What size generator

badgerhowlin

Hi,

Im thinking this is the best place for this question.
I have an 8kw heat pump with a soft start motor.

Can anyone tell me what size Genny i would need to run this.
There might be a few lights and a TV also on when its running.

Thanks

2011

First of all you need to work out what the total load is.
I would size the generator so that the generator could never be more than 80% loaded. That way the generator is never under too much strain.

Remember your generator will be rated in kVA, not kW.
The bulk of your heat pump load is the compressor which I would expect to have a power factor of roughly 0.9
A load of 8kW with a power factor of 0.9 is in fact 8.89kVA

badgerhowlin

NIBE F1245- 8 kW
Supplied power at 0/35°C * 1,62 kW
Delivered power at 0/35°C * 8,19 kW
COP 0/35°C * 5,05
Supplied power at 0/35°C ** 1,64 kW
Delivered power at 0/35°C **7,67 kW
COP 0/35°C **4,68
Rated voltage 400 V 3NAC 50 Hz
Min fusing (fuse type C) excl immersion heater 16 A 16 A
Volume water heater 180 litres 180 litres
Max pressure in storage heater 1,0 MPa (10 bar)
Immersion heater, 9 kW

Is that of any help? (Immersion is never turned on)

2011

badgerhowlin wrote: »

NIBE F1245- 8 kW
Supplied power at 0/35°C * 1,62 kW
Delivered power at 0/35°C * 8,19 kW
COP 0/35°C * 5,05
Supplied power at 0/35°C ** 1,64 kW
Delivered power at 0/35°C **7,67 kW
COP 0/35°C **4,68
Rated voltage 400 V 3NAC 50 Hz
Min fusing (fuse type C) excl immersion heater 16 A 16 A
Volume water heater 180 litres 180 litres
Max pressure in storage heater 1,0 MPa (10 bar)
Immersion heater, 9 kW

Is that of any help? (Immersion is never turned on)

I don't see any mention of power factor.
You could contact the manufactuer and ask.

Is this a 3 phase unit?
I am not clear on what size the overall load is.
In you post above you give a few different loads, I assume they are from different componets within the heat pump itself.
Perhaps it would be best to contact the manufactuer and ask what size the overall load is, overall power factor etc..
What size MCB supplies this unit?

If the immersion is never used disconnect it or size the generator so that it can handel the load if the immersion was turned on.

Bruthal

The 8kw heat pump part is likely the heat output of the device, as in the heat collected from the ground via an evaporator, and transferred to the point of use via the condenser. So the 8kw wont really be the compressor supply demand.

Therefore power factor wont matter too much, as the compressor supply power looks like 1.62kw form OP description. Likely 3 phase as well at that size of compressor.

It has a 9kw immersion heater as well. Probably 3 x 3kw heaters powered from a 3 phase setup.

2011

Bruthal wrote: »

The 8kw heat pump part is likely the heat output of the device, as in the heat collected from the ground via an evaporator, and transferred to the point of use via the condenser. So the 8kw wont really be the compressor supply demand.

I was thinking that myself, but I have never seen a heat pump with that small an output, not even a single phase one and this appears to be 3 phase.

Bruthal

2011 wrote: »

I was thinking that myself, but I have never seen a heat pump with that small an output, not even a single phase one and this appears to be 3 phase.

It seems to be some sort of combi unit. Certainly the compressor will be a lot smaller than the heat pump rating. All the compressor does is transfer heat from one place to another.

It seems to have a 9kw electric immersion. That would be the main use of a 3 phase supply. But a near 2kw compressor will work a lot more efficiently with a 3 phase supply too. Single phase induction motors are only low torque yokes suitable for small applications.

Bit surprised at the 8kw (small)output myself if it is designed to heat rooms. Would probably make a good water heater though to heat large volumes from the heat pump.

Maybe it can be reversed and used as a cooler too.

2011

Bruthal wrote: »

as the compressor supply power looks like 1.62kw form OP description

I installed a heat pump a number of years ago. The input was in the region of 8kW and it heated a house that was in excess of 3,000 sq. feet. From what I can recall the electrical load was primarily the compressor but also smallish submersible pump. Despite the fact that the compressor has a soft start of some kind a slight dimming of the lights was noticeable when ever the compress kicked in.

I would be very surprised if this heat pump has a compressor as small as 1.62kW

It has a 9kw immersion heater as well.

I am confused by this to be honest. I have no idea what the purpose of the immersion would be. In my (admittedly limited) experience of heat pumps I have never seen any with a heater of any kind. To me a 9kW immersion unit kind of defeats the whole purpose of having a heat pump in the first place.

