Page 455 - 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

Fully pumped systems
Modern heating systems utilise pumped primary circuits as well as pumped
heating circuits. By installing 2 × two-port zone valves or a three-port
mid-position valve, the user can have hot water only, heating only or a
combination of both. There are three basic types:
1 the Honeywell Y-plan, which uses one three-port motorised mid-position
valve
2 the Honeywell W-plan, which uses one three-port motorised diverter valve
3 the Honeywell S-plan, which uses two two-port motorised zone valves.

Fully pumped systems offer a better choice of both system design and boiler
choice and, because the need for gravity circulation has been eliminated, fully
pumped systems give much greater scope for installation options, especially
when positioning the boiler, as the need for the boiler to be lower than the
storage cylinder is no longer a consideration.
Full thermostatic control is available to both hot water and heating circuits by
means of a cylinder thermostat, a room thermostat and thermostatic radiator
valves.
Fully pumped systems heat up much more quickly than semi-gravity systems,
offering savings on fuel and operating costs, and both Y-plan and S-plan systems
can be used with natural gas, liquid petroleum gas (LPG) and oil appliances.
The Honeywell Y-plan utilising a three-port motorised mid-position valve

The three-port motorised mid-position valve controls the flow of water to
the primary (cylinder) circuit and the heating circuit. The valve reacts to the
demands of the cylinder thermostat or the room thermostat.

This system uses a single three-port motorised mid-position valve to control
the flow of water to the central heating circuit and the hot water circuit.
Feed and It is controlled by a cylinder thermostat and a room thermostat.
expansion cistern Individual thermostatic radiator valves independently control the
temperature of each room.

Automatic Cylinder Room
22 mm vent pipe air valve thermostat thermostat
15 mm cold feed
Mid-position
valve

Programmer
System
bypass
Wiring
centre

22 mm flow and return pipes
p Figure 7.6 Y-plan system

443

9781510416482.indb 443 29/03/19 9:02 PM