What Are the Different Types of Building Ventilation?

Building ventilation is divided into natural ventilation and mechanical ventilation, which means that the polluted air in the building is discharged directly or after purification, and then fresh air is added to maintain the indoor air environment in compliance with hygienic standards. Its purpose: to ensure the exclusion of indoor pollutants to ensure the thermal comfort of indoor personnel to meet the needs of indoor personnel for fresh air.

Ventilation can be used

Provides the necessary amount of oxygen for residents' life, mainly breathing and cooking, preventing excessive CO ₂ and unpleasant odors. Because of people's breathing, the indoor air is polluted anyway. Ventilation is required to replace fresh air. It is estimated that adults need about 30 m ³ of fresh air per hour, so the number of people in the room is particularly important. Yagro et al. Gave the ventilation efficiency, that is, the ratio of the effective air flow in the entire area to the total air supply.

Air temperature has a great relationship with indoor odor. When the indoor temperature is 18 ° C, people do not feel uncomfortable about the smell. Then each person in the room needs 30m ³ of fresh air per hour, and when the indoor temperature rises to 30 ° In order to make people feel uncomfortable about the smell, each person in the room needs 50m ³ of fresh air per hour.

If there is a bad smell in the room, it should be eliminated first, and ventilation is the best way.

For kitchen ventilation, there is a heat balance method, which determines the number of ventilations based on the cooling load of kitchen drinking utensils, people, lamps and building envelopes and the indoor and outdoor temperature. The number of ventilations is determined according to the size of the kitchen and the amount of exhaust air. The method is based on theoretical calculations or the amount of harmful substances produced during the cooking process in the laboratory or in the laboratory, as well as the harmful concentration of outdoor air. According to sanitary standards, the allowable concentration of kitchen air is used to determine the ventilation volume required to dilute harmful gases. Method, using a mechanical local exhaust hood, which directly removes harmful substances on the hood surface, and improves the efficiency of harmful substance discharge. Its efficiency is 30% to 35% higher than that of comprehensive exhaust; the hood mouth air speed control method enables the hood mouth air speed to be controlled at 0.25 0.35 m / s.

The amount of natural ventilation exhaust is affected by indoor and outdoor temperature, humidity, atmospheric pressure, wind direction, and wind speed. The exhaust capacity is small and the exhaust volume is very unstable. Sometimes the exhaust outlet is in a positive pressure state, and reverse irrigation occurs. However, it is currently not possible for our country to achieve mechanical exhaust on all covers.

For the living room and office, natural ventilation should be adopted, and outdoor cold air should be used to infiltrate indoors in cold areas to compensate for fresh air. ^[1]

This is to provide comfortable thermal environmental conditions to the room, that is, to prevent discomfort caused by warmth and wet skin. Thermal comfort ventilation depends on the temperature, water vapor pressure and air velocity inside the building. In hot areas, the indoor sanitation index temperature for human comfort is approximately 31.5 ° C.

According to research by the Institute of Labor and Health, Chinese Academy of Medical Sciences. When the ambient temperature is below 35 ° C, the effect on body temperature, skin, temperature, and pulse does not change much, and the amount of sweating appears to increase. When the ambient temperature is higher than 37 ° C, the above changes

It is far beyond the normal physiological range, and has adverse effects on the cardiovascular system. Therefore, the calculated temperature of the outdoor ventilation in summer is 33 ° C, and a temperature difference of 2 ° C is allowed. Therefore, the temperature at the working place is subject to 35 ° C. ^[1]

The heat capacity of air is very low, so when the building is not ventilated, the indoor air temperature will approach the temperature level of the inner surface of the envelope structure, and its value is close to the temperature of the outer surface. The latter is related to the color of the wall, and also to the product of the structure's thermal capacity and thermal resistance.

When the building is ventilated, outdoor air enters the room at its original temperature, and mixes with the indoor air during the flow, and performs heat exchange with the various surfaces of the room according to the temperature difference between indoor and outdoor.

According to observations, when the exterior is gray, the maximum and minimum values of the inner surface of the west wall and the room temperature are reduced due to ventilation. When it is white, the maximum temperature rise and fall depends on the wall material.

The amount of ventilation depends not only on the material of the wall, but also on the thickness of the wall. If the wall is thin, continuous ventilation has a greater cooling effect on the maximum temperature. For the same thickness, the material with lower thermal resistance and heat capacity has a greater cooling effect on ventilation.

Closing and opening all windows has a great impact on room temperature. The window closing temperature is relatively low. If one window is opened, the room temperature can be increased by 0.5 ° C, and the opening of two windows can be increased by about 1 ° C. Open all to increase the room temperature by 3 ° C, open the single-sided window to the west, increase the room temperature by 2.5 ° C, and open the east-facing window, which will only increase by about 1 ° C.

The effect of ventilation depends on the temperature difference between indoor and outdoor. When the indoor temperature is higher than the outdoor temperature, ventilation can reduce the temperature. On the contrary, the effect is reversed. Therefore, the room temperature is high in the evening and night, and the ventilation effect is good.

In hot areas of China, the regulations for heating, ventilation and air conditioning stipulate that the hottest monthly average temperature of the year is 28 ° C and the average relative humidity is 75% higher. Choosing the right materials in this area is important. ^[1]