Anybody here use Mini-Splits for HVAC?

[IndyGunworks]

I have been planning a new construction house for well over a year now, and I have finally gotten to the point where I can start thinking about some of the finer details like HVAC. As of right now the house is going to be a two story with a lofted area in the middle of the first floor. I am planning on around R40 in the walls with minimal thermal bridges, and blown in cellulose at R 60 in the ceiling.

In my research as far as the most economical way to heat and cool I did a few calculations. I had always thought I would use propane but when I did the math it doesn't make as much sense. Also the shortages we had last winter make me a little more concerned about relying on propane as well.

Assuming a 95% efficient furnace and 1.70 per gallon propane will cost me $20 per million BTU's. at 2 dollars a gallon it will cost 23 dollars per million btus and at 3.00 per gallon 34 dollars per million btu. 95% effiecient is not a realistic number once you consider the ENTIRE system. with loss's in the ductwork ect.
1.70 is the current price per gallon that I could get it for not including the delivery charge. I do own a 1,000 gallon tank.

I had considered geothermal very hard, but when you look at the COP of the system and not just the unit itself it runs close to a cop 3. I thought I would be OK with that given that it would still work when it was really really cold outside and shouldn't need to have any supplemental heat.

THEN I found the mini splits. no expensive ductwork to make the system less efficient, and from what I have read the advertised COP really is what you get. My current electric rate is at .10 cents per kwh. and has only risen 2 cents in the pasts 4 years. it is purchased from the Wabash valley power association.

I can run a COP of 3.0 nearly all the time and that give me a price per million btu at 10 dollars. they are designed to run to -5 with a cop of 2.0 which would cost 14.95 cents. I have read many stories of some of the units running all the way down to -15 w/out any need for emergency heat. My back up heat for this system would be cheap plug in radiators that would be 100 percent efficient and cost 30 dollars per million btu's..

with the mini splits being able to ramp up and ramp down based on individually set zones in the house I only have to use exactly what I want to use and no more. that alone should save a few percentages over a standard forced air system.

With that in mind, does anybody see any flaw's in what I propose?
Does anybody on here have any mini splits in their house?
Any drawbacks to this idea?

 

[Crbn79]

I have been planning a new construction house for well over a year now, and I have finally gotten to the point where I can start thinking about some of the finer details like HVAC. As of right now the house is going to be a two story with a lofted area in the middle of the first floor. I am planning on around R40 in the walls with minimal thermal bridges, and blown in cellulose at R 60 in the ceiling.

In my research as far as the most economical way to heat and cool I did a few calculations. I had always thought I would use propane but when I did the math it doesn't make as much sense. Also the shortages we had last winter make me a little more concerned about relying on propane as well.

Assuming a 95% efficient furnace and 1.70 per gallon propane will cost me $20 per million BTU's. at 2 dollars a gallon it will cost 23 dollars per million btus and at 3.00 per gallon 34 dollars per million btu. 95% effiecient is not a realistic number once you consider the ENTIRE system. with loss's in the ductwork ect.
1.70 is the current price per gallon that I could get it for not including the delivery charge. I do own a 1,000 gallon tank.

I had considered geothermal very hard, but when you look at the COP of the system and not just the unit itself it runs close to a cop 3. I thought I would be OK with that given that it would still work when it was really really cold outside and shouldn't need to have any supplemental heat.

THEN I found the mini splits. no expensive ductwork to make the system less efficient, and from what I have read the advertised COP really is what you get. My current electric rate is at .10 cents per kwh. and has only risen 2 cents in the pasts 4 years. it is purchased from the Wabash valley power association.

I can run a COP of 3.0 nearly all the time and that give me a price per million btu at 10 dollars. they are designed to run to -5 with a cop of 2.0 which would cost 14.95 cents. I have read many stories of some of the units running all the way down to -15 w/out any need for emergency heat. My back up heat for this system would be cheap plug in radiators that would be 100 percent efficient and cost 30 dollars per million btu's..

with the mini splits being able to ramp up and ramp down based on individually set zones in the house I only have to use exactly what I want to use and no more. that alone should save a few percentages over a standard forced air system.

