Cooling systems are used for a variety of purposes, such as for refrigeration or air conditioning. One common type of cooling system is a vapor compression refrigeration system. A vapor compression refrigeration system generally includes, among other things, a compressor, a condenser, an expansion valve, and an evaporator, along with a refrigerant and a series of valves and pipes.
As is known in the art, circulating refrigerant enters the compressor where it is both pressurized and heated as a result of the pressurization. This heated vapor is then passed through the condenser which allows the vapor to dissipate heat and thus change to a liquid state. The condenser acts as a heat exchanger by rejecting the heat of the system to an external medium. The liquid refrigerant then passes through a thermostatic expansion valve (TEV or TXV). The TEV creates a substantial pressure drop causing part of the liquid refrigerant to flash evaporate. The liquid and vapor refrigerant mixture then circulates through the evaporator. While in the evaporator, the ambient air of the space to be cooled warms the refrigerant causing more of the liquid portion to evaporate thus absorbing the heat from the ambient space. Ideally, the refrigerant leaving the evaporator will be mostly vapor. This vapor then passes into back into the compressor and the cycle repeats.
One issue that arises with current cooling systems is that specific compartments or spaces may have optimal temperature and moisture requirements that differ from contiguous compartments or spaces. This arises, for instance, in refrigerated cases at the supermarket when foods having different characteristics are stored in the same case with a single controller. The operating costs of the refrigerated case may be higher than necessary because the case will have to be kept at the cooler of the competing settings to prevent food spoilage.
In addition, it is possible that some refrigeration cases require more cooling than others in order to maintain a desired temperature, even if the desired temperature is the same. Additional cooling requirements can result from external factors, such as the exposure to more ambient heat in some refrigerant cases, or placement near warmer zones of the building.
Current cooling systems are limited in their ability to maintain desired temperature in food display cases. Typical control systems for refrigeration include an evaporator pressure regulator valve that is operable to adjust pressure within the evaporator responsive to temperature measurements taken from inside the refrigerator. For example, the temperature measurement used for evaporator pressure regulation may be taken from the air exiting the evaporator (evaporator discharge air). In many cases, there are multiple evaporators connected to a single evaporate pressure regulator device. In such cases, it is not possible to regulate individual case temperature in this manner.
In alternative systems, the flow of refrigerant into an evaporator unit may be regulated responsive to a temperature measurement of the discharge air. Such systems, however, combined with other necessary control systems such as frost control, require extensive wiring and large installation costs. In many cases, the evaporator pressure regulator may be implemented as a mechanical feedback control valve. The use of mechanical feedback reduces wiring costs but is less responsive and less reliable.
Accordingly, there is need for an arrangement and/or method for controlling temperature within refrigerator cases, particularly in large systems, that overcomes the disadvantages of the prior art.