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So this may be the wrong forum to ask this in, but it is for an investment, so I figured I'd give it a shot. I'm renovating an apartment building and I was looking to outfit the apartments with mini-split heat pumps. The property is in NJ, and if there is one downside to air-air heat pumps is extracting heat in cold temperatures. The average temp in January here is 32.5 degrees, but it gets down to the single digits a few times a year, and a rare occassion a few degrees below zero. I am having the most difficult time finding any real world data on these heat pumps. The stats posted on the manufacturer sites are all over the place and I don't think they are accurate. One of the few heat pumps that does seem to have accurate data is the Mitsubishi Hyper Heat products, but they are about the most expensive mini-splits you can buy. Seeing as this is an investment, and I need to do 20 apartments, I was hoping for a more cost effective solution. Nobody understands tech stats and money better than a forum full of cheapskates like myself, so I figured this might be a good place to ask. Does anybody have any evidence on what systems will work? It's not like I can buy one and return it if it doesn't work out. I also have to wait until next winter to find out if it will work. The last thing I want is the building to have no heat on a cold day. I had an engineer do a heat loss calculation, and they range from 3.5k-7k btus at 0 degrees F.

Help me fatwallet, I've been looking for days!

Thanks in advance

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If you hired an engineer to do a heat loss calculation, why don't you hire him to design your system and select your equipment?

Heat pumps are generally not effective below 40 deg. F.

Do you pay utilities or do your tenants?  Without knowing the building, it's impossible to make a system recommendation.

BobM73 said:   1. If you hired an engineer to do a heat loss calculation, why don't you hire him to design your system and select your equipment?

2. Heat pumps are generally not effective below 40 deg. F.
 

  
1. Agree

2. WTF?

Do these units have an electric heat backup?
If so, they will heat at a lower temp.

I take it you can not use a traditional furnace or boiler?
Mini splits work well for AC, but they are expensive to install for what you get.

HVAC-talk dot com would be a better forum for your questions.

Yeah I agree saying 40 degrees is a bit of an over generalization. The issue with air source heat-pumps is as the temperature drops they are able to collect less heat and at the same time the heat loss from the house goes up so at some point you hit a balance point where the heat pump is only able to replace the heat leaving the house and below this point you will need to supplement with an additional heat source frequently resistance heat strips though in some instances you can just cut over to a different heat source such as a natural gas furnace (my setup for the downstairs of my house). So really the balance point is going to depend on the ability of the heat-pump to generate heat and how well insulated and sealed house/apartment is. Also heat-pumps energy consumption drops with temperature so while their efficiency falls they are still quite efficient at lower temperatures the problem is you have to supplement their energy with another source and if that is resistance heat it is going to be far less cost effective.

In my case my downstairs unit is either all heat-pump or all natural gas and I am able to set the cut over based on outside temperature (there is a sensor outside that feeds the thermostat). At my house the balance point was between 30 and 35 degrees (higher number was for windy days). I say was because my house is a lot tighter now but I haven't retested the balance point. Anyway at least when I was doing testing once I hit 30-35 degrees my heat-pump would run near continuously and might start to lose ground. I currently have the cut over set to 40 degrees though I am pretty sure I could go lower now, I don't because natural gas is so cheap.

OP your temperature ranges sound like mine and my upstairs heat-pump/resistance heating is able to heat the house just fine down to below zero F on the rare nights it happens. That said at that point the resistance strips are doing a lot of the heating (but not all of it) and thus if your electric rates are high you could be spending quite a bit on those nights the circuit for my strips is 90 AMPs so they can burn a lot of electricity.

It is impossible to advise you without some more numbers. What do you pay for electricity, is NG an option, etc.

You lose capacity dramatically as outdoor air temperature drops. You also lose efficiency.   Heat pump technology is improving, but it's not there yet.  I would not install a heat pump in a climate such as the OP without supplemental heat.

