Without some form of cooling, problems or even complete failures will occur due to heat buildup within enclosures if the heat load is beyond the ability of the cabinet’s natural convection cooling to dissipate. The chart shows various panel temperature rises above ambient temperature due to watts of wasted heat load, and the various BTU/hr cooling results.
Uninsulated NEMA 12 and above metal panels dissipate heat via natural convection, which occurs primarily along its vertical walls -- not from the top as intuition might lead us to expect. So, one simple cooling solution for low heat loads is to place equipment in oversized panels that maximize vertical height over width and depth as much as possible. As the figure indicates, in ideal conditions -- a freestanding panel with airflow all around it, no sources of heat such as transformers sitting on top of it, etc. -- a 72 x 36 x 24" panel can convect almost 500 W of waste heat with only a 27°F (15°C) rise in panel temperature above ambient. That is great if your ambient is climate controlled and never rises above 75°F (24°C), but few environments are that ideal. Also, most heat loads are far larger than 500 W. Finally, in addition, the cost of such an oversized panel, especially if it must be stainless steel, can exceed the cost of other cooling alternatives.
If the required panel internal temperature is below the peak ambient the panel will experience at its location, then a below-ambient cooling solution such as air-to-water heat exchangers, compressed air or air conditioning is a must. With a sufficient ΔT between the panel requirement and the outside, ambient air temperature will exist. A heat pipe-based heat exchanger can be a suitable and cost effective methodology.