inside the tubes to the moist air. The rate of heat transfer from the hot water to the colder moist air is often called the heating coil load (Qsensible), in Btu/hr, and is calculated from Equation: Q sensible= m * Cp (T2– T1) Or
Q sensible= 60 * V * ρ* Cp (T2– T1) Where •Q sensible= sensible heat in Btu per hour •m = mass flow rate of air, lbs/hr •V= volume flow rate of supply air, cfm •ρ= density of supply air, lb/ft3•T2, T1= moist air temperature at final and initial states of an air-conditioning process, °F and the mass flow rate of supply air Or more accurately from psychrometric chart: Q sensible= m x (h2- h1) Where •h2, h1= moist air enthalpy at final and initial states of an air-conditioning process, Btu/lb For sensible cooling: A sensible cooling process removes heat from the moist air, resulting in a drop of its temperature; The sensible cooling process occurs when moist air flows through a cooling coil containing chilled water at a temperature equal to or greater than the dew point of the entering moist air. The sensible cooling load can also be calculated similar way as sensible heating equation. COOLING AND DEHUMIDIFICATION
In a cooling and dehumidifying process, both the humidity ratio and temperature of moist air decrease. Some water vapor is condensed in the form of liquid water, called a condensate. The most commonly used method of removing water vapor from air (dehumidification) is to cool the air below its dew point. The dew point of air is when it is fully saturated i.e. at 100% saturation. When air is fully saturated it cannot hold any more moisture in the form of water vapor. If the air is cooled to the dew point air and is still further cooled then moisture will drop out of the air in the form of condensate. This can be shown on a psychrometric chart as air sensibly cooled until it becomes fully saturated (the dew point is reached) and then the air is cooled latently to a lower temperature. This is apparent on the psychrometric chart as a horizontal line for sensible cooling to the 100% saturation curve and then the process follows the 100% saturation curve down to another point at a lower temperature. This lower temperature is sometimes called the Apparatus dew Point (ADP)of the cooling coil. In reality the ADPof the cooling coil is close to the cooling liquid temperature inside the coil. Chilled water or refrigerant may be the cooling liquid. The psychrometric process from state point 1 to 2 to 3 may be shown as a straight line for simplicity.
The total amount of cooling input to the air approximates to; Q1-3= m x (h1- h3) The sensible heat removed is: Q1-2= m x (h1- h2) The latent heat removed is: Q2-3= m x (h2- h3) Where: •Q = Cooling energy (Btu) •m = mass flow rate of air (lbs/hr) •h = specific enthalpy of air (Btu/lbs) found from psychrometric chart.