Don't believe me?  How about the Department of Energy?

http://energy.gov/energysaver/articles/air-source-heat-pumps

Quote: 

When outdoor temperatures fall below 40°F, a less-efficient panel of electric resistance coils, similar to those in your toaster, kicks in to provide indoor heating. This is why air-source heat pumps aren't always very efficient for heating in areas with cold winters. Some units now have gas-fired backup furnaces instead of electric resistance coils, allowing them to operate more efficiently.

/Quote

Don't get me wrong, I'm not against heat pumps - I have a hybrid heat pump / gas system in my house.  But due to multiple issues with pressure limiting, I switch to gas at 40 deg.

I just retrofitted a few rentals and my restaurant with the Fujitsu ones that work down to -15 degree. I was very skeptical for the restaurant as it has a lot of heat loss. I set them at 72 and at times throughout the winter, they never dropped more than 2 degrees below the set point even with 0 degree outside temps. I have 2 15k btu ones heating 3200 square of dining space and that area is not insulated the best. I would say that each unit cost me about a 100 per month to run. I have a 60000k (5 ton) heatpump for the kitchen around (500 square feet) and it wouldn't keep up with heating that area in 20 or below exterior temps, the grid backup kicked in. I am in Central PA, btw.

BobM73 said:   
Don't believe me?  How about the Department of Energy?

http://energy.gov/energysaver/articles/air-source-heat-pumps 

Quote: 

When outdoor temperatures fall below 40°F, a less-efficient panel of electric resistance coils, similar to those in your toaster, kicks in to provide indoor heating. This is why air-source heat pumps aren't always very efficient for heating in areas with cold winters. Some units now have gas-fired backup furnaces instead of electric resistance coils, allowing them to operate more efficiently.

/Quote

Don't get me wrong, I'm not against heat pumps - I have a hybrid heat pump / gas system in my house.  But due to multiple issues with pressure limiting, I switch to gas at 40 deg.


I can't believe I did something as stupid as talk about home heating here instead of just referring the OP to http://hvac-talk.com/vbb/forumdisplay.php?1-AOP-Residential-HVAC 
OP: quit reading this thread and go to the link I just gave you.


There's so much fail in what you quoted and your belief that it has anything to do with the OP's discussion of ductless mini splits I don't know where to start.
1. The systems asked about in this thread don't have any backup, electric or gas. Anything I say in the rest of this post are of no value to the OP, I'm just trying to offset some misconceptions you're spreading.
2. You can't just pick an arbitrary temperature like 40 degrees and say heat pumps aren't effective below that point. I'm heating a 3br house with the cheapest split heat pump (not mini split) you can buy, 1 1/2 tons, and it'll keep my house at 68° down into the low 20s outdoors.
3. I've never heard of an installation sized so small that it needed auxiliary heat to keep up at temps as high as 40 degrees. 
4. When your aux is electric resistance heat, there is pretty much no temperature at which the heat pump is considered economically ineffective, because the most basic 13 SEER/8 HSPF unit has a COP greater than one at -10°F. The heat strips are downstream of the coil and the heat pump stays on at low temps with assistance from the heat strips.
5. In your setup, with natural gas aux heat, you should set for the economic balance point. If you just guessed that the BP was 40° without knowing anything more than the article you quoted, you're probably doing it wrong. My electricity is 13.7 cents per kWh after tax, there often is no economic balance point for people on a NG line because gas heat is cheaper my electricity at all outdoor temps. In my home, with a 95% propane furnace, I switch over to propane at 20° because my little 1.5 ton heat pump can only raise the house temperature about 47° above ambient. My heat pump is cheaper than propane down to about 5°, but I need the propane to keep the house warm at temps below 20°, and with a furnace for aux heat you can't run the pump and the aux at the same time.

