News

Make sure your HVAC system isn't working overtime

Nina Winham
For bchydro.com

If you commute to work by bike, you're saving energy and doing good for the environment. But if your heating and cooling system takes up cycling, you've got an energy efficiency problem on your hands.

The problem is called "short cycling", a too-rapid shifting between heating and cooling modes.

"What you're doing is you're expending energy to cool your air, and then soon after, expending energy again to heat the air," says Vince Hanada, a Power Smart Engineer with BC Hydro. "On and off cycling is not only inefficient,  it can lead to wear on your equipment."

Hanada says cycling can happen for several reasons. One is when you have your thermostat's heating and cooling "set points" too close together.

"The set points are never an exact thing," he says. "There's what is called overshoot. For example, you set your cooling at 21 degrees Celsius. But it may overshoot [cool beyond the target temperature] – and drop the temperature to 19 degrees. If your heat is also set near 21, you'll wind up with a heating cycle immediately. What you want is to set the two points far enough apart to avoid simultaneous heating and cooling."

It's recommended that heating and cooling points be set at least three degrees Celsius different from each other. Proper adjustment of set points can save up to 10% on your energy bill.

Hanada says programmable thermostat systems are helpful because they often allow a lockout, which prevents cooling in winter or heating in summer.

"This is becoming more common now, but in the past building managers were often afraid of not meeting occupancy comfort – they didn't want complaints," says Hanada. "So they would just let the system do what it would do, with no regard to energy used."

Short cycling can also occur in HVAC (Heating, Ventilation, Air Conditioning) systems that utilize a single rooftop unit to provide both heating and cooling. Hanada says companies with such units should ensure their controls are properly adjusted to lengthen the cycles between heating and cooling.

"That way they run at a lower kilowatt hour demand for a longer period of time rather than cycling up and down to a high kilowatt hour demand – you save energy that way," he says.

Hanada suggests keeping a regular maintenance schedule and asking the technician who services your equipment to "optimize the system to avoid short cycling." Again, he notes that this helps to avoid premature wear, and to delay the need for a costly unit replacement.

Other tips to ensure your HVAC systems aren't running up your energy bills are ensuring you keep HVAC components clean, inspecting components (regularly for leaks and other problems, and taking advantage of HVAC controls. Teaching employees about energy efficiency is also an important way to make sure the thermostat settings stay where they should – and the system isn't cycling its way to a record energy bill.

Nina Winham is a Vancouver-based sustainability consultant and a regular contributor to bchydro.com.