Page 178 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

3 THE RELATIONSHIP BETWEEN

ENERGY, HEAT AND POWER

The relationship between energy, heat and power is such that it is almost
impossible to have one without the other two. Below is a list of units for
energy, heat and power.

l The unit of power: the watt is the SI unit for power. It is equivalent to one
joule per second (1 J/s) or, in electrical units, one volt ampere (1 V·A).
l The unit of heat: the joule is the unit of heat; 4.186 joule of heat energy
(which equals one calorie) is required to raise the temperature of 1 g of water
from 0°C to 1°C.
l The unit of energy: also the joule (see above).
l Specific heat capacity: the specific heat capacity of a substance is the
amount of heat required to change a unit mass of that substance by one
degree in temperature. It is measured in kilojoules per kilogram per degree
celsius (kJ/kg/°C).

Heat energy is transferred because of temperature difference – for example,
heat passes from a warm body with high temperature to a cold body with low
temperature. The transfer of energy as a result of the temperature difference
alone is referred to as heat flow. The watt, which is the SI unit of power, can be
defined as 1 joule per second (J/s) of heat flow.
In this part of the chapter, we will investigate the energy/heat/power/temperature
DEGREES
relationship, and its implications for the building services industry.
Celsius Kelvin Farenheit
100 373 212
Temperature

Temperature is simply the degree of hotness or coldness of a body or environment,
and is expressed in terms of units or degrees designated on a standard scale,
0 273 32
usually celsius (centigrade) (°C) or kelvin (K).
Celsius (°C)

This scale, using increments of 1 degree (1°), is the most widely used by the
- 100 173 - 148
building services industry. In simple terms, it has a zero point (0°C), which
corresponds to the temperature at which water will freeze. When this scale is
used, the degree symbol (°) should accompany it, i.e. 21°C.

- 200 73 - 328
Kelvin (K)
This has the same increments as the Celsius scale, but has a minimum temperature
- 273 0 - 460 that corresponds to the point at which all molecular motion will stop. This
temperature is often called absolute zero and is equal to −273°C. Therefore:
C K F
p Figure 3.11 The relationship l −273°C = 0K, or
between celsius, kelvin and
fahrenheit l temperature K = temperature °C + 273.
The degree symbol (°) is not used when using the Kelvin scale, i.e. 21 K. The
two scales (C and K) are, for the most part, interchangeable. The SI unit of
temperature is the kelvin; however, when discussing temperature difference,

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