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Locating Crossover In Large Building
I have a building in DC, approximately 100 condos, that I believe is experiencing a crossover issue which is causing problems with their domestic hot water.
I am tagging you because when I did a google search for crossover detection methods I came across the “Mark Eatherton Method”https://www.aceee.org/files/proceedings/2016/data/papers/1_59.pdf
There are about 20 hot water risers in the building. The return lines come off the tops of the risers. The water heater is on the roof. The main hot water line goes to the bottom floor then splits out to the risers.
The water heater is in the center of the building, with 10 risers on the West and 10 on the East. There is a flow balancing valve on each return line.
The last four risers on only the East side of the building are having issues with either getting zero hot water or having to run the faucet / shower for 40+ minutes until it gets hot. 20 condos total. The rest get hot water fine.
There is a hose connection at the end of the main return line. I often find air stuck in return lines and blowing the air out restored proper return water flow. I bled and got a tiny bit of air. I also tried closing the balancing valves on every return and bleeding out each one individually. Got no air.
I have felt return lines going back and forth between hot and cold. In one apartment I got a lot of sediment out of the bathtub faucet. And also found that the sinks went cold when the bathtub was turned to hot.
I am fairly certain there is a crossover issue here. Problem is there is at least 20 condos that I am going to have to check. Luckily each condo has it’s own individual isolation valve on the hot and the cold.
So as of right now this is my plan -
1. shut hot water off to condo. Open all faucets to drain hot water. See if water stops coming out of hot side. If not, there is a crossover.
2. If condo is determined to have a crossover, start shutting off supply to each faucet until crossover is found.
I would love to hear anyone else’s advice who has dealt with this issue before. I’ve dealt with it quite a few times, but not on this large of a scale. And most of the time I find the crossover was caused at a janitor’s sink with a hose.
Note - I already pulled and checked their recirculating pump. It is working properly. Impeller in good shape.
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