Heat transfer obeys natural laws just like water obeys the law of gravity. You cannot change these natural laws but, you can “do some work” to reduce your energy bills.
We all know that water flows down hill. If you want water to move up hill you have to “do some work” to get it there. If you do not want water to flow down hill you have to “do some work” to stop it like building a dam. “Doing some work” is like paying your energy bill because it causes some discomfort.
The first thing you need to know is that heat naturally flows from a hot area to a cold area.
Heat moves in three ways
One way heat moves is radiation. We all know that if we are exposed to direct solar radiation we can feel the heat from the sun flowing directly to us. The sun is very hot so the heat flows from the sun to the earth. Sunburn is the result of solar radiation.
The second method of heat movement is called conduction. Conduction describes heat moving through a solid. The handle of an iron fry pan gets hot by conduction. We insulate our house walls and attic to slow down the conduction of heat through the structure of the building.
Convection is the last type of heat transfer. Convention refers to moving heat by moving either air or a fluid that has been heated.
An example of convection that we use to heat our houses is a forced air furnace. The furnace heats air that is pushed through the house, by a blower, to heat up the house. This movement of warm air is an example of convection. Heat is carried, by the air, from the furnace to the house.
Convection can also work against us. An example is warm air flowing up a chimney that conveys heat out of a house in the winter.
In the summer, we have more heat than we want in our living spaces. We force heat to move the wrong way by taking heat out of our houses and putting it out in the hotter outdoors. This takes a large input of energy to accomplish because we are “doing some work” against the normal flow. It is like pushing water up hill, it takes a lot of energy.
In the summer our furnace fan, moves warm air to the cold coil inside the ductwork. This is convection, using air, to move the heat from hot to cold.
Energy Saving Action Items
Heat flows into our homes when it is hotter outdoors, than indoors. We can slow it down by shielding and insulating our house. Shielding and insulation is like building a dam to delay water from flowing down hill.
By shielding, I mean shade trees and radiant barriers like aluminum foil or special paint. Shielding that either blocks the sun or reflects radiant energy back where it was coming from stops the sun’s rays from heating our houses. Solar window screens act as partial sun blocks. Reflective radiant barrier materials act like a mirror and reflect or deflect radiant heat away from your house. Reflective film on windows works this way.
We want the solar radiation to hit our houses when it is cold outside in the winter. Planting trees that give summer shade and let the sun shine in during the winter are a natural way to have seasonal shielding.
The other way heat travels is by conduction through materials. Insulation acts like a speed bump slowing down the movement of heat through materials like roofs, ceilings, floors and walls. The more insulation you have the slower the heat moves. The R number rating on insulation materials indicates how well they resist the conductive flow of heat. The higher the R number the more it slows down the flow of heat. For more information on this read my articles about insulation.
We like convective heat transfer when warm air moves from the furnace through the house. We also like it when warm air moves from the house to the cold coil of the air conditioner. We do not like convection when it helps heat escape up the chimney, around windows, or under doors.
Saving energy means having high efficiency equipment to move heat only to where we want it to go. It also means doing the best possible job of blocking or slowing down the movement of heat where we do not want it to go.
Improving your home’s weather sealing, radiation shielding and insulation are some of the very best things you can do to reduce your energy bills.
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