New Technologies Shaping the Future of A/C

David Wegbreit | Assistant Editor

Bitzer compressors will change the world of school bus air conditioning. At least Matt Lish, Bitzer’s U.S. director of transport sales, hopes so. Together with Carrier Transicold, Rifled Air Conditioning, Thomas Built Buses and TransArtic, Bitzer has installed the first-ever transit-style compressors in front-engine school buses.

“Until now, warmer states accepted inferior equipment because that’s all the industry could provide,” Lish said.

While transit-style compressors have been available for rear-engine buses for years, until now only “swash-plate” or automotive-style compressors could fit in more common front-engine buses. Fleet managers complained about finicky compressors or compressors that died at the worst possible time. While most installed two compressors in tandem to extend the life of the system, many fleet maintenance managers saw an extra compressor as just another component that could break.
Bitzer’s new compressor is smaller and lighter than anything used before, and Lish says the new compressors will live as long as the bus.

“It’s A/C the way it should be,” Lish said.

Working With OEMs
But Bitzer isn’t the only company changing school bus air conditioning. Following trends in the automotive industry, school buses are quickly adopting the technology. Ten years ago, only a handful of special needs buses had air conditioning. Today, most special needs buses have air conditioning and as many as half of regular route buses in some of the warmest states have air conditioning. With more companies providing better technology and more districts choosing to order only buses with A/C, 80 percent of buses in the warmest states may have cooling technology in another 10 years. According to Trans/Air President and CEO Rick Lehnert, school bus cooling systems have been more complex than their car and truck counterparts because they have not been built into the total vehicle design. Unlike their automotive counterparts, school bus chassis manufacturers could not spread out the cost of the tooling and engineering required to design efficient systems over hundreds of thousands of vehicles. As a consequence, school transporters had to endure systems that didn’t meet their needs.

But as the market for air conditioning grows, school bus and chassis manufacturers will begin to work closely with A/C manufacturers. Stringent 2007 EPA engine emission standards have brought Trans/Air and other companies into an even closer relationship with chassis manufacturers. By working together, they’re building better systems. Trans/Air now uses 3-D computer models to design the best compressors and the best mounts before chassis even roll off the line.

Companies like Trans/Air are also incorporating more computers into the A/C system itself. Trans/Air recently developed a climate control system for Navistar International that heats, cools and dehumidifies the driver area separately from the passenger area. Trans/Air now uses microprocessors to monitor voltage and cycle the cooling system, helping to prevent common causes of compressor failure.

With increasing pressure from parents, A/C has quickly become a must-have item in many states. As students and parents get used to year-round air-conditioning reliability becomes even more important. Just a few years ago, these cool buses were luxuries that kids dreamt of.

“When we first installed air conditioning kids came out of the woodwork with notes from their doctor saying that they could only ride on the air-conditioned bus,” said Joe Reed, the assistant director of transportation at Florida’s Palm Beach School District.

Making Maintenance Easier, Giving a Little More Headroom
Carrier Transicold recently developed its own industry first: Micro Channel Heat Exchangers, which are more resilient heat exchangers that draw less power and use less refrigerant. Like microprocessor controls, they’ve been in cars and trucks for years but are just making it into school buses. Coupled with Carrier’s new, increased volume vector fans, the Micro Channel Heat Exchanger puts less strain on bus electrical systems while keeping output high. Unlike conventional, tube and fin designs, the new condenser coils can be cleaned with a high-pressure wash.

According to Bill Schroyer, the director of fleet management for the Florida Department of Education’s school transportation division, keeping condensers clean is one of the best ways to maintain the life of an A/C system.

Rifled Air Conditioning has made similar robust construction a hallmark of its design. Its namesake rifled tube construction also makes its condensers strong enough to be washed with a high-pressure hose. This means Rifled Air systems are easier to clean and maintain.

Rifled Air has recently designed a series of bulkhead evaporators. These are designed fit into the bus’ bulkhead and give the bus a cleaner look with more headroom. Cheyne Rauber, Rifled Air’s general manager, says he expects bulkhead sales to make up half of his evaporator sales this year. Ken Jones at Longhorn Bus Sales in Houston says he’s already noticed a big push for integrated bulkhead evaporators.

“With all the cameras and video equipment, extra head room becomes more important,” Jones said. ACC Climate Control has recently released its own solution for these spaces where headroom is critical. With just a 7-inch profile, ACC’s new low-profile evaporator and bulkhead evaporator are designed for areas where a bulky evaporator might create a dangerous blind spot for onboard cameras.

Other companies have shifted their product offerings to offer even more for school buses. Building on their success with the D5 School Bus HVAC platform, Thermo King will release the SR 250 and SR 350 line of one-piece roof top condensers. While more expensive than skirt mounted units, roof top units are more efficient, because the air they pull in is cooler than the warm air near the hot pavement.

High Tech Not Always Best
For some, the initial investment in new cooling technologies is too high, especially when the technology’s newness makes it maintenance intensive. While about 40 percent of his fleet will have A/C this year, Charlie Aquino, Seminole County Public Schools’ director of fleet services, wishes his high-tech systems were more reliable. Until recently, he found that the state-mandated digital controls on his A/C systems were failing and needed to be replaced too often.

Now his 200 buses have low-tech, manual switch and dial control systems and he says he’s much happier for it.

While American Cooling Technology recently released a new vertical evaporator that protrudes less into the seating area and is easier to clean, company Vice President

J.R. Lucas says he is focused on improving existing technology and expanding customer service.

“Compressors don’t die,” Lucas said. “They’re killed.”

A.C.T. has focused on offering consultation to help each customer pick the products that fit their needs and expanding efforts to train technicians on preventative maintenance and repairs.

Instead of incorporating new technology, Lucas said he wants to improve existing components. By using larger hoses, lighter condenser cores and more robust components, he says he hopes to create a more reliable, more tolerant system without introducing newer, more expensive components.

The Next, Next Wave
Down the road, cooling technology may face new challenges. Just as the industry switched from R12 refrigerant over a decade ago, some speculate that the industry will switch again in the near future. Dupont and Honeywell are both developing alternative refrigerants that may contribute to reducing global warming. Many are satisfied with refrigerants as they are and believe that, once again, where the consumer automotive industry goes, the school bus industry will follow.

“When Detroit changes, our industry will change,” Lucas said.

Its unlikely that cooling system prices will drop significantly in the years to come. But as A/C manufacturers offer more products with greater reliability, more districts will be inclined to go make the change. For now, the top question facing many of these next generation air-conditioning manufacturers is “How many, and when?”