Hydronic System Pressure Maintenance with Pre-Piped Components
/If your hydronic heating or cooling system is operating correctly, you probably rarely check or even think about the pressure. Fortunately, the system installer likely did think about pressure and installed the proper components to ensure the system operates between its critical pressure limits. Except for an expansion tank and air separator, the components are often installed as a pre-piped assembly, ensuring long-term peace of mind and eliminating tedious piping work. In this blog post, we explain what these components are and the role each plays in pressure maintenance.
Maintain Minimum Pressure
Insufficient pressure can cause a number of issues in hydronic systems. Water may not fill terminals at the system's top, resulting in air binding within the heat transfer coils. Water cannot enter an air-bound coil, so no heating or cooling can take place until this air is expelled. Air may also be released from the solution at low-pressure regions such as the pump suction, which, in extreme cases, will cause pump cavitation.
An adjustable pressure-reducing valve (PRV), set to the desired pressure, automatically adds water to pressurize the system as needed. Many PRVs include a built-in check valve to prevent hot, high-pressure water in the hydronic heating system from flowing backward through the boiler feed, potentially contaminating the domestic water supply. While a check valve should prevent backflow into the domestic water supply, most jurisdictions also require the installation of a reduced pressure zone (RPZ) or a double check backflow preventer upstream of the PRV.
A small make-up valve is usually adequate to maintain the system pressure under normal circumstances. A bypass around the PRV is sometimes installed to allow quicker system fill on startup. The system pressure must be continually monitored to prevent over-pressurizing the system when the bypass is opened.
If you are curious about how to calculate the required minimum pressure in your system, check out this JMP Study Hall blog.
Avoid Over Pressurization
Once we have established the lower pressure limit and installed and set a PRV, we can focus on limiting the maximum pressure in the system.
The maximum working pressure of the system equipment, piping, and components usually determines this pressure. A properly sized, installed, and pre-charged expansion tank should prevent the system pressure from exceeding the maximum pressure. We cover expansion tanks and the sizing requirements in this JMP Study Hall blog.
A correctly sized pressure relief valve is also needed to limit the maximum pressure in case the expansion tank fails. This valve opens at a factory-set pressure and dumps some water to prevent the system from exceeding the set pressure.
Select Pre-piped Make-up Assemblies for Peace of Mind
HYFAB offers thoughtfully designed packaged make-up assemblies to facilitate all of the above functions. Standard assemblies come in ¾ and 1-inch and are available with PRV ranges from 10 to 75 psi. We even include a line-sized bypass to allow quick fill when needed.
Components of a Pre-piped Make-up Assembly
A pressure gauge is installed to measure system pressure regardless of whether the PRV is active or the bypass is in use. We also install a pressure/temperature (PT) port upstream of the PRV to measure incoming water pressure. An optional gauge can be installed in place of the PT port if continuous monitoring is desired. Relief valves with 30 to 125 psi settings are shipped loose with a nipple for easy field installation.
These compact assemblies are made of copper pipe and bronze fittings and include a dielectric nipple to prevent galvanic corrosion when connected to ferrous system materials. Line-sized RPZ or double-check backflow preventers are also available as a field-installed option. Each backflow preventer is supplied with a nipple for field installation.
Ask your sales rep for a packaged make-up assembly to simplify pressure control for your next hydronic system installation.
