Most heating professionals have a few good stories up their sleeve to share while enjoying a boiler-side chat with peers.
Here’s one that Gary Sprague, HVAC systems manager at the Providence (R.I.) Housing Authority, occasionally talks about.
It’s big. And there were plenty of oddities, such as snow-melting steam geysers and wasteful temperature control.
Years ago, when the big PHA central plants with aging infrastructure were cranking out Btu, some residents weren’t getting enough heat. Others were throwing it away.
During winter months, it wasn’t uncommon for under-heated tenants to turn on and open ovens to provide more heat. For those who got an overdose of Btu, they would simply open windows.
Of course, the problem was a vexing one for budget-minded caretakers. The heating systems and distribution piping were many decades old. Housing managers with tight budgets had no choice but to sustain “bandage” repairs, though ultimately major surgery was necessary.
PHA provides homes for more than 2,600 families with all units located within the city limits. The housing authority had much to gain and to risk with a retrofit using new technology. But given the energy and labor costs already invested with the original steam system, it was a risk worth taking.
Many of the PHA-managed buildings were constructed in the 1940s, ’50s and ’60s. Between the time of construction until 2008, little changed with mechanical rooms, terminal units and the piping in-between.
“Three properties totaling about 805 family units used district steam heating systems,” Sprague explains. “Between 2008 and 2010, we began a sweeping renovation that decentralized these systems.”
The level of difficulty experienced with the old steam-distribution piping directly stemmed from varying levels of deterioration and the age of the development served by the piping. Many of the pipe systems were no longer serviceable. Little steam geysers springing up through snow-covered lawns had become commonplace.
“Our annual expense to simply maintain the aging steam piping was more than $100,000,” says Sprague, who’s been with the housing authority for 23 years.
Aside from the financial burden of maintaining the aging distribution system, it hindered PHA in other ways. Providence has a city ordinance that requires operators to tend to large boiler systems 24 hours a day, seven days a week and 365 days a year anytime there is a call for heat.
Decentralization at its finest
In a three-year timeframe, PHA set out to dismantle old steam equipment and piping while installing new condensing boilers and distribution systems. With the new systems, two to six apartment buildings are grouped together and served by a single satellite mechanical room.
In each mechanical room stand several Thermal Solutions modulating-condensing boilers. The boilers range in size from one to 750,000 Btu to 1.5 million Btu. The boilers ramp up and cascade down depending on the load and are placed side-by-side, with communication between the boilers being as simple as a phone cord, ultimately interfacing with the building management system and remote monitoring. This allows multiple boilers to receive input from the same outdoor temperature sensor, header supply sensor and returning water sensor, greatly simplifying wiring and saving installation time.
To further minimize operator duties, Thermal Solutions uses a patented radiant burner that never needs to be pulled for cleaning or yearly service — a filter is simply changed once a year. The combination of easy installation, simple maintenance and a 97% efficiency rating made boiler selection easier for PHA managers.
Primary, secondary and tertiary piping carries hot water out of the boiler rooms and to the individual apartments. Super-insulated polyethylene supply and return lines, trenched underground, leave the boiler rooms through pipe sizes as large as 9 in. diameter and taper to 2 in. by the time they reach the individual buildings. Inside, 3/4-in. fin-tube baseboard is the only source of heat.
The replacement project progressed on schedule and when completed, the new systems had the effect PHA hoped for and savings were as projected. Tenant complaints diminished and energy bills plummeted. DHW distribution boilers are now coupled with electric cogeneration units, which are used to produce domestic hot water and to feed the electric grid.
A better way to pump
“One of the main issues before the retrofit was the lack of control we had over the centralized system,” says Joseph Rubino, who has served as PHA’s building systems and control manager for 12 years. “The next step was to incorporate a central monitoring system so we didn’t need to staff the boiler rooms 24/7. We’re now one of few housing authorities in the country with this kind of automation at our finger tips.”
From his office, Rubino can monitor every boiler, every pump and every water heater PHA owns.
As a result of the monitoring capability, a new cost associated with operating the updated hydronic systems became evident. Despite the inefficiencies associated with the old steam system, electricity was never used to actually move heat. With a hot water system, pumping costs became a reality.
In late 2012, PHA’s two oldest developments were chosen as the litmus test for a new approach to hydronic circulation.
Chad Brown was the first public development built in the state. The 198-unit, 20-building division was built in 1940 for returning World War II veterans. Admiral Terrace, adjacent to Chad Brown, is similar. In 1953, the 16-building complex was constructed for returning Korean War veterans and their families.
When the original decentralization project wrapped up in 2009, circulation through primary piping was handled by large in-line pumps. Tertiary piping, which consists of a loop through each of the individual buildings, was pressurized by older circulating pumps. The expense for continuous operation of the pumps was substantial.
While seeking a replacement for the teriary pumps, Sprague contacted HVAC distributor Automatic Heating Equipment to help size a correct replacement pump. PHA soon purchased a sample Taco Viridian pump before deciding to use the technology throughout both the Chad Brown and Admiral Terrace developments.
“The pumps we removed consumed 5.9 to 7.5 amps per hour,” PHA Senior Project Manager Paul Stockman says. “Those pumps ran around the clock during the heating season.”
The Viridian is a wet-rotor pump that uses an ECM motor to eliminate 80% of energy consumption when compared to a standard commercial pump of the same size. With fully automated variable-speed operation, simple Web-style controls and capacities up to 375 gpm, the Viridian line meets a wide range of closed-loop heating and cooling applications. Stockman notes at full throttle the pumps consume 1.8 to 3.5 amps per hour, but unlike the original pumps, they also shut off and modulate to meet the exact demand for hydronic heating water.
An Ethernet connection on the pump allows for remote control, monitoring and adjustment without requiring the involvement of advanced IT or commissioning personnel.
A big win
Sprague explains each of the 36 individual buildings at Chad Brown/Admiral Terrace is served by a single Viridian. “The savings from the pump swap-out are more than we expected,” he says. “You can see that the multiplier for the savings is substantial.”
A commissioning agent was hired to complete a post-retrofit data analysis and energy report which further assured PHA the retrofit was well worth the investment. At $0.11 per kilowatt hour, each Viridian in the system, given typical run time, saves $50 per month during the heating season when compared to the original pumps. With 36 individual buildings now serviced with the new pumps, that’s more than $21,000 annually.
“Not only is electric consumption reduced, but by modulating its speed the pump reduces pressure at the zone valves, which allows for better temperature control within the units themselves,” Taco Director of Product Management Steve Thompson explains. “All told, there are three controls that influence this pump. It’ll speed up and slow down according to pressure differential, turn on and off via the local aquastat and can be controlled from the external building management system that Joseph Rubino designed.”
Stockman says the new pumps have provided energy savings and no maintenance issues since installation. “The savings don’t take into account the greatly improved tenant comfort provided by more accurate pumping,” he says.
Sprague adds: “It’s always been our goal to look to the future for ways to save energy, and this project has proven to do that.”
The project was so successful that it has become the template for other similar projects, including The Boston Housing Authority. Replacing centralized plants with modular boilers and variable-speed pumping has proved itself to be a win-win combination for reducing energy and maintenance costs.
Richard L. Medairos, P.E., is a senior systems engineer and senior trainer at Taco. He has more than 38 years of experience in engineering, project management and planning.
