As technology improves and demand for chilled school buses rises, more and more of the yellow vehicles are being outfitted with air conditioning systems.

Although obtaining the desired cooling effect remains the top priority, the industry is seeing a trend toward more integrated products that complement the design of the vehicle and increase passenger safety.

Innovations and trends
One of these new integrated air conditioning components is called an in-wall or bulkhead evaporator. It is built right into the bus above the aisle or seats and increases the available headroom on air-conditioned school buses.

“This evaporator is made to fit in the bulkhead area above the front windshield and then above the rear emergency exit door,” says Dave Oberdorff, product manager at Carrier Transport Air Conditioning in York, Pa. “You don’t have the protrusion down from the ceiling of eight or nine inches.”

Some states have determined that they do not want front-mounted evaporators encroaching into the passenger area because of the chance of a child hitting his head on the evaporator in an accident.

So far, four states — New York, New Jersey, Ohio and Michigan — have legislated that nothing can come down more than two inches from the ceiling of the bus, Oberdorff says.

Another trend that manufacturers are seeing is a rooftop-mounted air conditioning system. Here, most of the air conditioning unit is on the roof rather than inside the vehicle, eliminating the intrusion into the passenger compartment.

Some of the states that are currently looking at these types of systems are California, Florida and Texas.

“Our priority is the location of the unit and venting,” says Jill Gayaldo, transportation director at Rocklin (Calif.) Unified School District.

Rocklin Unified recently purchased a new bus that has the air conditioning mounted on the roof to allow for more storage space under the bus.

According to Cheyne Rauber, general manager of Rifled Air Conditioning Systems (RAC) in Archdale, N.C., it is also important to find ways to manufacture air conditioning components at a lower cost as long as the quality remains the same. That’s why RAC has designed a condenser for school buses in particular that attaches to the side skirt of the bus instead of being bolted into the floor of the vehicle, which can reduce manufacturing costs.

Espar Heating Systems in Mississauga, Ontario, has added air conditioning options to its heating systems. It now manufactures an independent, electrically driven air conditioning system that, unlike others, does not need any outside engines and doesn’t use on-board fuel.

Espar offers two lines of these electrical systems: one is an under-the-bunk mounted system and the other is a rooftop-mounted system. According to John Dennehy, vice president of marketing at Espar, this system can increase fuel savings and boost engine life through reduced idling.

Industry involvement
Air conditioning manufacturers are also getting more involved in the school bus industry, whether they are joining specification committees or working with engine and chassis manufacturers.

“It’s been very good for the industry to have an impact on future legislation and in the future designs of buses,” says J.R. Lucas, co-owner of American Cooling Technology (ACT) in York, Pa.

Mike Yestrumsky, sales manager at Thermo King in Minneapolis, agrees, stressing the importance of manufacturers’ industry involvement. Yestrumsky takes part in the Texas school bus committee meetings in Austin, Texas, where they discuss what kinds of specifications should be followed for school buses. He suggests that state specification committees contact manufacturers of air conditioning to participate in their process.

{+PAGEBREAK+} Maximum cooling
There is a lot to be taken into consideration when spec’ing a school bus for air conditioning. Manufacturers agree that an air conditioning system has to be specifically designed for the vehicle and that school bus operators should make sure they are buying from a company with experience in outfitting school buses.

But there are other things that can be done to maximize the cooling effect such as tinted windows, insulated bodies and white roofs to help keep the inside cool when outside temperatures are soaring.

“It’s proven that the white roof will reduce the heat transfer into the vehicle,” says Lucas at ATC.

Especially for those who live in the hotter areas of the country, a white roof can lower the interior temperature by seven or eight degrees over a yellow roof. Add well-tinted windows to reflect the heat and a good amount of insulation and you’ll get better cooling capabilities for your school buses.

Climate Comfort Technologies in Commerce City, Colo., for instance, offers a roof-mounted air conditioning system that gives customers the choice of a yellow or a white roof.

Increase of buses with A/C
Although air-conditioned school buses are still more prevalent in southern states, manufacturers are seeing a trend toward equipping school buses with air conditioning across the country.

