Efficient Indoor Clothing: Thermal Fashion

image courtesy of lululemon athletica / flickr CC BY 2.0

image courtesy of lululemon athletica / flickr CC BY 2.0







If everyone wore a sweater, vest or light jacket indoors on colder days, we’d need less energy to heat buildings. On a world wide basis, the energy saved could equal the output of about 197 large power generation plants.<1>    Sure, it might not be worth wearing a little extra clothing on every cold day – but to the extent we do so, the savings in energy and CO2 emissions are substantial.

image courtesy of Kamiceria / flickr by-nc-nd/3.0/

image courtesy of Kamiceria / flickr by-nc-nd/3.0/



Someday, most buildings will be designed to maintain indoor temperature with efficient and non-polluting energy features like optimal building orientation, insulation, natural and controlled ventilation, reflecting and absorbing surfaces, solar panels, and other provisions.<4><2><3>. In the meantime, a little more clothing can make a big difference!




A Part of Big Bend Power Station near Apollo Beach, Florida, coal-fired, Installed capacity 1730 MW image courtesy of Wknight94 talk / Wikimedia CC-BY-SA-3.0

A part of Big Bend Power Station near Apollo Beach, Florida, May 2011, coal-fired, installed capacity 1730 MW
image courtesy of Wknight94 talk / Wikimedia CC-BY-SA-3.0

Take a look at a large power plant and you get a feel for just how massive it is. The energy output of 197 of these plants is truly huge! Thinking about so many large power plants helps visualize the gigantic amount of energy that can be saved by wearing sweaters and vests indoors.

Our count of large power plants is just an analogy. Actually, much of the energy used to heat buildings comes directly from natural gas and other sources, not from power plants. And, of course, we’re just making a point by using only one sweater in our equation when billions of garments would actually be needed world wide. However, the energy to provide the needed sweaters and vests is much less than the energy saved by wearing them indoors.<1>

197 large power plants represent about 13% of the total output of all the world’s power plants.<5>

