Cool Comfort: Hamming it up with Nature
by: Paul Kando
When sunshine arrives on Earth, most of it turns into heat. The atmosphere traps enough heat to keep the planet's climate temperate enough to sustain life. And when things overheat, mother nature has a simple 3 step way to cool things down: 1. When water absorbs heat, it evaporates. 2. When air is heated, it becomes lighter, so it rises. 3. And since the warmer the air, the more moisture it can hold, the rising air takes with it both the water vapor and the heat of evaporation. That heat is taken from the surroundings, cooling them down.
It takes a lot of heat energy to turn liquid water into vapor, close to a thousand BTUs per pound of water. This is why evaporating water is a good way to cool things. When Hurricane Katrina passed over the warm waters of the Gulf of Mexico, it absorbed a lot of heat energy, fueling the monstrous, Category 5 storm that hit New Orleans. Meanwhile the Gulf's waters lost so much heat, that the Gulf cooled almost 5 degrees. Perspiration is another example: moisture from the skin evaporates, takes heat away and cools the skin.
photo credit: glazedhamsandmore.com
Perspiration is another example: moisture from the skin evaporates, takes heat away and cools us. Heat, Air and Moisture (call it the "HAM principle" to make it easy to remember) interact constantly in nature. They create our weather, determine our climate and even regulate the growth of plants.
Not surprisingly, our home also operates according the HAM principle, where our comfort depends on how well we are able to work in concert with its dictates: 1. If you are absorbing heat from the warmer air around you, you feel warm; if you are losing heat because the surrounding air is cooler, you feel cool: the air temperature has a lot to do with comfort. 2. If heat is radiating toward you (e.g. from a wood stove), you will feel warm, if you are radiating heat to a cold window nearby, you will feel cold. All objects in the universe radiate heat toward other objects that are cooler. Our bodies are no exception. So, radiant temperature is another factor in our comfort. 3. If moisture is moving toward you, you will feel warm, if it moves away from you, you will be cooled: Air movement and, with the air, the movement of moisture it has absorbed are another factor. 4. Moisture: are you absorbing or losing moisture? If the relative humidity is high you generally will feel warmer than if the humidity is low, even if the temperature in the room is exactly the same. 5. Finally, your comfort (not to mention your health) depends on good air quality: air to breathe that is clean and free of mold, pathogens and chemical pollutants.
In general, we are comfortable when the temperature is around 70° and the relative humidity around 50-60%. Therefore, in the heat of summer, we want our homes to be cooler and drier than the outdoors. In winter we want the opposite. The trick is to control heat flow, air flow and moisture flow in our houses, without fouling up the air and without wasting energy.
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Heat flows in three different ways: conduction, radiation and convection. The first two can be controlled by insulation. The third, convection, takes place as heated air becomes lighter and rises, taking with it the heat it has absorbed. This heat flow cannot be controlled by insulation. This is why, on a freezing winter day, it is not enough to wear warm sweaters. We must also have on a windbreaker to stop the cold air from flowing through to our skin. Likewise, in a house we must stop the heated air from flowing out by blocking its path. Luckily, blocking the flow of air will also block the flow of heat and moisture absorbed in it, simplifying our task.
Older houses built by traditional methods don't do any of this very well. In fact, they side-step all the real issues mentioned here with the rallying cry "houses must breathe". Indeed, when houses do breathe, the air quality will be reasonable and much of the moisture in the indoor air will eventually escape to the outdoors. The problem is that so will the heat. In effect the house - and its occupants - will be cooled all winter long according to mother nature�s well established HAM principle.
We used to deal with this problem by adding more heat, by burning more fuel. We cannot afford to do this any longer for several reasons: Fuel keeps costing more and more as growing demand outstrips a shrinking supply, We are forced to rely on distant, foreign fuel supplies we can only access at the heavy price of a foreign policy that causes people around the world to hate us and wish us harm. And we are learning that fouling the atmosphere with the carbon we emit by burning fuel oil damages the very climate we depend on to live and prosper.
photo credit: Habib Dagher, University of Maine, Orono
Most of us would agree that to keep filling a bucket with a hole in it is not a very clever way to try to deal with the loss of water. Better to plug the hole. The same is true of our leaky homes: the energy we pour into them just keeps leaking away. Fixing the problem begins with plugging all the leaks. But to be able to do that, we have to know where the leaks are, how big they are and how best to fix them. Our need for clean, fresh air also presents a dilemma: how much can we tighten our house before we create an unhealthy place to live? Does keeping more of the heat inside not also mean accumulating more pollutants? Such questions demand reliable answers before we tighten our houses. We need to know the right combination of things we must do to come up with the best results.
To be sure, there are general rules that apply to every house, but they can carry us only so far. It is beyond question, for instance, that windows lose air faster than the surrounding walls. Therefore, installing insulating window inserts you can make yourself is always a good investment. And it is a no-brainer that if a house leaks so badly that you can feel the cold air rush at you as you watch the curtains move in response to the wind outside, it must be sealed and tightened. But where is the point when tightening leads to other problems, such as unhealthy indoor air?
Questions like this can only be reliably answered by an energy audit, which measures and tests your house in several ways and analyzes the results, in light of all we have discussed above. The report and recommendations that result will present you with the best, safest and most cost-effective course of action to take, tailored to your needs, your house, and your specific circumstances. For more on energy audits and resources that can help you have a comfortable home without wasting energy, check out the rest of our site.