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Incorporate high-performance energy efficiency measures into your new office development and reduce energy costs for years!
The technical guides below explain how and why you should incorporate energy efficiency strategies into your next office project.
Glazing properties are important because they affect thermal comfort and control the amount of solar heat allowed into the building. The two key properties are assembly thermal conductance (U-value) and solar heat gain coefficient (SHGC). Building codes have increased minimum performance requirements, but opportunities still exist to further improve window properties without moving to costly triple-pane glazing.
Many manufacturers offer low-cost double-pane commercial glazing systems that exceed code-minimum properties. Cost and energy savings can be balanced by specifying good double-pane glazing units and thermally broken frames. High-efficiency glass may cost around 15%-25% more than glass with code-minimum properties, with simple payback between 5 and 10 years, but the incremental cost may be substantially less for some products and systems. Higher-performing glazing may also reduce HVAC system size and cost, and may eliminate the need for perimeter heating systems.
Window properties can have a big impact on occupant comfort, daylight harvesting potential, and overall quality of space. Selecting higher-performance glazing can improve the thermal comfort in areas adjacent to windows. Spectrally selective coatings allow transmission of visible daylight but limit solar heat gain.
Many excellent glazing products are available. Special attention should be given to framing systems, since overall system performance matters most. Quality frames limit thermal transmission and air infiltration.
South, east and west glazing should be specified with an SHGC of 0.35 or less.
Specify glazing products with the target assembly U-values above. Note that center-of-glass (COG) U-value is not the same as assembly U-value. Assembly U-value takes into account both COG U-value and frame conductance.
A thermal modeling report should be completed for curtainwall systems to determine the assembly (glass and spandrel) U-value. For factory-built windows, confirm assembly U-value and SHGC meet requirements based on NFRC data.
It's about more than choosing LED light fixtures, which provide higher-quality illumination and use less energy than other lighting types. Reduce lighting power without sacrificing functionality by decreasing total installed wattage through thoughtful design and consideration of necessary light levels.
High-efficiency LED lights have longer lifespans and can significantly reduce or even eliminate maintenance costs. No additional cost is required for disposal of hazardous materials, as is needed with fluorescents.
For a lighting power density (LPD) of 0.50 W/sf, annual energy savings range from 5% to 8%, depending on building operating schedule.
By using LED fixtures and light levels consistent with Illuminating Engineering Society of North America (IESNA) recommendations, a best-practice interior lighting power density may cost less than meeting the baseline with fluorescent fixtures, meaning payback is immediate.
LED lighting offers better glare control and uniformity than alternatives.
Improved lighting quality is linked to improved employee morale, leading to increased productivity and fewer lost staff hours.
Lower installed lighting power density contributes less waste heat, which can have the ancillary benefit of reduced summer cooling costs.
Specify LED fixtures with a target LPD of 0.64 W/sf or less and light levels consistent with IESNA recommendations. Many offices can achieve lighting power density values as low as 0.45 W/sf with current technology.
Target selection of fixtures meeting DLC QPL premium performance requirements:
A thoughtful lighting control scheme reduces energy use and increases lighting lifespan without affecting the comfort or productivity of building occupants.
Lighting controls are already required by code, so implementing a more aggressive control strategy adds little to no additional first cost.
Assuming a design lighting power density value of 0.64 W/sf and targeting full shutoff controls within 20 minutes, annual cost savings are up to 1% per year.
Due to low first cost, interior lighting controls typically payback within the first year.
In contrast to fluorescent lights (which have a reduced lifespan with frequent switching), LED lights are not adversely affected by frequent switching, and in fact last longer with a more aggressive controls strategy due to reduced run-hours.
Occupancy-based control for open office spaces is now required by code. New products that integrate controls in light fixtures make installation and commissioning easier. Properly zoned and commissioned controls are responsive to occupants, and contribute to perceptions of safety and quality.
Design lighting controls with more granular zoning to increase savings potential and to allow for short time-delay-to-off following vacancy without impact to functionality.
Alternately, implement multi-level or stepped shutoff control of light output, such as 50% reduction in 5 minutes, followed by full shutoff in 20 minutes from vacancy.
Consider networked lighting controls, which allow for advanced lighting control strategies such as task tuning to further increase savings, functionality and ease in making changes.
As with all control measures, post-occupancy commissioning and verification is important to ensure lighting operates as designed. Consider sensor calibration and adjusting time delays.
As with interior lighting, exterior lighting efficiency is about more than just choosing LEDs. Thoughtful design addresses any security concerns strategically while not exceeding recommended light levels. Designers should incorporate high-efficacy fixtures from the array of LED products on the market.
