UPDATED: Air Source Heat Pumps/Air Con - Full Info & Guide, is it cheaper to run than mains gas?

ProfessorChao5

Any one tried running their heat pump in conjunction with the octopus agile tariff?

matelodave

not me - I use less leccy overnight than I do during the day which means it doesn't really match. I'd be paying lower rates when I use the least and higher rates during the day and evenings when my consumption is highest. Even my hot water generation only accounts for around only 2kwh kwh (unless its really really cold outside) a day so shifting it to the cheap time wouldn't really save all  that much.

You'd need to do a half hourly evaluation of your consumption over a suitable period to see how well your consumption would fit in with the Agile pricing structure. As you'd expect the energy consumption of an ASHP is related to the outside temperature and when its in operation. As we set back the overnight temps by a couple of degrees then it's consumption decreases, frequently to virtually zero. TBH my consumption doesn't really match with e7 either.

A cheap single rate suits me best. The daily consumption of my heat pump at this time of year is varying between around 30-60kwh depending on how cold it is outside and most of that is during the day and evening. Add in the cooking, washing and other stuff which get done during the day then the balance between night and day is even worse. There's no way I'd manage to persuade my wife to do the washing, ironing or vaccying overnight during lower tariff periods. I cant even get her to be a bit frugal with the use of hot water.

We have ours reasonably well controlled with thermostats in each room to control the underfloor heating and the heatpump but we effectively heat the rooms that are in use from 7am to 10pm with hot water heating from 04:30 so we've got hot water for our morning ablutions.
I do have an energy monitor which data logs consumption at six second intervals so I know pretty well what it's consuming and when (I can also download spreadsheet data if I want to analyse it further)
Other people may have a different opinion but this is how our has worked for the past ten years.

ProfessorChao5

I am more thinking shifting the load, so run the heat pump when the price is low to charge the buffer and DHW cylinder then the heat can be drawn from them as usual providing the store is large enough. So I know I need X kWh in the buffer everyday and Y kWh in the DHW cylinder every day use a controller to automatically charge the two tanks appropriately every day and the cheapest times. 

A bit like what people are doing with batteries with the agile tariff 

matelodave

You really need to try doing the sums - a normal heatpump is most efficient at around 35 degrees and the cost of running it goes up quite rapidly until it gets to around 55 and then they have to use an immersion heater to get any higher. High Temperature units are available but they aren't as efficient

So trying to store lots of heat in a tank  of water  at say 55 degrees would need an extremely large tank which you'd have to "charge in around say 7 hours (on E7). Dunno what the equivalent low cost times are for agile. Most people don't get much above a COP of around 2.5-3.0 but you'll be lucky to get even two running it at 55 so assume 1.5- 2

Consider that a 3kw storage heater takes 7 hours at 3kw to store 21kwh of heat and then translate that to the amount of heat you'd have to store to provide enough for the whole house for the whole house - probably around 100kwh or more on a cold day. Assuming you are raising the tank temp from 20-55 that's a rise of 35 degrees the calculation is  Pt = (4.2 × L × T ) ÷ 3600 which equates to around 2500litres of water to store 100kw at 55 degrees.
Divide 100kwh by the size of heatpump you are contemplating (say14kw = around 7 hours with a COP of 2 = about 50kwh of leccy (which is about what my 11kw heat pump consumes when it's zero outside) but my heating flow is lower than 40-42 degrees and my hot water is 45. It consume more leccy when its colder than zero outside and less when it's warmer.

Granted you may not use 100kwh every day day but you'd need the capacity just in case, otherwise you'd be using supplementary heating at peak rates to cover the shortfall.

I'm not trying to turn you off the idea but you need to think it through very carefully as the installation costs (and size of the installation) may well make the whole idea impractical.

When I installed my heatpump, I did contemplate thermal solar (my tank is equipped with solar coils) but the cost was around £1500 at the time (ten years ago).We only use about 2kwh a day to heat our hot water tank,, which even now only cost us = 25p a day (even less ten years ago) x 365 = approx £100 a year., That's over 15 years to pay back (although I guess I could have got the FIT) which would have improved it somewhat. but we'd already spent a lot more than we'd intended to on the heating system already.

Mikeeuropa

Funnily enough I was just looking at a heat pump leaflet from Master Therm advertising the fact their pumps can be itegrated with Octopus Agile to take advantage of the varing price throughout the day. The graph below shows the cost "over a normal 24-hour period" - I take it they mean "typical" rather than normal but anyway....

I should point out that I've no association with Master Therm or Octopus! In fact, I'd never heard of Master Therm until yesterday and you'll see from previous posts on this thread that I'd talked myself out of going for a heat pump to replace the oil boiler in my house.

