Constructing college, university buildings wisely: HVAC
Aravind Batra, PE, LC, LEED AP, Principal, P2S Engineering Inc., Long Beach, Calif.
Craig Buck, PE, LEED AP, Associate, RMF Engineering, Charleston, S.C.
Jeffrey R. Crawford, PE, LEED AP, CCS, Vice President, Director of Higher Education & Research Market, Ross & Baruzzini Inc., St. Louis
Andre M. Hebert, PE, BEMP, LEED AP BD+C, Principal, Senior Mechanical Engineer, EYP Architecture & Engineering, Boston
Sergiu Pelau, PE, LEED AP, Principal, Syska Hennessy Group, New York City
Scott Robbins, PE, CEM, LEED AP BD+C, Senior Vice President, WSP | Parsons Brinckerhoff, Boston
CSE: What unique HVAC requirements do college/university projects have that you wouldn’t encounter in other buildings?
Robbins: Colleges/universities are unique in that they have almost every building type under their responsibility. They need to understand and maintain all these buildings—laboratories, libraries, residence halls, classrooms, athletic arenas, dining facilities, hospitals, and offices. As designers, we need to understand the uniqueness of these buildings and provide designs that meet university requirements.
Buck: From an HVAC perspective, system flexibility and control is a challenge that we face working with universities that we don’t see with other owners. Many times these facilities are going to be renovated in 5 or 10 yr, and the program of the space may change drastically. This means that the infrastructure needs the flexibility to meet a variety of needs with a minimal amount of renovation.
Batra: Unique HVAC requirements in college/university include 24-hr operation for research facilities, offpeak and weekend operations, outside-air requirements, and higher air-change requirements for lab facilities.
CSE: What changes in fans, variable frequency drives (VFD), and other related equipment have you experienced?
Hebert: The single biggest shift we have seen is the near-total adoption of direct-drive fans in lieu of belt-driven fans for many HVAC applications. The drive losses and maintenance costs associated with belt drives are generally a thing of the past. Additionally, the direct-drive fan packages have the added benefit of being more compact, thereby enabling a more modular approach to air-handling unit (AHU) fan section design. It is now very common to see fan arrays replacing the large base-mounted fans in AHUs. This movement has in large part been made possible by the advances in VFD technology and the resulting decrease in VFD size and cost.
Batra: Changes have included fan-wall and smaller electronically commutated motor-type fans that have plastic housing/blades and harmonic reduction, surge suppression, and improved reliability in VFDs.
Buck: All of these technologies have become more efficient and reliable. The introduction of the fan array, for both redundancy and energy efficiency, has been the biggest change in fan technology. Also, the improvements in all equipment with regard to space acoustics have created environments that are more conducive to learning, which is critical to successful buildings at colleges and universities.
Robbins: Almost every pump and fan system we design are provided with VFDs. Their cost and reliability have improved to the point where they make sense versus motor starters. Even with constant-volume systems, we use the VFD to balance the system versus a circuit-setter, which saves energy.
CSE: When retrofitting an existing building, what challenges have you faced and how have you overcome them?
Batra: The challenges that we have faced are the availability of existing record drawings for the facilities, the ability to keep the existing building functional while systems are being retrofitted, and the ability to replace the existing HVAC units in the same location as existing units.
Robbins: Building retrofits are extremely important. There are many existing buildings operating every day as poor energy performers. The biggest challenges are cost and space. Many universities struggle with substantial expenses for renovations versus new construction. Renovation work is more challenging due to the existing conditions. You need to do the work upfront to understand the existing conditions and structure, as they can limit options.
Buck: The first challenge is always determining what is actually installed. As-built drawings tend to be scarce for existing buildings and are oftentimes inaccurate. Once we have determined the actual building conditions, determining how to modify the existing system to meet the needs of the scope of work is the next challenge. The existing building infrastructure may not have the ability to handle the necessary upgrades, or the actual existing system’s performance may be unknown. This is often true of controls, as most owners want digital controls, but the existing building may not have the necessary infrastructure to accommodate digital controls for a limited area. At the same time, the existing systems need to be brought up to current codes, which can also be problematic.
Hebert: Space constraints, historical considerations, structural limitations, and floor-to-floor heights are just some of the challenges we face when designing new, high-performance HVAC systems for an existing building. We have found that a multifaceted approach is always required to find the optimal solution. Our first focus is always on load reduction through a thorough analysis of every load component—envelope, equipment, lights, ventilation, and people. Flexibility, redundancy, and diversity must also be closely evaluated. Only once we are confident that all the design parameters have been clearly identified, will we begin to explore various system options with the owner. Options often include central versus distributed systems, dedicated outdoor air systems, chilled beams, displacement ventilation, and countless other strategies to optimize the building’s performance.
CSE: Have you specified any combined heat and power (CHP) systems on a campus? If so, please describe the system.
Batra: Yes, we have specified CHP systems that have included a fuel cell system and an absorption chiller system that uses the waste heat from the fuel cell system to meet the cooling requirements of the facilities.
Pelau: The Cooper Union New Academic Building is provided with radiant-system ceilings for heating and cooling. Radiant temperature is one of the factors that contribute to environmental thermal comfort, along with mean temperature, humidity, and air movement. Because water has the capacity to absorb four times more heat than air, the volume of conditioned air has been reduced by 35% in spaces that use radiant ceilings (classrooms and offices). Cornell Information Science building includes a combination of active and passive chilled beams and air handlers with energy-recovery systems (energy wheels). An innovative engineering feature employed here is the use of both active and passive chilled-beam systems in the same spaces. In rooms with high cooling loads, we found that by combining active chilled beams, which have higher cooling loads, with passive beams at the perimeter, we could achieve the appropriate balance of meeting the cooling load and ventilation airflow. Both buildings include radiant floor heating for the lower levels. Manhattan College Student Center includes air-handling units working together with a variable refrigerant flow (VRF) system.
