On Sat, Toby Kelsey wrote:

Joe Fischer wrote:
I was thinking of getting more mass inside the insulation,
masonry only has a specific heat about half that of water, but
100,000 pounds of concrete inside the insulation would mean
that 50,000 BTU would have to be lost for the temperature
to drop one degree.

Are phase-change materials currently a cost-effective way
of improving thermal mass?
Toby

I haven't priced them, eutectic salts can be custom
mixed to any temperature phase change and they are
much better than passive mass like concrete because
energy is transferred without a change in temperature
of the salts (in the selected range).

But even so, the extra thick walls of a house is
an advantage that works several ways as a buffer to
temperature changes.

I lived in a permanent barracks near San Antonio
in 1948 that had walls two feet thick, and outdoor
temperature changes were hardly noticed without
any heat or air conditioning, and temperatures
could swing 60 degrees from 4 AM till 2 PM.

The problem with salts is where to put them,
maybe a DIYer could put them in used 2 liter bottles
and stack them in unused space, but most existing
houses don't have a good place to put them.
They need to be in fairly small containers or
pipes so that room air can be circulated through
them to get a rate of heat transfer high enough.

Joe Fischer