EcoHome is in the process of building our next demonstration low-energy house, and to do so we have partnered with a company that manufactures frost-protected shallow foundations (slab-on-grade) that are heated with air rather than liquid. There are many advantages to air-heated radiant floors over hydronic radiant floors, but none greater than the ability to inject solar-heated air into the thermal battery which is the concrete slab floor.
Solar air heating panels are a growing trend in green building online, with one notable shortfall – the heat that is generated is difficult to store or control. Many people take advantage of the relatively simple and affordable nature of air-heated solar panels (compared to photovoltaic panels) to harness the energy of the sun to heat garages and workshops, but solar radiant air-heating has yet to be a viable and reliable option for well-balanced home heating. Until now ….
When looking for a heat-storage solution that would allow us to incorporate solar-air heating panels into our design in an "engineered" and reliable way, we approached Legalett, a manufacturer of slab-on-grade insulating concrete form kits for problem soils and air-heated radiant floors, to see if high efficiency solar air panels could feed air directly into their existing in-floor duct work. They welcomed the challenge and engineered the system that will be the main heat source of our new (as close as we can get it to ) Zero Energy home. Needless to say that we will be incorporating high efficiency insulation and air tight building envelope just like Passive House design.
Legalett's existing radiant floor heating process consists of a closed-loop network of 4-inch tubes running through the concrete with a heater box embedded directly in the floor. In this case, added to that system are 6-inch tubes (seen in video) that will feed air to air solar panels on the south wall of the house. Air heated by those solar panels in winter, when the sun's angle is lower, will be fed into the floor heating radiant system, which will reduce the energy demand on the heater coil. Conversely and cleverly, in summer if the heat isn't needed in the house, the heat is diverted to an air/water heat exchanger for heating the hot water tank instead. What this adds up to is Energy savings; ideal for Passive Solar Homes, ZNE, PNE, LEED & Passive House projects.
Generating solar domestic hot water when heating is not required also serves to protect the panels from damage that can occur due to overheating in summer.
In the springtime, our pre-fabricated house with dense-packed cellulose walls will be delivered and installed on the slab. Below is a short video of the solar heated floor slab construction, stay tuned for more on the house that will be seated on it!
Back breaking work...been there done that!! Good job guys!!
Hi Fred,
Glad you liked it! Every slab we've done in the past involved building wooden forms first, so the fact that we didn't need to drive stakes into the crushed stone with a sledge hammer made this one seem like a picnic!
How big is the footprint of this house? Single floor?
Hi Igor,
It's a 2 story house, the main floor is about 1,000 sq ft with a bit less on the second story. Here is a link to more info on the house, it's in french but you can see some image of the interior. https://batimentprefab.ca/la-maison-eco-habitat-s1600/
Can you speak to the advantages of forced air radiant floor heating vs water? Also, in another article you mentioned how photovoltaic ends up being more useful/versatile for water heating than direct solar water heaters - is that how this is working? I'm confused as to how the solar air heater panels will also provide hot water.
Hi Alex
In the mechanical room there will be a heat exchanger that in summer months will generate hot water instead of hot air, and frankly I haven't seen the inside of that machine yet myself. The engineers at Legalett designed it, and this being the first one there is limited information on it to date. As we get to that stage we will most definitely feature something on our pages about it when that time comes.
And yes, there is an article where we speak of possibly increased benefits of solar water heating with PV solar panels powering standard water heaters instead of setting up a dedicated thermal solar system. The theory being, that when no water heating is neccessary, your solar investment is working for you to provide power. But, that theory that did predate a few things, first of all this particular system - which doesn't have actual 'liquid' panels, so it avoids the maintenance issues and other hassles of liquid systems, but as this is still experimental we don't have anything we can report yet on total costs and benefits. The second innovation that may rebut that PV / water heater theory is an innovative new panel system by Viessman which you can read about here.
And here is our page on air vs hydronic heating. I was a hard sell myself at first but having done it both ways I am a total convert to air now.