Schemes and measures to prevent flue gas recirculation In the centralized smoke exhaust system that has been put into use, the scheme for preventing flue gas recirculation can be basically divided into two types: one is to rely on the special structure inside the vertical flue to stop the back; One is to rely on a check valve on the outer branch of the vertical flue to stop. The former solution has no action mechanism, and can avoid the sticking of the oil and the sticking of the check valve after a long time of use. In the early days, the mother-in-law flue was adopted, that is, the exhaust of the kitchen in this floor first entered the sub-flue, and after rising one layer, it was transferred to the mother (main) flue. Later, the transformer-type flue was developed, relying on the contraction of the cross section in the main flue at the entrance of the user branch pipe, and the static pressure generated by the increase of dynamic pressure to avoid backflow. The common feature of these flue ducts is that the structure is relatively complicated and the requirements for production, installation and commissioning are high. Once the interior decoration is completed, it is difficult to eliminate any faults in the flue, and the quality inspection department cannot check the internal quality. The latter solution simplifies the vertical flue to a single-tube flue, making fabrication, installation, and acceptance much easier. Even if a small amount of sediment is accidentally dropped during construction, it will not block the flue or change the smoke exhaust performance. Moving the check function to the check valve outside the flue greatly facilitates installation and maintenance. Quality inspection and property departments can detect and manage at any time. The check valves that have been used in the city are mainly of gravity type and electromagnetic type. The gravity type structure is simple and the cost is low; the electromagnetic action performance is more reliable and the price is higher. After many improvements, an oil filter net is added in front of the valve to extend the valve usage time. If you find that the action is not working after long-term use, you can take it off at any time. The valve body and the valve plate are made of aluminum alloy, which meets the fire protection requirements. For this reason, it is recommended to use a vertical exhaust flue centralized discharge scheme with a check valve.
The amount of exhaust air volume is related to the effect of the exhaust smoke and the cross-sectional area of ​​the flue. Since the relevant national standards have not yet been formulated, it is still a question to be continued. The amount of exhaust air is first related to the performance of the range hood used. Generally, the exhaust air volume of the range hood can reach 500m3/h or more in a free state. When the system resistance increases, the exhaust air volume will drop significantly. The performance of the deep-cover type range hood currently popular on the market is better than this model, so the flue design based on this measured model is relatively safe. The early design standards of Shanghai were limited by the economic conditions at that time, and the design air volume per household was 200m3/h. The reason is that the size of the residential kitchen at that time was small, and the architectural design strictly controlled the cross-sectional dimensions of the vertical exhaust flue. In recent years, due to the improvement of residential design standards, the average kitchen area is above 5m2, and the new design standard is intended to increase the exhaust air volume to 250m3/h.
The simultaneous use of the coefficient and the use of the coefficient are also related to the cross-sectional area of ​​the flue. In general, the more residential floors, the smaller the usage factor. According to the survey, the multi-zone residential 530-630 hood at the same time the maximum operating rate of 50%. Although this period of time is the most concentrated period of cooking in a day, since the cook usually only starts up when the oil pan is used, the coefficient of use is not high at the same time. In the early design, the simultaneous use coefficients of 60% (six layers or less), 50% (sixeen layers or less) and 40% (less than 30 layers) were used. Considering that some residents in the field often belong to the same unit, the commute time is relatively consistent, and in order to improve the design standards and ensure the emission effect, it is proposed to increase the simultaneous use factor to 83%, 72% and 60% respectively. The starter is concentrated at the bottom as the most unfavorable condition.
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