WAY OT - Ductless mini splits - AC

[NHAero]

Residential equipment can only be in heating or cooling, as you say. Most equipment can be set up to have an auto changeover from one mode to the other, although that often leads to more energy use as it essentially is trying to control to one temperature setpoint and can switch back and forth all day. I don't know if there are options to set a deadband within which no heating or cooling is occurring.

If your office had a central system then all the spaces would also be in either heating or cooling, so that aspect is common to both types of systems. In larger heat pump systems there is the option for internal heat recovery in the outdoor unit, so simultaneous heating and cooling can occur, and rejected heat from a zone in cooling is transferred to a zone requiring heat.

You might ask the person who is responsible for your office system if it has an auto changeover option.

Originally Posted by sokyroadie

If you have multiple indoor units and need to switch often between modes heat/cool I think they suck. In my office we have 5 indoor units running off of 1 outdoor unit and all 5 have to be set on heat or cool - royal pain since a lot of days we need heat in the morning and cool in the afternoon. You will avoid that if just using to cool.

[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?

[NHAero]

What is in the linesets is a refrigerant, R410A. No freeze issue.

I haven't looked into the DIY versions. Our spec calls for the lineset to be drawn down to a very low vacuum to purge all water, and pressure tested for 24 hours, and then checked with a leak detector. It's hard for me to imagime this being a DIY project, but maybe there are products that pull it off. These systems run at 450 psi or so (I'm sure Jan Heine has a supple heat pump with low trail that runs at 30 psi, maybe that's the ticket

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?

[CDollarsign]

I had a Fujitsu Halcyon system in my old house in Cincinnati. It could support up to 6 heads as it was a 4 ton unit. It was a pretty great addition to a house built in 1895. The are quiet and efficient. You may notice them on the walls are first if you don't get a ducted unit, but you wont see them after a few weeks.

One feature that the new ones have is wifi control similar to a nest thermostat. We had remotes everywhere that would get lost.

One word of caution would be to make sure you hire a reputable installer. I don't think I would go with the cheapest HVAC contractor on these.

[cp43]

Originally Posted by wc1934

Massachusetts - gas heat - forced hot water (baseboard). wont really be using the mini splits for heat - heads are just formatted that way.

We converted from oil fired steam heat and electric baseboards, to all mini splits. Living in MA also. We're very happy with the system.

We have 4 heads on the first floor, and a large air handler in the attic for the second floor. Running on 2 outside compressors.

The compressors come in different sizes, you'll need the correct capacity for the number of heads that you want to run from a single compressor.

We have Mitsubishi, two years in, it's been great.
Even with all our heat being from electric now, our electric bill is lower in the winter than it was with the electric baseboards + oil. Plus, we don't have to buy any oil anymore.

FWIW, we didn't do the installation our selves, we had an HVAC company do it.

Chris

[Tandem Rider]

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?

Currently, all the small AC (and heat pump) equipment is still coming with 410A, there are a couple of different refrigerants on the near horizon that run at lower pressures (a good thing) but they aren't being sold yet.

[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.

Originally Posted by Tandem Rider

Currently, all the small AC (and heat pump) equipment is still coming with 410A, there are a couple of different refrigerants on the near horizon that run at lower pressures (a good thing) but they aren't being sold yet.

[AngryScientist]

ah hah.

i was working under the incorrect assumption that these systems operated as a traditional chilled water AC system, which would only require insulated chilled water (or other heat xfer fluid) lines which would run at much lower pressure.

perhaps that is impractical for residential operations. my background is with BIG stuff.

[eddief]

when in doubt, size UP! Lots of variables including windows, insulation, sq ft, etc. My Fujitsu installed 5 years ago has been an ongoing mystery. I do think it was undersized for my many windowed house with not very much insulation. It works hard to heat and cool at the limits experienced here in NorCal...which are not very challenging relative to other climes.

My neighbors have 2 Mitsubishi units and those seem to work flawlessly. My head unit has no readout, just blinking lights. My system has the thermostat in the head unit. My remote has a temp readout but you can increase or decrease the temp and see the readout changing on the remote, but unless you are pointing the remote directly at the unit, the unit don't get the message...as the number increases on the remote anyway.

Also in coldish and high humid conditions my unit goes into defrost mode for way longer than is comfortable, giving the room a chance to cool down rather than comfortably retaining the heat.

In my hood way more Mitsubishi dealers than Fujitsu. And one service company would not even service my unit since they did not install it. It's a mini split jungle out there.

[cp43]

Originally Posted by eddief

when in doubt, size UP! Lots of variables including windows, insulation, sq ft, etc. My Fujitsu installed 5 years ago has been an ongoing mystery. I do think it was undersized for my many windowed house with not very much insulation. It works hard to heat and cool at the limits experienced here in NorCal...which are not very challenging relative to other climes.
snip..

I should add that before we moved to the mini splits, we had quite a bit of work done on insulation/energy efficiency. I don't think our mini split system would keep up if we hadn't done that part first.

Chris

[mike_b]

Originally Posted by eddief

when in doubt, size UP!

No, when in doubt make your contractor do a load calculation by following the ACCA Manual J procedure.

[NHAero]

This is always what I recommend. You lower the cost of the minisplit installation, and the energy cost, and make your house more comfortable and durable. And if you buy solar, that system gets smaller too.

Originally Posted by cp43

I should add that before we moved to the mini splits, we had quite a bit of work done on insulation/energy efficiency. I don't think our mini split system would keep up if we hadn't done that part first.

Chris

[NHAero]

Exactly - heat pumps don't do well when over-sized

Originally Posted by mike_b

No, when in doubt make your contractor do a load calculation by following the ACCA Manual J procedure.

[NHAero]

Because of refrigerant constraints (e.g., flammability) you will see more equipment that looks like this - the refrigerant stays in the outdoor unit, and the heat transfer to the building is water-based. That will also give the potential for using carbon dioxide as the refrigerant, which is efficient and can work at very low outdoor temps, but works at 1,500-2,000 psi so no way it's a site-built refrigerant system.

Originally Posted by AngryScientist

ah hah.

i was working under the incorrect assumption that these systems operated as a traditional chilled water AC system, which would only require insulated chilled water (or other heat xfer fluid) lines which would run at much lower pressure.

perhaps that is impractical for residential operations. my background is with BIG stuff.

[AngryScientist]

Originally Posted by NHAero

Because of refrigerant constraints (e.g., flammability) you will see more equipment that looks like this - the refrigerant stays in the outdoor unit, and the heat transfer to the building is water-based. That will also give the potential for using carbon dioxide as the refrigerant, which is efficient and can work at very low outdoor temps, but works at 1,500-2,000 psi so no way it's a site-built refrigerant system.

in my mind, a water based system with all of the refrigeration cycle components outside is a much more desirable design. doing a little research there are definitely residential chilled water ac systems out there right now, but for the reasons you mention, hopefully they will expand the options in the future. cool stuff.