# Energy Efficiency Reference/Refrigeration/Technology Primer/Common Terms

• Approach Temperature: Difference temperature difference between the liquid/gas in the heat exchanger as it exits compared with the surrounding medium that serves as a heat source or sink. A 100% effective heat exchanger would have an approach temperature difference of 0F. Does not have to be constant but will vary based on the operating conditions at the heat exchanger.
• Condenser Effect: Heat exchanger in which the refrigerant gives off energy to the surroundings and condenses from a gas to a liquid.
• Cooling Effect<: Change in enthalpy in the evaporator as the refrigerant absorbs energy and evaporates.
• Discharge Pressure, Condensing Pressure, High-side Pressure: Pressure at the compressor discharge at which the refrigerant condenses. Condensing pressure fluctuates with outside temperature on air-cooled or evaporator units.
• Enthalpy: Enthalpy is sometimes called total energy because it includes internal energy (u), the work done in a particular process (pv). and change of phase.
• Evaporator: Heat exchanger in which the refrigerant absorbs energy from the surrounding as it evaporates from a liquid to a gas.
• Compressor Work: Change in enthalpy as the refrigerant is compressed.
• Rejected Heat: Change in enthalpy as the refrigerant condenses.
• Latent Heat of Vaporization: Change in enthalpy as the refrigerant evaporates from a saturated liquid to a saturated vapor at a specified pressure.
• Minimum Approach Temperature Difference: Approach temperature difference across a heat exchange with the heat transfer coefficient maximized. This can be measured for clean condenses or evaporators with all heat exchanges fans running at full power.
• Minimum Discharge Pressure: Air-cooled and evaporative condensers maintain the minimum discharge pressure by cycling fans or controlling speed. Plant personnel control the minimum pressure set point.
• Refrigerant: The refrigerant is the "working fluid" which evaporates to absorb the latent heat of vaporization from its surroundings. Thereby cooling the surroundings. To permit the refrigerator to operate continuously, the refrigerant vapor is compressed and reconverted to liquid effectively moving energy from where the refrigerant vaporizes to where is condenses.
• Suction Pressure, Low-side Pressure: Pressure at the inlet to the compressor is also the pressure at which the refrigerant evaporates.
• Tons: A measure of the cooling capacity usually applied to larger cooling systems and heat pumps. One ton of cooling represents the ability to absorb energy at a rate originally determined by melting 1 short ton (2000 ponds) of ice in 24 hours. Now, 1 ton = 12,000 Btu per hour, 3,520 watts.