Good plan for a minisplit?
So I previously was ruling out a minisplit for the new home. However I notice Mitsubishi released a new single-head Hyper Heat unit that is now 21 kbtu instead of just the 9 k and 12 k. I think this opens up the discussion again.
Zone 6, 7200 HDD, design temp of -13. First floor footprint is about 1650 sqft. There is a full basement, with most of it finished. Total heat load for main floor and basement is 21k and 14k cooling.
Due to rebates from Feds and local utilities, we can get a 2-ton geo [GSHP] installed with vertical wells, HRV, and ducting for $12k net. About $10k for a 2-ton ASHP and gas furnace backup, HRV, net price.
The 21k minisplit runs about $2,200 online, plus a few hundred for linesets and other hookup items. I was thinking the option would be the 21k unit on the main floor so as the output reduces at lower temps, it should still hit design loads on the main level. Then install a 9k unit in the basement, Those are around $1600, plus lines sets. So I am calling it $5k installed. Now I need to add an HRV and ducting, so around 3k there, maybe less. This works out to 8k. Add a few hundred bucks for a couple electric heat strip backups in the bedrooms.
What this does not include is ASHP rebates I can get from the local utilities. I believe I can get $3500 back in rebates for an ES 3.0 home, so that could take that 8k down to $4500. The same rebate is used in the above pricing for geo and ASHP.
With that being said, obviously the upfront investment is considerably less then geo, and the net is less then half. However my biggest concern is the air circulation and if this plan lends itself as a candidate for a minisplit. I have read every thread on here I could find. Read about HRV moving fresh air, read about powered fan through wall exchangers, etc. All could be an option if needed. However I just want to post up my plan and see if anyone has any feedback on options or location.
My thought was to place the head on the wall outside of the master bedroom facing the stairs.
According to the spec sheets, the 30′ throw will get it to the kitchen easily and into the back bedroom. The basement has a similar setup with bedrooms to the left and open space to the right. the 9k unit would mount in a similar spot. A direct vent gas fireplace would be installed in the living room and that could provide backup heat easily for that entire space.
Is there any thoughts on the placement of a head or any concerns about conditioning of the space?
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Funny, I've been struggling with the same dilemma, GSHP vs ASHP. I love the simplicity of a minisplit. With the geo system you will need sufficient duct work which means a manual D which means a good install and how will that interact with the ERV delivery. A lot of extra details to work through. With a minisplit and one head the only trick is getting the conditioned air around the whole floor (you have a big footprint). You might look at a single head but that goes to ducts and centrally locate it so you could deliver to a few rooms (above master, stair, bathroom area?). With your small heating loads, I don't think it would be too risky plus having the elec strips back up helps. Granted there is ducting but I would argue a much simpler system and probably don't need a Manual D since the ducts runs could be short and straight.
I started leaning towards a dedicated ERV duct system to ensure great IAQ and I've seen some passive home case studies (your heatloads are relatively small) suggesting with a good envelope you don't need a robust heat delivery system as the structure should stay rather consistent in temperature. Plus a good erv duct system will help with distribution of air.
On the flip side, once the investment is made in geo, no more fossil fuel, but a lot of electricty which you can offset with some PV later. The geo pumps can be loud so you'll want to make sure they are strategically located. If you have not checked out the Diakon Altherma system give it a look. They have a bunch of options for ground source to water heat delivery and also domestic hot water.
What I'm doing is planning the ERV/HRV duct layout and size with heat distribution in mind. I chose a larger than needed unit throttled by a timer to run 20 minutes on 40 minutes off . I can select more on time if needed. Building exhaust to the ventilator will come from my bathrooms and kitchen and fresh air from the ventilator will be distributed independently to every other room. Hopefully the ventilation airflow will distribute the effect of a single mini split located in my biggest room (which has the highest heat loss due to most window area). Another thought on your situation. look closely at the Mitsubshi specs for the different size of hyper heating mini splits the biggest throttles to the sane minimum output as the smallest. So I'd recommend that you use two of the biggest which will cost about $200 more but give you a lot more total heat when it gets really cold outside. Hopefully eliminating any need for supplemental heat.
I have several homes to caretaker that are very well insulated but not to PH Levels, more like Energy Star. They all have very even temperatures when I am in them. I have shot them from cellar to ceiling with IR meters and they just don't seem to stratify vertically or from room to room. That all said it is your home. The gas fireplace to me is perfect to offset any cool effects that heat pumps are associated with.
I think it depends on the occupants. The size isn't as big a deal as the compartmentalization. Iam skeptical to the hrv providing the same level of distribution and comfort as a traditional heat pump distribution. Some people will be fine with it while others may complain.