Interior mass wall as a thermal collector for radiant heat
I am going to defer to the experts here because I can not find any examples of what a client wants to do, and I do not have an engineering background to talk my out of the current situation.
Basically I am beginning to work with a client that wants to build a passive solar house. They want to build the entire house out of concrete, floors walls and an internal mass wall. Which fine, I just need to size the glazing to the amount of mass within the structure. But the strange thing that the client wants to do is to run radiant tubing within the interior mass wall. However it is not to heat the home, but to use the direct solar gain on the wall to heat the fluid running through the wall.
Now I do not see this as a very effective strategy to heat the home. I think it may pull more heat from the space as the cooler water is running through the system. So I guess it could be a decent way to help cool the place. However it does not account for de-humidification since the project is in climate zone 4A
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Joshua,
Who is designing the house? You?
You are probably correct that it is time to "defer to the experts." If you don't know how to size the south-facing glazing for a passive solar house with extensive thermal mass, you or your client needs to hire a consultant with experience. That might be an architect, an engineer, or a passive solar designer.
A major project like this can't be designed on the back of a napkin -- nor in a few paragraphs on the GBA question-and-answer page.
The consultant you select should be able to use appropriate energy modeling software (for example, the Passive House Planning Package) to be sure that your glazing guesses will work.
I am the consultant helping another architect design the home. What I don't understand is why the client wants an internal mass wall with radiant tubing in it to collect the direct solar gain to heat the fluid. It seams backwards to me. I feel the fluid running through the pipes is going to suck more btu's from the wall than the sun can provide and will not adequately heat either the wall or the fluid to have any real benefit, and completely loose the effectiveness of having an interior mass wall.
My first reaction to this idea is that if this is how the client wants to passively heat up DW, then a solar thermal system on the roof will be much more efficient and cost effective and can provide heating for hydronic baseboards, radiant floors, or what ever back up heating system we end up using.
Right now this is schematic phase, I I just want to have a valid argument for why I don't recommend the radiant tubing in the interior mass wall.
if this is passive solar utilizing activated concrete walls, i don't think PHPP would really be able to model that accurately, but i might be wrong.
thermally activated building systems can work beautifully (and seem to be significantly better for cooling) but i don't see the interior space heating up enough to really carry that heat to other parts of the house effectively (or when needed)
i know of several projects that utilize just the passive solar part, fairly effectively and maintain low-energy numbers. page 16 of this PDF (german, http://www.akoeh.de/media/Tagungsband_Teil3.pdf) has guenter pfeifer's haus kinzy, which is similar to the system you described, minus the activated concrete.
pfeifer works w/ energy consultants that have developed fairly sophisticated software to accurately model the gains and dispersal of heat through the house.
The strange thing isn't the thermal collection wall but the entire project. A passive solar house should generally not have more than about 15% of its floor area in solar glazing. Beyond that, and an active heat storage and retrieval system will be required. Once glazing exceeds 7% of floor area, additional direct-gain thermal mass is necessary to prevent overheating and to store the heat for release on a diurnal cycle.
This mass should ideally be 4" thick if one surface is continguous with the interior (e.g. slab) or 8" thick if both surfaces are available (e.g. trombe wall or interior wall). More thickness than that results in a thermal lag (time decrement) with a cycle greater than 24 hours.
With such excessive mass in this house, the concrete will not increase in temperature sufficiently to warm DHW tubing to any degree or even to offer good sensible radiant return. The thermal inertia will overwhelm any attempt at controlling indoor temperatures.
This project sounds like a disaster. If neither you as consultant nor the primary architect has a clue about passive solar design, the client better find someone who understands the design principles involved.
See my article "Designing a Passive Solar Slab" in the April/May issue of Home Power for more on this subject.
No, this is the clients current wish list. I am sitting down with the architect tomorrow to discuss the project. Like I said, we are in schematic design phase. So we are setting up the goals and systems. I just wanted to find out if someone has used an internal mass wall as I described before. All the other issues you mention Robert I can work through with the architect and client and get the project to work properly.