Minisplit System for a Passive House
I am on the building committee working on a Habitat For Humanity project in southeastern Mass. The project is a three bedroom 1400 sf passive house construction. 900 sf on the first floor mostly open space with one bedroom and a bathroom and 500 sf upstairs with two bedrooms and a bathroom. I ran my own manual J with some online software that come up with a design load of 11,348 BTU/HR.
The first contractor mentioned that he would do a manual J load calculation and quoted a 24K Fujitsu outdoor unit with a 12K wall mount unit downstairs and 2 7K units for the upstairs bedrooms. When I asked why the second floor bedrooms each had a unit but not the first floor. He acknowledged that he had missed the first floor bedroom and he would redesign using a 36K unit with an additional 7K downstairs. When I asked about the manual J he said he couldn’t find the paperwork. I asked for a redesign using one head on each floor. Final design is an 18K outside unit with a 12K downstairs in the open area and a 7K upstairs in the hall.
This made sense until I read the specs, the 18K unit has a max heat output 22K at 5 degrees and a minimum of 6,200 at 47 degrees. This seams way over designed assuming my manual J is correct. My thought is to recommend two single zone wall mounts a 9K downstairs and a 9K upstairs as this is the smallest size, I can find a spec on. Hopefully I will get a second quote next week. Any thoughts on this are greatly appreciated.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part