Although the floor's surface temperature would
The temperature sensors used at the addition
be slightly lower at the outer edge, the design
were type-T, copper-constantan thermocouples.
strategy was to use the additional heat lost to the
The sensor wires were crimped together at the end
subgrade to keep the footing frost-free.
and coated with an epoxy. A cap was then heat-
Also note in Figure 4b the non-frost-susceptible
shrunk around the sensor to make it completely
(NFS) drainage layer, perforated drain tile, and 8-
waterproof. The thermocouples were connected
mil plastic film. These are specified to minimize
to low-resistance switches located inside the addi-
any moisture from coming in contact with the
tion and read using a digital thermometer. The
insulation or foundation.
overall accuracy with the type-T sensors is
The temperature strings were read once a week
by the weather technicians. Because it is a first-
Temperature sensors were installed along the
order weather station, meteorological data were
east side of the addition because it was thought
that the coldest ground temperatures would occur
there. The building profile is narrow along this
side and thus the heat loss from the building to the
ground is minimal. Also, the east side of the addi-
Construction on the foundation began in June
tion is kept free of snow for vehicle parking.
1990 and the project was completed in December
During the spring of 1990, 64 temperature sen-
1990. No precise length of time can be attributed
sors were installed to get a temperature profile of
to the foundation construction phase because the
the SIF. After a winter's worth of data, it was obvi-
crew was continually pulled from the site to work
ous that additional sensors would be needed be-
on other projects. However, conversations with
cause the frost line was penetrating deeper than
the site foreman revealed that a substantial
anticipated and more detailed temperature infor-
amount of time was saved: he estimated the SIF
mation was needed under the ground insulation.
took 12 weeks to complete whereas a conven-
Sixteen additional sensors were installed during
tional foundation would have taken 34 weeks.
the summer of 1991. The location of all sensors can
Construction of the SIF is similar to a conven-
be seen in Figure 5.
tional foundation and is very straightforward.
Because of scheduling conflicts, temperature
Figure 6 depicts the excavation along the east side
sensors were not installed above the slab insula-
of the addition. The laborers are leveling the bot-
tion or within the floor itself. This would have
tom of the excavation; the footings will be placed
been useful in determining the comfort level of the
at this elevation. In Figure 7 the footing and stem
floor. Comments on comfort were verbally provid-
wall have been poured and the excavation has
been backfilled to the top of the footing. (The man
ed by the weather technicians using the facility.
Figure 5. Location of temperature sensors.