Airside Vs. Refrigerant Performance Measurement

When it comes to performance measurement and air conditioning systems, most master technicians gravitate to one of two measurement techniques, the airside or the refrigerant side.

Refrigeration experts will challenge anyone that questions pressure and temperature measurements on the refrigerant circuit as the only legitimate methods of determining equipment performance. On the other hand, an experienced airhead will fight to the death to defend his belief that airflow, pressure and temperature testing will deliver superior performance every time.

So who’s right? Both are fluids, both transfer heat and are essential to the performance of a system. The truth is an individual who has mastered both the air side and the refrigerant circuit will prevail every time when it comes to measuring air conditioning performance. Let’s take a look at each method and consider the best of both worlds.

Refrigerant Circuit Measurement
There has been substantial focus over the last few years on the refrigerant measurement and diagnostic practices in utility and government programs. They’re called RCA programs (Refrigerant Charging and Airflow.) Several amazing new refrigerant instruments coupled with software such as the Service Assistant and the Testo 523 are leading refrigerant diagnostics and performance into the 21st century.

These instruments calculate super-heat and sub-cooling values based on a wide scope of refrigerants and provide troubleshooting solutions that experienced technicians would take years to master. Equipment performance can be calculated and essential tables are built into the software.

However without the 400 CFM per ton airflow over the indoor coil being verified, current refrigeration tables provide little help. Also, unless data is available from the manufacturer that matches current indoor and outdoor conditions, interpretations of refrigerant test numbers remain questionable. There are heated discussions as to whether or not these instruments can accurately determine airflow through the equipment.

The primary concern is that the refrigerant circuit is limited to equipment performance. Duct system losses outside that circuit are invisible from this diagnostic portal.

Airside Performance Measurement
Airside measurements, if they include airflow, pressure and temperature can be effectively used to interpret the performance and efficiency of the entire system. If these values are applied to effective system performance formulas, they can open wide new diagnostic doors and provide efficiency solutions.

One sure win for the airheads is that the air system measurements look beyond the box and see the performance of the entire installed system, not just the operation of the equipment. The idea that the equipment efficiency is the definitive measurement of energy savings should have died years ago.

On the other hand, airflow measurements, like refrigerant readings can lead you down the wrong path. Airflow measurement without temperature measurements that ignore the performance of the refrigerant system can draw an incomplete picture about efficiency.

High Tech Solutions for Low Tech Problems
Jim Brown, of Mountain Home Arkansas, once taught me the weaknesses of using high tech solutions to solve low tech problems.

One risk of solutions gained using today’s high end technology is that we assume the makers of today’s technology are capable of leading us to the best solution every time. The best solution is to have all the high tech tools and know how to use them, but then to have the knowledge and wisdom, gained through experience, to bring the entire system and its performance into a single efficiency rating.

While we’re at it, we cannot forget the heating side. How can efficiency be achieved without testing and adjusting the combustion circuit along with the airside?

One of the weaknesses in our industry today is code compliance attempting to force slices of efficiency together by applying disjointed test methods and slivers of engineering practices in an attempt to create efficiency for consumers.

Just like the refrigeration circuit cannot deliver efficiency independent of airflow testing, we’re fortunate to have a test method that sees the entire system and its performance as a whole.

After years of progress in measuring the performance of HVAC systems, it seems we are just beginning to see the value of a single system performance rating number that assures all the factors are considered when declaring the installed efficiency of an HVAC system.

The answer is for air conditioning system performance is using both airside and the refrigerant side measurements to maximize system performance.

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 procedure for measuring airside performance, 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.