Heating, Ventilation and Air Conditioning (HVAC) Systems

Heating, ventilating, and air-conditioning (HVAC systems) account for 39% of the energy used in commercial buildings in the United States. Consequently, almost any business or government agency has the potential to realize significant savings by improving its control of HVAC operations and improving the efficiency of the system it uses. To strike the optimal balance between controlling costs and getting the most value from your HVAC system, it’s vital to incorporate a strategic planned maintenance program into your yearly budget and to take full advantage of the opportunities planned maintenance provides you. Planned maintenance will prolong the life of the equipment, optimize energy efficiency, limit or eliminate unexpected repair and replacement costs, and maintain optimal comfort level.

 

High Performance Features

Employing high-performance HVAC equipment in conjunction with whole building design can result in significant energy savings. Typically, a 30% reduction in annual energy costs can be achieved with a simple payback period of about three to five years. And, if the payback threshold is extended to seven years, the savings can be about 40%. These figures apply to buildings that offer conventional comfort (e.g., 70°F in winter, 76°F in summer).

Fundamentals of Energy- and Resource-Efficient HVAC Design

Consider all aspects of the building simultaneously Energy-efficient, climate responsive construction requires a whole building perspective that integrates architectural and engineering concerns early in the design process. For example, the evaluation of a building envelope design must consider its effect on cooling loads and daylighting. An energy-efficient building envelope, coupled with a state-of-the-art lighting system and efficient, properly-sized HVAC equipment will cost less to purchase and operate than a building whose systems are selected in isolation from each other.
Decide on design goals as early as possible A building that only meets energy code requirements will often have a different HVAC system than one that uses 40% less energy than the code.And the difference is likely to be not only component size, but also basic system type. See WBDG Functional—Meet Performance Objectives.
“Right Size” HVAC systems to ensure efficient operation Safety factors for HVAC systems allow for uncertainties in the final design, construction and use of the building, but should be used reasonably.Greatly oversized equipment operates less efficiently and costs more than properly sized equipment. For example, oversized cooling systems may not dehumidify the air properly, resulting in cool but “clammy” spaces.It is unreasonable and expensive to assume a simultaneous worst-case scenario for all load components (occupancy, lighting, shading devices, weather) and then to apply the highest safety factors for sizing.
Consider part-load performance when selecting equipment Part-load performance of equipment is a critical consideration for HVAC sizing.Most heating and cooling equipment only operate at their rated, peak efficiency when fully loaded (that is, working near their maximum output).However, HVAC systems are sized to meet design heating and cooling conditions that historically occur only 1% to 2.5% of the time. Thus, HVAC systems are intentionally oversized at least 97.5% to 99% of the time. In addition, most equipment is further oversized to handle pick-up loads and to provide a factor of safety. Therefore, systems almost never operate at full load. In fact, most systems operate at 50% or less of their capacity.
Shift or shave electric loads during peak demand periods Many electric utilities offer lower rates during off-peak periods that typically occur at night. Whenever possible, design systems to take advantage of this situation. For example, energy management systems can shed non-critical loads at peak periods to prevent short duration electrical demands from affecting energy bills for the entire year. Or, off-peak thermal ice storage systems can be designed to run chillers at night to make ice that can be used for cooling the building during the next afternoon when rates are higher.
Plan for expansion, but don’t size for it A change in building use or the incorporation of new technologies can lead to an increased demand for cooling. But, it is wasteful to provide excess capacity now—the capacity may never be used or the equipment could be obsolete by the time it is needed. It is better to plan equipment and space so that future expansion is possible. For example, adequately size mechanical rooms and consider the use of modular equipment.
Commission the HVAC systems Commercial HVAC systems do not always work as expected. Problems can be caused by the design of the HVAC system or because equipment and controls are improperly connected or installed.A part of commissioning involves testing the HVAC systems under all aspects of operation, revealing and correcting problems, and ensuring that everything works as intended. A comprehensive commissioning program will also ensure that O&M personnel are properly trained in the functioning of all systems.
Establish an Operations and Maintenance (O&M) Program Proper performance and energy-efficient operation of HVAC systems can only be ensured through a successful O&M program. The building design team should provide systems that will perform effectively at the level of maintenance that the owner is able to provide. In turn, the owner must understand that different components of the HVAC system will require different degrees of maintenance to perform properly.

Table courtesy of WBDG

 

High Performance Practices & Solutions

 

Case Study

Crosstown Concourse

Author: Trane

Crosstown Concourse building managers, Commercial Advisors, and the Crosstown Development Team knew that increasing market value of the property was essential to revitalizing the neighborhood. They also realized it was equally important to lower operational costs, promote sustainability, and maximize asset potential to increase value for building owners; allow tenants to conduct effective commerce; and help property managers attract tenants. The group sought the resources of a strategic partner to align with them in building this community.

 

Additional Resources