Office buildings focus on air quality, energy efficiency, HVAC systems

Designing office buildings in a post-COVID world is a challenging task with engineering variables such as HVAC systems

By Consulting-Specifying Engineer February 10, 2021


  • Elena Bollas, PE, Mechanical Engineer, Page, Austin, Texas
  • Timothy J. Hedrick, PE, Principal/Electrical Engineer, RTM Engineering Consultants, Schaumburg, Ill.
  • Dan Luzius, LEED AP, Principal, DLR Group, Seattle
  • Jon Silhol, PE, LEED AP BD+C, Mechanical Engineer, SmithGroup, Phoenix

Describe an HVAC ventilation system you’ve worked on or encountered in an office building that included hoods, fire suppression systems or other specialized ventilation systems.

Jon Silhol: We typically work with commercial kitchens which have Type I and Type II hoods. Dedicated exhaust systems are provided for the different hood types. We have designed the ventilation systems in a variety of ways. Whether it is a dedicated makeup air unit or part of the larger mechanical system. This depends on the mechanical system that is being used in the other parts of the building and the available space for additional equipment.

What unique heating and cooling systems have you specified into such projects?

Jon Silhol: I live in Phoenix, so you could say almost every project is in a difficult climate. In 2020, the Phoenix area saw 144 days with a temperature of 100°F or hotter with 53 days of those days having a temperature of 110°F or hotter. Both of these are records for the number of days above these temperatures.

Direct expansion, air-cooled equipment is popular in the Phoenix area for several reasons. The equipment is typically located on the roof where temperatures can routinely be above 120°F. This equipment has been derated for the high ambient temperatures. I have designed more than 500,000 square feet of underfloor air distribution systems in the Phoenix area. These systems are challenging in the Phoenix area due to high envelope loads. Unique aspects have been designed to accommodate for the envelope loads while maintaining comfort cooling at the interior areas.

Elena Bollas: VRF systems are growing in popularity with office buildings.

What new IAQ requirements do you anticipate in light of COVID-19?

Jon Silhol: I do believe the ASHRAE COVID-19 guidelines will become part of the standards over time. Some of these are typically incorporated into buildings now such as MERV-13 filters. However, we could start to see humidification systems incorporated into office building designs in the future. I’m also curious to see what happens with ventilation. Airside economizers can be used in office buildings. Are cooling coils designed for increased capacity so that 100% outside air can be provided for longer periods of time? Also, what happens to the demand-control ventilation, which encourages less outside air? Do the code and baseline energy requirements get revised? I can see more unidirectional airflow systems be used in buildings such as underfloor air distribution or displacement. These systems do not mix air and can remove particulates from the occupiable space better than traditional overhead systems.

Elena Bollas: We foresee a mix of different requirements being implemented, depending on the space type and use. One item that has potential to be a universal change is IAQ monitoring requirements. There has already been in uptick in interest on achieving WELL certified buildings, which has a large focus on monitoring and reporting air quality. While this may require owners to have stricter specifications and the need for more building automation system control points, the end result is a proactive approach to maintaining a building’s system and air quality.

Dan Luzius: IAQ has always been a significant factor in any HVAC design with our clients. As such, the question has become “Can we do more?” We see our clients updating internal design standards much sooner than local jurisdictions or ASHRAE. Such requirements will likely require IAQ well above and beyond the filtration and increased ventilation improvements we’re implementing today.

Also, we anticipate requirements moving more toward the monitoring of indoor spaces. The ability to collect, analyze and report IAQ data with the HVAC system reacting accordingly will become increasingly more important as we come out of the pandemic.

DLR Group’s new sonrai IAQ building analytics platform is helping building owners do just that — using their building data as a means to transparently communicate air quality and health and wellness data to their building occupants and for developing actional intelligence.

What unusual or infrequently specified products or systems did you use to meet challenging HVAC needs?

Elena Bollas: Ultrasonic humidification. We designed an office space within a museum, containing numerous exposed (uncased) artifacts. We had to meet very specific temperature and humidity ratio throughout the entire building. The main AHU could react to maintain temps on a regular basis. However Central Texas has large weather swings in the spring and late fall and thus the need for supplemental humidification for short intervals lead us to choose an ultrasonic humidifier built into the AHU.

Jon Silhol: We have used underfloor air distribution and chilled beam systems for build-to-suit office buildings. We would like to use these systems in all building to reduce the energy consumption, but they do not have a return on investment for speculative office buildings in the Phoenix market. We use energy recovery systems to meet a project energy goals. Even though energy recovery doesn’t have a payback as it would with a higher ventilated building such as a laboratory or health care facility, there still is enough of a payback to invest in the technology and energy savings.

How have you worked with HVAC system or equipment design to increase a building’s energy efficiency?

Jon Silhol: We do this on every project. We balance the building’s budget and energy performance and the design system efficiency is always better than the code minimum. We have designed systems from simple air-cooled solutions to chilled beam systems. It’s always about finding the best mechanical system that fits the building type and budget. We designed Arizona’s first net zero building using a combination of air-cooled equipment, evaporative cooling and natural ventilation.

Elena Bollas: Yes, I recently worked on an office building project located in downtown Austin, Texas, that incorporates a VRF system and a DOAS. The VRF system actually allowed for an exception in ASHRAE 90.1 for an economizer and our energy model still calculated a significant energy savings percentage for a fully glass building.

What is the most challenging thing when designing HVAC systems in office buildings?

Dan Luzius: Designing for office buildings has a unique set of challenges compared to other facility types. One of the more challenging aspects is balancing first cost, code compliance and the right-sizing of systems with a constantly changing occupancy. We design our systems with the anticipation of the building undergoing a tenant improvement in as little as three to five years from now. Additionally, there are only a handful of MEP system options that comply with the local energy code, none of which is that “flexible.” Ventilation systems are particularly challenging as building occupancy can change significantly year over year.

Elena Bollas: Minimizing the vertical space the HVAC systems require and the coordination needed to allow offices to have higher ceilings are both challenges. At the start of projects, we also must address an owner’s emphasis on personal occupant comfort. While zoning may not be the most challenging thing to establish in design, it is definitely a step in the design process that should be given significant thought to avoid the too hot/too cold complaints from tenants after occupancy.

Jon Silhol: The most challenging aspect is aligning the building’s budget, baseline mechanical system and energy goals. Often office buildings are focused on first cost more so than other building types. We have come across building owners who want to use a mechanical system that is less efficient than the required baseline. This makes it challenging to provide an energy-efficient building, let alone meeting the energy code. However, using our integrated approach and in-house energy modeling, we are able to find solutions that accomplish all the project goals.

Have you specified a radiant heating or cooling system into an office building? Describe the project.

Dan Luzius: The design of a 180,000 square feet global technology client’s building in Kirkland, Wash., was broken out into three phases with a core and shell design in the first phase; the second and third phases were split between the first and second floor tenant improvements. The HVAC systems consisted of a DOAS with heat recovery sized for airflow rates two times ASHRAE 62.1, and a four-pipe active chilled beam system providing space conditioning with user control at the zone level. The central plant providing heating and chilled water is comprised of a series of air-cooled chillers, high-efficiency condensing boilers, dry cooler and heat pump. Low-temperature chilled water is delivered to the DOAS cooling coils and high-temperature chilled water is deliver to the active chilled beams through the chilled water distribution piping. Low temperature heating water is delivered to the DOAS heating coils and active chilled beams through the heating water distribution piping. The project was awarded LEED Platinum and achieves a 30% energy savings over ASHRAE 90.1-2007.