making ice and staying warm

Benton Lake on the Bootlegger Trail was one of my three standard observing sites.  Great Falls, with about 60,000 people, had too many lights for amateur astronomy so I had to drive to find a dark sky.  Over time I came to learn Benton Lake's microclimate.  On clear nights from May to October the wind would often drop to dead calm a few hours before dawn and the atmospheric turbulence would drop making the sky very transparent.  It was worth reasoning with the alarm clock at 2am. (the area also preserves a lot of real prairie - something rare these days - along with some great bird watching.  The dawn chorus on the lake in the Summer is amazing)

 

These transparent nights often felt chilly - much cooler than it had been a few hours before.  I'd be dressed for the cold, but you would feel it on your face.  The air temperature could be 45°F, but it almost felt like freezing.  One night I looked up at the sky holding a notebook to estimate a distance.  My face felt warmer.  Moving the notebook away instantly brought the cold back.  Radiation cooling.

 

Physics tells us heat moves from warmer to cooler bodies.  It can be transferred by conduction when the bodies are in contact, by convection when a fluid like air or water transfers the heat or by radiation.  In this case we're talking about thermal radiation - any object with a temperature above absolute zero gives off electromagnetic radiation - the wavelengths are determined by the temperature of the object.   You happen to be a radiant being.   Your skin gives off infrared light in a spectrum that peaks with a wavelength around 9.4 microns - compared to visible light which ranges from 0.4 to 0.7 microns.¹  Standing outside my skin was losing heat mostly to local air - mostly moisture in the air.  On very transparent nights there is little moisture in the air.  Some of the radiation from my face gets transferred directly to space, which is very cold.  By holding up the notebook I'm sending my heat to the notebook rather than space.  

 

This was neat.  I measured a nearly 10°C temperature drop from air temperature.  For fun I decided to see if I could make it.  I made a shallow insulated basin out of an old pan that I surrounded with straw and styrofoam - anything I could find to insulate it from the warmth of the ground.  My Montana record for making ice is an air temperature of 6°C - about 43°F.² 

 

Although radiation heat transfer is an important mechanism for transferring heat, we tend to think of convection when it comes to home heating.   I'm reminded of that now with our first heating days of the season and  some video calls with a friend in London.  Her place has poor heating and she's often buried under a blanket or some other form of insulation.  I'm warm enough with a furnace and forced air heating, but it heats a large volume that is mostly unused.  

 

A variety of fixes are possible.  With new housing it is now possible to create very comfortable spaces with very little additional energy input.  The problem is these designs require new construction and house lifetimes are close to a century.  Most of us will never have that option.  Instead we look for easy fixes.  

 

The first order of business is to find air and seal air leaks - they're a convective loss. Weatherstripping is inexpensive and easy to apply.  Microclimates can be created in rooms where you tend to sit - in the 19^th century screens were used to block air loses and people sat in hooded chairs facing a fireplace.    Expanses of glass, if they aren't taking in a lot of sunlight, allow heat to transfer from objects in a room to the colder outside.  Insulated glass is expensive and not terribly efficient, but curtains work well - particularly at night. 

 

Using less convention heating and more radiation.  Usually this means electric IR heaters with glowing elements.  They use short wave infrared radiation - it can burn human skin is generally uncomfortable.  In the past decade longwave IR heaters have appeared. They put out heat close to body temperature and are quite safe.  A huge advantage is you can point them at an area where you happen to be living.  They're finding use in some exercise and yoga establishments - usually in the ceiling looking down or on walls.  

 

That leaves nanoclimates.  ARPA-E has several projects that try to heat or cool where people are rather than unoccupied areas.  There are some exotic ideas like active and passive smart fabrics, but in the meantime you can build your own nanoclimate using the conventional technology of insulated clothing.  Room temperature is usually quite a bit cooler than our skin temperature, but feels comfortable given the metabolic heat our body needs to get rid of and the average amount of clothing we wear.  By wearing extra insulation you can turn the thermostat down and remain comfortable.

 

I've done a bit of hunting but there doesn't appear to be much research documenting indoor Winter temperatures in the years since WWII.  The little that has been written suggests shirt sleeve temperatures for sedentary behavior is recent - perhaps only during the past 30 years.  In Northern Europe sweaters were almost universally used indoors as recently as the 70s.   

 

Air happens to be a poor conductor of heat, so trapping it close to the skin creates a good insulator.  In fact the insulating property of clothing can be measured.  The most popular unit is the clo (guess where the name came from?).  It isn't a standard, but is easy to understand - 1 clo is the insulation equivalent of underwear, socks, and a business suit.³ 

 

You can get into the calculations, but sitting and watching TV might be comfortable at 21°C (70°F) with 1 clo of clothes.  Assume part of that is a heavy sweater (about 0.3 clo) - take that away and you need nearly 24°C (75°F) to remain as comfortable.  Long underware is great - about 0.7 clo. You should be ok watching tv in good comfort at 17°C.  Here you have to think about warm socks or booties.  Cooler still perhaps a warm cap.   The other trick is to be physically active.  Don't worry about calculating values - just experiment!⁴

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¹ The spectrum for a blackbody at skin temperature.  You're not a blackbody, nothing is, but this is close enough.  This can be detected with infrared cameras which color code different wavelengths giving a sense of surface temperature.

