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Winter Energy Review: Heat Pumps, Solar Gain, and Smart Saving Strategies

Introduction: As the winter chill finally set in this January, I took it as an opportunity to assess the performance of my heat pump and insulation, and explore additional ways to optimise energy usage and save costs. Long story short but I learned that the sun provides significantly more benefit than I had initially assumed.

Gathering Data for Insight: To accurately gauge my home’s energy performance, data was key. As mentioned in my final post, the current landscape of energy data management is a fragmented array of apps and sources. Nonetheless, I managed to configure my phone to record hourly heat and humidity readings through a smart speaker over a week. The challenge was to piece together this information with data on energy consumption and solar generation and external temperature. While some energy disaggregation tools exists, I haven’t used them so for now, I’ve used logical deductions and historical trends to draw conclusions.

Internal temperature during the week of the 14th to 21st January 2024 ˚C

Home Temperature and Efficiency: The results were encouraging. You can see the graph of the internal temperature above graph in ˚C and also with the external temperature and periods of sunshine. The house consistently maintained a comfortable temperature between 18-21 degrees Celsius. The heat loss averaged about 1 degree every 3 hours with an external temperature around 3 degrees Celsius – a testament to insulation. Interestingly, the heat pump’s operation didn’t show dramatic spikes, thanks to the gentle warmth from our underfloor heating system. There are no hot spots or cold spots.

Internal temperature on the 15th January 2024 ˚C

The Impact of Solar Gain: A significant insight was the substantial effect of solar gain through our south-facing windows noted in the above by the sun logos (the extreme peak was simply the speaker in direct sunlight). When the curtains were open during sunny days, the interior temperature noticeably increased, even without active heating. This natural heat was a welcome addition.

Energy flow around the house with yellow denoting solar and green denoting battery flows

Analyzing Energy Demand: Breaking down the household’s energy usage painted a detailed picture:

  • Heating was scheduled to run early morning (3 am to 6 am) and in the evening (3:30 pm to 9 pm).
  • Hot water heating began at 5 am until reaching 45 degrees Celsius.
  • The boiling water tap remained active throughout the day.
  • Usage of lighting and cooking appliances peaked during active hours.
  • The immersion heater had a 2-hour slot once a week.
  • Constant, minor power draws came from appliances like fridges and the security doorbell.
  • Electric cars charged overnight.
  • Solar energy was a dual benefactor, heating the house and charging the batteries during the day.

Energy flow into the house based on the smart meter

Energy Flow Insights: On a typical day like the 15th, the energy dynamics were revealing. We imported 46 kWh of energy, supplemented by 10 kWh from solar power. With an average daily consumption of around 20 kWh for running the house and heating water, the heating system accounted for approximately 36 kWh. This translates to about 1.5 kW of loss per hour. However, considering the heat pump’s efficiency of 200-300%, the actual energy loss might be closer to 4-6 kW.

Future savings: Being on an EV tariff means my overnight use between 11:30 and 05:30 are super cheap therefore, I’ve shifted more load to these times. Heating both the house for the morning (especially the underfloor areas) and hot water in time for showers is done in at cheap rates. I delay the dishwasher and washing machine to run in these times too and am looking into charging the battery from the grid, albeit cognizant of the impact on longevity.

This was just a bit of fun for now and I’m keen to find quantifiable improvements. I remain however forever wondering if this will all get easier. I’m searching for the HEMS app that does it all (Home Energy Management System).

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