Mini Split for keeping a garage above freezing?

JakeCK

As the title asks, are there any mini splits out there that are designed to have a low set point for heating. I'm talking like 40f here. Just enough to keep stuff that can't take the cold from getting damaged. Batteries, paint, chemicals, etc. 

Most I've seen have a minimum in the low 60's or higher. I'm looking for an economical way to heat and cool a two car garage. Gas isn't an option, I'm not willing to run a gas line the 70ft from my house to it, and while resistance heating would work it'd be expensive. This seems like an area where a heat pump would excel.

veteransteamhvac

Yes, install a mini split, any well regarded brand will be fine, no need to be picky. Have it properly sized for your space. You will be happy at whatever temperature you ask it to maintain in the space.

JakeCK

veteransteamhvac said:

Yes, install a mini split. Have it properly sized for your space. You will be happy at whatever temperature you ask it to maintain in the space.

The issue isn't sizing, the issue is most mini splits do not allow a set point as low as I would want to set it for heating 

pecmsg

Most have a minimum indoor temperature, 50 or 60 sounds right.

wmgeorge

JakeCK said:

veteransteamhvac said:

Yes, install a mini split. Have it properly sized for your space. You will be happy at whatever temperature you ask it to maintain in the space.

The issue isn't sizing, the issue is most mini splits do not allow a set point as low as I would want to set it for heating 

My Mitsubishi will not go lower than 63 or so. Insulate your garage and door.

rsilvers

Probably you can just use an external thermostat that calls for heat at 40. Just make sure the unit allows for thermostat wires. 

Personally I keep my garage heated to 45-50. 

pecmsg

It’s the same as trying to run your A/C at 40* outside air. There not designed for it. Can it be done yes but a lot of re-engineering required. 

sunlight33

The min. heat function on Fujitsu keeps temperature at 50f, however the blower on indoor unit will always be on, otherwise the unit cannot sense the indoor temperature.

JakeCK

aggravating. I was hoping for an off the shelf solution out there somewhere. Wanting to heat a garage to a just above freezing temperature can't be that uncommon.

pecmsg

JakeCK said:

aggravating. I was hoping for an off the shelf solution out there somewhere. Wanting to heat a garage to a just above freezing temperature can't be that uncommon.

As I said earlier it more complicated then just a thermostat. 

sunlight33

Just use an electric heater with a temperature controlled outlet.

Hot_water_fan

Most I've seen have a minimum in the low 60's or higher. I'm looking for an economical way to heat and cool a two car garage. Gas isn't an option, I'm not willing to run a gas line the 70ft from my house to it, and while resistance heating would work it'd be expensive. This seems like an area where a heat pump would excel.

I'm interested in hearing if you find one! That COP would be amazing.

These must be some valuable paints, chemicals and batteries!

JakeCK

Hot_water_fan said:

These must be some valuable paints, chemicals and batteries!

Not really but it is a case of value added. Not only would I be able to keep these things in the garage year round, if I want I can work out there year round too. A heated and cooled garage is a nice thing when you want to do some wood working or need to work in the car when it's 85f or 10f outside.

JakeCK

pecmsg said:

JakeCK said:

aggravating. I was hoping for an off the shelf solution out there somewhere. Wanting to heat a garage to a just above freezing temperature can't be that uncommon.

As I said earlier it more complicated then just a thermostat. 

Oh I know, that is why I was hoping to find one that had that purpose in mind and was designed for it. Last night I was trying to explain to a coworker how mini splits work with their inverter compressors and why it's difficult to just slap a t-stat on them. He had asked if I could just get something like a nest. He didn't understand that even a "smart" nest thermostat is still just a light switch as far a traditional HVAC system is concerned. 

JakeCK

sunlight33 said:

The min. heat function on Fujitsu keeps temperature at 50f, however the blower on indoor unit will always be on, otherwise the unit cannot sense the indoor temperature.

