Brave new system recycles office- generated heat
When Nancy McKenna arrives for work in the morning at Boston's new Transportation Building, she begins two jobs at the same time. As she starts typing, she has already begun a second job -- helping to heat the building. Shunning furnace and fossil fuels, this conventional red-brick government building uses a system that recovers heat from its 2,000 employees (a body gives off 250 Btu per hour -- the equivalent of a 75-watt light bulb). In addition to body heat, the system also hoards warmth from office lights, machines, and computers -- warmth which feeds 20 to 30 percent of the building's energy appetite. Designed by Henry Eggert and Howard McKew of Boston's Shooshanian Engineering Associates, this ``bring your own heat'' feat also included a bold stroke for this cold-weather area -- not installing a backup steam-heat system.
So last February, when New England dished up its usual winter fare -- flying snow, howling winds, and near zero F. temperatures -- the inside of this eight-story, 880,000-square-foot structure was a comfy 72 degrees.
And this has brought warm smiles from employees. ``It's been great,'' says Miss McKenna, who moved in last February with the first wave of employees from the Massachusetts Bay Transportation Authority. ``Last winter the building was warm, and last summer it was cool,'' she says.
Chief engineer Laszlo Fleischer, who oversees the heating and cooling operation, sits in his office, warm air pouring from thin vents next to the window, and pronounces the system a success so far. But he says, ``There are still some minor hitches, like small pockets in the building that stay too cool or warm.''
After the 1979 energy crisis, building planners and engineers became energy bounty hunters, tracking every excess Btu they could get their hands on to bring soaring fuel bills down. Since the inner offices of most buildings overheat and require air conditioning, even in winter, the plan for the transportation building was simple. Put this waste heat to work.
The system, which doubles as an air conditioner in the summer, takes the warmth generated by people, machines, and lights from the core of the building and transfers it to the cool outer offices.
A network of circulating cool water coils absorbs this waste heat from inner offices, cooling them in the process. The water, now heated about 10 degrees, flows down to a 300-ton heat pump, where the heat is removed and transferred to a separate hot water coil that circulates up to the building's cool outer offices.
As the heat pumps take heat from water, they are also generating a tremendous amount of waste heat themselves, which is trapped and used to provide the remaining 70 to 80 percent of the building's energy needs. While the system's heat pumps require loads of electricity, comparable oil costs would be greater.
Storage is the key. Three 250,000-gallon water tanks sit in the basement acting as heat banks, where warmth is deposited when there is an excess and withdrawn when there is a shortage. If employees are absent and machinery and lights are not in operation for, say, a three-day weekend, these huge concrete water tanks feed out their stored energy as needed, keeping building temperatures hovering around 72. In summer the flip side of this process takes hold, and the system works as an air conditioner. Cold water, chilled by compressors to about 44 degrees during the night and stored in the mammoth tanks, circulates throughout the building, cooling air that is vented into rooms.
Masterminding the entire operation is a Honeywell Data 1000 computer smack in the center of the system control room -- its ``eye'' scanning a host of information on the flows of water and air, as well as building and tank temperatures. From a host of options -- closing off this vent, opening up that tank -- it sends out commands to keep optimum temperatures.
Situated in Boston's theater district, the building was designed so as not to waste a Btu. Thick walls and recessed windows of double-paned glass are two of the features that trap heat or cold from escaping. In a separate system, solar panels on the roof provide 80 percent of the domestic hot water requirements for lavatories.
While this is not the first building to use the chiller/ heat exchanger system, it is said to be the first to rely solely on it without a backup system that could kick in, should the system malfunction. In Toronto a 20-story skyscraper uses this system, but it includes a backup of steam heat. Howard McKew, design engineer, says the price tag for Boston's system was $9 million, which saved $1 million over a conventional heating system that would have required a backup boiler and chimneys.
Savings have yet to be calculated because retail outlets and restaurants planned for the first floor are still unoccupied. This ``high energy space,'' says Mr. McKew, is squandering the closed system's energy.
But a building of comparable size using conventional heat eats up roughly 90,000 to 100,000 Btu per square foot per year, while this design uses 60,000 Btu, due to the building's energy efficiency and heat recovery system. This 30 percent savings is only a computer projection at this point, however. ``We have projected a net savings of the equivalent of 300,000 gallons of oil a year, or about $400,000,'' says Mr. McKew.