Hydronic System Protection - a must
You'll need hydronic system protection if you're going to install hydronic heating in your home or shop. It's required to protect you, your home and the system.
It's not difficult to install, and it gives you peace of mind knowing that you've addressed whatever might go wrong.
Let's first take a look at how water behaves, and then let's look at system protection components to see what they are and how they work.
How Water Behaves
Water exists in three states, solid, liquid and gas. We know the solid form as ice and the liquid form as humidity or steam. The liquid form is good old water that is the essential element for life and nearly everything we do.
In it's liquid form, water will expand roughly 4% from near freezing to near boiling. We need to take this into consideration since we're going to start with water that is roughly 55 degrees F and heat it to about 160 degree F. We need to accommodate this natural expansion.
When water freezes, it expands considerably. How much it expands isn't important. Any expansion in the system will cause a pipe break and equipment damage, so we need to keep it from freezing.
Boiling water expands tremendously. Again, how much isn't important because any creation of steam will dramatically increase system pressure. A situation where we "flash to steam" will cause our system to "air lock" and damage will be caused through melted components or explosion. It also presents a risk of personal injury, so we need to keep our system hot, but not to the point where it's going to boil.
Hydronic System Protection Features
To address freezing, we need to locate distribution lines indoors where we won't experience temperatures below freezing. In very cold climates, hydronic systems use anti-freeze mixtures to give the system freeze protection in the event of a prolonged power outage that causes the house to go cold.
To address the natural expansion of water, there are two items we need to install. First, an expansion tank that allows expanding water to fill a rubber bladder inside a metal housing under air pressure.
This component allows heated water in the system to expand into the housing against pressure maintained by the bladder. When the water cools, it retreats back into the system under pressure of the bladder.
Second, we need a pressure relief valve to serve as a backup in the event that abnormal conditions cause a spike in system pressure. In this case, the abnormal conditions we want to avoid are pump motor or impeller failure, flow obstruction, or a power outage. Any of these will cause flow to slow or stop, and this will risk water flashing to steam and causing a spike in system pressure.
Providing backup electric power is also a useful hydronic system protection feature, but not necessary unless you have a homemade system like mine where a wood stove is the source of heat. In such cases, you just can't stop the input of heat to the water that is now at a standstill in the face of a power outage.
To provide a backup, you can run the pump off of an inverter, power the inverter with a battery, and charge the battery with a batter charger that takes it source of power from household AC. When the power fails, the battery supplies the inverter and the pump never sees the power outage. With a sufficiently large battery, a small circulating pump can run for many hours, thus allowing you plenty of time to "coast the system" to a stop.
There are many other approaches to providing hydronic system protection, but these are the basic considerations. The hydronic system protection features you employ are largely a matter of choice based in part on system design and configuration. Fail-safe features and designs that are inherently safe are most desirable.
Knowing how water behaves and how your system works are two good first steps to specifying which hydronic system protection features are best for you.
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