3 Keys to Maintaining a Comfortable Cab Temperature

With heavy equipment typically operating in extreme climates and harsh temperatures, a common challenge for OEMs when designing cabs is maintaining a comfortable temperature for operators. Since numerous factors impact a cab’s internal temperature, the solution is almost never to simply incorporate more powerful equipment into your HVAC system. Thoughtful analysis of both the cab’s external heat load and the ducting system can allow you to optimize both of those areas. And then consequently the most accurate and cost-effective components can be incorporated into the HVAC system, creating a good working environment for the operator.

1. Limit External Heat Load – The first steps of analyzing a cab’s heat load is to determine where it’s coming from. While the most obvious answer is any windows, there are several other factors at play. Depending on the cab’s location on the machine itself, you may have heat from the engine or other components coming from underneath or next to the cab. Or if the cab’s weldment is particularly dense or large, for example a ROPS/FOPS certified cab, it will also have a higher heat load. Finally, any exposed internal steel will also radiate heat into the cab. There are structural or design elements that can mitigate those issues, including adding a sun shield or utilizing thicker plastic or carpeted headliners. Windows with UV filters, for example, can reduce UV penetration by 85%. Taking some steps to limit the heat getting to the operator is a good first step and will help you more accurately determine your HVAC system requirements.
2. Correctly Select HVAC Components – Once you’ve determined the heat rejection needed for a cab and the size evaporator and condenser needed for that amount of heat, the most important thing to note is that the condenser should be 30% larger than the evaporator rating. Condensers are typically located outside the cab and are exposed to dirt, leaves, and other environmental factors. That gives you a safety net in case anything keeps it from functioning at its peak. Something else to consider is the fin style in the evaporator. For example, in a recent cab design, we were able to increase the evaporator’s cooling capacity 15% by transitioning from 2-bit aluminum fins to a quantum fin style inside the evaporator coil.
3. Optimize Airflow in the Cab – That equipment does the work of supplying cold air to the cab but ensuring that it actually gets to the operator is the next step. The bulk cooling method, in which the cold air is unrestricted, is the simplest option. However, since some amount of heat is still coming into the cab from all directions, that air will likely be warmed up by the time it reaches the operator and will have the perception of not actually being cool. A ducting system is much more strategic but requires analysis. The farther air must travel and around more corners diminishes the cooling effect. The SAE J1503 test standard for off highway equipment maintains that there are certain points on an operator that air must be cooled down from a fully heat-soaked unit within one hour. The best way to meet that standard is to optimize a cab’s ducting system, ensuring sufficient airflow, and keeping the operator cool.