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Vital Signs
Project: Siegel House Case Study
Hypothesis Development and Hypotheses
Following our visit to the Siegel House, we regrouped back at Berkeley to discuss our
preliminary findings and decide on the hypotheses that we would test in this
investigation. This page presents our findings after a day with the Siegels and then the
five hypotheses we eventually settled on. It briefly discusses how and why we chose each
hypothesis, and then at the end of each hypothesis statement, a link connects to the data
and analysis associated with that hypothesis.
Preliminary Findings: Uncomfortable Conditions
Motivated Changes to the House
Almost before our investigation began, we discovered some interesting facts about the
Siegel House that helped us shape our hypotheses.
The Siegels are the second owners of this house--the first owners moved out after only 2
years--and they have made some major modifications since they moved in, 16 years ago. Most
important, they were never happy with the ability of the thermosiphon loop design to keep
the house comfortable in winter or summer. They added a central heating and
air-conditioning system so they could keep the house warm enough during the winter, and so
they could cool the house during the 2-3 worst weeks of the summer. Also, they replaced
the wood stove in the living room with a high-efficiency wall fireplace that uses air
ducts behind the fire enclosure to recover heat by venting air around it.
Another problem area that the Siegels addressed is the kitchen. Because there was a
two-story ceiling above that space, the Siegels were always cold there due to the heat
rising up away from them as they worked on the first floor. They added a floor above the
kitchen area at the east end of the living room, splitting the open two-story space into
two floors. This modification mitigated the cold feeling in the kitchen and provided some
additional living space--Mr. Siegel now has his office in the upstairs section.
They also added a row of operable windows high on the south wall that separates the living
room from the sunspace. The windows bring extra light into what they considered an
overly-dark living room, and allow them to vent warm air from the sunspace directly into
the living room. They also think that there is some direct gain of solar energy through
these windows and into the thermal mass in the living room.
 A
baffle obscures the location where the
top ducts should be located
This last modification may have affected the thermosiphon loop. The windows were installed
up near where the openings to the ducts are. Unfortunately, there is a baffle that
obscures the point where the roof of the sunspace meets the wall, so a simple inspection
from floor level does not reveal if the ducts are still open.
 Section diagram of the
blocked thermosiphon loop (10 k gif)
Regardless of the what's happening at the ceiling, the bottom ducts are definitely
inoperable. The Siegels stuffed these with newspaper because they felt that cold air was
circulating, via the ducts, underneath the floor of their living room and cooling it. They
blocked the ducts to prevent this cooling.
When asked about losing any heat they might have gained from the loop system, they said
that they didn't think the loop ever worked that well, so there wasn't much of a loss, if
any. They rarely felt any airflow moving through the ducts when the house was in its
original configuration.
Hypotheses
Based on these findings, we developed five hypotheses about the physical performance of
the Siegel House to test. The five hypotheses are presented here, then each is described
in more detail on the rest of this page.
- The sunspace will overheat on sunny days.
- The rock storage is acting as thermal mass, though not in the manner
intended by the original design.
- The sunspace floor should act as thermal mass to help even out
temperatures there.
- The sunspace will exhibit extreme radiant temperatures which will act in
parallel with high and low ambient temperatures to create uncomfortable conditions.
- The two-story open living room will exhibit a significant stack effect.
Sunspace Overheating
 Interior
view of the sunspace in the
Siegel House, looking east
Our first hypothesis is based on the fact that the thermosiphon loop in the Siegel House
did not seem to be working. We were disappointed that we would not get a chance to test
this passive solar strategy we had often read about. We figured, however, that if a main
design feature of the house was not working properly, we should be able to discern some
clear consequences in our temperature data.
To formulate our hypothesis, we began by investigating the way the loop should work. As we
discussed in the Passive Solar Features
section of this report, the theory behind the system is that the sunspace collects solar
energy, the ducts transfer the energy, and the energy is stored in the "rock
tubes" where it is given off at night when it is needed. If the transfer mechanism is
not working, then the sunspace should have no way to exhaust the energy it collects and
the rock storage should not have any energy to store and release as designed. In other
words we expected the sunspace to be hotter than it should and the rock storage to be
cooler than it should. For our first hypothesis, we focused on the sunspace only.
