Follow Your Noise
A makeup-air unit we sold was only delivering half the required airflow to a new country club's golf-cart- maintenance shop. The grand opening was in a week, and we had “obviously engineered and sold a unit that was too small.”
Upon arrival, I was met by the owner, mechanical engineer, architect, and test-and-balance (TAB) contractor, as well as a host of others who apparently had nothing better to do that morning.
The air handler had a backward-incline fan and was situated in the ceiling of the parts-storage area, next to the shop. It pulled in outside air via a short length of ductwork connected to an outside-air grille. Downstream of the air handler was a rather large electric duct heater, its size dictated by our Colorado winters. The tempered air was discharged into the shop. After doing a walk-around, I started up the fan and checked its operation. As I suspected, the fan was running backward.
While mentally patting myself on the back for making such a quick diagnosis in front of so many obviously impressed parties and muttering comments under my breath about the shallow end of the genepool, I swapped two leads at the starter to reverse the fan, basking in the knowledge of my intellectual superiority. With a flourish, I restarted the air handler. It now delivered absolutely no air. None. Nada. Zippo.
The smug faces of the owner and his crew made it obvious they already had performed this sleight of hand and obtained the same results. All eyes were upon me now, awaiting some great pronouncement from The Expert. I was clueless. A quick recheck of the fan showed the rotation was correct.
After starting and stopping the fan several times, hoping for divine intervention, I noticed a faint, short-lived whirring noise every time I shut off the air handler. The noise seemed to be coming from within the ductwork upstream of the air handler. Ignoring some rather rude and sarcastic comments, I sought the source of the noise. Atop the duct, I found flexible conduit protruding out of a crudely cut hole in the sheet metal. The conduit ran to the motor starter, which had wires connected to an auxiliary set of contacts.
Peering into the outside-air grille revealed a motorized isolation damper just before the air handler. The damper, motor, and linkage were inside the ductwork. Aha! The small damper motor energized when the fan came on, but could not overcome the load put on it and remained closed.
I bypassed the auxiliary contacts, opened the damper, and started the air handler. Voila! We had plenty of airflow — enough, in fact, to close the airflow switch in the large electric duct heater for the very first time.
I installed new relays to solve the problem, and assured them there would be no extra charge for testing the building's smoke detectors and fire alarm system.
What a shame the 19th Hole wasn't open yet.
Craig Van Wyke
LONG Mechanical Solutions
Aco-worker who was absentmindedly fiddling with a rubber band suddently yelped, “Check this out!”
It seems he had stumbled on the basics of refrigeration. Stretching and relaxing a rubber band repeatedly makes it hot. While in the stretched position, it is hotter than the surrounding air and, consequently, rejects heat.
When the rubber band is subsequently relaxed and touched to your lip, amazingly, it is cold.
The four stages of refrigeration can be demonstrated by the rubber band as follows:
Compression. Repeatedly stretching and relaxing the rubber band is analogous to what a compressor does to a refrigerant — it adds energy to it, which makes it hot.
Condensing. While in the stretched position, the rubber band is hotter than the surrounding air and rejects heat.
Expansion. The rubber band goes from stretched to relaxed. Because it now contains less heat, it is cooler than the surrounding air.
Evaporation. While in the relaxed position, the rubber band is cooler.
Cold fusion is next, I guess.
Gary Gabriel, PE
CDH Partners Inc.
Apples and Gravity: Take 2
Apple-storage warehouses have to be airtight. The atmosphere inside has elevated carbon-dioxide levels and essentially no oxygen, which protects the apples.
Two brothers bought a warehouse that had been used for another purpose and proceeded to seal everything up for an airtightness test. Such testing usually is performed by inflating the building and looking for leaks.
One brother was inside, and one was outside. As the pressure built, the roof lifted a bit. The roof was supported with 6-in.-by-6-in. wood columns. Suddenly, the columns began to fall over.
What to do?
The brother inside jumped onto a fork lift that was handy and positioned it under the joists toward the center of the building. The brother on the outside left and recruited some additional help. With a lot of muscle, they opened a small door long enough to get some people inside to reset the columns again. The building then was deflated.
The building is now storing apples.
Send “war stories” of 500 words or less to the attention of Michael G. Ivanovich, Editor-in-Chief, HPAC Engineering, The Penton Media Building, 1300 E. Ninth St., Cleveland, OH 44114-1503; e-mail: [email protected]; fax: 216-696-3432. Authors are paid $50 per published War Story.