Unit 317 Session 1 Types of Central heating System and their lay

​Types of Central heating System and their layout

​Central heating is a vast and complex subject.

There are now more options with regard to sources of heat, pipe materials and heat emitters than ever before.

Environmentally friendly technology and the re-emergence of underfloor heating has meant that the customer can now afford to be selective about the system they have installed into their property.

Open Ended

How many types of central heating system can you think of?

​Modern domestic central heating systems fall into two categories, which are based on the way the system is filled with water and the pressure that the system operates at.

​Low pressure, open-vented systems

​Sealed, pressurised systems

These are fed from a feed and expansion cistern located at high level.
These can be fully pumped or gravity systems. 

​Low pressure, open-vented systems: 

Open Ended

What do you think is meant by the term 'gravity system'

​One pipe system

​ Two-pipe semi-gravity system

​ C-plan plus system

Open Ended

The previous 3 systems relied on gravity circulation for the hot water, what problems do you think this causes?

​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.

​Y-plan system

​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.

​W-plan utilising a three-port motorised diverter valve

​The W-plan is very similar to the Y-plan. The main difference is that the system uses a three-port motorised diverter valve. This means that either the hot water circuit or the heating circuit can be opened but not both circuits at the same time. It is known as a hot water priority system.

​The S-plan has two two-port motorised zone valves to control the primary and

heating circuits separately by the cylinder and room thermostats respectively.

This system is recommended for dwellings with a floor area greater than 150 m2

because it allows the installation of additional two-port zone valves to zone the

upstairs heating circuit from the downstairs circuit.

A separate room thermostat and possibly a second time clock/programmer would also be required for upstairs zoning.

​​The S-plan

​Zoning: a process where living spaces and sleeping spaces are individually

controlled via independent time clocks, room thermostats and motorised

zone valves.

​S-plan system

Multiple Choice

Can you name the Low pressure, open-vented system in the picture?

• S-Plan

• Y-Plan

• ​One pipe system

• Two-pipe semi-gravity system

• C-plan plus system

Multiple Choice

Can you name the Low pressure, open-vented system in the picture?

• S-Plan

• Y-Plan

• ​One pipe system

• Two-pipe semi-gravity system

• C-plan plus system

Multiple Choice

Can you name the Low pressure, open-vented system in the picture?

• S-Plan

• Y-Plan

• ​One pipe system

• Two-pipe semi-gravity system

• C-plan plus system

Multiple Choice

Can you name the Low pressure, open-vented system in the picture?

• S-Plan

• Y-Plan

• ​One pipe system

• Two-pipe semi-gravity system

• C-plan plus system

Multiple Choice

Can you name the Low pressure, open-vented system in the picture?

• S-Plan

• Y-Plan

• ​One pipe system

• Two-pipe semi-gravity system

• C-plan plus system