Cooling capabilities have become a critical design consideration during the early stages of system development due to increased processing performance, smaller package and system footprints, and the requirement to operate in the harshest environments. Asking the right questions early on can help identify the cooling architecture that best fits your system.
Historically, conduction-cooled 3U VPX systems were often designed around roughly 50 W per card, but today, 100 W modules are increasingly common. Designing around today’s current power requirements can lead to cooling solutions that become inadequate as processing demands, component densities, and mission capabilities evolve. Understanding both present and anticipated heat loads enables you to select a cooling architecture that maintains performance, reliability, and scalability throughout your system’s lifecycle.
Before selecting a cooling architecture, engineers should first develop a clear understanding of their system’s thermal profile. Start by identifying every significant heat source, including CPUs, GPUs, FPGAs, RF devices, networking modules, switches, storage, and power electronics and evaluate how much heat each generates under typical, peak, startup, standby, and simultaneous operating conditions. Rather than designing an unrealistic worst-case scenario or an overly optimistic average, use these insights to establish a realistic operating heat load.
Calculating your total system heat starts with understanding your per-slot thermal burden. Below are common ranges based on per-slot power dissipation.
Payload | Thermal Burden | Description |
<50 W per slot | MODERATE | A modest thermal load for modern VPX |
50 - 100 W / slot | WARM | Normal to high-performance compute territory |
100 - 150 W / slot | HOT | Modern high-performance 3U compute - This is where cooling becomes a major system level design consideration |
150 W + / slot | HIGH HEAT DENSITY | Advanced thermal management should be evaluated early |
*Note, these ranges are just a guideline and not absolute limits.
For example, a four-card payload with:
2 x 150W AI/GPU modules
1 x 100 W CPU/FPGA module
1 x 75 W switch I/O module
= 475 W from payload electronics alone.
Calculating total system heat isn’t just adding up the thermal rating of your cards. Your payload power is not necessarily your total chassis heat, since power conversion loss, fans, pumps, storage, and other supporting devices can also contribute to the system’s overall thermal load. So, if in the above system, the power supply must deliver 475W to the electronics and is operating at 90% efficiency, you’d need a required input power of ~528W and would need to account for a power conversion loss of 53W.
Finally, estimate where the highest thermal concentrations are likely to occur. Even a preliminary understanding of potential hot spots can influence cooling strategy, airflow paths, and component placement, helping ensure the thermal solution is optimized for real-world performance. A single 150 W card can dominate the architecture if its heat is concentrated around one GPU/FPGA and the thermal path from that component to the chassis is poor.
Every cooling solution introduces its own size, weight, and power (SWaP) requirements that must be balanced against the performance goals of the full system. Larger heat exchangers, higher airflow rates, liquid cooling loops, pumps, and cold plates can significantly improve heat removal, but they also consume valuable volume, add mass, and require additional electrical power. In many defense platforms, these resources are already limited, making thermal management a design tradeoff rather than a standalone engineering decision.
Total watts alone don’t determine the cooling architecture.
For example, 1000W isn’t necessarily harder to cool than 600 W; how tightly that heat is concentrated and what space and thermal paths are available matter just as much. 1,000W distributed across ten 100 W cards in a large rack with unrestricted conditioned airflow can be comparatively manageable while 600 W packed into four 150 W 3U cards inside a sealed ½-ATR enclosure can be a much harder thermal problem.
Your cooling architecture cannot be evaluated independently from the system it’ll be installed into. Tips to help you select a cooling architecture that not only dissipates the required heat but also aligns with your system’s mechanical, electrical, and operational requirements include:
Ambient temperature, altitude, humidity, dust, salt, solar loading, shock, vibration, and enclosure ingress requirements all influence how efficiently heat can be dissipated from embedded systems. Using the same cooling architecture in different operating environments provides a different level of cooling. Evaluating environmental conditions early in the design process allows you to select a cooling solution strategy that maintains reliable performance under rugged conditions.
By understanding your system’s mission profile and environmental requirements, you can choose cooling techniques that deliver consistent thermal performance:
For example, let’s consider a system housed in the unpressurized equipment bay of a high-altitude aircraft. On the flight line, the system may sit in a 55 °C ambient environment, potentially exposed to direct sunlight. Solar loading can raise the enclosure surface temperature above the surrounding air temperature, further reducing your thermal margin. If your maximum allowable thermal-interface temperature is 85°C, a 55 °C ambient condition leaves only a 30°C temperature differential to move heat away from the system.
