When it’s cold outside, cooling equipment is likely the last thing on your mind. However, winter can be a great time to upgrade, repair, or reset your cooling system.
Scheduling cooling adjustments during the heating season offers two advantages: HVAC technicians have more time available outside their peak season, and better wintertime maintenance helps you avoid the need for summertime emergency service.
To keep your system at peak efficiency, consider these tips.
Stick to Preventive Maintenance Schedules
Routine cleaning, a frequently deferred maintenance task, can have a significant impact on energy efficiency, according to the Federal Energy Management Program (FEMP)’s O&M Center of Excellence.
A 1997 study by Pacific Gas & Electric in California found that a dirty condenser coil can increase compressor energy consumption by up to 30%. In addition, dirty filters allow unfiltered air to bypass the clogged filter altogether and deposit grime on the evaporator coil, which is much harder to clean than a filter is to replace.
“You should check the filters at least once a month. Depending on the type of filter you’re using, it may only need to be changed every 90 days or even every six months,” says Wes Brookover, service manager for HVAC firm McClintock Heating & Cooling. “The condenser coil is easy enough to clean – you can buy coil cleaner, spray it on the coil, and hose it off – but the evaporator coil is inside and you need to remove panels to access and clean it, so I recommend using a licensed contractor.”
Does your property utilize a cooling tower? The same principle of regular cleaning applies there too, says Tom Ryder, customer support and business development tech at Delta Cooling Towers, a manufacturer of cooling towers, systems, and air strippers.
“Efficiency-related preventive maintenance applies to changing the packing, much like the oil or gas filter in your car. This way the car engine – or in this case, the cooling tower – doesn’t have to work harder in order to maintain proper cooling temperatures,” Ryder notes. “Also make sure the cooling tower’s air intake louvers are free of build-up and debris.”
Check and Correct Settings
Preventive maintenance for cooling equipment should include periodic inspection of settings that can affect its performance and efficiency. Chief among your HVAC system’s energy consumers is the compressor, Brookover notes, so it pays to make sure the compressor can operate at peak efficiency.
You should also periodically measure the refrigerant charge and correct it if necessary. Fixing an incorrect refrigerant charge can save 5-10% on cooling costs, FEMP says.
Using the manufacturer’s chart, look up the evaporating temperature that corresponds with the measured suction line pressure, then measure the actual suction line temperature. The difference between these two numbers is called the superheat temperature, FEMP notes. In most direct pressure systems, this usually falls between 10-20 degrees F.
If your system has a thermal expansion valve, FEMP recommends that you also check the degree of subcooling against the manufacturer’s recommendations.
Changing the thermostat settings can also lower your energy spend, particularly if the previous setpoints were overridden in response to a thermal comfort complaint. If your facility has programmable thermostats, make sure you’ve arranged for a temperature setback during off-hours, Brookover says.
“I would recommend a setback of no more than 4 degrees F.,” Brookover explains. “If you want it to be 72 degrees when the building is occupied, I wouldn’t let it go above 76 when it’s unoccupied. You’ll spend more to cool back down than you would save by keeping the air conditioning shut off all day.”
Fix Leaks and Malfunctions
Leaks and poorly performing equipment can stymie your best efforts to shore up cooling efficiency, so as you give the rest of the system a tune-up, keep an eye out for components that need repairs.
Ductwork leaks, for example, are fairly common, Brookover notes. Unfortunately, this problem is also frequently overlooked unless a sudden leak triggers a significant spike in energy consumption. Sealing duct leaks and restoring the integrity of the unit cabinet can save around 20% of your annual cooling consumption, FEMP advises.
Common corrective actions including simple screw or latch replacements, patching or replacing gaskets, and replacing missing screws on any loose access panels. The condensate drain pipe may also leak air, so be sure to recharge P-traps or U-bend water traps for condensate drain pans.
If you have an economizer, also check it for malfunctions, which FEMP notes can include a jammed outside air damper; jammed, broken, or disconnected linkage; a nonfunctioning actuator; or inaccurate air temperature sensors. These issues impair the economizer’s ability to sense and respond to the temperature of the outside air vs. return air.
Additionally, an economizer that’s not operating properly can actually waste energy. If the outside air damper is stuck open, the HVAC system has to work harder to heat or cool the excess outdoor air.
FEMP recommends a twice-yearly test of economizer function using the following three steps:
- When the system is mechanically cooling, make sure the economizer is using minimum outdoor air settings.
- Cycle the minimum position potentiometer from 0 to full open. Watch the damper to make sure it can operate freely and without obstruction the entire time.
- On a cool day when the damper is open, warm the outdoor air temperature sensor with your hands or an electric hair dryer to see if the damper moves to its minimum position. If it doesn’t, you might need to recalibrate the sensor or deal with malfunctioning economizer controls.
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Janelle Penny firstname.lastname@example.org is associate editor of BUILDINGS.