The Season of Transition
By: Gary B. Xavier
When summer wanes in the northern climates the days turn cooler in the south as well, requiring heating systems to be readied for the cooler months, and cooling systems, depending on the location, to be shut down or at least minimized for the cooler weather.
Heating System Start-Up
Whether a heating system is a furnace, such as a rooftop unit, or a boiler, if it burns natural or LP gas, the fireside surfaces most likely need little cleaning. Oil-fired burners, on the other hand, will typically have soot deposits on the boiler heating surfaces. If the burner was serviced at the end of the previous heating season, it should be ready for winter start-up. If not, the burner should be cleaned and inspected by a qualified burner technician.
Once the burner has been cleaned and the heat exchanger carefully inspected to make sure there are no leaks of flue gases – which contain deadly carbon monoxide (CO) – into the conditioned space or the mechanical room, a flue gas analysis should be performed to ensure the burner is tuned properly.
In addition, the controls should be checked for proper operation and the burner should be tested for a short time to make sure it starts, operates, and shuts down properly. This is an excellent way to ensure a trouble-free start on the first cold night.
On a furnace, the heat is transferred with air, requiring the use of filters, fans, and perhaps ductwork to carry the heated air to the conditioned space. The air distribution system should be inspected, checking the fans, dampers, louvers, grilles, and ductwork for dirt and debris, and signs of mold or mildew.
Boilers may also use the same air distribution system, with hot water or steam coils in the air handler. If the building is air-conditioned, either evaporator coils or chilled water coils may be in the ductwork as well, and the condensate pans associated with them need to be cleaned and disinfected for the winter season.
Filters are a very important part of the air handling system, and the filters should be inspected, cleaned, and replaced as necessary. Visual inspection of the filters is not usually sufficient to determine the filter’s ability to perform its task, so a pressure drop test or a planned routine changing of the filters is recommended.
Both water and steam boilers need waterside care, and if the boiler was properly laid-up for the summer, the change of seasons should not require much waterside attention.
If the boiler was not prepared for summer lay-up, then the water treatment should be addressed thoroughly before the boiler is restarted for the heating season.
The furnace, boiler, and burner manufacturer’s recommendations and guidelines should always be followed.
Cooling System Shutdown
In the northern regions, air-conditioning systems may be completely shut down for the winter. But as levels of building security and data equipment cooling needs have increased, air-conditioning systems may be required to run twelve months per year even in the coldest climates.
In the warmer areas, the cooling system will most likely need to be operational every day of the year and the heating system may be needed at night.
Both of these situations require the HVAC systems to be monitored and maintained continuously.
Air-cooling/air-cooled units need little attention at the end of the cooling season if they are to be shut down for the winter. Outside coils should be cleaned, and if conditions warrant, the coils can be covered to prevent damage from accumulation of snow or ice. If the coils are covered, however, care should be taken to prevent the infestation of rodents that may nest under the covers. They often chew wiring, insulation, and even component parts which may do serious damage.
If the cooling system is to be operational during the colder months, the use of head pressure controls, often called low-ambient controls, will most likely be necessary. As the outdoor ambient temperature decreases, the high side (head) pressure drops, resulting in a loss of cooling capacity. Head pressure controls should be checked to make sure they are fully functional during the colder months.
If the building cooling is provided by a chiller system, chilled water systems are susceptible to freezing if the coils are exposed to outside air temperatures below the freezing point of water. The coils can be drained if necessary, but typically freeze-stats are used to close the outside air dampers when the temperature drops to near 32°F.
The operation of the freeze-stats and the outside air dampers should be checked to make sure they will provide the proper protection from a frozen and ruptured coil.
On a system that uses a cooling tower, both a closed-circuit cooling tower and an open-circuit cooling tower need to be prepared for cold weather. If the tower operates in just warm weather, it will need to be drained, cleaned, and given a thorough inspection before the winter season.
If the tower is used year ‘round, it may use basin or sump heaters to keep the tower water from freezing. The heaters may be electric or steam, and both types should be checked to make sure they are operational before the weather necessitates their need. Heaters often become covered with scale or sludge, which can cause the heater to overheat and fail. They should be carefully cleaned and checked for proper operation.
Closed-circuit cooling towers, often used for water-source heat pump systems, may be operated in cold months with the tower water drained, but the condenser water is in the closed loop within the tube bundle. This may require protection from freezing the condenser water fluid, so a glycol solution is typically used. If the system has glycol, the glycol concentration should be checked before the onset of cold weather to ensure the proper freeze point of the fluid. The pH and corrosion inhibitor level of the glycol should also be tested to make sure it is within the glycol manufacturer’s recommended parameters.
Regardless of the climate, most buildings will experience temperature differences during a change of seasons, requiring building personnel to take an active role in preparing the HVAC equipment for whatever Mother Nature sends its way.