By Eugene le Roux, FSAIRAC, and Eamonn Ryan
Continuing from the previous discussion, it’s clear that combat vehicles present a cluster of extreme and overlapping heat sources – each of which needs to be accounted for in the design of an effective climate control system.
Each vehicle must be approached as a unique thermal system, requiring custom calculations. Freepik
- Firewall heat ingress: Though an insulated firewall typically separates the crew area from the engine and power pack, heat conduction and radiation still occur through this large panel. The sheer surface area and proximity of the power pack to the crew compartment means this barrier must be considered in any heat load assessment.
- Human heat and metabolic load: In most office environments, designers assume a metabolic heat load of 100–130W per person. In contrast, combat vehicle crew members, such as the driver or gunner, can exert up to 400W or more, depending on the level of physical activity. In a sealed, confined space:
- Breathing, perspiration and body heat become major contributors to overall thermal load
- The driver, often located farthest from the main cool air entry point, suffers the most from insufficient air circulation
Although placing a secondary evaporator closer to the driver might seem like a practical solution, it introduces a new hazard: in the event of refrigerant line rupture due to projectile penetration, high-pressure gas could escape into the crew compartment, posing serious risks to crew health and visibility.
- Ventilation and fresh air intake: Even in sealed environments, a supply of fresh air is necessary for both physiological and safety reasons. However, drawing in air from the external environment – often hot and dusty – adds significantly to the cooling load. Filtering and pressurising this air adds mechanical complexity and power requirements.
- Tropical roofs: An effective but often overlooked solution – a practical yet underutilised method of reducing solar heat gain is the installation of a tropical roof. This consists of an external steel plate mounted above the vehicle hull, with a ventilated air gap in between. This acts as a thermal shield, blocking direct solar radiation before it can heat the main hull. While adding a tropical roof increases the mass of the vehicle, this can often be compensated by reducing the thickness of other hull panels – maintaining protective performance while achieving better thermal performance. Such design trade-offs are essential in modern combat vehicle development.
Conclusion
The development of effective air-conditioning systems for combat vehicles is far more complex than traditional applications. The absence of insulation, presence of high-energy systems, human factors and the hostile external environments all combine to make standard HVAC design rules obsolete.
Each vehicle must be approached as a unique thermal system, requiring custom calculations and thoughtful component placement. As operational demands and technological sophistication increase, so too does the need for robust, intelligent climate control systems that ensure both crew safety and mission success.
By understanding and accurately accounting for these extreme heat loads, engineers can design next-generation HVAC solutions that are not only survivable but sustainable for extended missions in the harshest environments.
