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Does my HV AC design looks OK

Darko9000 | Posted in Mechanicals on
Hi everybody,
We live in the Raleigh area, North Carolina, my wife and I are building our retirement home and we wanted to be efficient and tightly built, just the way TUCO from Breaking Bad would say it!

Looking for a sanity check on my HV AC equipment. What I am trying to accomplish is to build the house as close as I can to a passivhaus standard. I am shooting for 0.6 ACH 50 air tightness but would probably be happy with 1.5 ACH 50.

The house is 2 by 6 construction 24 inches on center.
The first floor of the house is approximately 2000 square feet out of which zone 1 is 1336, zone two is 431 and zone three is 227.

The front of the house is facing West.
The walls will be filled with the open cell spray foam, the exterior is zip sheathing which will be completely air sealed, this is followed by two inch thick polyiso insulation, ½” air gap and then exterior brick.

All windows are European tilt and turn, triple pane low E windows, I think they are rated R7 when converted.

The whole house is electric only, (we have 14 kw solar on the shop roof) with an induction cook top, I do not have any exhaust fan in a bathroom or kitchen going outside, however I have just purchased Panasonic Intelli-Balance 200 ERV, 60-200 CFM FV-20VEC1 and I’m planning to run 4 inch hard piping to several areas in the house and picking up the returns from the kitchen and bathrooms.
 
The roof rafters are made out of 2x 10s, they will be filled with open cell spray foam.
The house is sitting on a sealed crawl space that is lined on the inside with a 2 inch thick XPS Styrofoam, the whole thing will be sealed off with a 15 mil vapor barrier and I will be installing Dehumidifiers.

Later down the road I am planning to install radiant floor heat. A couple of years ago I have installed a radiant floor heat in my shop, and I absolutely love it, so for now I am looking to purchase a heat pump, we would primarily using this for cooling only but heat would be there as a backup.

I have found a place online that will do a manual J calculation for a fee, and these guys came back with 43000 btu for cooling.

My local HVAC contractor wanted to install 5 ton ac with 50 ft of ductwork in crawlspace.

I have read many articles here on green building advisor where tightly built houses can be cooled with 1 ton of AC for over 1000 square feet
 
So that being said, I’m looking to go with a 3 Zone mini-split as follows:
Outdoor 3 zone condenser 24000 btu

Zone 1:  A 12000 btu 4-way ceiling cassette–which would be main living area, kitchen, Laundry, Half Bath, Foyer and Closet, 1336 SF

Zone 2:  A 9000 btu Slim Duct in the attic which will feed Master Bedroom, Master Bathroom and Master Closet, all piping would be rigid 6 inch, I’m assuming I wouldn’t need to insulate these because I am inside my envelope, 431 SF

Zone 3:  A 7000 btu Slim Duct Guest Bedroom (Bedroom 3), Bath and Closet, same as zone 2.  All duct runs would be 6 inch rigid pipe, 227 SF
Please see attached picture.
 
Thinking about going with Fujitsu “aou24rlxfzh” mini splits because their slim duct goes down to 7000 btus
 
Does anybody see anything wrong with this setup? Or even better, have any suggestions to improve on things?
 
Thank you very much,
Please excuse my spelling, English is not my first language
 
Darko Erickson

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