30 ©ESP Ltd. Sept 2008
Bubble-Top Units
Bubble-Top Units
Bubble-Top units, manufactured from either cop-
per or stainless steel, accommodate the expansion
of the heated water by using an internal air-bubble
which is generated and trapped at the top of the
unit during commissioning.
External Expansion Unit
As the name implies, External Expansion units
utilise an expansion vessel to contain the expanded
heated water. The expansion vessel can be installed
directly onto the unit, or, if required remotely sited
with the Inlet Control Group. These units are
manufactured from copper, glass-lined steel or
stainless steel.
The Direct-Fired Unit, normally manufactured
from glass-lined steel or stainless steel, again uses
an expansion vessel to accommodate the increased
volume of the heated water. Predominantly in-
stalled in larger domestic or commercial premises,
these units can be either gas or oil fired.
A recent development now available in the UK
is the Combi Storage unit. This type of unit in-
corporates the benefits, features and controls
associated with Unvented Systems but has a
limited storage capacity of hot water.
Ideally, the mains supply pressure to the prem-
ises should be a minimum of 2 Bar to ensure
the superior performance associated with the
Unvented System and, although all Unvented
Systems will operate at supply pressures as low
as 1 Bar, the benefits will be reduced.
External Expansion Unit
Direct-Fired Unit
Unvented Systems can also be used in conjunction with tank fed supplies and
booster pump sets, although these installations are usually confined to com-
mercial premises. Unvented Systems are suitable for use in conjunction with
electric, gas, LPG or oil heating appliances but MUST NOT be used with
solid fuel appliances.
The majority of Unvented units available today are certified to comply with
the requirements of Building Regulation G3, either by the BBA (British
Board of Agrément) or the WRc (Water Research Evaluation and Testing
Centre) and are supplied with a complete package of controls - either factory
fitted or supplied as an Unvented Kit - which must be installed in strict accor-
dance with the relevant manufacturer‟s instructions.
UNVENTED HOT WATER STORAGE SYSTEMS AND CONTROLS
