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The technical challenges for fanless 8th gen desktop PCs

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Introduction

This article focuses on our area of expertise, fanless PCs with powerful desktop CPUs. We only supply high quality solutions that are tested to be suited for intense use. We often see competitors selling fanless PCs with CPUs that will cause problems if used intensely for more than a few minutes because they either do not know or care about the requirements of fanless cooling.

Although the latest 8th Generation desktop CPUs from intel are "better and faster" than the previous 7th Generation CPUs, there are important changes that have impacted on their use in fanless PCs. As a result our product ranges do not have a one-for-one upgrade from the 7th Gen to the 8th Gen CPU.

The 2 main technical changes in 8th Gen CPUs impacting fanless use are:
  • The increase in cores (i3 now 4-core, i5 and i7 now 6-core) means higher performance, but increased power use compared to previous equivalent models.
  • The 35W TDP CPUs now have 100°C Tjunction limit compared to 80°C Tjunction for 7th Gen 35W TDP CPUs.

Taking each of these points in turn: 

Increase in CPU Cores

The increase in cores means more heat and therefore more cooling is needed. On the upside the increase in cores means you can now get a higher level of performance at each price point. So for example you can now get "i5 performance" by buying an 8th Gen i3 product. But on the downside the i3 now needs cooling performance similar to the old i5.

Impressive improvements have been made by intel, as the new i5 8500T has a passmark performance matching the older i7 7700T (although 10% less single-core performance), and it uses less power and generates less heat than the i7 7700T. But under heavy load it still produces 25% more heat than the i5 7500T that it replaces.

The most marked change is the i7 8700T, which although marketed as a 35W TDP CPU, has been proven by our testing to perform more like a 50W TDP CPU. It is able to generate significantly more heat than the 7th gen i7 7700T, and a result is not suited to our Ultimate Fanless or FC8 fanless cases which perform well up to 40W TDP.

Change to Tjunction limits 

The second point about Tjunction (CPU temperature) limits is important, as the 7th Gen 35W TDP "T" CPUs would start to throttle the clock speed a little once the CPU temperature passed about 77°C, as it tried to limit the CPU temperature to 80°C. It did this very effectively so it would be hard to notice the throttling. Although intel CPUs (especially the i7) easily breached the stated 35W TDP rating this Tjunction limit added a "backstop" to stop overheating. It meant that if the fanless cooling was not doing a good enough job the CPU would help out, and the whole product’s temperatures would be kept at safe levels. As our products are designed for intense use it would only be in extreme use scenarios where these limits would be experienced.

As the 8th Gen 35W TDP "T" CPUs now have a 100°C TJunction limit, the CPU will not throttle until extremely high temperatures close to 100°C are being reached. In a fanless PC if the CPU is reaching anywhere near these temperatures the whole product is likely to have passed safe operating temperatures… the motherboard, memory and SSD are all likely to be at unsafe temperature levels.

Conclusion

It is even more important than ever for a fanless PC with 8th Gen CPU to have a cooling solution that is matched to the heat levels that can be produced. Many of our customers are using our products for business critical applications so we ensure all our fanless PCs can be used safely both intensely and for extended periods. 

See our 8th Gen Fanless PCs here. More models being added soon.