Isolation: First the Body, Then the House
The reports and books that describe the importance of energy efficient heating systems and home insulation. However, nothing has been said or written about the potential for energy savings of clothing, despite all the advances that have been made in this area.
Modern thermal underwear offers the possibility of lowering the thermostat without sacrificing comfort or shine. The potential energy savings is huge, the cost negligible.
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| Isolation: First the Body, Then the House |
This article explains scientifically and statistically how to maintain thermal comfort regardless of the indoor temperature by wearing appropriate clothing.
Thermally isolating the body is much more energy efficient than isolating the space in which it is located.
In recent decades, the insulation of homes and the energy efficiency of heating appliances have improved considerably. These advances have produced significant energy savings in fuel consumption. Despite population growth, rising levels of comfort, and a tendency to build larger homes, total energy consumption for US home heating dropped from 5,320 million BTUs in 1993 to 4,300 million BTUs. in 2005, 20% less (source). The same trend is observed in other industrialized countries.
However, heating consumes huge amounts of energy, almost all of it from fossil fuels and if that were not enough these figures do not take into account the energy used to demolish old buildings and build new, more energy efficient homes. Some studies indicate that it takes 35 to 50 years before this incorporated energy recovers. This means that if a new, efficient building did not last that long, it would cause greater energy consumption - although in the statistics it will appear otherwise.
It is expected that there will be further improvements in the energy efficiency of buildings and heating systems, but apart from the built-in energy necessary to make homes more efficient, an additional problem arises that prevents the rapid and pronounced reduction in energy consumption: the cost.
Introducing insulation into homes and more energy efficient heating appliances is expensive, which means that many people simply cannot afford it. There is also the problem of "split incentives": the owner of a rented house has no interest in improving efficiency while the tenant pays the heating bills.
Ambient Indoor Temperature
Another way to reduce energy consumption for heating without these disadvantages is to lower the temperature in the thermostat and put on more clothes. Although ambient temperature is almost never mentioned as a factor in energy use, it is a determining factor in the energy consumption of heating systems - just as the speed of a car is a determining factor in the energy consumed by the motor.
Specifying how much energy can be saved by reducing the thermostat depends on the outside temperature. In temperate climates, lowering the thermostat only 1 ° C gives an energy saving that can be estimated at around 9 to 10 percent (sources: 1 & 2 - P20, pdf).
From what I have been able to find out, no one has published a scientific report on the evolution of the average winter temperature indoors throughout recent history. Today, the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) recommends an indoor winter temperature between 21 and 23 degrees Celsius. A Dutch report (Pdf, in Dutch) mentions that there was an increase in the average indoor winter temperature between 20 ° C in 1984 to 21 ° C in 1992. David MacKay mentions an average ambient temperature of 13 ° C ( 55 ° F) in the United Kingdom in 1970.
Although these fragmentary data are far from sufficient to demonstrate that there has been an increase in the average temperature in the interiors, it is enough to have the experience of many people of sufficient age to verify that watching television in T-shirt in winter is a relatively phenomenon recent. There seems to be no doubt that our level of well-being has gradually increased thanks to better heating systems.
We have to take into account that the reduction of energy consumption in indoor heating thanks to the construction of more efficient homes was less than 20 percent from 1993 to 2005. This reduction could have been achieved by lowering the thermostat 2 ° C. thermostat from 22 ° to 18 ° C would achieve energy savings of at least 35 percent. And, as we will see, even lower indoor temperatures are perfectly possible without sacrificing comfort.
Our body as a heating system
When we talk about heating, we don't take into account the fact that it is our own body is a heater. Our body temperature is approximately 37 ° C, and much of the skin temperature is around 33 ° to 34 ° C. Because the temperature of the environment is often lower, our body constantly radiates heat outside. A small percentage of this heat is due to breathing, but most of our heat emission occurs through the skin. To limit this heat transfer from the skin to the environment, most mammals (and birds) are covered with hair (or feathers). Humans do not have this protection and that is why we have resorted to clothing since we left behind our origins in Africa (where it was so hot to survive without additional layers of clothing).
Clothes do not heat on their own - they only regulate, decreasing, the speed with which body heat escapes outward. This occurs by heating the air layer between skin and clothing. Air is a relatively bad conductor of heat, which is the same: a good insulator. The same technique is applied when insulating a house. The only difference is that in the case of a building, more rigid and bulky insulating materials can be used because a building does not have to move or feel comfortable.
