Properly balancing one-pipe steam systems requires right sizing air vents on radiators. This is a typical situation and cheap to fix, von Braun says.
Tuning or upgrading boiler controls can increase boiler efficiency. Boilers in many building are set to send 180 degree Fahrenheit (F) water to the system year around. Boiler controls can be tuned with outdoor resets that only send 180 degree F water during extreme outdoor temperatures, otherwise water temperatures are scaled back based on outdoor temperatures, Zuluaga explains.
The 20-story, 151-unit co-op at 180 East End Avenue, New York, is replacing antiquated steam boiler controls with Heat Timers with outdoor temperature resets. The old controls were causing boiler short cycling, which increased fuel consumption, says Michael Scorrano, managing director at the En-Power Group, Katonah, N.Y.
Alternatively, apartments can be outfitted with temperature sensors that communicate with the boiler. The controls adjust the hydronic loops better by either running the system longer or turning off pumps when the system has satisfied internal temperatures, Scorrano explains.
VentilationVentilation systems present big opportunities for improving energy efficiency. In mid- and high-rise buildings mechanical ventilation is typically provided by central exhaust systems with roof fans connected to vertical shafts. Exhaust registers at each floor draw air from kitchens and baths.
Zuluaga frequently sees improperly balanced systems delivering too little ventilation to lower floors and too much ventilation to upper floors. The nine-story, 106-unit Carlyle Towers in West Caldwell, N.J., offers a case in point.
Cooling at the Carlyle is provided by a central chiller and fan coils. During the summer top floor residents complained of being too hot.
An audit found the ventilation system sucking 250 cubic feet per minute (cfm) from the kitchens and baths on the upper floor. “In the summer this meant that 250 cfms of hot, humid air was drawn into the apartments,” Zuluaga says. “Meanwhile the lower floors might have been drawing 20 cfms.”
Kitchens and baths were retrofitted with Constant Airflow Regulators (CAR). A CAR is a duct boot end and register cover with an air mechanism that uses air pressure to evenly regulate air flow.
The audit also discovered poorly sealed ductwork causing the roof exhaust fans to pull excessive amounts of air from building cavities. Leakage was reduced with Aeroseal, a polymer-based sealant injected into the ducts.
Since the retrofits natural gas usage is down 25 percent, resulting in a $19,000 annual savings. Installing smaller roof fans saved an additional $6,000 in energy costs.