Hi there All,
Young designer here attempting my finest to employ some better style concepts.
Dealing with a gut renovation of a 1940s removed single family home in northern Queens, NY. It is 3,000 sf spread over 2 stories, plus cellar, and occupiable attic. The house is getting new self-adhered WRB (air barrier), spray foam to make a conditioned attic (I tried to promoted for exterior poly iso), R-12 poly-sio continuous insulation, and new R-15 or R-21 cavity insulation depending on cavity size. Shooting for less than 3 ACH50. Actually, simply present NYC energy code minimums, but leagues above where the house is presently.
The biggest concern is the heating and cooling system. I have actually read here that it’s finest to do a single-zone ducted unit per floor in these circumstances, however the owner wishes to do wall mounted mini splits with a head in each space. I did a Manual J which put your house at ~ 25k BTU heating load and ~ 22k BTU cooling load. My strategy to deal with the Handbook J and the owner’s desires was to spec a 36k BTU Mitsubishi Hyper Heat that supports up to 11 indoor units. This system can modulate down to 13k BTU cooling and 12.6 k BTU heating. This capacity will be spread out across seven air handlers sized as best I can to satisfy the load of each space:
— 4,000 BTU system in the cellar rec space
— 2 6,000 BTU systems outdoors floor plan 1st floor
— 3 4,000 BTU systems on the second flooring, one per each bedroom
— 6,000 BTU unit in the attic rec room
I know the unit is large based on the computation, however my argument here is that the single bigger system can have it’s minimum capacities divided between more indoor units. The owner nevertheless would like redundancy constructed into he system and have two outside units, so that there would still be cooling in your house if one of the condensers failed.
I comprehend his issues, but I think this technique will cause issues like brief cycling, bad humidity control, and increased expense, since the smaller sized condenser units basically have the very same minimum heating and cooling capacities as the 36k BTU condenser.
I essentially simply wished to see if anyone had any other recommendations or thoughts to share. Thanks!