I am curious about the DNO remark on harmonics. I can find no warning in the S E WPL 25AS literature about harmonics being troublesome. So I had a dabble at working out what the power consumption of the compressor is for full air-derived thermal heat output.
The unit has integral electric heating elements (selectable 3kW, 3.2kW or both) for boost heating of water and emergency heating if the compressor heat pump fails. At page 16 are details on the uses for the heating elements - here it states that the emergency /booster heaters might be an optional connection depending on what other calorific heating is available for space heating and hot water. This could then be an option for the OP if he has a back up gas boiler. I think that they should be connected and switched on via a timer to provide at least function d) below.
Connect the electric emergency/booster heater if you want to utilise the following appliance functions:
a. Mono energetic operation If the heat pump cannot reach the dual mode point, the electric emergency/booster heater ensures both the heating operation and the provision of high DHW temperatures.
b. Emergency mode Should the heat pump suffer a fault that prevents its continued operation, the heating output will be covered by the electric emergency/booster heater.
c. Heat-up program (only for underfloor heating systems) Where return temperatures are <25 °C, the electric emergency/booster heater must provide the necessary heat for screed drying.
d. Pasteurisation control The electric emergency/booster heater starts automatically when the pasteurisation control is active in order to regularly heat the DHW to 60 °C to protect it against the growth of legionella bacteria.
At page 18 of it are details of the electrical supply connections. terminal block X5 supplies the electric heaters and block X3 the inverter. So, the ASHP unit has separate external supplies (albeit they might be derived ultimately from the same consumer unit) with a fuse/mcb for each of the heaters and inverter (and also the control supply block X4). See page 39 third column from right for details of the size and type of the fuses/mcbs. The mcbs are C32A - inverter, and 2 x B16A - 2 x heaters and 1 x B16A - controller. The maximum current is stated to be 35A - I think this excludes the electric heaters because the maximum power of the boost heaters is 6.2kW or circa 25A and my calculated average power consumption of the compressor for A-7/W55 heat output of 13.97kW and a Coefficient of performance of 2.35 is 13.97/2.25 = 6.2kW so another 25A. (The table gives a figure of 5.94kW. I guess the difference is down to auxilliaries such as fans and pumps. ) I don't know why the maximum power consumption without emergency/booster heater is stated to be 8.9kW (cf 6kW) - maybe short term running of the compressor at a higher output?
Summary - using the ASHP inverter compressor alone I reckon consumes circa 6kW. If ithe emergency/booster heaters are activated alongsidde the inverter compressor then the consumption is either 9kW or 12.2kW.
I do not think a single 6kW inverter driven load is excessive in an urban setting but maybe for a weaker distribution network in a rural setting it could present a harmonic be problem hence the need for reinforcement especially if more than one system is connected.
Certainly a high load factor single phase ASHP load of circa 12kW on top of the usual household loads would require greater capacity in the cables leading to your home and in your street. I think this is the main reason for the upgrade to 185mm2 (circa 350A per phase). Waveform-Wavecon Cables | Eland Cables - https://www.elandcables.com/cables/waveform-wavecon-cables
The unit has integral electric heating elements (selectable 3kW, 3.2kW or both) for boost heating of water and emergency heating if the compressor heat pump fails. At page 16 are details on the uses for the heating elements - here it states that the emergency /booster heaters might be an optional connection depending on what other calorific heating is available for space heating and hot water. This could then be an option for the OP if he has a back up gas boiler. I think that they should be connected and switched on via a timer to provide at least function d) below.
Connect the electric emergency/booster heater if you want to utilise the following appliance functions:
a. Mono energetic operation If the heat pump cannot reach the dual mode point, the electric emergency/booster heater ensures both the heating operation and the provision of high DHW temperatures.
b. Emergency mode Should the heat pump suffer a fault that prevents its continued operation, the heating output will be covered by the electric emergency/booster heater.
c. Heat-up program (only for underfloor heating systems) Where return temperatures are <25 °C, the electric emergency/booster heater must provide the necessary heat for screed drying.
d. Pasteurisation control The electric emergency/booster heater starts automatically when the pasteurisation control is active in order to regularly heat the DHW to 60 °C to protect it against the growth of legionella bacteria.
At page 18 of it are details of the electrical supply connections. terminal block X5 supplies the electric heaters and block X3 the inverter. So, the ASHP unit has separate external supplies (albeit they might be derived ultimately from the same consumer unit) with a fuse/mcb for each of the heaters and inverter (and also the control supply block X4). See page 39 third column from right for details of the size and type of the fuses/mcbs. The mcbs are C32A - inverter, and 2 x B16A - 2 x heaters and 1 x B16A - controller. The maximum current is stated to be 35A - I think this excludes the electric heaters because the maximum power of the boost heaters is 6.2kW or circa 25A and my calculated average power consumption of the compressor for A-7/W55 heat output of 13.97kW and a Coefficient of performance of 2.35 is 13.97/2.25 = 6.2kW so another 25A. (The table gives a figure of 5.94kW. I guess the difference is down to auxilliaries such as fans and pumps. ) I don't know why the maximum power consumption without emergency/booster heater is stated to be 8.9kW (cf 6kW) - maybe short term running of the compressor at a higher output?
Summary - using the ASHP inverter compressor alone I reckon consumes circa 6kW. If ithe emergency/booster heaters are activated alongsidde the inverter compressor then the consumption is either 9kW or 12.2kW.
I do not think a single 6kW inverter driven load is excessive in an urban setting but maybe for a weaker distribution network in a rural setting it could present a harmonic be problem hence the need for reinforcement especially if more than one system is connected.
Certainly a high load factor single phase ASHP load of circa 12kW on top of the usual household loads would require greater capacity in the cables leading to your home and in your street. I think this is the main reason for the upgrade to 185mm2 (circa 350A per phase). Waveform-Wavecon Cables | Eland Cables - https://www.elandcables.com/cables/waveform-wavecon-cables
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