Page 495 - 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

Electrical central heating controls

Modern central heating systems cannot function without electrical controls.
They are required at every stage of operation, from switching the system on
to shutting it down when the temperature required has been reached. They
provide both functional operation and safety, and are a requirement of Building
Regulations Document L: Conservation of fuel and power.

No matter how good the central heating design, or how accurate the
calculations, the system requires proper control to be effective, efficient and
economical to run. The types of control that are added to a system can greatly
improve its performance. Even older systems can benefit from the addition of
modern and effective controls.
In this part of the chapter, we will look at the various controls for central
heating systems, their function and how they ‘fit’ into modern systems.
Before we look at the various controls, we must first consider the implications
of Document L, which was updated in 2013. The main points are listed in
Table 7.16.

 Table 7.16 The main implications of Document L
Recommended minimum standards for control of new heating systems
Dwelling over With hot water Boiler interlock
150m 2 cylinder At least two space heating circuits each with independent time control, a room
thermostat and TRVs
A hot water circuit with independent time control and a cylinder thermostat
No hot water Boiler interlock
cylinder (combi At least two space heating circuits, each with independent time control, a room
boiler) thermostat and TRVs
In existing buildings one of:
l Flue gas heat recovery
l Weather compensation
l Load compensation
l Smart thermostat with automation and optimisation
Dwelling up to With hot water Boiler interlock
150m 2 cylinder A space heating circuit with independent time control, a room thermostat and TRVs
A hot water circuit with independent time control and a cylinder thermostat
No hot water Boiler interlock
cylinder (combi A space heating circuit with independent time control, a room thermostat and TRVs
boiler)
In existing buildings one of:
l Flue gas heat recovery
l Weather compensation
l Load compensation
l Smart thermostat with automation and optimisation

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