Hypothesis 1: The sunspace will overheat on sunny days.
Methods, data, and analysis for this hypothesis
Thermal Mass in the "Rock Tubes"
 View
of the rock storage tubes in the
Siegel House, looking north
Concerning the "rock tubes," we believe they are also unable to function as
thermal storage as originally intended due to the modifications made to the Siegel House.
The loop is blocked, so heat from the sunspace cannot charge the rock mass in the tubes.
Through talking with the Siegels, however, we discovered they believed the rock tubes were
in fact working as thermal mass, though not in the manner intended by the original design.
They believe that one of their remodels created a different way for the thermal mass to
act.
The Siegels added windows high on the wall that separates the sunspace from the living
room. The Siegels believe that these windows allow sunlight to directly strike the rock
tubes, and thus charge them with heat. The day we were in their house it was raining, so
we could not investigate this claim through observation. So, we hypothesized that the rock
tubes do act as thermal mass, and proposed to use a profile angle calculation, the data
from our temperature sensors, and a computer simulation run using Energy-10 to
prove the claim.
Hypothesis 2: The rock storage is acting as thermal mass, though not in the manner
intended by the original design.
Methods, data, and analysis for this hypothesis
Thermal Mass in the Sunspace
 The sunspace in
the Siegel House
Our third hypothesis is rooted in discussions with the Siegels about their sunspace, and
from thinking about the thermal mass of the "rock tubes." Through discussing
their house with them, we learned that the Siegels are planning a remodel of their living
room and sunspace. They feel that the sunspace is unusable to them most of the time
because it is either too hot or too cold! They also feel that it isolates them from the
outside by creating an unusable space between their living area and the yard.
To fix this problem, they want to take out the wall that separates the sunspace from the
living room, and eliminate some of the windows in the sunspace. They feel that taking out
the windows will help reduce the overheating in the space, and connecting it to the living
room will allow the temperature there to be influenced by the central heating and
air-conditioning system.
With our first hypothesis, we hope to help explain some of the overheating problems, but
thinking about thermal mass in conjunction with our second hypothesis led us to consider
the thermal mass in the concrete slab floor of the sunspace. "How it might work to
even out temperatures in the sunspace?" we asked ourselves. The sunspace seems to be
just the kind of space we described as being suitable for thermal mass use--it heats up
significantly during the day and cools off significantly at night. So, the mass in the
floor should help even out temperatures in the sunspace.
Hypothesis 3: The sunspace floor should act as thermal mass to help even out temperatures
there.
Methods, data, and analysis for this hypothesis
Radiant Temperatures in the Sunspace
After developing the previous hypothesis about mass in the sunspace floor, we thought
further about the overheating problem. We realized that much of the discomfort in the
sunspace may be due to extreme radiant temperature swings in the sunspace, and not solely
due to high and low air temperatures. We think these radiant temperatures would overpower
any effect the mass of the floor might have to even out the air temperatures there.
Hypothesis 4: The sunspace will exhibit extreme radiant temperatures which will act in
parallel with high and low ambient temperatures to create uncomfortable conditions.
Methods, data, and analysis for this hypothesis.
Stack Effect in the Living Room
 A view of the
Siegel's
two-story living room
We began putting together our last hypothesis by considering one of our discussions with
the Siegels. The discussion was about why they added the floor above the kitchen, dividing
the open two-story space into two floors. They felt that a lower ceiling over the kitchen
would help keep that space warmer by preventing all of the warm air from rising up away
from the people in that area. The fact that the kitchen was an uncomfortable place to be
frustrated them greatly, and even after the remodel, they still consider the kitchen to
be, in their words, "terrible to use."
We decided it would be interesting to investigate this stack effect in the part of the
living room that continues to be open for two storys. Such an effect would have
significant energy-use implications because all the warm air would rise up away from
people to an unoccupied area, as well as making the first floor cooler than might be
comfortable.
Hypothesis 5: The two-story open living room will exhibit a significant stack effect.
Methods, data, and analysis for this hypothesis
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