<1>A very, very approximate calculation of the number of large power plants that represent the energy savings from wearing a sweater or vest indoors:
The average outdoor surface temperature varies considerably depending upon location. For simplicity, we’ll use New York City as a representative location. We’ll base our analysis on the discussion of Heating Degree Days (HDD) at http://en.wikipedia.org/wiki/Heating_degree_day#Example_of_use .
First, we’ll consider the situation in which the occupants do not wear indoor sweaters, etc. For a typical New York City winter day with high of 40°F and low of 30°F, the average temperature is likely to be around 35°F. For such a day we can approximate the HDD as (65 – 35) = 30. A month of thirty similar days might accumulate 900 HDD . A year (including summer average temperatures above 70°F) might accumulate an annual 5000 HDD.
Second, consider the situation in which the occupants wear indoor sweaters, etc. We’ll assume that the occupants will be comfortable with an indoor temperature 4 degrees Fahrenheit lower than if they did not wear sweaters, etc. In this case, the winter day HDD will be about (61 – 35) = 26, resulting in about 780 HDD for a winter month and about 4100 HDD annually (which also reflects the fact that there are more days of the year when little no heating is required).
This gives us an annual reduction in HDD of from 5000 to 4100: a reduction of 18%. Since the HDD measure is proportional to the energy required to heat a building, the wearing of sweaters, etc., gives us an 18% reduction in energy consumption. (We’ll assume the energy needed to produce, maintain and dispose of the sweaters, etc., is relatively insignificant.)
To estimate the total world energy consumption for space heating in buildings, we can note the following quote from http://www.iec.ch/etech/2012/etech_0712/tech-1.htm : “The building sector accounts for more than 35% of the world’s total energy demand, of which 75% is for space heating and domestic water heating”, according to the IEA (International Energy Agency).” So roughly 26% (75% of 35%) of world energy demand is for space heating and domestic water heating. United States experience provides a quick estimate that energy used for space heating is about 3 times that used for water heating (see the pie charts at http://www1.eere.energy.gov/buildings/betterbuildings/neighborhoods/why_ee_upgrades.html ). This indicates that, very approximately, 20% (three fourths of 26%) of world energy demand is for space heating.
The International Energy Agency estimates 2010 world final energy consumption at about 8,400 Mtoe (http://www.iea.org/publications/freepublications/publication/kwes.pdf#page=30). If 20% of this energy is for space heating while 18% of the space heating can be saved by wearing sweaters, etc., then the world savings is roughly .2 x .18 x 8,400 = 302 Megatonne of oil equivalent [Mtoe] = 3,512,260 Gigawatt hours (GWh).
The Big Bend Power Station in Florida is a representative large electric generating plant whose full output rate is about 2,000 megawatts (http://www.tecoenergy.com/news/powerstation/). If we assume the average output level is 80% of this, then the plant produces about 365 days x 24 hours per day x .8 x 2,000 megawatts = 14,016,000 megawatt hours, or 14,016 gigawatt hours (GWh), of energy annually.
Dividing the total “sweater savings” by the energy from a single large power plant gives us the number of large plants needed to produce the amount of energy that could be saved by the sweaters: 3,512,260 / 14,016 = 251 large power plants.
The equation at the top of this blog post, “1 sweater = 197 power plants”, is used as an analogy to help visualize the enormous amount of energy to be saved. However, this equation does not really make sense. We can’t equate sweaters and power plants, since they’re two completely different things. Much of the energy savings would come, in reality, from reduced burning of natural gas or other fuels, rather than in reduced use of electricity from power plants. We also need billions of sweaters: not just one.
To make our estimate more realistic, we’ve adjusted the count of 251 power plants to allow for the energy needed to provide everyone with a sweater or vest.
We’ll assume that each person needs one additional sweater or vest each year, at a cost of $50 each (in US dollars).
Some portion of this $50 goes to pay for energy used to make and deliver the sweater or vest. The energy used includes energy to provide water and feed for animals, energy to extract and process petroleum products used in fabrics, energy to build and run weaving machines, energy to ship materials and final garments, and so on. Compared to all of the various products and services provided within the world economy, garments do not seem to be highly energy intensive. Thus we’ll make the very approximate assumption that the energy used per dollar of output for sweaters and vests equals the average energy used per dollar of output for all products and services.
We’ll be conservative, and use an energy per dollar statistic for the US economy, which is relatively energy intensive. The Energy Consumption per Real Dollar of Gross Domestic Product (GDP) for the US in 2010 has been estimated as 7,500 Btu (as conservatively estimated on the high side by reading from the graph, not the chart, at http://www.eia.gov/totalenergy/data/monthly/pdf/sec1_16.pdf).
The energy consumption to produce one of our sweaters or vests is then ($50) x (7,500 Btu per $) = 375,000 Btu = 110 KWh.
World population in 2010 has been estimated at 6.9 billion people (http://www.prb.org/Publications/Datasheets/2010/2010wpds.aspx).
This gives us an estimate of the energy needed annually to make the added sweaters and vests: 6.9 billion x 110 KWh = 759,000,000,000 KWh = 759,000 GWh.
If we divide the output of our representative power plant into the energy to make the sweaters and vests, we get an estimate of the number of large power plants needed to produce enough energy to provide the added garments: 759,000 GWh / 14,016 GWh = 54 large power plants.
So, our adjusted representation of the net energy savings from wearing a sweater or vest indoors is about 251 – 54 = 197 large power plants.
<5>The International Energy Agency’s data for 2010 shows world electricity generation at a total of about 21,500 TWh (http://www.iea.org/publications/freepublications/publication/kwes.pdf#page=26). Using estimates calculated in Note 1, the amount of energy that can be saved by indoor sweater wearing is about 3,512,260 – 759,000 = 2,753,260 Gigawatt hours (GWh) = 2,753 TWh, or about 13% of total world electricity generation.
Categories: Small Changes

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