I think a lot of the opinions discouraging the OP from using exclusively heat pumps are from people with conventional heat pumps.  Mini-splits using inverter technology (like the Mitsu Hyper Heat, or certain Fujitsu or Daikin...perhaps other....models) do not suffer from the same drop in performance as conventional split systems.  The inverter continually varies the compressor speed so that the heat pump maintains high efficiency.  It essentially adjusts the refrigerant flow rate to maximize heat collection/rejection in the appropriate coils.  Mitsubishi advertises something like 90% of the rated heat capacity at 0*F.  As long as you get a mini-split that uses an inverter-driven compressor and it's output is high enough at your minimum design temperature (an accurate load-calc is essential), I wouldn't worry about it being the only heat source in that climate.  If you're really concerned, you could always oversize the heating capacity a bit.  Oversizing is usually very bad for a conventional split A/C system, but with a mini-split using an inverter, it can adjust the refrigerant flow rate & the fan speed to still keep the humidity down.

As far as alternative brands, check out Daikin & Fujitsu.  The HVAC-Talk forum previously mentioned would also be a good resource to find alternative brands.  Generally speaking, the Mitsubishi systems are second to none, but as a FWer, you're probably looking for nearly equal performance in another brand at a fraction of the cost, so check out the other brands.

Thanks, Shelby.
Your post is more reasonable than my last one, in which I continue off on the non mini-split tangent while complaining that we're off topic.
+1 on the idea that the three reputable names involved are Mitsu, Daikin, and Fuji, and that inverter driven systems are probably necessary if there is no backup/aux heat.
Since landlords are notoriously cheap, it might be reasonable to fill the building with Gree.
I'd probably put them wherever there are outside walls, and hope that the interior rooms can get by without heat, but you really need professional design help here.

Size can be in OP's favor here in dealing with dips below design temps. How long can a severe cold snap last, and what's the thermal inertia of a 20 unit building? It's possible that a setup which barely holds its own at 20° can withstand 15 hours at 0° without a major drop in interior temps if building mass is large in relation to heat loss.
Just know that with any all-electric setup, if the power goes out for two days, your tenants will be living in hotels and probably blaming you for it.

Shelbycobra said:   I think a lot of the opinions discouraging the OP from using exclusively heat pumps are from people with conventional heat pumps.  Mini-splits using inverter technology (like the Mitsu Hyper Heat, or certain Fujitsu or Daikin...perhaps other....models) do not suffer from the same drop in performance as conventional split systems.  The inverter continually varies the compressor speed so that the heat pump maintains high efficiency.  It essentially adjusts the refrigerant flow rate to maximize heat collection/rejection in the appropriate coils.  Mitsubishi advertises something like 90% of the rated heat capacity at 0*F.  As long as you get a mini-split that uses an inverter-driven compressor and it's output is high enough at your minimum design temperature (an accurate load-calc is essential), I wouldn't worry about it being the only heat source in that climate.  If you're really concerned, you could always oversize the heating capacity a bit.  Oversizing is usually very bad for a conventional split A/C system, but with a mini-split using an inverter, it can adjust the refrigerant flow rate & the fan speed to still keep the humidity down.

As far as alternative brands, check out Daikin & Fujitsu.  The HVAC-Talk forum previously mentioned would also be a good resource to find alternative brands.  Generally speaking, the Mitsubishi systems are second to none, but as a FWer, you're probably looking for nearly equal performance in another brand at a fraction of the cost, so check out the other brands.

  Thanks for the response, I have found that mostly to be true. The three brands you mentioned do indeed offer performance well beyond what I need. What I don't understand is the DC inverters they are using. DC inverters are used on pretty much all the middle of the range models, but the only models that specifically state they are more than capable at sub zero temps are the 3 brands you mentioned, and the models are the most expensive you can buy. It's almost as if there are 3 tiers. The older AC only, which are useless below around 30 degrees. The DC inverter design, which seems to become almost useless to somewhere around 5 degrees, and then the 3 brands you listed that have special inverters that allow ultra low temp operation. I don't care all that much about efficiency ratings as pretty much all of the DC inverter heat pumps are very efficient. My primary problem is that all of the other heat pumps are fine in 99% of conditions, I'm trying to avoid raising my hardware by 50% just to cover the 3 days out of the year that are below most of the unit's operating range.

