Office building HVAC design has changed
COVID, employee well-being and indoor air quality issues have all changed the way office building HVAC systems are designed
- Daniel Donahoe, PE, Senior Mechanical Engineer, LEO A DALY, Omaha, NE
- Tyler Jensen, PE, LEED AP, Studio Leader, ESD, Chicago, IL
- Brad McNiff, PE, LEED AP, WELL AP, Principal, GHT Limited, Arlington, VA
- Gerald Williams, PE, LEED AP, Senior Mechanical Engineer, CRB, St. Louis, MO
What unique heating and cooling systems have you specified into such projects? Describe a difficult climate in which you designed an HVAC system.
Tyler Jensen: We have used underfloor air distribution systems for multiple built-to-suit office buildings. UFAD provides superior indoor air quality, energy-efficient cooling and ventilation and maximum flexibility for office renovations. It works best to condition interior office zones with stable cooling requirements. Separate, dedicated perimeter heating/cooling systems such as fan coil units can then be used to handle the envelope so the system is well-suited to accommodate different climate zones.
Brad McNiff: In the Washington, D.C., metro area, the summers are incredibly humid. In a recent new construction office project, the owner mandated that, as an occupant benefit, manually operated windows be incorporated into the building façade. To help manage indoor temperature/humidity levels and reduce the potential for these windows to be an energy consumer, we incorporated an operable window advisory system. This system included LED green lights at perimeter windows, which would light up to inform occupants when ambient conditions were favorable for window use. When ambient weather is outside specified ambient temperature and humidity thresholds, the lights are off.
What new indoor air quality requirements do you anticipate in light of COVID-19?
Brad McNiff: We are already seeing requests for higher efficiency filters (MERV 13 or better) for recirculating air systems. Maintaining ASHRAE minimum or better ventilation rates is extremely important. While appropriate for some applications, accessory technologies (example: ultraviolet germicidal irradiation) for airstream infection control are not likely to become widespread for standard HVAC systems.
Gerald Williams: ASHRAE Standard 62.1: Ventilation for Acceptable Indoor Air Quality, will likely need to be updated to address the spread of airborne pathogens similar to COVID-19 by increasing air filtration requirements for certain occupancies and increasing minimum outside air requirements during occupied times. The current method of high throw mixing diffusers that create turbulent air may need to be reconsidered for the future of office environments.
What unusual or infrequently specified products or systems did you use to meet challenging HVAC needs?
Brad McNiff: At Metropolitan Park, the first phase of Amazon’s HQ2 development in Arlington, Virginia, our team realized potential for heat exchange with groundwater otherwise directly rejected by the building’s permanent foundation dewatering systems. We used this consistent supply of cool water to shed load from the building cooling towers, thus saving condenser water system energy and reducing cooling tower potable makeup water needs by thousands of gallons per year.
Have you specified a radiant heating or cooling system into an office building?
Brad McNiff: GHT incorporated radiant slab hydronic heating systems at the main entry lobbies of the Amazon Metropolitan Park project in Arlington, Virginia. The indoor radiant heating systems will improve occupant thermal comfort and function as part of a transitional comfort zone between the building’s fully conditioned areas and the cold Arlington winters. Outdoor radiant slab heating systems just outside the lobbies will provide snow and ice melt, reducing maintenance staff labor and injury risk and negating the need to use environmentally harmful salt or chemicals.
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.
Tyler Jensen: We have recently worked on designs for multiple core and shell life sciences office buildings. The buildings are specifically designed to support tenants who have both lab and office programs. Labs typically require 100% outside air systems to maintain safe indoor air quality and to make up air for lab fume hoods. With a high volume of cooled, dehumidified air being delivered to the labs, some reheat is needed year-round. As such, exhaust air energy recovery and heat recovery chillers are important to help minimize energy demands.
How have you worked with HVAC system or equipment design to increase a building’s energy efficiency?
Brad McNiff: A critical step in energy optimization, and one that is often oversimplified, is to understand the building’s load profile in order to select equipment efficiencies based on how that equipment is expected to operate most of the time. Optimizing by percent load and run-hours has potential to significantly reduce annual energy consumption when compared with peak-load optimization. At Amazon’s Metropolitan Park in Arlington, Virginia, we used energy modeling strategies to predict system loads for each hour of the year and developed custom IPLV curves to select major HVAC system components.
What is the most challenging thing when designing HVAC systems in office buildings?
Brad McNiff: Identifying user needs, which often change over the course of a project. Understanding what the HVAC system needs to do (i.e., what conditions you need to satisfy, how flexible does it need to be, where is growth anticipated, etc.) is key to formulating a solid design strategy. Once you have a solid basis of design in place, many questions that arise throughout a project can often be answered by referencing that document.