Octopus Heat Pumps

koru

matt_drummer said:

My 9kW did not cycle on and off, my house just got very hot.

But couldn’t you have set it to turn off when the house got too warm? I thought you let it overheat because this was less inefficient than letting it cycle on and off. 

Reed_Richards

There are two ways to operate a heat pump.  You can treat it as much like a gas boiler (with Weather Compensation) and set the temperature using a room thermostat in a suitable location, balancing the radiators in other rooms so they reach the desired room temperature at the same time as the thermostat-controlled room.  The thermostatic control will tend to cause the heat pump to cycle on and off, although not too much if you get the Weather Compensation settings right.

The other way is to rely entirely on Weather Compensation without the use of a room thermostat or thermostatic radiator valves and just balance the incoming water temperature to match the needs of the house for whatever the outside temperature is.  If you get this perfectly tuned then you can hold your house at a constant temperature at all times whilst the heat pump is on at all times, just working hard enough to maintain the necessary water temperature.  This is supposed to achieve a better efficiency.  Matt can explain what went wrong in his case but without any thermostatic controls (except for the Leaving Water Temperature) then it's possible for the house to get too hot and you can't set the ASHP to turn off if that should happen.    

matt_drummer

koru said:

matt_drummer said:

My 9kW did not cycle on and off, my house just got very hot.

But couldn’t you have set it to turn off when the house got too warm? I thought you let it overheat because this was less inefficient than letting it cycle on and off. 

Yes, I could have done that and it was what Octopus thought I should do.

And on some days this is ok. But many times the house was too warm in just a few minutes, it was way too much for our house.

But in general, the initial 60 minutes of a heating cycle were the most inefficient and consumed the most electricity, it took a long time to settle down to using the minimum amount of electricity. In the inital stages it uses much more.

But continually turning it on and off I would use more electricity.

This also meant I would keep getting big chunks of heat and then nothing for a couple of hours waiting for the house to get cold enough to heat again. 

It was like a massively oversized gas or oil boiler, not what I wanted from a heat pump.

I wanted something that would put in a steady amount of heat that was more or less equal to the heat loss of the house.

The Madoka room thermostat could not operate as intended, the heat pump couldn't modulate its output any lower and at times the initial heat output was so much that it would just turn off.

Other manufacturers do better at shorter cycles, the Daikin is very aggressive in the first 30 to 60 minutes of a heating cycle.

I did find a way to tame this with the 9kW but that was only really possible due to it being grossly oversized.

I still have the same issue with the 8kW.

I can run my heating at 26/27c flow temperature, my radiators are big enough to do this. 

With a room temperature of 21c and a mean flow temperature of 25c my radiators can output at least 2,500w

But I struggle to do it because for the first 20 minutes the Daikin heat pump runs the circulation pump at full speed.

This means I get over 5kW of heat for the first 20 minutes even at a flow temperature of only 26c.

It then takes another 10 minutes to reduce the flow rate, in this 30 minutes the heat pump has over powered my radiators and cannot run.

However, I have learnt a few tricks over the last few months and I can now get it to run continuously at 27c flow temperature.


It's all great saying just run the heat pump for 15 minutes an hour or whatever you need but in reality it is not so easy.


Get whatever heat pump you want, if you think you can make a 9kW Daikin Altherma 3 work to your satisfaction then go for it.

rjmachin

I have just had an email from National Grid saying at this time they are unable to approve the installation of the heat pump.

This is because it would exceed the maximum demand of the fuse.  (it's a 100amp fuse - I have an EV and had to upgrade for that)

National Grid said I would need to either

• upgrade the supply to a three phase service
• install a load limiting device
  

I am presuming the load limiting device would be cheaper, but how does it work?

If, for example, I charge my car from 00:30 - 4:30, and the heat pump comes on a 04:00 (for example), will the limiter drop the car charger to half speed (16amps?) for the half hour cross over, or would it be permanently limited all the time?

Octopus haven't contacted me yet, just had the email from NG, so expecting something soon from Octopus

Reed_Richards

I have what is nominally a 12 kW heat pump but they only problem that my installer had with the DNO was finding the right figure for the maximum current to supply to them.  It's certainly not the ~50 Amps that 12 kW would imply.  And In fact my mains fuse is only 80 A. 

I suspect either the DNO has been supplied the wrong information or they have misinterpreted what they have.  I bet if you were forced to install a current limiting device it would never actually activate.  

michaels

rjmachin said:

I have just had an email from National Grid saying at this time they are unable to approve the installation of the heat pump.

This is because it would exceed the maximum demand of the fuse.  (it's a 100amp fuse - I have an EV and had to upgrade for that)

National Grid said I would need to either

• upgrade the supply to a three phase service
• install a load limiting device
  

I am presuming the load limiting device would be cheaper, but how does it work?

If, for example, I charge my car from 00:30 - 4:30, and the heat pump comes on a 04:00 (for example), will the limiter drop the car charger to half speed (16amps?) for the half hour cross over, or would it be permanently limited all the time?

Octopus haven't contacted me yet, just had the email from NG, so expecting something soon from Octopus

Interesting, can't see why they would think an EV and heat pump might put 100A at risk. 

May have implications for us if they take info from the smart meter as we do hammer the TOU tariff already with off peak heating (3kw of electric heaters), hot water heating (3kw immersion) and dishwasher and washing machine running (2.5-3kw each when heating?) plus charging two leafs (v2h at 5kw and granny at 2.5kw) so it would look like we don't have much headroom but of course a heat pump would replace the heat and hot water loads.

Still Octopus have now gone completely quiet again re a possible survey date so it doesn't seem like it is an immediate problem.

Gerry1

rjmachin said:

National Grid said I would need to either

• upgrade the supply to a three phase service
• install a load limiting device
  

I am presuming the load limiting device would be cheaper, but how does it work?

It's called a smart meter.  They all have Load Limiting baked in.  If you go over the limit when LL is activated it'll be a case of Computer Says No and the whole supply will be cut off.

Reed_Richards

Gerry1 said:

It's called a smart meter.  They all have Load Limiting baked in.  If you go over the limit when LL is activated it'll be a case of Computer Says No and the whole supply will be cut off.

So that's "limiting" in the sense of limiting my calorie intake by not eating anything?  If the supply is cut off, how do you get it back on again?

Gerry1

@Reed_Richards You reduce your demand.

https://www.engineeringnews.co.za/article/eskom-to-roll-out-load-limiting-to-more-gauteng-areas-following-fourways-pilot-2024-02-01

https://www.lbc.co.uk/news/risk-blackouts-uk-new-gas-power-plants-net-zero/

rjmachin

Gerry1 said:

@Reed_Richards You reduce your demand.

https://www.engineeringnews.co.za/article/eskom-to-roll-out-load-limiting-to-more-gauteng-areas-following-fourways-pilot-2024-02-01

https://www.lbc.co.uk/news/risk-blackouts-uk-new-gas-power-plants-net-zero/

But how does / should it work practically?

I currently have:

• Electric cooker / hobs
• Tumble Dryer
• Dish washer
• Washing machine
• 7kW car charger

Would they really find it acceptable to cut off all power if the car charger and heat pump reached the limit?

I imagined (maybe incorrectly) that something would be needed to reduce the power being used by a device if it needs to.

For example, I have seen that the MyEnergy devices have the ability to place a limit and reduce the power used if needed.  (However, I do not have these devices and are too expensive to justify the cost - My heat pump cost would increase from £1,260 to around £2,500)

I guess I need to speak to my Octopus Heat Pump Install Coordinator and see what they say.