Winter Air Conditioning | Effects on DBT, WBT, DPT, RH, Specific Humidity, Enthalpy, Specific Volume

This article discusses the basics of Winter comfort air conditioning and its effects or possible changes on Dry Bulb Temperature (DBT), Wet Bulb Temperature (WBT), Dew Point Temperature (DPT), Enthalpy, Specific Volume, Relative Humidity (RH) and Specific Humidity or Humidity ratio with the help of a Psychrometric chart.

Winter Air Conditioning - Option 1

Winter Air Conditioning - Option 2

Effects of various parameters on Winter Air Conditioning

• In winter comfort air conditioning, the dry bulb temperature (DBT) and specific humidity (also known as humidity ratio) will rise. This is because, in winter air conditioning, the outside air or the ambient air is cold and dry, which is well beyond our comfort level. The reason for the cold weather in winter is obvious. However, the dryness or low moisture content in the air is because of the reason that, as the temperature is low, the air molecules or bubbles will be smaller in size and it cannot hold more water or moisture in it. Hence by winter air conditioning, our motive is to increase the room temperature and humidity content in the air. So DBT and specific humidity increases.

• In winter comfort air conditioning, the final relative humidity (RH) can be lower or higher than the initial value. This is because RH is dependent on both DBT and specific humidity. So the relative magnitude of DBT and specific humidity will decide whether RH will increase or not. 

• In winter comfort air conditioning, both dry bulb temperature and wet bulb temperature will increase. The wet bulb temperature isotherms are depicted inclined in the Psychrometric chart and have an increasing trend towards the northeast (right of Psychrometric chart). So when DBT is increased or specific humidity is increased, then the wet bulb temperature lines move towards the right and hence WBT increases.

• Enthalpy and specific volume lines also show the same trend as wet bulb temperature. That is in winter comfort air conditioning, enthalpy and specific volume will increase. 

• In winter comfort air conditioning, DPT also increases. This is because, when specific humidity is increasing then obviously DPT will also increase.