At altitude, that same system may operate at 40,000 ft, where standard air density is only about 25% of sea-level density. This means that if this were a 500W system designed around forced-air cooling at sea level, it may require substantially more airflow, platform-provided conditioned air, or an alternative cooling approach to be successful for this program.
In this example, we would also need to consider how humidity, temperature, and pressure transitions could introduce condensation risk, as well as the continuous vibration environment transferred through the aircraft structure.
At this stage, the objective is to establish a continuous and effective thermal path that efficiently transfers heat from individual components to the ultimate heat sink, whether that is an integrated cooling solution within the enclosure or an existing thermal management system on the host platform.
Different cooling approaches exist, each addressing specific power requirements, space constraints, and operational environments.
Cooling Approach | What It Is | Where It Fits | Key Considerations |
Forced-Air Cooling | Requires fans, sufficient airflow, and unobstructed intake and exhaust paths to effectively remove heat from the system. | Lower to moderate heat densities where adequate airflow and clear intake/exhaust paths are available and exposure to contaminants is not critical. | Ambient temperature, altitude, airflow/CFM, pressure drop, fan power, environmental sealing requirements. |
Conduction Cooling | Depends on a chassis or host platform with enough thermal mass and heat-sinking capability to transfer heat away from critical components. | Rugged or sealed applications where airflow through the electronics is limited or undesirable. | Card-edge temperature, interface resistance, chassis/cold-wall capacity, local hotspots |
Enhanced Air / Air Flow-By / Air Flow-Through | Uses engineered airflow paths that bring cooling air closer to or through the payload module | Higher-power payloads where standard forced air or conduction begins to become limiting but liquid cooling may not be necessary or practical. | Flow rate, pressure drop, slot pitch, module compatibility, sealing, heat-exchanger design |
Platform Liquid Cooling | Relies on access to an existing liquid cooling infrastructure with compatible coolant interfaces and sufficient cooling capacity. | High heat densities when the vehicle, aircraft, or ship already provides suitable liquid-cooling infrastructure. | Coolant temperature, flow rate, pressure, interface compatibility, platform dependency |
Self-Contained Liquid-to-Air Cooling | Uses a closed-loop liquid cooling system to reduce dependence on platform-supplied coolant but still requires adequate airflow and heat exchanger capacity to reject heat to the surrounding environment. | High heat densities when platform liquid is unavailable or undesirable but the system can still reject heat to ambient air. | Pump/fan power, heat-exchanger size, airflow at the rejection point, maintenance, added SWaP |
Hybrid Cooling Solutions | Combine multiple cooling methods to supplement existing thermal infrastructure when a single approach cannot effectively manage the system's total heat load. | Applications where no single thermal path can meet the full combination of heat load, packaging, and environmental constraints. | Added integration complexity, interfaces, controls, qualification, maintenance |
Your decision doesn’t stop at air, conduction, or liquid. Consider the full heat transfer path and what your final rejection point is. Remember that your material selection, interface resistance, airflow path, and chassis design will all affect how heat can be removed effectively.
Sometimes the ‘best cooling performance’ isn’t the ‘best architecture’. Every cooling approach introduces tradeoffs across performance, complexity, cost, maintainability, and lead time. For some applications, air or conduction cooling may provide the right balance of simplicity, reliability, and cost. For others, higher heat loads or limited airflow may justify new sealing considerations, validation steps, or service planning. Consider where you can accept complexity and where you cannot.
Alongside SWaP considerations should be lifecycle costs. A cooling solution with a smaller initial footprint or lower upfront cost may require more frequent maintenance, higher operating power, additional redesigns, or earlier replacement over its service life. Evaluate both immediate integration benefits and long-term operational costs when selecting a thermal management approach.
There’s no universal answer to which cooling architecture is “best,” only the one that’s best for your system, at your heat loads, within your SWaP constraints, and under your specific environmental demands. Efficient cooling architectures prevent the need to protect against overheating with reduced cycle rates and computing power by ensuring that your system can maintain its performance at high ambient temperatures.
At LCR we help you evaluate these tradeoffs early, balancing thermal performance with cost, complexity, maintainability, lead time and future growth. Approaching each design with these five questions ensures that your cooling architecture is derived from the system’s actual constraints, not assumed from precedent.
Discover how LCR can help provide cooling architectures to fit your specific needs.