Buildings that implement best-practice efficient exterior lighting can expect to save 2% to 4% of building energy costs, with payback in one year or less.
LED lighting offers better glare control and uniformity than alternatives, contributing to improved facial and object identification. Customer satisfaction and comfort can be achieved with lower installed lighting power designs, while reducing light pollution and trespass. Safety and security concerns can be met without exceeding desired light levels. The inherent dimmability of LED fixtures provides potential for tuning light levels post-installation, providing opportunity for additional energy savings.
Compare your project's watts per square-foot of parking and drive area and watts per linear foot of doors to the recommended targets in this guide.
Do not exceed Illuminating Engineering Society of North America's (IESNA) recommended light levels (0.2 to 0.5 foot-candles for parking lots) for the building's exterior lighting zone.
Confirm any specific security issues requiring enhanced lighting.
Target selection of DLC QPL premium performance requirements:
Even the most efficient lighting designs can further benefit good lighting control strategies. Dim building mounted and pole mounted fixtures during nighttime hours while turning off landscape and accent lighting.
https://betterbuildingssolutioncenter.energy.gov/sites/default/files/attachments/exterior_lighting_savings.pdf
Thoughtful lighting control zoning and sequencing reduces energy use and increases lighting lifespan without affecting functionality.
Lighting controls are required by the energy code, so implementing a more aggressive control strategy does not add to the first cost of a project.
Implementing best-practice exterior lighting controls results in electric energy savings of 1% or 2%, with payback in a year or less due to low initial cost.
Simply increasing light levels does not necessarily enhance safety or security. A U.S. Department of Energy report (PNNL-18173) suggests that high-quality exterior lighting design contributes to safety and security.
Effective control of exterior lights can also reduce light pollution and light trespass.
Group exterior lights into at least three zones: Building-mounted fixtures, pole-mounted fixtures closest to the building, and pole-mounted fixtures farthest from the building.
When operating hours are known, implement schedule-based controls to turn off or significantly reduce all but essential dusk-to-dawn fixtures after expected use of the parking area.
When operating hours are unknown, consider motion controls to turn off or significantly reduce lighting in unoccupied areas. More granular zoning of large exterior parking areas increases savings, as sensors only activate some portion of exterior area lighting.
Many offices use rooftop units (RTUs) to provide building cooling and ventilation. RTU air conditioning efficiency is measured as an Integrated Energy Efficiency Ratio (IEER). RTUs with higher IEERs use less energy to cool a space. Consortium for Energy Efficiency (CEE) publishes tiers of efficiency ratings to help design professionals specify efficiencies.
Some offices may use chiller equipment to cool chilled water. For this equipment, specify an Integrated Part Load Value (IPLV) 10% better than the code minimum.
Efficient RTUs are a low-cost energy efficiency upgrade. Units may cost $19 to $65 more per ton of cooling, with a typical incremental cost of less than $0.30/gsf.
Cooling electricity cost is reduced by 10% or more in a typical application, resulting in a simple payback of less than five years.
High-efficiency RTUs add value to your building project, which can increase sale price or lease rates. Net present value is expected to be +$0.03/gsf or more.
There are two efficiency ratings for RTU air conditioners, EER and IEER. EER (energy efficiency ratio) is an efficiency rating when the RTU is at full load on the hottest day. However, the RTU may be at full load less than 1% of its life.
IEER (integrated energy efficiency ratio) takes into account the RTUs part load efficiency. IEER is a better representation of the energy efficiency of the rooftop unit.
The most efficient RTUs and chilling equipment have variable speed compressors and fans with integrated controls. These systems can match the exact cooling load required, saving energy over staged compressors which tend to overcool the air at part load conditions.
Specify or schedule a rooftop unit that meets the Consortium for Energy Efficiency (CEE) High Efficiency Commercial Air Conditioning and Heat Pump Initiative Tier 1 Minimum IEER. For even better performance, specify rooftop units at CEE Tier 2, CEE Advanced Tier, or even higher IEER.
For a system type other than those listed by CEE, specify rated efficiencies 10% higher than the code minimum requirement.
Many offices use gas-fired heating in rooftop units (RTUs) or boiler hot water heating systems to heat the building. The efficiency for units can be improved by using condensing heat exchangers in the equipment, which allow heat to be captured from water vapor in the products of combustion.
Heating fuel use is reduced by 10 to 15% or more in a typical application when using condensing RTUs or boilers.
Condensing boilers cost 20% to 25% more than a standard boiler and should generally have a simple payback within four to five years.
Condensing RTUs can cost about $5 per MBH more than regular RTUs. A typical payback period for condensing RTUs is ten years.
