Latent heat is the heat when supplied to or removed from air results in a change in moisture content - the temperature of the air is not changed. Heat loss from electrical equipment like switch-gear, transformers and variable frequency drives.Įnthalpy change and temperature rise when heating humid air without adding moisture. ![]() The Great Sensible Heat Factor is the ratio sensible to total heat in a cooling coil. Latent and sensible cooling loads to consider when designing HVAC systems.Įlectric heating of an object or mass - temperature change vs. Performance and efficiency terminology related to heat pumps and air condition systems. air flow and temperature.Īrithmetic and Logarithmic Mean Temperature DifferenceĪrithmetic Mean Temperature Difference in Heat Exchangers - AMTD - and Logarithmic Mean Temperature Difference - LMTD - formulas with examples - Online Mean Temperature Calculator.Ĭooling and Heating - Performance and Efficiency Terminology The Sensible Heat Ratio can be expressed asĪir Conditioning systems - heating, cooling and dehumidification of indoor air for thermal comfort.Īir - Heating, Cooling, Mixing, Humidifying or Dehumidifying Processesīasic air changing state processes - heating, cooling, mixing, humidifying and dehumidifying by adding steam or water - psychometric diagrams and the Mollier charts.Īir - Humidifying by Adding Steam or WaterĪir can be humidified by adding water or steam.Īir heating buildings - heat supply vs. Using (3b) the total sensible and latent heat removed from the air can be calculated as H t = (1.202 kg/m 3) ( 1 m 3/s) (( 77 kJ/kg dry air) - (28 kJ/kg dry air))įrom the psychrometric chart we estimate the water enthalpy in the hot air to be 18.7 Btu /lb dry air, and the enthalpy in the cold air to be 11.8 Btu /lb dry air. Using (3) the total sensible and latent heat removed from the air can be calculated as = 1.08 q dt + 0.68 q dw gr (4) Example - Cooling or Heating Air, Total Heatįrom the Mollier diagram we estimate the water enthalpy in the hot air to be 77 kJ/kg dry air, and the enthalpy in the cold air to be 28 kJ/kg dry air. estimate enthalpy with the Mollier diagramĭh = enthalpy difference (btu/lb dry air).Total heat due to both temperature and moisture can be expressed in SI units as: Latent Heat Load and Required Air Volume Chart (pdf).Latent heat load - humidifying and dehumidifying - and required air volume to keep temperature constant at various temperature differences between entering air and room air are indicated in the chart below: = 9.5 (Btu/hr) Latent Heat Load and Required Air Volume Chart H l = 0.68 (1 cfm) (( 40 grains water/lb dry air) - ( 26 grains water/lb dry air)) Using (2b) the latent heat removed from the air can be calculated as The relative humidity of the air is 70% at the start and 100% at the end of the cooling process.įrom the psychrometric chart we estimate the water content in the hot air to be 40 grains water/lb dry air, and the water content in the cold air to be 26 grains water/lb dry air. Using (2) the latent heat removed from the air can be calculated as The relative humidity of the air is 70% at the start and 100% at the end of the cooling process.įrom the Mollier diagram we estimate the water content in the hot air to be 0.0187 kg water/kg dry air, and the water content in the cold air to be 0.0075 kg water/kg dry air. ![]() Latent evaporation heat for water can be calculated asĭw gr = humidity ratio difference (grains water/lb dry air)ĭw lb = humidity ratio difference (lb water/lb dry air)Īn air flow of 1 m 3/s is cooled from 30 to 10 oC. estimate humidity with the Mollier diagram.H we = latent heat evaporization water ( 2454 kJ/kg - in air at atmospheric pressure and 20 oC)ĭw kg = humidity ratio difference (kg water/kg dry air) Latent heat due to the moisture in air can be calculated in SI-units as: Sensible Heat Load and Required Air Volume Chart (pdf).Sensible heat load and required air volume to keep the temperature constant at various temperature differences between make up air and room air: = 21.6 (Btu/hr) Sensible Heat Load and Required Air Volume Chart Using (1b) the sensible heat added to the air can be calculated as Using (1) the sensible heat added to the air can be calculated as Q = air volume flow (cfm, cubic feet per minute)ĭt = temperature difference ( oF) Example - Heating Air, Sensible HeatĪn air flow of 1 m 3/s is heated from 0 to 20 oC. The sensible heat in a heating or cooling process of air (heating or cooling capacity) can be calculated in SI-units asĬ p = specific heat of air (1.006 kJ/kg oC)
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