SB: Re: Passive solar SB designs

[Derek Roff <derek@unm.edu>]

> We talk of "passive solar design" in our structures, and Chris
> wisely has sought information on it, as we did when my wife and I
> designed our SB home a few years back. My question is this: Is
> there ever really a net energy GAIN, over the course of a year, by
> using the concept of windows to heat our homes?

An important question.  We want a large net gain of heat through the 
windows during the heating season, and a minimum of heat gain through 
the windows during the cooling season.  Plus, light and views all 
year around.

The climate will make a tremendous difference in both the potential 
for solar gain, and the best fenestration design to achieve it.  In 
sunny New Mexico, people routinely put in a tremendous amount of 
south facing glass, and have uncomfortable (and often ugly) homes as 
a result.  Even at our modest latitude of 35 degrees North, windows 
are losing energy for eighteen or more hours a day during the winter, 
and gaining energy for six or less.

Too much glass leads to large daily temperature swings.  Many 
overglassed houses around here are too warm on many a winter 
afternoon and too cold every morning.  Better insulation and smaller 
windows decrease temperature swings and can improve comfort, net 
solar gain and overall performance.  This is one of the advantages of 
SB construction- relatively small windows can provide all the needed 
heat gain with lower heat loss and better aesthetics.

The frequency of clouds, average external temperatures and wind 
speeds, and the proximity to Rob Tom's house* can have a significant 
effect on the potential for solar gain and heat loss through windows. 
In any climate, seasonally removable external reflectors can double 
or triple the solar gain through a window.  Internal window 
insulation, removed during heating hours, and replaced late each 
afternoon, can help, too.  But none of my friends has kept up their 
resolve to move window insulation twice a day for very long.  For a 
gizmologist like myself, mechanization seems worth investigation.

Solar collectors other than windows may be necessary in many places. 
A combination of active and passive systems is sometimes appropriate. 
Smaller, more efficient and reliable pumps combined with cheaper, 
higher output solar panels, give us options that weren't available 
even five years ago.  I believe that is possible in most places to 
design and build a comfortable house that maintains a warm, fairly 
stable interior temperature, without burning any fuel.  I hope that 
enough people will continue to develop and experiment with solar 
design, so that we can learn how to do that in many more climates 
fairly soon.

Derelict

* A proposed international standard for "northness."

Derek Roff
Language Learning Center, Ortega Hall Rm 129, University of New Mexico
Albuquerque, NM 87131  505/277-7368 fax 505/277-3885
Internet: derek@unm.edu

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