I haven't spent much time on HVAC-talk or other forums comparing the quality of mini split systems. I would imagine quality might be slightly more important than with a conventional system. I'm planning to add a mini split to an enclosed patio and plan to purchase from alpinehomeair or airconditioner.com. I would probably try to do the same for one of my rentals. It doesn't make sense to pay for the top of the line efficiency units, unless you're paying for the electricity and you have astronomical utility rates (you're in NJ, maybe you do)

You'll see a lot of people have strong opinions about different brands, however I think for the most part it's noise. The last time I had a furnace go out in a rental, I got 3 quotes for replacement, and I asked them to break out equipment and labor. I was going to have to wait a couple days even for the local guys to get a unit, so I ordered a furnace from alpineair, and it arrived in 2-3 days. I didn't have to pay tax on the furnace, I paid one of the HVAC guys to install the furnace, and I paid half of what the same guy had quoted me to provide the furnace and install.

What type of units are you using now? Do you have to make physical changes or rewire to accommodate a mini split?

taxmantoo said:   Thanks, Shelby.
Your post is more reasonable than my last one, in which I continue off on the non mini-split tangent while complaining that we're off topic.
+1 on the idea that the three reputable names involved are Mitsu, Daikin, and Fuji, and that inverter driven systems are probably necessary if there is no backup/aux heat.
Since landlords are notoriously cheap, it might be reasonable to fill the building with Gree.
I'd probably put them wherever there are outside walls, and hope that the interior rooms can get by without heat, but you really need professional design help here.

Size can be in OP's favor here in dealing with dips below design temps. How long can a severe cold snap last, and what's the thermal inertia of a 20 unit building? It's possible that a setup which barely holds its own at 20° can withstand 15 hours at 0° without a major drop in interior temps if building mass is large in relation to heat loss.
Just know that with any all-electric setup, if the power goes out for two days, your tenants will be living in hotels and probably blaming you for it.

  The building design is a cube, so it is ideal for retaining heat. This was my logic as well. The problem is that I have to purchase and install 20 of these things with no way of verifying if that is true. That would be quite the nightmare if it was 0 degrees for 18 hours. Many of these heatpumps don't just get "less" efficient in the colder temps, they just stop working entirely. Due to the lack of manufacturer data I am having trouble ensuring this does not happen. Even if they pumped out 1/3rd of their design heat I would be fine with that as it would likely be enough for the building to stay comfortable. For example, I had to laugh when I saw one manufacturer rate the AC operating range from 5 degrees F (-15C) and their heat pump was operational from -5 F (-15C) They did not even take the time to adjust the celsius temp, so who knows which temp is a typo. It seems to be a common problem. Most of them give the rated heating output at 29 F and 17 degrees F, but then state somewhere else it will put out heat to 0 or -5. This is not good data at all. I've called the manufacturers too, and all they can tell you is what the stats I'm already looking at are. The reason for the post on this forum, is I'm looking for anecdotal evidence, as it seems that is the only option left.

Also landlords are cheapskates in the same way any business owner needs to minimize expenses. The cheap way of doing things is commonly perceived (especially by trades peoples) as the lazy way or the wrong way. In reality the landlord probably has 10 different ways of doing something, each way with it's own investment strategy for whatever results are needed.

To answer any assumptions before they are thrown out, yes I am trying to get the results I want while spending as little as possible, only a fool would do otherwise.

ksuwldkat said:   I haven't spent much time on HVAC-talk or other forums comparing the quality of mini split systems. I would imagine quality might be slightly more important than with a conventional system. I'm planning to add a mini split to an enclosed patio and plan to purchase from alpinehomeair or airconditioner.com. I would probably try to do the same for one of my rentals. It doesn't make sense to pay for the top of the line efficiency units, unless you're paying for the electricity and you have astronomical utility rates (you're in NJ, maybe you do)

You'll see a lot of people have strong opinions about different brands, however I think for the most part it's noise. The last time I had a furnace go out in a rental, I got 3 quotes for replacement, and I asked them to break out equipment and labor. I was going to have to wait a couple days even for the local guys to get a unit, so I ordered a furnace from alpineair, and it arrived in 2-3 days. I didn't have to pay tax on the furnace, I paid one of the HVAC guys to install the furnace, and I paid half of what the same guy had quoted me to provide the furnace and install.

