A Tale of Two Temperatures

Jan. 1, 2007
One upon a time, in the land of heating and cooling there were two Delta-Ts that were often mistaken for one another. Nearly every technician in the land assumed they were exactly the same. But in fact, although they were related, they were very different.

One upon a time, in the land of heating and cooling there were two Delta-Ts that were often mistaken for one another. Nearly every technician in the land assumed they were exactly the same. But in fact, although they were related, they were very different.

The older Delta-T was named “Equipment.” He was by far the most popular and had been around forever. Everyone measured him all the time and knew everything about him. He was listed on nearly every furnace nameplate. In the province of air conditioning, everyone knew his numbers; in humid regions he was known as 18 to 20, and where it was nice and dry they called him 20 to 22.

They younger Delta-T was named “System.” Although much more important and far more influential than Equipment in the lives of nearly everyone in the land, few were even aware that he existed or could easily be measured. He suffered from thermometer envy.

System knew he was by far the most important, but Equipment got all the attention. He was anxious to be employed by every tech, waiting and waiting to reveal the truth about the poor system performance, but few employed his services.

“If only I could get the best techs to measure return grille temperature and supply register temperatures, and simply subtract to find the difference, then all could see for themselves how much they were missing by only measuring Equipment,” System sighed.

He knew there were times that Equipment boasted 60F temperature rises and that although that was very important, he also knew if they would add his measurement to their service testing they would find the same systems, with only a 30F Delta-T due to low airflow, return duct leakage, poor insulation, and other problems.

Season after season across the land, service techs of every size, shape, and favorite equipment manufacturer only measured Equipment, assuring their customers that all was well.

However, as the heating season of 2007 set upon the land, a deep chill crept into many homes and businesses. Design conditions were exceeded everywhere, once happy customers began complaining of regular discomfort and fast rising utility bills.

Contractors assured the inhabitants of their obvious comfort with great fervor and zeal by presenting load calculations that assumed little or no duct loss and adequately engineered air flow. But the citizens were still left with chilly feet and empty wallets. Little did they know, true comfort could be found if only they understood System.

Week after week, the people suffered. Technicians were all working overtime and their call back rates went through the roof. Frustration ran high around every furnace, heat pumps were failing right and left, and technicians were helpless to provide relief.

But alas, no comfort could be found in the land. “Take out our 4-tons and put in 5-tons” the people began to chant, sure that a bigger unit would solve the problem. Finally the contractors began to sweat. But this only brought temporary relief to a few. They leaned on their technicians harder and harder to service equipment better and better. But alas, their efforts were in vain. They just didn’t get system losses outside the boxes in which they had their heads buried.

The people demanded relief, and finally their pleas reached the frigid ears of the king. Even the palace had become cold and drafty. The king’s architects assured him their engineers designed excellent systems and that the problem was not theirs. Night and day, every furnace in the castle was serviced over and over and endless service invoices were laid at the feet of the king, assuring him every piece of equipment was perfect and mechanically sound, and that he really should be comfortable.

In utter disgust, the king called for one service tech to be flogged twice a day with a 12 gauge whip, 40 lashes each, until a solution could be found. Although the people were delighted, comfort could not be found.

After three days, few service techs could be found in the land. The energy efficiency inspectors from the king’s utility company were sent to find more techs to flog. All the government activity seemed to take the people’s minds off their discomfort. The papers reported the valiant efforts of the Department of Efficiency and the king’s ratings were climbing. But with no techs to be found, the only tech the energy efficiency inspectors could capture was a lowly air balancing service tech named Airhead.

Airhead was shackled and brought before the king for flogging.

Airhead had been hard to find. He and his friend, System, had been diagnosing comfort problems one at a time all throughout the land. He had been referring work to many heating contractors by specifying simple duct repairs and restrictive filter replacements to solve the comfort epidemic. They had become enormously successful. Other HVAC contractors were so embarrassed by the simple system repairs that Airhead and System were prescribing, they were hesitant to share the information with the king.

The king found the people delighted in ruthless questioning of the service techs before each flogging. The king’s Department of Efficiency would ask a dozen senseless questions to each technician about laboratory equipment efficiency ratings and tight ducts until each technician broke down and cried, then the flogging would commence. The crowds would cheer.

Airhead was strapped to the whipping post with a top quality grade of duct tape. Then the first question came.

An arrogant and highly educated researcher demanded “Airhead, recite the SEER formula!”

“That has little to do with our comfort problems,” replied Airhead.

A hush fell over the cold crowd. The researcher was baffled and began to stutter. Throughout the floggings, equipment efficiency had been the top issue. Surely no technician before had had the gall to dismiss the king’s favored question.

“Tell me the specified duct leakage at 25 Pascals according to the king’s decree!” spewed the researcher.

Airhead calmly answered, “Although it’s a good try, tight ducts are not right ducts. The king is quite misguided in promising his subjects that tight ducts assure comfort and efficiency, but it’s a step in the right direction.”

The researcher was outraged, but the king was intrigued and commanded Airhead to continue.

“The best way for our people to solve this comfort epidemic is to test each heating system by applying all the applicable the laws of physics. The data needed to apply these laws is only found by implementing ancient air balancing measurements laid down long before this kingdom was established.”

“Continue.” said the king as he curiously stroked his beard.

Airhead pulled System from his pocket and showed him to the king. “You see, your Majesty, the equipment works just fine, it’s very well-made and extremely capable of keeping you and your subjects warm and cozy. But Equipment has lead your people astray and lulled your researchers into the belief that if the equipment works, then the system must be working well also. But only by measuring System can we discover duct losses that cause the system to operate at and average of 60% of equipment capacity.”

The crowd gasp at his wisdom while System smiled from one end of his thermocouple to the other.

“Once we understand duct loss by taking System, only then does it occur to us to measure static pressure and check fan airflow. Once we know fan airflow, then we know to check system airflow with the balancing hood. And once we know delivered supply airflow, then we can measure system delivered Btu and discover real system efficiency.”

The crowd cheered and a tear came to the king’s eye. “Continue my son,” pleaded the king.

“Well sir, as soon as we measure system delivered Btu and find system losses are poor, the readings will pinpoint the problems with our systems and our technicians can fix them, and we’ll all be comfortable again. Once the techs heal up from the floggings, that is . . . your Majesty.

“Duct sizes can be increased, restrictive filter surface area will be expanded, more powerful fans can be used, added duct insulation can be employed and high system efficiency will become the law of the land.”

“Kneel my boy,” commanded the king, as he drew his sword and knighted him Sir Airhead.

A white horse was brought forward and multiple golden quick response thermocouples were laid around the neck of Airhead. As he mounted his trusty steed, the people showered him with praises and gifts.

As he rode off into the sunset, Airhead heard the king pledge, in a loud commanding voice; “From this day forward our laws will demand, Live Measured System Performance for the benefit and comfort of our fair citizens!”

Airhead wondered if the decree would stick, since the Department of Efficiency would probably mess things up with rebates and the researchers would argue that live system field testing did not meet laboratory steady state conditions, but that’s another fairytale . . .

And they all lived comfortably and enjoyed real system efficiency ever after.

Rob “Doc” Falke serves the industry as president of National Comfort Institute a training company specializing in measuring, rating, improving and verifying HVAC system performance. If you're an HVAC contractor or technician interested in a procedure to measure System Delta-T, in addition to Equipment Delta-T contact Doc at [email protected] or call him at 800/633-7058. Go to NCI’s website at nationalcomfortinstitute.com for free information, technical articles and downloads.