KW per ton
The term kW/ton is common used for large commercial and industrial air-conditioning, heat pump and refrigeration systems. The term is defined as the ratio of the rate of energy consumption in kW to the rate of heat removal in tons at the rated condition. The lower the kW/ton the more efficient is the system.
KW/ton = Pc / Hr
Where
• Ps = energy consumption (k W)
• Hr = heat removed (ton)
Coefficient of Performance-COP
The Coefficient of Performance - COP - is the basic unit less parameter used to report the efficiency of refrigerant bas ed s ystems. The Coefficient of Performance - COP - is the ratio between useful energy acquired and energy applied and can be expressed as:
COP = Hu / Ha
Where
• COP = Coefficient of performance
• Hu = Useful energy acquired (Btu)
• Ha = Energy applied (Btu)
COP can be used to define either cooling efficiency or heating efficiency as for a heat pump.
‹ For cooling, COP is defined as the ratio of the rate of heat removal to the rate of energy input to the compressor.
‹ For heating, COP is defined as the ratio of rate of heat delivered to the rate of energy input to the compressor.
COP can be used to define the efficiency at a single standard or non-standard rated condition or a weighted average seasonal condition. The term may or may not include the energy consumption of auxiliary systems such as indoor or outdoor fans, chilled water pumps, or cooling tower systems. For purposes of comparison, the higher the COP the more efficient the system.
COP can be treated as an efficiency where COP of 2.00 = 200% efficient for unitary heat pumps, ratings at two standard outdoor temperatures of 47°F and 17°F (8.3°C and -8.3°C) are typically used.
Energy Efficiency Ratio – EER
The Energy Efficiency Ratio - EER - is a term generally used to define the cooling efficiency of unitary air-conditioning and heat pump systems. The efficiency is determined at a single rated condition specified by the appropriate equipment standard and is defined as the ratio of net cooling capacity - or heat removed in Btu/h (not in tons) - to the total input rate of electric energy applied - in watt hour (not in kW). The units of EER are Btu/W-hr.
EER = Hc /Pa
Where
• EER = Energy efficient ratio (Btu/W-hr)
• Hc = net cooling capacity (Btu/hr)
• Pa = applied energy (Watts)
This efficiency term typically includes the energy requirement of auxiliary systems such as the indoor and outdoor fans and the higher the EER the more efficient is the system. Energy efficiency ratio is further categorized as Energy efficiency ratio (EER) and Seasonal energy efficiency ratio (SEER):
‹ The cooling equipment systems such as room air conditioners, heat pumps etc used in residential and small commercial buildings often express cooling system efficiency in terms of the Energy Efficiency Ratio (EER).
‹ The central air-conditioning equipment used in large residential and commercial buildings expresses cooling system efficiency in terms of the Seasonal Energy Efficiency Ratio (SEER).
Recommended selection of room air conditioners is EER of at least 9.0 for mild climates and over 10 for hot climates and for central air conditioning system it is tested to be as high as 17 units. The U.S. Government's minimum efficiency level is 10 SEER for split systems and 9.7 for packaged units.
Efficiency - Heating Systems
Turndown Ratio = Maximum Firing Rate: Minimum Firing Rate (i.e., 5:1, 10:1, 25:1)
Overall Thermal Efficiency = (Gross Btu Output / Gross Btu Input) x 100%
• Overall Thermal Efficiency Range 75%–90%
Combustion Efficiency = {(Btu Input – Btu Stack Loss) / Btu Input} x 100%
• Combustion Efficiency Range 85%–95%
