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Rooftop HVAC now a candidate for efficiency upgrades

Rooftop HVAC units

Power Smart testers like what they see in variable speed controllers

When the lights are getting dingy or the refrigeration unit is showing its age, it's easy to notice that an energy efficiency upgrade might be in order.

But it's not so easy to spot deficiencies in certain types of HVAC (heating, ventilation and air conditioning) equipment. And one of the often-overlooked systems is the rooftop unit.

Rooftop HVAC units, known as RTUs, are commonly used on small and medium-sized commercial buildings such as shopping malls and smaller office buildings. They're used in part because they're out of sight, on the roof.

"Over the years, a lot of these systems have been getting older, but we've seen very little retrofitting activity amongst our customers," says Jorge Marques, manager of of technology and innovation with BC Hydro.

Marques was a presenter at the 2013 Power Smart Forum, in a session entitled "Why (and How) to Adopt New Energy Efficient Technologies." And he knows his RTUs.

Variable speed controller senses temperature and CO2

Marques' group at BC Hydro tests new technologies to understand their value for efficiency upgrades. He thinks they've found a winner in a new technology that can be added to existing rooftop units to significantly lower their energy usage.

"Typically, most of these systems run at a constant volume. If they're switched on, they're just blowing air through the space, no matter what the occupancy, no matter what time of day. It's either on or off," he says.

New controller technology provides variable speed control, so the rooftop unit only operates at the volume needed. Sensors monitor the temperature in the indoor space, as well as the level of carbon dioxide in the air — a proxy measurement for how many people are in the space, and how stale the air is.

"Clearly, at 11:00 in the morning mid-week in a shopping mall, there's probably less need for ventilation than on a weekend at Christmas time," says Marques. "This controller just attaches right into the existing rooftop unit. It provides the control that otherwise would require a much more expensive system."

Energy efficient HVAC controller offers 25-40 per cent savings

Marques' group has tested the RTU variable speed controller at Richmond Centre Mall, upgrading 22 units in all. He says the results have been impressive, with an estimated 25-40 per cent savings per rooftop unit and a three year payback.

Given that the primary uses of electricity in most commercial spaces is for HVAC and lighting, the potential for savings in energy use and overall operating costs is significant.

"One of the reasons we're focused on this system is the prevalence of rooftop units," says Marques. "They're everywhere. Every small commercial building that's got ventilation, it's probably a rooftop unit. So the conservation opportunities really add up across the province, across all the different types of customers."

Marques says the conservation innovation team will be reviewing the results of their test and determining whether RTU controllers should be added to Power Smart incentive programs. But he says even without an incentive, it's a worthwhile investment.

"Energy efficient technology is changing so fast now, compared to how long it used to take for something new to come into the market; now it's like a couple of years instead of decades," he comments. "To continue to promote energy efficiency going forward, we have to keep an eye on what these technology trends are."