Page 503 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 7 Central heating systems

so as to ensure that the boiler does not fire when there is no demand for
heat. In a system with a combi boiler this can be achieved by fitting a
room thermostat. In a system with a regular boiler this can be achieved
by correct wiring interconnection of the room thermostat, cylinder
thermostat, and motorised valve(s). It may also be achieved by more
advanced controls, such as a boiler energy manager. TRVs alone are not INDUSTRY TIP
sufficient for boiler interlock. A free copy of the CHeSS
Note 2 (from CHeSS): An automatic bypass valve controls water flow in specifications is available at:
accordance with the water pressure across it, and is used to maintain a http://bpec.org.uk/downloads/
minimum flow rate through the boiler and to limit circulation pressure CE51%20CHeSS%20
when alternative water paths are closed. A bypass circuit must be installed if WEB%20FINAL%20JULY%20
the boiler manufacturer requires one, or specifies that a minimum flow rate 08.pdf
has to be maintained while the boiler is firing. The installed bypass circuit
must then include an automatic bypass valve (not a fixed position valve).
Care must be taken to set up the automatic bypass valve correctly, in
order to achieve the minimum flow rate required (but not more) when
alternative water paths are closed.
Source: Energy Saving Trust (2008) Central heating system specifications (CHeSS)

Underfloor heating

Underfloor heating has been around for many years. The Romans used a warm
air system 1500 years ago, to good effect. It is only fairly recently that its
benefits have been rediscovered. With the arrival of new technologies such
as air and ground source heat pumps and solar heating, underfloor heating
becomes not only a viable option for the domestic dwelling but one that will
also save money and energy, reduce CO emissions and, as a consequence, help
2
save the fragile planet on which we live.
The design principles of underfloor central heating
systems

An underfloor heating system provides invisible warmth and creates a uniform
heat, eliminating cold spots and hot areas. The temperature of the floor needs
to be high enough to warm the room without being uncomfortable underfoot.
There is no need for unsightly radiators/convectors because the heat literally
comes from the ground up. Underfloor heating creates a low temperature heat
source that is spread over the entire floor surface area. The key phrase here
is low temperature. Whereas most wet central heating systems containing
radiators and convectors operate at around 70°C to 80°C, underfloor heating
operates at a much lower temperature, making it an ideal system for air and
ground source heat pump fuel sources. Typical temperatures are:
l 40–45°C for concrete (screeded) floors
l 50–60°C for timber floor constructions.

Traditional wet central heating systems generate convection currents and
radiated heat. Around 20 per cent of the heat is radiated from the hot surface
of the radiators and, if furniture is placed in front of the radiator, the radiation
emission is reduced. A total of 80 per cent of the heat is convection currents,
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