Back to school
December 1, 2009
The Sheet Metal Workers union Local 265 training facility is a high-tech trade school, but it prefers “old school” mechanical equipment when it comes to teaching students about deep vacuums, wet/dry bulb temperatures, and gas pressure measurement fundamentals of HVAC service.
The full five-year HVAC service apprenticeship school is a state-of-the-art learning center and was one of the first of its kind when founded nine years ago with over $2 million in funding from the Carol Stream, Ill.-based union.
The school has hands-on learning equipment such as six commercial rooftop units, 10 electronics training boards, a 15-ton air handler, 15-ton hermetic chiller, variable-air-volume boxes, direct-digital-control building-automation systems, and an array of digital testing gear.
“We established the school’s service division because our contractor members were continually finding themselves in the situation of installing mechanical equipment, so why not train their service techs for installation, start-up and service?” said Craig Krueger, an instructor who handles all of the service division’s education along with Paul Monteith.
Looking backThis 27,000-square-foot school sometimes forgoes technology, however. Not because of equipment costs, but because there are still instances where officials say old-school mechanical methods are better than new equipment.
“Just because something is digital or new, doesn’t necessarily mean it’s the best method,” Krueger said.
Krueger had a total of 17 years of experience with C&D Heating and Cooling in West Chicago, Ill.; and commercial service work with WestSide Mechanical in Naperville, Ill., before joining the sheet metal school to help spearhead the service division.
For example, the technique of evacuating refrigeration systems to a deep vacuum for the purposes of boiling off moisture has become an important part of the school’s extensive, yearlong refrigeration training. The evacuation training is especially critical today due to the HVAC industry’s conversion to R-410A refrigerant and polyolester oil, which has an affinity to moisture that can lead to system problems.
The school teaches evacuation with electronic as well as mechanical micron gauges, such as the Tigar Mic by Canada’s Cliplight Manufacturing of Toronto, which uses a conventional mechanical diaphragm technology instead of thermistor, thermocouple or Pirani technology common in today’s digital gauges.
“Since a mechanical micron gauge dial takes you from 28.8-inches of mercury on your compound gauge down to the 20-micron endpoint, it really features the last critical inches of vacuum where most work takes place when removing moisture,” Krueger said. “It creates an overview that’s just an all-around better concept from a student learning standpoint. This is also one of several examples of analog or mechanical technology carrying an advantage in the field too, because batteries or AC power aren’t needed. Plus, we’ve seen digital results on many brands vary day-by-day, whereas analog mechanical gauge pressure readings are from a direct source (pressure) and don’t vary.”
Going digitalDigital gauges use electronic sensors that respond to a drop or increase of heat transfer to give deep vacuum pressure readings, according to Paul Appler, director of research at Cliplight and the inventor of the Tigar Mic.
“Refrigeration oil accumulation on the sensor skews accuracy because it acts as insulation against the heat,” Appler said. “Mechanical pressure gauges work on the direct-acting differential pressure principal, instead.”
Pulling and maintaining deep vacuums of 500 microns to boil off moisture has become a critical industry issue and a major part of Krueger’s teaching. Students are instructed on the school’s various rooftop units supplied by Carrier Corp. and other brands.
Krueger says some service technicians today wrongly attempt deep vacuums with conventional charging gauges. These dials aren’t detailed enough to indicate the critical 500-micron threshold where moisture is boiled off to achieve the ultra-critical “dry” system.
The training facility goes “old school” with other equipment too, when teaching students topics such as the fundamentals of refrigerant charging through superheat on a fixed-metering device system. There are digital models on the market; however, Krueger prefers to use a manual model by Bacharach that students actually sling through the air to get wet-bulb readings.
“We lined up a lot of digital models and performed wet bulb readings, but the manual model was the only one that had consistent repeatability,” he said.
Likewise, the school also uses a U-tube manometer by Dwyer Instruments for gas pressure readings.
While “old school” is the school’s norm for deep vacuums, wet bulb/dry bulb and gas pressure readings, Krueger added that an array of other field tests have become simplified and expedited because of cutting-edge digital technology from a host of brands the school uses such as UEI, Fieldpiece, Fluke and others.
Additionally, digital technology can’t be circumvented when teaching modern-day troubleshooting of DDC systems. School officials say they are lucky to have a Johnson Controls Metasys system to use for installation, start-up and diagnosis, an SPX Cooling Technologies cooling tower; and a 400,000-Btu boiler from Burnham Hydronics.
It’s a mix of “old school and new technology that gives students the best of both worlds with which to analyze and service HVAC systems, Krueger said.
It must work: Local 265 students won the apprenticeship service competition two of the last three years among hundreds of entrants from sheet metal union locals nationwide.
This article was supplied by Cliplight Manufacturing.