
Central NY
If I recall correctly, my Fujitsu unit has a minimum temperature setting of 50 degrees F.
 

JRP3

Member
Sep 17, 2007
215
Just talked to a local installer, $5K+ for a Mitsu Hyperheat 18K BTU system installed !!! Um, no thanks.
 

CaptSpiff

Minister of Fire
Jan 13, 2014
527
Long Island, NY
I never considered there would be a minimum temperature setting. This thread suggests it might be an issue if the unit doesn't have it's own built in resistance heating, if I understand correctly https://hvac-talk.com/vbb/showthread.php?998911-Lowest-Thermostat-setting-for-heat-pump
Thanks for that link. If the minimum indoor control settings are for 50degF, but the manufacturer recommends keeping the indoor setting above 63degF (to allow for effective defrosting of the exterior unit), then maybe these mini-splits are not the best choice for low use vacation cabins.

Anyone have some practical experience with this? Kind of circling back to the OP wanting to heat a garage or workshop at 50degF for a long stretch.
 

maple1

Minister of Fire
Sep 15, 2011
10,646
Nova Scotia
Just talked to a local installer, $5K+ for a Mitsu Hyperheat 18K BTU system installed !!! Um, no thanks.
I would get more estimates from others. Ballpark here for 18k Daikin installed is around 4k. That's Canadian $.
 

JRP3

Member
Sep 17, 2007
215
Finally got around to doing this, went with a 24K BTU Mr Cool DIY unit because I wanted the warranty and I liked the sealed pre-charged line set. $1,600 for the unit plus another $400 for mounting bracket, line set cover, disconnect, etc.
 

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Highbeam

Minister of Fire
Dec 28, 2006
18,322
Mt. Rainier Foothills, WA
Finally got around to doing this, went with a 24K BTU Mr Cool DIY unit because I wanted the warranty and I liked the sealed pre-charged line set. $1,600 for the unit plus another $400 for mounting bracket, line set cover, disconnect, etc.
So how do you like it? 30 amp circuit?
 

JRP3

Member
Sep 17, 2007
215
Yes 30 amp circuit. It's been too warm to really test it, won't really know how it works until I get sustained temps below 35F or so. The most I've done so far is raise the garage from 56 to 66 in an hour with outside temps in the low 50's. 768 sq ft garage with 10ft ceilings and spray foam insulation. It pulls about 7 amps on each 120V leg.
 
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