Heat Pump - KwZ usage through the roof

NedS

john-306 said:

matt_drummer said:

My water tank has just been heated using 700W at a COP of 4.46

It generated 3.05kWh of heat

I get 15p per kWh for solar export.

The cost of heating my tank with the heat pump was 10.5p (15p x .0.7, the solar export I gave up) and if I had used any form of direct water heating it would have cost me 45.75p

So I am 30.25p better off today by using the heat pump.

That's excellent COP for HW

I'm due to have same as your heat pump fitted in 2 weeks, but nowhere near your sized radiators. 
I've only got solar with 6.4kwh battery at present.

I'm assuming I'd struggle with heat pump in winter to only use the battery through the higher pricing hours if I go to the Cosy tariff?

Thanks.

I'm thinking the same as you - that Cosy looks a great tariff for those with an ASHP and batteries that can shift the majority of their usage to the cheap Cosy slots. The battery basically needs to be large enough to allow it to be fully charged during the cheap 3h slots, and then last for the next 6h of normal/peak rate. If you can load shift other usage a bit too, into the cheap slots, that will help (put the washing machine on at 6am and the dishwasher on at 10pm). At least you should be able to fully recharge between 1-4pm and then completely avoid importing in the 4-7pm peak. You can also try increasing the house temps slightly in the Cosy cheap slots and setting back the temp by a degree or so outside of that, which may help, depending how quickly your house loses heat and how much fluctuation you can tolerate.

Unfortunately we don't have batteries, so I'm planning on sticking with Agile, but we are tracking Cosy closely on the Octopus Compare app to see how it compares.

As Matt says, it's all about the average price you pay. You may struggle on the very coldest days, but for 95% of the year, you may be able to run at or near an effective import price of 11p, and with a SCOP of 4 it will be less than half the price of gas.

NedS

john-306 said:

matt_drummer said:

My water tank has just been heated using 700W at a COP of 4.46

It generated 3.05kWh of heat

I get 15p per kWh for solar export.

The cost of heating my tank with the heat pump was 10.5p (15p x .0.7, the solar export I gave up) and if I had used any form of direct water heating it would have cost me 45.75p

So I am 30.25p better off today by using the heat pump.

That's excellent COP for HW

Just checked our data for June, July and Aug where we've been running a DHW cycle once daily (and mostly no heating), our monthly SCOPs have been 3.52, 3.72 and 3.78. The heat pump was only installed in June so we were still tweaking the setup at the start, hence the small improvement into July and August, so I'll say we are averaging a SCOP of 3.75 during summer just heating DHW.

Pile_o_stone

NedS said:

We can schedule the DHW cycle to run at the cheapest time of the day, and then shower at our convenience. It would be far less flexible trying to limit showering using the electric shower to the cheaper Agile slots. I don't think the family would take well to showering at 3:30am or waiting until 2:30pm in the afternoon for a shower. For this reason, the amount paid for that 1kWh to heat the DHW tank may be significantly less than the amount paid to take that electric shower using the same 1kWh.

For us an ASHP is a more efficient and ultimately cheaper way to heat DHW.

A good point, well made! 
I hadn't considered the possibility of heating a tank of HW during off-peak tariffs. Thanks.

JEdelman

Update: we’re currently in the process of having the inspection carried out but already a number of major issues have been identified. This is the insulation on the pipes going into the house which I’m told is seriously inadequate. 

JEdelman

An update on this. Sadly, despite some minor works from the installer (two larger rads and some silicon over exposed areas) we remain in the same boat. On cold weather days we are burning through £26 worth of electricity and the temperature upstairs fails to get to 17C with barely any heat coming from the radiators. Our usage per year for the heat pump alone is 9,138.37 kWh. The installer says this is not excessive and that the upstairs should not be set above 18C (it's currently set at 21C during the day). Google tells us that the usage is more than double what it should be. Any thoughts or inspiration welcome.

QrizB

JEdelman said:

An update on this. Sadly, despite some minor works from the installer (two larger rads and some silicon over exposed areas) we remain in the same boat. On cold weather days we are burning through £26 worth of electricity and the temperature upstairs fails to get to 17C with barely any heat coming from the radiators. Our usage per year for the heat pump alone is 9,138.37 kWh. The installer says this is not excessive and that the upstairs should not be set above 18C (it's currently set at 21C during the day). Google tells us that the usage is more than double what it should be. Any thoughts or inspiration welcome.

Can you tell us the current settings for your heat pump controller? For example last year (if I'm reading things correctly) it was set for a fixed 50C flow temp; is that still the case?

You said your EPC rating was "B". Also on the EPC it should say how many kWh of heat your propety needs, for space heating and fr hot water. Can you share those numbers too?

