C
Calorific value (kWh/kg or kWh/m3;
MJ/kg or MJ/m3)
The energy content per unit mass (or volume) of a fuel released in combustion.
Canadian well (or Provençal well)
The Canadian well consists of passing a proportion of fresh air through pipes
buried in the ground, before it enters the house. The principle is to make passive
use of geothermal energy.
A PVC or baked earth pipe is inserted in the ground at a depth of about 2m. Typically, its diameter will be between 20 and 30 cm, one of its ends is open to outside air, and it is provided with protection against water, insects and rodents. The other end may be fitted with a circulating fan (15 W for 200 m3) and carries air inside the room.
In winter, the soil at this depth is warmer than the outside temperature, and
therefore the cold air is preheated as it passes through the pipes.
In summer, the soil is colder than the outside temperature, and therefore, the
well will make use of the relative coolness of the ground to moderate the temperature
of the air input into the residence.
Some rules have to be respected to make sure that heat can be exchanged correctly between the ground and the air:
Candela (cd)
Candela is the unit of luminous intensity. The luminous flux emitted by a wax
candle to a solid angle equals approximately 1 cd.
Casual gains
See Internal heat gains.
Clear sky
In any month, the sky conditions producing the mean maximum daily global radiation
on a horizontal surface.
Clo
A unit measuring the thermal
resistance (or insulation value) of clothing.
1 clo = 0.155 m²K/W.
Closed-loop system
A system in which solar-collector air circulates in a closed channel between
the collector and heat storage or radiating surface. Room air does not enter
the system, as is the case with an open-loop system.
Coefficient of performance
(COP)
The coefficient of performance for a system is the energy output divided by
the energy input, i.e. for a heat pump this would be kWh heat output per kWh
electricity input (3-4 is a realistic range). For a solar air system the COP
is kWh hot air output per kWh electricity consumed by the fan/s (15-30 is possible
according to monitored projects).
Cold bridge
See Thermal bridge.
Color
Color is a sensation, this means a physiological process in the brain. The electromagnetic
spectrum from 380 - 780 nm wavelength is percepted as light by the eye:
magenta | at appr. 410 - 440 nm | ||||||||||
blue | at appr. 440 - 490 nm | ||||||||||
green | at appr. 490 - 540 nm | ||||||||||
yellow | at appr. 540 - 600 nm | ||||||||||
orange | at appr. 600 - 630 nm | ||||||||||
red | at appr. 630 - 770 nm |
A mixture of wavelegths from 400 to 700 nm causes the sensation of 'white'
light. The color 'brown' is a dark orange and the color 'black' is simply missing
light, that means no radiation within the visible electromagnetic spectrum.
Combustion air
The air required to provide adequate oxygen to fuel-burning appliances.
Comfort zone (usually with reference
to thermal comfort)
The range of values of the environmental variables, sometimes expressed in the
form of a temperature equivalent, the combined effect of which is perceived
as comfortable or acceptable.
Condensation
The deposition of moisture held by the air in a room onto an internal surface.
This occurs when the temperature of a surface is below saturation
point relative to the water vapour content of the air, i.e. too low to hold
the moisture in vapour form.
Conduction
Mode of heat transfer within or between materials at different temperature involving
transmission of kinetic energy at molecule level; the rate of heat transfer
depends on the thermal
conductivity.
Convection
Mode of heat transfer in fluids (air or water) or between a surface and adjacent
fluid due to difference in temperature.
Conventional heating
See Auxilliary heating.
Conversion
The changing of a substance or the energy in it from one form to another.
Conversion loss
the amount of energy lost in the changing of one form of energy to another form.
Much of this energy loss is in the form of waste heat.
Conversion efficiency
The percentage of usable energy that is left after an energy conversion.
(Efficiency = Energy output / Energy input).