[Strawbale] water in attic cross post 5

[Shody Ryon]

Re: Low cost thermal mass

From: "Paul V." <cruisenewsnet at ...>

> I have been looking at solar house designs where the
thermal
> mass is in the attic. There are a lot of reasons
that I would like
> to avoid putting a lot of weight up in the attic

Hi Paul;

Why do you think that it is "a lot of weight" ? Have
you
calculated it? Or is this a guess, based only on fear?
Generally, even in cold cloudy climates, where the
storage
needs to be much larger, it is still only about the
same weight
as the code requirement for bedrooms and other
secondary
areas. It is less weight than your living room, dining
room,
family room, kitchen, and other common areas are
minimal
designed to support. It is also possible to
design/build such
a system with a third or less, heat storage, though
that will
reduce the number of cloudy days that the house can
get
through, on stored heat. However, the reality is that
in
almost all case, the heat storage, which is best
located
over the sunspace, usually set directly above the load
bearing wall between the sunspace and the living
space.
Structurally, it is generally easy. Exactly what is it
that
you are worried about?

>. The main reasons of avoiding an attic thermal mass
> system are less load on the construction materials,

Why are you concerned about that? The structure
should be designed to handle the load it needs to
carry.
It is not even a large load. For instance, where I
live,
the minimum design loading for all roofs, is TWICE
as much as the load for a typical attic heat storage.
Besides, my heat storages are usually self-supporting.
They don't even bear on the attic floor.

> lower chance of building failure and personal
> injury if things go bad.

Please, never walk under a bridge, or inside of
a commercial building. They have to carry far
greater loads, over far longer spans. Think
about it. Then, hopefully you will shed your
irrational fear, rather than taking on more.
An attic heat storage, typically will weight
about a fourth as much, per square foot,
as the load on the roof of an earth
sheltered house.

> I am thinking it might be better to invest in a
> photovoltaic/battery powered blower and
> insulated ducts to move air around.

You can do that, but grid power is a lot
less costly, and it is realistic to expect PV
prices to drop considerably, in the next five
years. You can still have a battery backup,
with grid power. There is usually no reason
to insulate the ducting, unless you are running
it through an unheated space, which should
just be avoided. It is fairly easy to have
individual heat supplies for each room, or
since the house should be well insulated,
just one for seveal rooms.

> I am assuming that the losses would be greater
> and the lifetime cost would be higher
> than an attic system.

For what?

> So how to build a low cost easy to build thermal
mass system?

Putting it in the attic makes it work better
passively.
It also puts it in an area that does not use main
floor space.
However, thermal mass can go most anywhere, like in
the wall between the house and sunspace, or even down
under the floor. But, under the floor requires a
pretty big
blower to move all that air, while the sun is shining.
The
attic also insulates the living space, from having any
ceiling heat losses.

> The first thing that comes to my mind is a well
insulated
> garden shed filled with barrels and bottles.

That sounds like a terrible idea. It will cost a lot
to build an additional super insulated building. It
will
have a lot of surface area, so a lot of heat loss. It
will
also have a lot of heat loss, moving heat to and from
it.

>> Another idea for a 2l water bottle system is to
build
> 4'x4'x8' modules out of OSB on 2x6 skids, then find
> some way to put spacers around the airtight box and
> fill cellulose insulation all the way around,
wrapping
> in plastic and covering with a tarp. One inlet and
one
> outlet for air on either of the 4'x4' ends.

Twenty-one bottles will only store about 90BTU/°F
Even for a house that is about 600ft² you could need
80-90 of those things, depending on your climate.

> This might end up being a very long system,

Yes, maybe 700 feet long.

> it may have to be stacked and double back on itself.

> Maybe get an old insulated truck or trailer and fill
> that with barrels and bottles?

Cool! you can park your yard full of them ;O)

How about...instead....just having the attic designed
to support the relatively small load, of the thermal
storage?

-Laren Corie-


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