In order to properly estimate the renewal and maintenance costs of air-conditioning equipment, it is necessary to establish the optimal renewal cycle considering equipment deterioration and failure. As a method to understand the tendency of equipment failure with age, there is a method to collect and analyze operation data as well as repair history for each equipment over a long period of time. However, it is not practical in terms of time and cost.
This study proposes a method to properly estimate the renewal and maintenance costs of air-conditioning equipment by using the periodic inspection data of air-source heat pump chiller (AHP) that is the main component of the air-conditioning system and is greatly affected by failures. In general, periodic inspection data is easy to collect, and shows the past diagnosis result of equipment at a given interval. The evaluation of the lifetime characteristics of AHP is performed by reliability analysis using the Weibull process model based on the degree of deterioration and repair history information that are collected from the periodic inspection data.
As a result, a theoretical equation for optimizing the relationship between the usage period of AHP and the renewal and maintenance costs is figured out. AHP cost optimization with the actual failure and cost data is evaluated using the theoretical equation.
The followings are main points of this study:
(1) Repairable system data for reliability analysis are prepared from the periodic inspection data. Poisson's process, non-homogeneous Poisson's process (NHPP), and regeneration process are known as models of repairable systems. This study proposes a Weibull process model adopting NHPP.
(2) The proposed Weibull process model can be applied not only for predicting failure occurrence and degradation progress, but also for evaluating the renewal cycle of equipment by combining it with cost information.
(3) Two theoretical models are proposed: the Weibull process model for the repairable system data that can account for covariates and the model for optimizing the relationship between equipment costs and repair costs using failure tendency.
(4) As a result of the evaluation of the renewal cycle of AHP using the failure and deterioration information that is obtained from the repairable system data, it turns out that about 30 years is the most economically reasonable.
(5) The cost-optimization model can be applied to the system evaluation of multiple equipment. Furthermore, it can be developed into a model that can evaluate the renewal cycle of equipment based on the actual situation by considering the energy consumption efficiency of the equipment.
(6) It is necessary to continue to accumulate field data on degradation and failures of equipment in order to understand the failure tendency more accurately based on the actual condition with reliability analysis using the Weibull process model.