Naturally, the isolation of the body is much more energy efficient than the isolation of the space in which this body is located. Insulating the body only requires a small layer of air to be heated, while a heating system must heat and keep all the air in a room warm to achieve the same result.
The thermal properties of clothing: the unit of measure "clo"
The insulating properties of clothing can be expressed in "CLO" -units, where a "clo" unit is equal to the thermal insulation necessary to keep a person at rest (for example, someone who relaxes on the sofa) indefinitely comfortable at a temperature of 21 ° Celsius. The “clo”, derived from the English word “cloth”, in Spanish, “clothing”, is not an international standard unit (the international standard unit of thermal resistance is m² K / W, where 1 clo corresponds to 0.155 m² K / W), but it has the advantage of being easy to understand: a “clo” is equal to the isolation of a man dressed in a three-piece suit (shirt, pants, suit jacket) and fine underwear.
Burton, who defined the clo unit, wrote in 1946:
"It seemed to us that we could explain even to a general or admiral, without giving him a physics class for which he had neither time nor patience, that his uniform had about a thermal insulation clo unit, the other clo unit, and that together they would provide a total of two clo units. ”
In Europe, a similar unit called “tog” (British slang for clothing) was developed, which amounts to 0.645 clo. Both values can be compared with the R value of the construction of insulation materials, where 1 clo equals 0.88 R (or 1 R equals 1,137 clo). The clo value is more used than tog, so here we will use the American unit. The values in clo units of clothing items are calculated using a thermal dummy.
The maintenance of thermal comfort
The clo unit is an interesting unit because it allows us to calculate precisely what clothes we have to wear to feel comfortable at any indoor ambient temperature. According to the "Encyclopedia of Health and Safety," the clo value required to maintain a neutral thermal sensation rises to around 2.7 clo at an indoor temperature of 10 ° Celsius. When the indoor temperature drops to 0 ° C, the necessary thermal insulation rises to 4 clo.
As a general rule, each change of 0.18 clo units compensates for a 1 ° C decrease in air temperature (according to the American Society of Heating, Refrigeration and Air Conditioning Engineers - ASHREA).
A “clo” is equal to the thermal insulation necessary to keep a television addict in a typical business suit, comfortable for an indefinite time, at a temperature of 21 ° Celsius
In this way, the clo value of any piece of clothing and of any set can be calculated. ASHREA, ISO and some other research teams have listed hundreds of individual pieces of clothing with their corresponding clo values (see sources).
A short sleeve shirt has a value of approximately 0.10 clo, while a sleeveless shirt offers approximately 0.06 clo, a panty is approximately 0.20 clo. A short-sleeved shirt has an insulation value of 0.15 to 0.25 clo, while a long-sleeved shirt offers around 0.20 to 0.30 clo.
from 0.20 to 0.40 clo, the pants offer from 0.25 to 0.35 clo, and a long or tunic skirt 0.22 to 0.77 clo. The underpants add a thermal insulation of 0.05 clo, while the socks provide 0.04 to 0.10 clo. The long underwear offers from 0.20 to 0.35 clo for the top, as well as the bottom.
All these values can simply be added to calculate the total "clo value" of a set of clothes. An alternative method is to measure the thickness of a set of clothes: each layer of 2 centimeters thick results in a value of 1.6 clo.
Energy cost savings
In view of this data, it can be easily demonstrated how small changes in insulation in clothing can have a profound impact on heating costs and energy expenditure. A person wearing briefs (0.05 clo), light socks (0.05 clo), a T-shirt (0.10 clo), a thick long-sleeved shirt (0.25 clo), a sweater (0.30 clo) and long pants (0.30 clo) is protected by a total thermal insulation of 1 clo, which means that this person will remain comfortable resting in front of the television at a temperature of 21 ° Celsius.
However, without the thick shirt and sweater, this value drops to 0.55 clo. This means that watching television using only one shirt requires an air temperature of 24 ° Celsius in order to maintain thermal comfort which would lead to an increase in energy consumption of 20 to 30 percent.
On the other hand, if this person combines his original set (including thick shirt and sweater) with a complete set of long underwear, he elevates his insulation to 1.7 clo, which would allow him to continue to feel equally comfortable at approximately 17 ° C , but saving 30 to 40 percent in heating and energy use costs compared to the normal winter suit, being the savings, compared to the outfit of only one shirt on the upper body of 50 to 70 per percent in heating costs and energy consumption.
How many pieces of clothing can be worn?
