Simplified optimization method for preliminary design of HVAC system and real building application

Abstract

HVAC systems (heating, ventilation, and air conditioning) are recognized as the greatest energy consumers in commercial and institutional buildings. Generally, designers use common sense, historical data, and subjective experience in designing these systems; this includes the number of systems chosen and the grouping of the zones served by these systems. HVAC energy efficiency is not an easily calculable criterion during the selection of these systems; usually the first selection criterion is the weakest investment cost. In this article, we present a simplified optimization method for preliminary design of HVAC system using the zones’ daily profile loads. A global load ratio is applied as an optimization function. The global load ratio represents the relationship between the system's real load and its possible maximum load for a given period. The variables for the optimization problem are: (i) grouping of the zones served by the systems and (ii) number of systems serving the building. Type of system was preselected for the present study, but this could also serve as an optimization variable. The correlations between global load ratio and energy consumption were shown using an office building. Then, this method was applied on an existing institutional building and compared with the detailed optimization method. In the second method, the HVAC energy consumption, calculated using DOE-2 software, was used as the optimization function. The comparison made among the existing, reference, and optimized buildings (all sharing the same constraints) have yielded significant energy savings for HVAC energy consumption. A life cycle cost analysis has also been done to estimate savings in terms of investment, operation and maintenance costs. These savings depend upon building configuration, the constraints imposed, the types of HVAC systems selected, and the control strategies for these systems.

Acknowledgments

Magdalena Stanescu, PhD, Eng., Associate Member ASHRAE, is Project Manager. Stanislaw Kajl, PhD, Eng., Student Branch Advisor Member ASHRAE, is Professor. Louis Lamarche, PhD, Eng., is Professor.