The Minisplit that could

zvalve

Can minisplits heat and cool a house in Michigan near Detroit without a supplemental heating system?

ChrisJ

There's a big difference between can, and should.

BobC

Yes they can but you could well go broke paying for the electricity. It gets pretty cold in the winter there and a minisplits efficiency drops as temperatures go below freezing.

You need detailed info on the minisplits COP vs outside temperature and then you do a calculation using the heat loss of the house, the cost of the two fuels per btu. With all that data you can figure the cost of each system for an average year. Don't forget the cost of the defrost cycles on the minisplits when it gets below freezing.

Bob

SuperJ

Properly sized and selected mini split systems can run fine in Michigan (they do in Ontario). Look into Fujitsu cold climate heat pumps, they are rated down to -18 and they don't actually shut off even if it gets colder, but the capacity and efficiency continues to drop.

You should be able have an annual COP between 2 and 3 depending on equipment selection. You want to select a unit with a high HSPF (heating seasonal performance factor). High efficiency units will be above 12 and low efficiency multi splits between 8-10. The HSPF calculation includes defrost but by default applies to climate zone 4, there are some geographical charts to derate the HSPF ratings for colder climates.

You energy costs will probably be higher with mini splits than natural gas at today's rates. If you have solar, don't have NG, or are looking to move away from fossil fuels they can be great option.

1:1 units are more efficient than the multi splits, because each head modulates over a wide range, whereas multi splits indoor units are basically on off and the outdoor unit just steps it's modulation to match the number of running indoor units.

The whole design of the system needs to be designed with mini splits in mind. This might mean ducted units serving multiple small rooms. With short runs to a nearby closet or bulkhead rather than home run to the basement. Fans are low static pressure so ducting needs to be sized appropriately. A common mistake is put a single oversized head in each bedroom. The smaller heads are about 6000 btu and the bedrooms often have a much smaller heat loss, this leads to poor efficiency and temperature control. Better to put a small ducted unit in to serve a couple adjacent rooms with a similar load profile. Bigger open spaces can be served by wall or floor mounted units. The wall heads are very effective at throwing air over a pretty large space and distance.

There are drop in air handlers that can replace furnaces, but they aren't nearly as efficient as wall mounted or low static ducted units.

You may want to have a bit of electrical resistance heat to provide a bit of capacity for polar vortex conditions where temperatures are below design conditions. This happens for few enough hours of the year that it's sometimes better to size mini splits tightly to the heat loss (or even 85% of the heat loss), and use electric heat/wood stove/ etc, to make up the balance. In Scandinavia they often size to less than 100% with the ASHP and make up the final 15% with local resistance heating. This ensure the equipment will be within it's efficient range of modulation and not short cycling for the bulk of the heating hours.

Sizing requires a similar approach to modcons and zoning, you need to consider minimum heat loads and modulations to keep everything running nicely. Micro zone improperly and it's miserable.

Also, wall mounted units by default run off the entering air temp sensor. If located too close to the ceiling this can be a problem. Consider mounting the units a foot or more down from the ceiling (lower is better), and using an external wall mounted temp sensor (there are wired and wireless options, some are just a cheap remote mount thermister).

I'd recommend posting some specifics of your project to the QA section of greenbuildingadvisor.com Those guys are in love with mini splits and are pretty helpful in identifying potential problems with your approach.

Steamhead

Not sure why this thread was posted in the Steam section.... are you considering tearing out steam to put in mini-splits?

If so- DON'T.

JUGHNE

I would not consider any HP as the only sole heat source for a house unless it was located in the south.

Also, IMO, running any HP down to the bottom temp puts extra wear & tear on the compressor. The defrost cycle makes any compressor strain and moan.

You reach the point of diminishing returns as the temp drops.
Any literature can claim heat production at 0 or below, but how much heat? And as the temp drops your house needs more.

Any single component failure can disable any HP. That is why conventional designs have enough resistance elements to maintain the inside temp.

I know I am an old school old guy, but 40 years of dancing with HP's.....most of which are mini-splits BTW....puts me with this attitude.

I live in a fairly "super insulated" house with radiant heat, HP would run cheaper than our NG. But I would have to sleep in the garage as just the mention of HP/FAF systems will upset the boss of the house.

BTW, if you have a steam system, I would keep it as back up, IIWM.

mikeg2015

One challenge is that in Michigan, the summers are mild, so you need to oversized for heating, and will short cycle and could struggle to remove humidity in summer.

Would be a good match with a propane radiant system for really cold weather. Better than electric furnace or baseboard or conventional heat pump.

butcherpete

mikeg2015 said:

One challenge is that in Michigan, the summers are mild, so you need to oversized for heating, and will short cycle and could struggle to remove humidity in summer.

Would be a good match with a propane radiant system for really cold weather. Better than electric furnace or baseboard or conventional heat pump.

on a whole house system, yes
But the mini splits are modulating
and with multiple heads, works even better