What’s so special about office buildings? Learn about HVAC and plumbing
With 12 years of experience in HVAC design, Anderson is senior associate and Mechanical Engineering Lead for the company’s Colorado offices. He supervises the Denver mechanical team and ensures each project’s success.
Serving as Associate Principal, Slyziuk first joined the firm in 2006. Her portfolio includes data centers, courthouses and other high-profile projects.
As a principal in the firm’s Boston office, Walsh-Cooke brings more than 30 years of industry experience to the table. His areas of focus include sustainable, zero net energy and environmentally responsible design, enhancing the environmental performance of new and existing buildings.
Anthony “Tony” Zaudtke
Zaudtke joined Mortenson in 2018 as MEP Design Phase Manager, bringing extensive engineering experience. He graduated from North Dakota State University in 2001 with a Bachelor of Science in Electrical Computer Engineering.
CSE: What unique heating or cooling systems have you specified into such projects? Describe a difficult climate in which you designed an HVAC system for an office building project.
Slyziuk: Dedicated outside air systems with chilled beams and/or sensible-only cooling terminal units are gaining popularity for office buildings with sustainability objectives. A DOAS is unique because it decouples latent and sensible cooling to be handled by the DOAS unit and the chilled beams/sensible-only terminal units, respectively. There are significant energy savings potential by means of energy recovery at the DOAS unit and elevated chilled water temperatures serving the sensible cooling system. A DOAS also lends itself well to an office building because less plenum space is required for the same amount of cooling compared to a typical variable air volume distribution system.
CSE: What types of unique building pressurization have you designed in office buildings? Describe the project.
Anderson: We designed a large workplace remodel project in Colorado Springs that included a new kitchen, servery and dining area for the more than 1,200 building occupants. The kitchen included new variable–speed hoods, controlled so that as the cooking temperature under the kitchen hoods vary, the hood exhaust air flow was also varied, to save fan energy. To keep up with the varying kitchen exhaust, the makeup air to the servery and dining area used variable speed controls, in unison with the exhaust, to maintain a negative pressure relationship and contain cooking odors.
Slyziuk: As most geographical locations in the U.S. now require economizers per IECC or ASHRAE 90.1, engineers should be aware of pressurization control issues associated with airside economizers. When ambient weather conditions permit, outside airflow is increased into the building to reduce mechanical cooling at the air handling unit’s cooling coils. As a result of the increased outside air, means of relieving this air out of the building is now required. This is typically achieved via a relief fan, either at the AHU or elsewhere in the building and consideration should be given to control of that fan. Control methods could include fan tracking between supply and relief or modulating the relief fan to respond to differential pressure of the building relative to the exterior.
CSE: What unusual or infrequently specified products or systems did you use to meet challenging heating or cooling needs?
Slyziuk: Office buildings are looking to maximize not just floor area but vertical height as well. Vertical floor-to-floor heights can oftentimes be reduced by using alternative HVAC systems such as chilled beams or variable refrigerant flow systems. For example, a chilled beam system does not require as much overhead space as a typical VAV distribution system because it uses chilled water piping and minimizes large runs of ductwork. This system could potentially allow for additional floors of the office building given a set height or it could reduce the overall height and therefore the cost of the project.
CSE: How have you worked with HVAC system or equipment design to increase a building’s energy efficiency?
Anderson: We have found success in interlocking lighting occupancy sensors in conference rooms with the HVAC system and changing a zone from occupied to unoccupied if no occupants are sensed in the room. In addition to occupancy sensors, combined temperature and carbon dioxide sensors are common and allow reduced ventilation during periods of minimal occupancy when CO2 is within standard limits.
CSE: What best practices should be followed to ensure an efficient HVAC system is designed for this kind of building?
Slyziuk: There are so many possible design solutions for an office building HVAC design. It is imperative to understand the client’s operational intent to realize the necessary flexibility and/or separation of areas to help determine HVAC solution. As a best practice, regardless of the system type, the mechanical equipment should be proposed with efficiencies greater than code required minimums. However, mechanical systems alone cannot ensure efficient buildings. The HVAC system capacities can be reduced in size provided the building envelope is designed to exceed code minimums. Additionally, designing the lighting systems with efficient fixtures or with LED can significantly reduce the mechanical system sizes as well. The very best practice is to engage every discipline during design to help provide a holistic approach to the building’s efficiency.
Anderson: Engineers should be thoroughly familiar with how each space functions within the building and how the occupancy changes over time. Determining how many HVAC zones are provided within the building and how the zones are separated and controlled, will factor into whether the HVAC system is overheating or overcooling spaces and wasting energy. Simple controls sequences should be implemented in VAV systems to reset the supply air temperature upward or downward based on the majority needs of the connected zones, as well as static pressure adjustments in the system providing a reduction in fan energy.
CSE: What is the most challenging thing when designing HVAC systems office buildings with multiple tenants that have very different needs?
Slyziuk: Designing for flexibility while also being conscious of project cost is often a challenge; we are thus balancing between provisioning for multiple tenants’ potential demands and costs.
Anderson: The most challenging thing when designing HVAC systems in office buildings with multiple tenants is ensuring each tenant has the opportunity and flexibility to meet the majority of their needs in the space. Providing enough shaft space for additional ductwork, roof space for supplemental equipment or spare capacity in the utilities and pipe sizing, are all options to assist the future tenant.
CSE: What are some of the challenges or issues when designing for water use in such facilities, particularly high-rise offices with high water needs and various pumping needs?
Anderson: Quite often the water needs of a future tenant are not known at the time and must be estimated during design with enough flexibility provided for different types of tenants. The challenge with not knowing the specific water needs of each tenant is to not oversize the piping unnecessarily, driving up first costs.