By Eugene le Roux, FSAIRAC, and Eamonn Ryan
When people think of air conditioning design, they usually imagine comfortable cooling systems in homes, offices, or even standard vehicles.
Combat vehicles break almost every rule of conventional HVAC planning. Freepik
However, one of the most demanding and unconventional environments for climate control is inside combat vehicles. While this may seem like a niche topic, it holds considerable interest for those involved in defense engineering, HVAC design for extreme environments and vehicle systems integration.
Designing air-conditioning systems for combat vehicles is not just about comfort – it’s a mission-critical necessity. Crew effectiveness, endurance and even survival can depend on maintaining a habitable environment inside an armoured hull exposed to extreme temperatures and battlefield stressors.
This article outlines why traditional HVAC calculations fall short in this context and why so many attempts to create effective systems have failed. In fact, each combat vehicle type demands a unique approach due to significant differences in structure, usage and thermal loads.
Note: chemical protection systems are sometimes integrated into the HVAC setup, especially in military applications where protection against NBC (nuclear, biological, chemical) threats is required. However, this complex and specialised area falls outside the scope of this article.
Why conventional heat load calculations don’t apply
Most HVAC systems, such as those designed for commercial buildings or civilian vehicles, rely on predictable models of heat load – mainly based on human occupancy, insulation levels and external environmental conditions. Combat vehicles, however, break almost every rule of conventional HVAC planning:
- No windows, no radiant escape: Combat vehicles have no fenestration – no windows, skylights or standard ventilation paths. This immediately alters air circulation assumptions and limits passive cooling.
- High surface temperatures due to direct solar radiation: Unlike insulated buildings, these vehicles are often constructed from solid steel with little or no internal insulation. Insulation, even if initially applied, tends to detach over time due to vibration and shock, rendering it ineffective. Steel hull surfaces exposed to direct sun can easily reach 70°C, and without internal barriers, this heat is radiated directly to the crew. The interior surfaces can reach the same temperatures, drastically increasing the cooling demand just to maintain survivable conditions.
- Heat-generating equipment inside the hull: Combat vehicles are loaded with power-hungry electronics – computers, sensors, targeting systems and electronic actuators – all of which generate heat. Unlike office equipment, these systems are always on during operations and often operate under stress, further increasing internal thermal gain.
- Thermal load from expended weapon shells: A uniquely military source of internal heat load is the accumulation of hot, empty weapon shells after firing. These metallic objects remain inside the vehicle for extended periods and act as heat reservoirs, further elevating the internal temperature.
- Transmission components beneath the crew: To maximise space efficiency, high-power transmission components – handling hundreds of kilowatts – are sometimes located directly beneath the crew compartment. These systems produce substantial thermal output, adding to the internal load from below.
