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Moving Pictures
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# Posted: 6 Jan 2013 14:56
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Hey folks.
The Lady and I are well into designing an off-grid home with anticipated construction start for this summer.
The home isn't a "cabin," per se, but I figured I'd fire out a query. Our construction technique will be slip-form masonry (concrete walls, foam insulation) and therefore quite airtight.
Conundrum: ventilation. I've done some research on HRV systems, and they seem to involve ducts, energy and other things that just don't fit into a plan that forecasts a little more than 1,100 watt-hours of PV power per day.
Our primary source of heat will be a small masonry heater (Finnish stove), supplemented by a touch of passive solar.
I do plan on some vents: standard AC fans for each of the two bathrooms, a vent for the battery bank and - if we decide on gas as a secondary cooking option - a vent for the gas cooktop.
My intent, all the way along, was to bring a duct from the outside through the floor (concrete, slab on insulated grade; will be heated by liquid in pex tubing heated from coils in the masonry heater core) to feed the heater. Now I'm wondering if I should consider some other means of bringing outside air in.
Clearly, a HRV isn't going to work. Unless I can brew up some low-tech, DIY thing.
Thoughts?
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Rossman
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# Posted: 6 Jan 2013 15:35
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There are some off-grid HRV systems, this guy's blog mentions a 24V unit for his off-grid application?
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MtnDon
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# Posted: 6 Jan 2013 15:49
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Quoting: Moving Pictures technique will be slip-form masonry
Have you considered pumicecrete? It uses light weight pumice as aggregate; it's light as it has lots of air in it. Depending on where you are it may be hard to get or expensive. I have friends here in NM who have built a home with the material. Walls are 18 inches thick.
They built on a concrete slab (insulated with R15 foam under the slab. They have a small HRV from Fantech IIRC, with They are PV powered and just built in enough capacity to run the HRV. Some things are difficult to do well without some electrical power. Their ducts run in a conditioned false ceiling... all the attic insulation is above the ductwork. It is only 6 inch metal piping so was not too bad costwise. The HRV is virtually silent. You need to look at the controls to tell it is running.
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Moving Pictures
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# Posted: 6 Jan 2013 16:15
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Rossman: aware of the link. Doesn't solve my quandaries.
MtnDon: we are waaaaaay away from any volcanic anything. Great idea, but probably not feasible for this area.
The issue I have with the HRV concept is multifold:
a) Energy use. Poking about, the power to run these things is not insignificant - 35-80 watts, day in and day out? That's insane - and represents 80 per cent to 200 per cent of our current total energy calculations. It would make off-grid challenging and expensive (as in, doubling our planned battery bank capacity and module expense.)
b) Ductwork. That's pricey, and seems incompatible with our design, relying on only a 400-square-foot upper storey and cathedral ceilings (nowhere to hide ducts.)
c) Philosophy. The idea, to me, clashes with the whole off-grid, low-tech, small-footprint concept. These things seem to be stuck in the typical modern-era problem of relying on some energy-consuming gizmo to do the work.
I'm looking at the idea of a passive system, wherein duct-drawn air from the outside is brought through sections of the masonry heater brickwork to warm it - and this air is then drawn into the home while the masonry heater draws stale air from the house.
Thoughts?
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exsailor
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# Posted: 7 Jan 2013 14:40
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You might want to check out this site; www.mb-soft.com/solar/intake.html I won't pretend to understand the venting systems all of you are talking about. I am not even sure if this will be a help or not. Natural convection might be the answer your looking for.
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Rossman
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# Posted: 6 Jun 2013 19:18
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Moving Pictures: Realize this thread is a bit old but as I get closer to building our off grid residence I ended up finding this HRV which is only 13.5W or some such...
http://www.venmar.ca/39-air-exchangers-eko-1-5-hrv.html
Did you ever come to a better solution than an HRV? For my building permit I have to provide "manufacturers specifications for HRV and furnace/heating apparatus"...so I'm pretty much stuck with an HRV I guess...the Venmar is the best I've found so far.
Cheers
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