Saturday, May 16, 2009


I've already written about the rule of three in two previous posts (5/7/09 and 5/10/09). But the rule of three only covers air, water, and food. Survival without any heat is not something we'd be dealing with, since that would indicate a temperature of absolute zero. Therefore survival under conditions of cold (ie, freezing to death) depends greatly on the temperature, clothing, and body mass/condition. Still, if I could make a huge generalization, following the rule of three, I'd say that human beings could last three hours without sufficient warmth--which would put warmth after air but before water and food in terms of necessities.

The first and most important source of warmth for human beings is our own body heat, which comes from the stored energy (aka calories) in food, which ultimately comes from energy stored by plant which they get from photosynthesis. I was at a workshop on solar power a few weeks ago where the instructor (George M, a long time solar enthusiast--see his blogs at solarray and Daily Kos) asked how many of us now use solar power. Only a couple of people raised their hands. He announced that the rest of us were liars--we all use solar power; all of the energy that we use to live and move comes from the sun via plants (as I outlined above).

How much warmth do we generate? Considering the normal body temperature is 98.6 (Farenheit), a lot. The problem is that we lose that heat quickly as it radiates off our bodies. This is why clothing and blankets keep us warm: they hold in the warmth that is generated by our own bodies. In very well sealed and insulated buildings, the very presence of people can warm the building. One company used to have radio ads on ways people could stay warm and one of them suggested throwing a party with lots of people and everyone dancing and moving and giving off lots of heat. Since exercise uses more energy, you give off more heat when you are exercising (which is why you can feel hot running around on a cool day).

So a lot of the principles of staying warm are about conserving energy. I will talk more about this when I get to my posts on temporary and permanent shelter.

Since the sun is our main source of energy, it makes sense to talk about ways to use solar energy for heat. George, our instructor for the workshop on solar power, claimed that the basic principles of solar energy were easy: black/dark materials absorb heat, white/light/silvery materials reflect heat, and clear materials let in the heat but protect from wind.

The simplest device he showed us was a solar cloche that he made from old soda bottles. (He also made a video of it.) It doesn't warm us, it warms our plants--by surrounding plants with bottles filled with water. The sun heats the water, which slowly gives off heat.

A little more complicated (but not much) is the Windowbox Solar Air Heater that he's made from about a hundred dollars worth of materials (most of the expense is the insulation board he uses to make it). A bigger version of this could heat a house (and, in fact, we have a type of this on the house I presently live in).

These are basically examples of passive (with the exception of small fans) solar power. Passive solar doesn't use much in the way of moving parts and doesn't need mechanical or electrical devices to keep it going, so it's cheaper and more reliable--and lasts much, much longer than conventional or even active solar power.

One of the most important things to keep in mind for passive solar heating is using materials to store heat--this is known as thermal mass. It can be as simple as dark rocks or a dark stone or concrete wall that absorbs heat and gives it off later, when the sun goes down. (Things filled with water can work similarly, as in the solar cloche above.) Bioshelters (solar greenhouses) use these principles.

Solar energy can also be used to make simple ovens and cookers. They are being used extensively in developing countries, but more affluent areas may need to learn these tricks as they become less affluent. My favorite is making a parabolic cooker out of an old satellite dish.

The most common ways of generating heat (for cooking or keeping warm) in western societies is through the use of fossil fuels. Sometime electricity is used for this process, which is a very inefficient method--my rule on electric use is: electronics (computers, tvs, radios, etc) use the least, followed by motors, followed by lights, followed by heating--in other words, using electricity to heat (or cool) something is the least efficient way of using it.

Because fossil fuels are going to become harder to tap and more costly, I want to look at nonfossil fuel methods of generating warmth. One of the most common methods of creating warmth before the use of oil and gas (and still quite common today) is burning wood.

Henry Ford suggested you should “Chop your own wood, and it will warm you twice.” Although wood is a renewable resource, there are limits to how much it can be exploited. Forests have been clearcut for firewood. In addition, wood smoke contributes to global warming (sending carbon into the atmosphere) and can be a major air polluter. I remember seeing bumperstickers that said 'Split Wood, Not Atoms' in the Connecticut River valley in the seventies. It seemed unlikely that a lot of people would do that, but woodstoves did become popular. Twenty years later there were winter days when a haze of woodsmoke would hang around valley towns.

If you are going to heat with wood, try to use an efficient method. Pellet stoves generate less biproducts compared to regular wood stoves but wood pellets do release more particulate matter and whether they contribute less to global warming is debatable.

Another efficient way of burning wood is in a 'rocket stove'. These produce less pollution than a regular stove and can be simply made using low-cost materials.

Biogas is another fuel source. While typically thought of for powering vehicles, it can be used for heating as a replacement for natural gas.

Geothermal heat uses the natural heat of the earth (as well as the heat stored by the earth from the summer solar warming) to warm homes and buildings.

Compost heaps can also be used to heat greenhouses and other things.

It's strange to be posting on this as the summer is coming and it's getting warmer, but winter will return, and given the probability of rising oil prices in the future, we may all be looking for new sources of warmth.

Bruce Anderson and Malcolm Wells, Passive Solar Energy--Contains lots of information on solar basics, solar windows, solar chimneys, solar walls, solar roofs, solar rooms, and even passive solar cooling systems--plus cute drawings by Malcolm Wells--available from BuildItSolar as a free download--the BuildItSolar site also has a mammoth amount of information on do-it-yourself solar projects
Ken Butti and John Perlin, A Golden Thread--Solar energy isn't a new idea--this book documents '2500 Years of Solar Architecture and Technology'
eHow, How to Build a Compost Heat Exchange System--Step by step instructions on how to use compost to heat water
Franklin Research Center, The First Passive Solar Home Awards--A book from 1979--apparently there were no more awards--published jointly by the US Departments of Housing and Urban Development and Energy--contains an enormous number of examples of passive solar with basic diagrams for each
Scott Kellogg and Stacy Pettigrew, Toolbox for Sustainable City Living--The chapter on 'Energy' contains information on creating Biogas, Passive Solar, and Rocket Stoves--and the passive solar section contains information on how to create parabolic solar cookers
Helga Olkowski, Bill Olkowski, Tom Javits and Farallones Institute, The Integral Urban House--Contains a chapter on Solar Technology that includes Window Box Collectors, Thermal Storage, Trombe Walls (thermal collecting walls), and using Attached Greenhouses--this book has been recently re-issued by New Society Publishers
Ray Wolf, Gardener's Solar Greenhouse--Contains step by step construction plans for building a solar greenhouse--may be out of print--check your local library

Quote of the Day: “Pour down your warmth great sun!” - Walt Whitman


SoapBoxTech said...

I love wood stoves and fireplaces. Luckily we had land with plenty of deadfall. Enough that I am clearing it out now and cutting the wood up into firewood to sell. Still plenty left to feed the forest floor though, since we've haven't been burning wood for awhile and there seems to be a lot of deciduous trees dying off.

This is an even more interesting post since I have been working on a greenhouse design for year round operation, based on compost heated water. Maybe I am too late...

MoonRaven said...

Thanks for your comments, SBT. I'm glad you're able to do some of your heating with wood. I hope that all the deciduous trees dying off isn't the sign of something bad happening in your woods.

I'd love to hear more about your greenhouse design...