With that in mind, does anybody see any flaw's in what I propose?
Does anybody on here have any mini splits in their house?
Any drawbacks to this idea?

I'd like to see a -15 degree unit. Heat pump systems in general become unreliable for heating under 10 F. After this you've gotta switch to emergency heat.

 

[IndyGunworks]

I have been reading on a lot of the green building forums (those guys love these things for whatever reason). I have read at least 10 different people using these in northern Canada and not having to use emergency heat at all. the more expensive units are rated to still work at -15, but I will probably get a unit rated for -5.

Do you have experience with any of the mini split heat pumps? it seems that because the ramp up and down based on demand that they would be less prone to needing emergency heat.

here is a video of one running at -12

https://www.youtube.com/watch?v=n8q9jnkaPOk

 

[Crbn79]

Yes, I've used and installed them before. The problem you run like with the video is 95 degrees isn't very much. You want the temp split on systems to be between 30-70 degrees depending on manufacturer. A traditional gas/electric/propane furnace blows out around 120-140 degrees. With a coil temp of 95 you're likely to have a vent temp around 85 degrees or so. This isn't very efficient heating at this temp range. Plus the unit will likely shutdown for a 30 min defrost once every hour or two.

Even running your system at a 65 degree thermostat setting, it will run non-stop and struggle to get there even in a very well insulated home. There are calculations which will give you a go/no go answer if you'd like. They will involve a knowledgable tech to take measurements, and R values into account.

 

[churchmouse]

Yes, I've used and installed them before. The problem you run like with the video is 95 degrees isn't very much. You want the temp split on systems to be between 30-70 degrees depending on manufacturer. A traditional gas/electric/propane furnace blows out around 120-140 degrees. With a coil temp of 95 you're likely to have a vent temp around 85 degrees or so. This isn't very efficient heating at this temp range. Plus the unit will likely shutdown for a 30 min defrost once every hour or two.

Even running your system at a 65 degree thermostat setting, it will run non-stop and struggle to get there even in a very well insulated home. There are calculations which will give you a go/no go answer if you'd like. They will involve a knowledgable tech to take measurements, and R values into account.

OP has been using the formulas from sites on line. I see some big pluses with these for what he wants to do but like you I am not a real HP fan.

 

[Crbn79]

OP has been using the formulas from sites on line. I see some big pluses with these for what he wants to do but like you I am not a real HP fan.

I think they have a place. However, you should have an emergency heating system. Even a high Seer system will struggle when it's -20 out. This past winter alone the Indy area got hit with -26 if I remember correctly.

 

[churchmouse]

I think they have a place. However, you should have an emergency heating system. Even a high Seer system will struggle when it's -20 out. This past winter alone the Indy area got hit with -26 if I remember correctly.

I have seen his basic plans and what he intends to do. It is a sound approach. I would like to sit down with you over lunch (I am buying) and discuss some of the facts and figures about this project. He will have a lot of open areas and circulation may be an issue. The fan coil units offered are very flexible. They do come with heat strips. The control of the multi-area systems looks doable in his situation. Energy cost is a factor.

 

[IndyGunworks]

I am in for the lunch.... Ill bring the plans, and I will buy. I didn't realize these could come with heat strips... that's an even bigger plus in my book.

I am hoping to have a wood stove in the house to supplement during the times when the emergency heat may have to be used, that will keep my net usage to a min. even running strictly resistance heat I am only 10 dollars more per million BTU's which would be MORE than offset by the amount of time that I would be half the cost of propane. Not to mention the futures of propane are more than likely going to increase at a faster rate than electric. I am hoping to eventually piece together a roughly 10kw solar aray with enough storage to last for a 24 hour period of no sun and power outage. After 24 hours I would recharge the battery bank w/ a propane generator.

