The connection between HVAC and plumbing is often misunderstood. Standard central ACs and heaters are tied in with plumbing systems, especially when you consider condensate drains, refrigerant tubing, and how extreme cold can freeze plumbing lines. But in a hydronic system, HVAC components and water lines essentially form an integrated system. In its most basic form, it consists of an air handler connected to a boiler.
How a Hydronic HVAC System Works
In a hydronic system, hot water or steam carries heat through a home or building. The most common setup can heat water to up to 200℉. Water is pumped, circulated, and radiated to distribute heat. There are five major categories of hydronic systems. They include low-temperature water (LTW), operating at less than 250℉; medium-temperature water (MTW), running at 250℉ to 350℉; high-temperature water (HTW), operating at greater than 350℉; chilled water (CW), running at 40℉ to 55℉; and dual-temperature water systems (DTW), which combine the functions of an LTW and CW system.
Hydronic System HVAC and Other Components
The most important parts of a hydronic system include:
- Heat Source: A gas, oil, or electric boiler may be used. Common varieties include cast iron, steel, and copper water-tube boilers. The boiler unit is typically placed in the back of a commercial building and usually fills with water automatically when levels drop.
- Geothermal Heat Pump: This increasingly popular option is a highly efficient source of heat, which is drawn from the ground or a body of water. Vapor compression is used to extract heat to warm circulating water.
- Expansion Tank: Since water expands when heated, the expansion tank holds the extra volume of water so it doesn’t damage the system. It is an important pressure control feature.
- Centrifugal Pumps: Are designed to circulate hot water from the heat source to the terminal units, or air handlers. A motor drives corrosion-resistant impellers that keep water flowing through the system.
- Air Separator: As the air gets trapped in the piping, the air separator removes it, which helps avoid corrosion. The separator has a wire screen that traps air bubbles while water passes through; as bubbles get larger, they move to the air vent.
- Air Vent: Typically installed above the air separator, the air vent consistently removes air from the system. It can be a manual device or an automatic type in which vents open and close automatically.
- Terminal Units: A terminal unit can be a finned-tube radiator, the simplest option, which usually provides heat around the perimeter of a building. Fan-coil units circulate air across heating/cooling coils and into a room using an electrically driven fan. Terminal unit variations also include central air-handler heating/cooling coils, convectors, unit heaters, water-to-water heat exchangers, radiant heating/cooling panels, and others.
- Strainers/Hydronic Filters: These are typically circular screens installed within piping to capture dirt and debris. Strainers must be cleaned, which requires turning the water off, removing the screen, cleaning it, and reinstalling it. Refilling the system requires removing any air that gets trapped during the process.
Other hydronic system HVAC components include shutoff valves that allow service personnel to isolate components before repairing or replacing them. A shutoff valve can also be used to increase or reduce flow. If makeup water is introduced, a fill valve and backflow preventer are required to ensure polluted water does not flow back to clean water sources.
Hydronic Safety Devices
A pressure-reducing valve is often integrated with the fill valve to decrease pressure when necessary, while a water-regulating valve can automatically add water if pressure abnormalities are detected. A low water cutoff valve can cut power to the boiler if the water level falls below a certain threshold. When expansion pressure is high, a pressure-relief valve discharges excess water. A high-limit control can cut power to the heat source if it gets too hot.
And like any other heating or cooling system, hydronic system HVAC components are operated with a thermostat. Other controllers may enable operators to manage temperature, flow valves, pumps, zone functions, and other elements that need to be adjusted and regulated.
Contact Air Stars
Air Stars installs and fixes ACs, furnaces, heat pumps, ductless systems, and more while also providing electrical and plumbing services. We serve customers throughout Salem and the Willamette Valley. Arriving on time in fully stocked vans, our technicians strive to resolve any problem in one visit. Making service affordable is a priority, which we do through competitive pricing plus special offers, a comprehensive maintenance plan, and financing options. To learn more about our heating and cooling services and schedule a visit, call 503-832-4438 today.