Whether school districts outfit their buses with air conditioning is determined by a variety of factors. It depends on whether a district has a year-round school program, how much funding they have available and how many special-needs students they are transporting.

But many special-needs students who have to be in a temperature-controlled environment are now being mainstreamed into the school system.

“Due to the increase in the number of special-needs students whose IEP requires that we regulate the temperature inside the bus, we have increased the number of air-conditioned buses in our fleet,” says Archie Denard at West Bloomfield School District in West Bloomfield, Mich. “We have added two in the last year alone.”

Although air conditioning can be added to a bus after it is assembled, it’s much easier to install the compressors on the engine before it goes on the chassis and before the body goes on the bus.

“In some cases you have to partially disassemble a brand new bus in order to put in air conditioning,” explains Oberdorff at Carrier. “Now, a lot of buses are being air-conditioned at the factory that builds the bus so they can get better access to the engine.”

{+PAGEBREAK+} A safety issue?
Manufacturers also seem to widely agree that air-conditioned buses might be safer for children, which should be taken into consideration when looking at purchasing air conditioning systems.

“Operators have told us that they’ve noticed that with air conditioning you get increased driver satisfaction and concentration,” says Rick Lehnert, president of Trans/Air Mfg. in Dallastown, Pa.

There is also a concern about emissions and pollution. If the windows are down because there is no air conditioning on the bus, children could be breathing in toxic diesel fumes.

“Comfortable drivers drive safely; comfortable kids aren’t opening windows, jumping up and down and doing other things,” Thermo King’s Yestrumsky says. “Safety is a big issue.”

All in all, it appears that more and more states are increasing the usage of air-conditioned school buses.

“You wouldn’t really think about buying a car without air conditioning anymore,” Oberdorff adds. “I can see that same trend probably over a longer period of time coming true on school buses.”

Performance-based specs
Consensus has not been reached on an industry standard when it comes to the rating of air conditioning units, but manufacturers seem hopeful. For years, people were using BTU (British Thermal Units) ratings to measure the cooling capacity, but there are no set standards to rate the capacity of BTUs in air conditioning.

“One manufacturer’s 66,000 BTU system may be quite different than another’s,” Yestrumsky says.

Until there is an industry-wide standard, performance-based specs are the preferred way of spec’ing the capacity of air conditioning systems. Under performance-based specs, the air conditioning system must be able to pull the temperature of the interior down to the temperature specified by the customer.

“Performance testing seems to be an ongoing trend,” says Rauber at RAC. “Rifled Air has always pushed for performance-based specs. This way it’s up to the manufacturer to put in the correct system to meet the needs of the customer, and at the end of the day this gives the customer the best system for their money.”

Performance-based specs involve what is called a pull down test. During a pull down test, the bus with the manufacturer-recommended system is taken into a heating chamber. ACT’s Lucas explains the process of a pull down specification:

The interior of the vehicle is heat soaked for one hour to a temperature of 95 degrees Fahrenheit at 50 percent relative humidity. The air conditioning is turned off during this time, and the windows are opened. At the end of one hour, the windows are closed, the engine is started and the air conditioning system is turned on, while maintaining an outside temperature of 95 degrees. Within 30 minutes or less, the interior temperature of the bus should drop to an average temperature of 72 degrees, plus or minus two to three degrees. The temperature is measured between the floor and the ceiling at the front, middle and rear of the bus.

Proper maintenance is key
To keep an air conditioning system running properly, all manufacturers emphasize the need for preventive maintenance care.

“The main problem is lack of maintenance,” says Lucas. “People buy the air conditioning, they turn it on and just let it run, but they do not clean the filters and they don’t check the belts.”

If you want the air conditioning unit to last, it’s important to keep the evaporator air filters and the condenser coil clean and check pressures on the system to avoid leaks. Oberdorff at Carrier adds that a periodic cleaning for condensers located under the bus is a good idea, just to wash out any leaves, twigs, dust and dirt that might have collected over the year.

For electrical systems, it is crucial to keep the batteries charged and in good condition as well as keeping the electrical connections in good shape and avoiding corrosion.