Condensing gas-fired heating technology uses non-corrosive heat exchangers to capture heat from the waste vapor in the combustion process.
Condensing boilers save the most energy based on lower entering water temperature. Many designers know to lower the water temperature leaving the boiler, but the hot water return temperature should be as low as possible to take full advantage of a condensing boiler system.
Properly maintaining the products of combustion is an important part of a condensing furnace RTU or a condensing boiler. Check with your designer to properly dispose of condensate.
Specify rooftop units (RTUs) with a condensing furnace that has a minimum gas heating efficiency of at least 92% per Section 2.39, Thermal Efficiency, ANSI Z21.47.
An alternative to air conditioning units with gas-fired furnaces is to use heat pumps, which can reverse the air conditioning process to heat the building in winter. Heat pumps can be air source, water source or ground source (geothermal). Efficiency can be further improved by using variable refrigerant flow (VRF) technology.
Heat pump efficiency is rated in Integrated Energy Efficiency Ratio (IEER) for cooling and coefficient of performance for heating. The Consortium for Energy Efficiency (CEE) publishes tiers of efficiency ratings to help design professionals specify efficiencies.
Higher-efficiency heat pumps are a low-cost energy efficiency upgrade. Units may cost $50 to $100 more per ton of cooling, with a typical incremental cost of less than $0.30/gsf.
Heating and cooling electricity cost is reduced by 10% or more in a typical application, resulting in a simple payback of less than 5 years.
Heat pumps can reject heat to air, water or ground. Efficiency is generally improved with water source heat pumps, but it requires more equipment, like a dry cooler, cooling tower or ground loop to reject heat. VRF technology improves efficiency by allowing “simultaneous heating and cooling”; a space in cooling can reject heat to a space that needs heating, reusing energy that would be rejected from the building.
The most efficient heat pumps have variable speed compressors and fans with integrated controls. These systems can match the exact cooling load required, saving energy over staged compressors that tend to overcool the air at part-load conditions.
Specify or schedule a unitary heat pump that meets the Consortium for Energy Efficiency (CEE) High Efficiency Commercial Air Conditioning and Heat Pump Initiative Tier 1 minimum IEER.
Air source heat pumps shall have a minimum Integrated Energy Efficiency Ratio (IEER) that meets CEE Tier 1 efficiency ratings.
Alternatively, specify rooftop units at CEE Tier 2, CEE Advanced Tier, or specify an even higher IEER for more energy savings.
Where no CEE Tier 1 rating is listed, specify a minimum efficiency 10% better than code minimum.
Office occupancy schedules vary significantly from hour to hour, and areas like conference rooms may spend a good portion of the day empty. Demand-controlled ventilation (DCV) can be used to reduce outside air intake when these are not occupied and move outside air to the spaces that are occupied. With increasing focus on energy performance and occupant health, it is important to control delivery of outside air to manage energy and air quality.
Simple DCV consisting of CO2 sensors in open offices or large conference rooms typically cost around $1,500 per sensor. If occupancy sensors for lighting are being installed, these can be integrated to provide control for DCV for small offices and huddle rooms.
A simple DCV system can save 6% on cooling and heating costs annually, generating a simple payback of 4 to 6 years.
A more advanced DCV system can save as much as 23% cooling and 40% heating costs, with a simple payback of 2 to 3 years.
Improved ventilation systems improve indoor air quality, leading increased occupant productivity. High carbon dioxide levels can lead to drowsiness; CO2 sensors help bring in fresh outside air.
Locate CO2 sensors in large conference rooms and open offices; locating sensors in the return duct is less effective at directing outdoor air to occupied rooms.
Smaller rooms like offices and huddle rooms can have occupancy sensors to reduce the building outdoor air intake. Many of these rooms require occupancy sensors for lighting, and these can be coordinated with the HVAC building automation system.
Specify CO2 sensors in large conference rooms and open offices. Conference rooms over 500 square feet require DCV per the energy code.
Refer to ASHRAE Guideline 36-2018 High Performance Sequences of Operation for HVAC Systems for outside air control of single-zone and multi-zone variable air volume air handling units. DCV is only as effective as the controls installed on the system.
Additional savings can be attained by using occupancy sensors in small rooms and resetting outside air using the sequences in ASHRAE Guideline 36-2018. In addition, ASHRAE 62.1-2016 2.6.7.2 now allows breathing zone outdoor airflow to be reduced to zero for zones in an occupied standby mode.
Perhaps the most effective way to reduce water heating energy consumption is to first reduce hot water demand, specifically through the installation of low-flow faucets and showerheads. EPA’s WaterSense program provides an easy way to find fixtures that perform effectively at lower flows.
