Low Loss Header (Llh) - Buderus Logamax plus GB162 Applications Manual

GB162 Applications Manual

2.2 Low Loss Header (LLH)

2.2.1 General Information
GB162 GB162
Fig. 2 Two Boiler System with Low Loss Header
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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 or multi boiler
installations of appliances with small water volumes to separate
the flow of water and heat between boiler and the system loops.
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
Logamax plus GB162 applications manual | 03.2013
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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 LLH is required in systems with low mass boilers and multiple
zones with zone pumps. The LLH ensures a constant flow rate
through the boiler independent of how many zones are calling
and independent 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.
Technical specifi cations are subject to change without prior notice
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