Why HVAC Systems are Less Efficient than You May Think

I recently presented some test data to a government energy official that portrayed very low operating efficiency of systems in their current HVAC efficiency program. Although he acknowledged their current programs were saving little or no energy, he was struggling to understand why high efficiency equipment and tight duct systems we’re not doing the job. Let’s take a look at what we found.

The Statistics

We pulled test data from over 20 systems from our CommonCents™ database. This is an online testing and diagnostic software that NCI members use to collect and analyze information and present their findings to their customers. These were systems that had complied with his program’s energy standards and all had received substantial incentive payments. Here’s what we found:

• The average operating efficiency was 63% of equipment rated capacity at the time of the test.

• The average total external static pressure was operating at .86-in. of pressure with an average maximum fan rated pressure of .57-in.

• The system delivered airflow at the supply registers averaged 261 CFM per ton at the registers.

• The average energy loss through the duct system was 21% of the heating or cooling generated by the equipment. This is a combination of leakage and thermal loss from the duct systems.

• Individual room airflows were from 0% of required CFM to 642% of required.

As I explained the statistics above, it became clear these measurements were new to this man. The nature of each measurement and how these contractors gathered this live system field data had to be explained in great detail. Even though he had over 20 years of HVAC energy efficiency program experience under his belt, basic live system test data was new to him.

What’s Missing?

Together we concluded that HVAC energy efficiency programs of the past and the methods that have been used to determine if energy was being saved have been missing critical pieces of the puzzle.

There’s no doubt that using high efficiency equipment is a good idea. Also, the principle that duct should be sealed and tightened is an essential element of a well operating HVAC system. ACCA Quality Installation standards recommend these actions and they’re valid.

He was having trouble understanding why these two functions of their program failed to deliver the savings they had assumed they were receiving all over the past 20 years.

Missing Link Number One

Although the programs had been verifying the manufacturer’s energy efficiency ratings determined in the laboratory, that verification assumed that the installed equipment was operating at that same level of efficiency in the field. As shown by the statistics above revealing the average operating efficiency at 63% of equipment rated capacity, it’s clear that a piece has been missing from the HVAC system efficiency puzzle.

The effects of the duct system and the building on the equipment efficiency were completely missed by the verification testing of his program. Basic live system testing required in the manufacturer’s specification had been excluded from the program verification.

The result: Over 30% of HVAC system efficiency that was being lost was invisible to the managers of this program.

Missing Link Number Two

While sealing the duct systems is highly incentivized, it’s assumed, and has been for decades, that tight ducts alone are a solution. Once again, as shown by the average system static pressure of .86-in. and the average delivered airflow of 261 CFM per ton when the ducts were sealed, it was simply assumed that the ducts were sized correctly.

When ducts are undersized by 25%, which most systems in the US are, simply sealing them is a recipe for disaster. Often the leaking return duct is the only thing that’s keeping the cooling coil from becoming clogged with ice or the high limit switch from continually shutting down the system.

The result: The current energy efficiency program accepted a duct tightness test confirming only the lack of leakage as evidence the system was working. The program did not include live system measurements that would have verified the fan rated pressure and the delivered airflow to the space that would’ve easily confirmed the system was not operating within the manufacturer’s specifications.

Outside of Government Programs

While government and utility programs are a key driver of efficiency, many of us are struggling to deliver improved performance directly to our client on a daily basis outside of these programs. We struggle to show our clients that our work is superior to the minimum standards of most of these programs.

It’s becoming harder and harder to get our clients pay for real results above these programs. The impact of their marketing and the claims of efficiency are quite persuasive.

Perhaps some information in this article can be helpful in persuading your customers to do business with you at a level high above your local efficiency programs. These live operating efficiency measurements take very little time to take in the field. Invite your clients to join you as you test them and have them participate in the testing. Simply compare their statistics to the manufacturer’s engineering data and explain the differences in simple terms they can understand.

Then craft a solution to solve the performance issued found in their system and price these repairs equal to the increase in efficiency you will make in their systems. Create your own efficiency program.

Rob “Doc” Falke serves the industry as president of National Comfort Institute a training company with technical and business level membership organizations. If you're an HVAC contractor or technician interested in a free procedure showing you how to measure total external static pressure, contact Doc at [email protected] or call him at 800-633-7058. Go to NCI’s website at nationalcomfortinstitute.com for free information, articles and downloads.

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