UFAD - Using an Under Floor Air Distribution system in a 1980's Earth Sheltered Home?
If you look through my past posts, you'll see I always seem to bring the weird ones here. So this one is really weird.
Last week we bought a house that will hopefully be our retirement home in 20 or so years. It is effectively a 2500 sf ranch built entirely in concrete - including the roof. Dirt is mounded up on the roof and all sides except the south facing side (toward the street). In fact, from the street, you wouldn't know that it isn't just a normal ranch house.
Inside the concrete shell is the wood framed house itself. The floor is sleeper joists covered with 2 sheets of 3/4 plywood, and sleeper rafters above serve as the mounting point for the sheetrock of the 9' ceilings. From the front, and from the inside, you'd never know it wasn't a typical house.
What is different, and why I'm here, is the HVAC system. Somewhere along the line, one of the owners must have had a new system put in so it is not as originally designed.
How was it originally designed? As a UFAD - Under Floor Air Distribution. Each of the rooms has floor registers in the places you'd normally expect them - but there is no ductwork - they are just open to the pseudo crawl space and concrete slab below. The sleepers are raised so there is about 8" open below then (not to the current 18" code I know). All around the outer edges of the concrete slab at the walls, you can see the inside wall under the floor has a raised concrete footer up to the floor header - AND - it is sealed with 2" of styrofoam insulation as well. There is no insulation between the floor joists themselves, just around the outer walls to create an airtight space.
Over in the unheated mechanical room is the only place where there is a opening to the floor - right next to the forced hot air furnace.
Sadly, all this sits open, and unused. Someone, at some point later, seems to have run new ductwork in the ceiling to all the rooms and added 2 central returns in the hallway ceiling (the returns might be original, hard to tell), and then put in a standard oil-fired furnace (which is in great shape I might add). The mechanical room opening to the floor below is left open, as are the floor registers in most of the rooms.
I know that this kind of thing would have been pretty unheard of in 1980, especially residential. I've looked through all kinds of HVAC sites (including HVAC TALK), and UFAD is only ever referenced in commercial situations. And I've looked through the contractor map here at HVAC talk, and none of you are even near our place in Stroudsburg, PA.
There's no rush to tackle this - but I know the house is not operating nearly as efficiently as it could - with open, uninsulated space under the house. It's sealed everywhere but the mechanical room, but that openness obviously is a source of lost heat. Some day, when it's time to update the furnace, I will want to try to use this space again.
I don't know why they abandoned it - perhaps the contractor who replaced the original system didn't understand it. Perhaps the slab cooled the warm air too much before it got to the far side of the house. Perhaps there was a fear of moisture buildup (heat recovery ventilation systems didn't exist back then). Perhaps there it was just too far ahead of its time and the equipment of the day wasn't well suited for it.
Any thoughts from you guys?