The Energy Detective: The Case of the Baffling Blockage
Infrared camera found the problem; sawing to see inside showed what it was.
Oct. 2, 2014 — A lot of folks who used to work for me still stay in touch, and not long ago, my pal Nate e-mailed me with a real puzzler. A building at which he was working was converting from steam heat to hydronic (forced hot water) heat. A hydronic heating system has the potential to cut a building's heat and hot water consumption in half — or better — if the existing system is steam.
But there is that little matter of correct execution. To achieve its full savings potential, a hydronic heating system generally must include four things: a low-water-content boiler or boilers; the ability to vary boiler output over the full range of the heating load; variable speed pumps; and room-by-room heat control.
No Heat in Half
Nate was having a more fundamental problem. The new system whose construction he was overseeing was not sending any heat to half the building — even though everything looked perfectly OK.
We went through the usual suspects. Pump on? Check. Pump impeller spinning? Check. All valves open? Check. Boiler energized and making heat? Check. Is the pressure drop across the pump correct? Uh, well, someone decided to save money and delete the pressure gauges.
Regardless, it sounded like it could be a blockage in the pipe. That's the first idea any time there is a heat distribution issue, yet it's almost never the problem. You'd be amazed at how many times a contractor has "fixed" a "blockage" in a hydronic system by installing either a more powerful pump (even though the original pump was already oversized) or one or more unnecessary additional pumps.
In this case, any actual blockage would have to be amazingly serious, and with no visible external evidence of its location.
Nate told me he had felt along the pipes to see where they went from hot to not-so-hot, but it was difficult to tell just by feel. And copper pipes conduct heat so well, it's possible that a pipe that felt warm on the outside could be misleading.
Getting IFfy
I asked Nate if he had an infrared (IF) camera. Not one of those inexpensive temperature guns, but a full-fledged camera that could take an infrared photo of the pipes. Fortunately, he did. I suggested scanning the pipes in the boiler room to see if any kind of obvious pattern emerged.
Nate and his colleagues had to remove a fair amount of pipe insulation to track down the location of the still-theoretical blockage, but after some effort they found what looked like a smoking gun — a large pipe tee fitting where the pipe was hot on one leg and uniformly less hot on the two other legs.
OK, great — but why would a large tee in a brand-new heating system be blocked? It made no sense.
No sense, that is, until Nate ordered the contractor to cut open the tee with a Sawzall. There, stuck inside the pipe (see photo), was a grimy T-shirt that had been used as a rag when the plumber was sweating the pipe. Perhaps he should have used a sweatshirt, but whatever he should have used, he should have removed it before closing up the pipe.
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Tom Sahagian is Senior Program Director, Technical Services, at Enterprise Community Partners.