Geothermal related to cooling in Michigan.

[Sigarms]

I didnt read every response, but if you buy the highest seer rated mini split you can find

SEER2 ratings with mini splits at the end of the day are the least of your concearns for 2 primary reasons.

1 - AHRI ratings are very misleading because generally with ductless system, just as the name implies, there is no ductwork. You can take a "high end" 30 plus SEER2 system from any ductless manufacturer, take the same manufacturer and make it a dedicated horizontal ducted unit or a 4 way multi position ducted unit (like most all major HVAC brands make in the US) and you'll be at around 18 SEER2 because it's ducted.

2 - The meathod in which AHRI actually rates inverter compressors can be very misleading because they only use two stages and the actual capacity that the system can provide is actually more misleading because AHRI rated condition for heating is at 47F OAT, which is complete BS because no one does a load calculation at that outdoor design temp.

Most important factor is understanding the engineering data provided by the manufacturer and knowing the the actual heating AND cooling capacities that system can provide for the area to have the air conditioned at what outdoor factor.

Most model numbers given by ductless manufacturers is the capacity that system can cool at 95F OAT maintaining a certain indoor temp given either in dry or wet bulb. So a system with a "24" in it (I'm only pretty familiar with Fujitsu, Mitsubishi and Daikin and this is the case) will give you 24,000 BTU/h of cooling at 95F outside and a certain indoor temp, either 80F or 70F with the bulb given as well). The issue is exactly how much heating and at what outdoor temp will the system give you?

In the very southern states, heating of course is not important. However, even in NC, the general indoor design temp is for 20F-23F outside air temp. That said, when it comes to ductless mini splits, even in my area of NC, I prefer to go with 100% heating down to 5F OAT if there is no supplemental heat (suplemental heat is a huge factor). M

When it's 95 outside you expect the system to keep you cool inside, but by the same token, if it's 20F outside, you expect the system to keep you warm.

Looking at 10 different models from 6 different manufacturers, a 24K cooling system will give you anywhere between 8,178 BTU/h of heating @ 17F outside air temp, up to 29,300 BTU/h heating @ 23F OAT or 27,000 BTU/h heating at 17F OAT. But, guess what? They all provide 22/24K of cooling @ 95F OAT.

The same for multi zone systems.

If KennyG's church is maintaining 72F inside air temp at 0F outside air temp without any supplemental heating, those systems most likely cost more than a cheaper line because it's actually providing "good" heat (even though they are rooftop units, most likley the standard outdoor unit as putting the outdoor unit on a roof is more common for commercial applicaitons vs on the ground for residential applications).

10 years ago there were about 90 different ductless mini split manufacturers being sold in the US. Now, I'm certain there are more "brands", but most are from a handful of manufacturers (perhaps 10 or so max) that are relabled.

Now, where it gets tricky is commercial applications where cooling is nessesary for lower outdoor temps because even if a 24K system will give you 24k of cooling at 95F, that is not always the case when it's 20F to 0F outside (kitchens, server rooms, hospitals, commercial areas witha lot of glass).

This is why you go off the engineering data guide and not the submittal sheets LOL

 

[mikester]

The mini-split heating capability in low temperatures is much better than some would have you believe. We installed them at my church for the offices. We have two rooftop units supplying wall units in six offices (no ductwork) and performance has been very good. I don't think we've seen any -20 weather since we put them in but at 0 deg F outside they maintain 72 degrees inside with no problem. Overall economy has been good although we don't have a way to directly compare to the previous system, since we were previously heating as an extension of a gas fired hot water system with supplemental resistance heating.

Agreed

I am running two cold climate minisplits and have baseboard as backup. We regularly get down to -20oC (-4oF) with a few days at -30oC (-22oF) and the baseboards never kick in.

Backup heating is a good idea. We also have two woodstoves which can heat the whole house comfortably during power outages.

 

[tradosaurus]

I'm at the planning stage of a summer/ retirement home in mid Michigan. My basic question is: Is using a ground source heat pump significantly more economical than a traditional central ac that just uses the outside to dump the heat? My current home electric bill is closing in on $400 per month in the cooling season. During the heating season my electric bill is around $160 and my natural gas is about $125. I love cold and hate sweating as you can see. Does anyone with real experience know if a geothermal system for cooling would offer a drastically better energy bill. The new property has a slightly higher electrical cost per KWH but less than 1 cent. I supplement heating with wood and am not really concerned about heat. Also considering the climate trend I believe that cooling is a bigger factor for me to consider. Thanks.

I would talk to people that live in the area you are wanting to move. My bet is they either don't have A/C or have small window unit(s) when needed.

 

[KennyG]

I would talk to people that live in the area you are wanting to move. My bet is they either don't have A/C or have small window unit(s) when needed.

It's funny how our expectations have changed. Almost every house in my area has central A/C. There are people who shut all the windows and turn on the A/C on the first warm day and never open a window until fall. Most people are like me and only run the A/C on the limited hot and humid weather we have. But almost no one would consider buying a house without central A/C.

