The Energy Detective: A New System for Tracking Down Leaks

First Steps

The original goal was to install a small water meter on the hot and cold supply pipes to each apartment, but this approach soon proved to be too expensive as a retrofit (although it would be much more cost-effective in a new construction or major rehab). Instead, a submeter was installed at the base of each cold water riser only. This yielded the best balance of leak-location and cost. Hot water (DHW) risers were ignored because the constant flow of recirculated water would likely mask any leaks.

For every gallon of water that runs through it, each submeter sends a hardwired pulse signal to a central data-logger in the basement. The logger sends the data to a website where it can be monitored at any time. When any submeter fails to show zero water consumption for more than a day or so (particularly during the early morning hours), there is almost certainly a leak. The building staff then inspects all the kitchens or bathrooms served by that riser until the leak is found and repaired.

The meters were installed using so-called press-fit pipe-joining technology instead of traditional soldered joints. Doing so not only reduced labor cost, but also made it possible to install meters even when the riser shutoff valve did not hold. It was a huge advantage.

The cost of running the data wires and installing the loggers averaged roughly $800 per submeter, but that figure is deceptively high because of the initial learning curve — the mature cost should be about half that. Nonetheless, the pilot is evaluating a wireless system to further reduce installation cost.

Note that it is critical to avoid "line-sizing" the submeters, that is, a two-inch riser does not require a two-inch meter. We found that a three-quarter-inch meter can handle the vast majority of risers found in the project — none was larger than two inches and almost all the buildings were six stories or less. Larger risers in taller buildings will no doubt require meters larger than three-quarters of an inch, but line-sizing must still be avoided. Smaller meters are less expensive, easier to install, and can detect smaller leaks.

Money Back

This system pays for itself. Assuming an installed cost of $2,500 per meter and New York City water costs, the annual cost of leaks of various intensities is as shown in the table below.

Each meter would need to alert only one 0.5-gpm leak to pay for itself in well under a year. Actual installed costs could be lower depending on the skill of the installer and the complexity of the basement.

Photo by Tom Sahagian