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Y and W type plans can be used, but the need for additional relays is not practical. It is much easier to convert Y and W type plans to S types from the start. 8.8 Bivalent Systems For bivalent systems, it is necessary to disconnect the internal immersion element from the relay inside the heat pump control panel. Taking the live and neutral outputs from this relay extend this wire to the boiler. Isolate this cable through a fused double pole spur switch and mark on the switch that the supply comes from the heat pump. Follow the wiring diagram as shown in Figure 8-11 for a bivalent system. MCB 230V 50Hz LN E 45 6 7 8 9 10 1 Limit 2 c 1 Control 2 c Programmer Heating zone valve CH HW Fuse Fuse L Off O Bl Br Gr Off O Bl Br Gr DHW Zone Valve Relay 3 N 13 Room Thermostat Cylinder Thermostat L N E E N L In Out Solar pump Solar controller Panel sensor Cylinder sensor 2 CCH HW 12 3 Heat pump S-Plan controls connections IMPORTANT Do not take the Neutral from the heat pump to feed the boiler circuit. This will create an imbalance at the MCB and cause nuisance tripping. Always take the neutral supply from the existing S-Plan wiring centre. Electrical 25 Figure 8-14: Connection diagram for Grant solar thermal system Domestic Hot Water 9.1 Temperature Control The desired hot water temperature stored in the cylinder can be adjusted on the BTC controller. As already mentioned, the heat pump works most efficiently at lower temperatures but these temperatures are not suitable for domestic hot water which should always be stored at about 60.C. 9.2 Heat Pump Cylinders As the water temperature from the heat pump is lower than traditional systems, a much larger coil is required inside the cylinder to transfer the heat efficiently. Grant Engineering has a range of 7 stainless steel cylinders from 90 litres to 300 litres with coil areas of up to 3.5m.. Visit for more information. These cylinder have been designed to match the output from the Grant Aerona heat pumps for maximum efficiency and faster re-heat times when compared to standard type indirect cylinders. 9.3 Temperature Boost It is possible to use the heat pump to raise the DHW temperature to 60.C. During the summer, this may be preferable, when the external ambient air temperature is high. However, during the winter, it would not be economical for any heat pump to try to raise the water temperature to this level. As a result, Grant has developed a control system that will take the temperature of the existing cylinder from 45°C to 60°C, after the cylinder thermostat has switched off the hot water operation of the heat pump. This system uses both the existing cylinder immersion element and cylinder thermostat, but operated via an ‘addon’ relay and override switch enclosed in a separate unit to be mounted next to the cylinder. This system is fully automatic but can be overridden by the user if required, i.e. the user can switch on the immersion element using the override switch to manually boost the hot water cylinder temperature. The DHW boost pack contains a power relay and an additional 2-pole isolator. LN E 45 6 7 8 9 10 1 Limit 2 c 1 Control 2 c Programmer Fuse Fuse Fuse HIg Zone Valve MCB 230V 50Hz L L Off O Bl Br Gr Off O Bl Br Gr DHW Zone Valve To domestic hot water booster relay coil (see Figure 9-2) 230V/24 Vac Transformer N 13 N Room Thermostat Cylinder Thermostat Immersion element 12 11 10 9 8 7 6 5 4 3 2 1 BTC Heat Pump PCH Controller Compressor 2 HW CH C 32 1 Heat pump S-Plan controls connections CH HW Return sensor Outdoor sensor Supply sensor Relay 2 in heat pump control panel LN E 45 6 7 8 9 10 1 Limit 2 c 1 Control 2 c Programmer Fuse Fuse Fuse HIg Zone Valve MCB 230V 50Hz L L Off O Bl Br Gr Off O Bl Br Gr DHW Zone Valve To domestic hot water booster relay coil (see Figure 9-2) 230V/24 Vac Transformer N 13 N Room Thermostat Cylinder Thermostat Immersion element 12 11 10 9 8 7 6 5 4 3 2 1 BTC Heat Pump PCH Controller Compressor 2 HW CH C 32 1 Heat pump S-Plan controls connections CH HW Return sensor Outdoor sensor Supply sensor Relay 2 in heat pump control panel 9 Domestic Hot Water 23 24 22 21 20 19 18 17 16 15 14 13 Figure 9-1: Connection diagram for DHW booster system Domestic 27 NB. Setting this override switch to OFF does not stop the automatic operation of the immersion element. The required relay, manual override switch and enclosure are available from Grant Engineering UK Ltd as a kit. For details of this Automatic Domestic Hot Water Boost Kit (Grant Ref. HPDHWBK1) refer to Section 15 of these instructions. When fitted, this kit interrupts the electrical supply between the existing immersion heater and the fused immersion switch. Refer to Figures 9-1 and 9-2 for electrical connection details. With the cylinder thermostat set to 45°C, when the heat pump raises the DHW cylinder to this temperature, the cylinder thermostat switches to the ‘satisfied’ position. The resulting switched live from the auxiliary (normally open) contact of the...

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