Low-flow plumbing fixtures are typically low-cost measures. The full installed cost (including labor) is around $8 for faucet aerators and $12 for showerheads, with a typical lifespan of 10 years. The incremental cost going from baseline to low-flow is even less. Simple payback for low-flow hot water fixtures can be less than a year just considering energy cost savings, not including water savings.
These strategies have the additional benefit of reducing potable water usage which, like energy efficiency, is a key component of sustainable building design. This is recognized by building rating systems, and can be part of a building’s environmental brand and marketing. In addition to water heating fuel savings, reducing potable water consumption also saves significant energy expended in purifying, distributing and subsequently treating water, an important part of the total energy picture of the built environment.
Low-flow plumbing fixtures have wide market penetration and are available in many styles. Look for WaterSense-labeled products when specifying plumbing fixtures. For public restrooms, consider sink faucets with sensor-actuated valves to further reduce water waste and promote a sanitary environment.
For mass wall types like precast and masonry, approximately two inches of insulation is required by code. For steel framed walls to comply with code, cavity insulation will likely need to be supplemented by approximately 1.5 inches of exterior continuous insulation. In both wall assemblies, adding another inch or more of insulation may make financial sense for a building. It can reduce heating and cooling equipment size and energy costs while also improving occupant comfort. Designers should calculate assembly U-values, not just clear-span U-values, and minimize or eliminate wall penetrations and other thermal bridges.
One-inch-thick extruded polystyrene (XPS) insulation has an incremental cost of 0.33 $/ft2, and 1.5” thick XPS has an incremental cost of 0.50 $/ft2. While payback for this measure is 8 years, the lifetime of the wall system is typically equal to the life of the building itself, often 50 years or more. Therm savings are typically 3% per year and kWh savings are just under 0.5% to 1% per year.
There are three primary types of continuous insulation used in precast wall systems — extruded polystyrene (XPS), expanded polystyrene (EPS) and polyisocyanurate (polyiso) — but some building codes now require exterior insulation to be rigid mineral wool insulation boards or other non-flammable material types. In most cases, XPS or EPS work well in commercial applications as continuous insulation. Batt insulation or spray foam may also be used in stud cavities of masonry, wood or steel-framed wall systems, but those applications require careful consideration of moisture transport.
XPS typically is R-5 per inch. It maintains its R-value in cold temperatures. Over time, the R-value will decrease slightly. XPS also has vapor and air barrier properties. EPS is typically R-4 per inch. It is less dense, which requires increased thickness compared to XPS. It is slightly more permeable than XPS. EPS is less expensive than XPS.
Polyiso typically is R-6 per inch, however this R-value decreases in cold temperatures.
Designers should use caution when designing wall assemblies. Avoid penetrations though the continuous insulation. This is common around loadbearing areas that support the roof deck, as well as window and door openings.
An assembly U-value calculation should be done to ensure mass wall assemblies achieve a U-value of 0.06 Btu/hr- ft2-F and steel framed wall assemblies achieve 0.043 Btu/hr-ft2-F. If there are significant penetrations through the layer of continuous insulation, further increasing the thickness of the continuous insulation layer may be required to achieve these targets.
When specifying continuous insulation, state the required thickness for each type of insulation allowed to achieve the desired minimum-aged R-value.
Deciding whether to include roof-mounted solar photovoltaics (PV) in a new building design can be complicated and require input from multiple stakeholders. However, a few simple choices during design can ensure the building is solar-ready and can reduce the construction costs related to adding solar later by up to 60%.
Solar PV systems perform best when shading from vegetation and neighboring structures is minimized. To the extent possible, site buildings in the least-shaded portion of a lot, designating shady areas for parking and driveways.
Rooftop solar systems weigh three to six pounds per square foot, so a solar-ready roof must be able to support this. Minimizing the amount of rooftop equipment and placing all such equipment in a centralized area on the north side of the roof will maximize space and minimize shading for a future solar system.
To accommodate photovoltaics (PV), the electrical system must have conduits routed from the roof to the main electric panel. Space should be left near the panel for equipment such as inverters, controllers and switches.
In all as-built drawings and submittals, be sure to record details about design choices made with solar in mind. Consider including details on the code sheet.
If the approximate size and location of a building is known, the ComEd solar calculator can be used to estimate system power and energy production.
On the site plan, indicate the portion of the roof designed to accommodate future PV panels. Provide sufficient roof structure to support this load.
Size the electrical room to accommodate future solar PV equipment.
Visit ComEd.com/Solar to determine if solar is right for you.
