Battling the complexity of designing government facilities: HVAC
Mohamed Abdelmoneim, PE, Peng, LEED AP BD+C, Senior Electrical Engineer, EYP, Washington, D.C.
Raymond Krick III, PE, LEED AP, Project Manager, RMF Engineering, Baltimore
Allen Poppe, PE, MBA, Principal Mechanical Engineer, Mechanical & Chemical Group, Manager, Stanley Consultants, Muscatine, Iowa
Rick H. Troberman Jr., PE, LEED AP, CBCP, Mechanical Engineer, EEA Consulting Engineers, Austin, Texas Lindsay
Zanders, PE, PMP, Sr. Project Manager/Director of Projects, Primera Engineers Ltd., Chicago
CSE: Have you specified distinctive HVAC systems on any government, state, municipal, federal, or military facilities? What unusual or infrequently specified products or systems did you use to meet challenging HVAC needs?
Troberman: For the barracks project at Fort Sam Houston in Texas, we specified DOAS that required much lower dew points than what we would typically specify in other facilities. This was driven by a specific requirement by the U.S. Army Corps of Engineers due to the army’s struggle with dehumidification and mold issues in barracks facilities where there is a higher density of personnel with moisture conditions, such as showering facilities and sometimes moisture-ridden clothing and equipment following missions or training activities.
Krick: We were recently tasked with adding energy recovery to an existing HVAC system at a biosafety level 4 (BSL-4) lab for a federal client. We specified a customized, high-performance energy-recovery system that included energy-recovery coils, automated controls, and a skid-mounted hydronic unit. The energy-recovery coils that were installed in the existing air handling units (AHUs) served as both preheat and energy-recovery coils. The hydronic coil replacement also helped solve some controllability issues the client was having with the existing steam preheat coils. This specialized system allowed us to integrate energy recovery into an existing AHU that did not have space for an additional energy-recovery coil.
Zanders: Since government buildings tend to be older and with aging infrastructure, they have likely undergone several renovations over time. Renovating these existing buildings presents a unique set of challenges with the HVAC systems. Due to their age, these systems often fail to meet current codes. Meanwhile, existing infrastructure limits space for the introduction of new equipment and systems. Modular and scalable equipment and systems are then specified for these tight renovations. Additionally, decentralized systems, like VRF, allow a team to reuse some existing air-distribution infrastructure in a new purpose and only introduce small piping to the already crowded above-ceiling space.
CSE: Have you specified variable refrigerant flow systems, chilled beams, or other unique HVAC systems into a government, state, municipal, federal, or military building? If so, describe its challenges and solutions.
Poppe: We used a VRF system for a recent design. This military facility included barracks with small rooms. Complying with ASHRAE 15: Safety Code for Mechanical Refrigeration required careful attention. We had to divide the VRF system into smaller zones to limit the refrigerant charge to acceptable quantities. We are also using chilled beams on a current design project with an aggressive energy goal. The challenge with this system is designing a cost-effective solution. There are several different design approaches including four-pipe, duct-heating coil, and six-way valve arrangements, with significant cost implications depending on the arrangement selected.
Troberman: The barracks project has DOAS, but also VRF for zone-level space heating and cooling. This was driven by the energy requirements for the total building to achieve the lower energy use.
Zanders: VRF systems are excellent for renovations in government buildings. Oftentimes, forced-air systems do not provide adequate air to meet current codes and standards. Applying a VRF system reduces the air demand, allowing for the reuse of a slightly modified AHU system. The refrigerant lines added are small and flexible to fit into often cramped, renovated, above-ceiling spaces.
Krick: We have attempted to specify unique HVAC systems into several government projects and have received pushback. The challenge is that many facility managers and maintenance personnel are reluctant to stray from the traditional systems that they have a comfort level with maintaining. Some of the reluctance is due to the need for additional training, and some has to do with a bad experience in early generation installations of the emerging technology.
CSE: What unique HVAC requirements do such projects have that you wouldn’t encounter in other projects?
Zanders: Projects using public funding must leave the design open for competition. This is to encourage applications from multiple vendors to avoid inflated pricing. As a result, designs aren’t typically centered on a specific make/model of equipment or software protocol as they would be for projects in other markets.
Troberman: The dedicated outside-air and VRF components to our barracks design would be seen in dormitory and/or hotel projects, but the very prescriptive requirements with respect to very low dew points are most likely unique to the military. This is primarily due to the military’s focus with respect to preventing the indoor-air quality (IAQ) issues in their facilities.
CSE: When retrofitting existing government, state, municipal, federal, or military facilities, what challenges have you faced and how have you overcome them?
Troberman: When retrofitting older buildings, it is hard to find the space needed for all the new HVAC equipment in addition to the other COMM infrastructure. When you are retrofitting buildings built in the 1940s, 50s, and 60s, you end up needing more HVAC equipment than the building was originally designed for-if it originally had HVAC at all. Trying to squeeze the necessary HVAC equipment above ceiling can be a challenge.
Krick: We do a lot of major renovation work, and some of the greatest challenges result from using existing mechanical spaces. Most of the facilities we work in have much lower floor-to-floor heights and weren’t originally designed with the space to support AHUs for modern air-change rates or load requirements. If the owner rejects alternative systems, then we often design a custom AHU to maximize the usable space available. Planning for access to service and maintenance was also an afterthought in many older facilities, and the need to move equipment in during renovation often necessitates knockdown construction of large equipment, such as AHUs.
Zanders: Renovating existing buildings is the greatest challenge because of the age of most of these buildings. As a result, HVAC systems do not meet current codes and existing infrastructure limits space for the introduction of new equipment and systems. In cases where several agencies are housed within a single building, the challenge is to minimize the impact on the other spaces. The HVAC system in question may serve additional floors or adjacent spaces outside the scope of work. Rebalancing deficient air systems for a specific client or project may impact the environment of these outside-the-scope spaces, causing discomfort to occupants and complaints to building management. Modular and scalable equipment and systems are used in these tight renovations. Additionally, decentralized systems, like VRF, allow a team to reduce demand on existing air-distribution infrastructure while preserving or improving supply to the outside-the-scope spaces on a shared system.
CSE: When addressing indoor air quality issues, what best practices or tips do you have for other mechanical engineers? Describe air-change rates, particle concentrations, humidity, and other issues.
Krick: The potential for IAQ issues for facilities can not only occur during building operation, but also must be planned for during construction. The Sheet Metal & Air Conditioning Contractors’ National Association Indoor Air Quality (SMACNA IAQ) Guidelines for Occupied Buildings Under Construction is an excellent reference for protection of the HVAC system prior to building occupancy.
Zanders: IAQ is reliant on code. Typically, the IAQ code requirements follow ASHRAE, so we don’t see any drastic differences between publicly funded and privately funded projects.
Poppe: We regularly include DOAS in the design to satisfy space-ventilation requirements. These units are often designed to satisfy the entire latent capacity in the spaces as well. Our designs for military facilities also comply with UFC 3-410-01: Heating, Ventilating, and Air Conditioning Systems. This document requires a minimum efficiency reporting value (MERV) of 8 for prefilters and MERV 13 for final filters. Note that MERV 13 filters are required to achieve LEED Indoor Environmental Quality (IEQ) Credit 5. Many of our LEED projects pursue additional IEQ credits for outdoor-air-delivery monitoring, construction indoor-air quality, and low-emitting materials.