# What color house?

I assume a dark color will absorb the heat and awhite will reflect heat, so if
you live in the Midwest, what's a good compromise?

Pure white would seem perfect in the summer to keep out the solar heating, but
in the winter you would welcome the heat gain. Am I stuck with middle gray, or
is there an established scientific answer?

2. ### Guest

What happened on cloudy days?
NREL says 930 Btu/ft^2 falls on a south wall in Des Moines on an average
24.4 F December day, so 1 ft^2 of white R20 south wall with a U2 airfilm
conductance would lose about 24h(65-24.4)1ft^2/(R20.5) = 47.5 Btu/day.

We could model a dark south wall like this, viewed in a fixed font:

930/24h = 38.75 Btu/h
--- 20
|--------|-->|------------www--- 65 F
--- |
|
1/2 |
24.4 -----www-------

which is equivalent to:

1/2 20
---------www-------------www--- 65 F
|
| 24.4+38.75/2 = 43.78 F
---
-
|
-

with a heat loss of 24h(65-43.78)1ft^2/20.5 = 24.8 Btu/day.

With an 8'x48' wall, the difference is 8x48(47.5-24.8) = 8698 Btu/day.
If a single-glazed air heater gains 0.9x930 = 837 Btu/ft^2 and loses
6h(80-24.4)1ft^2/R1 = 334 on an average December day, for a net gain
of 503, the dark wall is equivalent to 8698/503 = 17 ft^2 of air heater.

Nick

3. ### mikeGuest

Don't remember all the details, but some kid won the national science
fair prize for a roof that looked like a stairway.
Black on the vertical surfaces and white on the horizontal surfaces.
Average reflectivity went down as the sun moved south for the winter.

4. ### Guest

PE Norman Saunders patented "solar staircase" has mirrors for treads
and transparent risers...

But shading based on detailed summer sun angles isn't as effective as
80% vertical shadecloth over the outside of a window, since a lot of
summer sun is diffuse, eg 65% on a south wall in Austin in August.

Nick