High expectations for high-performance buildings: HVAC
- Dave Clute, NREL Energy Executive, BOMI-HP, VP, Intelligent Building Group Operation Director, Environmental Systems Design Inc., Chicago
- Paul Erickson, LEED AP BD+C, Building Performance Practice Leader, Affiliated Engineers Inc., Madison, Wis.
- Richard Holzer, PE, NCEES, LEED AP BD+C, HBPD, Principal Engineer, Southland Industries, Garden Grove, Calif.
- Tim Kuhlman, PE, RCDD, CDT, Associate Principal, TEECOM, Portland, Ore.
- A. Brian Lomel, PE, LEED AP BD+C, CxA, WELL AP, Director, TLC Engineering for Architecture, Orlando, Fla.
CSE: What unique HVAC requirements do high-performance building projects have that you wouldn’t encounter in other buildings?
Lomel: I’d say an increased amount of integration among the disciplines and trades. The more subcontractors and the greater the performance goal, the greater potential for confusion.
Holzer: High-performance buildings require HVAC systems with low-energy consumption using products and approaches that tend to have higher first costs than “conventional” systems. High-performance buildings increasingly emphasize occupant comfort—thermal and also acoustical and visual.
Clute: HVAC controls in a building are often at the core of an intelligent or high-performance building. It could be said that the intelligent building market has grown up around HVAC controls and represents the next natural step in the evolution. HVAC control systems and their providers are generally very comfortable with the basics of Ethernet networking, multiprotocol integration, custom web user interface development, sequence-of-operations programming, and more. The software capabilities of HVAC-control systems have evolved from text-only display of real-time data to crude color line drawing graphics to today’s rendered user interface images, kiosks and dashboards, report generation, analytics, diagnostics, and more. The software capabilities were added to HVAC-control systems by manufacturers and developers to solve specific HVAC-control issues, but it turns out that the same software is very useful to layer on top of many other building systems.
CSE: Have you specified distinctive HVAC systems on any such facilities? What unusual or infrequently specified products or systems did you use to meet challenging HVAC needs?
Erickson: Increasingly, we are focusing on the building envelope as part of the HVAC system. An integrated approach between architects and engineers can reduce heating and cooling loads, which in turn, allows us to apply some of the more efficient systems (radiant slabs, radiant panels, chilled sails, passive ventilation with ceiling fans). Phase-change materials also cross architecture/engineering boundaries, which we’ve applied on multiple projects as means to reduce cooling loads. From a more active system perspective, we’ve been designing a variety of high-performance, runaround-loop, energy-recovery systems that dramatically increase the opportunity and extent of air-to-air and air-water energy recovery. We also have been using heat-recovery chillers at both the building and campus scale to move energy around facilities. The Stanford Energy Systems Innovations project that we led capitalizes on simultaneous heating and cooling demands at a campus scale, using large-scale heat-recovery chillers. Larger thermal energy-storage tanks allow Stanford to keep the units running more often and meet the daily nonsimultaneous heating/cooling needs as well.
Clute: Every project is unique, but what we are seeing in high-performance buildings is more control at the edge of the network-based control systems. It is always desirable to design a control solution around the idea of stand-alone modular hardware components and attempt to push control logic as far out “to the edge” as practical. The goal is to ensure that each distinct piece of mechanical equipment is controlled by a dedicated microprocessor controller, which can operate the equipment on a stand-alone basis if network communications are lost.
CSE: Have you specified variable refrigerant flow (VRF) systems, chilled beams, or other types of HVAC systems into a high-performance building? If so, describe its challenges and solutions.
Holzer: VRF systems have decreased in price over the past few years, reducing the financial challenges that they once faced. Attention must be paid to code-mandated maximum refrigerant quantities. This can require increased quantities of condensing units and additional piping to keep the allowable refrigerant mass within code limits. Convective hydronic systems, such as chilled beams, as well as the radiant hydronic systems—panels, sails, floors—require careful attention to water-supply temperatures to reduce the potential for condensation. Displacement-ventilation systems can achieve low energy consumption and high occupant comfort. Integration of the large supply diffuser areas necessary for some displacement-ventilation systems can be a challenge for the architectural design. Fortunately, the low diffuser face velocity and architectural screening elements installed over the diffuser face allows for excellent integration with interior architectural design.
Lomel: ASHRAE Standard 15: Safety Standard for Refrigeration Systems puts a limit on the amount of refrigerant in occupied spaces, limiting the use of VRF systems. Costs of VRF systems limits the feasibility and the need for dedicated outside-air systems (DOAS) adds to the overall cost.