Energy Performance Certificates. DHW. PRESENTED BY. LEVEL 3 BUILDING SERVICES TRAINING. Domestic Hot Water Production
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
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.
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.
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 4500litres.
Direct System of Hot Water Supply
Electrically heated Loft mounted
Cylinder with built-in cold water
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.
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.
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.
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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