How Much Energy Is Your HVAC System Wasting?

The secret to saving energy in your facility may not be in deep retrofits or sophisticated new systems. It may be as simple as finding and fixing the causes of energy waste in your existing HVAC system.

When time and budgets are already stretched, it’s easy to adopt an “out of sight, out of mind” mentality. As long as the system is running dependably, what could be wrong? As a matter of fact, your system may be working harder than it needs to in order to maintain its usual performance. Investigate these five areas of your HVAC system to see if any are needlessly wasting energy.

1) Filthy Filters

It’s easy to fall behind on preventive maintenance like filter changes, but this simple act can actually avoid a lot of waste. When filters are too clogged, the system has to work harder to push the same amount of air through as before.

“I had a situation in a sewer plant where dust and dirt in the air from neighborhood construction combined with dew and coated the outsides of the plant’s bag filters to the point where they basically weren’t filters anymore, just solid blocks that air couldn’t be pulled through,” says Russ Keeler, Principal of Chason Energy Consulting Engineers. “Most organizations call for a filter service to come in and change the filters, but this is where the accounting department and the facilities management department clash. When money gets tight, the first thing they do is cut back on maintenance, and the easiest thing to do is reduce the frequency of filter changes. It’s an extremely short-sighted economy measure.”

Newer systems with direct digital controls can monitor the pressure drop across filters and alert you when it’s time to change them, but “all systems are not new with direct digital control,” explains Keeler. “Older systems are going to have more problems complying with filter changes, and that has to do with the staff’s experience and how much they’re stretched. I change filters every two months or so. With modern systems it’s a lot easier to keep track of when you need to change filters than it is with a system that’s 20 years old.”

2) Coils That Need Cleaning

If your coils are dirty, the heating and cooling components of your HVAC system can’t condition the incoming air properly, which means they’ll have to work harder to accomplish the level of conditioning you need. Both indoor and outdoor coils are vulnerable to grime, explains Curtis VanNess, General Manager of HVAC Forensics for Donan, a forensic engineering firm. “If you’re in a coastal location, the saltwater in the air can actually degrade the coils,” VanNess says. “If you’re in the Midwest, the water in your sprinkler system may be high in mineral content. If the sprinkler is watering the air conditioning unit, that can also degrade the coils. Another common issue is mowing grass. If you’re blowing yard clippings near your air conditioner, it can get sucked up into the coil and block it, and it won’t cool your building as efficiently. Dust from construction or pollen in the air can also get sucked into the unit.”

Particles in the indoor air can also cause issues, VanNess explains. From occupants tracking in dirt particles from outside the building to sweaters shedding lint into the air, indoor coils are at risk for all kinds of accumulation.

“Think of when you’re vacuuming and you see dust particles in the sunlight. All of that gets sucked into the circulation system,” VanNess adds. “If you don’t change your filter properly or the filter has an improper seal, that dirty air will go into the indoor coil and can block it. It could also attach to the blower wheel, which would cause it to increase its amp draw and waste energy.”

3) The Wrong Ventilation Rate

How much fresh air is your system bringing in? ASHRAE requires 10 cfm per person for most spaces, so VanNess recommends starting with a simple review to make sure your ventilation system is bringing in the correct percentage of outside air. “That’s simply checking to see how much is coming through the dampers,” VanNess explains. “That goes back to controls – if you don’t know how to measure it, you need to hire a controls expert to come in and tell you. One of the best ways to assist with energy costs is to check the dampers and have your controls reviewed.”

Older systems likely have a fixed ventilation rate no matter what the actual occupancy is, so you may be over-ventilating unintentionally, especially if you don’t have HVAC controls that can vary the intake, Keeler explains.

“If you take a VAV system where you throttle back the amount of supply air, especially in the winter, that doesn’t really cut back the amount of ventilation, which increases the percentage of ventilation air and the heat requirement,” adds Keeler. “There are more recent innovations where you can use a CO₂ detector to monitor how much outside air is needed. If the system was designed for 10 cfm of ventilation per person, that’s a fixed number, but if you have half of the occupancy the space was designed for, ASHRAE Standard 62 allows you to use a CO₂ detection system to scale back the ventilation rate. It’s an indirect measurement of how many people are in the building, but it works.”

One project Keeler worked on in McLean, VA, involved a church with widely varying occupancy throughout the week. The building was packed on Sundays with up to 2,000 people in the building, but during the week the occupancy could be as low as 100.

“Fairfax County allowed us to show that you could throttle back the ventilation during non-high occupancy hours to reduce the amount of energy they were expending on outside air,” Keeler says. “By using a CO₂ detection system, they had one-twentieth of the energy expenditure during the week. Those controls can have a payback of well less than a year, so if you don’t have a variable ventilation system now, you should look closely at that – it’s probably one of the biggest energy savers you can have.”

4) Faulty Dampers

Motors, links and controls can all cause problems with dampers, leading them to let in too much or too little air, even if your system is designed to bring in the optimal amount. In one case VanNess investigated, the system was never installed properly, leading to the coils freezing.

“It almost never freezes in Texas, but it did a few years back. This case was at a hospital and the installer didn’t wire the damper motors properly,” VanNess explains. “The frozen coils caused millions of dollars in water damage to a hospital that was under construction. It’s imperative that we check the damper motors and linkages and have backup systems in place. We see a lot of installers who install the equipment, but never test it to see if the dampers actually open or close. Get the system commissioned.”

If your HVAC controls are more than five years old, it might be worth it to upgrade to a newer package, VanNess adds: “If you have a good control system, you can reduce your energy costs by quite a bit just by opening and closing these dampers and valves. The energy efficiency standards on these new controls are unbelievable – some are up to 30-40% more efficient than older models.”