A “heat recovery hybrid ventilation system” is the combination of passive stack ventilation and mechanical push-pull ventilation. Two heat storage boxes are connected to the natural EA stack and the underfloor natural OA duct. The alternation is done periodically in a way of that the outdoor air is drawn through one of 2 boxes contains earth tiles and the indoor air is exhausted through the other box. After the heat in the exhaust air is stored in the box connected to the stack in time of the natural ventilation, the stored heat is recovered by the supply air in time of the mechanical backward ventilation. The system functions reversed in the box connected to the natural OA duct. Fan operation is controlled by the air temperature in in-outside chambers of the box.
The purpose of this study is the development of the heat storage box and the appropriate control system. First of all, the prototype box was made considering space to install and the sizes of parts as follows.
- Box: Readymade Expanded Polystyrene box size of 600mm long, 350mm wide, and 200mm deep inside.
- Earth tile: Interior finishing tile made from diatomaceous earth size of 6.5mm thick, 300x150mm.
- Backward fan: 12V DC propeller fan with 120mm in diameter
In this paper, we proposed the numerical simulation model to simulate heat transfer in the heat storage box and evaluated the adequacy of the model by comparing the measurement and the numerical simulation results on the prototype box. The measurement has been done in 2 constant temperature rooms, and the exhaust fan was installed to simulate natural stack ventilation.
As a result, assuming that the amount of heat storage material is about three times as high as that of the prototype box and the EA / OA is switched when the outside and inside temperature of the box becomes the intermediate temperature between the room and the outdoor, it is estimated that the heat recovery efficiency is about 70% and switching time is 16 - 17 minutes.