Humidity control, heating-cooling systems

In the summertime the heat load with humidity control is removed by cooling systems based on mechanical refrigeration or naturally cold water (see Perry s Chemical Engineers Handbook, 3d ed., pp. 758-797). Make-up heat and humidity control in the winter is incorporated in the air-conditioning system, if available. Separate heating systems use steam from the power plant, or. small gas- or oil-fired heat. Enclosed finned heat exchangers are popular in both forced draft and natural circulation systems with small hot-blast or unit heaters provided in many... 

This necessitates plant capable of control of temperature by being able to add or subtract heat from the air and control of humidity by being able to add or subtract moisture. The system also comprises fan(s), filtration, and a distribution system and may include noise control. Other terms such as cooling or comfort cooling may be met and these can be taken to mean an ability to lower the temperature of the air by refrigeration but without full control of humidity. Moisture may be removed as an incidental characteristic of the cooling coil. The term air conditioning is sometimes used where control of humidity is not included. It is essential to employ clear specifications of performance. 

In building control the controlled parameters include basic functions such as discharge air temperature, space temperature, humidity and fan control. The benefits of such a control system in an intelligent, integrated heating and cooling network include repeatable and individual parameter or area (zone) control. Individual comfort control has been shown to increase employee output and provide an annual productivity gain of over 1000 per employee. 

Temperature and humidity are controlled to ensure worker comfort and product quality. When excessive exhaust occurs, the supply system would need to supply more outside air than the minimum required for proper ventilation, resulting in more heating and cooling energy. 

An environmental control system for a manned spacecraft typically includes a condenser for controlling cabin temperature and humidity. As the moistureladen air is cooled in the small channels of the condenser, water normally condenses out as water droplets. In a microgravity environment, these water droplets tend to become entrained in the air stream and carried back into the cabin, failing to achieve water separation. In such an instance, the cabin air could become foggy. To effectively remove water from the air, heat exchanger surfaces could be coated with a hydrophilic zeolite... 

The lamp was set in the test chamber, which was equipped with a temperature and radiometric control system. The specified uninsulated black panel sensor was used for measurement of temperature. The sensor was mounted on a support within the specimen exposure area so that it received the same radiation and cooling conditions as the test samples. The ambient temperature at a distance of 150 mm from the chamber was maintained within the 18°C-23°C range. Ventilation and air conditioning systems eliminated superfluous heat and humidity. 

The basic principle is the same as for the warm-up humidiflcation method, as a dew point humidifler also depends on water evaporation. However, its structure is much more complex. First, water is evaporated to steam, becoming the humidifier gas then this high-temperature gas is cooled to saturation. Next, the water content of the gas can be accurately calculated according to the saturation vapor pressure at this temperature, after which the gas is heated to the fuel cell temperature and supplied to the fuel cell. The dew point method can accurately control gas humidity, but it consumes a huge amount of energy and requires a complex system. 

---