Technology Corridor
How effective are federal energy efficiency regulations?
New buildings must meet federal energy efficiency guidelines, which have historically used site-energy measurements as the metric for building energy consumption. Using site-energy measurements, though, ends up favoring the use of electricity from the grid, rather than using electricity produced on site.
This issue is significant because Congress, in the pending energy bill, is considering a provision that would give incentives to builders and developers based on reductions in the site-energy consumption of their buildings. These incentives-unless limited specifically to reductions resulting from improvements in the building envelope, such as construction materials, insulation, glazing, and shading-would be nothing less than federally funded disincentives to on-site generation. And they would come at a time when the federal government is ostensibly promoting combined heat and power and district energy systems because of their high total energy efficiency and potential to reduce environmental emissions.
The site-energy measurement metric creates a bias toward using electricity from the grid because most losses from producing and delivering electricity placed on the grid occur upstream of the building meter, and therefore do not show up in the site-energy measurement efficiency calculation. In essence, all the inefficiencies of producing electricity happen off-camera. When electricity is produced and delivered on site, the site-energy "camera" captures losses inherent in making electricity, and so in comparison to electricity from the grid, appears inefficient. But a look at all the numbers, not just the ones on site, tell a different story.
Energy process inefficiencies experienced upstream of the customer's meter total approximately 73 percent for grid electricity, but only 10 percent or less for natural gas, propane, and fuel oil. By focusing solely on site-energy measurement, the legislation being considered would encourage building design approaches that result both in higher total energy consumption and in the emission of greater quantities of pollutants associated with building energy consumption. While site-energy measurement may be simple and straightforward, it violates Einstein's recommendation that "solutions to problems should be as simple as possible, but no simpler." In this case, the pursuit of excessive simplicity results in significant error.
How the Numbers Work
The site-energy measurement metric divides the sum of the various forms of energy consumed in the building (in Btus) by the gross floor area of the building (in square feet) to represent the average energy efficiency of the building.
The argument often used to justify the site-energy measurement approach is that it is simple and straightforward. True, it is simple to read the energy utility meters or energy supplier invoices and convert the measured energy consumption into common units. True, it is straightforward to merely sum all of the energy inputs and divide by the gross floor area of the building to obtain the site-energy metric. Although simple and straightforward, this method is wrong as an energy consumption metric. It ignores all of the losses that occur in the production, processing, conversion, transportation, and distribution of the energy to the building site, and the significant differences in the magnitude of these losses among various energy sources. Site-specific energy measurement and total energy measurement are very different processes. Concentrating on site-specific measurement removes incentives to increase overall total energy efficiency.
Systematic Shortcomings
The shortcomings of the site-energy measurement approach are best illustrated by comparing the primary energy consumption and the site-energy consumption of a typical building using five different combinations of energy sources and energy end-use equipment. The five combinations of energy source and energy end use equipment are:
- All electric-grid electricity supply;
- All electric-on-site electric generator, no heat recovery;
- Mixed fuel supply-gas space heating and water heating, all other end uses electric;
- Combined heat and power (CHP) system-recovered thermal energy provides space heating, space cooling, and domestic water heating; and,
- District energy system-recovered thermal energy provides space heating, space cooling, and domestic water heating.
The commercial building used in this analysis is a 100,000 square foot building of recent construction, with average space heating and space cooling requirements. We'll assume an energy consumption requirement of 88,000 Btu/ft.2, or a total of 8.8 billion Btu per year.
All-Electric Building Configuration, Served From Utility Grid
In the all-electric configurations, this consumption is the equivalent of approximately 2.6 million kwh/year, with an average electric demand of approximately 300 kilowatts and a peak demand of approximately 750 kilowatts, assuming an approximate 40 percent load factor. Based on the Energy Information Administration's estimates in its End Use Intensities in Commercial Buildings, 27 percent of the energy consumption in such a building would be used for space heating, 5 percent for space cooling, and 7 percent for water heating. The balance of the energy uses in the building-including ventilation, lighting, cooking, refrigeration, and office equipment-is assumed to be powered by electricity in all cases.
When the building is configured as an all-electric building, served exclusively from the grid, supplying the building's annual 8.8 billion Btus site-energy consumption requires a total energy consumption of 32.6 billion Btus per year. Total energy consumption includes all of the energy required by both the generator and the transmission system, up to the building's electric meter. This conversion from site energy to total energy is based on a 27 percent total energy efficiency. The all-electric, utility grid supplied configuration is the reference configuration for this analysis.
