Weather - Insulation vs Thermal Mass: We
had record cold temperatures this week in Tucson as
arctic air dipped way down across the country. Our nights
were in the teens and days in the 30's. I was told we
were colder than parts of Alaska! I can't ever remember
it being that cold in the fourteen years I have lived
here. Usually, storms bring cloudy weather, so my solar
heating is not at its peak, but this cold brought clear
skies, so I could really see how my sunroom
works. I have no central heat.
house is like a heating/cooling unit where I adjust
it according to the outside temperature, to maintain
the best internal temperature. I'll explain. As I studied
natural building, I learned two of the main features
in passive solar house design are insulation and thermal
mass. Thermal mass heats up in the sun and insulation
does not transmit heat. They are often confused. Think
of a rock and a straw bale sitting next to each other
in the sun. The rock would get warm as the sun shone
on it. If the night had been cold, the rock might still
be cool. The straw bale would not change temperature
noticeably. The rock is thermal mass. When you burn
your feet on a hot, sandy beach, you are feeling the
effect of thermal mass. Anything made of rock, concrete,
earth, sand, tile, and adobe is thermal mass. It gets
warm in the sun and it gets warm from the light of the
sun, not the transmitted heat. So, you can have glass
in-between the sun and the thermal mass and it will
still heat up. I've never heard of water referred to
as thermal mass, but it must be, since it heats up in
the sun also. I think rubber tires would be considered
thermal mass, also. You get the idea. A thick exterior
thermal mass wall will heat up in the sun and slowly
transmit that heat into the house, unless the night
cools it off before the heat reaches the interior of
the house. I am no expert on adobe, thermal mass walls
because that is not what I need in the hot desert climate.
agreed with several articles I read, that the optimum
house design is one with insulation in the exterior
walls and ceiling, but thermal mass in the interior
to maintain an even interior temperature and help hold
onto your heating and cooling methods. If you are in
a perpetually cold climate, then you might want thermal
mass in your walls, so you can let the house heat up
from the sunlight all the time and transmit that heat
to the interior. I don't live in such a cold climate,
which is why I chose insulation for my exterior walls.
Most of the time, I am working to keep heat out of the
house. You know how I insulated my walls - with straw
bales - and if you read the book, then you know I used
R-30 batts plus a radiant heat barrier in the ceiling.
The R factor of bales varies with the bale, but it runs
in the 30's to 40's. I have very large, solid bales,
also. Insulation in the ceiling is very important. A
radiant heat barrier is double-sided foil (stronger
than kitchen foil) that is laid inside the roof to reflect
the temperature of the roof back outside and the temperature
of the house back inside.
said that, this is how my house works in cold temperatures:
the south winter sun shines directly through the sunroom
windows and heats up the earthen floor and the earthen
plasters on the walls. I open the french doors from
the sunroom into the house and let the heat pour into
the house. When the sun goes down, I close the french
doors and let the thermal mass of the interior maintain
the temperature through the night. It does an amazing
job and my house will only cool off a few degrees overnight.
My house was about 70 in the days when I got home and
cooled to about the upper-60's. I don't have thermometers
around the house, but I should do that. I should put
one in the sunroom and then in the main room to really
be able to report on how it all works. Stay tuned .
. . As a practical note, however, the sun blazing through
windows for days on end, really does bleach the colors
out of things. I cover my chairs and carpet in the sunroom
with towels or sheets most of the winter to keep their
colors. I know this is a problem if you have your south-facing
windows shine directly into your living room.
morning the outside temperature was in the upper 30's
and my house is in the mid-60's with no heating used
beyond the sun yesterday and last night. However, I
do have baseboard heaters I can pull out in cloudy weather.
Often, our coldest weather is cloudy and I really can
feel how much this cuts down on the solar heat gain.
But in this cold front, I was cozy. Now, I'll go outside,
take the sheets off my plants and see what survived.
Cactus is the most amazing stuff! I survives from about
20 degrees to 120 degrees on very little water. I'm
just not sure if it was ready for the teens.
it Simple - and be kind!