Not an answer to your question, but if you had a common compressor, wouldn't the building owner have to foot the heating bill?
I've seen a photo or two showing outside units for individual mini-splits mounted on the exterior wall of a multi-story building, accessible from the balcony for each apartment. Not pretty, but probably more efficient and individually metered.
Thanks for the reply, David. You're right - it does boil down to whether they need individual metering or not. Mounting the compressors on the exterior probably won't fly, although I've seen photos of those too...in Europe, where they seem to be willing to let form follow function. :)
I'd still love to hear from anyone who's actually put them in a multi-family project - anybody?
Yes, this can be done and is done.
Many of the ductless heat pump manufacturers have these types of units available. The most well-known is 'City-Multi" from Mitsubishi. The ratio of indoor units to outdoor units depends on the design heating/cooling load and equipment capacity, but, yes, there are probably options where you could have 20 indoor units running off of just 1 outdoor unit.
King County Housing Authority has installed mini splits on a multifamily in Boulevard Park. It is called Boulevard Manor. It is a 72 unit complex. All the outdoor units are on the roof. It is not a 'city multi, I think they used Daikon. Each individual tenant pays their own bill.
If you want to use one outdoor unit I think city multi with mitsubishi is your best bet. I would consult with Ecotope for alternates. They are in the city, call and ask for John Heller.
I have had good luck with Advanced energy management, they are a ductless heat pump installer and a mitsubishi approved contractor. call them for a bid, analysis. 253-250-8170,
Great info, Dan - thank you!