That actually might be ok. I plan on insulating the garage with r13 polyiso and replacing my very old wood garage doors(with pealing lead paint) with insulated doors anyways. This is a concrete block garage with brick on the front. A very well built block garage I might add, the size of the I-beam header over the doors actually surprised me.

I wonder how much energy it would actually use to keep it above 50... I wouldn't supposed Fujitsu mini splits have a warm weather shut down do they? Once insulated I would bet the garage would easily stay above freezing until it got down into the mid 20's for an extended period. 

I'm reading the listed features and functions on the Fujitsu halcyon model. I'm liking the third party device control for home automation. I could make this sing and dance to what ever song I want possibly.

ratio

Mitsubishi has the PACsomethingsomething-US thermostat adapter that'll allow a standard stat to control a mini split. I doubt you'll find something designed to operate with a 50° indoor temp, but there's a decent chance it'll work without failing too obnoxiously quickly.

DJD775

I don't know where you live but I suspect after you insulate your garage you will not need much heat to keep it above freezing. Might be a good idea to calculate the heat loss of the garage to get an idea how much heat you will need. As mentioned earlier by sunlight33 your best bet might be some type of electric resistance heat with a thermostat. Unless you need the AC function as well you are not likely to have a good return on investment over electric resistance.

JakeCK

DJD775 said:

I don't know where you live but I suspect after you insulate your garage you will not need much heat to keep it above freezing. Might be a good idea to calculate the heat loss of the garage to get an idea how much heat you will need. As mentioned earlier by sunlight33 your best bet might be some type of electric resistance heat with a thermostat. Unless you need the AC function as well you are not likely to have a good return on investment over electric resistance.

I do want the capability to cool it too. The design temp for my area is 7f. Granted that is assuming you want to keep it above 68f inside, I do not. Normally I'd aim for a low temp but would want to bring it up into the 50-60s range when working in there. I haven't had a chance yet to do a heat loss on the building, so I can't even guess at how many btu's I'd need. But I still feel that a heat pump is my best option for heating and cooling it and tbh I have spent more money on gaming computers than what I would spend on the hardware for this. There is also the advantage of using less amperage when it is running compared to electric resistance heat. Which is a bonus when you are running power hungry tools.

JakeCK

DJD775 said:

I don't know where you live but I suspect after you insulate your garage you will not need much heat to keep it above freezing. Might be a good idea to calculate the heat loss of the garage to get an idea how much heat you will need. As mentioned earlier by sunlight33 your best bet might be some type of electric resistance heat with a thermostat. Unless you need the AC function as well you are not likely to have a good return on investment over electric resistance.

I do want the capability to cool it too. The design temp for my area is 7f. Granted that is assuming you want to keep it above 68f inside, I do not. Normally I'd aim for a low temp but would want to bring it up into the 50-60s range when working in there. I haven't had a chance yet to do a heat loss on the building, so I can't even guess at how many btu's I'd need. But I still feel that a heat pump is my best option for heating and cooling it. There is also the advantage of using less amperage when it is running compared to electric resistance heat. Which is a bonus when you are running power hungry tools.

One other advantage I thought of is the ability to control humidity. Right now when there is a large swing in temperature it gets really humid in there. Generally happens when it starts off real cool in the morning and quickly warms up outside. Garage stays cool because of the thermal mass and then causes moisture issues. I've actually had tools and shelving rust before because of that.

ChrisJ

If the garage was cool, and remained cool but it warmed up outside, how does that cause moisture issues inside? Is infiltration that bad? Humidity issues like that typically happen when it's hot and suddenly cools off.

I also suspect under such conditions (the garage is cool) the minisplit isn't going to do anything for humidity as it's not going to be cooling.

I'm guessing it's a foregone conclusion that if you're not willing to keep the temperature above 40 in the winter you probably won't keep the air conditioning set at 65 in the summer. A typical dehumidifier will do far better under such circumstances.

ethicalpaul

Infiltration would be that bad every time the garage door was opened. My garage in Michigan would suffer from this during the shoulder seasons when the garage contents could be significantly cooler than the outside air when I happened to open the garage.

