Help me understand heating/cooling principles

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SUMMARY

The discussion centers on the principles of heat transfer and airflow dynamics within a closet with two double doors and specific gaps. The user observes that when fans are oriented to blow ambient air into the closet, the lower shelves become 2 degrees hotter than the upper shelves. Conversely, when the fans expel air, the upper shelves are 2 degrees hotter than the lower shelves. This phenomenon is attributed to the stratification of air temperatures and the behavior of warm air rising, leading to uneven temperature distribution based on fan orientation.

PREREQUISITES
  • Understanding of thermodynamics, specifically heat transfer principles.
  • Familiarity with airflow dynamics and stratification of air temperatures.
  • Knowledge of fan orientation effects on air circulation.
  • Basic concepts of temperature measurement and calibration.
NEXT STEPS
  • Research the principles of convection and how it affects temperature distribution in enclosed spaces.
  • Explore the effects of fan placement and orientation on airflow efficiency.
  • Learn about thermal stratification and its implications in HVAC systems.
  • Investigate methods for improving temperature uniformity in small enclosed areas.
USEFUL FOR

This discussion is beneficial for HVAC engineers, electrical equipment designers, and anyone interested in optimizing temperature control in confined spaces.

lavalin
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Hello

I have a closet with two double doors. There’s a 3mm gap between the doors and a 10mm gap down the bottom. I have a few fans mounted above the doors in the wall.

Ambient air is always 2-3deg cooler than inside the closet due to some electrical equipment I have running in there.

I have 2 shelves in the closet. On each shelf there’s a temperature sensor which are closely calibrated. Between the shelves and the doors is a 150mm gap.

When I orientate the fans to blow ambient air in, the lower shelves are about 2 degrees hotter than the upper shelves. When I orientate the fans to extra air out of the closet, the top shelf is about 2 degrees hotter than the bottom shelves.

Just curious to understand the science behind why this is happening.

Also if I pull air into the cabinet which is 2deg cooler than inside the cabinet, what happens to the warm air inside the cabinet? Does it simply mix and just cool down over time? Or is there another explanation
 
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lavalin said:
I have a few fans mounted above the doors in the wall.

... inside the closet due to some electrical equipment I have running in there.

When I orientate the fans to blow ambient air in, the lower shelves are about 2 degrees hotter than the upper shelves. When I orientate the fans to extra air out of the closet, the top shelf is about 2 degrees hotter than the bottom shelves.

Just curious to understand the science behind why this is happening.
When the fans blow air in at the top, the outflow of the heated up air is at the bottom.
When the fans blow air out at the top, the outflow of the heated up air is at the top.
 

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