All-Electric Building Configuration, Served by On-Site Natural Gas Generator
Reconfiguring the building to an all-electric building supplied by an on-site gas generator results in a site energy efficiency of 30 percent. Part of this efficiency derives from the use of natural gas, which loses only 10 percent of its energy during transport to the customer's meter. So overall, by using an on-site gas generator, the site-energy consumption of the building increases by approximately 230 percent, from 8.8 billion Btus per year to 29.3 billion Btus per year. The total energy consumption of the building remains unchanged from the all-electric, grid-supplied configuration consumption of 32.6 billion BTU per year. In this case, while the site-energy consumption has increased dramatically, it has done so with no increase in total energy consumption. The overall efficiency of the energy production and delivery process is unchanged, even though most of the losses experienced in the process have been relocated from upstream of the building meter to downstream of the building meter. Yet from a site measurement perspective, building energy efficiency appears to have fallen precipitously.
The on-site generator without heat recovery configuration admittedly is an unlikely configuration for year-round operation, but it represents the impact of on-site generation for peak shaving or load management. Such on-site generation systems will become more common as customers are exposed to real-time pricing of electricity due to energy industry restructuring. As the above example suggests, this shift to on-site generation would not decrease building energy efficiency, as a site measurement standard would indicate.
Mixed Fuel Building Configuration, Natural Gas Space Heating and Water Heating
When the building is reconfigured for mixed fuels, using pipeline natural gas, rather than grid electricity, for space heating and water heating, site-energy consumption increases by 14 percent, from 8.8 billion Btus per year to 10 billion Btus per year. This increase is the result of the energy losses in the natural gas equipment used to provide both space heating and water heating service to the building. However, the total energy consumption in this mixed fuel configuration decreases by 20 percent, from 32.6 billion Btus per year to 26.2 billion Btus per year. This reduction occurs, in spite of the relatively lower efficiency of the gas fueled equipment used in the building, because of the substantially higher efficiency of natural gas delivery from the well to meter than the generation and delivery of grid electricity. In this configuration, the building appears to be less energy efficient, when measured on a site-energy consumption basis, but is actually more efficient on a total energy consumption basis.
CHP Building Configuration-Recovered Thermal Energy for Space Heating, Space Cooling and Water Heating
When the building is reconfigured to receive energy service from an on-site CHP system, the site-energy consumption increases by 105 percent, from 8.8 billion BTUs per year to 18 billion Btus per year. In this configuration, thermal energy recovered from the electric generator at the site is used to provide the energy required for space heating, space cooling, and domestic water heating. While the site-energy consumption more than doubles-a highly undesirable result based on a site-energy consumption metric-the total energy consumption of the building declines by 39 percent, from 32.6 billion Btus per year to approximately 20 billion Btus per year. In this configuration, the building appears to be dramatically less efficient when measured on a site-energy consumption basis, but is actually dramatically more efficient when measured on a total energy efficiency basis. Efficiency increases because the CHP system captures and uses waste heat instead of rejecting it into the atmosphere.
District Energy System Building Configuration-Recovered Thermal Energy for Space Heating, Space Cooling and Water Heating
The final building configuration assumes energy service from a district energy system, which would provide both electricity and thermal energy to the building site. The recovered thermal energy would be used, as in the CHP case, for space heating, space cooling, and domestic water heating, while electricity provided by the district energy system would be used for all other building end uses.
This configuration raises some interesting philosophical questions. The building is supplied with electricity generated away from the building site and delivered to the building through an electric meter. If the thermal energy recovered from the district energy system and delivered to the building is ignored, this measure would result in a site-energy consumption reduction of 39 percent, from 8.8 billion Btus per year to 5.4 billion Btus per year. In total, energy consumption would bereduced of 39 percent, from 32.6 billion Btus per year to 20 billion Btus per year.
If, on the other hand, the quantity of recovered thermal energy used in the building is measured and included in the site-energy consumption, the site-energy consumption would increase by approximately 36 percent, from 8.8 billion Btus per year to approximately 12 billion Btus per year, while the total energy consumption would still decrease by 39 percent, from 32.6 billion Btus per year to 20 billion Btus per year.
Getting to Real Efficiency
The total energy consumption reductions achieved in the mixed fuel, CHP, and district energy configurations are very significant, ranging between 20 and 39 percent. Yet the site-energy consumption metric not only fails to predict these total energy consumption reductions, but it is consistently counter-predictive.
While increases in the efficiency of grid electric generation, transmission, and distribution would reduce the total energy consumption in the all-electric utility grid configuration, both federal energy programs and pending legislation focus on site-energy consumption reduction. The result? Increased total energy consumption and the emission of additional criteria pollutants. Focusing on site-specific energy efficiency in isolation will doubtless result in counterproductive solutions.
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