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.”
5) Unchecked Wear and Tear
Even the best-designed system can’t avoid the side effects of long-term use. Your HVAC system is full of moving parts that wear out, and it is vulnerable to damage just like any building system. Keep an eye on these areas for energy-wasting conditions.
Refrigerant charge: “One energy efficiency issue I’ve seen in the field is when a previous field tech doesn’t properly charge the refrigerant consistently,” says VanNess. “There are many reasons why that might occur. Sometimes it’s due to experience, and sometimes it’s because we can only charge refrigerant when the weather is warm. If you build your building or replace your HVAC system in February and the HVAC team comes in then to charge it up, they should come back in the spring to check it and make sure it’s charged correctly, but sometimes that doesn’t happen. It will still run, but not as efficiently as it’s supposed to.”
Ask for a startup sheet from your HVAC contractor any time you install new equipment, VanNess recommends: “You may not be able to understand what all the numbers mean, but at least you know they did the job because they filled out that form. Then if there are problems in the future, you can look back at the sheet and see that they added 4 ounces of Freon on X date.”
Weather: Hail in particular can damage rooftop HVAC units and make it tougher to pull in air, Keeler notes.
“A bad hailstorm bends all the fins and makes it difficult for air to flow through, which increases the head pressure and reduces the efficiency of the system, increasing energy consumption,” Keeler explains. “The pressure drop becomes high and the fans have to work a lot harder to pull air through there. The first thing you’d do afterward is combing the fins, and then you should put a hail guard on, which is a really inexpensive addition. It’s hard to believe that people economize the 1% cost differential of putting a hail guard on vs. not putting one on.”
Missed inspections: A small problem like a broken belt, refrigerant leak or a capacitor that’s about to fail can turn into a breakdown quickly if you don’t catch it in time, VanNess explains. “Small parts that cost a few hundred dollars to replace can end up costing you hundreds of thousands of dollars in down production time,” VanNess adds. “If your maintenance team doesn’t have an HVAC expert, it’s important to have a good commercial HVAC contractor taking care of your preventive maintenance schedule.”
The inspector should have at least 5-10 years of experience on commercial HVAC systems and any licenses required in your state, VanNess says. Inspections should be comprehensive and cover everything from belt wearing to coil cleanliness and the degradation of motors and other components.
“If they see a motor with a low mega-ohm reading, for example, the inspector should begin to have that conversation with you: ‘Your motor is 10 years old and its life expectancy is 12. You may get 3 more years, but you need to be prepared,’” VanNess adds. “A good preventive maintenance tech will give recommendations on changing out parts. The biggest thing is customer service. If they want to sell you something, they should know what they’re talking about. Interview potential technicians – picking one that you trust is probably the most important decision a facilities manager can make. There are professionals and then there are salesmen.”
Janelle Penny firstname.lastname@example.org is senior editor of BUILDINGS.