Engineering workable, successful office space: HVAC
Whether new or retrofit, office buildings can be a challenge for the mechanical, electrical, plumbing (MEP), or fire protection engineer. Air quality, DOAS, and HVAC systems are discussed.
- Julianne Laue, PE, LEED AP, BEMP, Senior MEP Engineer, Center for Sustainable Energy Mortenson Construction, Minneapolis
- Tony McGuire, PE, FASHRAE, Founder, McGuire Engineers Inc., Chicago
- Nathan Snydacker, PE, LEED AP, Vice President, ESD Global, Chicago
CSE: What unique HVAC requirements do office structures have that you wouldn’t encounter on other structures?
McGuire: I do not find any unique aspects in office structures beyond the need to be sensitive to the client’s needs and desires. That occurs in all types of projects.
CSE: In your experience, have alternative HVAC systems become more relevant? This may include displacement ventilation, chilled beams, etc.
Laue: During the design charrette process, high-performance HVAC systems are usually discussed; however, it can be difficult to incorporate these systems in spec office buildings. With an increased focus on building performance and the adoption of more energy-efficient building codes, high-performance systems will be seen less as "alternative" and become the mainstream design choices.
Snydacker: Displacement ventilation works very well for open areas, and we have designed these systems for call centers and libraries. However, it has limitations when the floor plate has enclosed spaces or offices. Chilled beams are very practical for use along perimeters, but again can cause the space to become less flexible for future renovations if used throughout the floor plate due to hard-piped connections.
McGuire: We have done displacement ventilation and also chilled beam designs. These were driven by project specifics.
CSE: What updates in fans, variable frequency drives, and other related equipment have you experienced?
Snydacker: While not terribly new, use of electronically commutated motors (ECM) in fan-powered box terminal units has become less cost prohibitive over recent years with more manufacturers offering this as an option. Utilizing an ECM with a direct digital control (DDC) interface to a building management system (BMS) allows tremendous flexibility for retrofits with the ability to easily rebalance airflows. They can also allow for fan speeds to be decreased when zone setpoints are met to improve overall system energy efficiency.
McGuire: All HVAC equipment and systems are regularly being upgraded by manufacturers.
CSE: What indoor air quality (IAQ) challenges have you recently overcome? Describe the project and how you solved the problem.
Snydacker: Many of our projects deal with renovations to increase the workplace density either on a specific floor or throughout a facility. When a building is repurposed or a renovation is implemented to increase workplace density, limitations within the existing building air handling system for minimum outside air become a challenge. This becomes an opportunity for consulting on options ranging from replacement of existing coils, replacement of the full air handling unit (AHU), or addition of a supplemental dedicated outdoor air system (DOAS).
McGuire: We have not experienced any IAQ problems in our designs. Over the past 10 years, I have provided expert witness services on a number of buildings that had IAQ problems.
CSE: What new trends in dedicated outdoor air systems (DOAS) have you encountered in office buildings?
McGuire: Several of our expert witness assignments were the result of improper DOAS designs. We have used DOAS but not in office buildings.
CSE: When working in high-rise structures, what tips/tricks can you offer? Define any points engineers should consider in these vertical structures.
McGuire: Roughly 65% of our office building work is in high-rise structures. I could go on and on discussing this aspect.
CSE: How do you deal with stack effect in larger office buildings, or in those with central open atriums?
Snydacker: Where possible, separating areas adjacent to vertical pathways (such as elevator lobbies) with demising partitions can aid in minimizing stack effect. Use of entry vestibules can also help mitigate stack effect issues. The 175 W. Jackson building in Chicago showcases two large light wells within the massive floor plate within the building. At this building, we implemented a design solution taking advantage of natural air buoyancy through these light wells for the main building return air path.
McGuire: I chaired a Building Pressure Task Force for the Chicago Committee on High Rise Buildings. This is an item that could require a roundtable on its own.
CSE: In densely packed workspaces, how do you achieve optimal HVAC and air quality?
Snydacker: Increased population means increased amounts of ventilation air. Air movement can also help in occupant comfort. Use of series fan-powered terminal units can provide continuous air movement within a space while also achieving proper zoning and variable primary airflow efficiencies. Increased efficiency through modulated fan speeds when space temperature setpoints are met can be achieved with direct digital control (DDC)/electronically commutated motor (ECM) control of series fan-powered terminal units.
McGuire: Densely packed workspaces can become HVAC “disaster zones.” Each has its own unique problems. Call centers are one example that we have seen a number of times.