By Doug Coffey, PE, President
“Winter is coming” means one thing to Game of Thrones fans, but something entirely different for building Owners and maintenance staffs. As winter draws closer and temperatures begin to drop, those who haven’t adequately prepared their buildings’ systems may see a number of issues appear, ranging in inconvenience from chilly occupants and higher energy bills all the way to burst pipes and emergency repairs.
Designing systems to withstand frigid weather is a significant consideration for engineers of commercial building HVAC systems; maintaining the systems designed to prevent winter problems is equally important. To ensure your systems operate as intended, below are a list of items – categorized by system type – to review and verify before that first blast of ice-cold weather hits.
Air Handling Units with Heating/Cooling Water Coils
- Verify that any run-around pumps at heating coils function below their outside air setpoint.
- Verify that outside and relief air dampers close when the unit is off.
- Verify that minimum outside air dampers open when the unit is running to maintain a slight building positive pressure. Negative buildings induce untempered outside air through doors, windows, cracks, etc. and can lead to occupant discomfort.
- Test the operation of the freezestats.
- Address any outside air mixing problems that have been neglected since last winter to avoid nuisance freezestat trips.
- Consider cycling chilled water pumps at very cold outside air temperatures to prevent chilled water coils from freezing.
- Verify that combustion air dampers or combustion air units are functioning. Test end switches which can lock out the boilers if malfunctioning.
- Verify that leaving water temperature controls are functioning.
- Unless the boiler is a condensing type, maintain return water temperatures above 140º F to avoid condensation of the flue gases.
- Test operation of operating/standby pump changeover.
- Verify that boiler safety controls are functional.
- Verify that pumps, boilers, controls, etc. on standby power for emergency heat will function during a power outage.
- Verify that the expansion tank has air and is not flooded.
Gas-Fired Rooftop Units
- Visually inspect the condition of the heat exchangers for signs of corrosion or cracks.
- Verify that space/discharge air temperature controls are functioning.
- Verify that outside air intake hoods are in place and secure.
- Verify that the outside air damper returns to minimum position when the unit is in heating mode.
Terminal Heating Devices
- Verify operation of perimeter finned tube radiation controls. Properly functioning perimeter heat can significantly improve occupant comfort.
- Verify operation of vestibule cabinet unit heaters as well as loading dock heaters. Both areas are susceptible to freezing sprinkler pipes.
- Inspect/replace any filters located in terminal devices
- Periodically inspect duct-mounted electric/hot water reheat coils to verify they are not clogged with dirt.
- On electric coils, verify the operation of the airflow switches and the condition of the contactors on all stages of heat.
- Did you install any new/temporary water piping during the summer in areas that are exposed to freezing weather? Burst pipes can cause considerable damage.
- Verify the freeze temperature of the glycol solution in air-cooled chiller systems. If the system has had leaks and been pumped up with water, the freeze point temperature has increased.
- Thoroughly drain cooling towers not needed for winter cooling.
- Thoroughly drain irrigation systems.
- Winter ice storms can lead to extended power outages. Verify operation of standby power generators and check fuel levels.