Faulty Installations Slash System Efficiency
Contractors Should Consider Airflow, Temperature, Pressure, and More
Credible HVAC contractors will attest: Energy efficiency ratings are meaningless if equipment is improperly installed. The National Institute of Standards and Technology (NIST) recently released a report confirming substantial equipment efficiency is lost due to design and installation flaws. The report is based on a three-year study that examines the impact of building, equipment, and climate effects on HVAC equipment efficiency. Duct leakage, refrigerant undercharge or overcharge, low indoor airflow, and oversized equipment with undersized ductwork have the most potential to significantly degrade equipment efficiency. Additionally, the report revealed when two or more faults occur, efficiency degradations can be additive, compounding the increased consumption.
It Starts with Design
According to Glenn Hourahan, senior vice president, research and technology, ACCA, the typical HVAC system loses 30 percent of its energy efficiency out of the box as a result of poor installation practices.
“Failure to follow energy standards results in a substantial penalty and energy consumption for consumers,” Hourahan said.
“Contractors know this and they’ll tell you. The NIST report quantifies, for the first time in this industry, results when a particular practice is not followed. So, if you’re in Texas or California or Washington, District of Columbia, or wherever, and your airflow is off by 30 percent, you can quantify it and say, ‘Well, this is going to have a 15 percent impact on energy consumption. I’m going to draw more energy than I did before.’ It quantifies several things, like the impact, and it identifies which elements are most important.”
Many installers use the ANSI/ACCA 5 QI Standard, “HVAC Quality Installation Specification,” which specifies what to measure, how to measure, and the measurement tolerances for unitary residential and commercial HVAC systems. Carter Stanfield, director, air conditioning technology department, Athens Technical College, Athens, Georgia, said the QI Standard is a great tool because it provides a detailed list of things to be completed.
“If you look at the installation standard, you will see it actually begins with a proper load study and system selection before the equipment is installed,” Stanfield said. “You can’t have a quality installation of a system that is not right for the job. Quality installation starts with proper design. This is usually the first place it goes wrong.
“Not enough attention to detail is paid on the front end,” he continued. “It’s kind of like building a house and not bothering to put a good foundation on it. If you construct a building on sand and don’t put any foundation on it, you shouldn’t be surprised when the walls shift and crack and things fall in because you don’t have anything to hold it up. It’s kind of the same way in air conditioning. You need to start with how much heating and air conditioning you actually need and work from there.”
The problem, Stanfield said, is that installers tend to skip that first step.
“There are all kinds of different rules of thumb, but they’re usually not terribly accurate. It’s just a whole lot easier than doing it right. Sometimes people are in a hurry, or they may be a little bit lazy, and they don’t do everything they should to ensure they have the properly sized unit in the first place.”
The Dreaded Ductwork
Paul Wieboldt, owner of Tradesmen Heating & Air Conditioning and Tradewinds Appropriate Technologies LLC, both in Waco, Texas, specializes in Manual J load calculations, Manual D duct design, and Manual S system selection for contractors, architects, and homeowners.
“I’ve seen the results of testing the performance of air conditioning by measuring airflow, taking temperatures, and determining duct leakage. In my experience, the average new home is only producing about 62 percent of its rated performance due to deficiencies in design based a lot on tradition, but not good science,” Wieboldt said. “That equates to customers paying more money for a product that never gets delivered. For every dollar the customer is paying for electricity, they’re only getting 62 percent of the product. If that’s what you were getting for gasoline, you’d be very disappointed.”
Air is invisible, so it’s hard for consumers to tell when there is a problem, which is why contractors use tools to demonstrate what air is doing so they can better explain to customers why they are paying so much and feeling so uncomfortable, said Wieboldt.
“Using an airflow capture hood, we can show the customer the proper amount of air that should be delivered out of a register when a system is properly designed. When the customer is informed the system is not performing as it should, he or she is highly motivated to have the ducts fixed,” he said.
Wieboldt referred to ducts as the “red-headed stepchildren” of the HVAC industry because they’re often passed over in favor of adding refrigerant or replacing units with new equipment.
“I explained to a fellow a little while ago, if you’ve got a new air conditioning unit and you had bad ductwork, that would be like having a heart transplant, but still having blocked arteries,” he explained.
“How long would that new heart work well when the arteries are clogged? It was obvious to him changing out one part, but not fixing the root cause, would be sort of a waste of money, whether it’s your heart or air conditioner. Ductwork is easily ignored because it’s so hard to get to — it’s in a hostile environment in most places. It’s easier just to swap out equipment. And, of course, manufacturers heavily advertise the equipment, and there’s just not a whole lot of touchy-feely marketing and advertising for ductwork. It doesn’t have the curb appeal.”
Testing for Quality Control
According to David Richardson, curriculum developer and instructor, National Comfort Institute (NCI), testing a system after installation is extremely important for installers. “It’s the only way a contractor is truly going to know systems are performing as promised,” Richardson said. “That’s also going to allow the contractor to uncover and provide corrections for issues with the job before their customers ever know they exist.”
It’s also a good form of quality control to minimize callbacks. “A lot of times, guys use callbacks as a way of determining whether they did a good job,” Richardson said. “Unfortunately, callbacks aren’t a technical way of determining a job’s value. It’s a pretty broad guess. But, if they’re taking a measurement, they can actually prove how good of a job they did. Testing is extremely important. I don’t think I can stress that enough.”
Contractors should be looking for issues such as low airflow, excessive temperature losses, temperatures that are not in range, pressures that are out of tolerance, excessive leakage, and static pressures that are out of range, among other things.
“Duct leakage testing is one that’s really been hammered on,” Richardson said. “But, that’s really only one parameter of an operating system and there are some other aspects that need to be addressed in addition to duct leakage. A technician should be looking at the pressures of the system, such as total external static pressure, filter pressure drop and coil pressure drop, and verify all of these are within factory specifications.
“Fan airflow testing is another way contractors can accurately ensure installations. This ensures the unit’s delivering what’s required based on the system size that’s installed, both on the cooling and heating sides. Another thing to watch for is leakage and temperature loss because you can have a piece of equipment that is operating perfectly, but just from temperature losses alone, it’s losing 50 percent of the equipment capacity through the duct system, just through temperature losses. We’ve seen that a lot. It’s one of the most overlooked aspects of any installation verification — making sure the Btu are making it from the equipment into the building.”
Contractors who are truly verifying their work should be keeping track of results with a report they can then share with customers. Richardson said customers should be asking to see results to ensure they’re getting what they’re paying for.
“A lot of people don’t know what questions to ask. They base it on the equipment’s efficiency ratings,” Richardson said. “They don’t seem to understand that those efficiency ratings were achieved in a laboratory environment, which has perfect conditions. Once that piece of equipment is taken out of those laboratory conditions and put into a customer’s crawl space or attic, every variable that piece of the equipment was rated at just changed. If they’re getting 90 percent of the Btu they’re paying for, then that contractor’s done a great job. It can be very hard, depending on the conditions of the duct system installed, to get 90 percent of the equipment’s rated capacity.
“Installers are having to quantify the invisible,” Richardson continued. “A lot of times, customers can feel the results immediately.”
Publication date: 2/9/2015