Decentralized Poly-generation of Energy: Basic Concepts - Design for Micro-Combined Cooling, Heating and Power Systems - page 35

If it is thermal, the calorie is used additionally. A calorie (cal) is the quantity of
energy necessary to raise the temperature of a gram of pure water by a Celsius
degree, or the quantity of energy lost by a gram of pure water, in which case
temperature decreases by a Celsius degree. The conversion is 1 cal = 4,184 J.

￿

On the other hand, in many areas of the Anglo-Saxon world, especially in the
United States, the temperature scale used is that of Fahrenheit ( ° F). The melting

temperature of pure frozen water at sea level is of 32 ° F, and the boiling point of

pure liquid water is of 212 ° F. Thus, 32 ° F corresponds to 0 ° C and 212 ° F cor-

responds to 100 C.

In the same areas, the BTU (British thermal unit) is used to measure thermal
energy. A BTU is the energy necessary to raise the temperature of a lb of pure
liquid water by a degree Fahrenheit. The conversion is 1 BTU = 1055 J. The energy
transfer rate (the power) is de

° C. As a result, 1 ° C = (5/9)(F 32) ° For1 ° F = (1.8 - 32 ° C) °

−

ned as 1 BTU/h = 0.293 W. If the useful energy is
electric, its unit is Wh. The conversion is 1 Wh = 3600 J.
(b) If the energy units are de

ned in keeping with the primary energy of the

source, they depend on the calori c power of the fuel used as reference. Thus, if it is

petroleum, the unit is the petroleum equivalent kg, whose symbol is kg oe.
Changing the nature of the reference fuel changes the energy unit. For example, kg
is used for coal and m 3 gas equivalent is used for pit gas. Table 1 presents the
conversion factors for energy units in different systems of measurement.

1.3 Energy Conversion

One of the fundamental laws of physics is the law of energy conservation, according
to which, in physical processes, energy cannot be created or destroyed, increased or

Table 1 Conversion factors for energy
Units m 3 gas kJ kcal kWh kg ce kg oe BTU

1 kilojoule (kJ) 1 0.2388 0.000278 0.94781

0.000034 0.000024 0.000032

1 kilocalorie
(kcal)

4.1868 1 0.001163 3.96831

0.000143 0.0001 0.00013

1 kilowatt-hour
(kWh)

3,600 860 1 3412

0.123 0.086 0.113

1 kg coal
equivalent (kg ce)

29,308 7,000 8.14 27,779

1 0.7 0.923

1 kg oil
equivalent (kg oe)

41,868 10,000 11.63 39,683

1.428 1 1.319

1m 3 natural gas 31,736 7,580 8.816 30,080

1.083 0.758 1

1 British thermal
unit (BTU)

1.0551 0.252 0.000293 1

0.000036 0.000025 0.000033