Commercial Buildings

View thorough guidelines on reducing energy consumption in commercial buildings and kitchens.

Proper operation and maintenance of gas fired systems can save a significant amount of natural gas. Here are some ideas for reducing energy consumption in your gas fired systems through proper operating and maintenance procedures.

HVAC

Minimize the opening of the outside air dampers on air handling units and rooftop package equipment. Ventilation code dictates that the dampers should be open adequately to provide a minimum of 20 cfm per occupant. By multiplying the number of occupants by 20 cfm, you can determine how much ventilation is required and set the dampers accordingly.

Ensure that the outside air intake dampers are closed during nonoccupied hours. Ventilation is required only during occupied hours.

Make sure that automatic exhaust and ventilation dampers are operating properly. Sticking or nonfunctioning dampers can result in heating excessive amounts of outside air and subsequent natural gas waste.

Automate bathroom exhaust fans during nonoccupied hours or turn off fans when bathrooms aren't in use. This minimizes the amount of cold outside air that enters the building.

Minimize the openings of exhaust dampers on rooftop package units and air handling units. This reduces the amount of cold outside air that must be brought into the building to make up for the exhaust air.

Boilers

Tune the boilers to assure that excess O2 is within acceptable levels. If excess O2 levels are too high, a significant amount of the heat from the combustion gases is swept up the stack prior to getting useful work out of it. At high fire, the excess O2 levels should not exceed 6%.

High excess CO levels are an indication that incomplete combustion is taking place. In other words, unburned fuel is going up the stack and, as a result, is wasted. Ensure that excess CO levels do not exceed 200 ppm.

Ensure that the heating and air conditioning duct system return air vents are clear of obstructions. When the vents are obstructed, the air handling system will draw into a vacuum and attempt to compensate by drawing in additional outside air. This results in the need to add additional heat to the air stream.

Set the heating thermostat at about 68°F. This set point will maintain comfort conditions while minimizing energy consumption. Comfort conditions are defined by ASHRAE as that temperature when 80 percent of occupants are satisfied.

Scale and corrosion buildup on furnace heat exchangers will reduce heat transfer and result in inefficient operation. Perform periodic maintenance on the heat exchangers to minimize deposit build-up.

Scale build-up on boiler tubes will inhibit heat transfer across the tube surface. Because heat is not being transferred from the hot combustion gases to the water, the combustion gases exit through the stack at a higher temperature than is optimum. As a result the boiler must burn additional gas to meet the hot water/steam requirements of the system. High stack temperatures are usually a good indicator of scale build-up on the tubes of the boiler. The tubes should be either mechanically or chemically cleaned during the next shutdown. The stack temperature should not exceed the saturated steam temperature plus about 200°F.

Check and repair/replace steam traps as necessary. A leaking steam trap can result in hundreds, or even thousands, of dollars in additional natural gas consumption each year. The higher the pressure of the steam system, the more often the steam traps should be checked.

Excessive steam escaping from the feedwater tank vent usually indicates that there is an internal steam leak within the steam system. Most often, this steam leak is due to faulty steam traps. Typically, the escaping steam will be white in color and will be exiting the vent at a high velocity. Grey, slow steam plumes are typically just flash steam exiting the feedwater tank and are not an indication of inefficient operation.

Optimize the lead/lag operation of your boilers. As a rule, boilers operate most efficiently between 70 and 100 percent of their rated capacity. They typically operate less efficiently in the lower end of their operating range because of the tendency toward high excess air levels. For example, when there are two boilers of equal size, it is more efficient to operate one of them at 70 percent capacity than two of them at 35 percent capacity.

It is more efficient to continue to operate a boiler at low-fire than it is to shut the boiler off. When the boiler is shut down, it goes into the post-operation purge mode. This extracts a significant amount of heat from the boiler. When the boiler is going to start up again, it goes into the prepurge mode, once again extracting heat from the boiler. Each time the boiler comes on line, it spends the first few minutes of operation replacing the heat that was lost during the purge cycles. This is wasted energy.

Set the thermostat back to 55°F for nonoccupied hours.

Reset the temperature of the hot water serving the heating coils as a function of outside air temperature. As outside air temperature goes up, the supply temperature of the hot water can be set downward. This can be done manually or automatically. However, automatic control will require some modification to the existing piping system and control system.

Consider preventive measures such as changing air filters, checking temperature settings, adjusting equipment operation schedules and cleaning light fixtures.

Use energy-efficient equipment and building technologies to reduce building loads, thus lowering your electric, heating and cooling bills.

Capitalize on the heating, cooling and electrical load reductions you have realized through previous upgrades by allocating the funding to reevaluate heating and cooling loads and HVAC systems for possible downsizing.