Passive Solar Basement Efficiency
The graphs below summarize the results for the 2010-2011
heating season.
Click on the graph for a larger version.
The graph above shows the observed daily average temperatures for the
2010-2011 heating season. The grey squares (along with the y axis on
the right edge of the plot) show how many hours per day the backup
propane furnace ran. The lower graph shows the ratio of daily average
surface solar flux to the top of atmosphere solar flux. The surface
solar flux on a horizontal plane is measured by the weather station, and
the top of atmosphere solar flux is calculated for the date and
location. Sunny days have a solar transmission near 0.7, and cloudy days
have lower values.
It was a relatively warm season, except for three few day periods of
wicked cold. During the first cold snap around New Years frozen water
vapor in the propane tank prevented the furnace from working and the
house got colder than desired. During the second cold snap in early
February we were away and let the house get quite cold, though we were
at home for the third cold snap a week later. The furnace only ran for
around the time of the two cold snaps when we were home. We were also
away in late April and let the house cool down.
Due to the reflectors in front of the basement windows, the basement air
temperature usually averaged above 80o, except during
extended cloudy periods. Since the basement was warmer than in past
years we needed to close the basement vents during sunny periods and
even occasionally open the windows on warmer afternoons. About once a
month from early February to early May we increased the tilt of the
reflectors from 0o to 28o to follow the increasing
solar elevation angle. On May 29 we tilted the reflectors back down to
0o and the basement cooled off rapidly over the next few
days.
Click on the graph for a larger version.
The above graph shows the total heating degree days (HDD) accumulated
through the season and total BTUs provided by the propane furnace in our
house. These HDD are defined relative to the standard 65oF.
The furnace BTUs are calculated using the 70,000 BTU/hour furnace rating
and the time the furnace is on as measured by the computer.
This season the furnace was used for 10.4 hours, consuming about 8
gallons of propane. The ratio of BTUs to heating degree days divided
by the floor area of the house (1508 square feet) is plotted in the
lower panel. This ratio is called the heating intensity index, and is a
measure of how efficient the house is.
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