I am considering wiring in some DC outlets into each room when I build which would allow me to run a light and a fan in each room w/out an inverter having to kick on. that would allow me to cycle the appliance such as fridge and freezer on when I am producing power and off when I am not (so they don't draw at night when I would need the power for the heat pump)

If the cost of solar ever gets down to around 2k per kw then I would be able to go completely off grid providing I have a large enough battery bank. the propane would be a hedge against cloudy days, and w/ 1000 gallons of storage I should be able to last a very long time even if I cannot get refilled. If I were to have a primary heat source ran off propane, I would only have a little over a years worth of energy stored. I would like to reserve the propane for only the necessities as a hedge against a grid down scenario. At that point I would only want to keep the house above freezing to protect the pipes, and use the gas for cooking.

 

[Crbn79]

I have seen his basic plans and what he intends to do. It is a sound approach. I would like to sit down with you over lunch (I am buying) and discuss some of the facts and figures about this project. He will have a lot of open areas and circulation may be an issue. The fan coil units offered are very flexible. They do come with heat strips. The control of the multi-area systems looks doable in his situation. Energy cost is a factor.

If heat strips are an option, he should definitely do it. It's easier to do it and not need it, than to need it but you didn't do it. Heat strips certainly won't increase the cost by more than a few % of the overall price.

Just dug through some Govt lab tests: A 16 seer 5ton mini-split will provide 85 degree supply air @ -9.7 degrees outdoor temp 67 degree return air. Where as the same system will provide 130 degree supply air @ 30 degrees outdoor temp 67 degree return. So you drop from a split of 60 degrees to 18 degrees.

That's a 66% heating loss. No tests done beyond -9.7 but if you develop a temp curve and the drop continues linear, you could be down around a 90% heating loss @ -20.

 

[IndyGunworks]

further I understand that heat pumps don't produce near as comforitable of a home with the lower register temps. while I am trying to build as comforitable of a home as possible, I don't want to pay 500 dollars a month to heat and cool. 300 a month or less is my target usage, and I think with my current plan that's doable. If I were to go with a propane furnace for primary heat there is NO WAY I could have long term sustainability should I not be able to get propane delivered something that happened this past winter.

My parents live between cinci and Dayton, and they live in a 3,000+ square foot log cabin. their electric usage on a heat pump (including the times the emergency came on) last year during jan and feb were around 4,000 kwh's that's ALOT. I have never been uncomforitable in their house even with the lower register temps. I do love my gas furnace where I am at now, but its just not feasible out where I am building. If they were to have had a mini split system instead of a central heat pump then they would have been able to turn the temp down in at least 3 or 4 rooms and significantly decreased their overall usage. they are empty nesters with a big house, and a central system just doesn't allow for energy conservation of individual spaces.

they layout of my house is much better than theirs as well as I really don't even have a hallway in the house, everything is off the main area which would lend itself well to a wood stove for emergency or supplemental heat.

 

[IndyGunworks]

If heat strips are an option, he should definitely do it. It's easier to do it and not need it, than to need it but you didn't do it. Heat strips certainly won't increase the cost by more than a few % of the overall price.

Just dug through some Govt lab tests: A 16 seer 5ton mini-split will provide 85 degree supply air @ -9.7 degrees outdoor temp 67 degree return air. Where as the same system will provide 130 degree supply air @ 30 degrees outdoor temp 67 degree return. So you drop from a split of 60 degrees to 18 degrees.

That's a 66% heating loss. No tests done beyond -9.7 but if you develop a temp curve and the drop continues linear, you could be down around a 90% heating loss @ -20.

temps that cold don't happen all THAT often around here. when they do its normally short lived. I have read where someone actually metered a mini split when it was 5 degrees outside and they had a COP of 2. while it would have to run a lot more esp w/ defrost cycles, that would still cost me 15 dollars per million btu's vs 20 assuming the bests current propane price.

