| Substantial temperature sudden-drops (△Tsd) at bird level in the initial stage of pad cooling process has become the main inducement of asthma, rhinitis and other respiratory diseases for birds in summer. This problem is commom in arid regions or hot seasons and attracting increasing concerns. Preliminary field measurements have shown that the acute cold stress on birds will appear when the temperature fluctance reaches 5℃ within 20min, which will had adverce effect on birds’healths and production. In this study, outside climate affecting △Tsd was analysed. Numeraical simulation (CFD) was used to research the airflow distribution was calculated when the cooling pads were installed in different location on the end wall and sidewalls. Then the superposed influence on air distribution was studied with different combinations of cooling pads, roofs and windbreaks in tunnel ventilation. This reaserch provides the following findings:(i) The relationship between the temperature fluctance and outside relative humidity (RH0) was researched and the temperature drop would get above 5℃ when RH0≤60%. The relationships between wetted ration of cooling pads and temperature drop, the water volume and the specific wetted area of pads were researched. These will provide theory basis for constructing the new control system (NCS) against △Tsd.(ii) There are large ventilation volum during hot seaseons in intensive layer production and the area of one side of end wall can’t match the cooling pads needed. In most poultry houses, the extra cooling pads were installed on the end of longitudinal walls, and made the inlets like a "["shape. The air velocity was measured and the large zones of lower ventilation was found in the aisles adjacent to the sidewalls. The CFD simulation predicted that air velocity in the aisles close to the sidewalls can be significantly improved when the extra cooling pads are moved away for a certain distance from the end wall. For houses with 12m width, the uniformity of airflow in all aisles can be significantly improved when this distance is about 3m.(iii) The effect on the airflow distribution at birds occupied level by installation of deflectors after cooling pads and the windbreaks near roof. The results indicated that the cooled and warm air existing the pads can be completely mixed by the deflectors after pads and the temperature fluctance of mixed air can be regulated, but the air movement was changed. The windbreaks can guide the airstream above the cages to the birds occupied level. The air velocity near cages increased notably and dead zone dispeared. The suitable space distance between windbreaks is 6-9m, at this moment, in this situation, the airstream is relative straight and the air restriction is small. The lower edge of roof windbreaks has little influence on the movement path of airflow, but will affect the cross-sectional area of the tunnel ventilation. Therefore, it should be installed as low as possible in the case of normal operation of other equipments.(vi) On the basis of these studies, NCS was contructed for pad cooling system. The temperature near the exhuaxt fans (Tlast) was used to control the startup of pump. When Tlast reached to the max temperature preset, the NCS would judge the the range of RH0 at that moment and control the running state of pump. When RH0≥80%, the pump will not run because of poor cooling effect. When 60%<RHo <80%, the pump will be controlled by "on-off" mode. When RH0≤60%, the pump was controlled by "4-stage" mode. The field testing of NCS was carried out and show the temperature fluctuation of bird level was maintained with 3.5℃ and △Tsd was successfully avoided. |
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