A thermostatic expansion valve could be used to control refrigerant flow in a chiller system. This sort of valve controls the refrigerant flow into the chiller’s evaporator. It consists of a capillary tube that is connected to a small bulb, both of which have a thermostatic charge. This charge is typically the refrigerant that the chiller system uses. When there is an increase in the pressure on the thermostatic charge, a diaphragm attached to the valve experiences a higher level of pressure, which opens the valve to let more refrigerant into the evaporator.
Electronic expansion valves are of more recent origin than thermostatic expansion valves. They are more commonly used on systems that are larger and expensive enough to justify the cost of the electronic valve. These electronic valves can be used together with digital control systems to control the refrigeration system, using various input variables from the system. This sort of system makes for more efficient control of the refrigerant system. In some systems, for instance, one electronic expansion valve can control flow in either direction, handling the load of two thermostatic expansion valves.
Fixed Flow Control
Some air conditioning systems use various fixed flow control mechanisms. These include devices such as capillary tubes and pistons. This is a simple and relatively inexpensive mechanism, but it isn't as efficient as others.
Air conditioning systems also use thermal expansion valves to control refrigerant flow. This method is more sophisticated than the fixed flow control method. The expansion valve adjusts the flow of refrigerant based on the temperature of an evaporator coil. These flow control systems make for higher levels of energy efficiency.