Study on Electric Heat Source Aging based on Long-term Operation Records

<p>In recent years, there has been a growing interest in energy conservation and reduction of CO2 emissions throughout the life cycle of buildings, and as an effective means, operational improvement using data stored in a building automation and control system(BACS) is widely recognized. Heat pumps for air conditioning systems, which consume the most amount of energy in a building, are expensive building equipment. In addition, they are operated for a long time in the life cycle of the building. Therefore, maintenance to sustain their efficiency is very important. Against this background, this study analyzed long-term BACS data of heat pumps, examined the methods of "Unification of conditions to be able to compare" and "Set standards for comparison" for the degree of aging, and proposed a method that enables a quantitative evaluation. Specifically, Section 1 analyzes the attributes of the heat source equipment within the scope of this study, Section 2 investigates a method to compare the efficiencies of heat pumps in order to unify comparison conditions, Section 3 focuses on standards for comparing the efficiency of heat source equipment, Section 4 evaluates the degree of aging using the proposed method and reflects the findings of Sections 2 and 3, and Section 5 performs a trial evaluation of the maintenance effect using the proposed method. The scope of analysis is BACS data for centrifugal refrigerators (n = 63) and air heat source heat pumps (n = 24) (approximately 11 years on average), which are maintained at the manufacturer's recommended level. As a result, the following findings were obtained. (1) The variability ratio of COP was defined as an index for evaluating the degree of deterioration by a trend analysis of the explanatory variables used in the multiple regression equation. After examining the interval for calculating the variability ratio of COP, it was concluded that an interval of 100 h is appropriate. (2) For the data period used for the multiple regression analysis, it was shown that the data of the entire period was suitable to evaluate the change in the efficiency over time. In contrast, when the period is limited, it becomes easy to detect operation changes within the period. Additionally, this indicates the possibility that this method can be used for fault detection. (3) When evaluating the degree of deterioration using the variability ratio of COP, the effects of explanatory variables varied depending on the model, and the fluctuation range of the variability ratio of COP depended on the fluctuation range of the explanatory variables. (4) As a result of the evaluation, the variability ratio of COP of the centrifugal refrigerators and the air heat source heat pumps was generally within the ± 10% range, and as a median value, no aging was observed within the scope of analysis. (5) In order to evaluate the performance change due to maintenance using the proposed method, a comparison was drawn with a total of 257 maintenance records (brush cleaning, chemical cleaning, O/H). As a result, an approximately 2/3 improvement was observed before and after maintenance. This fact verifies the hypothesis that “there is a possibility that the condition after maintenance is maintained close to the condition at the time of installation, regardless of whether it is good or bad, by performing maintenance”. </p>