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The respective tables of data were generally developed by using the more complex transfer function method to determine the various cooling loads for different types of heating. [2] [3] The results gained by doing so are then normalized for each type of heat gain used for the tables, CLTD, CLF, and SCL. [4]
At a certain plane in the room, the airflow rate returned to the upper zone is equal to the supply air. The plane divides the room into occupied zone and upper zone and leads to thermal stratification: the hot and contaminated air is concentrated in the upper zone, and the air in the occupied zone is cool and fresh. [2]
Displacement ventilation is best suited for taller spaces (higher than 3 meters [10 feet]). [2] Standard mixing ventilation may be better suited for smaller spaces where air quality is not as great a concern, such as single-occupant offices, and where the room height is not tall (e.g., lower than 2.3 meters [7.5 feet]).
ASHRAE Standard 62.2 was adopted in 2004; it clarifies the ventilation air requirements for low-rise residences. The Standard specifies that forced ventilation is required in houses with infiltration less than 0.35 ACH. [2] This is typically accomplished with heat recovery ventilation or exhaust fans running constantly or periodically.
During winter months, for example, an air conditioning register can be closed to prevent cold air from being pulled from the room. This allows the hot air to mix more completely with the cold air in the room, improving the efficiency of the HVAC system. [7] (The return should be efficient enough to draw off the cooler air.) [10] [11]
Diagramatic operation of a thermal wheel Ljungström Air Preheater by Swedish engineer Fredrik Ljungström (1875–1964). A thermal wheel, also known as a rotary heat exchanger, or rotary air-to-air enthalpy wheel, energy recovery wheel, or heat recovery wheel, is a type of energy recovery heat exchanger positioned within the supply and exhaust air streams of air-handling units or rooftop ...
Air changes per hour, abbreviated ACPH or ACH, or air change rate is the number of times that the total air volume in a room or space is completely removed and replaced in an hour. If the air in the space is either uniform or perfectly mixed, air changes per hour is a measure of how many times the air within a defined space is replaced each hour.
A duct with less than 0.75 mg/100m 2 is considered to be clean, per the NADCA standard. [7] A Hong Kong standard lists surface deposit limits of 1g/m 2 for supply and return ducts and 6g/m 2 for exhaust ducts, or a maximum deposit thickness of 60 μm in supply and return ducts, and 180 μm for exhaust ducts. [8]