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This LEED Gold-certified project includes an energy modeling savings of 20% below the baseline, which is difficult to achieve on a laboratory. Photo: Robert Benson
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Designers and owners of laboratories in the academic, health care and pharmaceutical fields express a keen interest in sustainability overall, and energy conservation in particular. And when they have this discussion about a project on the boards, they usually assess energy savings using LEED’s yardstick: the ASHRAE 90.1 Energy Standard, which quantifies energy reduction in dollars per year. Cost is certainly a valid measure of energy savings; it’s a unit of measure that transcends all disciplines and is major decision driver in the design process.
However, if we’re really discussing sustainability and our client’s goal is a “carbon neutral” lab building, is a cost-only metric most appropriate? Can it influence our design decisions in unintended ways? Perhaps carbon avoidance has value as a measure of the viability of a proposed energy-conserving opportunity. If so, a laboratory building owner and their designer might well approach the goal of sustainability in a different manner than if dollar savings, or, for that matter, energy-use avoidance are the measures.
Consider this: in the U.S., 87% of greenhouse gas emissions are related to energy consumption, according to the U.S. Energy Information Administration’s most recent figures (July 2008). The rate has been increasing by about 1% a year since 1990. Moreover, at an average annual rate of 1.8%, the commercial sector’s emissions have grown the fastest over the past 18 years. In total, the commercial sector emits 1 billion metric tons of energy-related carbon dioxide (CO2) annually—80% from the power plants providing the electricity used in commercial buildings1.
In response to these alarming figures, industry associations and building owners have organized to do what they can to reduce their buildings’ impact on climate change. For example, in 2002, the American Institute of Architects established “Architecture 2030” to work toward the design of carbon-neutral buildings. On the owner’s side, in 2007, charter signatories of The American College & University Presidents Climate Commitment established a framework to address global warming by garnering commitments from higher educational institutions “to go climate neutral.” As of January 2009, the commitment had more than 605 signatories.
The U.S. Dept. of Energy has formed a series of alliances with their national laboratories and the private sector called the Commercial Building Alliance. One of their stated goals is for all new buildings to be “net zero” by 2025. A “net zero” building is one that annually generates as much energy as it consumes.
Global warming “101”: clarifying terms
The terms greenhouse effect, global warming and carbon footprint are frequently are used in the mainstream media, as well as among designers and building owners, as they engage in conversation about the issue of climate change. Although it may seem elementary, it is worthwhile to agree on these terms. With that in mind, here are some points to consider.
Power generation often uses fossil-fuel combustion; e.g., coal burned in a boiler creates high-pressure steam, which rotates a turbine, which in turn rotates a generator to produce electricity, which is distributed to commercial and residential customers. One combustion reaction product is carbon dioxide (CO2), which enters the atmosphere.
Solar energy enters the atmosphere in the visible region of the spectrum. The Earth cools itself by radiating energy to space in the infrared region of the spectrum. However, carbon dioxide readily transmits visible light but absorbs infrared light, which prevents the Earth from radiantly cooling itself and leads to higher surface temperatures. This effect has been called the greenhouse effect, and the gases--CO2, methane and water vapor--that drive this effect are called greenhouse gases. The greenhouse effect increases the Earth’s surface temperature; thus, the term that is used is “global warming.”
“Carbon footprint” is defined as the impact on the environment in terms of greenhouse gases produced, and it is measured in tons of CO2. To “go carbon-neutral” is to effectively reduce or, ideally, erase that footprint.
For example, retrofitting a building’s lighting system results in reduced use of electricity. Because less electricity is used, then less fossil fuel is burned to create that electricity, and less CO2 is emitted into the atmosphere (i.e., the building’s carbon footprint is reduced).
About 70% of the electricity generated in the U.S. is the result of combustion of a fossil fuel, chiefly coal and natural gas. The remaining 30% of the electricity generation is from nuclear, hydroelectric and renewable sources; these sources do not release CO2 into the atmosphere and are therefore carbon-neutral.
Calculating the carbon footprint of a building driven by heating, cooling and receptacle uses (plug loads) involves analyzing the building’s energy use, calculating the energy use at the source (e.g., power generating station) and determining the related CO2 production.
Measuring sustainability
The value of energy-conserving measures can be measured in three ways: energy avoidance, cost avoidance and carbon avoidance:
- Energy-use avoidance (in terms of million Btu/yr). An energy-conserving opportunity will reduce the use of electricity or heating energy, and this is reflected in a reduction in the energy use intensity (EUI) of the building, or its annual energy use per area (million Btu/ft2/yr).
- Cost avoidance (in terms of $/yr). Because the energy-conserving opportunity reduces the building’s energy use, the building’s electricity and heating energy bills will decrease (i.e., LEED ASHRAE 90.1 standard).
