WAY OT - Ductless mini splits - AC

[572cv]

We have a three head mini split setup here in Vermont. It is Mitsubishi, and the installer/dealer was a diamond level operation. I strongly recommend getting the best installers with as much experience as possible for a multi head installation. Ours required a couple of visits for proper balancing and charging of the refrigerant, so that heads would not chatter or whine when they were working. The tech who did the work was extremely knowledgable and precise, and kept at it till he got it right. These systems are pretty sophisticated, but when they work as designed, they are a joy.

NHAero is offering fabulous advice in this thread. He's a serious expert on this stuff.

[unterhausen]

I need to get this done. I have decided to get one unit on each side of the house, but I think I would like at least 3 heads on each one. It seems like there really is only one trustworthy installer in this area, hopefully they aren't too busy.

Our house is all electric heat, no A/C. It can be miserable in the summer. The HVAC guys always want to run ducts through the attic, which is really a bad idea. And I'm not giving up any basement space either. Mini splits are a much better solution.

[NHAero]

One thing to watch out for is oversizing based on the number of rooms you want conditioned. Say you have a small house with 6 rooms. The smallest outdoor unit I know of that does six zones is 48,000 BTU/hr. Two small 3 zone units are the same. The load may be half that, so the systems run time is short, and they do a poorer job of temperature stabiity and dehumidification. They modulate, but the turndown is still limited, and it is more limited on the multi-zone units. At this point in some cases i will use up to three single zone products to get the best performance rathger than one multi, on some jobs.

Angry, one argument against water-based distribution in houses is that residential HVAC contractors in general do a poor job of pipe insulation and so one ends up with a lot of dripping lines, esp. at fittings and valves, and sometimes mold. Refrigerant linesets are mostly home run and much harder to screw up the insulation.

Originally Posted by unterhausen

I need to get this done. I have decided to get one unit on each side of the house, but I think I would like at least 3 heads on each one. It seems like there really is only one trustworthy installer in this area, hopefully they aren't too busy.

Our house is all electric heat, no A/C. It can be miserable in the summer. The HVAC guys always want to run ducts through the attic, which is really a bad idea. And I'm not giving up any basement space either. Mini splits are a much better solution.

[unterhausen]

I thought the main advantage to minisplits is they run at part power so you can get more of the dehumidification effect? But I suppose that depends on the control.

[NHAero]

True. Until the load drops below their turndown range, then they cycle on and off. The best case is that the unit runs at part load all the time - the best dehumidification and lowest energy use.

In the single zone systems the turndown is amazing. My ducted single zone Fujitsu has an 8:1 turndown range - on Monday, my system heated my house using 1.4 kWh and when it was running was drawing less than 250W.

Originally Posted by unterhausen

I thought the main advantage to minisplits is they run at part power so you can get more of the dehumidification effect? But I suppose that depends on the control.

[pasadena]

I put my mini split in myself.
It was easy. They heat and cool.
There are DIY kits that work great too.

Originally Posted by AngryScientist

Good topic, as we are considering an addition that will use these. I would install myself for sure. havent looked into the options yet, but i would need cooling only, not heat.

we see these all over the city and tows around here in old brick and stone buildings where getting ducts in would be either impossible or a nightmare. they seem to work well, at least from a cooling perspective.

what is the typical heat transfer fluid? i assume something that does not need outdoor freeze protection?

[wc1934]

Originally Posted by 572cv

We have a three head mini split setup here in Vermont. It is Mitsubishi, and the installer/dealer was a diamond level operation. I strongly recommend getting the best installers with as much experience as possible for a multi head installation. Ours required a couple of visits for proper balancing and charging of the refrigerant, so that heads would not chatter or whine when they were working. The tech who did the work was extremely knowledgable and precise, and kept at it till he got it right. These systems are pretty sophisticated, but when they work as designed, they are a joy.

NHAero is offering fabulous advice in this thread. He's a serious expert on this stuff.

You got that right - and he was also kind enough to let me pick his brain via a phone call!!!

[Rabaja]

Very helpful discussion. We have an HVAC contractor put in a Daikin two-head/single compressor system in a few weeks. Our house was built in 1926 and retrofitted with a ducted AC system. They couldn’t put ducts into the two bedrooms, so we’re using a mini-split system for those rooms. Love the idea of a mini-split on paper - energy efficient and (very important) quiet. Let’s see how it turns out in practice. I didn’t know about mini splits two weeks ago, so this thread is very educational. Thank you!

[dziehr]

We're in Boston/Jamaica Plain and have a Mitsubishi compressor outside running 3 mini-splits--they work really, really well.

Last summer, we wanted to add one more mini-split in a guest room and had the option of either: a) replacing the existing compressor (with a newer one with 4 heads, but would also have to replace the perfectly working earlier edition mini-splits...$$$) or b) adding a single additional compressor to run one more mini-split; after dragging our heels a bit, we ultimately did the latter and have been very happy. All of the work (past and most recent) has been done by NETR. Good folks. We saved a few hundred on the most recent work with MA rebates. If you're interested in NETR, send me a DM (I have a referral form that will save both of us $100, I believe).

