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Back-Up Heating Source
Solar Thermal Collector Systems normally
require a back-up heating system. Typically
this is the existing gas or oil boiler that is
used to boost the Domestic Hot Water
(DHW) supply on days when there is
insufficient solar radiation.
The existing boiler is used to boost the
storage cylinder either using the top coil of a
twin coil cylinder or the bottom coil of a
secondary hot water storage cylinder that is
fed by the solar pre-heat cylinder.
High Temperature Limits
Any components in close proximity to the
collector can be exposed to brief periods of
up to 160
°
C temperatures, when the pump
turns ON after stagnation. Therefore, the
high temperature limits of all components in
the system must be known and cannot be
exceeded. It is also advisable to ensure that
components (e.g. pumping station,
expansion vessel, etc) are located
hydraulically as far from the collector in the
solar loop as is possible. Typically this will be
hydraulically close to the storage cylinder.
Temperature Control
The solar controller should have a “max tank
temp” function to protect the tank from
being overheated. Hot water storage
cylinders should comply with the local
building regulations and be fitted with the
appropriate safety features for over-
temperature and over-pressure protection.
Anti-Scald / Tempering Valves
Anit-scald mechanisms are required in order
to comply with the MCS MIS3001 Section
4.3.3 Requirement : “Incorporate a means to
limit the water at all points of use to no
more than 60°C or lower depending upon
scald risk factors”.
This requirement can be met by using
Thermostatic Mixing Valves (TMVs) within
2000mm of all points of use to limit the
temperature to no more than 46°C (or less
depending upon the use). Alternatively a
TMV at the outlet from the hot water
cylinder limiting the output temperatures to
55°C to 60°C can be used or also by
providing a thermostatic device to limit the
solar input to the hot water cylinder. A
combination of the above may also be
acceptable.
Closed Loop Max Incoming
Pressure
For closed loop systems, the solar loop must
operate at no greater than 3.5 Bar and have
an expansion tank installed to accept fluid
expansion.
If a single wall heat exchanger is used, the
solar loop operating pressure must be below
the water main pressure.
Maximum Allowable Pressure
The maximum allowable operating pressure
for the solar collector in any system