FEATURE
TRAINING
AND TECHNICAL
“An increasing number of people are becoming aware
of smart controls, which enable them to remotely
control the operating times/temperatures of their
home heating system via a tablet or smartphone”
Energy saving options aplenty
under Boiler Plus
HPM’s technical expert, John Love, looks at the
four energy saving options that must be considered
when a new combination boiler is installed into an
existing property under Boiler Plus.
Last month, I explored the
updated requirements for the
installation of boilers in existing
buildings, promoted as the new
Boiler Plus standard.
While making the minimum control
requirements of a boiler interlock
and time and temperature control
mandatory, rather than simply good
practice as previously, the change which
is likely to have the biggest impact is in
respect of the installation of gas-fi red
combination boilers.
When installing a new combination
boiler into an existing property, or
replacing an existing one, in addition
to the boiler interlock and time and
temperature control, it must also
incorporate at least one of the following
energy saving options, and it is these
options that I am going to look at:
1. Flue gas heat recovery (FGHR)
2. Weather compensation
3. Load compensation
4. Smart controls with automation and
optimisation functions.
FLUE GAS HEAT RECOVERY
Flue gas heat recovery (FGHR) systems
recover heat from the fl ue gases leaving
the boiler, in a similar way to a condensing
boiler, but use this recovered heat to
preheat the mains cold water entering
the boiler, rather than heating the boiler
return water. This reduces the energy
needed to heat the domestic hot water to
the required level.
Of course, virtually all modern boilers
will be condensing ones with primary
heat recovery built in, in the form
of a larger primary condensing heat
exchanger, and the addition of a FGHR
system can further increase the effi ciency
by around four per cent.
The drawback is that with a cost of
Vokèra by Riello created a Boiler Plus fl ow diagram in light
of the changes to legislation that came into force on April 6
between £500 and £700, in addition to the
boiler cost, the technology is unlikely to
be fi nancially viable for all but a few large
households with very high domestic hot
water demands.
Whether we will see a marked
reduction of cost in the years ahead
remains to be seen.
WEATHER COMPENSATION
Condensing gas fi red boilers start to
recover heat from their fl ue gases when the
fl ue gas temperature is reduced to below
57ºC, which is the dew point temperature
of the water vapour in the fl ue gases.
To achieve this, we need to get the water
returning from our heating system to
below 54ºC and the lower the temperature
the more effi ciently the boiler operates.
With a boiler which is operating at a
fi xed fl ow temperature then, although
the larger heat exchanger will recover
more sensible heat from the fl ue gases, it is
unlikely to enter condensing mode except
on start-up from cold.
Of course, if the heating system
is designed to operate at a low fl ow
and return temperature, for example
70ºC/50ºC, then the boiler will operate in
condensing mode most of the time.
However, this will require the heat
emitters (radiators) to be larger in order
to give out the required amount of heat at
the reduced temperature.
Provided the boiler control system has
the capability of operating the burner
at a variable fl ow temperature, rather
than just modulating to maintain a
fi xed temperature, then using weather
compensating controls will mean that
the boiler fl ow temperature, and thus
return temperature, will reduce as the
outside temperature increases, so enabling
the boiler to enter condensing mode of
operation far more frequently.
An increasing number of boilers are
now being manufactured with the control
circuitry incorporating an interface which
enables connection to external weather
compensation and other controls which
vary the water temperature, rather than
just giving simple on/off control.
Some already have compensated
control built in so that all you have to
do is connect in an externally mounted
sensor. A combination boiler will revert to
maximum temperature operation while
there is a domestic hot water demand.
LOAD COMPENSATION
An alternative to weather compensation is
load compensation, which is a function in
many smart controls and programmable
thermostats.
These devices measure the gap between
what the internal temperature is and what
the user requires and modulates the boiler
burner down to a minimum fi ring rate as
the gap reduces.
SMART CONTROLS
An increasing number of people are
becoming aware of smart controls, which
enable them to remotely control the
operating times/temperatures of their
home heating system via a tablet
or smartphone.
Automation is the function which
allows this remote operation and it can
incorporate occupancy detection and/or
geolocation, which automatically starts/
stops your heating based on the distance
you are away from home.
Optimisation is a mode of control which
monitors the rate of change of internal
temperature under varying conditions so
that it is then able to calculate how long
it will take for the property to reach the
desired comfort level, and then adjusts the
on time to achieve this.
36 Heating & Plumbing Monthly | JUNE 2018 | www.hpmmag.com
/www.hpmmag.com