Robbins: I have not specified any, but we have been asked about them and done a few studies.
CSE: What indoor air quality (IAQ) or indoor environmental quality (IEQ) challenges have you recently overcome? Describe the project, and how you solved the problem.
Buck: Humidity control, given the IAQ requirements, proves to be the biggest challenge we continually have to overcome. The amount of outdoor air required to accomplish the necessary IAQ requirements, in conjunction with the high humidity levels of our climate, means proper dehumidification and humidity control is critical to the success of our projects. This is accomplished through proper equipment selection and sizing as well as system controls. During renovation projects, infiltration into existing building envelopes also makes for challenges in controlling humidity as well as preventing mold and mildew from forming. This, again, requires proper system selection and sizing as well as controls.
The Watt Family Innovation Center at Clemson University provided a unique challenge because the system was an underfloor air distribution (UFAD) system. It did not allow for the typical supply-air temperature (around 55 F) due to occupant comfort issues, although the level of dehumidification due to the humid climate was still necessary. The necessary supply-air temperature for a UFAD system is typically closer to around 65 F, so being able to dehumidify and then sensibly heat the air back to the necessary supply-air temperature without introducing new energy is difficult. This was accomplished in the air handler by dehumidifying the air using chilled water, and then using some amount of return air from the building to reheat the air up to the required supply-air temperature for the UFAD system.
Batra: IAQ issues were being encountered in one of the math and science buildings at one of the community colleges, due to dry trap primers. Dry trap primers from eye washes in labs caused a foul sewer and chemical smell that traveled to non-lab spaces. The issue of dry trap primers was corrected to resolve the foul smell issue.
Robbins: Most of the IAQ issues we find are in existing buildings where there is little or no ventilation. Adding ventilation improves the comfort of the space, but will increase load for the building. Installing energy-recovery units are useful for minimizing the energy impact.
CSE: Have you specified more alternative HVAC systems on college/university projects recently? This may include displacement ventilation, underfloor air distribution, variable refrigerant flow (VRF) systems, chilled beams, etc.
Robbins: We have used a variety of alternative HVAC systems recently. There was a geothermal heat pump system where we provided a central heat pump to simultaneously generate chilled and hot water serving the science building. Using 135 F water from the heat pump, we were able to heat an existing large greenhouse previously heated from the steam plant, which reduced the building’s carbon footprint. We also designed a side-wall supply system for classrooms and underfloor displacement for auditorium spaces. Low supply allows us to increase the supply temperature to the space, saving energy. We dehumidified the air at the air-handling units using condensing water from the chiller for free reheat while reducing the fan power at the cooling towers.
Batra: Yes, we have specified displacement ventilation, UFAD, VRF systems, and chilled beams in educational facilities.
Buck: The HVAC system at the Clemson Watt Family Innovation Center is a UFAD system. The alternative HVAC system uses a pressurized floor plenum to deliver cooling to each floor through in-floor variable-air-volume diffusers.
Pelau: The Cooper Union New Academic Building had a green roof installed on the eighth-floor low roof. The green roof reduces energy consumption and mitigates several urban problems by reducing stormwater runoff, which in turn eases the burden on local sewers and water-treatment plants. The MEP design ensured that no potable water is used for rooftop irrigation; instead, rainwater is being collected in a 4,000-gal rooftop stormwater tank. Our engineers designed the overflow from the rooftop irrigation tank to be routed into a secondary 1,500-gal storage tank located on the second floor. This secondary tank is using the water stored as a greywater system for flushing toilets on the first floor, cellar, and subcellar levels of the building.
CSE: Describe a challenging building envelope project you recently designed in a college/university.
Robbins: I recently worked on a student center with a large open area within the core of the building. The roof and south-facing wall are mostly glass. With all the cooking activities and students within the building, the latent load can be substantial. We used computational fluid dynamics (CFD) analysis to review the airflow to these spaces and inform the design regarding thermal comfort.
Pelau: Both the Cooper Union and Cornell CIS buildings have a high-performance building envelope with a double-wall façade. The exterior face of the façade is a 50% perforated metal skin, which provides sufficient external shading that allowed the use of an efficient, low-cost curtainwall behind this screen (exterior façade). This façade construction reduced both cooling and heating energy consumption for the building as well as peak loads and equipment capacity. The challenge was identifying the extent of load reduction this secondary metal skin would provide by calculating the U value and the shading coefficient of the entire assembly. This was resolved through a number of iterations of the Sankey diagrams of the sun rays through the glazing, with and without the perforated skin.
Crawford: We recently designed a new multi-use, off-campus, university apartment complex located on a major thoroughfare in a very trendy neighborhood. The architect wanted the side of the building facing the street to be a glass wall, and, unfortunately for us, that side of the building faced south. As a result, we performed energy modeling of several different glazing options and external fin configurations to determine the optimum combination of glazing and fins to minimize the impact of the sun in the most cost-effective manner.
Buck: The Clemson Watt Family Innovation center has a large, three-story atrium that is primarily a glass storefront. Ensuring proper space cooling proved to be a challenge, given the radiation and convection components created by such a large glass façade. The challenge was tackled from both an architectural and a mechanical perspective. Architecturally, solar shades were provided to help reduce the solar heat gain. Mechanically, in-floor chilled beams using air from the raised floor plenum as well as chilled water for cooling and building heating water to provide additional heating capacity, were installed at the perimeter of the space to deal with the remaining solar and convection loads.
Batra: We are currently designing a building envelope that incorporates a phase-changing material on the south-facing walls that absorbs heat during the day and releases the same during the night to keep its surface temperature constant at 72 F.