Air conditioning purchases are on the rise in the school bus industry and the demand for high-tech, heavy-capacity units is likewise increasing. Year-round schooling and an increase in mainstreaming of special-needs students are a couple of the main factors behind this trend. Air conditioning has even been written into statewide school bus specifications in some states, like North Carolina.

"We have more schools running year-round programs and more districts starting up in early- to mid-August than ever before. It is hot here in August and stays warm for a couple of months," explains Derek Graham, pupil transportation director for the North Carolina Department of Education.

According to air conditioning manufacturers, Texas and Florida are also ahead of the pack in outfitting school buses with air conditioning systems.

"All of our buses are purchased with air conditioning these days. We started doing it a few years ago, and others have followed suit," says Joe Reed, assistant director of transportation and maintenance at the School District of Palm Beach County in West Palm Beach, Fla.

Still, not all operators, even those in warmer climates, are leaping into fleet-wide air conditioning installation. The main impediment to the cooling trend — budget constraints. At Midland (Texas) Independent School District, 34 of the fleet's 165 buses will be equipped with air conditioning systems this year for use on special-needs routes. Transportation Director Willie Tarleton would like to install air conditioning across the board, but lack of funding will not permit it. "Over the last few years, I've been requesting an increase in budgeting for air conditioning units," he says. The price of the systems, he says, has increased over the years. But the quality of the systems has also grown. "The technology seems to be of vast improvement," he says.

Performance-based specs
In the past, air conditioning systems were marketed based on BTU (British Thermal Unit) ratings that measured their cooling capacities. One company frequently competed with another by advertising their product at a slightly higher BTU rating (for instance, 120,000 BTUs versus 100,000).

The user was the one who lost in that competition, says Dave Oberdorff, marketing manager at Carrier Transport A/C Industries in York, Pa. "Each user was kind of at the mercy of the air conditioning manufacturer to tell them how many BTUs their equipment should be," he says. The move to performance-based specs, however, has re-assigned the power to the user, who simply tells the manufacturer how he or she wants the system to perform.

For example, you could request that the interior of the bus be cooled 20 degrees in 30 minutes. "It's up to each manufacturer to determine which of their equipment it would take on that particular bus to meet that specification," explains Oberdorff.

Most manufacturers are moving to performance-based specs. According to Cheyne Rauber, sales and marketing manager at Rifled Air Conditioning (RAC) Systems in Archdale, N.C., performance-based specs make for higher-quality systems because manufacturers are forced to build the systems to meet the user's requirements.

When it comes to testing a system's performance, says Rauber, there are three locations in the vehicle — center, rear and front — that must meet the temperature criteria. "There can be no more variation than 2 degrees in each of those locations," he says. You need good airflow from different locations to keep the cool air circulating. This is where planning comes into play. You need to get the proper combination of blower locations.

As an added option, RAC offers a Driver's Package, which includes a blower-motor at the end of the ductwork that points at the driver, cooling the occupant most often neglected by typical air conditioning systems.

Rick Lehnert, president of Trans/Air Mfg. in Dallastown, Pa., however, warns against getting too comfortable with performance-based specs alone. "We believe in a three-pronged approach," he says. This includes the performance specs, system specifications and a proven company with a quality system that is ISO9001 compliant. "We've had some users who awarded a bid based on performance specs only and then the system didn't last or meet industry standards," he says.

Improved hose systems
Most manufacturers offer an improved system of hoses and fittings. Instead of the old rubber hoses and mechanical crimp fittings, they are offering steel fittings and hoses with vinyl teflon liners at very little increase in cost. According to J.R. Lucas, co-owner of American Cooling Technologies (ACT) in Emigsville, Pa., improved hose systems reap big rewards. "These new hoses and fittings greatly decrease the chance of leaks and cut down on installation time," he says. "Instead of having your barrier hose with fittings you have to crimp at the end, it's just a little cage and a clip, and it clips right into place. The hose is flexible and it reduces leaks, which is one of the biggest maintenance problems."

All major manufacturers have their own version of the improved hose and fittings system. The price is only slightly higher than the price of the older hose system, and it will continue to come down as the demand rises. By the beginning of next year, Carrier will be 100 percent converted to its Quick-Click hose and fitting system.

"The number one warranty claim on air conditioning used to be refrigerant leaks. And a lot of times, because you lost the refrigerant and the oil in the system, you'd lose the compressor," explains Oberdorff. Though the price of the improved hose system is slightly higher than its predecessor, Oberdorff says that you get your investment back in almost the first year by reduction in vehicle downtime. It costs between $150 and $300 more per vehicle for the improved hose system. However, Oberdorff points out that it costs about $500 to replace a compressor.

More powerful alternators
"Alternators are absolutely and positively critical to the air conditioning system," says Lehnert at Trans/Air. It's important to work closely with the bus manufacturer on spec'ing the proper-sized alternator to support your air conditioning system. Otherwise, you may be in for a maintenance nightmare down the road.

