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Cylinder Types

Directly Heated

 

In this system the water drawn from the storage cylinder has passed directly through the heat exchanger of the appliance.

directcylinderfig indirectcylinderfig

Indirectly Heated

 

In an indirect system (see figure) the stored water is heated by a calorifier (heat exchanger) within the storage cylinder. This calorifier can be either a coil type or an immersion type(as shown further down).

Cold water storage tank

Circulator

Hot Taps

Direct Cylinder

Circulator

Cold water storage tank (for hot water)

Cold water storage tank (for central heating)

Indirect Cylinder

Coil Inside Cylinder

Hot Taps

Direct System

coiltype

Cold Feed (from cold water storage tank)

Vent Pipe(going to cold water storage tank)

To draw off points i.e hot taps

Primary Flow From Boiler

Primary Return To Boiler

Coil Type

Indirect System

immersiontpecylinder

ImmersionType

Vent Pipe(going to cold water storage tank)

To draw off points i.e hot taps

Cold Feed (from cold water storage tank)

Primary Flow

 

Return

Vent pipes

Vent pipe

The heat exchanger is connected by flow and return pipes to the heating appliance and there is no direct contact between the water in the appliance and the water drawn from the taps. This sytem is particularly suitable in hard water areas, as water circulating through the heat exchanger is not continually replaced with fresh, thus minimisng formation of scale.