- Carbon avoidance (in terms of tons carbon/year): Because the avoided energy implies a reduction in CO2 generated, the energy-conserving opportunity also reduces the building’s carbon footprint.
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With this LEED-certified project, the organization of the building footprint, core area and structural bays provides efficient and flexible space. Photo: Anton Grassl/ESTO
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An in vivo experiment
One of the things that makes a laboratory building starkly different from a commercial office building is the requirement for 100% air exchange. The lack of recirculation means laboratory buildings ordinarily require enormous energy to heat or cool outside air.
Recently, our firm, KlingStubbins, and the owner of a discovery lab discussed use of a glycol-runaround heat recovery system to reduce energy use. This technology recovers energy from the exhaust airstream to preheat or precool the outside airstream. One coil is placed in the exhaust airstream and another coil is placed in the outside airstream. Glycol is pumped between the two coils; in the winter, the glycol is heated by the exhaust airstream and transfers that heat to the outside airstream.
The proposal increased the annual electricity use by 31,057 kWh (106 million Btu). Adding the heat recovery coils in the airstream adds a pressure drop that the fans have to overcome, causing additional electricity use. Even though the system saves electricity in the summer (chiller electricity use decreases), the fan power increase outweighs the chiller savings. The proposal, however, decreases the annual natural gas use by 2,445 million Btu because of the heating savings in the winter.
This opportunity can be judged in three ways, using the parameters discussed above:
- Energy-use avoidance. There is a net savings of 2,339 million Btu, which decreased the building’s EUI by 21,000 million Btu/sf-yr, or about 9%.
- Cost avoidance. The forecasted savings associated with this energy avoidance is $29,000; this was compared with the installed cost of $250,000, to develop a simple payback period of 8.6 years.
- Carbon avoidance. Using some assumptions about the regional mix of fuels used to generate electricity, the increase in CO2 emissions due to implementing heat recovery is 31 tons of carbon dioxide. However, the corresponding decrease because less natural gas is burned in the winter is 143 tons CO2. The net decrease in CO2 is therefore 112 tons a year. (If this project were located in a region where power is generated using less carbon, the numbers would vary. For example, if the project were in an area where power was generated by carbon-neutral means, the carbon footprint reduction would be greater: 143 tons.)
In this example, all three metrics indicated reduction. In many cases all three metrics agree since they are closely related. Reducing energy consumption reduces our energy bills and the carbon emissions related to generating that energy. However, this is not always the case.
In most regions of the country, the cost of electricity varies throughout the day as the utility company must cope with large sways in demand. Customers are charged a premium during on-peak hours (day) and see a setback off-peak (night). One design strategy to take advantage of this is ice storage. In commercial buildings, occupancy, peak cooling demand and peak electrical rates occur during the day. Using the building’s cooling system to produce and store ice at night, and then melting the ice during the day for cooling effectively shifts the building’s cooling demand from the costly peak hours to the less expensive off-peak hours.
If the cost variation in electricity from peak to off-peak hours is great, ice storage can yield significant cost savings and a favorable payback. However, producing ice for cooling is actually a less efficient process overall than traditional cooling systems; it takes more energy to produce each ton of cooling. In traditional cost-centric metrics, this is a favorable design option even though there is a net increase in energy consumption. In this example, measuring cost and energy yielded different outcomes. Since energy cost can vary depending on time of day, season and the type of fuel consumed, is measuring energy directly the most accurate measure of sustainability?
Suppose two buildings located in different regions of the country have identical energy consumption. One building is located in a region whose energy production is predominantly coal, while the other’s hydroelectric. The coal region’s CO2 emitted per MWh of energy produced can be more than four times higher than in the hydroelectric region2. According to the LEED rating system, these two buildings would be identical from an energy standpoint and eligible for the same number of energy-reduction related credits--yet the global carbon impact of one building is significantly higher than the other.
What is the “real” or “right” measure of a sustainable laboratory? As these examples illustrate, there is no one answer for it all depends on the owner’s goals. Ultimately, designers and owners alike need a better understanding of the goals of sustainability -- energy-use avoidance, cost avoidance or, indeed, carbon avoidance. From that understanding, we can design a solution and measure its performance in a valid manner.
Chris Leary, AIA, LEED AP, is a principal at KlingStubbins, Boston. Mark M. Maguire, PE, LEED AP, is an engineering design principal at the firm’s Philadelphia office. Phillip Cunningham, PE, LEED AP, is a mechanical engineer at KlingStubbins, Boston.
References
1. U.S. Energy Information: “What are greenhouse gases and how much are emitted by the United States?” http://tonto.eia.doe.gov/energy_in_brief/greenhouse_gas.cfm. Retrieved October 2010.
2. U.S. EPA, Emissions and Generation Resource Integrated Database (eGRID2007), 2007.
Published in Laboratory Design newsletter: Vol. 15, No. 12, December, 2010.
