HVAC codes and standards: cooling and energy efficiency
Codes and standards dictate the design of HVAC systems; however, there are ways to improve the design of nonresidential buildings to achieve maximum energy efficiency.
- Examine owner and local codes for cooling system designs.
- Define HVAC codes and standards.
- Understand cooling systems to maximum energy efficiency.
Data from the 2012 Commercial Buildings Energy Consumption Survey (CBECS) shows that the United States consumes 6,963 trillion Btu of energy generated for commercial buildings. Figure 1 shows that 44% of commercial building energy use is for HVAC and refrigeration. National survey data shows approximately 50% of the HVAC energy is used for cooling, ventilation, and refrigeration purposes.
Efforts to reduce energy use led to the development of energy codes and standards to establish minimum efficiency requirements for new-building construction, building additions, and renovations. Providing comfort cooling and energy efficiency in nonresidential buildings is an ongoing task for engineers and designers as they increasingly have to focus on energy-efficient building codes and high-performance buildings. A building's energy impact is determined by initial design decisions, operations, and the owner's project budget. Energy codes and standards present designers with guidelines to enforce minimal energy savings through efficient design and implementing various equipment technologies.
Adopting codes and standards for energy efficiency
Designers in the HVAC industry must be familiar with codes and standards. Standards define the industry's agreed-upon minimum technical requirements, procedures, guidelines, and instructions for engineers, designers, or manufacturers. They also establish the industry's minimum standard of care. Standards in the United States are mostly voluntary consensus standards, which means they are regularly maintained and are developed through a consensus process. Examples of industry organizations that develop voluntary consensus standards are ASHRAE, Sheet Metal and Air Conditioning Contractors' National Association (SMACNA), NFPA, and IEEE. These standards may or may not be written in enforceable language.
In contrast, a code is a standard that has been enacted into law by an authority having jurisdiction (AHJ) such that a designer is legally required to comply with that standard. The code may also include references to additional standards that can also be enforced. This procedure is called, "incorporation by reference." An AHJ may amend the standard to incorporate or remove requirements, such as adding figures, charts, or tables, or amend the standard's language, such as replacing the word "should" with "shall."
In the U.S., the Department of Energy (DOE) is required by the Energy Conservation and Production Act to support, evaluate, and participate in energy code development as managed by ASHRAE and the International Code Council (ICC). DOE activities include evaluating energy and cost benefits associated with changes to ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings and International Energy Conservation Code (IECC). DOE evaluates ASHRAE Standard 90.1 as the reference standard for commercial-building energy efficiency, and IECC as the reference standard for residential-building energy efficiency.
IECC and ASHRAE Standard 90.1 address building systems such as building envelope, lighting (exterior and interior), minimum HVAC equipment efficiency, HVAC systems, service water heating, and system controls. The standards also set the minimum energy efficiency and system design requirements. Both references have adopted code language to increase state adoption and improve enforceability.
The U.S. does not have a national energy code or standard, even though the federal government supports the development of energy codes and standards. Because there is no national energy code, energy codes and standards are adopted at the state and local jurisdiction levels. The path that energy codes and standards take for adoption varies by locality. In general, energy code adoption is initiated when the DOE issues a positive determination based on the most recent version of ASHRAE Standard 90.1. The publication of a positive review sets in motion statuary requirements directing states and local authorities to certify they reviewed their building codes. All necessary updates are completed to meet or exceed the current edition of ASHRAE Standard 90.1. Many states also have their own code-update cycles that occur independently of ASHRAE, DOE, and IECC updates.
Each new edition of ASHRAE Standard 90.1 requires the DOE to issue a determination on whether the new edition will improve energy efficiency in commercial buildings over the existing edition. On Sept. 26, 2014, the DOE released a final determination that ASHRAE Standard 90.1-2013 would achieve 8.7% energy savings, 8.5% source-energy savings, and 7.6% site-energy savings above buildings designed under ASHRAE Standard 90.1-2010. Each state has 2 years to adopt ASHRAE Standard 90.1-2013 or update its existing commercial building codes and standards. With the 2014 determination, states will have until Sept. 26, 2016, to file compliance certifications with the DOE or request an extension.
Figure 2 shows the status of state energy code adoption as of April 2016. The codes, standards, and editions in force vary. Many states have adopted the IECC commercial code, which allows for an alternate compliance path through ASHRAE Standard 90.1. In jurisdictions that allow either compliance path, the designer must choose either IECC or ASHRAE Standard 90.1 as the design energy code and must complete the entire design using the chosen code. Designers are encouraged to consult with their local permitting agency and the AHJ to determine energy code requirements for states without an energy code.