 

There is a very strong temperature dependence in this curve ~ T⁴.  To calculate heat transfer you get some constants times (T⁴_hot - T⁴_cold).  Note that you need an absolute temperature scale where T_{absolute zero} = 0° ...  the Kelvin scale is appropriate. 

² I suspect I was doing even better one night in Taos.  It was late Spring with a strong of beautifully still and transparent nights.  I borrowed a pan and insulated it to the consternation of the B&B host.  I couldn't verify the air temperature, but there was  excellent ice production with a likely air temperature above 40°F.  Much more fun than the conference.

If you live in an area where this happens frequently it would be possible to build a more powerful 'freezer' - just increase the area of sky visible to the water container.  Think about a solar stove, except now the heat is transferred from the pot to the sky.

³ Roughly.  It is formally defined as a thermal resistance of 0.155 m²K/W.  Europeans use something similar called a tog (again, guess where the name came from) which is about 0.65 clo.  You can also compare it to R values - 1 R is 1.137 clo.  

Many clo values for conventional clothing (not exotic thermal underware)

⁴ There are new fabrics that are much warmer, more flexible and comfortable per unit weight than even a decade ago.  Check into outdoors clothing and look into what sedentary outdoor types (hunters) wear underneath their coats.  Some have clo values of 0.6 and adding a second layer traps even more air than two single layers given a combined value of 1.5. Wear this under normal clothing or even with a sweater and you can survive in a very cold room.  I used this approach to survive Sandy and an indoor temperature that dropped to 47°F (about 8°C) - not much warmer than the average refrigerator.  You do need a cap at these temperatures. 

I find a heavy sweater combined with modest moving around (not much more than being sedentary works well at 68°F.  At night I can drop to 62° at night with normal bed covers.  The fact leaks have been mostly sealed makes this even more comfortable.  When guests are over the heat gets cranked up to 72° - you get used to the lower temperatures.

In the US the idea of conserving in the home or while driving became a political issue around the time of Jimmy Carter.   Given the amount of personal conservation practiced during and before WWII there are probably some very interesting cultural issues at work.

 

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Recipe corner

 

Some comments on processed meat, red meat and cancer. This is old news.  Both processed meat and red meat have associated with increased cancer risk, but suggesting a causal link is extremely difficult in human studies.  Something has to have a very high mortality rate or have a good association over many studies and even generations of subjects to be considered causal.  At the same time other genetic risks tend to be much greater and probably modulate dietary risks.  The bottom line is that eating these foods may well elevate your risk, but that is a probability.  The risk elevation was found to be 18% if you regularly have about two ounces of prepared meat.  In real risk your chance of getting colorectal cancer goes from about 4.5% to 5.5%.  

Unless you have other risk factors the only behavior change may be between none and moderation.  If you're looking for an excuse to cut back on meat products, this may be a good one - otherwise just realize that all of us have a lot of risk factors with some of the largest being  out of our control.

A comment that might be useful.  Plant-based foods have been shown to be protective against cancer.  People who eat a lot of meat tend to eat less plant based foods.  The studies corrected for this, but you can improve your overall odds by moving to more of a plant-based diet.

 

 

 

Comments

[Jheri]

I live mostly in Paris and København. It is very common to keep a place on the cold side and dress appropriately indoors. During the day my thermostat is Paris is set for 18°. In København it has a North facing window plus it is alway cloudy so it is more like 20°. At night it is much lower. Visiting America in the Winter seems wrong. People dress like it is Summer and complain about the cold. You can buy some very nice sweaters and stockings for the difference in price.

[steve]

I grew up in the 60s Jheri. It was common and necessary to keep the house cold during the Winter. The thermostat never went past 60° (16°C) when I was a teenager. There was a small family room that was well insulated and had a small radiant heater. Four people and three dogs would spend much of their evenings there .. it would get toasty. This was just common sense at the time - no one would think of spending large amounts of money heating parts of a house you didn't need or heating to a level that a sweater or long johns could easily get you to.

[Steve]

Two readers had comments and and questions on low energy techniques for staying comfortable in the Winter. There are big payoffs heating mostly areas where people stay. I had forgotten about Kotatsu warming tables.

In Japan traditional wooden houses sometimes use a special warming table that becomes a center of family life during the Winter. The Kotatsu tables have a small built-in heater of 400 to 600 watts and are covered by an insulated quilt. I've seen and even used one without knowing what it was. When I was a teenager a neighbor one. She was Japanese and he had spent several years in the service working on a radar installation on the Northern tip of the Japanese Island of Hokkaido.

http://astrobeano.blogspot.no/2014/01/kotatsu-made-in-scotland.html

The downside is it would encourage sedentary behavior so perhaps a standing table variation is in order. You could wear a big quilt at a standing desk. Body heat should be sufficient with a good insulated quilt. Perhaps a Stay Puft Marshmallow Man theme?