To answer original question, I would think that through creative location of the thermostat you could get the behavior you want even though the system won't let you put the setpoint down that far.

Gsmith

As mentioned earlier, do a heat loss calculation on the structure with both your desired minimum indoor temperature (40-45, whatever) and the minimum temp provided by the minisplit you'd like to use. Maybe the difference is not significant, especially if you are installing good insulation. And, consider spending more on better insulation, those dollars pay back every year.

lkstdl

Get a simple temperature controller like an Inkbird.

Then go one of two routes:

Connect the minisplit into the 'COLD' output of the controller. You'd need to use a controller with appropriately sized relays based on your minisplit power requirements.

But maybe the minisplit doesn't like to be power cycled that often, or it won't restart after a "power outage", or you just don't want to mess with such large relays.

In this case, connect a small heat source into the 'HOT' output, and tape the minisplit's temperature sensor to this heat source. You want a heat source of roughly 2-4 watts -- just enough to warm up the minisplit's sensor, and make the minisplit think that it is 60F or so. I've used 10 watt resistorspaired with an appropriate ~6V wall wort to get the right amount of warmth.

Then just set the Inkbird "COOL" setpoint to say 45F. When the room temperature reaches 45F, the minisplit's sensor is warmed up to 60F, and it shuts off. If you are working in there and want it warmer, just unplug the Inkbird and the minisplit will operate as normal.

Make sure to set either a large differential or time delay on the Inkbird to avoid short cycling.

Luke

ChrisJ

lkstdl said:

Get a simple temperature controller like an Inkbird.

Then go one of two routes:

Connect the minisplit into the 'COLD' output of the controller. You'd need to use a controller with appropriately sized relays based on your minisplit power requirements.

But maybe the minisplit doesn't like to be power cycled that often, or it won't restart after a "power outage", or you just don't want to mess with such large relays.

In this case, connect a small heat source into the 'HOT' output, and tape the minisplit's temperature sensor to this heat source. You want a heat source of roughly 2-4 watts -- just enough to warm up the minisplit's sensor, and make the minisplit think that it is 60F or so. I've used 10 watt resistorspaired with an appropriate ~6V wall wort to get the right amount of warmth.

Then just set the Inkbird "COOL" setpoint to say 45F. When the room temperature reaches 45F, the minisplit's sensor is warmed up to 60F, and it shuts off. If you are working in there and want it warmer, just unplug the Inkbird and the minisplit will operate as normal.

Make sure to set either a large differential or time delay on the Inkbird to avoid short cycling.

Luke

There's absolutely no way that would work with a minisplit my friend.

pecmsg

Depending on the make & model it's just not going to like a continuous low temperature and probably shut down on various trouble codes.

One thing with minis is Do not try to operate outside of the design envelope.

JakeCK

ChrisJ said:

If the garage was cool, and remained cool but it warmed up outside, how does that cause moisture issues inside? Is infiltration that bad? Humidity issues like that typically happen when it's hot and suddenly cools off. I also suspect under such conditions (the garage is cool) the minisplit isn't going to do anything for humidity as it's not going to be cooling. I'm guessing it's a foregone conclusion that if you're not willing to keep the temperature above 40 in the winter you probably won't keep the air conditioning set at 65 in the summer. A typical dehumidifier will do far better under such circumstances.

Easy, warm moist air poured into a cool concrete garage = lots of condensation. NEO is a pretty humid place close to the shores of lake Erie, one of the few places in the world to get lake effect snow and rain. I wonder if we're considered a microclimate in meteorology? Anyways I can either choose to heat the garage, or choose to dehumidify it, or both with a dehumidifier. Depending on what the temperature is going to do outside informs what to do. It is not uncommon for it to start off in the 50s, shoot up into the 70-80s, and drop back down by dinner time. And during this process the concrete floor will look like someone just ran a damp mop over it. This same issue plays hell in the house too. I have to run a dehumidifier down in the basement for 7-8 months of the year.

