Choosing a Cooling Architecture: 5 Questions to Ask When Designing

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.

1. What is the actual heat load to manage across the full system – today and in the future?

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.

*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.

2. How much space, weight, and power (SWaP) can your cooling architecture use?

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:

• Identify your primary design constraint first: Determine whether your system is most limited by SWaP, available volume, airflow, or another design factor. Your dominant constraint will dictate which cooling technologies are the most practical and effective.
• Evaluate the complete cooling system footprint: Consider the space, weight, and integration requirements of all supporting thermal management components; this includes pumps, fans, ducts, hoses, manifolds, heat exchangers, reservoirs, and associated plumbing or electrical infrastructure.
• Account for the cooling system’s power budget: Determine how much electrical power is available for thermal management and assess how much power the cooling solution will consume.

3. What environmental conditions will the system need to operate through, and how will these conditions impact your thermal solutions?

• Ambient Temperature: Rugged embedded systems are commonly designed around operating environments extending from roughly -40°C to +55°C or higher, depending on the platform and installation. Evaluate the expected operating temperature range, higher ambient temperatures reduce the temperature differential available to dissipate heat. Consider how thermal performance may differ between sealed and ventilated enclosures.
• Humidity: Assess the potential for condensation caused by temperature fluctuations
• Altitude: Account for operating elevation, as lower air density at higher altitudes reduces the effectiveness of air-cooled thermal management systems.
• Solar Loading: Consider whether equipment will be exposed to direct sunlight. Solar radiation can significantly increase enclosure temperatures before heat generated by internal electronics is even considered.
• Contaminants: Identify environmental hazards such as dust, sand, salt fog, moisture, chemicals, or other airborne particulates that may require filtration, sealed enclosures, or specialized cooling approaches to maintain long-term reliability.
• Installation Constraints: Evaluate the physical installation environment, including available space, ventilation, equipment orientation, accessibility for maintenance, and the proximity of other heat-generating components that could affect 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.

4. What Can the Host Platform Provide?

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.

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.

 5. What tradeoffs are you willing to make?

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.

The Best Cooling Architecture Is the One That Fits Your System

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.