How Hydronics Works

Air Source Chillers provide cool water for a hydronic piping system

How Hydronics Works | HVAC Technical for Consumers - Hydronics refers to using water and for chilled water, steam boilers and hot water boilers and other methods of transferring heat using water. A boiler or chiller is used to heat or cool the water and then the water is transferred through the hydronic piping loops to heat exchangers such as coils or baseboards where heat is transferred from the water to the air for heating and from the air to the water for cooling to provide comfort for people or a process.

Hydronics is very popular in commercial and industrial HVAC applications for heating and cooling occupants in large buildings and providing heating and cooling for equipment and machines including computers and servers. Basically in a nutshell hydronics uses water to move heat from one place to another.

How Hydronics Works | Hydronics and Chilled Water Systems

Chillers chill the water in a typical application to around 45 degrees Fahrenheit. Water flows through a chiller barrel or a chiller heat exchanger where the heat from the water is absorbed into a refrigerant and then transferred to the outside of the structure using water usually to a cooling tower for a water source chiller or through refrigerant condenser coils for an air source chiller.

Hydronic Definition - a system of heating and cooling where water is used to transfer heat.

The condenser water for a water source chiller is pumped to a cooling tower where the process of evaporation is used to remove heat from the water. Once the water is cooled in the cooling tower it is pumped back to the heat exchanger or chiller barrel to absorb more heat from the refrigerant before being pumped back to the cooling tower. The condenser water is kept completely separate from the chilled water that flows through the evaporator barrel and is pumped to the heat exchangers inside the building for comfort or heat removal in the case of process cooling.

How Hydronics Works | Heat Exchangers

The heat exchangers for the comfort or process cooling inside the building can be large chilled water coils inside air handlers, fan coil units, VAV boxes, unit heaters, or baseboard type heat exchangers. This water is typically 45 degrees Fahrenheit as it is delivered to various types of heat exchangers. As air passes over the heat exchanger, usually pushed by a fan, the cool water absorbs the heat from the air and is returned to the chiller via chilled water piping to have the heat removed by the process of a refrigeration in the chiller. The cycle repeats itself over and over again providing cool chilled water to the heat exchangers inside the building.

Steam Distribution on a campus

Steam distribution piping used in industrial and institutional campus-type environments to provide an economical source of heating.

How Hydronics Works | Hydronics and Boiler Systems

How Hydronics Works

Hot Water Boilers provide hot water for a hydronic piping system

The process of hydronics can also be used with boiler systems. Hot water boilers or steam boilers can be used to heat water and deliver the water to heat exchangers inside the building for both comfort heating and process heating. A hot water boiler system will heat the water to 180 degrees Fahrenheit on a cold day and then a pump will pump the hot water through a piping circuit or a piping loop to deliver the hot water to heat exchangers such as a hot water coil inside an air handler, VAV box, or fan coil unit where air is passed over the coil.

The air absorbs heat from the hot water coil and then is fed through a duct system and delivered to supply diffusers for either comfort or process heating. Other types of heat exchangers for a hydronic hot water boiler system include baseboard heaters and radiators. After the hot water passes through the heat exchanger or coil it is returned by circulator pump to the boiler to be reheated.

Hydronic Piping Diagrams and Methods

Here are some basic hydronic piping diagrams for water flow. These methods have their own unique benefits given the hydronic system where they are used.

Hydronic Piping Diagrams 2 pipe direct return
Two-pipe Reverse Return Hydronic Piping Arrangement
MonoFlow Hydronic Piping
Steam to Hot Water Exchanger

How Hydronics Works | Steam Boiler Systems

Steam boiler systems are also used in hydronics as steam boilers will superheat the water and deliver the steam through a network of pipes and to radiators. The radiators are typically located in high load areas and as the heat is released from the radiators the steam condenses to water and is drained back through a hydronic piping loop back to the boiler for reheating. Some steam systems use gravity to return the condensed water back to the boiler and some steam boilers use a condensation pump.

Either way, the water is returned to the boiler to be made into steam once again. Some steam systems can utilize a large steam to hot water heat exchanger where steam is used to heat water to approximately 180 degrees Fahrenheit where it is distributed through a hydronic hot water piping system, not unlike the one used for the hot water boiler system described above.

How Hydronics Works - Hydronics Piping Systems

How Hydronics Works

Large Expansion Tank for a Chilled Water Hydronic System

Hydronics piping can have different arrangements from the simple to the complex hydronic piping system. The simplest is probably the single pipe system. Hydronic piping systems can also be two-pipe systems, three-pipe systems, four-pipe systems, and be a series or parallel loop arrangement with several heat exchangers.

Additional piping and heat exchanger arrangements can be found on the High Performance HVAC Boiler Water Loops page.  It is also necessary for the hydronic piping system to be properly balanced for even flow heating and cooling and protected from over-pressure with expansion tanks and pressure relief valves since the volume of water expands and contracts as it is heated and cooled.

Air management in the hydronic piping is also necessary to keep air out of the piping system as air will block the flow of the water and cause serious problems.

High Performance HVAC

How Hydronics Works

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