Bob Lee, president of Commercial Boiler Systems, Inc., Pembroke, Massachusetts, knows how to solve big problems. Some days he is selling and servicing 36 million BTU/hour portable snowmelter machines to airports. Other days he is being asked to revamp the domestic hot water system in an enormous school complex.

 Known for being an early adopter of innovative technologies, Lee knew that the Caleffi LEGIOMIX electronic mixing valve would be an excellent fit for accurate domestic hot water control and thermal disinfection at the Mashpee High School and adjoining Quashnet Middle School in Mashpee, Massachusetts.

Lee started his plumbing and heating career while he was in high school. He began working with his father and went on to found his own business in 2004. He has built his business with a reputation for fixing tricky projects.

“Every project we work on is odd,” he explains. “Things that are different, spark my interest. If you are constantly doing the same thing, you are going to get left behind.”

Great fit

All of which made Lee a great fit for the Mashpee schools’ DHW system upgrade. The initial scope of this Massachusetts school retrofit project was to replace aging thermostatic mixing valves that were in use for DHW. One of the three mixing assemblies was scaled up and struggling to maintain a proper mixed water temperature. 

That wasn’t going to cut it for Brad Tripp, facilities supervisor at Mashpee Department of Public Works. Out of the many buildings he is responsible for, he knows the gravity of consistently delivering the correct water temperatures in a school. He also has a keen eye for energy savings 

Working as a team, Tripp and Lee knew that they could tap into energy efficiency upgrade funding from Mass Save, a program formed in 2008 in conjunction with the state and its major utilities to provide incentives efficient plumbing and heating equipment.

“To ensure customers receive the benefits of high efficiency, the sponsors of Mass Save have created the Commercial and Industrial Water Heater Initiative, a market transformation initiative designed to promote and improve the availability of high-efficiency commercial water heaters,” Tripp adds. 

 All of which also made a great fit for the new proposed water heating system. Lee and the team rebuilt the system with new Lochinvar Armor water heaters and three Caleffi LEGIOMIX valves for different wings of the school complex. The high school and kitchen needed a 1-inch LEGIOMIX. The science lab and a separate mechanical room used a ¾-inch LEGIOMIX. The middle school also utilized a ¾-inch LEGIOMIX for temperature control. 

Weekly thermal disinfection

The basic sequence of operation is to thermally disinfect the hot DHW lines every week. When the building is at zero occupancies on a weekend night, the building automation system brings the DHW storage tank set point up from 150 degrees to 165 degrees. This saves energy because the tank is only maintained at 165 degrees during the short, weekly disinfection window. 

Next, the LEGIOMIX goes into disinfection mode, increasing the mixed supply temperature to be circulated with recirculation pumps. Caleffi ThermoSetter balancing valves are used to maintain recirculation temperature per branch as demand conditions change by modulating flow in each riser circuit.

Essentially, excess recirculation with thermal balancing is avoided, which reduces unwanted heat loss and unneeded water heater run cycles. In disinfection mode, the ThermoSetter offers a one-of-a-kind feature, a bypass cartridge to allow for a higher flow rate than normal balancing operation to get through all the branches, controlled through a 24VAC signal. The result is a well-coordinated thermal flush throughout the massive school campus.

The facilities had existing point-of-use mixing valves under all lavatories throughout the buildings. If someone happened to be in the building during the thermal disinfection, they would be protected from scalding while using the sink.

Flexible programming 

As is the case with just about all large projects, an interesting challenge came up during commissioning. 

Effective disinfection of legionella bacteria has a time and temperature relationship. A water temperature of 160 degrees is required to achieve immediate disinfection.

The smaller middle school system performed as anticipated; the temperature of the recirculation line reached the necessary temperature of 160 degrees quickly. 

However, the hot water recirculation line in the high school is very long and the return temperature was consistently colder than planned. Because they were using the digital control capabilities of the LEGIOMIX, they were easily able to program the larger electronic mixing valve at the high school to maintain a return temp of 144 degrees for 45 minutes. This approach works just as well as the quick 160 degrees return to kill the legionella bacteria.

The alternative may have been repiping the high school recirculation line, which would have meant major surgery to the building.

“The LEGIOMIX is easy, accurate, stable, and simple to work on,” Lee says. “I work in a lot of nursing homes and care facilities. Having accurate thermal mixing valves is a must. Avoiding scalding is essential.”

He also likes the tailpiece connection flexibility.

“I have used Caleffi products for years,” Lee adds. “I really like the double union connections. In, out, boom, boom, easy to install and service.”

Verifiable data

Beyond the technical flexibility of the LEGIOMIX, documentation is key. 

Building managers have the ability to log in to the automation system and see the exact temperatures, completed disinfection cycles and balancing valve open/close cycles. These data points help confirm that they are getting it right, beyond the last day of commissioning.

 “The ability to log in to the BMS and show the exact mixed water temperature at any given time from the data logging is important,” Lee says. “For people like Brad Tripp, that is worth a million dollars.”

Lee’s long-standing expertise, coupled with Tripp’s attention to detail, created a strong team that provided an excellent solution for the school district. Now, the students and parents may worry about that math test on Monday, but not wild fluctuations in the hot water fixtures.