New On-Demand Hot-Water Recirculation System from Taco

Close to twelve years ago, Advanced Conservation Technology (ACT) introduced the Metlund^® D’mand^® System to address the issue of water and energy waste while waiting for hot water to reach the tap at fixtures located some distance from the water heater. Now there is another system—well it’s

almost another system. Taco^®, the nation’s largest manufacturer of HVAC pumps, has just introduced its own version of the D’mand System.

The basic principles and operation of the Metlund D’mand system were covered in

EBN

Vol. 4, No. 2, but here’s a recap: The D’mand system is an electronically activated water-pumping system that quickly delivers hot water to a fixture while returning water that has been sitting in the hot-water pipes back into the hot-water tank. In retrofit applications, the D’mand system is typically installed under the sink farthest from the water heater. The pump may be activated on demand by pushing a button near the fixture or by activating a remote control, and it switches off when hot water reaches the temperature sensor (thermistor) on the pump at the fixture. The benefits include quick access to hot water (usually less than 30 seconds), the elimination of water waste while waiting for hot water, and energy savings.

The energy savings occur in several ways. First, water recirculated back into the hot-water tank is at least at the ambient temperature of the house; this is generally a lot warmer than the cold water coming into the house—so the water heater doesn’t have to use as much energy to boost it to the set temperature. Second, since the D’mand recirculation pump moves water more quickly than the fixture flow rate, less heat will be lost from the piping en route to the fixture. Third, with a D’mand system, occupant behavior may change. According to ACT president Larry Acker, homeowners often turn the hot water on and walk away, doing something else while waiting for hot water at the sink or shower; that can result in tremendous waste of both energy and water. Fourth, energy savings may be achieved if homeowners turn down the temperature settings on their water heaters. Acker learned about this practice in 1995 when he surveyed several dozen purchasers of the Metlund D’mand system; he was surprised to learn that many respondents had turned down the water heater setting because the water reaching their sinks was too hot—much hotter than before the D’mand systems had been installed. Finally, even greater energy savings will be realized if the D’mand system is installed in place of a

continuous-circulation system. Continuous hot-water circulation is used in most hotels and commercial office buildings, and it is gaining popularity in homes. The problem with this system is that even if the hot-water lines are insulated, significant heat loss and electricity use (from the pump) still occur around the clock (see feature article on water heating in

EBN

Vol. 11, No. 10).

In retrofit applications, the cold-water line serves as the return line for water being pumped back to the hot-water tank. In new construction, a third plumbing line is usually installed to serve as the return line. In this case, the recirculation pump may be installed at the water heater. It is still preferable to install the thermal sensor at the farthest fixture so the circulation pump shuts off before the hot water gets all the way back to the water heater. Since 1993, ACT has sold more than 30,000 on-demand recirculation systems, according to Acker, and sales have picked up dramatically in the past year.

For all intents and purposes, the Taco D’mand system is identical to the Metlund D’mand system. According to Doug Bird of Taco, “It’s exactly the same; we’re taking his technology and incorporating it into our pump.” The key technology in the D’mand system is the logic board that controls the switching of the pump, which ACT sells to Taco. “It’s like the Intel^® chip in a computer,” says Acker.

While the systems are very similar (ACT has long been using Taco pumps), Acker also points out a few differences between the ACT Metlund and Taco products. For one, Taco has incorporated the thermistor—which senses water temperature at the tap and tells the logic board to turn off the pump—into the casing next to the pump. Integrating the thermistor into the casing is a “very good idea,” according to Acker. “The temperature differentials will be more accurate,” he said. While ACT Metlund offers a motion-sensor option for its product line, that is not currently available with the Taco models.

More significant than the physical differences between the Metlund and Taco products will be the distribution differences. While ACT has had to really work to make the Metlund D’mand system available to builders and plumbers, Taco has access to a huge network of wholesale plumbing suppliers. The Taco D’mand will be distributed through “stocking reps” who sell to wholesale plumbing suppliers. ACT will concentrate on sales to utility companies for special water and energy conservation programs and on the direct retail side—such as Home Depot.

Like the Metlund D’mand, the Taco product will be available in three sizes (see table below). The 008-DM is the most common system, sized for most homes. The 0011-DM is suitable for light-commercial buildings and very large homes. The 006-DM is appropriate for smaller homes. The 008-DM is now available, and the other two models will come out over the next few months, according to Bird.

Whichever D’mand system is used, the water and energy savings can be significant. A new study from Oak Ridge National Laboratory, in which five D’mand systems were installed in older homes in Palo Alto, California, measured water savings of 900 to 3,000 gallons (3,400–11,400 l) and electricity savings (all the homes had electric water heating) of 67 to 400 kWh during a one-year period. Due to constraints of the study, savings were measured for only one end-use fixture in each house. The Oak Ridge researchers projected substantially greater savings in more modern, sprawling homes, in which several bathrooms and the kitchen may be located quite far from the water heater. ACT Metlund claims that a typical American household wastes an average of 9,000 gallons (34,000 l) of water annually waiting for hot water.

In a brochure about the D’mand system, Taco shows that if water consumption is reduced by 40 gallons (150 l) per day and the water heater setting is lowered, annual dollar savings (water, sewage, and energy) could total up to $180 with gas water heating and $500 with electric water heating. While these values may be exaggerated, the savings are clearly great enough to justify this system from a life-cycle costing standpoint—let alone the environmental benefits of resource savings.

– AW

For more information:

Taco, Inc.

1160 Cranston Street

401-942-8000

401-942-2360 (fax)

www.taco-hvac.com

Advanced Conservation Technology, Inc.

3176 Pullman Street, Ste. 119

800-638-5863, 714-668-1200

714-668-1927 (fax)

www.gothotwater.com