Heat Pump - KwZ usage through the roof

Reed_Richards

Something else.
  
Press the left or right arrow on the controller until you come to Menu, then press the OK
Press the left or right arrow until you come to Schedule then press the OK button
See if you have a schedule set for heating your DHW or if it is on all the time.

If your household sleeps for regular hours you can save money by turning off hot water heating overnight then having it come back on about an hour before you get up. 

My schedule is:

00:00 to 06:15    Off
06:15 to 07:00    55 C
07:00 to 22:30    45 C
22:30 to 00:00     Off

I get cheap electricity from midnight to 07:00 so I use that to make my cylinder 55 C, quite hot by heat pump standards.  Hopefully that will last us the rest of the day.  But to stop the water getting too cool if we use a lot of it the temperature is then set to 45 C for the rest of our waking hours. 

Reed_Richards

My theory so far is that your hot water cylinder is in a cold place and it, and the pipes that supply it, are insufficiently insulated.  It's set to be at 50 C 24/7 so it loses a lot of heat, which costs you money and because it frequently has to reheat the cylinder in cold weather then there isn't enough time left to fully heat your house.  Also, because your installer hasn't adjusted your Heatmisers to prevent short cycling then your heat pump sometimes operates inefficiently.

But that's all guesswork and some or all of it could be wrong.  The person from HeatGeek coming in October should be able to diagnose this for you, although it may take them some while if they are unfamiliar with LG heat pumps and have to work their way through the instruction manual.   

Pile_o_stone

From what I've read about heat pumps, the operating costs ramp up when you're heating water for taps rather than water for radiators, as the temperatures are higher. I'm in the process of moving house and will look to either buy a house without mains gas or will remove mains gas from the house. I will then have electric showers (hot water on demand), a quooker tap to provide hot/boiling water in the kitchen and small water heaters for the sinks in the bathrooms. I hate baths, so if there is one fitted, it will be removed. Essentially, the heat pump with therefore only be used just for central heating.

Any downside with this approach? If not, then could the OP retrofit this and have it pay for itself over a few years?

matt_drummer

Pile_o_stone said:

From what I've read about heat pumps, the operating costs ramp up when you're heating water for taps rather than water for radiators, as the temperatures are higher. I'm in the process of moving house and will look to either buy a house without mains gas or will remove mains gas from the house. I will then have electric showers (hot water on demand), a quooker tap to provide hot/boiling water in the kitchen and small water heaters for the sinks in the bathrooms. I hate baths, so if there is one fitted, it will be removed. Essentially, the heat pump with therefore only be used just for central heating.

Any downside with this approach? If not, then could the OP retrofit this and have it pay for itself over a few years?

You won't get the grant without DHW as far as I am aware so you would have to have a tank of some sort fitted. It doesn't mean you have to use it, of course.

The heat pump will be miles cheaper than your suggestion.

For half of the year my heat pump heats the water in the tank at a COP of over 4, it's worse in the winter but even then it is never below about 2.5.

I don't run a disinfection cycle, like lots of others, I don't think it is necessary.

With your proposals you will only heat the water you need but it will all be at 100% efficiency.

I don't think you will save anything over an appropriately sized hot water tank heated by the heat pump.

I use less than 1kWh a day of electricity on DHW at this time of year and not much more in the winter. It is not significant.

matelodave

As @matt_drummer suggests it will cost you more to heat water on demand at 100% efficiency than it will with a heatpump even if it's COP (efficiency)drops right down to 200%.  Although, that said, you may have the advantage that as the water is heated at the point of use then you wont get the wastage of water in the pipework between the tank and the tap. 

However as pointed out you wont get a grant for a heatpump that doesn't supply hot water as well, that's why Air to Air heatpumps don't qualify.

You'd have to do some careful sums to check it out but a Quooker at a grand or more to be installed isn't really a cheaper way of heating water - an electric kettle would cost the same to heat the same amount of money and would save the upfront cost.

Like matt says, I dont run the legionnaire cycle and at this time of the year I only need to run the heatpump for an hour or so once every two days to give us enough hot water for the both of us to shower every day (short showers with an eco shower head). We use a dishwasher and if we need boiling water then we heat as much as we need in a kettle (glass jug and base element so only heat as much as required).

IMO the energy requirement of the defrost cycle is greatly exaggerated and, as it uses heat generated by the heatpump anyway, the cost is pretty minimal.

My heatpump is now over 14 years old and was installed before people really knew what they were doing but I still reckon it achieves an efficiency of over 300% during the year. New pumps can usually do quite a bit better than that nowadays if they are specified, installed and operated properly

FreeBear

matelodave said: You'd have to do some careful sums to check it out but a Quooker at a grand or more to be installed isn't really a cheaper way of heating water - an electric kettle would cost the same to heat the same amount of money and would save the upfront cost.

Just been looking at boiling water taps in response to another thread. Whilst a Quooker will set you back some £1250, there are cheaper alternatives. I see Screwfix do a range starting at £225. No idea of quality or reliability.

Reed_Richards

Presumably a boiling water tap also requires a dedicated circuit to supply it?

Reed_Richards

JEdelman said:

I’ve taken the advice, contacted Heat Geeks and have a recommended engineer coming in October to carry out an inspection. 

@thevilla has become a bit disillusioned by Heat Geeks:
 https://forums.moneysavingexpert.com/discussion/6551444/heat-geeks/p1
(although there is still a chance that it might turn out alright in the end).  More importantly, Heat Geeks don't install LG heat pumps on any regular basis, if at all.  @JEdelman , if you can find a heat pump installer who works with LG heat pumps that might be a better choice.

FreeBear

Reed_Richards said:

Presumably a boiling water tap also requires a dedicated circuit to supply it?

The ones I looked at require (at a minimum) a 13A socket close by. At 1.5-2kW, the energy draw doesn't warrant a dedicated circuit.

With a tank capacity of 4l (seems to be a typical size for these things), you'd only use ~0.4kWh to heat a tank from cold to 98°C.

Pile_o_stone

FreeBear said:

Reed_Richards said:

Presumably a boiling water tap also requires a dedicated circuit to supply it?

The ones I looked at require (at a minimum) a 13A socket close by. At 1.5-2kW, the energy draw doesn't warrant a dedicated circuit.

With a tank capacity of 4l (seems to be a typical size for these things), you'd only use ~0.4kWh to heat a tank from cold to 98°C.

The quooker tap I was looking at had a 7 litre vacuum cylinder for storing a reservoir of boiling/hot water, which could be heated up slowly throughout the day, which I guess would be ideal for solar as boiling a kettle uses 3kw and would swamp most solar generation and result in energy imported from the grid.

On the DHW discussion, it would be interesting to know the cost of heating a cylinder of water, including kw/h losses from cylinders and pipework compared with instant heating of water. I currently have a large cylinder connected to my solar panels, so I get free hot water in summer. I don't know if this summer saving is offset in winter by using mains gas to heat that same large tank of water. 

Logically, I'd say that just heating the exact amount of water we actually shower with seems more cost effective than heating a large tank, some of which is used for showing, the rest just goes cold again. 

EDIT: We have a 350l thermal store that has 100mm of Kingspan type material for insulation. This in turn sits in a cupboard with a further 100mm of Kingspan panels in the walls. The cupboard is in a utility room in the centre of the house (i.e. no outside walls).  We still see heat loss at a rapid rate, probably most through the pipe connecting the top of the thermal store with the expansion tank in the loft.