Standard Bus Procurement Guidelines - APTAStandards.com

Standard Bus Procurement Guidelines
The air conditioning portion of the HVAC system shall be capable of reducing the passenger
compartment temperature from 110Ε to 90Ε F in less than 20 minutes after engine start-up. Engine
temperature shall be within the normal operating range at the time of start-up of the cool-down test
and the engine speed shall be limited to fast idle that may be activated by an operator-controlled
device. During the cool-down period the refrigerant pressure shall not exceed safe high-side
pressures and the condenser discharge air temperature, measured 6 inches from the surface of the
coil, shall be less than 45Ε F above the condenser inlet air temperature. The bus shall be parked in
direct sunlight with ambient temperature at 100Ε F and humidity less than 20 percent. There shall be
no passengers on board, and the doors shall be closed.
Manually controlled shutoff valves in the refrigerant lines shall allow isolation of the compressor and
receiver for service. To the extent practicable, self-sealing couplings shall be used to break and seal
the refrigerant lines during removal of major components, such as the refrigerant compressor
condenser. The condenser shall be located to efficiently transfer heat to the atmosphere, and shall not
ingest air warmed above the ambient temperature by the bus mechanical equipment, or to discharge
air into any other system of the bus. The location of the condenser shall preclude its obstruction by
wheel splash, road dirt or debris.
5.4.8.2 CONTROLS AND TEMPERATURE UNIFORMITY
All interior climate control system requirements shall be attained automatically. The operator shall
control only the defroster and operator's heater. The interior climate control system shall switch
automatically to the ventilating mode if the refrigerant compressor or condenser fan fails.
Temperatures measured from a height of 6 inches below the ceiling shall be within ∀5Ε F of the
average temperature at the top surface of the seat cushions. Temperatures measured more than 3
inches above the floor shall be within ∀10Ε F of the average temperature at the top surface of the seat
cushions. The interior temperature, from front to rear of the bus, shall not vary more than ∀5Ε F
from the average.
5.4.8.3 AIR FLOW
5.4.8.3.1 Passenger Area
The cooling mode of the interior climate control system shall introduce air into the bus at or near the
ceiling height at a minimum rate of 25 cubic feet per minute (cfm) per passenger based on the
standard configuration bus carrying a number of passengers equal to 150 percent of the seated load.
This air shall be composed of no less than 20 percent outside air. Airflow shall be evenly distributed
throughout the bus with air velocity not exceeding 100 feet per minute on any passenger. The
ventilating mode shall provide outside air at a minimum flow rate of 20 cfm per passenger.
Airflow may be reduced to 15 cfm per passenger (150 percent of seated load) when operating in the
heating mode. Heated air introduced into the bus shall contain no less than 20 percent outside air.
The fans shall not activate until the heating element has warmed sufficiently to assure at least 70Ε F
air outlet temperature. The heating air outlet temperature shall not exceed 100Ε F under any normal
operating conditions. Outside airflow may be cut off during initial warm-up, provided no manual
manipulation is required.
Technical Specifications 183 10/18/07