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Heat Pump + Dynamic / Smart Tariffs - what is your approach?

Air Source Heat Pumps (ASHPs)

Last Post by Carpenterstation 9 months ago

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JakeT

(@jaket)

Eminent Member Member

Joined: 2 years ago

Posts: 19

Topic starter 11/02/2025 11:51 am

Hi all,

I previously posted on trying to optimise my set up here:

https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/ecodan-ashp-how-to-optimise-my-set-up

The above was trying to find the optimal kwh use, which when you have a flat tariff is also the most cost effective.

However, I have recently signed up to the Tomato Energy - Lifestyle Tariff. This is a 'smart tariff' - and currently costs:

1. 5p per kwh from 01h00-06h00,

2. 14p per kwh from 09h30-11h30 & again from 20h30-22h30,

3. 23.26p per kwh all other times.

I have done my best to shift the rest of my daily load (dishwasher etc.) around to use the low rate windows, but I am looking to try optimise the heat pump now.

I was wondering if anyone else here has a similar tariff and can share what they have done to take advantage of it?

Obvious strategies that standout at me:

1. Put the DHW on a timer to only heat in the low cost windows.

2. For heating I could also put this on a timer - but I think the low cost windows are too narrow to fully heat the house / game any benefit from any efficiency lost as a result of the on / off nature. (plus I don't want the house to be hottest at 3am, and coldest during the day?)

3. Perhaps have a 'set-back' where the house is on auto adaptive to target 24c between 1-6am and set it back to 21c all other times?

Has anyone else got a similar situation? What are your strategies?

Jake

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Transparent

(@transparent)

Illustrious Member Moderator

Joined: 4 years ago

Posts: 2735

11/02/2025 4:47 pm

I can see what you're wanting to achieve @jaket

Some thoughts -

1: Adding a timer to only allow DHW heating when costs are lower might save money if the DHW temperature is set higher than the flow-temperature which you usually have for space heating.
How confident are you to make that change?

It's not just a timer, because you'll need to interrupt the system which controls the 2-way valve.

The heat-pump controller needs to know that it isn't just going to respond to the temperature sensor on the DHW tank.

2: You could certainly ensure that the DHW anti-legionella cycle only ran at night.

But it won't save a great deal because it probably only runs for an hour, once per fortnight.

3: Your greatest savings would be achieved by installing a storage battery which would be charged from the grid at 5p per kWh.
And you'd then run the heat-pump from the battery.

But that has ethical issues to be considered:

a) the 01:00 to 06:00 slot is only cheap because the Combined Cycle Gas Turbine (CCGT) plants are prepared to sell at a loss in order not to drop out of their more efficient combined cycle mode. It still contributes to global warming.

b) rapid charging of a storage battery causes losses at the local substation when your house is on a single-phase supply.

The cost of electricity does not reflect what's best for the environment.

Ofgem needs to address this, because the general population would be more motivated if it did.

Save energy... recycle electrons!

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bontwoody

(@bontwoody)

Noble Member Contributor

Joined: 4 years ago

Posts: 943

11/02/2025 7:30 pm

Thats a very competitive tariff! better than Octopus intelligent Go. The only downside for me is that I would lose the 15p per kWh export tariff. Curses.

House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60

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RobS

(@robs)

Estimable Member Member

Joined: 1 year ago

Posts: 56

11/02/2025 9:01 pm

Posted by: @transparent

↑

1: Adding a timer to only allow DHW heating when costs are lower might save money if the DHW temperature is set higher than the flow-temperature which you usually have for space heating.
How confident are you to make that change?

It's not just a timer, because you'll need to interrupt the system which controls the 2-way valve.

The heat-pump controller needs to know that it isn't just going to respond to the temperature sensor on the DHW tank.

Presumably the timer for timed DHW, that @jaket suggested, is just the standard feature of an Ecodan controller (and other heat pump controllers), so it's just a controller configuration change.

Agree about storage batteries giving the greatest savings, especially this time of year when there's so little solar.

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Carpenterstation

(@carpenterstation)

Estimable Member Contributor

Joined: 10 months ago

Posts: 45

11/02/2025 10:40 pm

Because the cosy octopus tariff has 3 low cost windows (still expensive compared to gas or LPG though!) we charge the batteries 3 times a day and discharge when Elex is pricey. Of course if we get any solar, then that charges instead of the grid. But precious little solar so far this year! (Did we even get daylight today?)

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