Trane 15K BTU mini-split in garage first impressions

[Von]

As part of my garage->shop transition, we had a Trane mini-split (NTXWPH15B112AA) installed a couple weeks ago.

My details for anyone considering similar: This is a 15k BTU unit. The garage is ~440 square feet with 8 foot ceilings. One wall is shared with the house and the insulation on the other three sides is just drywall. No insulation in the attic over the garage. The garage door is insulated. One window and entry door are recently upgraded. No other HVAC in play besides what comes from the shared wall with the house, which I think is more meaningful in the winter.

My biggest concern is if the unit could keep up, and it's fairly clear to me now it has no problem doing that. While it's been fairly mild (80s F) for most of the time since it was installed, it did catch the end of the last 90 F+ spell we had, and it's had no problem. I'm pretty sure it could turn the garage into a meat locker. The main benefit I enjoy is it can quickly bring the humidity down, much faster (and more quietly) than the dehumidifier I was using prior. And it is quiet, basically same level of noise as my air cleaner.

No idea on cost to operate yet. I'll update in a couple months when I get some notion.

One first world problem I've noticed is that the head unit does create a significant cold area right in front of it when it is running, which is currently where I have my bench. I'm still playing with all of its options to see if I can get it to spread the cool love better.

[BillyJack]

It should have to work too hard to maintain if you keep it on.

[Tom King]

Put a fan in place to blow the air sideways in front of the exit.

We're cooling 7,000 sq. ft. of house with one 18k unit.  We have three fans in doorways moving it in a big circle.  I've been playing with it all this hot Summer, trying to figure out the best way to circulate the air.  There are three regular heat pumps in various parts of our house.  They're all turned off now.   At first, I just had the fans on a couple of them running, and one was turned off, but the fans in doorways keep it all moving better than the different system fans did.

I put in this mini-split about three years ago when my aged Mother had to move in with us on short notice.  At first I thought she would want it warmer than we did, and needed a separate system for her suite.

Now that she's gone, that section back there is not used by us, and I've gradually lowered the output of that mini-split to the point where it's set at 69 degrees back there. Yesterday was a high of 95, and today is supposed to be 98.  Currently 92, and it's completely comfortable in the house, probably even a little bit too cool, but we're trying to stay ahead of the hottest day so far.

Our electric bill has been well over $100 a month less this Summer than last Summer, and probably even more comfortable.

This house is super, super insulated.  When the inspector looked at the insulation in the last addition, he said, "You know, code only calls for R30".  I said, "I don't care a bit what the code calls for.  I'm going to insulate the hell out of it."  It's paid off many times.  He said everything about it was a lot different than what he was used to looking at.

The 10 foot ceiling in that addition has 1" polystyrene foam board between the ceiling joists and the coffered ceiling.  The ends of the joist openings over the exterior walls have foamed in foam board with a baffle to pass air from soffit vents into the attic.  That keeps air infiltration into the insulation down to zero.  In between the joists are R38 batts.  Going across those batts are another layer of unfaced R38 batts rolled out the other way.  There is a suspended walkway down the middle of that attic that doesn't touch the insulation.  Access into that attic is a hinged gable end vent.  I haven't ever needed to go back up there.  The rest of the house is built in similarly effective insulation strategy.

The house is shaded by very large Oak trees.

edited to add:  I probably should account for the upstairs that we really don't use since the kids have been grown and gone.  It does get warm up there.  Too warm for normal living, but not really anything like it is hot outside.  That's probably 12 to 1300 square feet. I kind of forget how much is where.  I guess that acts as a good buffer that helps.   The dog complex takes up a good part of it too, but that's all on the first level on the North side, and is covered these days by the same mini-split.

[Von]

On 8/13/2023 at 10:09 AM, BillyJack said:

It should have to work too hard to maintain if you keep it on.

My shop use is sporadic. On average, I probably get other there 2-3 times/week due to other commitments. So I'm trying to decide when I leave it running in between and when just to fire it up on demand. It cools the space quickly, so that isn't an issue. I think it's mainly efficiency and avoiding big temperature and humidity swings on my project wood.

Thinking about it, I'll probably set it to maintain some large range, say 50-80F, and then tweak it when I want to use it.

Thoughts welcome.