Specifications

Logamax plus GB142 applications manual | 01.2012 Technical specifi cations are subject to change without prior notice
GB142 Applications Manual
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2.2 Low Loss Header (LLH)
2.2.1 General Information
GB142 GB142
Fig. 2 Two Boiler System with Low Loss Header
Supply
Supply
Return
Return
BOILER
SYSTEM
Fig. 3 Low Loss Header Overview
Modern compact wall hung gas appliances are often equipped
with boiler controlled modulating pumps, some of which are
also used for making DHW. These pumps are operating in ways
that optimize boiler efficiency and longevity, but are not suitable
for supplying the system at the same time. As a result the
system must be set up with hydraulic separation between the
primary and secondary sides.
A LLH is nothing more than a large pipe, installed between
the heat sources and the system. It is used in single and multi
boiler installations of appliances with small water volumes to
independently control the flow of water in the boiler loop and
the system loop.
When the circulating volumes between boiler loop and system
loop differs greatly, a LLH can help avoid over flowing or under
flowing one or the other. Over flowing can lead to noise and
erosion in the piping, and can be identified by a boiler or system
not coming up to temperature, or by a narrow delta T. Under
flowing means that the heat is not being transported away from
the boiler, causing it to bounce off the high limit.
In the system under flowing can result in too great a delta T,
resulting in considerable heat being shed in the beginning of
the loop and insufficient heat left for the remainder of the loop.
Installation of a LLH however requires a pump on the boiler
side and one on the system side.
As their flow rates are typically low, some manufacturers design
a LLH to include an air eliminator and dirt separator.
A typical example is a system with low mass boilers and
multiple zones with zone pumps. The LLH ensures a constant
flow rate through the boilers independently of how many
zones are calling and independently of the flow rate in the
system loop. It prevents pumps from working against each
other, resulting in balanced flows, even heat distribution, and
reduction of potential noise.