Designing efficient office buildings with visual appeal: HVAC

Office buildings can be highly complex, with complicated HVAC features and advanced technology. Experienced engineers share advice on how to handle these structures and identify trends impacting such structures now and in the future.

02/06/2018


 Jason Gerke Mechanical & Plumbing Group Manager, GRAEF, Milwaukee. Courtesy: GRAEFJames Hansen, PE, BEMP, LEED AP, Principal and Senior Mechanical Engineer, GHT Ltd., Arlington, Va. Courtesy: GHT Ltd.Tyler Jensen, PE, LEED AP, Senior Associate, Environmental Systems Design, Inc. Chicago. Courtesy: ESDJohn Yoon, PE, LEED AP, Lead Electrical Engineer, McGuire Engineers Inc., Chicago. Courtesy: McGuire Engineers Inc.

Respondents



The 2112 Pennsylvania Avenue project is an 11-story, 250,000-sq-ft trophy Class A commercial office building in Washington, D.C. GHT Ltd. provided MEP engineering design, energy modeling, and LEED documentation services on the project. Features include 1st-floor retail, a fitness center, and other amenities. Courtesy: SkanskaCSE: In your experience, what unique HVAC requirements do office buildings have that you wouldn't encounter in other buildings?

Gerke: One of the concerns about new office building designs is the lack of ceilings in many higher-end designs. The lack of ceilings puts the HVAC design at a disadvantage due to not having the space to acoustically "hide" VAV units or other devices that create sound. Additional consideration is required for these spaces without ceilings, such as lined ductwork, oversized mains and branches, or the type of HVAC systems used. Further, HVAC systems for office buildings must meet many energy-intensive requirements, such as long occupied hours, high outside-air volumes, and quick recovery from set-back temperatures in spaces transitioning from unoccupied to occupied. Office building occupants expect comfort in each building zone as they transition from one to another throughout a typical workday.

Hansen: In a word, flexibility. Commercial office buildings need to be able to cater to all tenant needs, from luxury law firms and associations to call centers, data-heavy technology firms, educational facilities, and even retail establishments. Designing core-and-shell office buildings that can support such a wide variety of end users requires careful planning and flexible and adaptable HVAC systems.

Jensen: HVAC systems for speculative core-and-shell office buildings need to be highly flexible to support different potential tenants and varying requirements. Potential tenants may want to operate their system outside of standard operating hours, accommodate high internal-heat gain, and have the option to provide backup power for their systems. The base-building HVAC system needs significant turndown capability and flexibility to adapt to different tenant configurations.

CSE: What unique or innovative HVAC systems have you specified on such facilities? What unusual or infrequently specified products or systems did you use to meet challenging HVAC needs?

Jensen: On a recent high-rise core-and-shell office project in Chicago, we employed a central dedicated outside-air system (DOAS) with heat recovery and floor-by-floor air handling units (AHUs). The floor-by-floor AHUs provide the utmost operational flexibility, which is attractive to many tenants.

Hansen: With such a diverse set of potential tenants in a commercial office building, often the most innovative HVAC system is one that can respond to the demands of a single tenant that occupies only a small portion of the building. Owners are increasingly demanding that small tenants not only have control over their space conditions and operating hours, but also can directly and positively impact utility consumption. VRF systems allow for customizable control, built-in energy metering, and high-efficiency operation, all of which have a positive impact on a tenant's relationship with the building they choose to occupy.

CSE: Have you specified variable refrigerant flow (VRF) systems, chilled beams, or other types of HVAC systems into one of these structures? If so, describe the challenges and solutions.

Hansen: VRF systems, chilled beams, and chilled-water fan-powered variable air volume (FPVAV) systems (all incorporating DOAS) have been successfully incorporated into the various office buildings GHT has designed in the Washington, D.C., office market. The biggest challenge is acceptance by the tenant and their brokers of these systems, which are relatively new to the United States. This obstacle is normally overcome through a thorough educational effort by the engineer-GHT has conducted tours and demonstrations of successfully installed and operating examples in the local market to educate owners and brokers on their benefits.

CSE: What types of waste-heat recovery, combined heat and power, or other systems have you designed for office buildings? Please describe the challenges and solutions.

Jensen: The latest versions of ASHRAE-90.1 require waste-heat recovery in many climate zones for all but the smallest airside systems. I have designed systems with sensible-only heat-recovery devices, such as runaround coils and plate-type heat exchangers, as well as systems with enthalpy wheels. Enthalpy wheels provide the most effective means for waste-heat recovery but were not allowed in Chicago for toilet-exhaust systems until recently due to cross-contamination concerns. Recent code changes relaxed the restriction, and I anticipate using enthalpy wheels for more office building systems.

Hansen: A recent GHT design for a nonprofit tenant in our area involved a gas-fired turbine, with waste heat captured for space heating, domestic hot water, and to drive an absorption chiller. We have also worked with a local utility provider in the area to reclaim heat from a large forced-main sewer as a consistent source of year-round heat rejection and heat reclaim. Successfully promoting these systems usually requires an owner or client that recognizes that a quick payback on such an investment is not the only qualifier for implementation. Likewise, successful implementation requires a design team and contractor that is willing to step outside of their comfort zone to embrace such innovative strategies.

CSE: What types of dedicated outside-air systems (DOAS) are owners and facility managers requesting to keep their facility air fresh?

Hansen: The HVAC systems that GHT Ltd designs and recommends almost exclusively revolve around the use of DOAS. The building owners we work with understand that, by decoupling outside air from space heating and cooling, they are able to decrease their annual energy consumption. Furthermore, they recognize that they can use heat recovery to increase tenant control for ventilation systems, allowing more easily controlled pressurization of their buildings. We have used DOAS systems for variable refrigerant applications, chilled-water FPVAV systems, and standard floor-by-floor air-handling applications.

CSE: What types of air balancing or environmental balancing do you include in your design? Describe the project.

Hansen: Requiring air and water balancing is standard practice for our commercial office buildings. Accurate air balancing leads to positive impacts on tenant comfort, noise levels, and indoor-air quality, while accurate water balancing (for hydronic HVAC systems) helps promote high-efficiency operation and extend the life of equipment. Sustainable buildings/energy efficiency

CSE: What unusual systems or features are owners requesting that help save energy and/or electricity when a space is unoccupied?

Gerke: Options for HVAC systems include scheduling, vacancy sensors, and carbon dioxide sensors to reduce energy consumption in unoccupied spaces in office buildings. We do not typically experience owners driving these system sensors. It is our design team that leads the owners to these solutions and works for their buy-in on these dependable methods to reduce building energy consumption.


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