Should I boost my heat pump during off-peak periods? - Will it save me money?

If you have a heat pump heating system then you'll likely be running it for a good chunk of the day, including overnight. On a standard tariff you'll probably want to drop the set point temperature overnight so that you're not spending more money than you need to by keeping the house warmer than it needs to be while you're asleep. But what if you have a time of use tariff with a cheap overnight period, like Octopus Go or Intelligent Octopus Go? Would it save you money by doing extra heating during cheap off-peak times? I decided to build a simple theoretical model of heating and heat loss in a spreadsheet to see if I could work it out. Brace yourselves, it's going to get nerdy.

Grab a copy of the G-sheets spreadsheet here (once open go to "File: Take a copy" and save to your own Google Drive):
https://docs.google.com/spreadsheets/...

Our home system summary:
6.8 kWp solar array split E/W
5 kW Gen 2 GivEnergy hybrid inverter
14.7 kWh GivEnergy batteries
A2A heat pump heating/cooling system
Myenergi eddi hot water diverter
Fiat 500e EV

00:00 Introduction
03:26 Downloading the spreadsheet
04:24 How the model works
18:49 Model assumptions and simplifications
26:04 Estimating your house heat capacity
30:18 Demo 1 - constant heating
32:38 Demo 2 - high thermal mass house (block work walls)
42:51 Demo 3 - low thermal mass house (timber frame)
48:33 Demo 4 - milder weather
50:07 Demo 5 - taking it to the extremes
53:22 Summary and closing thoughts

Please note that Tim is not a professional consultant, just an enthusiastic amateur, so cannot reply to requests for advice or opinions on specific systems or green investment opportunities. Thank you for your understanding.

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