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Circulated Hot Water Flow and Return System – Solar Water Heater with In-series Boosting
LEGEND
Temperature Settings
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AS 3498 requires that a water heater provides the means to inhibit the growth of Legionella bacteria in
potable water. To meet this requirement of AS 3498:
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A solar storage tank with its electric heating unit connected for in-tank boosting, and the secondary
water heater must always have their thermostats set to at least 60°C
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An in-series storage water heater must always have its thermostat set to at least 60°C
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An in-series continuous flow water heater must always have its preset outlet temperature setting set
to at least 70°C
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Water should not be circulated from a water heater with a temperature setting of less than 60°C.
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The return water temperature to the water heater must not be less than 55°C.
If the water temperature decreases by more than 5°C due to heat loss from the ring main, the preset outlet
temperature setting or thermostat setting of the secondary water heater or in-series water heater must be
set to above 60°C to ensure the return water temperature is not less than 55°C.
Temperature Limiting Device
A temperature limiting device cannot be installed in circulated hot water flow and return pipe work. The
tempered water from a temperature limiting device cannot be circulated. Where a circulated hot water flow and
return system is required in a building, a temperature limiting device can only be installed on a dead leg,
branching off the circulated hot water flow and return pipe.
If circulated tempered water were to be returned back to the water heater, depending on the location of the
return line connection on the water supply line to the water heater, then either:
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water will be supplied to the cold water inlet of the temperature limiting device at a temperature exceeding
the maximum recommended water supply temperature, or
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when the hot taps are closed no water will be supplied to the cold water inlet of the temperature limiting
device whilst hot water will continue to be supplied to the hot water inlet of the temperature limiting device.
These conditions may result in either water at a temperature exceeding the requirements of AS/NZS 3500.4
being delivered to the hot water outlets in the ablution areas, or the device closing completely and not delivering
water at all, or the device failing. Under either condition, the operation and performance of the device cannot
be guaranteed.
INSTALLATION – SOLAR STORAGE TANK
27
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