Why engineers should use a whole-system approach for design and construction
Using a whole-system approach to specifying equipment can lead to many benefits, such as improving the building’s energy efficiency.
- Summarize the benefits of taking a whole-system approach to building design and construction.
- Understand the value of a whole-system approach when specifying building systems.
- Examine the role energy codes and standards play when taking a whole-system design approach.
Looking holistically at the system helps ensure the most energy-efficient building performance to help owners and facility managers meet their sustainability and environmental goals. HVAC equipment and system components must operate together to achieve optimal results. This requires a method focused on total-system efficiency versus chiller-only or equipment-only optimization.
According to the U.S. Department of Energy, about 40% of the energy used in the United States is consumed in residential and commercial buildings-an amount greater than both of the transportation and energy sectors. In many commercial buildings, much of that energy is wasted. According to Energy Star data, the average commercial building wastes 30% of its energy.
Energy consumption and its impact on the environment has become one of the world's most pressing challenges. Organizations are paying closer attention than ever to their carbon footprint and how their buildings' energy use impacts the environment.
The buildings sector represents a great opportunity for improving energy efficiency. To address this, many businesses are setting increasingly stringent climate and environmental goals to lower emissions and drive efficiency. As a result, there is growing pressure to provide more efficient designs that not only perform when they are first installed, but also are sustainable over the life of the building.
While it's important to choose equipment that delivers high-efficiency performance, it's even more critical to take a whole-systems approach to building design and construction. This method puts engineers in a better position to help building owners and managers achieve their goals so they can minimize environmental impact and maximize building performance.
Energy codes and standards
There are many energy codes and standards to consider in building and system design. ASHRAE 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings defines the minimum energy efficiency standards for most commercial buildings in the United States. In addition, each type of HVAC equipment-from chillers to fans to variable refrigerant flow (VRF)-often has varying energy standards.
While it's important to look for equipment that not only meets but exceeds the ASHRAE 90.1, that's not the end of an energy-efficient design.
It's also key to consider how each component functions together to yield the performance of the system as a whole. The "system," in this case, can include HVAC equipment and controls, building automation, operating schedules, and service plans.
Simply installing high-efficiency equipment may not yield the building performance owners and managers are seeking. It's about more than just the energy efficiency of individual equipment-it's ensuring that all system components integrate for a seamless operation and energy savings throughout the life of the system.
Beyond ASHRAE 90.1, there is another standard to consider, ASHRAE Standard 189.1: Standard for the Design of High-Performance Green Buildings. This standard elevates the focus of system-level energy savings to a higher plateau by including commissioning, operation and maintenance, and renewable energy.
Whole-system building design considerations
A whole-system building design for HVAC equipment should start early in the buying cycle. Rather than comparing chillers, specifying engineers should compare different systems. For example, look at how a chilled-water system stacks up against a rooftop system or a VRF system.
Once the type of system that makes the most sense for the building is identified, start discussing specific components within the system. This "top-down" approach helps put the focus on what type of system best helps achieve the performance goals for that building.
Another consideration to keep in mind is that, too often, the bid process simply rewards the lowest bidder, even though building owners and facility managers may spend significantly more in maintenance and energy costs over the lifecycle of that equipment.
The answer is to reconsider the bid process and shift away from the "low bid always wins" approach. Instead, conduct a true lifecycle analysis.
For example, when purchasing a chiller, 90% to 95% of the total lifecycle cost stems from energy use, with the purchase price making up only 5% to 10% of the cost over the life of the unit. Choosing a chiller that costs 5% more upfront-but offers significant energy savings over the life of the system-can offer a lower priced, more efficient solution for building owners and facility managers. Using system analysis tools and the expertise of a partner who designs system-level building solutions can help. As the industry shifts focus from design (i.e. full-load) to part-load efficiencies due to the growing reality that units spend most of their operational time at part-load, it cannot be forgotten that the majority of the energy expense occurs during those times of greatest demand on the equipment, reinforcing the need for a dual focus on improved design and part-load performance.
Building recommissioning is another important step toward keeping equipment-and the entire system-functioning efficiently. Recommissioning is a systematic process of identifying underperforming building equipment or control systems and then bringing those systems back to their designed level of performance.
Refrigerant transitions to improve efficiency
The industry is now undergoing a transition in refrigerants, so it's important to be aware of the options. When considering next-generation refrigerant alternatives, it is recommended that the public and manufacturers balance direct and indirect environmental concerns including:
- Ozone-depletion potential
- Global warming potential
- Leak rates
- Energy efficiency
A whole-system view
System efficiency is impacted not only by refrigerant choice, but also by the type of system selected. For example, understanding how energy is transferred throughout a building to condition a space continues to be debated. With the new refrigerants, engineers will face new challenges and many are already reconsidering distributed air versus distributed water versus distributed refrigerant system choices. The risk is that a designer may unintentionally choose a less efficient system type by focusing on refrigerant selection.
Because every building is different, there is no easy answer. It requires careful analysis to determine the real payback, expected costs, and efficiency savings. The ultimate goal is improved occupant comfort with lower building energy consumption. This leads consulting engineers to focus more on the outcomes of design, shifting from product-focused to system-performance specifications, ultimately delivering sustainable competitive advantages for both the owner and the engineer embracing this approach.
Ryan Geister is the systems leader for Trane, a brand of Ingersoll Rand, and is focused on advancing strategies to drive system solutions for customers. He is the past chairman of the Air-Conditioning, Heating & Refrigeration Institute (AHRI) Chiller Section Committee, and a member of the AHRI Board of Directors. He has also been an ASHRAE member for 20 years.