Determination of the overall heat transmission coefficient (u-value) of vacuum glazing

The heat flow through a 1m x 1m sample of vacuum glazing has been measured in two independent ways. One measurement method uses a guarded hot box to make a direct determination of overall heat-transmission coefficient under standard test conditions. The other method uses a small-area guarded hot plate (specially designed for this purpose) to measure the local radiative and (negligible) gas conductance between the glass sheets. This instrument is also used to validate calculations of the heat flow through the support pillars. The overall heat flow is then obtained by combining the contributions from these processes with those due to heat flow through the conducting edge seal. The results obtained with the two methods are in very good agreement for the same external conditions. These results provide the first independent validation of estimates of heat flow through vacuum glazing based on the five separate processes that contribute to this heat transfer.Peer reviewed: YesNRC publication: Ye