effectiveness of 'freeze protection' setting on mini split

[tff]

I'm trying to figure out if i should switch an order from a mini split that does not have a 'freeze protection' low temperature heat setting to a unit that does. These are both Blue Ridge units. The one that does have an FP setting is a 46F set point.

I spoke with the technical advisor and he was of the opinion that if i really want to maintain a garage at a low temperature (say 46F) that the mini split is not for me and i should consider another method.

I don't understand this... if the unit has this feature, why not use it as a freeze protection setting.

In my case... 95%+ of the time I'm not going to be in the garage, so a 46F setting seems reasonable just to prevent the chill and keep things above freezing. When I'm working I'll crank it up into the 60's.

Opinions?

Thanks.

 

[SALIV8]

I'm a complete novice diy of a mini split system, just to be clear, but I think that freeze protection is a nice feature.

I'm not sure why the tech would steer differently.

If they were thinkn of a power outage that would effect most systems and typical mini splits revert back to their last setting once power is restored, as far as I know.

 

[tff]

Follow-up question, based on reading different things in owners manuals for such units. Is the freeze protection setting (46F in this case) meant to keep the room from freezing or meant to keep the unit's coils from freezing?

 

[LS6 Tommy]

The coils will not freeze. It's for room protection. His suggestion was probably based on the assumption that you were primarily looking to keep the garage from freezing and the A/C wasn't a huge concern, so another heat source would have been more cost effective.

Tommy

 

[dsimatt]

If there isn't much of a price change I would, it's easier to not use a feature you have than try to add it on later. Where you are at I think you could get away just setting the mini to it's lowest temp setting because you don't have a lot of really cold days.

I know my hyper heat has a heater coil in the bottom to melt any condensation buildup that falls off the coils, but doesn't sound like yours need that.

 

[Jackfre]

I'm not following the question. Mini-splits are tested at 17 & 47*. If you are worried about freeze-up buy one of the low temp heating units. The lowest temp units have base pan heaters in the condensing units. The condensing units are where you can run into freeze problems. When the defrost function kicks in the unit reverses and takes heat out of the building to melt off the outside coil. That moisture has to drain out the bottom of the condensing unit. I saw a unit in Maine that had frozen the drain hole and the ice has built up inside until it froze the fan in place. Don't go there. Raise the unit off the pad or wall mount it on a bracket to facilitate good drainage. You should not need the base pan heater in SC.

 

[McFarmer]

In South Carolina you might be OK but here in Iowa our mini split won't heat when it's much below 20 degrees.

 

[yeldogt]

I believe the OP wants a unit that he can set an indoor temp of 46. Most units don't have an indoor setting that low .. very few would ever need it. Many all electric vacation houses have a setting for this type of operation with electric resistance heat -- it allows you to be safe without worry and also keep the expensive electric off unless needed.

I really don't see the problem using a unit in this way as long as the capacity is there to deliver the BTU's in colder temps.

For my studio to fall to 46 degrees -- it would have to be very cold outside. The issue at that point would be how many BTU's can it provide to keep up with falling temps .... If you maintain a temp of 60 the space has a built in load of heat that must be given off first as the temps drop. Every cold winter there are always people at the beach who end up with frozen pipes because they don't understand the load at lower temps.

You should also do a heat load and cost -- to see if it's really worth going that low. Most mini splits are at least 3x resistance -- so it's not as expensive to maintain a higher temp. You will also not need as large a unit using it that way

 

[PoorOwner]

FP means the SET POINT at 46 degrees INSIDE, normally your controls is somewhere around 60-86F and cannot move outside of these ranges. Mitsubishi has a 50F setting, something meant for vacation home.

it does not mean your mini split will be harmed in anyway when it is cold OUTSIDE.

You have to see, how cold does your space get without any heating supplied? If it is never below 46 or just in the 40s, running the mini split for prevent freezing is a waste of power.

 

[tff]

Thanks for everyone's comments. I may not be clear nor even rationale in what i'm asking about.

I'm thinking that there would be an advantage to having a mini split unit that can maintain a heated temperature lower than 60F in a detached garage. 2 reasons... sometimes 60F is actually kind of warm working in a garage and when I'm not in the garage I'm thinking that I don't want to keep it at 60F but something lower. (Even though I'm in SC, there are winter days that can stay in the 20 to 45F range outside.) So when I saw this unit with a 46F setting, i thought that would be an advantage.

(Based on a comment above... does it mean that this 46F setting would be resistance heating and therefore not efficient, or would it still work as a heat pump).

Thanks.

 

[yeldogt]

Thanks for everyone's comments. I may not be clear nor even rationale in what i'm asking about.

I'm thinking that there would be an advantage to having a mini split unit that can maintain a heated temperature lower than 60F in a detached garage. 2 reasons... sometimes 60F is actually kind of warm working in a garage and when I'm not in the garage I'm thinking that I don't want to keep it at 60F but something lower. (Even though I'm in SC, there are winter days that can stay in the 20 to 45F range outside.) So when I saw this unit with a 46F setting, i thought that would be an advantage.

(Based on a comment above... does it mean that this 46F setting would be resistance heating and therefore not efficient, or would it still work as a heat pump).

Thanks.

They don't have resistance heat .. some units did many years ago when they did not work as well (not VS).

