Steps before selecting an HVAC system

When beginning a new project, design engineers often are tempted immediately to try to answer the question, “What HVAC system should I design?” However, there are a few activities that should be undertaken first to uncover holistic solutions for high-performance, cost-effective buildings, including:

• Document the project requirements. For project teams to know what success looks like, an owner’s project requirements (OPR) should be developed to provide the guard rails between which potential solutions are selected. An effective OPR includes energy and sustainability goals, functional requirements, building usage schedule and occupant counts. Finally, it should include financial criteria for decision-making, such as a maximum payback period and/or discount rate to use in a life-cycle cost analysis.

• Analyze local climate. The local climate has a significant influence on how an HVAC project uses energy. By studying typical meteorological year weather files for a site, patterns begin to emerge as to which strategies are most promising. Some strategies are easy to identify because energy codes have climate-specific requirements for building insulation, economizers and exhaust-air energy recovery. However, it may be more difficult but just as important to know in which climates evaporative cooling, natural ventilation, night flushing and solar strategies are most effective.

• Understand typical energy use for the building type. Many buildings fall into one of a handful of prototypes with anticipated energy use patterns. These patterns can be found in the Energy Information Administration's Commercial Building Energy Consumption Survey, the Department of Energy's Commercial Prototype Building Models, or a “simple box” model created by the energy modeler using inputs appropriate to the building type. Understanding the particular pattern for a building type and the reasons for this pattern helps to identify strategies that get the biggest bang for the buck.

• Conduct a load-reduction analysis. Since mechanical systems make up a large percentage of the construction budget in health care facilities, it is often critical to use energy modeling early in design to reduce the cooling and heating loads on HVAC systems, leading to smaller equipment sizes. Viable strategies include improving the building envelope and reducing lighting power. These strategies can be shown to save not just energy costs, but first costs as well through the reduction or elimination of mechanical systems.