When we talk about common clothes, raising the clo value of a set is basically achieved by adding more weight in clothes. A general rule is that the "clo value" is equal to 0.15 times the weight of clothing in pounds. This is the same as saying that the clothing that provides 1 clo of insulation weighs 6.6 pounds or 3 kg.
The relationship between thermal comfort and clothes weight explains why we tend to prefer a temperature higher than the addition of more clothes. If we want to remain comfortable at a temperature inside 0 º Celsius (4 clo), we should wear 26 pounds (12 kg) of clothes. U.S. Army He found in the 1960s that the maximum of clo units that would allow a man to maintain sufficient mobility and dexterity for military tasks would be between 4 and 5 clo.
A layer of thermal underwear allows the temperature of the thermostat to be lowered by at least 4 ° C, thus saving up to 40% of heating energy.
The extra weight of clothing limits our movements and also television addicts need to get up from time to time.
Long-tech underwear
However, things have changed. Military agencies, space and sportswear industry have greatly improved the heat / weight ratio of clothing in recent decades. This has led to the creation of a very varied and attractive line of light clothing with high clo values. A large part of this progress is achieved through the use of new synthetic materials.
Although these have been used in the manufacture of all types of clothing (sweaters, pants, jackets), their importance for indoor use is especially relevant in the case of long underwear. This layer of clothing (which is actually used in combination with briefs or panties) is the one that has the greatest potential to replace a heating system.
Pumping coefficient
Because it fits tightly around the body, long underwear has an optimal "pumping coefficient." The pumping coefficient is another factor that defines the insulation of the clothes, in addition to the clo value. It becomes the value that reflects the exchange of air produced by the user's movement.
Even the most leisurely people move from time to time, and this activity can modify the layer of insulating air around the body, momentarily disturbing thermal comfort.
Because the pumping coefficient is much more favorable for underwear than for baggy garments such as ponchos, wide pants or thick knit sweaters, long underwear offers more thermal comfort even with similar "clo" values. Another factor to take into account is the chimney effect: even without movement, loose clothing allows the trapped layers of air to be ventilated, thus reducing insulation.
Long underwear has more advantages over other clothing options. It does not hide the shape of the body which gives it a certain appeal, something that commonly worries both men and women. It can be worn under normal clothing, and last but not least, it can be worn in layers, further improving the insulation value: several thin layers trap more air than a single, more bulky layer.
According to the US Air Force, a layer of long underwear (long pants + long-sleeved shirt) has a value of 0.6 clo while two layers of underwear confer 1.5 clo. In other words, by using two layers, more than the simple sum of their "clo" values is achieved.
Combining this garment with a normal suit (or a more comfortable similar set), the thermal insulation rises to 2.5 clo, enough to keep a comfortable sofa addict indefinitely at a temperature of 12.7 ° Celsius only - very below today's common indoor ambient temperatures. This set of clothes could produce a reduction in energy consumption for indoor heating of up to 80 percent.
With two layers of thermal underwear, the insulation value is greater than its sum. What makes it perfectly possible to maintain thermal comfort at temperatures below 10 ° C.
Unfortunately, the clo values of modern thermal underwear have not been included in their documented general descriptions. However, even this fragmentary information suggests higher clo values than those of traditional long underpants. Well-documented calculations of amateur hikers (see for example here) show clo values of at least double those of long underwear mentioned by the US Air Force. (for example, 0.66 clo of the top piece only).
This would mean that the same thermal comfort could be achieved with the use of a single layer of that long underwear plus the equivalent of a winter suit (2.5 clo at 12.7 ° C), or the use of two of those Layers, in addition to the suit, could offer comfort for a person at rest in an indoor space at 0 ° C (using 4 layers of clothing).
Another indication of the energy-saving potential of technical underwear is the "clo" values of the different materials. According to the "Manual of technical fabrics", the heat / weight ratios of fiber fabrics such as polyester and acrylic are 2.5 to 8 times higher than those of woven and knitted fabrics such as wool or cotton (material used for traditional long underwear). Fabrics such as Thinsulate offer heat / weight ratios 13 to 17 times those of cotton and wool.
Synthetic materials or natural materials?
It may seem strange to promote the use of synthetic clothing in a blog like Low-tech Magazine. However, both materials; Natural and synthetic, they have advantages and disadvantages and both can be a sustainable option even though synthetic garments are made from fossil fuels. This is especially true when clothing is used as a substitute for a heating system, the energy saved by lowering the thermostat is much greater than the energy needed to manufacture the garments that make it possible. Indeed, these high insulation coefficients show how valuable fossil fuels are as material and how stupid it is to burn them.