DZ

[Tandem Rider]

Originally Posted by NHAero

Refrigerant leaks are the bane of these systems and poor installations. And they are a major component of climate change. R410A per pound has ~2,000 times the impact of CO2. So the whole industry is eager for lower impact refrigerants. One limit in the US vs. other parts of the world is that we have stricter limits on the flammability of the refrigerant so there are some that are used elsewhere that we aren't using.

CO2 has been in the industrial world for a long time. It's a pretty dirty and corrosive gas on the inside of a system (the inside of a 1yo screw compressor looked like it had been run under water) and it runs at very high pressures. In an AC application it will be in the 400s for the suction and around 1400psi discharge. Industry likes it due to cost, EPA regs, and the Carbon Credits it generates. In today's world it's not practical for residential use since only a few companies are able to service it.

I am seeing some R290 (refrigeration grade propane) in small refrigeration applications. I have seen it used for in AC systems in the past as well. I wonder how long until someone burns a building down with it out of ignorance. I have worked on some ultra low temp lab freezers that had a proprietary blend of refrigerants including butane in them.

[AngryScientist]

Originally Posted by Tandem Rider

CO2 has been in the industrial world for a long time. It's a pretty dirty and corrosive gas on the inside of a system (the inside of a 1yo screw compressor looked like it had been run under water) and it runs at very high pressures. In an AC application it will be in the 400s for the suction and around 1400psi discharge. Industry likes it due to cost, EPA regs, and the Carbon Credits it generates. In today's world it's not practical for residential use since only a few companies are able to service it.

I am seeing some R290 (refrigeration grade propane) in small refrigeration applications. I have seen it used for in AC systems in the past as well. I wonder how long until someone burns a building down with it out of ignorance. I have worked on some ultra low temp lab freezers that had a proprietary blend of refrigerants including butane in them.

All of the "anes" are super commonly used as refrigerants in the oil/gas industry; propane, butane, ethane. refineries, hydro crackers, large tank storage and terminals, etc. As you guess, there have been plenty of incidents over the years with rapid depressurizations, vapor coud explosions, etc. Things have gotten a lot safer through process controls and other mitigating efforts though, for sure.

i dont see those as feasible for residential hvac though.

[polyhistoric]

Watching this thread with interest (and a 125 yr old house in NE). One aspect I am not in love with is the exterior piping and plastic caterpillars climbing up the sides of the house. Has anyone done an installation with all the piping coming from an internal/central location - like an old chimney chase?

[cp43]

Originally Posted by polyhistoric

Watching this thread with interest (and a 125 yr old house in NE). One aspect I am not in love with is the exterior piping and plastic caterpillars climbing up the sides of the house. Has anyone done an installation with all the piping coming from an internal/central location - like an old chimney chase?

Our installation has the piping on the exterior of the walls. It is a downside of the typical mini split installation.

I think it's done that way for ease of installation. I don't think there's any reason, other than time/expense, that you couldn't have the piping run inside.

Chris

[pasadena]

I have a mini split that runs through the attic space. It only comes through the wall for the exterior unit and drain.

Running along the exterior wall is easy and you can use a paintable cover that hides the pipes and wires. Looks clean once painted.

[Marc40a]

I had a 3 head, 1 compressor unit installed in my house on the North shore by Morris Heating and Cooling about 4 or 5 years ago, maybe longer.

I went with Mitsubishi units and have no regrets. I did an energy audit through MassSaves, if I'm not mistaken, because that made us eligible for some State funds - I'm not so sure that incentive program is still funded.

Anyways... here are some things I've learned:

1.) You WILL use the heat mode. Aside from the coldest days of winter, you won't find a cheaper BTU.

2.) It's most efficient when it's on all the time. I've tried to be clever and set it up like a commercial building, turning on an off with an elaborate schedule but it is cheapest when you set it on a reasonable temp (no tropical settings or icebox settings) and have a day and night temp setting.

3.) Allergies are more of a concern than with the baseboard heat you've been using. The blowers blow everything in the room around. The air is continuously agitated.

4.) I'd recommend you keep the head units away from beds, if possible.

5.) They seem to dry the air in both heat and cooling mode. I use a humidifier in the winter.

6.) There's a lot of condensation in the unit in cooling mode. You'll want to keep the fan on the units running at a decent level. It literally costs pennies per day. I had a couple episodes where we could smell mold. It was from stagnant water in the drip pan.


I know that sounds like a lot of concerns, but I wouldn't change a thing with my system. My wife's been working from home for the past year and I shudder to think what our utility bills would've been with a conventional system.

Now, let's talk about getting you some solar panels, so you never pay an electric bill again and all this heat and cooling is free. That's what I did. ;o)