Heat and Ventilation for Passive Home
Hi there,
We are designing a 2500 sq ft certified passive home that will earth sheltered on three sides, a south facing windowed wall and a green roof in climate zone 6b.
We are wondering about the best heating and ventilation combo that this economical to install and operate for this type of house/location
We are way early in the prpocess, so I don’t have the peak heat load requirement, but have been reviewing:
1. Minotair or Zehnder HRV + hydro coil + heat pump air handler
2. Minotair or Zehnder HRV + hydronic heating (water sourced heat pump)
What other systems should we be considering?
Please direct me to additional references and resources to review as well.
Thanks!
Wayne
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Replies
Exciting! I'd steer clear of hydronics totally here - your heat loss will be too low. A ducted system (no hydro coil) will be the easiest/cheapest/likely most efficient. Just swapping an air-to-water for an air-to-air.
Thanks fo the opinion and direction. I agree hydronics may be over kill. The projec MEP engineer was suggesting it.
Definitely the engineering go-to. Resistance electric might be the cheapest if the load comes in low enough since cooling isn't a priority. You can make up for the low efficiency with solar PV.
I'm in virtually the same situation. Zone 6, passive house, same size, though not earth protected. We went with straight electric, with the same rationale. Regretted it big time. Not only did we end up needing cooling in the summer, the heating costs were surprisingly high. Now with heat pumps, and I project a simple payback period of 7 years.
2500sqft, ~230sqm, passive house means you are looking at max heat of 2300W or 7800BTU/h.
For heating and cooling equipment, your best is one of the smallest (9000BTU) slim ducted mini splits. Since the equipment cost on one of these is under $2k, with a COP between 3 to 4, there is really no reason to use anything else.
Your heating and cooling loads will be low enough that you can easily share the ducting with the ventilation system. Since you'll have to run ducting for the ventilation anyways, anything else would be adding cost and complexity for almost no benefit.
With a bermed house, depending on where you are in 6B, your issue will most likely be latent cooling. If outdoor air is dry enough to ventilate with it in the summer and shoulder season, a higher capacity HRV is all you need for moisture control. If not you will most likely also need a dedicated dehumidifier.
You can spend the money one of the fancier heat pump based ventilation systems that can dehumidify, but I don't think ROI on them usually works, a stand alone/ducted dehumidifier is probably a better option.
With bermed house, the challenge will be bringing natural light into a house. Keep in mind that no matter how efficient the house is, if it feels like a dungeon, you won't want to live there. Make sure to take extra care designing in natural lighting even if it creates an efficiency hit.