Bruthal

2011 wrote: »

I installed a heat pump a number of years ago. The input was in the region of 8kW and it heated a house that was in excess of 3,000 sq. feet. From what I can recall the electrical load was primarily the compressor but also smallish submersible pump. Despite the fact that the compressor has a soft start of some kind a slight dimming of the lights was noticeable when ever the compress kicked in.

I would be very surprised if this heat pump has a compressor as small as 1.62kW

Well the compressor is only the facility to transfer heat from one area or medium(ground), to another (water, air in rooms etc), which it transfers via the refrigerant. If the output(heat transfer rating) of this unit is 8kw, then the compressor will be a lot smaller than this. The coefficient of performance which is output/energy input can be between 2 and 4 for heat pumps probably. To get 4 is likely in ideal situations.

I am confused by this to be honest. I have no idea what the purpose of the immersion would be. In my (admittedly limited) experience of heat pumps I have never seen any with a heater of any kind. To me a 9kW immersion unit kind of defeats the whole purpose of having a heat pump in the first place.

Yea never seen any like that myself with the electric heater in it as well. That`s an air source one in your picture there.

Refrigeration cycle is simple enough though. If the boiling point of gasses can be grasped, i.e. refrigerant gas in that unit boils at -40c at atmospheric pressure, so it is compressed into a liquid in the condenser, gives off heat it has absorbed, passes through the capilary tube, or expansion valve in larger units and chillers etc, large drop in pressure, so it now drops to its more natural boiling point close to -40, absorbs heat from its surroundings, the ground in the case of this heat pump, passes through the compressor, and is compressed into liquid in the condensor, releasing the heat it absorbed in the evaporator.

A fridge does exactly the same, on a smaller scale. Removes heat from the fridge contents, and releases that heat into the room.

2011

Bruthal wrote: »

Well the compressor is only the facility to transfer heat from one area or medium(ground), to another (water, air in rooms etc), which it transfers via the refrigerant.

Yes, a glorified fridge "working in reverse".
I get that.

If the output(heat transfer rating) of this unit is 8kw, then the compressor will be a lot smaller than this.

True.
But that is tiny, at that size it could pretty much be fed from a socket circuit (if it were single phase).
Any heat pump I have seen is fed from at least a 6 or a 10 sq. cable.
The fact that it is three phase also suggests that it is unlikely to be so small.
I think we may have some incorrect information and/or we are missing some information.

That`s an air source one in your picture there

Yeah, the most simple diagram I could find to illustrate a lack of immersion elements:)
Same principle as a ground source but using water to heat the refridgerant instead of air blown by a fan.

Bruthal

2011 wrote: »

True.
But that is tiny, at that size it could pretty much be fed from a socket circuit (if it were single phase).

Yea but an induction motor of size approaching 2kw, while small in terms of load, really needs 3 phase to be of much use, particularly in efficiency terms. Not many single phase induction motors in general use above 2kw probably.

Any heat pump I have seen is fed from at least a 6 or a 10 sq. cable.
The fact that it is three phase also suggests that it is unlikely to be so small.
I think we may have some incorrect information and/or we are missing some information.

Just had a look at the actual specs of it. Supplied power for 8kw model is 1.64kw, delivered power is 7.67kw, and COP = 4.68

2011

Bruthal wrote: »

Supplied power for 8kw model is 1.64kw, delivered power is 7.67kw, and COP = 4.68

Just did a bit of a google.
To my surprise the figures seem plausible.

http://www.hpa.ie/faqs.html

The 9kW immersion and the three phase supply (not normal for domestic) threw me. I still can't understand what the immersion is about.

Bruthal

2011 wrote: »

Just did a bit of a google.
To my surprise the figures seem plausible.

http://www.hpa.ie/faqs.html

The 9kW immersion and the three phase supply (not normal for domestic) threw me. I still can't understand what the immersion is about.

Yea seems surprising about the immersion alright.

The OP will want a fair generator to power the whole thing anyway, although not so much needed once the immersion is left out.

adrian92

badger,

I do not know if you have had an answer. I would suggest something of the order of 10kVA based on the following;
9kW immersion heater not used.
rough estimate input power = 4kW
Poor power factor
minor extra loads.
l
maybe I missed the conversation - but I wonder why a generator rather than mains.

also the heat pump supplier could possibly provide you with a kVA input requirement.

Anyway - in the absence of any other info I'd run with next size up from 10kVA