APPENDIX/DIAGNOSTICS
Portable Calorimeters
Portable calorimeter boxes have been developed to measure in-situ envelope R-values, though the
measurement procedure has not yet been standardized. The technique can be used in new or
existing buildings, as long as there is a sufficient indoor-outdoor temperature difference. The
calorimeter is a five-sided, insulated box containing an electric heater. The open side of the box is
sealed against the outside wall that is being tested. Once installed, the heater is controlled to
maintain a zero degree temperature difference between the box and the building interior; thus all
the heat supplied to the box passes through the wall to the outdoors. The dimensions of the box
can vary but should be large enough to include several stud spaces so that their effect on the R-
value is included in the measurement. The test requires a fairly constant indoor temperature and an
o
O
average indoor-outdoor temperature difference of around 10 C (20 F). The outdoor temperature
need not be constant, but it must always be below the indoor temperature. The test must last
several days in order to avoid inaccuracies associated with envelope thermal mass effects, and the
test wall should not be subject to any thermal loading due to solar insolation. A more detailed
description of the technique and additional references is contained in Persily (1986 and 1988).
Heat Flux Transducers
The heat transmission of small areas of the thermal envelope can be measured with heat flux
transducers. The use of these devices to measure heat flux rates is described in ASTM C 1046, but
this standard does not describe their application for measuring wall R-values. Additional
information for this particular application is given in Persily (1986 and 1988). Heat flux transducers
are thin devices composed of a thermopile for sensing the temperature difference between the two
sides of the device. The thermal resistance across the transducer is known, and therefore the
measured temperature differences across it can be related to the heat flux through it. In a heat
transmission measurement of a wall section, several heat flux transducers are affixed at key
locations on the wall, and the heat flux at each location is monitored over time. The heat flux
measured at these locations is then related to the average temperature difference across the wall
during the test to determine its R-value. These measurements can be made on an envelope mock-
up, given some means of maintaining a temperature difference across it during the test. More
commonly, these measurements are made in the field.
PAGE D-3
Previous Page
