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The Energy Detective: The Case of the Rebellious Radiators

Tom Sahagian in Green Ideas on July 8, 2014

New York City

July 8, 2014

Benny couldn’t believe it, so he visited a few apartments to see if maybe the weather was overheating everyone’s imaginations. No such luck.

Contact Contractor

Benny figured the heating contractor might know what to do. The contractor came by, looked around the boiler room for a few minutes, and came back with a recommendation. “You need a couple of check valves,” he said, and it would cost Benny’s building $2,000.

Why hadn’t the contractor recommended the check valves when he installed the new domestic hot water tank several months ago? And why hadn’t the problem shown up before now? Benny needed a second opinion, so he gave me a call. I asked him to send me the contractor’s proposal.

It took a while before I understood what the contractor wanted to do. I recalled that I had spoken to the contractor about this very job months earlier. In the wake of an untimely failure of a tank-type water heater, I had told the building to replace it with an insulated tank that would be heated by boiler water. This would improve efficiency and reduce downtime.

The building had adopted my suggestion, but to save a few bucks had decided to let the contractor design the new system. Contractors have a lot of practical experience with equipment and its installation, but they generally lack the detailed insight required to design a proper system.

The contractor had installed the new hardware in the middle of the heating season, and everything appeared to be fine. But once the heating season began to wane, the flaw in the contractor’s design became apparent.

Flaw in the System

With the new system, a small pump was needed to send boiler water through a heat exchanger inside the hot water storage tank. Although the pump was small, when combined with convection in the heating hot water pipes, it was strong enough to send some hot water up to the apartment radiators. During the heating season, the effect of this unwanted flow was negligible; when the weather warmed up, however, it became a major nuisance.

The contractor had gone wrong when he placed the small pump in the wrong place. He didn’t realize that the location of the pump in the heat exchange loop had a profound effect on the flow in the rest of the system.

I drew a sketch showing where the pump should be located and sent it to the contractor. He objected at first, but eventually I was able to persuade him to make the change – at no cost to the client. He was about to install a similar hot water storage system at a nearby building and agreed to modify the original “design” in similar fashion.

With the pump in its rightful place, the unwanted heat disappeared and the complaints stopped. The residents — and Benny — were happy and cool.


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Tom Sahagian is Senior Program Director, Technical Services, at Enterprise Community Partners.

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