One of the many benefits of a hydronic system is the ability to upgrade individual components of a large system, which often provides substantial energy savings without huge expense or the need to disrupt building occupants.
Plumley Village Apartment Homes in Worcester, MA, is a 430-unit, private Section 8 housing complex built in the 1970s. It consists of 14, three-story apartment buildings and an 18-story high rise, and is owned and managed by The Community Builders, Inc (TCB).
The building owners wanted to retrofit the heating systems, specifically targeting energy savings without displacing tenants.
When first considering the project, TCB owners contacted the ABCD (Action for Boston Community Development), 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 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.
Low rise, high efficiency
Each of the 14 low-rise buildings is broken into ‘pods’ of six apartment units, for a total of 52 pods. 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 the use of a conventional boiler. A 60-gallon water heater connected to the boiler produced domestic hot water for each pod.
After visiting Plumley Village, Emerson Swan provided a design for the low-rise portion of the apartment complex. Their goal was to remove and replace the boiler serving one pod in a single day so that temporary equipment wasn’t needed. Outside of the mechanical room, the original hydronic system piping did not require changes.
The new design uses a 95+ percent efficiency condensing boiler. Because the new boiler systems prioritized domestic hot water, boiler capacity could be reduced by 40 percent, 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.
To reduce electricity use across the property , the original circulators were upgraded as well. New Taco system pumps, water heater pumps, and hot water recirculation pumps were installed.
Climate Zone, the contractor who won the bid, was changing out entire mechanical rooms in under a day. The new boiler are also smaller and quieter than the originals, providing more storage space and creating less noise.
High Rise retrofit
Unlike the first phase of the project, the high-rise tower at Plumley Village was served by a large district heating and DHW system located in a penthouse mechanical room.
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 hydronic system included three, 2,500 MBH boilers that supplied both heat and DHW via three, 80-gallon indirect water heaters.
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.
Again, the hydronic system piping and all heat delivery equipment was in good shape and was left in service.
Serious efficiency
Victory – and subcontractor Super Heat Mechanical LLC – installed six new, 500 MBH 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 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 the SelfSensing pumps respond to pressure changes without sensors, making them ideal for retrofit applications. Automated, variable-speed operation dramatically enhances electrical and fuel savings.
Comfort, savings, dependability
“Our managers are already talking to Emerson Swan about upgrading the hydronic systems at other properties,” said Justin Hamilton, facilities manager for TCB, who coordinated the Plumley Village project from the beginning of Phase 1.
“The gas savings as a result of this retrofit represents 25% of the three-year average,” said TCB Energy and Sustainability Analyst David Schmidt. That number does not include money saved as a result of the circulator replacements.
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.
Two-phase project benefits at glance:
- Total apartment complex fuel consumption has been 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%
- Rusty water, which was causing failure of circulators and boiler malfunctions, was flushed and further prevented with Fernox magnetic hydronic line filters
- For higher efficiency, DHW and space heating equipment was kept independent when replaced in the hi-rise portion of the project.
- Total installed capacity for hi-rise was reduced by 40%, while DHW storage capacity increased by 45%
- Maintenance time has fallen dramatically