 

[Carl_NH]

I concur with Sigarms, you need to dig into the details of each brand - especially for heating, the COP or HSPF (heating season performance factor). You can get COP by dividing the HSPF/3.412, which is the heat output per watt input.

Where we are in NH with Oil FHW main heat, plus 7KW solar, it's rarely below 10* close to 20* average and 2-3 days below zero in a typical winter. So the 17* rating is what I used for comparison and cost to operate when I bought a new one this summer (a 9K Tosot mini split)

The 4 Mini splits all single head 2 - 9K and 1-12K Mitsubishi Hyper heat, SEER 30.5 and HSPF of 11 and a Tosot 9K unit I installed this summer in our detached 3 seasons patio with a SEER of 19 and HSPF of 8.8.

For cooling as they all were similar, for heating I did a comparison between the 9 K units. Tosot 9 KW Per day and Mitsubishi 6 KW Per Day or $1.00 per day operating cost difference at $.30 KWH, or $150-180/season.

Total hardware Mitsubishi $2200, the Tosot $650 so it would take 7 + years before the total cost of ownership offset the efficiency.

The Mitsubishi run quieter, have a better low speed fan/inverter control vs the Tosot the inverter and indoor shut down when the set temp is reached.

Sum and substance, the big brands Fujitsu, Daikin, Mitsubishi have better heating performance as the main heat source, but the lower upfront cost of the Mr Cool, Tosot Pioneer etc. are attractive for cooling and seasonal heating if needed.

 

[deezler]

This thread about geothermal turned into an excellent discussion about heat-pump performance. Thanks everyone!

 

[hube2]

I have ducted mini splits + mu original oil fire baseboard. I keep track of that the temperature the furnace thermostat says it is. This is what I've noticed.

Normally, if I set the house on 72 the furnace will never kick on. The heat pumps are able to keep up and keep my house at a steady 72 when the temps outside are 10F or higher. The pumps are supposed to work down to -15, but they become less efficient as it gets colder outside.

Recently we had a cold spell with temps in the single digits and wind chills down to -10. They guy that installed them told me that wind chill does affect the efficiency of the pumps, I don't know if that's true or not, I don't believe it is. I do know that when it's windy and cold that does suck the heat out of my house faster so that would cause the pump to need to run more.

Anyway, during the cold snap the furnace thermostat thermometer would drop to 71 and the furnace would run, maybe once or twice a day. But not if it was sunny. I have the outside unit on the south side of the house. So I do know that it is affected by the sun warming up the outdoor unit.

I did not have AC installed when I built my house. We needed to use AC maybe half a dozen times a year. Whether it's because it's warmer in the summer or just because I'm getting old, we were running the window units more often. I couldn't take the noise any longer and this is why I had the pumps put in. I still only run the AC when we really need it on hot, humid days. It is saving me nothing on AC. However my electric costs per month are roughly 20% of what I was paying for fuel oil.

 

[LouNY]

This is an interesting thread.
I had two Mitsubishi split systems installed several years ago. My window units in this old house ran continuously and couldn't keep up some days. My heating system is an oil fire boiler with some kick space heaters and some baseboard in half the house, then a heat exchanger and blower for the other half of the house. In the winter I use a coal insert in my fireplace for "supplemental" heat.

My split system is two 36,000 btu outside heat pumps and 7 inside exchangers. The first year my electric cost dropped by 50% in the summer, compared to the window units.

Heating wise the split units are more cost effective then the oil fired boiler or even my coal insert till the outside air temps get to around 25F.

Most winters my coal insert will keep the half of the house that uses the baseboard and kickspace heaters from running, while using 30-50 pounds of coal per day $8-$9 per day at this years coal cost.

Oil this year was $3.70 gal when I filled up and my electric cost is about $0.20 per kwh and coal was $470 per ton. Mine is left over from 2 years ago at $300 ton. But this year will clean that out.

To sum it up the "mini-split system cools the house for half or less then window units did and does a much better job of doing so. Heating wise with my outside units down to 25F the splits are less costly then either of my other heating methods. I wish I had splurged and gotten the "hyper heat" units when I bought my system, then they would be more economical down to almost zero.
One benefit of have several indoor units is that each room has it's own thermostat unused rooms can be allowed to become uncomfortable to save money.

 

[hube2]

It's actually very hard for me to tell how much, if anything, I'm saving on AC. I did not do the calculations last summer after it was installed.

I have a 10KW solar array. What I have to do is look at what I generated vs the net metered value for the the same month before the heat pumps and compare that with that month after the pumps were installed. This gives me the difference in electric use and then I can use that number to calculate savings. It's a lot of work that I did not do while using the AC.

Before the pumps I did not use AC much even when I used it a lot, only on the hottest days. Last year I know for sure the AC cost me more because I was keeping the house shut and running the pumps because of the air quality in NY due to the fires in eastern Canada last summer. I have COPD and I was basically a shut in for most of last summer.

 

[westcliffe01]

The OP wanted cooling performance in summer. I get the impression he lives somewhere else in winter. The mini splits will give all he needs in summer and far better zone control than any central air system. Buy the highest seer value you can afford. Install some solar panels and it will cut down on your utility bill for sure. Hes not worried about winter heating people.