This invention relates generally to test equipment for air conditioning systems. More particularly, the present invention relates to a method and apparatus for calculating the super heat in an air conditioning system.
Proper maintenance of modern air conditioning systems requires that the operation of the system be adjusted periodically on the basis of various performance factors. One of the performance factors that is monitored is the degree of super heat present in the refrigerant between the evaporator and the compressor.
Air conditioners employ a refrigerant in a closed loop cycle to remove heat from the air contained in buildings and other structures. The air is drawn through a first heat exchanger wherein the refrigerant absorbs heat from the air. Typically, the refrigerant undergoes a phase change from a liquid to a gas in the heat exchanger to more efficiently remove heat from the air. The heated refrigerant is transported from the first heat exchanger to a second heat exchanger located outside of the structure where the heat is removed and discharged. If the refrigerant is in a gaseous state it is compressed and returned to a liquid form in the second heat exchanger. The cooled refrigerant is then transported back to the heat exchanger to remove additional heat from the air.
The refrigerant enters the first heat exchanger in a liquid state and is converted to a gaseous state as it is transported through the first heat exchanger. Generally, the refrigerant has been fully converted to the gaseous state before it exits the first heat exchanger. The gaseous refrigerant continues to absorb heat from the air and therefore becomes super heated. The degree of super heat is determined by the physical size of the first heat exchanger, the flow rates of the air and the refrigerant, the temperature drop experienced by the volummetric air flow, the temperature of the refrigerant as it enters the first heat exchanger, and physical characteristics of the refrigerant such as latent heat of vaporization and specific heat. The air conditioning system is designed for an optimum amount of super heating based upon all these factors. Therefore, the amount of super heating actually experienced in the air conditioning system is an indication of system performance.
Calculation of the degree of super heat requires measuring the pressure and temperature of the refrigerant. The saturated temperature for the refrigerant at the measured pressure is calculated by interpolating from a table of values or reading a graph. The degree of super heat is then calculated by subtracting the calculated saturated temperature from the measured temperature. Typically, this method results in inaccurate results due to the use of hand calculations and non-systematic use of the graphs or tables. In addition, many different kinds of refrigerants are utilized in modern air conditioning systems. Each refrigerant has a different physical characteristic requiring maintenance personnel to select the appropriate graph or table from among many possible graphs or tables. It is not uncommon for the wrong graph or table to be utilized, resulting in inaccurate computation of the degree of super heat.