WORCESTER, MASS. — Plumley Village Apartment Homes in Worcester, Mass., is a 430-unit, private Section 8 housing complex built in the 1970s. It consists of 15, three-story apartment buildings and a 16-story high rise, and is owned and managed by The Community Builders Inc. (TCB).
Beginning in 2013, a sweeping renovation targeted energy savings for heating equipment. Apartments were occupied for the duration of the project, adding some complexity.
When first considering the project, TCB owners contacted the Action for Boston Community Development (ABCD), who in turn brought in manufacturer’s rep firm Emerson Swan, headquartered in Randolph, Mass. Because of the high-efficiency equipment selected, the design-build project was funded by the ABCD through an NSTAR utility program.
Despite problematic wiring, hydronic piping full of corrosion and the challenge of working in an occupied building during the harshest winter in recent history, the end result was increased tenant comfort, substantially reduced energy costs, and less maintenance.
“Each of the 15 low-rise buildings is broken into ‘pods’ of six apartment units, for a total of 52 pods,” explained Justin Hamilton, maintenance supervisor for Plumley Village. “Each pod has a single mechanical room, which is little more than a closet in the stairwell.”
Before the retrofit, fin-tube baseboard radiation heated apartments with a 330 MBH atmospheric boiler operated at roughly 70% efficiency. A 60-gal. indirect water heater was piped as a separate zone and lacked a priority function. The large boilers took up most of the mechanical space, complicating service work.
After visiting Plumley Village in the fall of 2013, Emerson Swan’s Ralph Gates and Mike Oppel provided a design for the low-rise portion of the apartment complex. Their goal was to remove and replace all mechanical components for one pod in a single day so that temporary equipment wasn’t needed.
The new design uses a high-efficiency HTP model EFT 199 boiler. Because the new layout prioritized domestic hot water, boiler capacity could be reduced by 40%, meaning further energy savings and lower initial cost.
Old water heaters were replaced with stainless steel, Superstor 60-gallon units. The temperature of stored water was raised to 140°F, which eliminates any risk of legionella bacteria growth and increases the thermal capacity of the tanks. Scald prevention is provided by a thermostatic mixing valve on each tank.
Before the retrofit, existing circulators failed routinely due to water quality issues. New Taco system pumps, water heater pumps and DHW recirculation pumps were installed, as were Taco 4900 Series air separators. The existing system controls were discarded because the factory controls featured on the EFT boiler have the same capabilities.
System fluid fix
“The Phase 1 design was flawless,” said Hamilton. “Climate Zone, the contractor who won the bid, was changing out entire mechanical rooms in under a day, and there is more floor space and less noise with the new boilers. The only glitch came right in the beginning. The very first boiler locked out within 45 minutes of being fired.”
The initial design had included system flushing and installation of Fernox magnetic hydronic line filters, both of which were cut from the plan before the project went out to bid. This dirty water had been destroying the circulators before the retrofit, and ended up clogging the new boiler.
To avoid the problem, installers began flushing lines as they started each pod. The water that came out looked like mud. The Fernox filters were added back to the parts list, and boiler commissioning went smoothly from that point forward.
“Poor water quality was one of several challenges we fought at Plumley,” said Andy DiPietro, owner of Climate Zone. “But as they always do, Swan had a solution for it.” DiPietro, who began working for his father at age 12, launched Climate Zone in 2002. The company now serves commercial and residential clients in the Merrimack Valley and southern New Hampshire.
High rise retrofit
Unlike the first phase of the project, the high-rise tower was served by a large district heating and DHW system located in a penthouse mechanical room. As a result, renovations couldn’t take place during the heating season.
During the winter, TCB put the Phase 2 design out to bid. When the weather broke in the spring, Victory HVAC began to install the new DHW system before the old boilers were taken offline. In doing so, the building only lost DHW input for a four-hour period.
The existing system included three, 2,500 MBH boilers that supplied both heat and DHW via three, 80-gallon indirect water heaters. All pumps and boilers were severely oversized, while the DHW tanks were undersized. As a result, the boilers short-cycled on both heating and DHW calls. Without functional controls, the pumps had to be manually started and stopped, which required constant attention from maintenance personnel.
The new design separates the DHW and heating systems for maximum efficiency. This, combined with the advantage of modulating equipment, means that the system will never fire higher than it needs to, regardless of how small the call for heat is.
“This project is indicative of what’s possible when we get the opportunity to work with a guy like Gates who really knows the products he represents,” said Don Fleck, systems engineer for Victory. The firm serves Massachusetts and the surrounding states. Their 80 employees focus mainly on commercial projects, but their residential work has doubled in the past year.
“Emerson Swan does a great job of envisioning what’s possible in a building and selecting the best equipment for the application,” continued Fleck. “So the finished design is always a team effort between his office and ours.”
Victory — and subcontractor Super Heat Mechanical LLC — installed six HTP Mod Con 500 boilers for a combined space heating input of 3,000 MBH. The building’s load is approximately 1,650 MBH, so the new system provides 30% redundancy.
The huge system pumps were replaced with VFD-powered Taco SelfSensing SKV pumps. Unlike before, the new pumps start, stop and vary their speed automatically depending on the heating demand. This is typically only possible when pressure sensors are installed at every zone. But the design team could offer a unique solution because Taco’s SelfSensing pumps respond to pressure changes without sensors, making them ideal for retrofit applications as well as new construction. The pumps’ automated, variable-speed operation dramatically enhances electrical and fuel savings.
Much like in Phase 1, the existing system controls were removed and the boiler controls are used to operate the entire system, further reducing material and commissioning costs.
For DHW, three Mod Con 500 volume water heaters now achieve the same staged-input operation that the heating system has. For more efficiency and capacity, three, 175-gallon HTP storage tanks were installed.
The total heating and DHW capacity installed at the high-rise was reduced by almost 45%.
“Our managers are already talking to Emerson Swan about design-build projects at other properties,” said Hamilton, who coordinated the Plumley Village project from the beginning of Phase 1.
“While concrete energy data isn’t available until next heating season, the estimated gas savings represents 25.1% of the three-year average,” said TCB Energy and Sustainability Analyst David Schmidt.
But according to Hamilton, energy savings are only half the story. Boiler, controls and pump maintenance are now virtually non-existent, and complaints from tenants are at an all-time low.
Below are some of the two-phase project benefits at glance:
- Total apartment complex fuel consumption reduced by 25%.
- Complaints for lack of heat or DHW have all but ceased.
- Problematic control systems have been removed entirely.
- Low-rise apartments now have domestic hot water priority.
- Low-rise boiler capacity reduced by 40%.
- Taco SelfSensing pumps offer automatic, variable-speed operation.
- Rusty water, which was causing failure of circulators and boiler malfunctions, was flushed and further prevented with Fernox magnetic hydronic line filters.