FEATURE
TRAINING
AND TECHNICAL
There is nothing that can be done to avoid a reduced
boiler load factor during mild weather conditions
In this concluding article on energy
effi ciency advice for clients, I am
looking at upgrading of control systems.
Since 2002 it has been mandatory
to achieve a certain level of control in
domestic properties, and the current
(2013) update of the Domestic Building
Services Compliance Guide (which
complements Building Regulations) states:
• Each space heating circuit should
be provided with independent time
control and either: a room
thermostat or programmable
room thermostat located in the
reference room served by the
heating circuit, together with
individual radiator controls such
as thermostatic radiator valves
(TRVs) on all the radiators outside
the reference room, or individual
networked radiator controls in each
room on the circuit
• Dwellings with a total fl oor area greater
than 150 m5 should have at least two
space heating zones, each with an
independently controlled heating circuit
• Dwellings with a total fl oor area of
150 m5 or less may have a single space
heating zone
• Independent time control of storage
domestic hot water systems, and electric
temperature control of storage domestic
hot water systems using, for example,
a cylinder thermostat and a zone valve
or three-port valve, or if a valve is not
appropriate, a second pump.
When deciding what upgrades are
appropriate it is necessary to take account
of the payback period and the age and
condition of the existing boiler.
With an old fl oor standing boiler with
gravity circulation to the domestic hot
water and a pumped space heating circuit,
it would not be sensible to upgrade such a
system to fully pumped operation.
The reason is that this would require
costly piping alterations, and the boiler
itself may need replacing within the not
too distant future.
A recommendation for replacement
of the boiler should be made, but if
fi nances do not allow, what measures can
realistically be taken?
An existing programmer and room
thermostat could be replaced with a
wireless programmable thermostat, giving
greater fl exibility in programming, with
resultant reduced running costs,
and minimising the disruption of
additional wiring.
For the domestic hot water, a cylinder
thermostat and time control should
be fi tted to ensure that the boiler only
operates when there is a domestic hot
water heating demand, but there would
be no way of preventing overheating of
the domestic hot water cylinder when the
boiler is fi ring for a space heating load.
DIRECT ACTING THERMOSTATIC
VALVE
The only option now available is to fi t
a direct acting thermostatic valve on
the cylinder, but it has no electrical
interlock facility so their use must be
restricted to acting as high limit valves,
with the cylinder thermostat set at a lower
temperature and acting as the main
temperature control and providing the
boiler interlock.
It is likely that the boiler will be
operating very ineffi ciently when just
heating the domestic hot water, so it
may be possible to improve the part load
effi ciency by reducing its output, within
the limits permitted by the manufacturers
– if it is ‘range rated’, then put it right
down to minimum.
Fitting TRVs may be an option,
depending upon whether they will be a
straight swap for the radiator valves already
installed.
For an older boiler with a fully pumped
system and basic time temperature
controls, there may be the opportunity
of improving effi ciency by installing a
programmable wireless room thermostat,
which will allow the independent timing of
the space heating and domestic hot water
heating, if not already installed.
Again, there may be scope for down
rating the boiler, with resultant improved
part load effi ciency, and for installing
TRVs.
LIMITED UPGRADE OPTIONS
With a fairly modern boiler, which may
well be condensing, the upgrade options
may be limited.
An upgrade to a wireless programmable
room thermostat with optimising
control, if not already installed, plus the
installation of additional TRVs may be
possible.
If the property fl oor area exceeds
150sq.m. and it is not already zoned,
installing a zone valve and programmable
room thermostat for the upper fl oors may
be an option, provided piping to the fl oors
is separated from the lower fl oors.
It is also worthwhile checking whether
the boiler already has the facility for
outside compensated control.
Some modern fully modulating
condensing boilers have the option of
compensated control, but I have found
contractors not installing the necessary
outside detector.
The cost of the detector and wiring is
minimal and there is no reason why this
cannot be retrofi tted to a boiler, with
resultant considerably improved effi ciency,
because the boiler will operate in
condensing mode for much longer periods.
HPM’s technical expert, John
Love, explains how upgrading
control systems can lead to
more effi cient energy.
“Some modern fully modulating condensing
boilers have the option of compensated
control, but I have found contractors not
installing the necessary outside detector”
Providing energy effi ciency advice
A plumber installing a thermostatic radiator valve