Buying Guide: Rooftop units

Rooftop units are common among Ontario businesses – but is yours really as energy efficient as it could be?

In any type of building or business, proper heating and cooling is critical. It can make or break occupant comfort and productivity, plus in some cases, even affect the quality of the products being stored in the space. Yet, heating, ventilation and air conditioning (HVAC) is sometimes overlooked as a way to not only save energy but improve a business. For many businesses, they just have to look up to see the opportunity in front of them: rooftop units.

What is a rooftop unit and how does it work?

Rooftop units (RTUs) are a type of air handler – mounted to the roof, naturally – that provide heating, air conditioning and ventilation to the building it services. They’re sometimes called packaged systems, because all the equipment, such as coils, compressors and fans, are self-contained in one spot.
 
RTUs are a common HVAC choice for low-rise structures, like small to medium-sized office buildings, shopping malls, warehouses and restaurants. Depending on the size of the building, some facilities will have more than one unit to provide HVAC for different zones. Regardless of number, RTUs typically connect to a building’s ductwork to distribute conditioned air throughout.

Get proactive

Since they’re mounted on the roof, RTUs are “out of sight, out of mind,” so they’re easy to forget. That means many businesses’ RTUs aren’t optimized to be as energy efficient as they could be. RTUs are a little like home furnaces and air conditioners – we often don’t think about replacing them until the situation gets desperate. However, proactively replacing a unit is the smarter way to go. Just like you wouldn’t want to be caught having to replace your furnace or air conditioner at the last minute at home, you wouldn’t want to have your RTU fail.
 
Rooftop units typically have a lifespan of around 15 to 20 years.¹ However, older models and units that aren’t properly maintained could be using more energy than necessary. In that case, a proactive replacement, even before a unit’s lifespan is up, is a good idea. 
 
Historically, many builders over the years have turned to rooftop units because they’re more cost effective, but they weren’t always the most energy-efficient choice. Many buildings were constructed with them and switching to another system would be cost prohibitive in most cases.
 
Over the past several years, though, rooftop units have become much more efficient, so having an RTU-based system doesn’t mean it can’t also be energy efficient. And, by working with a qualified contractor, rooftop units can help curb energy use, plus keep a space more comfortable.

Request high-efficiency standards

Ask your contractor about the highest efficiency units possible. If you’re interested in upgrading, the energy-efficiency rating will depend on the unit’s characteristics, including its size. Use the chart below to see the minimum energy-efficiency ratio (or EER) your unit would need in order to qualify for incentives. 

Ready to start a retrofit project for your business?
There are two ways we can help:

Right size, right decision

Replacing an RTU presents the opportunity to take building design into consideration. In some cases, a building’s rooftop unit may have been installed without much consideration to how occupants would use the space, or even the building’s materials, such as roofing materials or insulation.
 
Just as you’d need the right-sized furnace and air conditioner for your home, the same is true for a rooftop unit. Your contractor can help assess your building size to determine the right size of unit. RTUs range in size, typically with three to 40 tons of cooling capacity, or more for custom units.
 
A qualified contractor can also consider how other energy-saving initiatives will affect what kind of RTU you need. For example, if you’ve upgraded your building’s lighting to more energy-efficient LED bulbs, your heating and cooling needs may have changed since your RTU was first installed. This would impact the size of the RTU you need.

Prioritize advanced controls

If your rooftop unit isn’t yet old enough to need replacing yet, a certified contractor can still retrofit it to save energy. Whether buying a new rooftop unit or retrofitting an existing one, keep advanced controls in mind. In fact, some control-based retrofit technology can deliver savings of around 50 per cent, according to Natural Resources Canada.²
 
Installing economizers can help an RTU function more efficiently. Economizers use outside and inside air temperature, and sometimes humidity, to optimize the use of outside air and compressors for cooling. For example, if the outside air is cooler than inside, the economizer will shut off the compressor and use that cooler outside air, which saves energy.
 
Variable frequency drives to adjust fan speeds are another great option. Instead of having just two fan speeds, variable frequency drives adjust based on occupancy levels and temperature, so the RTU heats and cools the space more effectively and efficiently.
 
Demand control ventilation (DCV) systems can also help save energy, since conditioning outside air is one of the most energy-intensive tasks your RTU takes on. DCV systems adjust the amount of fresh air ventilated into the space based on how many occupants are inside. That way, during hours with fewer to no people indoors, the whole HVAC system will use less energy.
 
If you have more than one rooftop unit, talk to your contractor about making sure each unit’s thermostat “speaks” to the others. That way, you can prevent inconsistent heating and cooling throughout a large space.

Don’t forget maintenance

Whether it’s time to fully replace your rooftop unit, or yours is still relatively new, regular maintenance is critical to maximizing energy efficiency and preventing equipment failure, saving you time and money.

Packaged rooftop units aren’t difficult to service, but they’re often forgotten because they’re out of sight. And because they’re on the roof, they’re exposed to the elements, so they need proper care.

Having seasonal maintenance from a qualified contractor four times a year can help your rooftop unit operate at peak efficiency. For example, changing filters is an important practice for energy efficiency, but it’s often overlooked. A qualified professional can perform this kind of maintenance to help you get the most out of your RTU. Plus, you’ll spot any potential issues early, so you won’t be caught in an emergency replacement situation.

Consider the non-energy benefits

Replacing rooftop units can ultimately have a major impact on people’s comfort levels. A properly maintained rooftop unit will not only save energy but can potentially contribute to improved indoor environmental quality, improving problems like allergies and asthma.
 
Finally, replacing your RTU is an important step in your overall sustainability strategy. Making your building more energy efficient can help support your larger efforts to be a greener business.
 
By making RTUs a priority, businesses across Ontario can save energy, improve their bottom line and transform their business for the better.

References

¹ Professional Retail Store Maintenance Association – Replacing and Retrofitting Rooftop Units through the Advanced RTU Campaign (pdf)

² Natural Resources Canada – Major Energy Retrofit Guidelines for Commercial and Institutional Buildings (pdf, pg 37)