My hope is that once I replace the garage doors a lot of those issues will be minimized, lessening the load all the way around. As of right now leaves can blow right under the doors, there is no weather stripping on them. 

GW

if someone put twizzlers to my head, I bet one could set up the traditional thermostat adapter (I've never done this) and make it work. Was it designed to do this: noper. Would it work? it might

ChrisJ

GW said:

if someone put twizzlers to my head, I bet one could set up the traditional thermostat adapter (I've never done this) and make it work. Was it designed to do this: noper. Would it work? it might

Black, cherry or strawberry?

GW

Cherry 🍒 

ChrisJ

GW said:

Cherry 🍒 

Never trust a guy that doesn't like black twizzlers.

  

lkstdl

pecmsg said:

Depending on the make & model it's just not going to like a continuous low temperature and probably shut down on various trouble codes. One thing with minis is Do not try to operate outside of the design envelope.

Can you help me understand this? I am not familiar with mini splits. I'm not doubting you -- I just would like to understand the science. What specifically is likely to fail or not work well?

Is it an issue with pressure being too high or too low because more heat is pulled off the indoor coil? Would the motor draw too much power?

Are we worried about corroding the heat exchanger somehow? Running a furnace or boiler with too low return temperature can cause sustained flue gas condensation, resulting in corrosion and premature failure of the heart exchanger. But the refrigerant in heat pumps is condensing and evaporating constantly, right? Isn't that integral to how they work?

ChrisJ

lkstdl said:

pecmsg said:

Depending on the make & model it's just not going to like a continuous low temperature and probably shut down on various trouble codes.

One thing with minis is Do not try to operate outside of the design envelope.

Can you help me understand this? I am not familiar with mini splits. I'm not doubting you -- I just would like to understand the science. What specifically is likely to fail or not work well?

Is it an issue with pressure being too high or too low because more heat is pulled off the indoor coil? Would the motor draw too much power?

Are we worried about corroding the heat exchanger somehow? Running a furnace or boiler with too low return temperature can cause sustained flue gas condensation, resulting in corrosion and premature failure of the heart exchanger. But the refrigerant in heat pumps is condensing and evaporating constantly, right? Isn't that integral to how they work?

I assume pressure would end up too low.
The part that confuses me is both indoor and outdoor coils are using variable speed fans and the unit has an EEV, and I thought even the compressors were variable speed so I would expect it to be able to compensate for an awful lot.......

It's not like a split unit with two fixed speed fans and a fixed orifice.
But maybe 0F outside and 60F inside is already compensating a lot. Or, perhaps even if the hardware can do it, the software wasn't designed to expect it so it won't work regardless.

pecmsg

lkstdl said:

pecmsg said:

Depending on the make & model it's just not going to like a continuous low temperature and probably shut down on various trouble codes.

One thing with minis is Do not try to operate outside of the design envelope.

Can you help me understand this? I am not familiar with mini splits. I'm not doubting you -- I just would like to understand the science. What specifically is likely to fail or not work well?

Is it an issue with pressure being too high or too low because more heat is pulled off the indoor coil? Would the motor draw too much power?

Are we worried about corroding the heat exchanger somehow? Running a furnace or boiler with too low return temperature can cause sustained flue gas condensation, resulting in corrosion and premature failure of the heart exchanger. But the refrigerant in heat pumps is condensing and evaporating constantly, right? Isn't that integral to how they work?

As I said operating outside design conditions for extended periods tend to issue trouble codes. Whin i go out to the summer house and turn mine on they'll shut down 2,3 may be 4 times until the building warm's up.

try it, keep us informed.

DJD775

@pecmsg
I understand what you are saying now. Outside of the indoor design envelope they are troublesome but once they reach and maintain the temperature range they were designed for they work fine. Not really involved too much in this thread but I'm always looking to learn new things. Thanks for clarifying.