Field Measurement of the Thermal Resistance of Office Buildings Available to Purchase

The results of field tests conducted during the winter heating season on the thermal performance of the building envelopes of eight office buildings situated in various climatic regions are presented. The exterior envelopes of these buildings are masonry and metal-panel-faced construction of different designs. In situ measurements of heat flow through the envelopes and of air temperatures were made using heat flux transducers, portable calorimeters, and thermistors. The influences of the length of measurement period and the time lag between the air temperature difference across the envelope and the heat flow on the determination of the thermal resistance are described. The calorimeter measurement generally gives lower wall thermal resistance values than the heat flux transducer because of the additional heat flow through highly conductive framing members. Heat flow and air temperature measurements carried out over a period of 48 h and longer are found to provide satisfactory thermal resistance data. The measurements' accuracy can be improved through correction of the data for time lag. The masonry and metal-panel-faced exterior walls of these buildings tested have widely varying thermal resistances, ranging from approximately 0.5 to 5.6 m² · K/W (3 to 32 ft²·h·°F/Btu). The measured values deviated from the predicted values by an average of 22%, and in one case by as much as 71%.