What type of units are you using now? Do you have to make physical changes or rewire to accommodate a mini split?

  My situation is probably a bit different, I'm rehabing the entire building, which includes rewiring it.

In an unusual circumstance, the 3 brands mentioned in this thread are legitimately the 3 brands which offer products that support ultra low temp operation. They are the most expensive models you can buy though.

I have a mini-split in Maine. It's primarily for AC, but I definitely heat with it in the shoulder seasons. In the dead of winter, I find that my model (Fujitsu Halcyon) does shut itself down between 0 and 5F. Otherwise, it primarily heats my ~900 sq ft upstairs (3 br, using 2 9000 BTU concealed units). It supports my downstairs, which is open concept, ~1100 sq ft, using an 18000 BTU wall mounted head. The main issue there is that it's positioned in a place where there's just no way to cover the whole floor. A second unit on the other end of my downstairs space would be a good idea. I do use FHW oil heat as primary on that main floor as a result. I keep my thermostats programmed and use oil + mini split for all recovery - in combination it happens fast. Remember, though, that the heat out of the blower is cooler than traditional FHA/FHW oil/gas. For instance, I have my boiler set at 185, and there's no way the mini-split outlet temp is hitting that. As a result, it doesn't necessarily feel as warm blowing at you.

I'm originally from NJ and I'm not sure that you'd want these as your ONLY source of heat in the winter. On average, I think it will be fine, but for those abnormally cold days I think you'd need a backup.

EDIT:  I just thought through this again.  This past winter, I can only think of one time where the entire system shut down, and we were below 0F.  The other times, in the 5 degree range, the downstairs unit backed off because the upstairs units have priority.  Just to clarify that a bit.

bzinsky2012 said:   
Shelbycobra said:   I think a lot of the opinions discouraging the OP from using exclusively heat pumps are from people with conventional heat pumps.  Mini-splits using inverter technology (like the Mitsu Hyper Heat, or certain Fujitsu or Daikin...perhaps other....models) do not suffer from the same drop in performance as conventional split systems.  The inverter continually varies the compressor speed so that the heat pump maintains high efficiency.  It essentially adjusts the refrigerant flow rate to maximize heat collection/rejection in the appropriate coils.  Mitsubishi advertises something like 90% of the rated heat capacity at 0*F.  As long as you get a mini-split that uses an inverter-driven compressor and it's output is high enough at your minimum design temperature (an accurate load-calc is essential), I wouldn't worry about it being the only heat source in that climate.  If you're really concerned, you could always oversize the heating capacity a bit.  Oversizing is usually very bad for a conventional split A/C system, but with a mini-split using an inverter, it can adjust the refrigerant flow rate & the fan speed to still keep the humidity down.

As far as alternative brands, check out Daikin & Fujitsu.  The HVAC-Talk forum previously mentioned would also be a good resource to find alternative brands.  Generally speaking, the Mitsubishi systems are second to none, but as a FWer, you're probably looking for nearly equal performance in another brand at a fraction of the cost, so check out the other brands.

  Thanks for the response, I have found that mostly to be true. The three brands you mentioned do indeed offer performance well beyond what I need. What I don't understand is the DC inverters they are using. DC inverters are used on pretty much all the middle of the range models, but the only models that specifically state they are more than capable at sub zero temps are the 3 brands you mentioned, and the models are the most expensive you can buy. It's almost as if there are 3 tiers. The older AC only, which are useless below around 30 degrees. The DC inverter design, which seems to become almost useless to somewhere around 5 degrees, and then the 3 brands you listed that have special inverters that allow ultra low temp operation. I don't care all that much about efficiency ratings as pretty much all of the DC inverter heat pumps are very efficient. My primary problem is that all of the other heat pumps are fine in 99% of conditions, I'm trying to avoid raising my hardware by 50% just to cover the 3 days out of the year that are below most of the unit's operating range.

