HVAC – Continuous Operation or More Zoning
Should I run a ducted heat pump system with ECM motors continuously or go with a more zoned approach with the units coming on and off as needed?
We are designing the HVAC and ventilation design for our new house in the Pacific Northwest, Zone 4 marine. The house is 2,200 sq. ft. with 2/3 of the square feet on the first floor and a smaller second floor. The majority of the windows face NW toward the view, 2×6 walls with Roxul batts, 10″ SIP panels for the lower level floor, vaulted gable and hip scissor truss roofs, high solar gain windows. The passive house heat load calculations put our peak load at 21,600 btu/hr with a design temp of 22F. Typically we have 3 months a year where we turn off the HVAC in our current house (same area) and ventilate naturally.
We have decided to go with a Mitsubishi or like heat pump. We will have electric radiant floors in the 2 bathrooms and a propane free standing stove in the kitchen. I am thinking of using the Ultimate Air 200DX ERV, eliminating the bathroom exhaust fans, and using the boost mode on the ERV. I am looking at the Mitsubishi multi-position ducted indoor unit that has ECM motors, 3 air speeds and very quiet indoor and outdoor units. We are trying to get all of the ducting in the conditioned space.
We want high comfort in the house without a lot of cold and hot areas which is why we moved away from mini-spits especially with our low heat load. The question we are working through now is should we have a single unit and run it full time or zone the upstairs and downstairs and have the system only come on when needed. Minimizing ducting for the HVAC and the ERV would help us.