Table 1 provides a summary of the HVAC cooling system energy and efficiency requirements according to the IECC and ASHRAE Standard 90.1. Corresponding equivalent code requirements between IECC and ASHRAE Standard 90.1 have been listed adjacent to each other where applicable. The IECC and ASHRAE have worked together over the years to make the two codes' language and requirements documents similar, if not identical. However, some differences do exist between the two documents; most notably, regarding allowable exemptions to particular code provisions.
Compliance with codes and standards
In addition to the previously mentioned codes and standards, the following resources may provide additional guidance and recommendations for high-performance building system design. ASHRAE Standard 189.1 Standard for the Design of High-Performance Green Buildings "provides total building sustainability guidance for designing, building, and operating high-performance green buildings." This standard may be applied to new construction, additions, and renovations to buildings. If ASHRAE Standard 189.1 is used for the design effort, the minimum system design requirements and equipment-efficiency requirements presented in that standard supersede the requirements presented in ASHRAE Standard 90.1. For example, ASHRAE Standard 90.1 requires demand-control ventilation (DCV) for high-occupancy areas served by systems with one or more of the following features: air-side economizer, automatic modulating outdoor air (OA) damper, or outdoor airflow greater than 3,000 cfm. ASHRAE Standard 189.1 revises the DCV requirement to include systems with an outdoor airflow greater than 1,000 cfm, thereby increasing the potential for energy-saving opportunities. Designers may find the ASHRAE Standard 189.1 User's Manual helpful because it provides explanatory material that further elaborate on the requirements and intent of the ASHRAE Standard 189.1.
ASHRAE's Advanced Energy Design Guides (AEDG) series also provides design and energy efficiency recommendations for various building types based on improvements to ASHRAE Standard 90.1 requirements. While the AEDG series was developed based on previous versions of ASHRAE Standard 90.1, the recommendations can still be applied to buildings designed to ASHRAE 90.1-2013 for possible energy savings. These guides provide recommendations on building envelope, fenestration, lighting systems, HVAC systems, service water heating, and plug/process loads arranged by climate zone. Even though the AEDGs are centered on new construction, the recommendations can be applied to renovations. While many of the AEDG recommendations are simply selecting between systems, the owner should be brought into the design process to ensure that the project goals are being met and the maintenance staff has the expertise to service the systems.
Establish project goals for energy efficiency
The design and use of high-performance HVAC equipment can result in significant energy and cost savings. Each design discipline has specific design requirements that must be met to comply with code. Each design discipline may also be presented with various opportunities for energy savings throughout the design phase. It should be noted and understood that energy savings in one discipline may enhance or detract savings and opportunities in another. This interaction applies not only to HVAC systems, but also to the envelope, lighting system, and, if under the control of the design team, the selection of office equipment. For the above reasons, design-team members must effectively communicate their design intent and required coordination items throughout the design process.
The first step in designing any efficient, effective HVAC system is to decide on energy goals early in the design process. Whether the project is new construction or a renovation, a thorough understanding of the owner's project requirements and budgetary constraints is critical. This is often accomplished through a "basis of design" document that clearly communicates the design team's understanding of the owner's requirements, project goals for energy efficiency, and goals to achieve or exceed the minimum code requirements per the owner's directives. These initial decisions will direct the selection of HVAC systems and equipment. A building that meets minimum energy code requirements will have a different HVAC system strategy and components than a building that achieves 30% energy savings beyond code minimum. In addition, highly efficient designs using high-performance HVAC systems most often require added effort and collaboration from all design-team members as compared with conventional designs.
HVAC cooling loads and equipment selection
For any new-construction or renovation project, a comprehensive knowledge of the building environment is critical. Many components affect HVAC loads and energy consumption including building envelope, fenestration (glazing and doors), lighting, plug loads, occupancy, and sequence of operations, to name a few. IECC and ASHRAE Standard 90.1 require building heating and cooling loads to be determined per ASHRAE Standard 183 or an "approved equivalent computational procedure." Standard 183 provides methods and guidelines for developing building HVAC load calculations. Remember, heating- and cooling-load calculations are not the same as building energy modeling. Energy models analyze the proposed design energy requirements as the system operates over the entire year. Load calculations measure the energy that the HVAC system must add or remove from the zone to maintain the design conditions.
Accurate HVAC load calculations lead to properly sized equipment. Modern computer-aided load analysis tools allow the designer to reduce excess oversizing by removing many uncertainties, such as diversity, equipment loads, shading, and weather. Designers should consider equipment safety factors carefully, or not apply them at all, to avoid unnecessarily oversized equipment. For example, it is unreasonable to apply a safety factor to the calculated building load when the load is assumed to occur on the hottest weather design day with all zones at peak conditions, all lights on, all equipment operating, and each room is occupied by the maximum number of occupants allowed by fire code (higher occupancy than is reasonable). Oversized equipment may operate less efficiently and at a higher capital cost. This affects the owner's project budget and operating expense. In addition, oversized cooling equipment may cycle excessively or not effectively dehumidify.