Mark Kelley, student transportation specialist for DoDEA Guam Schools, says that he learned this lesson the hard way. With average temperatures of 85 to 90 degrees Fahrenheit and relative humidity of 90 degrees all year round, air conditioned buses are the way to go in Guam. But when Kelley outfitted 10 of his buses with cooling systems, he was forced to replace alternators and batteries more quickly than on his non-air-conditioned buses.

"I discovered the alternator was rated at 145 amps under ideal conditions," Kelley says. "Normally, that would be more than enough for a school bus. But when the air conditioning units take 100 amps, that does not leave very much for the rest of the electrical systems on the bus." He solved the problem by upgrading to 200-amp alternators on air conditioned buses.

With operators and manufacturers working more closely together these days, the problem of under-capacity alternators is on the downswing. "I think you've seen over the past five years a big education of districts and everybody else on how to spec the right size alternator for the bus," says Jerry Peters, product manager for Carrier. The mindset, he says, is increasingly becoming "bigger is better."

Heavy-duty compressors
According to manufacturers and users alike, the industry trend is toward larger, transit-duty compressors on rear-engine transit-style school buses, as opposed to the smaller automotive compressors used on front-engine buses and small buses.

"The bus industry has been kind of neglected by not having a compressor of the right size," says Rauber at RAC. "We've almost always had to use an automotive-style compressor. The other choice is they've got the overkill option with big and expensive transit-style compressors."

Rauber says the compressor has always been the weakest link in the air conditioning system. The solution? RAC offers a 12.6-cubic-inch compressor that fills the void between the 10-cubic-inch automotive capacity compressor and the heavy-duty systems.

Many operators are spec'ing a single transit-style compressor on the top of their rear-engine buses. According to Peters, these larger compressors offer 20,000- to 30,000-hour design life, versus the approximately 5,000-hour design life of an automotive-duty compressor. With school buses being used for 10 to 12 years, a heavy-duty compressor will more closely match the life span of the bus.

"Everybody's decided to really make a maximum investment up front. You're talking about probably a $3,000-a-bus up-charge for the larger compressor. In Arizona, California and Southern Texas, the really hot zones of the states, that's all they use anymore," he says.

Terry Koerner, bus product manager for Thermo King Corp. in Minneapolis, agrees that the trend is toward heavy-duty compressors. "We're starting to see the school bus operators run their buses for a fairly long period of time. We feel that they're starting to look for higher quality, longer-lasting products," he says.

Lehnert at Trans/Air says he too has witnessed a move from dual automotive compressors to a single transit-style compressor. "A 21-cubic-inch transit compressor really fills that void between the big heavy-duty compressors and the automotive compressors," says Lehnert. "We see an increased concern for having the right size system and durable components."

In West Palm Beach, Reed says that he is going to pilot test an air conditioning system with a roof-mounted evaporator and condenser and heavy-duty four-cylinder compressor this summer. "These units will only work on a rear-engine bus, due to the large size of the compressor, but since this is most of what we purchase, we think it's a worthwhile test," he says.

Digital/electronic controls
Also new in the West Palm Beach specs are digital air conditioning controls. "They are very new and had to be imported to meet our specifications, but we felt the spec was necessary," says Reed. Digital systems record the temperature on an LCD display. This replaces the old knob-turning manual control system. "You can set the set-point depending on the conditions of the day and the passenger load. It gives the driver more flexibility," explains Carrier's Oberdorff.

But ease-of-use is not the only reason for electronic controls. There are also maintenance diagnostic capabilities involved in the more high-tech systems. "It gives a little bit on the service side in that we're monitoring how many hours those compressors are running. That helps with maintenance," says Peters.

Not everyone, however, is a proponent of electronic controls. Representatives at ACT and RAC say they think it's better to keep things simple. With electronic controls, mechanics need to be trained in diagnosing problems in order to repair them.

"We have a very simple philosophy. We want an average mechanic with average experience to be able to walk through and fix it over the telephone," says ACT's Lucas. Rauber agrees. "You get an electronic control that breaks down, it's pretty pricey and you have to have somebody who can fix it."

Installation, maintenance
Whether you go with more high-tech systems or stick to the basics, make yourself as knowledgeable as possible on the proper installation and maintenance of the system you choose.

Ron Despenza, transportation director at Clark County (Nev.) School District, says that it's key to have air conditioning installed at the factory. "With the dealer-installed systems, many times we've had the ducting in the bus screwed through the wiring in the side wall. There are literally hundreds of problems related to that," he says.

Once installed, Lucas says that the most important thing to focus on is preventive maintenance. "That's one thing a lot of people drop the ball on," he says. "Very rarely does an air conditioning system break because it's a bad system. It's usually a result of bad maintenance or improper installation." If you need help, he advises contacting your air conditioning manufacturer. In fact, he says, work closely with your system manufacturer from the beginning. Get help on spec'ing. The manufacturers want to help, he says, because it's a win-win situation — your system performs better and their company, in the process, looks better. For more information on the companies mentioned in this article, you can reach them at the following numbers: American Cooling Technologies Inc.
(877) 228-4247
Carrier Transport A/C Industries
(800) 673-2431
Rifled Air Conditioning Systems
(800) 784-5627
Thermo King Corp.
(952) 887-2200
Trans/Air Mfg. Corp.
(800) 673-2446