An Efficient Retrofit for Commercial Hot Water on Demand

Enovative’s control system for water heating cuts energy use and prolongs pipe life in multifamily buildings and hotels by recirculating hot water only when it’s needed.

By Paula Melton

Conventional hot-water recirculation pumps—a standard appliance in hotels, multifamily residential buildings, and other commercial buildings with high demand for domestic hot water—were never supposed to save energy. These devices are installed to get hot water to the tap quickly to keep tenants and hotel guests happy. If they prevented some lukewarm water from going down the drain, that was a welcome side-effect. But high-speed delivery comes at a price: building owners end up wasting energy and money constantly reheating and pumping water—despite the fact that most building occupants need hot water only once or twice a day. The recirculation systems also act as radiators, their wasted heat being added to buildings even during cooling seasons.

D’Mand Circ, from Enovative Kontrol Systems, is the first (and so far only) system to offer the next logical step for commercial hot-water recirculation. Designed as an energy retrofit for buildings that already have a recirculation pump installed, the system uses technology developed by the U.S. Department of Energy and commercialized by Advanced Conservation Technology.

Like its residential counterparts, which have been around for more than 15 years (see “Hot Water on Demand,” EBN March 1995 and “New On-Demand Hot-Water System from Taco,” EBN May 2006), D’Mand Circ will only recirculate water when two things are happening simultaneously: demand for hot water is increasing, and the water in the recirculation loop is not hot enough.

The system consists of a standard recirculation pump with added electronics and sensors that detect the flow rate and the water temperature in the supply and return lines of the recirculation loop; the electronic controller only turns the pump on when flow rates exceed one gallon per minute and water in the supply line of the recirculation loop has cooled below 100˚ F. Once the water temperature in the return line of the loop reaches 107˚ F, the controller turns the pump off again. According to Enovative, the pump never stays on more than ten minutes at a time, which typically means it will run one or two hours a day instead of 24.

Energy savings can be significant, but payback will vary. Scott Tucker, president of property management company RST Management, has been using the D’Mand Circ system in 35 buildings for more than a year; they were initially installed for free as part of a Southern California Gas Company pilot incentive program. According to Tucker, savings ranged from 12% to 21%, depending on building layout. A study commissioned by the utility showed that savings were universal but were more dramatic in taller buildings and those with larger hot-water storage tanks.

The primary method of controlling energy bills in buildings with recirculation pumps has been to install a timer that only allows recirculation at peak times. “You never know when someone is going to want a shower at four o’clock in the morning,” Tucker says, explaining the disappointing results, and then it takes several minutes for hot water to get to them. A timer ”saves energy and saves money,“ he notes, “but it causes aggravation.” With the D’Mand Circ pumps, “tenants didn’t know it was happening. It was pretty seamless.”

Without an incentive program, the D’Mand Circ electronics and sensors add more than $1,000 to the cost of installing a recirculation pump, but in addition to savings on water heating, the control system has two other advantages: it reduces electricity use as well as wear and tear on pipes. “Pinhole leaks develop on the circulation line more than any other line,” says Tucker. This is due to erosion corrosion, which is exacerbated by higher heat and greater water pumping speed. Less frequent recirculation should result in fewer leaks.

Enovative expects full availability in the U.S. by the end of 2011 and is in talks with utilities around the country about developing incentive programs.

– Paula Melton

July 1, 2011

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New On-Demand Hot-Water Recirculation System from Taco

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