Page 174 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)
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The City & Guilds Textbook: Plumbing Book 1
When a refrigerant gas is compressed, it changes its state to a liquid. During this
process a lot of heat and pressure are generated. When the pressure is released
quickly, it generates cold. Refrigerants’ ability to change their state quickly with
such wide temperature changes allows them to be used in refrigeration plants,
air conditioning systems and heat pumps. The process is known as the vapour
compression refrigeration cycle.
Vapour Vapour
Compressor
Evaporator Fan Condenser
Liquid & vapour Liquid
Expansion valve
p Figure 3.10 The vapour compression refrigeration cycle
The refrigerant vapour enters the compressor, which compresses it, generating
heat. The compressed vapour then enters the condenser, where the useful heat
is removed and the vapour condenses to a liquid refrigerant. From here, the
liquid refrigerant then passes into the expansion valve, where rapid expansion
takes place, converting the warm liquid into a super-cold vapour/liquid mix,
which creates the refrigeration effect. The vapour/liquid mix passes through
the evaporator, where final expansion to a vapour takes place. This then
enters the compressor for the cycle to begin again.
Glycol
Glycol is the name used for solar hot water system anti-freeze solution. It
is used for protecting solar panels from freezing during the winter when
mixed with water in the sealed solar panel circuit. It is available in two forms:
propylene glycol and ethylene glycol. Propylene glycol is the preferred chemical
for solar panels as ethylene glycol is highly toxic. The anti-freeze should be
checked regularly as its anti-freezing capability diminishes with time and the
solution can become corrosive with age.
Fuel oils (kerosene)
Kerosene is a fuel oil that is used with most domestic oil-fired boilers (see
Chapter 7, Central heating systems, page 461). Kerosene is a thin, clear liquid
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