Selecting the right HVAC equipment for critical facilities is extremely important. Unfortunately, there is confusion about how to do so, partially due to human comfort based cooling standards being utilized in electronic cooling applications.

Insufficient HVAC capacity means that a single HVAC system failure could result in elevated temperatures and place the electronic equipment you are trying to maintain at risk. 

Because this risk of under sizing is more or less “obvious”, engineers will often oversize the HVAC capacity without necessarily understanding the negative impacts of doing so:

  • Up front cost of purchasing “extra” HVAC capacity can be substantial. 
  • Oversized HVAC systems tend be less energy efficient and can suffer additional wear & tear due to excessive turn on-turn off cycles.
  • In a 1+1 (aka Lead/Lag) configuration, oversizing can make it extremely difficult to “manage” indoor RH (Relative Humidity). This can be mitigated by “adding load” which is less than optimal from an efficiency standpoint.

In the World’s largest electronic enclosures – data centers – cooling requirements are measured in sensible capacity. And yet, the human comfort method – measuring in “total capacity” -- is still generally used in electronic cooling applications. This paper examines how the “sensible” method can and should be used for electronic cooling applications.