9000kWh of electricity for the heat pump would sugest a COP of 2 or less (my patchily-insulated 1950s 3-bed semi is half the size of your new-build, but only uses ~9000kWh of gas a year). Something is very wrong somewhere.

matelodave

How many TRV's or room stats have you got. If you have underfloor heating is it zoned (have you got flow control actuators on the manifold. What times do you have heating and hot water. What are your flow temperatures set to - earlier you suggest that it was around 50 degrees, which TBH is too hot unless you are trying to run your heating like a gas boiler.

What did the Heat Geek actually say about the installation and system settings apart from criticising the insulation. I'm guessing that you would have got a heat loss calculation to establish the rad sizes required and the system design temperature. What did he say about the controls.

Perhaps a photo or two of the manifold, the tank, controller and even stats. Sometimes over controlling the system with TRV's and zone's just causes the unit to cycle rather than run gently in the background. 

Think of it like driving a car, you can go a bit slower and control your speed with the accelerator (which is how weather compensation works) or go flat out and use the ignition switch to control your speed which is how a thermostat operates. 

Have you got a smart meter, if so you can monitor how much leccy you are using in half hour segments during the day and with something like the Bright app you can also look back at historical data. It would be useful to see when all this energy is being used (especially overnight when you are all in bed)

We've got a 3 bedroom 140m2 bungalow with overlay underfloor heating which effectively runs 24/7. I have disconnected all the controls and it just uses weather compensation to control the temperature. All rooms are heated and our annual leccy consumption is around 7500kwh of which I estimate 4000kwh is for heating and hot water.
The system flow temp is around 30-35degrees depending on the outside temperature and inside its around 20 degrees. The floor temp is around 25-26 degrees. We set back the weather compensation by 4 degrees overnight. Our hot water is heated to 45 degrees once a day in the winter and once every two days in the summer.

JEdelman

Hi. Of course. On the EPC it says we should be using: 

• 6,414 kWh per year for heating
• 2,258 kWh per year for hot water.          
• Yes - the flow is set at 50

matelodave

Generally the EPC will tell you energy requirement to heat the house and hot water to specified temperatures. However it doesn't tell you how much energy that you'll actually use to achieve it.

Dont confuse heat requirement with energy consumption. A heatpump with a COP of 3 should give you 3kwh of heat with an input of 1kwh of electricity. You appear to be consuming more electricity than your heat requirement

I'd guess that if your EPC was anywhere near correct and you system was properly specified, installed, commissioned and used properly then you should actually using around a third of what you EPC suggests.

6414 divided by a COP of around 3.5 = approx 2000kwh  for heating plus 2258 divide by a COP of 2.5 = approx 1000kwh for hot water. ie a total of around 3000kwh with a heatpump. whearas gas or direct electric heating would be around 8700kwh.

If you reckon you are chewing through 9000kwk+ then there's got to be something very wrong somewhere.

Has your system got a back-up or boost heater. Mine has a 3kw immersion and a 6kw back-up heat either of which could be activated if the flow or hot water temperature is set too high (usually above 50degrees). The immersion will kick in if you have an anti-legionnaire cycle set to 60 or above. (I have both of mine disabled) A lot of early Mitsubishi EcoDan systems were using the backup heaters and causing the sort of problem that you seem to be experiencing. 

My EPC is a D and the energy requirement is 12500kwh for heating and 2500kwh for hot water and that's what I'd expect to use if I was heating directly with electricity or gas but with a heatpump I only actually use around 4000kwh (although I doubt I'm really achieving a COP of 4). Up until earlier this year when I think it changed, the EPC didn't do the COP calculation so did not reflect the efficiency (COP) of a heatpump compared with gas, oil or direct electric heating.

Spoonie_Turtle

Your house is almost double the size of ours (89m²) which is a 1940s semi-detached exposed on a hill with EPC C/D (scraped a C last time even though literally nothing had changed since the previous EPC).  Our heat pump at most has used 2500kWh in a year, without an optimal installation or setup and before I changed any settings which has brought it down to ~2100kWh max.  We do have an electric shower though so that accounts for most of our hot water usage, not from the heat pump.  Oh and our heat pump is a model with a heavy vampire load, it will quite happily use 40-70kWh in the summer months for nonexistent 'heating'!

Thermostat is usually set to 18℃, or 19 if we're really feeling it, but the kitchen and living room tend to get up to 21℃.  Heating is turned off overnight as we have no setback facility.  (Not ideal I know for efficiency, but we didn't need heating kicking in at 3am to keep us toasty.)

Double the size house and a few ℃ higher than our thermostat, but with an EPC of B in a new build, I cannot imagine that would require ~4x as much energy as ours.  9,000kWh sounds like trying to heat a giant draughty barn as well as a house!