How to monitor energy use in a passive house
The greatest selling point of a certified passive house is its verified energy performance. Unlike a conventional home, a passive house is carefully calculated during the design stage to predict exactly how much energy it will need for heating and cooling.
But, the reality of living in a passive design house is that energy consumption still occurs. Factors like appliance use, hot water systems, and resident behaviour play a role in the final energy bill. Learning how to track and interpret energy data allows homeowners to maximise the benefits of their passive house design investment.
Why do you need to monitor energy?
Given its highly efficient energy use, you may wonder why one would need to monitor energy performance at all. Passive house designs operate with such efficiency that energy monitoring becomes genuinely valuable. Unlike conventional homes where energy use fluctuates wildly based on weather and heating demands, a certified passive design house maintains consistent, predictable energy consumption. This stability makes it easy to identify when something isn’t working as expected.
Monitoring serves several purposes. It confirms that your passive building design is performing as promised during design and construction. It identifies opportunities to reduce consumption further through behaviour changes or appliance upgrades. It provides data to understand seasonal variation and plan for solar energy integration.
Key tools for energy monitoring
A modern passive home building relies on intelligent systems and simple tools to track its performance.
1. Smart meters and utility data
The simplest starting point is your electricity bill and smart meter data. Modern smart meters provide granular data on total consumption. Many electricity providers in Australia offer online portals or apps that allow you to track consumption hourly, daily and monthly. This helps residents see when consumption spikes and correlate it with activities like running the oven or a clothes dryer.
2. Dedicated monitoring systems
For a more detailed breakdown, you may opt for a dedicated monitoring system. These can be installed by your passive house builder during construction. They provide separate readings for key circuits, including:
- Heating and cooling: This tracks the energy used by your mechanical ventilation with heat recovery (MVHR) unit and any supplemental heating or cooling equipment like air-conditioning units.
- Hot water: Hot water generation can be one of the largest energy users in a passive house, depending on your system. Separate metering can show if your heat pump or solar hot water system is operating efficiently.
- Solar system: If your passive house has a solar system installed, as many do, you can track energy generation. This allows you to easily compare the home’s production against its consumption, a crucial step for achieving net-zero living.
3. Monitoring indoor climate variables
Performance monitoring goes beyond electricity use. Passive house designers in Australia understand that the goal is comfort with minimal energy. Key indoor climate variables should be monitored using simple devices:
- Temperature: A stable temperature (typically 20°C to 25°C) with minimal fluctuation across rooms is optimal in a passive house in Australia.
- Relative humidity: Maintaining humidity between 40% and 60% is vital for comfort and health. High readings might indicate an issue with the MVHR/ERV system or excessive internal moisture generation.
Analysing and improving consumption
Monitoring is only effective if the data is used to adjust your home and lifestyle to make improvements. For homeowners of a passive house in Australia, analysis should focus on identifying the ‘performance gap’ – that’s the difference between the energy predicted by the Passive House Planning Package (PHPP) software and the actual consumption.
The calculated PHPP predictions are provided by your passive house designer. You can compare actual energy use against these predictions to ensure the building is performing as designed. If there’s a significant difference, it might warrant an investigation by your passive home builder to check for unforeseen air leaks or insulation issues.
If overall consumption is high despite meeting the passive house standards required for certification, the issue lies with plug loads. This calls for an appliance audit, focusing on older fridges, dryers or excessive use of energy-hungry items like electric car chargers or pool pumps.
For homes with solar panels, monitoring the export and import data helps residents shift high-consumption activities (like running a dishwasher or washing machine) to times when the sun is generating power, maximising self-consumption and reducing the environmental footprint.
Doing regular monitoring and making changes accordingly helps make sure your passive house in Australia continues to deliver on the promises made during design and maintains its low operational cost for years to come.
