ASHP to heat water for a shower or electric shower?

QrizB

coffeehound said:

QrizB said:

coffeehound said:

Presumably the rating of a HP system in kW is not the power that it requires from the grid but an indication of its output based on a nominal COP?

Yes, the heat pump rating is the nominal output power.

Is it a nominal COP used for every similar system, or a more complex formula perhaps based on testing by the manufacturer, akin to a miles-per-gallon figure for cars?

Reputable manufacturers publish good data on their heat pumps, including COPs at varying internal and external temperatures.

Here is a (concise) data sheet for a Mitsubisi Ecodan:
https://library.mitsubishielectric.co.uk/pdf/book/Ecodan_PUZ-WM85VAA_Monobloc_Air_Source_Heat_Pump_Product_Information_Sheet#page-1-2

That particular heat pump claims a SCOP of 3.47 when producing water at 55C, and 4.79 when producing water at 35C.

I would expect there to be more data available on Mitsubishi's websites if you waqnt to go looking.

coffeehound

Reed_Richards said:

coffeehound said:

Presumably the rating of a HP system in kW is not the power that it requires from the grid but an indication of its output based on a nominal COP?

My heat pump is specified to perform down to -15 C.  At that temperature I suspect its actual CoP will be close to 1.  Presumably it will then be using something close to its rated output in electrical power.  But most of the time the power requirement will be much less.

Edit.  It has a dedicated circuit with a 40 A fuse 

I would guess that would work the other way around and that the output power of the HP would trail off as OAT falls.  At the end of the day, the HP is an electric pump and fans which work at a given input power.  If it starts powering up the resistive heater and immersion, then that is an additional load.  

QrizB

If you're feeling really nerdy, here is the data book for a slightly different model of Mitsubishi heat pump.

See section 5.2 under "Performance data" for heating performance.

https://www.mitsubishi-les.info/database/servicemanual/files/201803_ATW_DATABOOK.pdf

coffeehound

QrizB said:

coffeehound said:

QrizB said:

coffeehound said:

Presumably the rating of a HP system in kW is not the power that it requires from the grid but an indication of its output based on a nominal COP?

Yes, the heat pump rating is the nominal output power.

Is it a nominal COP used for every similar system, or a more complex formula perhaps based on testing by the manufacturer, akin to a miles-per-gallon figure for cars?

Reputable manufacturers publish good data on their heat pumps, including COPs at varying internal and external temperatures.

Here is a (concise) data sheet for a Mitsubisi Ecodan:
https://library.mitsubishielectric.co.uk/pdf/book/Ecodan_PUZ-WM85VAA_Monobloc_Air_Source_Heat_Pump_Product_Information_Sheet#page-1-2

That particular heat pump claims a SCOP of 3.47 when producing water at 55C, and 4.79 when producing water at 35C.

I would expect there to be more data available on Mitsubishi's websites if you waqnt to go looking.

Thanks so they seem to have quoted the nominal COP as that obtained for delivering water at 45 C between -10 to +20 OAT.   So is that the basic criterion for the headline power output?  And the steady-state consumption is the 9.1 amps = about 2.1 kW.   
They state that as 'MAX' so it shouldn't go much over that, apart from switch-on inrush current

QrizB

coffeehound said:

 And the steady-state consumption is the 9.1 amps = about 2.1 kW.   
They state that as 'MAX' so it shouldn't go much over that, apart from switch-on inrush current

I think the [MAX] in square brackets relates to the [22] also in square brackets, so max. current 22A.

coffeehound

QrizB said:

coffeehound said:

 And the steady-state consumption is the 9.1 amps = about 2.1 kW.   
They state that as 'MAX' so it shouldn't go much over that, apart from switch-on inrush current

I think the [MAX] in square brackets relates to the [22] also in square brackets, so max. current 22A.

Ah okay. so perhaps that is the switch-on current