Abstract
So-called energy crisis has become a serious world problem of late, and in air conditioning facilities, adoption of some sort of counter measure for the conservation of energy has become a necessity. And a concrete guide on the energy conservation problems in air conditioning system has been given by ASHRAE standard (ie: 90-75 entitled Energy Conservation in New Building Design) published in 1975. Cooling with outdoor air as one of the approved methods for the energy conservation in air conditioning system is introduced in this standard. In Japan, this method has already been adopted in a number of buildings since 1960's. However, unfortunately the detail quantitative estimations on the effects of energy savings does not seem to be established as yet. Therefore, we first pursued the effects of cooling with outdoor air by selecting a model building and estimating hourly heat-gains and heat-losses through a year. The following conditions are assumed in our trial calculations. 1) Model building: Office building having 11 floors with 2 basements. a) Total floor area is 5600m^2. b) Construction is reinforced concrete. 2) Air conditioning system: All air single duct system. 3) Indoor design condition: Summer; DB 26℃, RH less than 70% Winter; DB 22℃, RH less than 70% 4) Zoning: a) Single zone containing a whole building. b) Zoning into several divisions. i) 9th floor zone ii) East side zone including from 1st to 8th floor. iii) West side zone including from 1st to 8th floor. iv) 1st basement floor zone. 5) Required fresh air: 20m^3/h・man. We obtained the following results from our calculation on the basis of those assumptions. 1) Where a whole building is regarded as a single zone, the possible time of cooling with outdoor air is 11.5% of operating time through a year when the indoor temperature is maintained within the design condition. 2) The possible time of cooling with outdoor air is 15.3% of operating time through a year in the case of permitting the fluctuation of the indoor temperature between ±1deg. 3) 1.89% in the case of permitting the fluctuation of indoor temperature between ±2deg. In spring (April, May and June) and in autumn (October and November), so-called intermediate season in Japan, the ratio mentioned above were estimated at 23.4%, 31.1% and 36.9% respectively. Cooling with outdoor air can be done with either intermittent operation or continuous operation a day. However, it is undesirable that cooling with outdoor air, cooling by the use of chiller and heating by the use of boiler are alternately operated in a day, from the maintenance stand point of air conditioning system. Therefore, we pursued next the frequency-period when this cooling method is able to operate continuously for more than 3 hours in a day and then, the values of energy savings were checked, too. As a result, the values of energy savings of a whole building were estimated at 6.3% through a year and 17.1% in the intermediate season when the indoor temperature is maintained within the design condition. So, we feel that the cooling with outdoor air is one of the most available methods for the energy conservation in air conditioning system if an optimum self-controlled operating system is adopted.