Synthetic underwear not only has a higher insulation value than natural materials, but is more durable, comfortable (many people cannot tolerate wool) and can be very cheap. The main drawbacks of synthetic underwear is its high flammability and its tendency to attract dirt. Synthetic thermal underwear should be washed frequently, a process that consumes energy.
This is not as pronounced in clothing worn indoors as used for outdoor sports. It is well known that television addicts hardly sweat. On the other hand, synthetic clothing dries more easily, this means that it is not necessary to turn on the dryer after washing. And of course, we can wash the clothes in a pedal washer, and the hot water needed to come from a solar boiler, thus completely eliminating the use of fossil energy (and allowing you to warm up while doing laundry ...).
That said, synthetic clothes are not a necessity. Even the use of underwear, made of natural materials such as cotton and wool, provides energy savings. Cotton has a relatively low insulation value, but a full layer of long cotton underwear would add at least 0.4 clo to its thermal comfort - enough to lower the interior temperature by 2.5 ° C and save more than one 20 percent on heating bills.
The use of wool can more than double this potential savings by adding approximately 1 clo with a full layer of long underwear (which allows a reduction in ambient temperature by more than 6 ° C). Wool reappeared as a material used for hiking and mountaineering clothing in the 1990s, to the point that allowed Icebreaker to position itself as the first manufacturer in the market with thermal wool underwear.
The company uses New Zealand merino sheep wool, which produces some of the finest and softest wool possible. Patagonia also offers a collection of merino wool underwear, and several European manufacturers (Mammut, Woolpower and Helly Hansen) mixing merino wool with synthetic materials. This gives the clothing more durability - wool wears much faster than synthetic materials.
An advantage of wool over synthetic fabrics (and other natural materials) is that it keeps a good smell for longer. It is no longer necessary to wash frequently. The biggest drawback of merino wool is the price: It is difficult to find a complete set of long underwear for less than 200 euros. But we insist: this investment pays for itself quickly if the thermostat can be lowered.
Thermal comfort: more than clothes and air temperature
Thermal comfort not only depends on the air temperature and the thermal insulation properties of clothing alone. In fact, more than a dozen other factors, both personal and environmental, play an important role. However, environmental factors are much less important for thermal comfort indoors than outdoors. Indoor clothing does not have to be windproof, waterproof or able to absorb perspiration.
Beyond the air temperature, the environmental factors that influence thermal comfort are the average radiant temperature, relative humidity and air circulation. The last two are included in the definition of the clo value, as it is stipulated that the relative humidity must be less than 50 percent and the maximum air velocity of 6 meters per minute (stagnant air). The wind has a profound influence on the thermal insulation of clothes when we are outdoors, since it alters the layer of insulating air between the skin and the clothes. In indoor environments the movement of air is a factor not to be taken into account, although it should be considered that any air flow can reduce the thermal comfort of a set of clothes.
Radiant heat greatly influences thermal comfort when we are outdoors. Solar radiation can make you feel hot even when the air temperature is low. Indoors, the influence of solar radiation is much less. However, it can positively influence the thermal comfort of the interior, because the sunlight entering the room is absorbed by walls and furniture, and is gradually released. This occurs in passive houses and homes heated by a tiled stove, where radiant heat is an important factor in thermal comfort.
Environmental factors are much less important for thermal comfort indoors than outdoors. Indoor clothing does not have to be windproof, waterproof or able to absorb perspiration.
Together with the “clo value” and the “pumping coefficient”, the third factor that defines the thermal insulation of the clothing is the “permeability index”. The thermal properties of clothing are drastically degraded when wet, either by sweat or by external moisture. This can be very dangerous if you are exercising outdoors in a cold climate because at rest the body, sweaty, loses heat faster than if it were dry, which can lead to hypothermia and cause death. Naturally, the permeability index has no importance for television addicts, they don't sweat and the rain doesn't worry them in the least.
Indoor human activity
The most important factor that influences thermal comfort - even more important than the temperature of the air and clothing - is human activity, that is, the generation of body heat (the metabolic rate). For example, while 12 clo are required in clothing to keep a person at rest warm at an extremely low temperature of -40 ° C, only 4 clo is needed, when, at the same temperature, this person is walking, and only 1 , 25 clo when running at 16 km / h.
