Transcript SBEM Level 3 Non Domestic Energy Assessment

Energy Performance
Certificates
DHW
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LEVEL 3
BUILDING SERVICES TRAINING
Domestic Hot Water Production
The provision of domestic hot water generation should not be
ignored as a contributing factor to energy use, in some cases such
as hotels, this will be the largest onsite energy requirement.
There are numerous ways of generating domestic hot water, and
many hours could be devoted to differing methods and systems,
however this section will cover the most commonly used methods
which are likely to appear within a Level 3 Assessment.
Follow LATEST Conventions
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LEVEL 3
BUILDING SERVICES TRAINING
Indirect System of Hot Water Supply
Water in the boiler and primary circuit is not drawn off through the
taps. The same water circulates continuously throughout the boilers
primary circuit and heat exchange coil inside the storage cylinder.
Fresh water cannot gain access to the higher temperature areas
where precipitation of calcium would occur. The system is also used
in combination with central heating. with flow and return pipes to
radiators connected to the boiler. Boiler water temperature may be
set by thermostat at about 80C.
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SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
The above system uses a conventional boiler with a separate
pipework and pumpset to provide a primary LPHW supply to the
cylinder.
The boiler could either be dedicated for hot water production only, or
provide both hot water for domestic use and LPHW for heating
purposes.
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Direct System of Hot Water Supply
An electric immersion heater may be used within a conventional hot
water storage cylinder.
The immersion heater must be electrically earth bonded and the
cable supplying the heating element must be adequate for the power
load. Direct cylinders have no coil or annular heat exchangers..
Direct and indirect cylinders for industrial and commercial
applications are manufactured in copper and galvanised steel in
capacities up to and above 4500 litres.
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Direct System of Hot Water Supply
Electrically heated Loft mounted
Cylinder with built-in cold water
tank
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Gas Fired Water Heaters
Atmospheric and condensing water heater is basically a variation on
the multipoint type heater The water heater is a hot water storage
vessel, capable of very rapid heat recovery.
This type of water heaters application examples include small
hotels, schools, residential homes, student halls of residence, camp
sites and sports centres.
They function by a fanned gas burner discharges into a stainless
steel combustion chamber within a cylindrical water storage vessel.
From the combustion chamber the burnt gases descend into a
stainless steel spiral to exit at low level through a flue. Condensate
from the flue is trapped and discharged to a drain on the condensing
models.
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• Controls –
• Automatic electric ignition in response to a water temperature
thermostat.
• Limit thermostat.
• Overheat safety thermostat and warning light.
• Fan failure device and warning light.
• Manual on/off switch.
• Water supply - either: Cistern, gravity feed pipe and atmospheric
vent and expansion pipe.
• Or
• Direct connection to an unvented mains supply. Unvented supplies
require backflow prevention (check valve). an expansion vessel and
an expansion valve.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
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BUILDING SERVICES TRAINING
Electric Point of Use Water Heaters
An electric immersion heater may be used within a conventional hot
water storage cylinder. Alternatively, individual or self-contained
open outlet heaters may be located over basins. baths or sinks.
Combined cistern-type heaters can be used to supply hot water to
several sanitary appliances. Energy conservation is achieved with
an integral thermostat set between 60 and 65°C. This temperature
is also sufficient to kill any bacteria. The immersion heater must be
electrically earth bonded and the cable supplying the heating
element must be adequate for the power load.
This type of unit is used in a more efficient manner when in
conjunction with a time switch to mirror occupancy periods.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
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BUILDING SERVICES TRAINING
Electric Unvented Water Heaters (Small Capacity)
Small unvented water heaters are generally used for a situation
where a single heater is required to service the needs of multiple
outlets. This type of heater is normally supplied with a factory-fitted
temperature and pressure relief valve and expansion devices. This
type of installation is improved by introducing time control.
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Secondary HWS Return
To prevent user inconvenience waiting for the cold water ‘dead-leg’
to run off and to prevent water wastage. long lengths of hot water
distribution pipework must be avoided. Where cylinder to tap
distances are excessive, a pumped secondary flow and return circuit
may be installed with minimal ‘dead-legs’ branching to each tap. The
pipework must be fully insulated and the circulation pump timed to
run throughout the working day. e.g. an office system could be
programmed with the boiler controls. typically 8.00 am to 6.00 pm, 5
days a week. A non-return valve prevents reverse circulation when
the pump is not in use.
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LEVEL 3
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