The purpose of an hvac system is to move (transfer) heat from one place to another. Therefore, the use of hydronics is a logical solution to today’s energy situation.
Heating systems for homes have used water for many years. The oldest systems used a boiler to produce steam. This steam traveled through a pipe to cast iron radiators.
As the steam gave off its heat, it would turn back to water which is called condensate. Then it ran back down the pipe and was returned to the unit. These systems were referred to as single pipe systems.
They are no longer installed because of their low heat capacity. Also it was hard to control the temperature of individual rooms.
The next generation of steam systems used a separate pipe to return the condensate to the boiler. These systems incorporated a pump to return the water to the boiler. They are referred to as two pipe systems.
To overcome the problem of overheating individual rooms, thermostatic radiator valves were developed. These valves are installed on the individual radiators and have adjustable temperature settings. These valves open and close based on the room temperature and either allow or prevent the steam flow.
The next generation of hydronics used a lower temperature boiler. These units produced hot water and not steam. They were safer and easier to control.
The heat from the boiler was transferred to water and the water was pumped to radiators. These radiators were smaller and made of finned copper tubing instead of cast iron. As the air around them was heated, it would rise and pull cooler air into the radiator where it was heated. After the water had given up some of its’ heat, it was pumped back to the boiler to begin the process again.
Some other components are added to the basic system. When water is heated, it expands. Therefore, an expansion tank is added to allow for this and still maintain proper system pressure.
Another device called a temperature/pressure (T/P) relief valve is added. If a malfunction occurs and the expansion tank cannot keep the pressure low enough, this control automatically opens. This allows water to leave the system and causes the pressure to go down.
Normally, there is a certain amount of air in any water. When this water is heated, the air breaks free of the water molecules. This air collects in the highest points of the system and can produce what is referred to as an air lock. This will stop the water flow and therefore not allow the system to work. Devices, called air vents, are installed at the high points of the system to get this trapped air out of the system. Older systems use manual air vents and periodically someone had to go around and release the air. Modern air vents use a float switch and do this automatically.
There has to be a way to put water into hydronic systems. This is usually accomplished with an autofeed valve. This valve is connected to the homes’ cold water supply line. It reduces the pressure of the water, eliminates air and automatically maintains the proper amount of water in the system.