Note: The following is excerpted from “The Evolving Landscape for Energy Efficiency Retrofitting for New York City Commercial Buildings” by Daniella Leifer, Ryan North and Michael Bobker of the Baruch College CIUS Building Performance Lab and Ellen Sinreich of Green Edge LLC. The full report is available at http://www.baruch.cuny.edu/realestate/pdf/Evolving-Landscape.pdf.
Well-established energy efficiency practices and technologies are capable of achieving 15-25% savings with attractive cost-effectiveness. However, to achieve more ambitious goals, advanced technologies, which can reduce energy use by 50-60%, must be implemented. Among such technologies are better performing envelopes, heat recovery, alternative Heating, Ventilation, and Air Conditioning (HVAC) designs, on-site cogeneration, and enhanced building automation/management systems.
Some retrofit ideas are below.
Control of outside air intake and uncontrolled air infiltration
- Testing and adjustment of outdoor air quantities can be part of RCx and can yield large savings.
- Demand Controlled Ventilation (DCV) uses sensors to measure CO2 to automatically control ventilation based on occupancy. DCV is more practical for areas with variable occupancy, such as meeting rooms. Energy use savings are variable depending on the size of the spaces and how often they are occupied.
- Uncontrolled air infiltration can be cost-effectively reduced by air-sealing of envelope components and/or by restoring building pressurization. Comfort is improved.
- Economizer operation should be using maximum amounts of outdoor air when outdoor conditions are favorable. This can be a relatively low-cost retrofit. Requires on-going monitoring to assure proper function.
Uses available heat before it is rejected from the building
- Recover heat from exhaust-air, steam condensate, boilers, refrigeration condenser, data-centers.
- Various types of heat recovery systems (enthalpy wheels, heat pipes, run-around systems, cross-flow heat exchangers).
- Heat pumps can be used to boost temperature of recoverable heat.
- When combined with a heat recovery system, the replacement HVAC systems may be smaller in size than the system it is replacing.
Advanced envelope designs include passive and active elements, especially glazed elements (windows, curtain walls). High expense - generally relevant when windows or curtain wall are reaching end-of-life.
- Facade affects all the building systems in some way - impacting lighting levels, HVAC sizing, and occupant comfort.
- High-Performance Windows. Northeast combination of cold winter and hot summer suggests windows with low U-values and low-Emissivity (“E”) coating or film to reduce radiant heat flow. The Empire State Building energy efficiency upgrades will retrofit windows by incorporating a low-E film between re-fitted double glazing.
- Solar Shade Systems. Block direct summer sun from entering building. Can be fixed (such as a simple overhang), glazing tints or films, or mechanical system, with the latter more expensive to install and operate.
- Strategic Insulation may sometimes be appropriate for commercial buildings. For example, after infra-red scanning, the Empire State Building project incorporated reflective insulation placed behind perimeter convectors. In masonry buildings, exterior insulation may be attractive for certain facades.
- Re-skinning is the full replacement of curtain wall facades. Thermal bridging should be eliminated by careful detailing. Re-skinning materials are a critical decision with emerging options.
- Electrochromic glazing which changes tint in response to environmental signals (sunlight) via an electric current; used to control glare, solar heat gain, and fading. Although promising, the technology is still in its infancy.
- Double-skin construction. Popular in advanced designs in Europe. Allows for various operating modes, using wall as plenum, controlled opening of exterior skin, occupant opening of interior skin, etc.