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Two strategies for maximizing rooftop HVAC unit efficiency

Image of rooftop HVAC units

Rooftop HVAC units an overlooked savings opportunity, specialist says

Some energy efficiency opportunities are easy to spot. Inefficient and out-dated lighting will fade, flicker and burnout. Refrigeration units show their age with inconsistent cooling and a noisy compressor. But deficiencies in certain types of HVAC equipment aren't as obvious.

"Rooftop HVAC units (RTUs) in particular are routinely overlooked as energy-saving opportunities. It's the idea that something is easily forgotten or dismissed as unimportant if it's not right in front of us," says Reid Arkinstall, commercial marketing specialist at BC Hydro.

An RTU is an outdoor, roof-mounted air-handling unit that provides heating, ventilation and air conditioning to the building below. RTUs are also known as packaged systems because all of the components, including the coils that release and absorb heat, along with the compressors and fans, are housed in one unit or "package" and stored out of the way on the rooftop. RTUs connect directly into a building's central ventilation system to circulate air and are commonly used on low-rise commercial buildings, such as restaurants, warehouses and offices.

"Approximately 20%1 of commercial customers in the province have at least one rooftop HVAC unit," says Arkinstall. "Given the number of units and tendency for them to be neglected, the energy and cost saving potential for business owners with RTUs is significant."

Neglect impacts the performance of a rooftop HVAC unit

"When a rooftop unit suddenly breaks down, it's often the only time it gets attention. It's actually a lot like a car," Arkinstall explains. "Many of us only pay attention to vehicle maintenance once we run into an issue and can't pull out of the driveway.

"For instance, if you own a gas-powered vehicle, it's a good idea to rotate the tires and change the car's oil every 10,000 – 16,000 kilometres. Without this kind of preventative maintenance, there's a good chance the car will break down earlier than if it was cared for. The same thinking applies to rooftop HVAC units. Left unattended in harsh weather, these units will become increasingly inefficient and breakdown over time."

Two strategies for improving the efficiency of rooftop HVAC units

Arkinstall suggests two strategies for improving the efficiency of RTUs:

  • Have a qualified commercial HVAC specialist inspect your rooftop HVAC unit four times per year
  • Retrofit an existing rooftop HVAC unit with advanced controls

Preventative Maintenance

"As the saying goes, an ounce of prevention is worth a pound of cure," says Arkinstall. "Regularly having your RTU serviced by an HVAC professional – four times per year is ideal – is the best way to avoid costly, unforeseen repairs and to keep the unit in the best condition possible."

Advanced Controls

"Most rooftop HVAC systems run at a constant volume," explains Arkinstall. "When it's switched on, it blows air through the space, no matter what the occupancy is and no matter what time of day. It's either on or off.

"Advanced control technology provides variable speed control, which means the rooftop unit only operates at the volume needed. Sensors can also monitor the temperature of the indoor space, as well as the level of carbon dioxide in the air, to see how stale the air is as a measurement of occupancy."

Example of the cost versus benefit of advanced control technology

Advanced control Adding a variable frequency drive to a fan that's only two speeds (i.e., on or off)
Average project cost $4,000 CAD
Average electrical savings per year $2,000 CAD
Average % of project cost covered by BC Hydro incentive Up to 30%
BC Hydro program Business Energy Savings Incentives program
Return on investment 2 years or less

To improve the efficiency of your rooftop HVAC unit, lean on a BC Hydro qualified HVAC contractor

Financial incentives for rooftop HVAC units are available through BC Hydro's Business Energy Savings Incentives program. To get started, request a referral to get in contact with a BC Hydro qualified HVAC contractor; they'll help you determine the best next step.

1 2014 Commercial End-Use Study