Recently, the heat source renewal in existing office building has increased. In addition, many simulations have clarified that downsizing at the heat source renewal is effective in terms of both primary energy consumption and life cycle cost. Nevertheless, in most cases, the careful consideration is not clear at the heat source renewal, and the same equipment capacity as before the heat source renewal is selected. Probably, many engineers recognize the importance of selecting an appropriate equipment capacity based on their knowledge and practical experience. However, it is difficult to propose heat source downsizing, considering risk when a complaint occurs due to lack of capacity.
Therefore, to make it easier to propose heat source downsizing at the heat source renewal while suppressing risk of indoor environment deterioration, it is important to examine the feasibility due to heat source downsizing and envelope performance improvement in terms of both primary energy consumption and life cycle cost. The aim of this study is to the suppress selection of excessive heat source capacity and to promote the envelope performance improvement at the renewal. The results are as follows:
1) In the simulation model of existing office building that has reached at the heat source renewal in snowy cold cities, the building specifications were set from the previous investigation, and the air conditioning equipment specifications were set from the equipment selection by the peak heat load. Through this process, it was confirmed that the finally selected equipment capacity was more than 30 % higher than the peak heat load.
2) In the feasibility study by indoor environment evaluation by PMV, the heat source capacity that could maintain the indoor environment almost the same as before the heat source renewal was selected. Alternatively, it was clarified that there were more possible to size down for two size of BH and 1 size of GAR after envelope performance improvement.
3) Through this simulation, compared to before the renewal, it was confirmed that about half of refurbishment cost could be covered by the reduction in initial cost, against the increase in cost after envelope performance improvement. As a result, it was clarified that the reduction effect is 33 % in terms of primary energy consumption and 28 % in terms of life cycle cost at the maximum.