Amazon HXINUV, Installation Instructions A1, 28th June 2019
Operation
The HXINUV assembly uses two cylinder thermostats linked together on a latch to provide a buffered mode of operation for the heating
of the cylinder. The Buffer On thermostat is the standard dual control/safety thermostat fitted to the cylinder itself (which includes a
high limit overheat cut-out facility). The Buffer Off thermostat is teed into the plate heat exchanger assembly. This dual thermostat
arrangement allows a minimum set volume of water to be heated which helps reduce cycling of the boiler - this can be an issue with
conventional single thermostat systems - and thus the dual thermostat aids boiler efficiency.
When the cylinder temperature at the 'Buffer Off' position drops below its set point, it energises the 'Buffer On' thermostat; If this is
simultaneously calling for heat it turns the plate heat exchanger pump on. In parallel, this calls for heat from the boiler or heat source
via the two port energy cut out motorised valve. Primary heat from the boiler now flows down through one channel of the plate heat
exchanger; in counter-current, cool water from the base of the cylinder and/or cold mains water is drawn upwards through the other
channel. The cool water is heated and DHW passes out and into the top part of the cylinder. Heating of the cylinder continues until both
the buffer thermostats are satisfied.
A DHW temperature control valve modulates the primary heat flow in response to the DHW temperature observed exiting from the
plate heat exchanger, in order to maintain the stored DHW at the required set point. As the DHW flowing away from the plate heat
exchanger approaches the required setpoint temperature, the control valve reduces the primary flow, and vice versa.
A DHW flow setter controls the flow rate of DHW being created and fed into the cylinder. The set point of this component is defined by
the size of the available primary heat source and is adjusted during commissioning. In order to achieve the required flow rate it may be
necessary to adjust the plate heat exchanger pump speed as required.
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