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).