Abstract
The energy consumption in the commercial buildings sector has been still increasing in Japan. Especially, that for cooling and heating demands accounts for about 30%. In exciting buildings, which have an overwhelming proportion in the construction market, there is the possibility that the cooling / heating load is different as that at the point of design of the air conditioning system. Commissioning, which is a process to analyze the performance, find problems and apply adjustments, is an effective solution for operation improvement in such buildings.
We have investigated the effect of operation improvement through commissioning for a central heat source system installed in a hospital facility which has the total floor area of 13,364 m2 and 100 beds for in-patients. Possibilities for further energy saving were discussed based on the analysis of the seasonal variations of cooling / heating load and the system performance using the BEMS data. Several kinds of operation changes were examined by computer simulation using the Life Cycle Energy Management (LCEM) tool. We further demonstrated the effect quantitatively by applying the operation changes in the facility and also discussed the differences between the calculation and measurement.
The heat source system had two units of gas-driven absorption type chiller-heaters (ABS) and two units of electricity-driven air source heat pump chillers (ASHP) with ice storage function, where each capacity for cooling was 633 kW and 206 kW at the rated condition. The annual primary energy consumption was 2,153 MJ per the total floor area, which was about 14% smaller than the value from the DECC database. This is probably due to few surgical operations that consume a large amount of energy for sterilization and air conditioning. About half of the total energy was used for air-conditioning, in which two third of that was in the form of electricity.
At the original operation during cooling, chilled ice was stored in the one or two units of ice storage in the nighttime; the cold energy was used for cooling in the daytime. The rest of the cooling load was covered by the ABSs. We found that the heat sources produced too much cold energy compared to the cooling load throughout the season. The ice storage operation also resulted in a relatively lower thermal efficiency, which was a ratio of the energy consumption to the covered cooling load, than the ASHP without storage or the ABS. We therefore proposed decrease of number of the operated heat sources and non-storage operations. Simulations by the LCEM suggest that the maximum load can be covered by the one ABS, and the ASHPs lead to energy reduction in the low load period. As the result of the operation changes in the facility, we finally obtained energy reductions of 29 % in June and 18% in July in 2014.
In the heating season, the ABSs were originally operated throughout the season. The produced heat usually reached 1.8 times as large as the heating load. This is due to the large capacities of the ABSs compared to those of the ASHPs. We therefore proposed to adjust the produced heat by use of the ASHPs also for heating. The operation change provided an energy reduction of 25% in 2014 whereas the LCEM simulations predicted an effect of 40% in maximum. The difference seems to be due to a problem in the actual piping, where produced heat once passes through the storage tank even in the non-storage mode.
We conclude that a certain amount of energy reduction can be obtained by commissioning for the heat source system in both the cooling and heating seasons.