 

[Crbn79]

temps that cold don't happen all THAT often around here. when they do its normally short lived. I have read where someone actually metered a mini split when it was 5 degrees outside and they had a COP of 2. while it would have to run a lot more esp w/ defrost cycles, that would still cost me 15 dollars per million btu's vs 20 assuming the bests current propane price.

I'm right along with you. There's nothing that requires you switch over to emergency heat. If you remember this past winter we had almost 2 weeks of 0 or below temps. At the end of the day it's your house, your plans. You can go with a 25 Seer mini-split with no emergency heat option should you ever need it, I'm just stating I would not myself. I'd demand the option of kicking in the emergency heat should temperatures drop.

 

[IndyGunworks]

I had other not so pleasant plans for emergency heat, but if these units come with them, I cant think of any other way to reach my long term, and overall goals w/out going this route. I don't consider relying on propane being "off grid" when you have to rely on other people to deliver it. esp when you use quantities that don't allow enough storage for long term preparedness. At least this way I have the potential of self reliance should the price of solar come down, and provided I keep my net propane usage down to a point where my storage will last two years or more.

 

[Crbn79]

I had other not so pleasant plans for emergency heat, but if these units come with them, I cant think of any other way to reach my long term, and overall goals w/out going this route. I don't consider relying on propane being "off grid" when you have to rely on other people to deliver it. esp when you use quantities that don't allow enough storage for long term preparedness. At least this way I have the potential of self reliance should the price of solar come down, and provided I keep my net propane usage down to a point where my storage will last two years or more.

There are ideas which can be used for supplemental heat. I'll meet up with CM and get a better idea of what all is going on. Between the two of us I'm sure we can come up with something. There are many options, and they don't all involve propane/gas.

 

[IndyGunworks]

I am free after 3 today, and anytime Saturday or after church on sunday. I would love to be there to listen to the discussion so I have a better understanding of what my options are. That will make it easier so CM doesn't have to rehash everything, and he wont have to pay for the food either. Or beer depending on where we would go.

 

[Crbn79]

I am free after 3 today, and anytime Saturday or after church on sunday. I would love to be there to listen to the discussion so I have a better understanding of what my options are. That will make it easier so CM doesn't have to rehash everything, and he wont have to pay for the food either. Or beer depending on where we would go.

Works for me. I will be free Saturday afternoon. Trying to kick a cold atm, don't want to pass it along. If you get with CM and set a day/time I'll adjust my schedule if I can, only no go for me is Saturday before noon and Sunday before noon.

 

[HoughMade]

This is an interesting discussion. I am buying a new house and it has a sun room off the master bedroom with no A/C a not great heat. I was thinking a small dual zone mini split may be perfect to handle the sun room and the master bedroom when we don't feel like we need A/C in the whole house (the little savages can sleep though warm better than I can). I have found that when I'm awake and about, heat doesn't bother me, but trying to sleep....not so much. It seems a mini split would make the sun room 4 seasons comfortable (it is properly insulated) and keep the A/C off in the rest of the somewhat large house, many times.

I look forward to following this.

 

[IndyGunworks]

some mini splits have a dehumidify only mode. wouldn't draw as much power as active cooling, but a ceiling fan and dehumidification should make you feel ALOT cooler than what the actual temp shows.

 

[HoughMade]

Good point! This house has ceiling fans in every room except bathrooms (9 ceiling fans...I counted), so that and dehumidifying may really help.

 

[Crbn79]

Good point! This house has ceiling fans in every room except bathrooms (9 ceiling fans...I counted), so that and dehumidifying may really help.

Mini-splits are very versatile. I'm planning to install a dual zone mini split in my parents house for supplemental heat/cool. They have a sun/4 seasons room on the back of the house that added almost 400sq ft to the foot print. The second area to supplement will be a 500 Sqft master bedroom which just never got the proper air flow.