One of the most obvious reasons why our ancestors could withstand low indoor temperatures is because they were more physically active than most of us.
It is revealing that one of our cold defense mechanisms is to increase internal heat production. This is achieved first by tensing the muscles and ultimately shivering, these physiological processes, capable of multiplying by five the production of body heat, from 100 watts at rest, to approximately 500 watts.
The metabolic rate also has a profound influence on non-extreme temperatures. While a person at rest (comfortably repanting on the couch) requires a thermal insulation of 2.7 clo at an indoor temperature of 10 ° Celsius (50 ° F), this is reduced to only 1.7 clo if this person is performing a light activity (write, draw or have an animated conversation). In this case, the combination of underwear with the equivalent of a normal suit is enough to keep or heat it.
As a general rule, each 30-watt increase in heat production allows the comfort temperature to drop 1.7 ° C. On the other hand, when sleeping instead of being alone at rest, the necessary thermal insulation doubles - that is, for comfortable sleeping, 2 clo are required at a temperature of 20 ° Celsius. This is the reason why sleeping bags can have a thermal insulation of more than 10 clo.
Other personal factors, other than clothing or activity, may also contribute to thermal comfort. Men seem to tolerate lower temperatures than women, and both young children and the elderly need higher temperatures to maintain their thermal comfort. Research has shown that - even regardless of age and sex - people have different preferences when it comes to the ideal temperature. On the other hand, people also get used to the prevailing temperatures, this is easily appreciated in cultural differences. The clo values that have been established for different indoor air temperatures are no more than guidelines - personal and cultural differences have to be taken into account.
Hands and feet
The "clo value" takes into account the entire surface of the body and therefore includes the transfer of heat through the exposed parts of the body (head and hands, in some cases, also the arms, legs, feet or torso) . Both the insulation provided by the clothing and the skin coverage are determining factors in heat loss. In real life the two are correlated in the sense that winter clothing not only protects us better, but also implies a greater proportion of the body than summer clothes.
The most important factor that influences thermal comfort - even more important than the temperature of the air and clothing - is the production of body heat.
The hands and feet are always the first affected areas when thermal discomfort manifests itself. Together with the head and neck, they lose heat faster than other parts of the body. However, it is important to keep in mind that if the body as a whole is kept warm enough, the hands and feet are not greatly affected by the decrease in indoor temperature.
The cooling of the extremities is another defense reaction of the body, when the internal body temperature drops. This thermoregulatory mechanism - "vasoconstriction" - reduces blood flow to the capillaries of the skin, thereby improving isolation by limiting heat loss. This mechanism affects the entire surface of the body, but due to the small mass / surface ratio of the extremities, vasoconstriction has a more effective effect on hands and feet.
At extremely cold temperatures, vasoconstriction can save our lives - although it could cost us the loss of some fingers and toes, or worse. In order to maintain body temperature (which is vital for survival), the body first sacrifices fingers, toes and nose, followed by the extremities. Because vasoconstriction only occurs when body temperature drops, these dramatic effects do not happen if it is well sheltered.
If we wrap our neck and feet well, we will considerably improve our thermal comfort, making it unnecessary to wear gloves or caps indoors. Actually, it doesn't matter much which parts of the body we choose to isolate - the crucial thing is to limit heat loss, so that the internal body temperature remains stable. For example, if we covered ourselves indoors with a cap of great insulating capacity, we could do without everything else and feel comfortable at low temperatures wearing relatively light clothes.
Is it possible to live without heating?
Of course, this article does not pretend that we completely detach ourselves from heating systems, although in some climates it would be possible - saving not only heating costs, but also the costs of installing heating systems and other investments. However, for many of us, a heating system is still a necessity, if only because sometimes temperatures tend to fall below freezing (the pipes would freeze and maintain full thermal comfort through clothing would be very difficult ).
But even so, the use of thermal underwear would mean a significant reduction in energy consumption making it possible to reduce the average indoor temperature by a few degrees and shorten the heating season by a couple of months.
The potential energy savings, which proper use of clothing would produce, is so great that it cannot be ignored - although, in fact, it is just what happens. This does not mean that efficient insulation and heating systems should not be encouraged. To reduce energy expenditure on heating these three objectives must be pursued, but the improvement of insulation through the use of thermal underwear is obviously the cheapest and easiest to achieve.
A final drawback is that occasional visitors who do not wear these garments may feel uncomfortable even if you and your family are comfortable and may not be very polite to offer you an extra layer of thermal underwear.
