Performance of Air-Conditioning Systems PDF

___________________________________________________________________________ 3. PERFORMANCE OF AIR-CONDITIONING SYSTEMS 3.0 INTRODUCTION Net refrigerating effect, KW per ton of refrigeration and C.O.P are of extreme importance in the design and operation of A.C...

___________________________________________________________________________ 3. PERFORMANCE OF AIR-CONDITIONING SYSTEMS 3.0 INTRODUCTION Net refrigerating effect, KW per ton of refrigeration and C.O.P are of extreme importance in the design and operation of A.C. systems. The value of these factors depends on the refrigerant used, efficiency of the components and the temperatures of evaporator and condenser. 3.1 REFRIGERATING EFFECT The quantity of heat that each Kg of refrigerant absorbs from the refrigerated space is known as the refrigerating effect, For example, when one Kg of ice melts, it absorbs from the surrounding air and adjacent objects an amount of heat equal to its latent heat of fusion. If the ice melts at 0°C, it will absorb 80 K. cal/kg, so the refrigerating effect of 1 kg of ice is 80 K. cal. While selecting a refrigerant, care must be taken to ensure that it has better refrigerating effect. 3.2 EFFICIENCY OF REFRIGERATING MACHINE A refrigerating machine is a reversed heat engine and similar principles of efficiency are involved in both. The efficiency of a heat engine operating on carnot cycle between temperature limits T1 and T2 is given by the following formula. T1 – T2 Efficiencyc = ——————— Where, Ts are in ° kelvin. T1 Since the refrigerating machine is a reversed heat engine theoretical carnot efficiency for a refrigerating machine is given by the following formula. T2 Efficiencyc = ——————— T1 – T2 Where, T1 is the condenser temperature (absolute) T2 is the evaporator temperature (absolute) 3.3 CO-EFFICIENT OF PERFORMANCE ( C.O.P.) The co-efficient of performance of a refrigerating cycle is an expression of the cycle efficiency and is stated as the ratio of the heat absorbed in the refrigerated space to the equivalent heat energy supplied to the compressor. Heat absorbed from the refrigerated space C.O.P. = ——————————————————————— Equivalent heat energy supplied to the compressor. ________________________________________________________________________ ___________________________________________________________________________ 3.4 KW PER TON RATIO A measure of refrigerating machine efficiency that has been used is KW per ton. On an actual performance test under "standard" conditions for the type of service intended, the net output cooling rate in K. Cal / hr. is determined The average KW input to the machine during the test is also measured. The KW per ton ratio (KW/ton) is then calculated. 3.5 ENERGY EFFICIENCY RATIO (E.E.R.) A recently popular measure of efficiency, especially for unitary conditioners of small to medium capacity is the ratio K.Cal per hour per watt (K.cal/hr-W). This measure is called the "Energy efficiency ratio" (E.E.R.). The average cooling capacity of the unit is determined by a test run under standard conditions. The average power input to the condensing units in watts is measured. From this data the E.E.R. can be calculated by using the following formula. K.cal/Hr cooling rate E.E.R. = ——————————— Watts input ------------------------------- ________________________________________________________________________