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Hot and Cold Water System
All recommendations with regard to pipe work systems in this manual are generally
based on the use of BS/EN Standard copper pipework and fittings.
However a plastic pipework system can be used in place of copper internally as
long as the chosen system is recommended by the manufacturer for use in cold
and hot water systems and is designed and installed fully in accordance with their
recommendations.
It is also important that if an alternative pipework material/system is chosen, the
manufacturer confirms that the design criteria for the new system is at least equivalent
to the use of BS/EN Standard copper pipework and fittings or larger pipe sizes are
considered.
In these appliances the mains inlet pressure regulating valve is set to 1.5 bar and this
setting MUST NOT be adjusted. Therefore the flow rate from the appliance depends
upon the resistance of the hot water supply network, capacity of the incoming
mains and the characteristics of the pressure regulating valve
Mains Cold Water Supply
The BoilerMate A-Class HP-DEM appliance is designed to be connected directly to the
mains. The combination inlet valve incorporates the required check valve. The hot
water flow rate achievable is directly related to the adequacy of the cold water mains
serving the property. For this reason the cold water supply to the dwelling must be
capable of providing for those services which could be required simultaneously and
this maximum demand should be calculated. Also if a water meter is fitted its nominal
rating should match the anticipated maximum simultaneous hot and cold water
demand calculated in accordance with BS 6700. This could be 60 litres per minute in
some properties. 30 litres per minute is the minimum flow rate which is recommended
for an adequate mains pressure system to any property.
The Building Regulations L1A: New dwellings/L1B: Existing dwellings and the
requirements set out in the Domestic Heating Compliance Guide specify that "where
the mains water hardness exceeds 200ppm provision should be made to treat the feed
water to water heaters and the hot water circuit of combination boilers to reduce the
rate of accumulation of lime scale" .
To comply with this requirement the hardness of the mains water should be checked by
the installer and if necessary the optional factory fitted in-line scale inhibitor should be
specified at the time of order for hardness levels between 200 and 300 ppm (mg/l).
Where the water is very hard ie 300ppm (mg/l) and above the optional polyphosphate
type, inhibitor should be specified at the time of order. However, this will need to be
fitted by the installer at a suitable point in the cold water supply to the appliance.
The combination valve fitted to the BoilerMate A-Class HP-DEM unit incorporates a
pressure regulating valve set to provide a static operating pressure of 1.5 bar. On this
basis there must be at least 2.0 bar pressure at the inlet to the appliance. This pressure
must be dynamic (not static) and be available at the appliance when local demand
is at its maximum. For optimum performance, and for larger properties, we would
recommend that the dynamic pressure is in the range of 2.5 - 3.5 bar.
The combination valve also incorporates an expansion relief valve. The discharge from
this can be connected into the discharge pipe from the P & T valve. Further details of
how to treat this discharge are provided later in this manual.
As a general guideline, if a good pressure is available, a 15mm service may be sufficient
for smaller dwellings with one bathroom. However a 22mm service (25mm MDPE) is
recommended and should be the minimum for larger dwellings, or where only the
minimum recommended pressure is available.
If the incoming mains pressure exceeds 6 bar
at any time in a 24 hour cycle then a pressure
regulating valve set at 3.5 bar should be fitted
downstream of the stop tap where the cold
supply enters the property.
Equipment used in the system should be
suitable for a working pressure of up to 5 bar.
Page 17
DESIGN
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