  
Then use the units that operate down to 5F to hit your price point and then install electric baseboard heat as a backup/emergency option.  The latter is pretty damn cheap, it's just expensive to operate.  If you're not paying the electric bill, I don't see the issue.

sjwaste said:   
bzinsky2012 said:   
Shelbycobra said:   I think a lot of the opinions discouraging the OP from using exclusively heat pumps are from people with conventional heat pumps.  Mini-splits using inverter technology (like the Mitsu Hyper Heat, or certain Fujitsu or Daikin...perhaps other....models) do not suffer from the same drop in performance as conventional split systems.  The inverter continually varies the compressor speed so that the heat pump maintains high efficiency.  It essentially adjusts the refrigerant flow rate to maximize heat collection/rejection in the appropriate coils.  Mitsubishi advertises something like 90% of the rated heat capacity at 0*F.  As long as you get a mini-split that uses an inverter-driven compressor and it's output is high enough at your minimum design temperature (an accurate load-calc is essential), I wouldn't worry about it being the only heat source in that climate.  If you're really concerned, you could always oversize the heating capacity a bit.  Oversizing is usually very bad for a conventional split A/C system, but with a mini-split using an inverter, it can adjust the refrigerant flow rate & the fan speed to still keep the humidity down.

As far as alternative brands, check out Daikin & Fujitsu.  The HVAC-Talk forum previously mentioned would also be a good resource to find alternative brands.  Generally speaking, the Mitsubishi systems are second to none, but as a FWer, you're probably looking for nearly equal performance in another brand at a fraction of the cost, so check out the other brands.

  Thanks for the response, I have found that mostly to be true. The three brands you mentioned do indeed offer performance well beyond what I need. What I don't understand is the DC inverters they are using. DC inverters are used on pretty much all the middle of the range models, but the only models that specifically state they are more than capable at sub zero temps are the 3 brands you mentioned, and the models are the most expensive you can buy. It's almost as if there are 3 tiers. The older AC only, which are useless below around 30 degrees. The DC inverter design, which seems to become almost useless to somewhere around 5 degrees, and then the 3 brands you listed that have special inverters that allow ultra low temp operation. I don't care all that much about efficiency ratings as pretty much all of the DC inverter heat pumps are very efficient. My primary problem is that all of the other heat pumps are fine in 99% of conditions, I'm trying to avoid raising my hardware by 50% just to cover the 3 days out of the year that are below most of the unit's operating range.

  
Then use the units that operate down to 5F to hit your price point and then install electric baseboard heat as a backup/emergency option.  The latter is pretty damn cheap, it's just expensive to operate.  If you're not paying the electric bill, I don't see the issue.

  250+ amps of service at 240 volts that I didn't design the electrical for. Electric baseboard needs the feed cable to run through the thermostat, need breakers, 12 gauge wire, labor, etc etc etc.

bzinsky2012 said:   
sjwaste said:   
bzinsky2012 said:   
Shelbycobra said:   I think a lot of the opinions discouraging the OP from using exclusively heat pumps are from people with conventional heat pumps.  Mini-splits using inverter technology (like the Mitsu Hyper Heat, or certain Fujitsu or Daikin...perhaps other....models) do not suffer from the same drop in performance as conventional split systems.  The inverter continually varies the compressor speed so that the heat pump maintains high efficiency.  It essentially adjusts the refrigerant flow rate to maximize heat collection/rejection in the appropriate coils.  Mitsubishi advertises something like 90% of the rated heat capacity at 0*F.  As long as you get a mini-split that uses an inverter-driven compressor and it's output is high enough at your minimum design temperature (an accurate load-calc is essential), I wouldn't worry about it being the only heat source in that climate.  If you're really concerned, you could always oversize the heating capacity a bit.  Oversizing is usually very bad for a conventional split A/C system, but with a mini-split using an inverter, it can adjust the refrigerant flow rate & the fan speed to still keep the humidity down.

As far as alternative brands, check out Daikin & Fujitsu.  The HVAC-Talk forum previously mentioned would also be a good resource to find alternative brands.  Generally speaking, the Mitsubishi systems are second to none, but as a FWer, you're probably looking for nearly equal performance in another brand at a fraction of the cost, so check out the other brands.

