FEATURE
DOMESTIC BOILERS
& RENEWABLES
“While solar energy tends to be
most effective in the daytime,
people generally want to use hot
water in the morning and evening”
Integrating solar thermal into
existing heating systems
Using thermal solar technology and integrating it into an existing heating system allows
homeowners to save energy and fuel bills while maintaining a reliable source of heating and
hot water supply. Gary Perry, managing director of Altecnic, outlines how you can help your
customers attain the best of both worlds.
The long hot summer that we have
just experienced is testament to
the potential of solar energy to
provide hot water.
Even now as we move to the cooler days
of winter, solar systems will preheat the
water to reduce the reliance on a boiler
for heating and domestic hot water.
While solar energy tends to be most
effective in the daytime, people generally
want to use hot water in the morning and
evening. It follows then that this heated
water needs to be stored up for later use in
an additional hot water cylinder.
Importantly the installation of a solar
thermal system does not mean that
you need to remove a home’s existing
combination boiler or hot water cylinder,
in fact it is better to retain them. What is
needed is some technology to manage the
hot water so that it remains at a constant
temperature at the point of use.
In solar thermal systems with natural
circulation in the primary circuit and
a water storage cylinder with insulating
jacket, the temperature of the domestic
hot water in the cylinder can vary
enormously depending on the amount of
sun. It can reach very high temperatures
over long summer periods or in the winter
be too cool to use without extra heating.
SUMMER HEAT
In the summer if there is little water
usage, the hot water in the cylinder can
reach temperatures of up to 98ºC before
the temperature and pressure relief safety
valve are actuated. Obviously, water at
these temperatures cannot be used.
Even water temperatures over 50ºC can
cause burns very quickly. For example, at
55ºC partial burns on the skin occur in
about 30 seconds, whereas at 60ºC partial
burns occur after just five seconds.
This means that a thermostatic mixing
valve (TMV) is needed to reduce the
temperature of the water distributed
through the domestic water system to
make it suitable for the end user. For
safety reasons, we would recommend that
you set the temperature of the mixed
water that is distributed to the users at no
higher than 50ºC.
This mixing valve also keeps the
mixed water temperature constant
despite variation in inlet temperature
and pressure, and enables the high
temperature water in the storage to last
longer by distributing to the user’s circuit
at a reduced temperature.
You need to check that the mixing valve
has an anti-scald device so that it can shut
off in case of cold water supply failure.
WINTER LOWS
In the cooler months of the year you may
have the opposite problem in that the hot
water in the thermal storage system is not
hot enough.
To combat this, solar domestic water
storage cylinders are normally installed in
conjunction with a boiler or water heater.
It means that when the water is cooler
it can be diverted to the combination
boiler to be heated to the correct safe
temperature.
This process still saves fuel consumption
as the water from the storage is preheated
so the combination boiler does not have
to increase the water temperature from a
cold starting point.
To meet the increasing demand for
solar thermal systems you will find that
many manufacturers have produced
boiler connection kits so that you can
easily manage the interface between
both technologies for the benefit of your
customer. For example, the Caleffi 264
and 265 solar storage to boiler connection
kits automatically control and optimise
the thermal energy contained in the solar
water storage.
A thermostat with a temperature probe
measures the hot water flow from the solar
water storage, which in turn controls a
diverter valve on the inlet.
Depending on the set temperature,
the valve then diverts the water towards
the user circuit for mixing or activates
the boiler circuit. This valve modulates
the flow rates to optimise the energy
contained in the solar storage cylinder to
reduce boiler operation to a minimum.
For extra safety, an anti-scald TMV on
the outlet controls the temperature sent to
the user.
SAFETY IS PARAMOUNT
The advantage of using a kit is that safety
is paramount. It is designed to protect
the end user against scalding and any
legionella risks.
Modern innovations in valve technology
mean that you can integrate renewables
in to existing homes. Easy to commission
and install connection kits means that
such integration is easy to achieve.
Your customer will be delighted with
their energy saving, green installation
and be safe in the knowledge that their
hot water and heating is efficient, safe,
saves them money and reduces their
carbon footprint. As renewable heating
technology becomes more popular using
solar storage to boiler connection kits will
help you profit from this growing trend.
ENQUIRY NUMBER 114
Boiler connection kits, such as the Caleffi 264 and 265,
automatically control and optimise the thermal energy
contained in the solar water storage
40 Heating & Plumbing Monthly | OCTOBER 2018 | www.hpmmag.com
/www.hpmmag.com
