Hydronic Systems: Architecture and Operation

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Key Questions

The following key questions are answered in this module:

What is hydronics?
Hydronics is a means of heating and cooling using a fluid as the heat transfer medium.

What is the difference between an open system and closed system?
An open system has some point in the system open to the atmosphere, while a closed system is not open to the atmosphere at any point; the fluid is never exposed to anything outside of the system itself.

What are some examples of heat source devices?
Heat source devices include boilers, fluid-to-fluid heat exchangers, and water-source heat pumps.

Where is the pressure typically lowest in the system?
The lowest pressure in a system is typically at the expansion tank.

What are common causes for leaks in plate heat exchangers?
Causes for leaks can be corrosion, excessive pressure and material fatigue due to repeated temperature fluctuations.

Sample Video Transcript

Below is a transcript of the video sample provided for this module:

The sizing and selection of a tank should be made by a professional engineer or hydronics vendor who understands the system dynamics and design intent. However, as the operator responsible for system operation, you should understand the pressure settings and how they are determined. The low pressure setting, also called the fill setting, is the pressure required at the fill point that will assure enough pressure is available at the highest point in the system to guarantee that all air can be purged from the system when it is initially filled with water. The pressure is thus determined using the vertical distance between the fill point and the highest point in the system, plus a safety factor around five to 10 psi. The higher pressure is set based on the maximum allowable system pressure at the safety relief valve with the lowest relief setting. A 10-percent safety factor is deducted to avoid weeping at the valve. So, if you have a hydronic system with 125 psi fittings, but a relief valve at the boiler set at 50 psi, then your high setting would be nominally 45 psi. But how do you check the fill pressure once the system is operating? For example, you may want to confirm the bladder or diaphragm isn’t leaking. • Valve off the tank, isolating it from the system. • Drain the water from the tank. • Check the air pressure using the Schrader valve fitting and an air gauge • If the tank pressure is at the design fill pressure and holding, you know the bladder or diaphragm is good. Once confirmed, you can reintroduce the tank into the system, allowing the bladder on the water-side of the tank to be refilled from the make-up water system. Note that a closed system only requires make up when water is purposely removed or leaking. That means that the only acceptable make up water reading is zero gallons.