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ISAT 413 ─ Module I: Introduction to Energy Efficiency

Topic 2: Energy Efficiency and Energy Consumption

Defining energy efficiency and its measurement

Energy consumption in the residential sector

Energy consumption in the commercial building sector

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Defining Energy Efficiency and Its Measurement

Energy-Efficiency Concepts

a. Increases in energy efficiency take place when either energy inputs are reduced for a given level of service or there are increased or enhanced services for a given amount of energy inputs.

b. Energy efficiency is the relative thrift or extravagance with which energy inputs are used to provide goods or services. To be energy efficient per se is to provide services with an energy input that is small relative to a fixed standard or normal input.

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Energy Intensity

However, to the extent that the intensity measure is perceived as a use rate that reflects efficiency, intensity is inversely related to efficiency for a given service; that is, the less energy required to perform a given service, the greater the efficiency. It follows that a decrease in energy-intensity over time may correspond to an increase in energy efficiency depending on the level of other structural and behavioral effects.

Energy intensity is the ratio of energy consumption to a unit of measurement (e.g., floor space, households, number of workers, etc.)

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Measuring Energy Efficiency

The task of measuring and assessing energy efficiency and its change over time consists of the following:

• Deciding which effects should be considered as inherent in efficiency measurement and which are due to weather, behavioral, and structural changes to be eliminated or, at least, recognized in the measurement.

• Creating an appropriate categorization of energy services that provides the best possible framework of efficiency measure.

• Combining these statistical measures into a meaningful and understandable assessment of energy efficiency and its trends.

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Approaches to address Energy-Efficiency Trends

• Market-Basket Approach ─ The market-basket (a controlled set of energy services) approach is based on consistent measures of consumption per service unit for a benchmark set of energy services. The overriding problem may be a lack of efficiency measures for certain classes of services and the nature of the available efficiency measures.

• Comprehensive Approach ─ The comprehensive approach attempts to take all energy use into account. It is impossible to extricate all weather, structural, and behavioral changes from efficiency assessment using the comprehensive approach. Some economic sectors have poor or nonexistent information on energy use and/or characteristics associated with energy use.

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Energy Consumption

Energy consumption used in the intensity indicator can either be primary or site energy.

Primary energy is the amount of energy delivered to an end user (e.g., residential housing unit) adjust to account for the energy that is lost in the generation, transmission, or distribution of energy.

Site energy is the amount of energy delivered to an end user that is NOT adjusted to account for the energy lost in the generation, transmission, and distribution of the energy.

Demand Indicator

A measure of the number of energy-consuming units, or the amount of service or output, for which energy inputs are required.

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Energy Consumption in the Residential Sector

More than 90 million single family, multifamily, and mobile home households encompass the residential sector. Households use energy to cool and heat their homes, to provide lighting, to heat water, and to operate many appliances such as refrigerators, stoves, televisions, and hot tubs.

The energy sources utilized by the residential sector include electricity, natural gas, fuel oil, liquefied petroleum gas (propane), coal, wood, and other renewable sources such as solar energy.

Greater usage (electric heat pump, A/C, and appliances) of electricity contributed to an increasing gap between primary and site energy consumed in the residential sector. The losses in the generation, transmission, and distribution of electricity are more than twice the amount of electricity delivered to the household.

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Energy Consumption in the Residential Sector

In 1990, 52% of the total site energy was used to provide space heating.

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Energy Consumption in the Residential Sector

The dominant housing type is the single-family detached housing units (72% of the 94 million housing units in 1990).

Location is an important factor in determining energy consumption (In 1990, Midwest used 31% of the total site energy).

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Energy Trend

Among all households, the growth of total site energy consumption was nearly stable, with 1% growth per time interval.

Attached single-family housing units had a growth from 1984 to 1987, and a reduction from 1987 to 1990. (weather-unadjusted)

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Demand Indicators

Throughout the period, the fuel mix also changed in the U.S. households. The increased use of the electric heat pump, especially in the South, drove the 48% increase in the use of electricity as the main heating fuel.

The number of households is growing faster than the U.S. population. The household size has a decline from 2.73 members per household to 2.65 members per household in 1990.

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Energy-Intensity Indicators for the Residential Sector

The indicators presented here are based only on site energy not end-use site energy consumption.

The energy used for space heating may be presented as space-heating energy per square foot, but it would not make sense to use the square foot demand indicator to develop a water-heating intensity indicator. A more suitable energy-intensity indicator would be water-heating energy per household member.

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In the absence of adjusting consumption for weather deviations from the normal average, energy intensity appears to fall during the growth/growth interval, and energy efficiency may have increased, no matter which indicator is used.

Weather-adjusted energy intensity indicators, with the exception of million Btu per square foot, actually registered increases in energy-intensity suggesting decreases in energy efficiency over the growth/recession interval.

Energy-Intensity Indicator Trends

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Energy-Intensity Indicator Trends

Taking the characteristics, type of housing unit as an example, will demonstrate the advantages of comparing within an energy-intensity indicator and across the characteristic. The more detailed “micro-residential” energy-intensity indicator is more robust.

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Imperfection examples:

The influence of changes in the weather. Adjusting the intensities for weather, especially since the recent years have been mild, can explain a considerable portion of the reductions in these energy-intensity indicators.

Structural and behavioral influences affect all four indicators, some more than others.

Energy use per person account for population growth but does not address other issues.

Energy per household does not account for the expansion in the household floorspace whereas energy per square foot does.

No single energy-intensity indicator for the residential sector stands out as clearly superior to the others. The choice of indicator depends on the question asked and on data and source availability.

Strengths and Limitations of the Energy-Intensity Indicators

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Energy is used in the commercial building sector to provide services such as lighting, space conditioning, ventilation, water heating, refrigeration, powering office equipment, etc. The amount of energy used to provide these services depends on the activities taking place in the commercial buildings; for example, health care, food service, and so forth.

In 1989, the largest proportion of the energy used for energy services in commercial buildings was for space heating (35%) followed by lighting (18%), water heating (9%), office equipment (7%), space cooling (5%), ventilation (5%), cooking (5%) and refrigeration (3%).

For space heating, office buildings used 30% of the total site energy, but educational buildings used 54%.

Energy Consumption in the Commercial Building Sector

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During the growth/growth interval, the increase in adjusted consumption was less pronounced than the unadjusted trend, and the growth in total site energy consumption during the recession/recovery interval was even larger.

Commercial Building Sector Site Energy Consumption Trends

Total site energy consumption estimates can be adjusted not only for the weather effects, but also for vacancy effects. Adjusting estimates to omit vacant buildings, which use little energy, changed the trend in total site energy consumption during the intervals under study.

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Square-foot hours are surrogate measure of economic activity, it grew 22% during the growth/growth interval which may be attributed to the growth of retail sales in mercantile and service buildings.

Demand Indicators in the Commercial Building Sector

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In the early 1990’s, electric utilities aggressively promoted demand-side management (DSM) programs, especially in the Northeast to either reduce electricity demand at peak times or throughout the year.

Trends in Energy-Intensity Indicators in the Commercial Building Sector by Census Region

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The results in the two different intervals suggest that influences other than only changes in energy efficiency may be affecting the results.

Change in Energy-Intensity Indicators in the Commercial Building Sector

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Strengths and Limitations of the Energy-Intensity Indicators in the Commercial Building Sector