Manhattan tankless heater retrofit saves hassles, energy

Aug. 6, 2014
One of the smaller heaters had failed; the system was under a heavy strain to meet demand.  Building management took the crisis as an opportunity to reftrofit and upgrade the hot water delivery system.   

NEW YORK — The Caroline is a residential apartment building located on 23rd St., between 5th and 6th Ave., smack in the Flatiron District of Manhattan. It has and offers just about everything the movies have taught us to expect from a luxury rental in NYC: 24-hour white-gloved doorman, concierge, piano lounge, billiards room, 12,000-sq.ft. landscaped roof deck, valet parking, linen service — the works. Units feature granite countertops and stainless steel appliances in the kitchens and marble floors in the bathrooms.

One of the bathrooms in the Caroline apartment building.

But back in May of 2012, it also had a plumbing emergency in the making. Four water heaters — two smaller units for the upper floors and two larger ones for the lower floors — supplied domestic hot water to the building’s 431 units. One of the smaller heaters had failed and the system was under a heavy strain to meet demand.

“It was gushing water out of the bottom of it,” said Jordan Stern, president of Marplat Co., a manufacturer rep agency and stocking distributor located in Westbury, N.Y. “The water just ate through the two-inch plate steel of the old commercial water heater in about ten years. It’s crazy how quick it goes.”

Building management took the crisis as an opportunity to reftrofit and upgrade the entire hot water delivery system, but immediately ran into two difficult challenges.

The first was access. While the lower level heaters were in the basement, the upper level heaters (one of which was the leaker) had been craned into place when the building was constructed back in 2000, leaving no easy way to get the old system out or get the new system in. Stern has seen the problem time and again due to building trends in New York City over the last decade or so. “[Typically] they end up having to cut them down with a welding torch, then bring in the new equipment in pieces,” Stern said.

Bosch condensing, tankless water heaters.

The second problem was maintaining hot water supply while the retrofit was going on. The tenants of the Caroline pay a premium to not have the building’s problems become their problems. “This is one of the most expensive rentals in all of New York City,” Stern said. “This is not your standard building. This is like your Class-A, investment banker, Goldman-Sachs executive living in this building. So the big challenge was making sure they never knew we were changing out the hot water system.”

The solution to both problems was to use Bosch Therm C 1210 ESC condensing tankless water heaters cascaded in parallel. Tankless water heaters are commonly used in residential on-demand applications; however they can be used in a commercial tank loading application to suit variable demand. To head off future problems, a commercial tank loading design would also allow for complete system isolation for maintenance, as well as the ability to bypass certain system components in case of failure.

Moreover, the tankless units were small enough to fit through the 30-in. doorways to get to the building’s mechanical areas. Conveniently, the rooftop mechanical room had sufficient wall space — about 40-ft. to 50-ft. — to direct vent the units in series.

However, even after being shown the load calculations, the building owner and facility manger were still hesitant. “The biggest challenge was getting the facility manager to believe that we really could do it,” Stern said. “To see this tiny unit making boatloads of hot water was really spectacular… but the brand name, Bosch, is actually what sold him.”

A tech with Paramount Plumbing checks the connection of a C 1210 unit.

Paramount Plumbing of the Bronx, owned by Ralph Dimartino Jr. and Sr., was called in to perform the installation and work began in May. The building was divided into two zones, with 11 C 1210 units with storage tanks for the lower zone and six C 1210 units with storage tanks for the upper zone.

The storage tanks were 240-gal., unjacketed vertical tanks from Niles, chosen primarily for their profile and footprint. Paramount Plumbing was able to maneuver them in and out of elevators, up stairways the through those 30-in. doors.

The work went in stages with the first of the new units pumped into the existing water heater, essentially using it as a buffer tank. Then additional storage tanks were brought in one after another and piped in. “Every time they put another storage tank in they would run it during the day the next day, test it out, make sure it was good,” Stern said. “Then at night they’d shut it down and let the regular water heater run until we had worked out all the kinks in the system.”

Testing the system — making sure sufficient capacity was being maintained, making sure all units were operating at 90%+ efficiency 100% of the time — added weeks to the installation time. Building management stopped work for more than a week after the completion of the first (upper) zone before allowing Paramount to proceed with the second zone.

The system is basically run off the aquastat on the storage tanks. The aquastat on each tank is set up with a ten degree differential in temperature. The aquastat activates the pump which runs 4 GPM at 40 ft. of head per C 1210 unit on the wall. The units are flow activated, so each will turn on and fire identically.   

Installation was completed by September, with the tenants of the Caroline never having a disruption to their hot water supply. One year after the change-out, Paramount Pluming returned to see how the system was performing. Not only was everything running perfectly, “The building owners said they saw between a 10% and 12% reduction in their overall natural gas consumption,” Stern said. “That’s huge.” 

About the Author

Steve Spaulding | Editor-inChief - CONTRACTOR

Steve Spaulding is Editor-in-Chief for CONTRACTOR Magazine. He has been with the magazine since 1996, and has contributed to Radiant Living, NATE Magazine, and other Endeavor Media properties.

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