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Underground hydronic piping
We take care of the heating system at a large apartment complex with a total of fifteen buildings. Three Smith 28 series boilers provide the heat that are piped primary/secondary with four base mounted pumps. One of the boilers is redundant and one of the base mounted pumps is also redundant. The boiler room is centrally located and there are three sets of supplies/returns that exit the boiler room below grade. The underground heating supply and return pipes are four-inch copper with 1” fiberglass pipe insulation.
The boilers and pumps were installed about fifteen years ago, by others. We picked up the account a few months later and have been servicing the equipment since. System requires 190 degree supply water on design day.
With the help of the maintenance staff we learned that there was an underground leak last winter. As soon as spring arrived, we replaced a rotted section of underground copper pipe and assumed this was the only leak. Around that same time, we found the 6” air separator in the boiler room rotted and had to be replaced on an emergency basis. We suspected there were other significant pipe leaks in the system but were asked to let it go due to budgetary concerns. As we are all aware substantial leaks can have long term effects on the entire hydronic heating system. Constant make up water is eating up pumps, perhaps boilers, steel piping, expansion tanks, air separators, reducing valves, etc.
Today we learned that there are at least two more underground pipe leaks. It appears that one of the leaks is on the heating supply near the boiler room about seven feet underground. We’re tentatively scheduled to make the repair on this pipe next week.
The new Director is asking me for a long-term solution. Admittedly, I am not all that familiar with modern underground piping methods for heating pipes. I gather some still use regular old type L copper or schedule 40 steel, while others install large diameter pex or some sort of pre-insulated pex tubing. A quick calculation tells me the original designer was trying to move roughly 120 gpm through these 4” trunk lines. Once the underground pipe gets to the first building from the boiler room it splits into two or three 3” lines and feeds the other buildings (five per ‘zone’). I’m also curious if anyone is familiar with coating the inside of the heating and or domestic water lines pipes with some sort pumped in epoxy slurry?