Actual switch heat output (BTU/hr)

[GarrettMcW]

Hello.  I am coordinating heat loads with the mechanical consultant for telecom closets, and I'm concerned that the calculation method shown by Meraki for network switches may not be accurate.  The heat output chart shows a simple multiplication of the device's power consumption by the watts to BTU/hr conversion factor of 3.41.  However, in practice the power consumption of a switch with PoE devices connected does not entirely result in heat generated at the closet.  Some of the power drawn by the switch is delivered to the PoE endpoints, and that heat is produced at the endpoint.  For a fully loaded switch with many wireless access points connected, the difference in calculated switch heat output and real life heat output should be considerable.

Can Meraki please provide more accurate IDF closet heat load values?  I am specifically interested in values for the MS390 series.

Thanks.

[BlakeRichardson]

@GarrettMcW That is a question for support and unlikely to be answering in a community forum. Good luck with your question and feel free to share their response. 

[PhilipDAth]

The figures provided are the worse case.  I'd design for those.

I don't think Meraki could provide any other number for you.  They would have to know the amount of heat each of your PoE devices was converting form electrical energy, and they could not possibly know that.

[GarrettMcW]

Thanks.  I would argue it's not worst case, it's incorrect - or at a minimum needs clarification from Meraki.  The power draw numbers are provided "at full load" which would indicate the switch is providing its full capacity of PoE and has its CPU load pegged.  In that case, for a MS390-48FP, it would be delivering 740W of power to the PoE endpoints according to the spec sheet.  That's roughly 2500 BTU/hr which is being generated at the endpoints rather than at the switch, and turns out to be the bulk of what a simple calc would indicate is generated within the closet.

Too much cooling capacity can cause issues just the same as too little.  When an air conditioner short cycles because it's oversized, it won't run enough to control humidity.

[ConnorL]

Howdy @GarrettMcW, the only document/information Support can provide is what is detailed here:

https://documentation.meraki.com/MR/Other_Topics/Calculating_BTU_Consumption_for_Cisco_Meraki_Produc...

It's important to note:

Note: MS series switches with PoE capabilities have max power values that are significantly higher due to high PoE load at full capacity.

Hence the document provided the highest rated output for any given model (if it supports PoE).

[Uberseehandel]

Because I prefer switches to be seen rather than heard, I generally run fanless switches with only half the PoE capable ports used. If ambient temperatures stayed above 30C, I would expect the switches to get toasty. Above 25C I use a fan to keep the air circulating.

[Tom42]

I do a lot of heat load stuff for new buildings and generally give them these numbers from the datasheet as 'max heat gain' values.

In cases where I get further questions or this number ends up looking stupid (often we end up using a lot of UPOE mgig switching without a big POE load on it) I also provide an an 'estimated heat gain' figure which is a proportion of the max one.