Abstract
This paper presents a feasibility study of a fresh air load reduction system by using an underground double floor space. The fresh air is introduced into the double slab space and pass the opening bored through footing beam. The air is cooled by the heat exchange with inside surface of the double slab space in summer, and heated in winter. Then the heat is transferred to the adjacent soil through foundation slab and wall and to the room just above the mat through floor slab. The initial cost of the system can be reduced, because it doesn't need a pipe or duct in the ground as does the cool-tube system. A simulation model based on the simple 2-dimensional heat conduction equation was developed to simulate characteristics and performances of system. Validity of thermal simulation model was confirmed by comparison with field measurement. Using this simulation model following three issues were examined. Firstly, three factors that have effect on the system performances were investigated. It was shown that almost same annual thermal performance was obtained regardless the depth of earth-tube (examined for 0.7, 1.4 and 2.8m of depth, these are considered as realistic depth for actual building). The difference of annual cooling/heating rate by changing the room temperature just above floor slab as realistic range was below 8%. As air velocity become faster (0.05〜0.5m/s), annual cooling/heating heat rate increase from 5GJ/year to 420GJ/year for effective heating surface of 35〜7000m^2. Secondly, effect of fresh air load reduction was investigated. It was confirmed that this system is very effective to reduce fresh air load at different air velocity and effective heating surface, by annual fresh air reduction rate in different air velocity is 0.6〜37% for effective heating surface 35〜7000m^2. Finally, method and chart for judgment of introducing this system by comparison with the performance of total enthalpy heat exchanger was shown.
