Government building design: HVAC
When your client is the government, engineering design can be tricky, thanks to stepped-up regulations, budgetary concerns, and other considerations. Respondents discuss HVAC topics in government, state, municipal, federal, and military facilities.
- Ian Bost, PE, LEED AP, Principal, Mechanical Engineer, Baird, Hampton & Brown Inc., Fort Worth, Texas
- Robert Eichelman, PE, LEED AP, Technical Director, EYP Architecture & Engineering, Albany, N.Y.
- Paul W. Johnson, PE, LEEP AP BD+C, Vice President of Mechanical Engineering, Wood Harbinger, Bellevue, Wash.
- Katie McGimpsey, PE, LEED AP, Principal, Affiliated Engineers Inc., Rockville, Md.
- R. Scott Pegler, PE, LEED AP, Director of Mechanical Engineering, Setty, Fairfax, Va.
CSE: What unique HVAC requirements do government or military building structures have that you wouldn't encounter on other structures?
Pegler: Ventilation air opening locations are typically bound by ATFP standards so that the intakes are not easily accessible "aggressors." Using dedicated ventilation and exhaust systems for mail and receiving rooms as well as isolation controls.
Bost: They are still using steam heating. In our area this is an uncommon system type.
Johnson: Security issues that, for example, require ducts to have bars in them to stop intrusion.
CSE: What changes in fans, variable frequency drives (VFDs), and other related equipment have you experienced?
Bost: Growth in fan array technology (multiple, smaller fans). This approach to moving the air is less energy efficient but provides the owner with built-in redundancy. We are seeing a change in VFD specifications, away from full bypass, due to reduced replacement costs for VFDs.
CSE: What indoor air quality (IAQ) challenges have you recently overcome?Describe the project and how you solved the problem.
Johnson: In a recent project for the Boeing Co.'s clean room facility in West Jordan, Utah, we provided air handlers to pressurize the manufacturing facility and controls to maintain a specific pressure to minimize infiltration.
Bost: We've worked to provide the code-mandated amount of outside air in VAV systems while keeping the reheating loads down. Designing to the minimum required outside air quantities is forcing the minimum supply air in many spaces to increase.
CSE: Have you recently specified more alternative HVAC systems? This mayinclude displacement ventilation, underfloor air distribution, chilled beams, etc.
McGimpsey: I have recent experience working on several government and military projects where four-pipe active chilled beams were specified. Trox was the specified and successful supplier of chilled beams on two laboratory projects at the National Institutes of Health (NIH), one a new construction project and the other a major renovation of a wing in an existing and occupied building. These projects were firsts for NIH implementing chilled beam technology. Early studies and on-site mockups at the manufacturer's facility in the United Kingdom were done to assess performance of active chilled beams in achieving thermal comfort, to assess containment removal effectiveness of chilled beams and their effect on fume hood containment, to evaluate condensation potential, and to evaluate effect of infiltration through building envelope.
Johnson: Yes, and we've also specified VRF and ultra-efficient ground source heat pump systems.
Bost: We have not specified any alternative HVAC systems for government buildings. We have specified a chilled beam system at a private university classroom building.
CSE: Do you find it more challenging to retrofit HVAC systems on older buildings than installing on new?
Bost: Yes. Many existing buildings were constructed before central HVAC systems were common, and floor-to-floor heights can be less than desirable. Further, current technologies allow better structural member efficiencies, allowing for more available ceiling space when compared to existing structures. Also, many existing buildings do not have provisions for outside air ventilation rates that are mandated by current codes.
McGimpsey: Having recent experience on both major renovation and new construction projects, I find the existing buildings to be the bigger challenge. Existing facilities hold unforeseen conditions that can impact HVAC systems, such as existing utilities passing through the renovation area. The limited floor-to-floor height and existing structural systems also play a challenging role in overall spatial coordination and where infrastructure utilities can be routed.
Johnson: Yes, primarily due to access and installation of new equipment. In addition, existing buildings can have limiting requirements such as adjoining building impacts for air discharge locations, envelope penetrations, and structural impacts.