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Vital Signs
Project: Siegel House Case Study
Sunspace Overheating:
Hypothesis, Methods, Data and Analysis
Hypothesis
As stated earlier in this report on the hypothesis page,
we believe the sunspace will overheat on sunny days.
Methods
In order to investigate whether or not the sunspace was overheating during the day, we
decided to compare ambient temperatures inside the sunspace to the ambient temperatures
inside the living room. Because the Siegels can control the temperatures in the living
room, we assume the living room temperatures show the conditions the Siegels desire.
Comparing these to the sunspace temperatures, which the Siegels cannot control, would
allow us to see any periods and to what degree that the sunspace temperatures were higher
than the living room temperatures.
 A
section diagram of the sunspace and living room,
showing the location of the temperature sensors used
to test sunspace overheating
To do this, we placed a temperature sensor about six feet off the ground in the center of
the sunspace, and another about 6 feet high in the living room (see figure at left). We
fitted the thermistor of the sunspace temperature sensor with a radiation shield to keep
it out of the direct sunlight. We positioned the living room sensor so it would stay out
of direct sunlight, so we didn't use a radiation shield there. We set both sensors to log
readings every 16 minutes.
We expected that on sunny days, during the daytime hours the ambient temperatures in the
sunspace would be significantly higher than in the living room. This large difference in
temperature would represent overheating in the sunspace.
Data and Analysis
Here is a graph of the data we collected, plus outdoor temperature information from our weather data. The red line shows ambient sunspace temperatures,
the dark blue line shows ambient living room temperatures, and the light blue line shows
outdoor temperatures. The weather symbols at the bottom of the graph indicate the weather
patterns for that day, and the yellow shading highlights sunny days.
This graph shows how the sunspace overheats on sunny days (28 k gif)
As expected, the sunspace temperatures consistently exceed the living room temperatures in
the afternoons of sunny days.
However, we expected a more pronounced effect than we found. Some reasons we think may
account for less overheating that we expected include the following.
- This data was taken in February which is one of the colder months in central California.
If there is this much overheating in the winter, think about what the conditions will be
like inside the sunspace in the summer!
- The three weeks of this study were relatively cloudy ones, which is common for Davis in
the winter. In fact, Sunday 2/4, the first day shown on the graph, it rained the whole day
and the sunspace temperatures never rose above about 64 degrees fahrenheit.
- The ambient temperature sensor in the sunspace was placed at six feet off the ground,
vertically in the middle of the space. We placed the sensor at that level to monitor the
temperature that a person would feel while standing in the space. (A lower height may have
been more appropriate, but we felt any lower would intrude on the Siegels.) Temperatures
were probably greater even higher in the space.
Conclusions
Our hypothesis about the overheating proved true. We found that on sunny days the ambient
temperature in the sunspace reached quite high temperatures, especially considering this
study was conducted in February. The temperatures there often reached 80 degrees
fahrenheit, and one day almost peaked at 90 at occupied levels.
Though overheating does seem to be happening, at this time of year it appears that
overcooling may have a more significant impact on comfort in the sunspace. For most of our
investigation period, the temperatures in the sunspace were well below those in the living
room. The cooling that occurs in the sunspace must be due to the large amount of glazing
found there. The windows are all double-pane, aluminum-frame ones that do not have a very
high insulating value by today's standards (though they were probably state-of-the-art
when this house was built in 1978). Consequently, heat gained in the sunspace during the
day is quickly lost when the sun goes down. Every night except one, the temperatures in
the sunspace dipped below 60 F, and in a particularly cloudy cold spell at the end of our
investigation, the temperature fell below 50 F. On cloudy or rainy days (such as
Wednesday, 2/7) the temperature in the sunspace never reached the temperature in the
living room. So overcooling seems to be as important a problem as overheating in the
sunspace.
If the Siegels decide to go ahead with their remodel of the sunspace and remove the wall
to the living room, they may end up using a lot of energy to keep this space comfortable.
Unless they remove or modify some of the windows, a great deal of local heating and
cooling will continue to occur in this space, and the HVAC system is going to have to work
hard to keep up.
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