Jun. 09, 2025
All school bus manufacturers offer air conditioning options. Some install systems on the assembly line. Others offer systems that are installed by A/C manufacturer-qualified installers or the bus sales dealer, after the bus leaves the assembly line.
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OEM and after-market systems vary, from system installations that tie into existing OEM dashboard HVAC systems, to stand-alone complete air conditioning systems. The components that make up an A/C system are the compressor (mounted on the engine or a separate power source), dash evaporator (driver area), controls (switches, thermostats, electronics), hanging or flush evaporators, and rooftop or skirt mounted condensers.
There are so many different kinds of bus air conditioning systems to choose from, that it can be hard to figure out which one is just right for you.
Manufacturers are continually updating or adding new system configurator links through their dealer networks, so be sure that you pick the most economical and effective cooling system. Always work with your dealer to find the cooling system that is specific to your vehicle’s cooling needs.
Don’t compare apples to oranges, that is, “In-dash, tie-in systems to stand-alone propriety systems.” Get the right system for your bus, and be sure to consider the power draw that the A/C system will require, so that it does not impact your vehicle’s alternator capacity to maintain its battery charge.
Level the Playing Field
1. Have your system provider reference a performance pull-down test. The best and most important evaluation of a system is to measure the ability of the installed system to cool a bus interior.
2. Require BTU/hour system capacities to be recorded in an industry-standard format, such as the Society of Automotive Engineers (SAE).
The National Congress of School Transportation amended school bus A/C specification recommendations in . The resulting National School Bus Specifications & Procedures document, starting on page 49, paragraph B, recommend that two performance standards be used when specifying school bus air conditioning systems:
• Standard Performance — The installed air conditioning system should cool the interior of the bus from 100 degrees to 80 degrees Fahrenheit in 30 minutes.
• High Performance — The installed air conditioning system should cool the interior of the bus from 100 degrees to 70 degrees in 30 minutes.
The American Public Transit Association has specified its requirements:
• Capacity and Performance Requirements — The air conditioning portion of the HVAC system shall be capable of reducing the passenger compartment temperature from 115 degrees to 95 degrees in less than 20 minutes after engine startup.
• Hotter Ambient Conditions — The air conditioning portion of the HVAC system shall be capable of reducing the passenger compartment temperature from 110 degrees to 70 degrees, plus or minus 3 degrees, in less than 30 minutes after system engagement for 30-, 35- and 40-foot buses.
BTU Capacity Considerations
• Gross capacity (most typically used) uses the weakest link (lowest capacity) among the evaporator, condenser and compressor to determine overall system capacity.
• Net capacity (rarely used and difficult to measure) uses multiple simultaneous equations until the system is balanced.
There is neither a universal BTU (British Thermal Unit) capacity rating method currently being used in the bus air conditioning industry, nor any governing association to police the industry!
BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. Aside from the technical definition of BTU, bus air conditioning system BTU capacity is dependent on many variables. It requires that specific rating conditions be defined for each system component, since each has its own capacity.
Capacity ratings can change, higher or lower, depending on the rating conditions that are being used. So be aware that system BTU ranking is the lowest of the three-component values: Compressor, condenser and the evaporator rating.
Theoretical BTU/hour system ratings, when using realistic rating conditions at the various vehicle engine/compressor speeds, is a valuable piece of information to assess the application of the system to the vehicle type.
However, the best way to measure A/C system performance is to install an air conditioning system in the vehicle, operate the vehicle into the above-mentioned environment, and perform a standard or high-performance, pull-down test. This will then tell you that the air conditioning system you ordered to do the job is the one you got.
Editor’s Note: Reprinted from the March Issue of School Transportation News
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Selecting the right air conditioning system for your bus is critical to ensuring a comfortable ride for passengers, especially during hot weather. With a plethora of options available, it can be overwhelming to determine which system best meets your needs. In this comprehensive guide, we will delve into the different types of bus air conditioning systems, their components, performance standards, and how to choose the most efficient and economical option for your vehicle.
Contact us to discuss your requirements of school bus air conditioner. Our experienced sales team can help you identify the options that best suit your needs.
Further reading:Bus air conditioning systems can be categorized into two primary types: Original Equipment Manufacturer (OEM) systems and aftermarket systems.
– OEM Systems: These systems are integrated into the bus during its assembly. They are designed to work seamlessly with the bus’s existing HVAC systems, ensuring optimal performance and reliability.
– Aftermarket Systems: Installed post-production, these systems can either be tied into the existing dashboard HVAC systems or function as standalone units. They offer flexibility and can be tailored to specific cooling requirements.
Over the past 24 years, TKT EV Solution has grown to be the OEM of choice for 100% of China’s bus air conditioners and battery thermal management systems, such as Yutong, Nanjing Jinlong, Xiamen Jinlong, etc. (Bus Air Conditioners), CIMC, Xinfei, Hongyu, etc. In the international market, TKT is the OEM of Tata Motors, Tata Marco Polo, Daewoo Motors, etc., and exports to over 85 countries with sales and service centers.
A high-quality bus air conditioning system comprises several crucial components:
– Compressor: The heart of the system, typically mounted on the engine or a separate power source, compresses the refrigerant and circulates it through the system.
– Evaporator: Located in the driver’s area or throughout the bus, the evaporator cools the air by absorbing heat.
– Condenser: Mounted on the roof or skirt, it releases the absorbed heat to the outside air.
– Controls: These include switches, thermostats, and electronic controls to manage the system’s operation.
– Additional Evaporators: These can be hanging or flush-mounted, ensuring uniform cooling throughout the bus.
Performance Standards
When selecting an air conditioning system for ev buses, it is essential to consider the performance standards set by industry authorities. The National Congress of School Transportation and the American Public Transit Association provide guidelines to ensure systems meet minimum cooling requirements.
– National School Bus Specifications:
— Standard Performance: The system should cool the interior from 100°F to 80°F within 30 minutes.
— High Performance: The system should cool the interior from 100°F to 70°F within 30 minutes.
– American Public Transit Association Specifications:
— Capacity and Performance Requirements: The system should reduce the passenger compartment temperature from 115°F to 95°F within 20 minutes after engine startup.
— Hotter Ambient Conditions: The system should reduce the temperature from 110°F to 70°F (±3°F) within 30 minutes for 30-, 35-, and 40-foot buses.
Understanding BTU (British Thermal Unit) capacity is crucial in evaluating the effectiveness of an AC system unit. BTU measures the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.
– Gross Capacity: This is the lowest capacity among the evaporator, condenser, and compressor, representing the system’s weakest link.
– Net Capacity: Though rarely used, this method employs multiple simultaneous equations to balance the system.
It is important to note that there is no universal BTU rating method in the bus air conditioning industry. The most reliable way to assess a system’s performance is through a pull-down test, where the system’s ability to cool the bus interior is measured under specified conditions.
– Work with Your Dealer: Collaborate with your dealer to select a system tailored to your bus’s cooling needs. Consider the power draw of the system to ensure it does not overburden the vehicle’s alternator capacity.
– Performance Pull-Down Test: Require a performance pull-down test to evaluate the system’s ability to cool the bus interior effectively.
– Standardized BTU Ratings: Insist on BTU/hour capacities recorded in an industry-standard format, such as those provided by the Society of Automotive Engineers (SAE).
Choosing the right air conditioning system for your bus requires careful consideration of various factors, including system type, components, performance standards, and BTU capacity. By adhering to industry guidelines and working closely with your dealer, you can ensure that your bus is equipped with an efficient and effective cooling system, providing a comfortable environment for passengers and enhancing the overall travel experience.
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