Principles and Efficiency Analysis of Air Cooling and Dehumidification Processes

2024-02-08 11:22 YTE HVAC Senior Program Manager: BJ Chen

The cooling and dehumidification process of humid air involves both sensible and latent heat. During air cooling, part of the energy is dedicated to water separation (latent heat), while the remaining energy lowers the air temperature (sensible heat).

Cooling Humid Air - Sensible CoolingWhen the temperature of the cooling surface is higher than or equal to the dew point temperature of the surrounding air, the air is cooled without any change in specific humidity. This process primarily removes the sensible heat from the air.

Dehumidifying Humid Air - Latent CoolingIf the temperature of the cooling surface is below the dew point temperature of the humid air, the water vapor in the air will condense on the surface, removing latent heat.

Contact Coefficient - βThe efficiency of a cooling coil can be represented by the contact coefficient β, calculated as follows:

β = (xA - xB) / (xA - xC) = (hA - hB) / (hA - hC) ≈ (tA - tB) / (tA - tC)

Bypass Factor - BPFThe bypass factor (BPF or BF) is also used to represent the efficiency of the cooling coil:

BPF = (hB - hC) / (hA - hC) = (tB - tC) / (tA - tC) = (xB - xC) / (xA - xC)

The relationship between the contact coefficient and bypass factor can be expressed as BPF = 1 - β.

Heat Flow Through the Cooling CoilThe total heat flow through the cooling coil can be calculated using the formula:

q = m (hA - hB)

The total heat flow can be divided into sensible and latent heat flow, each with its respective calculation formula.

Example - Air Cooling and DehumidificationAir at 30°C and 60% relative humidity is cooled to 15°C. The surface temperature of the cooling coil is 0°C. Using the Mollier diagram, the enthalpy changes from 70 kJ/kg to 38.5 kJ/kg, with the contact coefficient calculated as 0.51. The total heat flow, sensible heat flow, and latent heat flow can be calculated using the given formulas.

This summary elucidates the principles of air cooling and dehumidification, highlighting the importance of understanding the processes of sensible and latent cooling in managing air quality and comfort.

If your on-site conditions are complex, it is essential to undergo rigorous calculations to achieve optimal temperature and humidity. You can also communicate with professional engineers from the YTE Temperature and Humidity Management Division through the YTE China service hotline or email.


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