Winter is over, the weather is warming up, and I've turned off my heating in preparation for summer. This video will explore the costs and energy usage of my heat pump over the past winter. Prepare for a lot of data and graphs!
Installation Recap
In December, Octopus Energy replaced my old boiler with a new 6 KW Daikin air source heat pump. Along with this, I upgraded some radiators and installed a new hot water tank. The installation has been impressive—the house remained consistently warm throughout winter, even on the coldest days. Noise levels have been minimal; inside the house, there's almost no noise from the pipes, and outside, the heat pump runs quietly, only occasionally getting louder during startup or hot water cycles.
Data Collection Methods
For those with a Daikin heat pump like mine, you can track both the electrical energy consumed and heat energy output using the MMI display. By selecting the energy data from the information menu, you can see the data for heating and hot water over the current and previous weeks. Dividing the heat energy output by the electrical energy input gives you the Coefficient of Performance (COP) value for the day. While the MMI data may not be perfectly accurate due to rounding, I've been recording this data weekly in a spreadsheet.
Additionally, I've installed a homemade device called an ESP Altherma to a data port on the heat pump. This, combined with a Shelly EM Pro to monitor power and energy, provides another estimate of the heat pump’s COP. Though this method is not highly accurate, it offers another perspective.
Energy Usage and Costs
Let's dive into the first graph, showing the energy used by my heat pump according to the Shelly EM Pro, broken down by week. The week starting January 8th was the highest at 160 kWh due to the coldest temperatures, while by the final week of May 6th, energy usage dropped to 24 kWh, leading me to turn off the heating.
Now, let's look at the COP values for each week. The MMI consistently reports lower heat energy output compared to the ESP Altherma method, typically around 79% of the ESP Altherma values. To present a challenging scenario for the heat pump, I used the Shelly energy data for consumption and the MMI data for heat energy output. This method ensures a conservative estimate of the heat pump’s efficiency.
Cost Analysis
I have a significant amount of home battery capacity, allowing me to charge batteries during off-peak hours and use this stored energy to power the heat pump, substantially lowering running costs. I'm on the Octopus Go tariff, designed for electric car owners, but beneficial for any home.
The following graph shows the weekly costs of running my heat pump under different scenarios:
- Blue line: Variable tariff at 24.5p per kWh.
- Orange line: Best-case gas cost for equivalent heat output.
- Red line: Worst-case gas cost compared to the heat pump’s efficiency.
- Green line: Actual costs using battery-stored off-peak energy.
Even with inefficiencies and occasional peak rate usage, the batteries dramatically reduce overall running costs. The final graph shows the total cost comparison, highlighting the significant savings from using the heat pump with battery storage versus a gas boiler.
Conclusion
Switching from a gas boiler to a heat pump was the right decision for me. The combination of the heat pump and battery storage has significantly reduced my energy costs and lowered my carbon footprint. Even without batteries, running costs would be comparable to gas, making the heat pump a viable, eco-friendly alternative.
No comments