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Supply-Air Short-Circuiting: Causes, Diagnosis and Design Solutions

An HVAC system can deliver the correct airflow, maintain the correct supply-air temperature, and even pass a conventional Testing, Adjusting and Balancing (TAB) inspection—yet still provide poor comfort and ineffective ventilation.

One possible reason is supply-air short-circuiting.


Supply-air short-circuiting occurs when conditioned supply air travels through an unintended or excessively short path toward a return or exhaust opening without adequately mixing with and conditioning the occupied space.


In cooling applications, this means valuable cold air can return to the AHU, FCU or other air-conditioning unit before absorbing the sensible and latent heat generated within the room. (Supply-Air Short-Circuiting: Causes Diagnosis and Design Solutions)


The consequences can include:

  • Hot or poorly conditioned zones

  • Uneven room temperatures

  • Excessive equipment operating hours

  • Poor ventilation effectiveness

  • High energy consumption

  • Temperature complaints despite apparently adequate cooling capacity

  • Unstable thermostat control

  • Humidity problems

  • Incorrect conclusions that the installed cooling equipment is undersized


However, the simple presence of a supply diffuser close to a return grille does not automatically mean that short-circuiting is occurring.

Supply-Air Short-Circuiting Guide

Download the full design guide PDF with detailed calculations, fan sizing, code compliance, and real project insights. Built for HVAC engineers and MEP consultants.  (Supply-Air Short-Circuiting: Causes Diagnosis and Design Solutions)




For detailed calculations, project-specific design, and authority-compliant solutions, contact our engineering team.

Phone : +94 76 720 5408

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