- A heat exchanger is a device to transfer heat from one fluid to another. Heat exchangers are used to control air heating, water heating and many other domestic and industrial applications. Houses with radiators pump hot water or steam through pipes to the radiators. The radiators function as heat exchangers, transfering heat from the water pipes to the air in the house.
- Zone valves are a way to save energy by controlling the heat exchangers. Many hot water or steam heating systems use a single pump to circulate the water. The hot water flows from a heater or boiler to the radiators, where it's used to warm the house. This cools the water, and the cool water is pumped back to the heater to start the process again. The problem with this approach is that it constantly heats the whole house, using a lot of energy. Why heat the bedroom during the day if you're downstairs in the kitchen or living room? A zone valve closes off part of the circuit to save energy by only heating what needs to be heated.
- In a zone valve heating system, the house is divided into several loops called zones. Each loop flows to a different part of the building, and each has its own zone valve. The valves are usually controlled by a programmable thermostat. The thermostat can automatically turn on heat to different parts of the house at different times of day.
- To open a valve, the thermostat sends a go signal to the valve, which turns on power to a motor. There are several different mechanisms by which a motor can open and close a valve. Typically, the motor turns a disk until it opens the valve. As the motor turns, it also moves a rotary switch--a switch activated by turning. When the valve is all the way open, the switch turns the motor off and the water can flow through the system unimpeded. The thermostat can also send a signal to close the valve, which turns the motor in the opposite direction until a different switch turns it off.
