Project: Siegel House Case Study
Thermal Mass in the Sunspace:
Hypothesis, Methods, Data, and Analysis
As stated previously on the hypothesis page, we believe
the sunspace floor will act as thermal mass to help even out temperatures there.
In order to gauge whether the sunspace slab influenced the ambient temperature of the
sunspace, we decided to look for the "lag" that is characteristic of thermal
mass in action. This lag is caused by the ambient temperature of a space reaching its high
or low consistently before the thermal mass associated with that space reaches its peak
high or low temperature.
To check for this lag, we measured and compared the temperature of the slab and the
ambient temperature of the sunspace. The proper way to measure the temperature of the slab
for this analysis would be to calculate an average temperature over different depths in
the slab. However, we were only able to measure the surface temperature of the slab
because we could not drill in the Siegel's floor, so in this analysis, we use surface
temperature as a proxy for the average temperature of the whole slab.
section diagram of the sunspace
showing the location of the temperature sensors used
to test thermal mass performance in the sunspace
To evaluate this in our case, we used the data from two of the temperature sensors we
placed in the sunspace. One measured the ambient temperature of the space. The thermistor
of this sensor was located about 6 feet off the ground, and covered with a radiation
shield so it would not receive any direct sunlight. The other data set we used is from a
sensor measuring the temperature of the slab. It was located underneath a table in the
sunspace, out of the direct sun, but in the center of the room. The thermistor of this
sensor was placed against the tile floor and held in conductive contact with the floor by
Data and Analysis
This graph shows the ambient and slab temperatures in the sunspace,
and indicates where lag is occuring (14 k gif)
The graph above shows the ambient and the slab temperatures plotted for the second week in
our investigation. We have identified the peak ambient temperatures and placed a vertical
dashed lines on the graph at those points. The peak-lines associated with high
temperatures are in red, and the lines for low temperatures are in blue. We have then
placed circles on the graph to help identify the "lag" between the peak ambient
temperatures (indicated by the vertical lines) and the peak slab temperatures. As you can
see, in the circles highlighted yellow, a small lag is noticeable. In the rest of the
circles, and especially the ones highlighted gray, there is little or no lag indicated. We
take this as showing there is some effect from the thermal mass of the slab, but not a
very pronounced one. And, as indicated by the weather icons at the bottom of the chart,
the lag effect seems most pronounced on sunny days when the slab can really charge.
Our measurement techniques may have taken away from our ability to get an accurate picture
of the action of the thermal mass sunspace floor. In the temperature measurements we could
not drill down into the Siegels' floor to get temperatures at different levels in the
slab, so we have to use a top temperature as proxy. But, we feel that we can still draw
some conclusions from this data. Our graph shows either no action or only small action of
the thermal mass, and so we believe it is not a strong force in affecting the temperature
inside the sunspace.
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