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HVAC Calculations and Duct Sizing

Gary D. Beckfeld, P.E.

This course presents the basic procedures for determining the cooling (or heating) unit and distribution system required for a building in order to maintain comfort conditions for people. These procedures include evaluating building heat loads, determining air circulation quantities, use of psychrometric processes, computing the cooling unit and air handler tonnage, and sizing the air distribution ducts.

Building heat loads from external and internal source are evaluated for both sensible and latent heat contributions. Heat conducted through walls and windows and through ceilings and floors from unheated spaces is considered. Walls constructed of layers of different materials, thicknesses and areas are included.

Air flow quantities are found for the conditioned space to maintain the desired temperature and humidity requirements. The effects of outside air infiltration are included and different methods of fresh air ventilation are examined.

A psychrometric chart diagram is used to indicate the processes of heating and humidification in the conditioned space. The air properties due to the mixing of ventilation and room air streams are determined from the chart. The enthalpy of the air entering and leaving the cooling coil is read from the chart as are the coil temperature and re-heater load.

The cooling unit and air handler size are found from the required flow rate and enthalpy change across the coil. Air handler flow and supply pressures are then used with air friction charts to select duct sizes such that all branches of the distribution system have equal pressure drop while having the required circulation quantities.

Finally, the heat load calculation methods using cooling load temperature differences (CLTD) and heating degree days (DD) are briefly reviewed.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

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NY PE & PLS: You must choose courses that are technical in nature or related to matters of laws and ethics contributing to the health and welfare of the public. NY Board does not accept courses related to office management, risk management, leadership, marketing, accounting, financial planning, real estate, and basic CAD. Specific course topics that are on the borderline and are not acceptable by the NY Board have been noted under the course description on our website.