Modern condensing boilers can be introduced to upgrade
existing industrial heating systems with the minimum
amount of upheaval and maximum savings, according to
Pete Mills, commercial technical operations manager at
Bosch Commercial & Industrial Heating

For those thinking of embarking on a
boiler replacement project, the good
news is that carrying out work to
upgrade a system needn’t be as intrusive as
you might expect. While one solution
definitely doesn’t fit all, there are ways and
means of integrating new condensing boilers
into existing systems and pipework, without
the risk of any contamination of the primary
boiler circuit or loss of performance.

Today, most high performance condensing
boilers need to be installed as part of a sealed
system, and those that don’t still benefit
greatly from being separated from an old
system where the water quality may be
difficult to control. In the industrial and
commercial sector, conversion from an open
vented to a sealed system can be tough to
achieve with potential leaks from old
pipework and fittings to consider, as well as
the possibility of corrosion problems if water
from an old system is allowed to circulate
freely around a new condensing boiler.

In situations like these, the most practical
way of overcoming this kind of problem is to
leave the existing system open vented while
separating the boiler primary circuit using a
stainless steel plate heat exchanger.

Introducing a plate heat exchanger to the
system ensures a safe and protected primary
circuit for the new condensing boiler, while
ensuring there is no risk of an increase in
corrosion to the existing system.

The most usual position for the plate heat
exchanger is to replace the low loss header
usually associated with modular boiler
cascade systems. In industrial and
commercial heating systems, fitting a low
loss header allows the creation of a primary
circuit, within which water velocity can be
maintained at the required constant,
regardless of changes or requirements in the
secondary circuits. In cases where plate heat
exchangers have been introduced there is no
longer a need for the low loss header as there
is now no chance of the system pumps
having influence over boiler shunt pumps.

From the point of view of control, the
plate heat exchanger functions in much the
same way as a low loss header. The system
strategy sensor is placed on the secondary
flow, which compensates for any flow
temperature loss across the plate heat
exchanger (typically at 5°C). However, it is
vital that the heat exchanger is correctly sized
to ensure both the correct heat transfer and
hydraulic resistance can be handled by the
boiler and the system pumps.

Over the years, condensing boiler heat
exchangers have become significantly more
sophisticated, as manufacturers have
optimised designs to deliver greater outputs
from highly efficient, compact exchanger
units. As a result of being smaller by design,
some heat exchangers can have small water
ways that are in danger of becoming blocked
if large debris finds its way in.

Depending on the system condition, the
addition of a strainer, a filter, or even a dirt
separator, on the common return to the plate
heat exchanger is recommended to protect
the unit from debris that has not been
successfully flushed from the old system.

Where plate heat exchangers have been
installed, the expansion vessel required to
accompany the installation can be sized to
accommodate the expansion of water of the
small primary circuit.

This is another plus for investors, as it
saves on both the cost and space of buying a
much larger vessel than may otherwise be
required if a plate heat exchanger is not
incorporated into the system design. It is
however, important to note that the filling
arrangement will still need to comply with
the requirements of the Water Regulations
relating to the size of the boiler and the
property – typically fluid category 4.

Finally, on the secondary side of the
heating system, the position of the existing
open vent and cold feed will need to be
considered carefully, as the changes made to
the system may mean further alterations are
required. Within the new system, the plate
heat exchanger effectively becomes the heat
source and therefore careful consideration
needs to be given to the positioning of the
open vent and cold feed in relation to the
existing heating pumps.

Although clearly there is a lot to consider
where any installation work is undertaken to
improve the efficiency of a current heating
system, above all it is reassuring for investors
to know there are ways and means of
managing the process within existing
parameters to make it as smooth and
effective as possible.