Most people are fearful of the cost to maintain a reasonable temp -- IMO 46 is not a reasonable temp. If you do maintain a temp that low the time to bring the space up to working temp will depend on the size of the unit and the amount of stuff in the garage. Obviously -- with a lot of stuff that's all 46 degrees ... it will take longer because you have to warm it all up.

With a HP -- you want to size closer .... the cost to bring up and down will eliminate much of any savings. And the output if a HP will not be as great as say a NG heater. The same is actually true for any heating system -- cost saving of large setbacks.

Most people don't have the benefit of using a space under different conditions with different heating equipment. Having built many spaces over the years -- spending time and money on insulation will allow for smaller equipment and overall cost and comfort gains. The cost difference to keep my 1700sf PA studio at 65 vs 55 is not enough that I would ever worry about it ... and I only use it on the weekends

 

[finn]

46 degrees is a pretty reasonable temp to keep, especially compared to an unheated alternative that may drop below well zero in the winter.

Your statement dissing setback strategies is flat out wrong. The higher the delta T between the inside of the building and outside, the greater the heat transfer and the higher your heating expense. A well insulated building minimizes the heat transfer to the atmosphere, but it doesn’t cancel the laws of thermodynamics.

 

[walta]

The “freeze protection” is necessary because the indoor part of the unit is designed to keep some water in its trap if the indoor temp falls below freezing the trap or indoor drain lines would likely be damaged and leak water inside the building the next time the unit operated in cooling mode.

The mini split should do fine maintaining a temp but will struggle if want to make big changes in the temp quickly.

If you want big fast changes may want a big heater to make the changes and use the mini to maintain.

Walta

 

[Milton Shaw]

The freeze protection was built into the units because they are primarily used in Hotel/Motel rooms. The feature was put there so the desk clerk would not have to go around and turn units on in unoccupied rooms at midnight on a cold night because they forgot to earlier. All the motels around here keep the units off unless they rent the room to save energy, so this feature was a God-send for them. A fix that sometimes works for thermostats to make them go lower is to intentionally install them not level. This makes it so that the mercury switches in them don't reach level and turn on at the designed low level of 55 but instead reach level at say 45.

 

[Ohmthis]

As has been stated, a mini split is not designed for large swings in temps. They are more for maintaining a desired temp. If you wanting a large swing, then the HVAC tech is not misleading you.

 

[yeldogt]

46 degrees is a pretty reasonable temp to keep, especially compared to an unheated alternative that may drop below well zero in the winter.

Your statement dissing setback strategies is flat out wrong. The higher the delta T between the inside of the building and outside, the greater the heat transfer and the higher your heating expense. A well insulated building minimizes the heat transfer to the atmosphere, but it doesn’t cancel the laws of thermodynamics.

46 -- is too cold for most people not commonly working in cold temps.

And .... there have been many studies on setbacks ...especially with HP's. It's not wrong when using a space frequently. I mention insulation in my post as being most important -- it's naturally going to make a difference ..and also the outside temp.

But -- swinging temps up and down just don't save huge amounts of money .. and with a heat pump can actually increase the cost depending on the frequency and setback. Even with NG I believe all was lost at 8 degrees.

I will absolutely drop my studio down (more) if I am going to be gone for two weeks -- but not 15 degrees ... And I'm running propane. With 15 years in this one space I can map it --

 

[firebirdparts]

I spoke with the technical advisor and he was of the opinion that if i really want to maintain a garage at a low temperature (say 46F) that the mini split is not for me and i should consider another method.

I don't understand this... if the unit has this feature, why not use it as a freeze protection setting.
.

I agree with you. If you have any interest in freeze protection, and it's a cheap option, do it. You live in South Carolina. I think it's ideal for you.

If you decide later on that you would like to maintain a temperature higher than 46 degrees, you can touch a button and do that. In that case, a heat pump is ideal for you. See what I mean?

 

[Ohmthis]

I agree with you. If you have any interest in freeze protection, and it's a cheap option, do it. You live in South Carolina. I think it's ideal for you.

If you decide later on that you would like to maintain a temperature higher than 46 degrees, you can touch a button and do that. In that case, a heat pump is ideal for you. See what I mean?

Can you explain your reasoning? Everyone who is in the industry has given the advice to keep a higher constant temp and to not have huge setbacks or temp changes. This is based on factual data and experience. This is not a knock, but do research and support this.

 

[ewang]

I think there is some misunderstanding about what "freeze protection" actually is on a mini-split heat pump, or any air-source heat pump.

Freeze protection is for the condenser, or the outside coil. When a heat pump is heating your space, the condenser is actually cooler than the outside air. During colder, or more humid cold days, the outside coil risks icing up, or freezing. The freeze protection is either an electric heat tape on the coil, or reversing valves that temporarily change the unit over to AC/cooling mode.

Freeze protection in this case is not referencing protecting the space from freezing.

 

[Ohmthis]

A lot of mshp have a “lower setting” that can be specifically set to hold the inside air temp. On all of the Mitsubishi units I’ve played with the lowest you can set the heat is something like 61*. With another button or control, you can bypass that and go lower, say 46-48*. It has nothing to do with the outside unit. There are thermistors on the coil and it thaws the coil at a certain temp.