A matter of varying degrees
As gas and electricity costs continue to skyrocket, building owners and facility managers are determined more than ever to lower heating and cooling costs.
Laboratory facilities, in particular, are large users of heating and cooling energy, in part because they cannot recycle conditioned air due to the hazardous nature of some research work. Building codes mandate that laboratory heating, ventilation and air-conditioning (HVAC) systems provide 100-percent conditioned makeup air to ensure the safety of occupants.
Energy costs to heat and cool a typical laboratory building average about $4 per square foot per year. Compare that with other building types — such as educational facilities, which average about $1 per square foot per year — and there's little wonder as to why owners of lab facilities are clamoring to integrate the latest technologies for reducing heating and cooling costs.
One of the more common energy-saving methods employed in lab facilities is recovering heat from the HVAC exhaust and transferring it back into the air-intake system for redistribution to the building. At first glance, this process of recycling heat may seem to be as effective as an umbrella in a hailstorm, but it works — and it is saving building owners substantial dollars.
During construction of Branford, Conn.-based Neurogen Corp.'s 20,000-sq.-ft. chemical research building, facility manager William Waldron specified the installation of a glycol-loop heat-recovery system to compensate for the building's heating and cooling costs, which average more than $6 per square foot per year.
"After salaries, energy is the second largest expense item in the pharmaceutical research industry," Waldron says. "It is not unusual for a facility such as Neurogen's to use 15 percent or more of the entire operating budget for energy. This is not out of line with the industry."
The heat-recovery system is essentially a heat exchanger containing coils filled with a solution of glycol and water. It extracts ambient heat from the workstation fume hood exhaust stream before it is discharged above the roofline. This heat is then transferred to the intake or makeup side of the building's HVAC system via the glycol/water solution and reintroduced as part of the conditioned air entering the building. As a result, the amount of energy needed to preheat the makeup air is reduced substantially.
"For every degree we add [to the incoming air], we reduce our energy costs by about 3 percent," says Waldron. "So a 10 F rise in intake air translates into a 30 percent energy savings. We are also helping contribute to a cleaner environment since less fossil fuel is consumed."
Waldron says that during the winter months, it's common for the system to recover 25 F.
During the summer months — or when the outside air temperature is above 80 F — the heat-recovery system is used to help cool the in-take air entering the building. When it's 90 F outside, the system can recover up to 5 F. "You need a big enough difference between outside and inside air temperature to make the system practical," adds Waldron.
A glycol-loop system was also installed in Pharmacia's new 176,000-sq.-ft. research building in Skokie, Ill., which houses scientists focusing on metabolism, toxicology and medicinal chemistry.
Although exact energy savings figures from the heat-recovery unit are not yet available, Steven Schultz, sustainability manager for Pharmacia, says that the system is certainly proving its worth.
"When the outside air temperature is 34 F or higher, we are able to shut off the preheat coils," says Schultz. "That means that the heat-recovery system is warming the incoming air to 55 F by itself, which means the system is picking up around 21 F."
Heat-recovery vs. VAV fume hoods
The Pharmacia facility also incorporates variable-air-volume (VAV) fume hoods, which further reduce the building's heating and cooling costs by adjusting the amount of air exhausted from the fume hoods in relation to the fume hood's open sash area, thereby reducing the amount of conditioned makeup air needed. Sensors monitor the sash position, calculate the open area and adjust airflow accordingly. If a sash is fully closed, it exhausts at 340 cubic feet per minute (cfm) instead of 760 cfm.
"Constant-volume fume hood technology would exhaust 760 cfm all the time, whether the hood sash is open, closed or somewhere in between," says Scott Moll, project engineer with Madison, Wis.-based Affiliated Engineers Inc., the mechanical engineer for the Pharmacia project. "So there's a lot of wasted energy."
Moll says that labs typically incorporate either heat-recovery technology or VAV fume hoods as an energy-saving measure, not both.
"Once you reduce the amount of conditioned air supplied and exhausted, that starts affecting the output of the heat-recovery system, and it does not offer as good a payback," says Moll.
However, collaboration of the building team early in the design phase showed that both technologies should be integrated at Pharmacia.
"We took into account avoided costs to meet a five-year payback schedule," adds Schultz. "By installing the heat-recovery system, we were able to downsize the preheat coils, the cooling coils, the associated piping, the pumps, starters and chillers, as well as a boiler and the water pumps and starters associated with it."
If faced with choosing either one of the technologies, Waldron recommends the heat-recovery system. "I like this technology because it takes people out of the equation," he says. "You're not depending on the fume hood sash position to save energy."
There are three general types of heat-recovery technologies: heat wheels, plate-to-plate heat exchangers and glycol-loop systems. The glycol-loop and plate-to-plate technologies are suitable for lab environments, says Waldron, because no exhaust air comes in direct contact with the intake air. Instead, the heat is transferred through a separate medium — a steel plate for plate-to-plate and a glycol/water mixture for glycol-loop.
Although water is the most ideal heat-transfer element, glycol is needed to prevent the loop from freezing in the winter. "The percentage of glycol in the mixture is tailored to the climate," says Moll.
As for the heat-wheel system, says Waldron, "It actually looks like a wheel and makes use of the principle that in moisture there's a certain amount of latent heat. You wouldn't use a wheel system for a lab because the droplets may contain germs."
One limitation of the plate-to-plate and heat-wheel systems, says Moll, is that they require the building's exhaust and supply systems to be in proximity. The Pharmacia building did not permit this, so a glycol loop was utilized.
Return on investment
With regard to overall costs — for the heat-recovery system hardware as well as energy charges — Waldron believes that a payback cycle of three years or less has made this solution economically sound for Neurogen.
"I have to think that with what's going on with natural gas prices, there will be renewed interest in heat-recovery technology as an energy-saving measure, even if there's a longer payback period." he concludes.