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Elliott Morss | August 30, 2014

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US Energy Consumption: Will Global Warming Help?

© Elliott R. Morss

July 2012

Introduction

Global warming is causing temperatures to rise. That will mean a greater demand for air conditioning and less for heating. Will the demand for more air conditioning be greater or less than the drop-off in heating demands? And what will the overall effect be on energy use? These are important questions because 32% of US energy consumption goes to the heating, cooling, and lighting of residential and commercial buildings[1].

US Energy Data

The International Energy Agency (IEA) collects data on energy supplies and uses for countries and regions. Table 1 is the 2009 information for the US. The data are standardized as million ton oil equivalents (MTOEs).

The Table is divided into two sections: Supply and Consumption.  Under Supply, a negative figure means that energy went to a particular use. For example, 427,255 MTOEs of Coal/Peat went to Electricity Plants. A positive figure under Supply means that energy was added to. For example, Electricity Plants generated 331,867 MTOEs of electricity and CHP Plants generated 12,430 MTOEs of usable Heat.

The Consumption section shows how the energy “products” were used. For example, Industry consumed 68,720 MTOEs of the Electricity produced. And Transport consumed 18% (258,912/1,462,524 MTOEs) of the US total.

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Table 1. – US Energy Supplies and Uses (MTOEs)

Source: IEA

The table shows several interesting things:

  • Coal, Crude Oil, and Nuclear are primarily inputs into other energy forms – see their very small Consumption figures.
  • Crude Oil is refined into Oil Products used primarily in Transport – see the negative figure on its Supply line and the positive figure on the Transport Consumption line for Oil Products.
  • Coal and Nuclear are used to make Electricity – see the negative Supply numbers for each on the Electricity Plants line.
  • From the consumption data, it appears that Residential buildings use about 18% of the energy supplied while Commercial buildings account for 14% of energy use.

Electricity Losses

Perhaps the most important point to draw from Table 1 is the energy lost. Of the 2,162,915 MTOEs of energy is supplied, the US gets only 1,462,524 MTOEs of energy consumption. That means 32% of the energy is lost in production. Where is energy lost? Summing the first 6 columns in the Electricity Plants row, it appears it took 836,216 MTOEs going to electricity plants to produce 331,867 MTOEs of electricity. That means 60% of the energy used to produce and transmit electricity is lost. That loss is 23% of total US energy consumption – huge!

How Energy Is Used

Let’s return to global warming. Consider first how energy is used in homes. Table 2 provides US Department of Energy 2009 estimates of residential energy use. There are two columns of data. The w/o losses column does not include the energy losses resulting from generating and transmitting electricity. The “w/losses” column includes the energy losses.

Table 2. – Residential Energy Use Shares

Source: US Department of Energy, EIA

In the “w/o losses” column above, the dominance of energy for room and water heating is striking. In the “w/losses” column, as one would expect, the high electricity uses, e.g. water heating, cooling, etc. increase substantially.

Table 3 provides energy use for commercial buildings. Here, I use only actual energy consumed.

Table 3. – Commercial Building Energy Use Share

Source: US Department of Energy, EIA

Energy for heating is again the largest energy user.

Consider next which types of energy are used in homes. 46% it comes directly from natural gas, a bit more than the 43% coming from electricity[1]. I say “directly” because 25% of US natural gas is used to generate electricity. Fuel oil, formerly the leading heating fuel (along with coal) now only has a 6% share, just ahead of propane/NGL (5%).

Table 4. – Energy Use in Homes, by Energy (in quadrillion BTUs)

Source: US Energy Information Administration

The heating of rooms and water dominate the uses (58%), with most of the energy supplied via natural gas. All the cooling (7.5%) comes from electricity. The other items in Table 4 are probably not very temperature sensitive.

Direct Evidence

In 2005, John Cymbalsky wrote “Impacts of Temperature Variation on Energy Demand in Buildings” for the Energy Department. In it, he assumed that State-level heating and cooling degree-days would reach the average of the five warmest or coolest levels that have occurred over the past 30 years by 2025. It was also assumed that warmer winters would coincide with warmer summers, and vice versa. Compared with the reference case forecast, heating degree-days are projected to be 11 percent higher in the cooler case and 12 percent lower in the warmer case by 2025, and cooling degree-days are projected to be 17 percent higher in the warmer case and 16 percent lower in the cooler case.

His conclusions are summarized in Table 5. In the warmer case, electric use would increase by 2,108 trillion BTUs, but overall energy use would fall because fossil fuel use would drop by even more – 5,718 BTUs.

Table 5. – Changes in Energy Use (trillion BTUs)

I quote from the author – note that he includes energy losses in making electricity in his calculations:

“Given that fossil-fuel-fired space heating is the largest use of energy in the two buildings sectors, it is not surprising that the cumulative change in the two weather cases is greatest for fossil fuels. The cumulative change in fossil fuel consumption in the buildings sector in the warmer case represents 2.4 percent of the cumulative amount of fossil fuels used in the buildings sector from 2006 through 2025. For electricity, the cumulative change is 0.2 percent of the cumulative amount of electricity (including conversion losses) used in the buildings sector over that period.”

He concluded that as a result of the population moving to states with warmer climates, population-weighted heating degree-days would decline by 3.2 percent, and population-weighted cooling degree-days would 4.1 percent from 2003 to 2025.

Conclusions

It appears that at least for the US, global warming will reduce the energy consumption of buildings. Air-conditioning demand will grow, but it will be more than offset by a reduction in heating consumption.


[1] Data in this section come from the US Energy Department. The data are slightly different than the IEA data. For example, IEA data have the electricity share slightly higher than the natural gas share.


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