Sandra wrote:
>I am both interested and lacking in knowledge, so if you like to talk
>about it, I'll listen.
Well . . . Here's a little more about the differences between radiant and
covective heating. And why I think radiant heaig is preferable. Excuse me
if I repeat a little from an earlier post; I'm trying to make it all make
sense. Hope it does. : )
First a few defintions of the differnent types of heat movement:
Conductive heat is heat that moves from one substance to another by
transfering heat through contact. Like a pot on the stove getting hot by
being in contact with the flame, or the water in the pot getting hot by
being in contact with the pot.
Convective heat is heat that moves within a substance in currents, heat
rising and cold falling. Like the water in the pot that gets hot
throughout because of the rolling currents.
Radiant heat is heat that moves from one substance to another by radiating
energy to other objects in line of sight. As the air in between has little
substance, it is not heated much by the radiated energy. Like the heat you
feel against your face when you sit near a fire, or the heat you feel from
the sun.
With typical house heating systems the goal is heat a lot of air to a high
temperature and circulate it through the space (convective heating). The
heat is created by transfering heat from fire or electric element to air
(conductive heat) and circulate the air by mechanical means (fan) and
natural convection currents. Older homes, in my area at least, had
furnaces under the floor, and the heat naturally rises up and circulates
through the house as best it can. This at least eliminates some of the
mechanical energy needed. Some of the problems of convective heating are:
Air is a good insulator, so it is difficult to heat. Air movement can
become uncomfortable as with draughts. Dust and other nasties can be blown
around the house. To feel warm the air around your body must be about 70
degrees, which means the air higher up near the ceiling can be 100 degrees
and your feet are still cold. This is inefficient because there is a
greater temperature difference between the air inside (at the ceiling) and
the air outside (or in the attic, upstairs rooms or apartments) the more
heat goes through the insulation to the outside.
Radiant heating does not try to heat the air. Instead, it heats the
objects in the room directly. Heat radiates from a warmer mass (wood
stove, solar or water heated floor, sun, etc.) to cooler masses (bodies,
furniture, walls, etc.) as long as something does not block the energy
(like a shadow does with light). This is why it is best to centrally
locate your wood stove and why the rooms that get the sunlight are the ones
that are warmer. Think of a campfire outside on a cold evening. The fire
can warm you, as long as someone isn't sitting in the way : ), without
heating all of the air around you. It isn't the air temperature that makes
you feel warm; it is the radiant heat from the fire. In a house heated
with radiant heat (wood stove, solar heat, heated floors, etc.) the warm
mass heats your body and the other objects in the house directly. Since
the air is only incidentally heated (by conductive heat, air touching warm
objects) it does not get very warm, except in the case of a high
temperature masses (wood stove) that the air can touch. Solar and hydronic
radiant heating use of a lot of low temperature heat(?), rather than a
little high temperature heat, which is more efficient since the air
temperature stays low meaning less heat loss through the insulation. It is
also easier and more efficient to make, transfer and move low heat, since
less is lost each step of the way. Radian heat can also eliminate the need
to move the air around making a more comfortable and healthier environment.
With warm floors (solar or hydronic) the heat is relatively even from the
floor to the ceiling which is more comfortable, eliminating cold feet when
the air above your head feels like the tropics.
So, for these reasons - which I hope make sense to somebody - I think
radiant heating deserves strong consideration in house heating and design.
That's it for now
Eric:
