To apply HVAC equations to real-world design problems, you need to understand the specific requirements of the project, including the building’s occupancy, climate, and load characteristics. By selecting the relevant equations and inputting the necessary parameters, you can perform calculations to size equipment, design duct systems, and optimize system performance. It’s essential to consider factors such as safety, energy efficiency, and cost-effectiveness when applying HVAC equations to ensure that the designed system meets the project’s requirements and constraints.