Function Schematic - Bosch Worcester Greenstar HIU E Installation And Maintenance Instructions Manual

Appliance information
2.12

Function Schematic

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Fig. 8 Function schematic
[1] Control unit
[2] Return sensor NTC (district heating)
[3] Central heating plate heat exchanger
[4] Central heating control valve
[5] Differential pressure control valve (if fitted)
[6] Flow sensor NTC (central heating)
[7] Heat meter (if fitted)
[8] Circulating pump
[9] Summer by-pass valve (if fitted)
[10] Heat meter flow sensor connection point
[11] Supply sensor NTC (district heating)
[12] Domestic Hot Water safety valve
[13] Flow turbine
[14] Flow regulator
[15] Domestic Hot Water outlet sensor NTC
[16] Domestic Hot Water control valve
[17] Domestic Hot Water plate heat exchanger
System description
If a summer by-pass valve [9] is fitted; in stand-by mode, the district
supply water flows from the district heating main, via the thermostatic
by-pass valve, therefore ensuring that hot water at 45 °C - 50 °C is
immediately available at the heat interface unit. This ensures a fast
warm-up of hot water at the tap, often referred to as keep hot function.
The above function is also available on a Sense II without the need for a
by-pass valve [9]. In this case, the domestic hot water control valve [16]
modulates to maintain 0 °C -60 °C at the primary water side of the heat
interface unit, depending on the temperature set for the by-pass
function in the controller settings menu.
Electronic keep hot function
▶ This function will allow a small amount of district
water to flow through the heat meter.
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The electronic control unit [1] provides fully modulated heating and hot
water control between maximum and minimum heat output. There are
two LEDs located on the top of the control unit [1] (visible through two
viewing holes in the top of the case). These indicate operating modes
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and fault conditions.
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If a hot water tap is opened, the flow turbine [13] is activated, the
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central heating control valve [4] remains closed and the domestic hot
water control valve [16] modulates, allowing district supply water to
flow through the domestic hot water heat exchanger [18] to maintain
the pre-set hot water outlet temperature, which is measured using a NTC
sensor[15].
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A domestic hot water safety shut-off valve [12] is provided in order to
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interrupt the hot water flow to the tap in the event of excessive hot water
temperatures due to a failure condition. The domestic hot water outlet
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temperature is adjustable between 30 °C - 60 °C on the heat interface
unit control unit [1].
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During a central heating demand, the domestic hot water control valve
[16] remains closed and the central heating control valve [4]
modulates, allowing district water to flow through the central heating
heat exchanger [3] to maintain the pre-set central heating flow
temperature which is measured using a NTC sensor [6]. A low energy
6720808928-18.1Wo
self regulating pump [8] is used to provide water circulation through the
central heating circuit. The central heating flow temperature is
adjustable between 30 °C - 80 °C on the heat interface unit control [1].
The district heating return temperature is measured using a NTC sensor
[2].The control unit [1] will automatically modulate the central heating
delivery to ensure low return temperatures back to the district network.
The district return temperature will be kept below the central heating
flow temperature. This function prevents the HIU working in case the
district flow and return connections are reversed.
The default district heating return temperature limit is 50 °C, this can
only be adjusted with a Sense II.
If a Sense II is not used as a permanent device within the customers
property for controlling the system, it is possible to connect a Sense II to
the HIU control unit during commissioning only, in order to a set the
maximum allowable return temperature.
The heat interface unit can operate up to a supply differential pressure of
80kPa (800mbar). For supply differential pressures above 80kPa
(800mbar), a differential pressure control valve [5] should be fitted.
This provides a controlled differential pressure of 30kPa (300 mbar)
across the heat interface unit as the supply differential pressure varies
up to a maximum of 400kPa (4000mbar), the Worcester KE Plus, E Plus
and E HIU's incorporate a DPCV as standard.
Control unit LED indicators
▶ When an obstruction e.g. a shelf is positioned above
the unit it may be difficult to see the LED indicators.
Worcester KE Plus with by-pass valve
▶ The maximum supply differential pressure is 400kPa
(4000mbar)
6 720 808 928 (2017/06)