Research On Field Detection And Identification Of Heat Transfer Coefficient Of Building Envelope

The heat transfer coefficient of building envelop is essential to the building energyconsumption, so the heat transfer coefficient has become an important parameter forfield detection in building energy efficiency. But at present，in our country the most usedheat flow meter method is limited by high temperature of indoor and outdoor, longdetection time and so on, the heat flow meter method can not be used comprehensivelyin our field detection in building energy efficiency, which has affected the work of thebuilding energy saving development actively in our country, therefore looking for a heattransfer coefficient of building envelope on-site detection method which is suitable forChina’s national conditions but not restricted by detection environmental conditions andshort detection time, it is the problem to be solved urgently for energy-savingconstruction workers. This paper aims to study on finding a rapid field detection methodof heat transfer coefficient of building envelope，which is suitable for China’s nationalconditions.The cold box-heat flow meter was used for on-site detection method in this paper,based on the hardware equipment selection of detection system and software design ofdetection system with VB language in the computer, and formation of the scene detetionsystem for the heat transfer coefficient of building envelope. Use the detection system toexperiments in the standard test conditions and non-standard conditions of indoor andoutdoor temperature, it can be not only tested the accuracy of the detection system instandard test conditions, but also obtained the larger error of the detection system in thenon-standard conditions; According to the detection results in the non-standardconditions, the author has established a heat transfer process model based on the theoryof system identification and identified it with the MATLAB system identificationtoolbox, finally, compare and analysis the detection results. The primary conclusionswere summarized as follows:1. Under the standard detection conditions (that indoor and outdoor temperaturewas over15℃), used the development detection system of heat transfer coefficient ofbuilding envelope to carry on experiment, the result showed that: The measured valueof the wall heat transfer coefficient with the detection system was smaller6%than thetheoretical value, the error in the practical project was allowed.2. Under the standard detection conditions, used the detection system for field detection during the2days of testing time, the detection results can be basically reachthe standards detection effect, effectively shorten the detection time.3. Under the non-standard detection conditions (that indoor and outdoortemperature was below15℃), used the detection system to carry on experiment, theresults showed that: The relative error of the heat transfer coefficient by detectingincreases with the decreases of the indoor and outdoor temperature, the relative errorwas19.4%when the indoor and outdoor temperature was in range of [10,15]℃.4. Under the non-standard detection conditions, using MATLAB systemidentification toolbox for identification, the results showed that: The relative errorsbetween the heat transfer coefficient obtained by the identification method and thetheoretical value was smaller than the cold box-heat flow meter method, and theaccurate of the identification algorithm obtained results improved with the indoor andoutdoor temperature increases,when the indoor and outdoor temperature was in therange of [10,15]℃,the relative errors could be reduced to9.7%.