But a very simple take on this is that if you avoid using electricity as far as you can between 16:00 and 19:30 you'll be quids in but that would mean your house getting colder during those peak hours. So, yes you would want to store some heat/energy to use during those hours, but I think that, if using a buffer tank, it could be much smaller than the calculations above gave? Or you might consider a battery (LG? Tesla?), more expensive up front, I know, but space efficient I think and the energy can be used on any electrical item in your house.

I might have to redo my sums and see if oil is staying or not!

matelodave

If you want more info on real Agile pricing then have a look at this website and try to refer it to when you need most heating (ie when its ever so cold). As I said, I'm not trying to deter you but you do need to do careful sums

https://www.energy-stats.uk/octopus-agile/

Ideally you need some sort of control that gets info from Octopus which boosts the output of the unit when energy is cheapest and can also anticipate variations in the temperature.
One problem I have with ours is when the there is a rapid fall in temperature it takes ages (3-4 hours or more) to respond.  You can improve the heating response times but at the expense of lowering the COP  and increasing the energy consumption.

I've no doubt that more sophisticated TOU controls for things like heatpumps which are enabled by the supplier (like E7 & storage heating) but they'd need to be more responsive to large temperature variations in the same way as gas and oil fired systems otherwise you'll end up using peak rates to supplement background heating.

ProfessorChao5

If you have the following info
- efficiency curve of the heat pump based on outside air temperature and the
-  flow temp of ASHP 
- cost of power 

This information could calculate the ‘cost of heat’ from the ASHP at any time and then when it drops below the set point the heat pump turns on. 

It could work with a bivalent system 

GGSid

matelodave said:

If you want more info on real Agile pricing then have a look at this website and try to refer it to when you need most heating (ie when its ever so cold). As I said, I'm not trying to deter you but you do need to do careful sums

https://www.energy-stats.uk/octopus-agile/

Ideally you need some sort of control that gets info from Octopus which boosts the output of the unit when energy is cheapest and can also anticipate variations in the temperature.
One problem I have with ours is when the there is a rapid fall in temperature it takes ages (3-4 hours or more) to respond.  You can improve the heating response times but at the expense of lowering the COP  and increasing the energy consumption.

I've no doubt that more sophisticated TOU controls for things like heatpumps which are enabled by the supplier (like E7 & storage heating) but they'd need to be more responsive to large temperature variations in the same way as gas and oil fired systems otherwise you'll end up using peak rates to supplement background heating.

This site is also useful for Agile... https://agileprices.co.uk/
That said since the 1st Jan, wholesale prices have been high, so Agile has not been as cheap. No idea if this is short term disruption or a long term dislocation but there's a very real change in the leccy price since start of Jan. 

GGSid

Mikeeuropa said:

Funnily enough I was just looking at a heat pump leaflet from Master Therm advertising the fact their pumps can be itegrated with Octopus Agile to take advantage of the varing price throughout the day. The graph below shows the cost "over a normal 24-hour period" - I take it they mean "typical" rather than normal but anyway....

I should point out that I've no association with Master Therm or Octopus! In fact, I'd never heard of Master Therm until yesterday and you'll see from previous posts on this thread that I'd talked myself out of going for a heat pump to replace the oil boiler in my house.

But a very simple take on this is that if you avoid using electricity as far as you can between 16:00 and 19:30 you'll be quids in but that would mean your house getting colder during those peak hours. So, yes you would want to store some heat/energy to use during those hours, but I think that, if using a buffer tank, it could be much smaller than the calculations above gave? Or you might consider a battery (LG? Tesla?), more expensive up front, I know, but space efficient I think and the energy can be used on any electrical item in your house.

I might have to redo my sums and see if oil is staying or not!

You could also consider Octopus Go. That gives you electricity at ~14p/kWh all day and 5p for 4 hours overnight. If you can achieve a COP of anything over 3 you'd get close to oil prices on cost per unit of heat.

loclnor

We have had an Ecodan ASHP installed with the tanks put in the loft of our bungalow - we find it very noisy so much so that at the moment I am sleeping in the spare room as the constant whining coming from the system (think it may be the buffer tank) is making my main bedroom too noisy to sleep in. It was the installers choice to put it in the loft and they seem to have just laid boards onto the joists with nothing between the boards and the joists (apart from the normal insulation between the joists) and then put the cylinder and pipework on top of the boards. When in the loft the noise is minimal, however around the house is a different story and it can be heard all day through the ceiling. Is this correct please? - if so how do I stop the whining which is worse in cold weather. The installers seem to think the noise is acceptable. Is it me?