Reliability Field Test of the Air–Surface Temperature Ratio Method for In Situ Measurement of U-Values

Abstract

This study proposes the air-surface temperature ratio (ASTR) method as an in situ measurement method to rapidly and accurately measure wall U-values in existing houses. Herein, the wall U-values were measured in situ applying the heat flow meter (HFM) method of ISO 9869-1 and the ASTR method. The results obtained using the HFM and ASTR methods were compared, and the relative error rate and accuracy of the measurements were analyzed. The aging rates of the wall U-values were compared and analyzed by comparing them with the wall U-values before and after the installation of retrofit insulation. Subsequently, the ASTR method was used to analyze the U-value measurement error rates according to the number of measurement days (one day to seven days). In addition, this method calculated the appropriate measurement period required to satisfy the measurement conditions. As a result, the mean relative measurement errors rates of the HFM and ASTR methods were ±3.21%. The short-term (one day) and long-term (seven days or longer) measurement results indicated the average error rates as approximately ±2.63%. These results were included in the tolerance range. Therefore, it was determined that the ASTR method can rapidly and accurately measure wall U-values.

Comparison of Infrared Thermography and Heat Flux Method for Dynamic Thermal Transmittance Determination

“…(4) The minimal measurement period should be 72 hours for stable boundary temperatures; otherwise, it should be more than seven days. (5) The minimal indoor and outdoor air temperature difference should be 10 • C. (6) It is necessary to achieve quasi-stationary conditions three to four hours before the measurement. 7The U-value should be approximated for the first 24 hours and 2/3 of the overall measurement period.…”

“…T e,j = T e,j − T e,j−1 /∆t (6) where ∆t is the time interval between two measurements. If m time constants are chosen (τ 1 , τ 2 , .…”

“…Designed and measured thermal characteristics (U-values) will decline during the time of building occupancy. It is clear these buildings require energy renovation to decrease energy consumption and increase energy efficiency, but to be able to calculate energy savings as well as return on investment one needs to know a baseline value of energy consumption, which means the real U-value of building elements must be known [6]. There are existing methods which are being used to determine (approximate) the U-values of existing building elements, like [7].…”

“…Repeating the steps(5) and(6) until the smallest square deviation S min is obtained. (9) A good approximation {Z} * of the vector {Z} is obtained this way.…”

Thermal Transmittance Measurements of the Historical Masonries: Some Case Studies

“…. is an exceedingly accurate diagnostic method when the data measured via the in situ measurement of thermal transmittance is in a quasi-steady state" [1,24].…”