October 2024 Chapter Meeting: Load Calculations Using the ASHRAE Heat Balance Method

Topic: Load Calculations Using the ASHRAE Heat Balance Method

Load calculations and HVAC system sizing are fundamental tasks in designing HVAC systems for all buildings. Considering load calculations have a dramatic impact on HVAC equipment size and HVAC system first cost, energy consumption, refrigerant quantity, and carry a significant amount of liability for the Engineer of Record, determining accurate loads is essential to any building, building owner, and design team.

Methods for calculating loads have changed significantly over time. “Traditional” methods assumed near instantaneous heat transfer or simplified the methods of estimating time-delay through weighting factors. These simplifications were made for a number of reasons including limited access to computing power and a lack of empirical tests for calculation methods.

Over 20 years ago, ASHRAE published (in the Handbook of Fundamentals) the Heat Balance Method for calculating loads.  This method is considered to be the most accurate and has some empirical testing to validate the calculation methodology.

This session explores how the Heat Balance Method is different from other methods, how energy code has impacted HVAC sizing calculation assumptions, and the impact of oversized and undersized systems on energy, comfort, and environmental impact.

The new ASHRAE HQ building is used as a case study in applying the Heat Balance Method for calculating loads for a building.

Presenter: Nathan Kegel | BEMP, LEED AP

Nathan has over 20 years of design and building performance simulation experience using a variety of design and modeling tools and platforms.  He has performed design and post-occupancy analysis on hundreds of buildings and dozens of building types all over the world.  He has built and led High Performance Design Teams, trained over 1,000 industry professionals on using and applying building performance simulation to the design process, and was the coach and captain of the ASHRAE Lowdown Showdown 2022 winners.  Currently, he trains building design professionals how to apply performance simulation and calculations of all types to the building design process.  He is ASHRAE BEMP certified, a LEED AP, and a RESET AP and serves as the co-chair of the Data Analysis and Reporting Working Group for MEP 2040.