Found the limit of the shop mini-split

tvrgeek

Scott
Corporate Member
Well, it is -5 out there, and the shop is just above 50. I have no supplemental resistive heat. 55 degrees delta. I am impressed. I remember when the best a heat pump could do was 35 degrees.
 

KenOfCary

Ken
Staff member
Corporate Member
Our primary heat pump had a hard time when the power was out and we were on the Generator. The auxiliary heat coils don't come on when on the generator. The thermostat was calling for auxiliary heat but it wasn't getting it. Set at 68 it only got up to 60 while the power was out and it was zero outside. The gas logs helped keep the great room warm enough to be tolerable.
 

pcooper

Phillip Cooper
Corporate Member
My shop mini-split had my shop at 68 when it was only 8 degrees outside yesterday, I thought that was incredible. Mine is a Sennville that I got from Amazon. They said not to expect a lot of heat in the coldest of winter, but it's outdone my expectations.
 

Bernhard

Bernhard
User
My shop mini-split had my shop at 68 when it was only 8 degrees outside yesterday, I thought that was incredible. Mine is a Sennville that I got from Amazon. They said not to expect a lot of heat in the coldest of winter, but it's outdone my expectations.
That is incredible! I will need tocheck into that brand.
Thx
Bernhard
 

JNCarr

Joe
Corporate Member
I have a Mitsubishi mini-split. About the same result as Scott's the other day: -8 outside, 59 inside. I had turned it down to 60. The run between the indoor and outdoor units is the max recommended so it's pretty amazing to get this result. The unit is 7 years old, so mid-life.
 

tvrgeek

Scott
Corporate Member
Mitsubishi. The installer said it was the only one he would dare touch.
Pretty big building, pretty small unit.
 

junquecol

Bruce
Senior User
Tomorrow I will change control board in our family room. Unit over there has trouble keeping up, which means heat strips aren't coming on. Same brand of heat pump in main part of the house has kept it 67 (thermostat setting,) with no problem. Heat strips are definitely working.
 

Gotcha6

Dennis
Staff member
Corporate Member
Energy Code requirements are making manufacturers design more efficient units. Looks like it's paying off.
 

DSWalker

David
Corporate Member
I have a Pioneer unit. I think it is 18k. 4 years old.

Set at 71, was holding at 61 with mid teen temps outside
 

Westpacx3

Jim
Corporate Member
I have a Mr Cool DIY 18k unit and it held a 10 degree swing as well. I have a vaulted ceiling so I had to put a small fan up there to get the air down to the floor. My shop is off the ground so I get a bit more cool coming through the floor. I might insulted it at some point but insulation and a wire mesh to keep animals out was going to cost. Last winter was not so bad. Probably cheaper to just run the temp up for the few times NC get a cold snap.
 

mike_wood

Update your profile with your name
User
Well, it is -5 out there, and the shop is just above 50. I have no supplemental resistive heat. 55 degrees delta. I am impressed. I remember when the best a heat pump could do was 35 degrees.
I had a Fujitsu for my shop >10 yrs. When it developed a coil leak I had to replace. My HVAC folks wanted to install a Mitsubitsi for $5.5k. I couldn't see that much to buy/install a unit the size of a suitcase especially since all the installation infrastructure (elec, wall holes) was in place. I said thanks but no thanks. Found that Mitsubitsi sells only to companies so started looking at other options. The fellow that normally does PM on my geo system suggested Pioneer. I checked them out and found their reputation and warranty was as good as any one else. I needed a 12k btu unit and they had their best unit on sale for <$1k. They drop shipped it to me for free and it was palleted and wrapped to prevent any damage. I enticed one of my local HVAC techs to install on weekend. So I got a new unit for <$2k just before the cold front hit. It was 11 for 3 nights in a row & never got above freezing during the day. I set the unit for 64 and it stayed that temp all during the cold snap. I really like the unit as the temp setting is displayed in large numbers I can read across the room and the remote works from 25 ft away. Neither of which which the Fujitsu did. I am happy. Even if it does not last as long as the Mitsubitsi I can buy two more and just about break even.
 

AllanD

Allan
Corporate Member
I have a three head mini-split due to arrive tomorrow. I will hopefully get it installed in a rental house this coming weekend. The old LP fired package unit was burning through their bank account. A toast to the Japanese engineers behind them.
 

gmakra

New User
George
Don't get to excited the "delta T" difference temperature that is being discussed here is an incorrect assumption.
The correct way to measure is take a set of gauges and measure the suction and discharge pressures and convert then convert pressures to temps via a PT chart which is on the gauges or in card form.True delta T will be 20 something.

If you look at the HVAC system (aka vapor compression cycle) as a circular track the freon will pick up heat and then discharge it. When you walk past an airconditioning unit and feel the hot air. That is the BTUs from inside and a bit of heat from the compression of freon. The longer the unit runs it will move more heat AKA BTUs.

A heat pump is nothing more than a conventional air conditioning unit with a 3 way valve in it the reverse the flow of refrigerant.

A 50 degree delta T would have engineers and manufactures beat down your door offering you royalties.
 

AllanD

Allan
Corporate Member
From my understanding, Delta T in residential air conditioning is the dry bulb temperature difference between the inside air coming into the return duct vs. the temperature coming out of the supply duct. When we take pressures and use the P/T chart to get saturated temps we are usually figuring out the superheat or the subcooling which is different than Delta T. Those can actually be too high or too low and need the charge adjusted. Too high of a Delta T may actually indicate poor air flow over the evaporator like a very dirty filter. Mini-splits can produce more Delta T, say 24 degrees in A/C mode as opposed to 18 to 20 for conventional A/C
 

SteveHall

Steve
Corporate Member
Mitsubishi.

Is it the "Hyper-Heating H2i" version? I know these cost a little extra, but that recent (2021) tech heats 100% to 5°F and then diminishing to -13°F. I think both Mitsubishi versions have clever reverse cycle defrosting that runs the exchanger in reverse for a few minutes to prevent ice build-up.
 

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