Heat pump system for a 5-plex?
I have a 5-plex that has 4 700 sq-ft 1 br apts, 2 on main floor, 2 on second floor (each with large living room, eat-in kitchen, medium sized bedroom, small full bathroom; kitchen is between the two other rooms and bath is off the kitchen) and one 500 sq ft studio-ish basement apt (350 sq ft main room, with hallway leading to tiny kitchen and 3/4 bath). Currently we have an old workhorse boiler with baseboard radiators in all the units plus the basement laundry room and the common entry/stairwell area. It works well, but is very expensive in our climate in Utah, where it gets down into the teens and sometimes lower, and it’s also probably near the end of its life. We also have a pretty decent rooftop evaporative cooler with one duct into the 4 non-basement apts. The tenants sometimes supplement with window a/c units in their west-facing bedrooms. Basement unit uses window a/c occasionally. Summer temps are above 100 on a couple of dozen days in mid summer (and getting worse). The building (stucco with a flat membrane roof and aluminum frame windows) has ok but not fantastic insulation. I am about to install solar panels on the building. I am considering whether it makes sense to size the solar system to accommodate conversion to an electric heat pump system. Reading about the pros and cons (including on this forum) makes me hesitate, however. My first concern is about how to size the system properly, and how many heads I will need in each unit. I understand there is a maximum of 8 heads per compressor, so I would likely need a system with 2 compressors (or 2 systems). I’m also concerned about having ductwork all over the place–it would have to go on exterior walls which might be pretty unsightly. Has anyone on this forum had experience with installing a mini split system in a small apartment building like this, in a climate like mine? Suggestions? Cautions? Other ideas?
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Greenfriend,
Almost all the new multi-family builds here now include mini-splits. Each unit gets it's own outdoor unit and several indoor heads. Keeping the units separate avoids a range of possible problems. This is a typical example. You can see the compressors on the balconies.
Thanks for your response. I guess you like the systems.
They seem to work very well here.
Who pays utilities? You or your tenants?
Please do a little research on multi-split systems and understand their shortcomings, especially when it comes to their minimum output and how that leads to short cycling and poor efficiency/performance in the shoulder seasons.
Also, most small multi-head systems can either be in heat or cool mode, but can't do both. Sharing outdoor units across apartments can lead to problems where one tenant could lock another out of heating or cooling.
Thanks for your response. Currently, I pay gas (current heating) but tenants pay electricity. When I get the solar panels, I have to aggregate the electric meters under my main account and then I can choose to either manually bill the tenants for their portion of the use or just add a reasonable flat per-unit fee to the rent--which is what I'm inclined to do. I didn't realize you can't heat and cool simultaneously with a multi-head system--that could be an issue I suppose although probably not very likely. I have done some research on the shortcomings, which is one reason why I was looking for input from people who've had experience, both good and bad, with these systems.
I have couple of rentals that use wall mounts for cooling only and the wall mounts are not zero maintenance. The filter on them doesn't do much so every couple of years you need the coil and blower wheel cleaned which is a pretty messy and expensive job. The drain line also clogs once in a while which can cause water damage.
Multi split with a bunch of wall mounts is fine for a condo where it becomes a homeowners responsibility but if you have to deal with them, I would look at other options.
The best is a slim ducted unit for each place, this does mean figuring out ducting. Not hard but also not easy unless there is a major reno. You want each unit would with its own outdoor unit powered from their meter. I've done this on some newbuilds and it works great. The only maintenance is a regular filter change.
My $0.02 would be to wait for a unit to be empty, fix it up and add the ducted unit. Keep the rest on hot water and hope the boiler makes it till all the units are updated. Worst case, swap out the hydronic baseboard with resistance ones if the boiler dies.
You would still have to figure out the load for each place, a good start is run the numbers based on the fuel usage of the existing boiler:
https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler
A ballpark is to split the heat loss to each unit based on the area of the exterior walls and roof of each unit compared to the whole multiplex. For more accurate umbers, you can run a manual J for the whole place and adjust it match the fuel usage based results. Fuel usage based numbers are much more accurate than even a good man J with all the unknowns from an older building.