Best HVAC Strategy in climate zone 4 for a ranch on slab?
Hi! I’m excited to create a low energy use home and was very interested in the Legatee air heated radiant system from what I’ve seen online but thinking it may not be ideal based on our more moderate climate zone. Would appreciate any feedback.
Asheville NC US Climate zone 4a Cooling degree days with base temp of 65F = 1103 Heating degree days with base temp of 65F = 3958 4000 SQFT Ranch Home
Requirements Cannot have any outdoor HVAC equipment due to sound level of the community 65F in bedrooms at night for sleeping comfort 72F during the day in main rooms and/or bedrooms Zoned system for comfort and energy saving Wanting to make sure house does not overheat due to sun, shading, seasons etc. Wanting to use smart thermostat such as Ecobee.
OPTION 1 - This seems pretty standard and solid. Slab concrete with insulation on top of slab Ducted geothermal ground loop HVAC (zoned) Zehnder ERV/HRV
OPTION 2 - This seems like it can be super comfy but may have issues due to overheating, not able to cool bedrooms well at night etc. Slab concrete with insulation outside of slab Legalett air heated radiant in slab (zoned) (bedrooms might get too warm at night?) ERV/HRV heat pump with AC cooling (zoned) (not sure if the AC would be strong enough?)
The Legalett air heated radiant floor is just an option with the slab on grade kit. You’ll need some sort of heating system, so its really just a matter of what type you’d like, whether that’s radiant floor heat, forced air, or just baseboard radiators.
You can have them engineer a slab only, and from what you say there is an additional benefit to that. Legalett floors are thicker than typical slabs, so there is more thermal mass in the home for balancing temperatures, which can be a great feature when designing a house for as much passive heating and cooling as possible.
The ‘real time’ effect is that you can often make it through a heat wave with no AC (or a lot less) since it can take many days for a slab to warm up. See this page for more details –
What are the pros and cons of thermal mass in homes?
As for it getting too hot at night, remember its on a thermostat so it will only get as hot as you want it. You can also design it in a way that the bedrooms are on a separate zone so you can keep them a bit cooler.
Things like the ducted geothermal ground loop can be great as well, though be sure to have it sloped so any moisture can drain out. There are some concerns of mold developing due to moisture and debris, so including some design feature for cleaning it is a smart move.
Here is another page that can help – our video on how to design and build a passive solar home, that is the first in our video series about building a passively heated and cooled home.