In past sessions of the AIA+2030 Educational Series, we explored strategies such as passive ventilation systems, high performance building envelopes, and daylighting design to reduce energy loads in our buildings. Session VII demonstrated that the next logical step in energy-efficient design is reducing the size of the mechanical system itself. This session – Right-Sized: Equipment and Control for Super-Efficient Building Systems – provided valuable insight into the process mechanical engineers use to determine equipment size. By understanding that process, architects can facilitate mechanical equipment selection and further load reduction.
The discussion began with a presentation from a group at Allen & Shariff. David Price, PE, Chris Drummond, PE, Heather Stapel, PE, and Mark Wolfgang, PE, set the tone with the premise, “Properly sized equipment operates more efficiently than oversized equipment.” They then got right to the point explaining that the key to right-sized equipment is in determining the actual loads that the building will experience instead of loads based on standard assumptions. Architects can and should take the lead in determining those actual loads by getting the Owner and the Engineers in a room discussing the anticipated loads early in the design process. This ensures that the right questions are being asked.
The team from Allen & Shariff explained that the equipment sizing exercise usually starts out with “rule of thumb” values in calculations. This is because many of the decisions that affect loads, such as the building envelope, internal loads, indoor design conditions, and Owner’s project requirements, have not been established in the early project phases. These types of assumptions can result in oversized equipment and systems that are expensive to install and operate. As more specific design and operational information becomes available, this information should be proactively conveyed to the mechanical engineer. Actual load values replace assumptions in the calculations and equipment size decreases.
Educating the Owner is also critical to successful equipment right-sizing. Oftentimes, Owner representatives have the typical industry performance criteria in mind. These industry standards, also based on rules-of-thumb, may have a higher safety factor than is necessary. Bringing the Owner and Engineer together early in the design process makes the Owner aware of the potential operational or comfort compromises that may occur with right-sizing equipment. Then the Owner can properly evaluate the trade-offs in the decision-making.
Allen & Shariff came back at the end of the evening to present a case study illustrating the difference in load calculation results when project-specific load data is used instead of rule-of-thumb values. The rule-of-thumb calculation resulted in a 95 ton chiller, (2) 750 Mbh boilers, and 28,000 cfm fans. The right-sized equipment using actual loads and project-specific design data results in a 60 ton chiller, (2) 500 Mbh boilers, and 18,500 cfm fans. With that kind of reduction, it is in everyone’s best interest to discuss the mechanical systems early and often.
Augmenting the right-sizing of equipment is the selection of smart controls that can save the building owner time and money in operating and maintaining the systems equipment. A team from Johnson Controls including Jeff Zacherl, Barry Veverka, Doug Jameson, and Candace Cuppett, presented a few types of digital controls systems on the market for automated building systems. The team explained that there are three components to every building automation system (BAS): hardware, software, and in-situ controls (sensors, switches, dampers, etc.). Depending on the complexity level of the application, a different BAS package would be appropriate. The complexity level considers building size, use, mechanical equipment type, and the operator.
Knowing who will be monitoring and maintaining the building systems and the BAS once the building is occupied is critical to the selection and success of the BAS. Who is monitoring and adjusting the system? Is it in-house staff either part-time or full-time? Is it an outside repair service? How does the Owner want the building to operate? What are the long-term plans for the building that may require adjusting or expanding the system later? Established Owner’s project requirements can lead to more intelligent equipment and controls selection which may yield the most significant energy savings.
The evening ended with a rousing discussion between audience and presenters. While frustration with the traditional design process was expressed by both sides, the group worked to reach an understanding of the ways architects can better contribute to the load reduction. Architects tend to think that increasing the R-value of the envelope is a key factor to high-performance buildings. While that is true to a certain extent, there is a point of diminishing returns with insulation. Beyond that point, there is more value in putting money towards improved fenestration, envelope tightness, and exterior shading. The engineers suggested that air infiltration is an area of the building envelope that could also benefit greatly from more attention.
The next session of the AIA+2030 Educational Series will be held on February 20th. Site Power: Renewable Energy Opportunities will delve into renewable energy options for Southwestern Pennsylvania such as solar, biomass, and ground source heating.