Viessmann Gives Public Housing Authority Flexible Options for Heat and DHW.
Posted on October 25, 2016
Like many public housing authorities across the country, Cambridge Housing Authority (CHA) in Cambridge, Massachusetts is responsible for thousands of rental units at dozens of sites. These complexes are comprised of a variety of structural types including high rises, traditional town house styles, and post- World War II three-story buildings. As the utility infrastructures of these projects reach the end of their useful lives, CHA is taking advantage of federal Rental Assistance Demonstration (RAD) funding incentives to replace aging boilers and domestic hot water heaters with more efficient, lower-maintenance alternatives.
The CHA Planning and Development Department oversees a six-year rollout that will ultimately affect approximately 100 buildings in locations throughout the city. While the goals for each site are similar – to replace atmospheric and older cast-iron module type boilers of about 82% - 85% efficiency with high [approximately] efficiency boilers that can also serve DHW needs – boiler room design and access varies project by project. By working with Viessmann, CHA gains flexibility: the Vitocrossal line of high-mass boilers can replace older boilers without requiring many piping changes; for tighter workspaces that cannot accommodate the Vitocrossals, the Vitodens line of low-mass condensing boilers, notable for their small size, can fit just about anywhere easily.
Tested in action
Now in the second year of the overhaul, CHA is moving forward based on lessons learned in earlier projects. Last year, Putnam Gardens, a housing complex serving 3 buildings and 122 units through one central boiler room, had experimented with three Vitodens B2HB-57, 199 MBH input to serve the complex’s DHW needs. “We saw the improvement in performance immediately,” says Gannon, who supervises a staff of twelve. “My guys really like them because of the ease of maintenance and the straight-forward nature of the control system.”
To support simpler, more rapid installations, Cambridge Housing Authority has taken advantage of Viessmann’s rack systems that incorporate all the boiler-to-piping connections, including the low-loss headers. “This made it much more convenient for us to do the piping work,” Gannon says.
After the initial success at Putnam, Cambridge Housing Authority has moved on with four additional projects including: Washington Elms, a 15-building, 175-unit complex with six boiler rooms, each served by varying numbers of Vitodens 200W B2HA-150, 490 MBH boilers for a total of 27 overall; Newtown Court, a 8-building, 268-unit project served by two boiler rooms, each with three Vitocrossal 200-CM2-400, 1445 MBH input; Woodrow Wilson Court with 6 of the Vitodens 200-W B2HW-150, 490 MBH, and continued Putnam Gardens improvements that added 4 of the Vitocrossal 200-CM2-620, 2245 MBH input for heat. A fifth complex, Jefferson Park, has just been torn down; it will be replaced by 6 buildings with 103 units, served by two boiler rooms with three Vitocrossal 200-CM2-186, 663 MBH input each.
Sophisticated design, dedicated support
The key to achieving high efficiency lies in the ability to reduce the temperature of the return water: the lower it is, the greater the opportunity to squeezed BTUs through condensation. Working with Viessmann, Cambridge Housing Authority tackles the challenges on multiple fronts.
“Terminal heating has to be sized for lower temperatures,” Gannon says. By maximizing the surface areas (either in fin-tube radiation or fan coil units), CHA is able to lower the running supply temperature to provide comfortable heat, and to get lower temperatures on the return.
By using the boilers to serve DHW, the Housing Authority not only has a more efficient way of supplying hot water, but another opportunity to lower return temperatures for greater heating efficiency as well. Through the use of Armstrong Brain mixing valves, CHA’s boilers get return temperatures ideal for condensing.
Together, CHA, Viessmann, and a host of mechanical engineers have been designing boiler rooms with a minimum of boilers to simplify maintenance, yet provide sufficient redundancy to guarantee comfort. Some of the future projects include cogeneration units for electricity; their hot water byproduct will reduce the boiler’s load and, in the peak summer season, may be able to produce sufficient DHW without running the boilers at all.
Given New England’s climate, CHA has a narrow installation window for its heating and DHW projects – June 15 through September 15 each year – making effective collaboration an absolute necessity for success. “Viessmann has been terrific,” Gannon says. In addition to conducting staff training on-site and at their facilities in Rhode Island, Tom Fullerton from Viessmann is always available for support. “They’re there whenever we need them,” says Gannon. “And that’s a very positive thing.”
CHA projects to date
· 3 buildings
· 122 units
· 1 boiler room
· 3 Vitodens B2HB-57, 199 MBH input for DHW
· 4 Vitocrossal 200-CM2-620, 2245 MBH input for
· 15 buildings
· 175 units
· 6 boiler rooms
· 27 Vitodens 200W B2HA-150, 490 MBH input for
heat and DHW
· 6 buildings
· 268 units
· 2 boiler rooms
· 3 Vitocrossal 200-CM2-400, 1445 MBH input for
heat and DHW
Woodrow Wilson Court:
· 2 buildings
· 89 Units
· 1 boiler room
· 6 Vitodens 200-W B2HW-150, 490 MBH
· 6 building
· 103 units
· 2 boiler rooms
· 6 Vitocrossal 200-CM2-186, 663 MBH input for heat
Vitodens 200-W, B2HA, Wall Mounted Gas Condensing Boiler