Hydronics

Hydronics () is the use of liquid water or gaseous water (steam) or a water solution (usually glycol with water) as a heat-transfer medium in heating and cooling systems. The name differentiates such systems from oil and refrigerant systems.

Historically, in large-scale commercial buildings such as high-rise and campus facilities, a hydronic system may include both a chilled and a heated water loop, to provide for both heating and air conditioning. Chillers and cooling towers are used either separately or together as means to provide water cooling, while boilers heat water. A recent innovation is the chiller boiler system, which provides an efficient form of HVAC for homes and smaller commercial spaces.

right|thumb|A hydronic fan unit heater used for maintaining warmth within an industrial setting. The fan draws cool, ambient air through the heat exchanger around the perimeter of the housing with pipes carrying hot glycol, and expels it out the centre.

District heating

Many larger cities have a district heating system that provides, through underground piping, publicly available high temperature hot water and chilled water. A building in the service district may be connected to these on payment of a service fee.

Types of hydronic system

Basic types

Hydronic systems can include the following kinds of distributions:

Automatic fill mechanisms

Hydronic systems are usually connected to a water supply (such as the public water supply). An automatic valve regulates the amount of water in the system and also prevents backflow of system water (and any water treatment chemicals) into the water supply.

Safety mechanisms

Excessive heat or pressure may cause the system to fail. At least one combination over-temperature and over-pressure relief valve is always fitted to the system to allow the steam or water to vent to the atmosphere in case of the failure of some mechanism (such as the boiler temperature control) rather than allowing the catastrophic bursting of the piping, radiators, or boiler. The relief valve usually has a manual operating handle to allow testing and the flushing of contaminants (such as grit) that may cause the valve to leak under otherwise-normal operating conditions.

Rapid condensation of steam can also lead to water hammer, which during rapid volume change from gas to liquid leads to a powerful vacuum force. This can damage and destroy fittings, valves and equipment. Proper design and the addition of vacuum breakers reduce or eliminate the risk of these problems.

Typical schematic with control devices shown

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