# air conditioning of a room

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The principle of heat transfer and thermal balance equations

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g1. Use the thermal balance equation to discuss the principles of heat transfer.Thermal balance occurs when the sum of the different types of heat flow in and out of thebuilding is zero. That is, the building loses as much heat as it gains and therefore the building issaid to be in thermo equilibrium. The thermal balance equation is given by:Q_c + Q_v + Q_s + Q_i + Q_e = 0WhereQc Conduction GainsQv Ventilation GainsQs Solar GainsQi - Internal GainsQe - Evaporative LossQc - Conduction GainsThis occurs when heat from outside flows through external building envelop. This occurs mostlyby conduction and to some extent convection. The external envelops are walls, windows, doorsand roofs. Heat flow depends on characteristic of the material making the wall, surface area andalso the temperature difference between the inside and outside. The total heat flow at anyparticular time is therefore given by:Q_c = U A \delta Twhere:Qc = the total instantaneous heat flow in Watts (W),DT = the instantaneous temperature difference between the inside and outsideA = the surface area of the building element, andU = the U-value of the building element.QV- Ventilation gainsThis occurs when inside air enters the building. This can be through natural leakage through thebuilding fabric (infiltration) or by intentional door and window (ventilation)where:Qv = Total ventilation gains in watts totalN =the number air changes per hour within the zone,V = the total inte

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