  Thanks for the response, I have found that mostly to be true. The three brands you mentioned do indeed offer performance well beyond what I need. What I don't understand is the DC inverters they are using. DC inverters are used on pretty much all the middle of the range models, but the only models that specifically state they are more than capable at sub zero temps are the 3 brands you mentioned, and the models are the most expensive you can buy. It's almost as if there are 3 tiers. The older AC only, which are useless below around 30 degrees. The DC inverter design, which seems to become almost useless to somewhere around 5 degrees, and then the 3 brands you listed that have special inverters that allow ultra low temp operation. I don't care all that much about efficiency ratings as pretty much all of the DC inverter heat pumps are very efficient. My primary problem is that all of the other heat pumps are fine in 99% of conditions, I'm trying to avoid raising my hardware by 50% just to cover the 3 days out of the year that are below most of the unit's operating range.

  
Then use the units that operate down to 5F to hit your price point and then install electric baseboard heat as a backup/emergency option.  The latter is pretty damn cheap, it's just expensive to operate.  If you're not paying the electric bill, I don't see the issue.

  250+ amps of service at 240 volts that I didn't design the electrical for. Electric baseboard needs the feed cable to run through the thermostat, need breakers, 12 gauge wire, labor, etc etc etc.

  
Then it sounds like you're buying the more expensive mini-splits.  What else do you want us to tell you?  You know where the temps in your area are going to go better than we do, so install the type of heating that's going to work on the coldest day. You said you're renovating the whole building, so the suggestion of electric baseboard as backup isn't really ridiculous if you're already doing work.  The only thing not discussed here is geothermal.  If you're really renovating the whole building, look into that, with whatever individual apartment setup you're comfortable with - FHW is common here.

OP look for a local rep for the various brands you're looking into.  I used to spec this equipment as a consulting engineer.  Those top three brands ave the super hyper models as well as conventional models.  I understand they sell those hyper style mitsus in the Boone nc area with lots of success and it gets pretty cold there. You can pull up their yearly weather data and compare it to yours.  Additionally a local brand rep can tell you where thy have sold them o as well as what temps it will produce how much heat.  Those reps want sells but they typically aren't interested in selling ou something that won't work because they don't want their phone ringing off the hook with issues.

taxmantoo said:   Thanks, Shelby.
Your post is more reasonable than my last one, in which I continue off on the non mini-split tangent while complaining that we're off topic.
+1 on the idea that the three reputable names involved are Mitsu, Daikin, and Fuji, and that inverter driven systems are probably necessary if there is no backup/aux heat.
Since landlords are notoriously cheap, it might be reasonable to fill the building with Gree.
I'd probably put them wherever there are outside walls, and hope that the interior rooms can get by without heat, but you really need professional design help here.

Size can be in OP's favor here in dealing with dips below design temps. How long can a severe cold snap last, and what's the thermal inertia of a 20 unit building? It's possible that a setup which barely holds its own at 20° can withstand 15 hours at 0° without a major drop in interior temps if building mass is large in relation to heat loss.
Just know that with any all-electric setup, if the power goes out for two days, your tenants will be living in hotels and probably blaming you for it.

Unless you have backup generators, if the electricity supply goes down the heat will go down as well -- oil systems need electric for fuel pumps, forced hot air needs electric for the blowers, many/most natural gas/propane systems use electric igniters instead of pilot lights, etc.

I have no technical knowledge to add, but, what is the current heating system being used and what is driving the decision to make improvements at this time? Can you install only one of these Mitsu Hyper Heat mini splits this summer, evaluate how that unit performs next winter, and then make a decision for the other 19? Calculations and performance data are fine and dandy, but despite all of that being done, the last time I replaced my Central AC, they goofed, and I now suffer during the dog days each summer with a system that can't keep the house at a reasonable set point. You're probably thinking.... the contractor screwed up.... and you know, he might have. How do you know yours won't? My guy came with plenty of recommendations and many years of experience.

If I was about to pay for 20 of these, I would absolutely prefer to test drive one first.



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