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Would a Passivhaus building reduce my energy bills?

Would a Passivhaus building reduce my energy bills? Passivhaus buildings are known for being low energy. How does this compare to traditional UK properties?


Crunching the numbers


To compare the cost of energy to run a Passivhaus home vs a typical UK home, we need to find out the following information:

  • The cost of energy (per kilowatt hour/kWh)

  • How much energy a Passivhaus building uses in kilowatt hours per square meter (kWh/m²)

  • How much energy a conventional building uses in kilowatt hours per square meter (kWh/m²)

  • We can then compare the two numbers to the cost of energy to establish the difference

The cost of energy


At the time of writing (April 2023), the UK price of energy is capped at an average of:

  • 34p/kWh of electricity

  • 10.3p/kWh of gas

  • Source: gov.uk | Energy Price Guarantee Policy Paper (March 2023)

Energy use within a Passivhaus home


Passivhaus homes are required to meet the following standard:

  • 60kWh/m² Primary Energy Renewable: This covers:

  • The total energy use of the building (inc. space heating) and;

  • The losses in generating, distributing and storing the energy within the National Grid (ie: 'grid losses').

  • As grid losses are included, the amount of energy billed to the end-user will be less. How much less will depend on the type of heating and hot water generation used. Each type of heating system (eg: gas boiler, heat pump, biomass boiler, etc) has an 'energy factor' associated with it that forms part of the energy modelling calculation. This means that the predicted energy use of each building will vary slightly. However, for simplicity, let's assume the following:

  • An energy factor of 1.5

  • This means that one third additional energy is required within the grid to generate the energy used within the building

  • Two thirds of the energy would be used and paid for by the end-user; equating to 40kWh/m²

To be clear, this is a approximate calculation to explain the Passivhaus methodology and provide an approximate indication of energy use. The amount of energy used within a building will vary slightly. This study, by the creators and early innovators of Passivhaus, studied the energy use of four Passivhaus buildings from 1990-2018. The energy consumption of each building, on average, was between 30-40kWh/m².


Energy use within a typical home


According to Ofgem, the average UK household uses the following amount of energy:

Energy Use

Example - home type and number of residents

Typical annual gas use (kWh)

Typical annual electricity use (kWh)

Low

Flat or 1-bedroom house; 1-2 people

8,000

1,800

Medium

2-3 bedroom house; 2-3 people

12,000

2,900

High

4+ bedroom home; 4-5 people

17,000

4,300

A key missing figure from this chart is the average size of a home (in m²) so we can calculate the kWh/m². Below I have added some typical figures (source: the National Technical Housing Standards):

Energy Use

Example - home type and number of residents

Typical annual gas use (kWh)

Typical annual electricity use (kWh)

Average size (m²)

Typical annual gas use (kWh)

Typical annual electricity use (kWh)

Total kWh/m²

Low

Flat or 1-bedroom house; 1-2 people

8,000

1,800

50m²

160kWh/m²

36kWh/m²

196kWh/m²

Medium

2-3 bedroom house; 2-3 people

12,000

2,900

61m²

197kWh/m²

48kWh/m²

245kWh/m²

High

4+ bedroom home; 4-5 people

17,000

4,300

90m²

189kWh/m²

48kWh/m²

237kWh/m²

Average

12,300

9,000

67m²

182kWh/m² (81% of total use)

44kWh/m² (19% of total use)

226kWh/m²

Based on these assumptions, a typical UK home uses around 226kWh/m².


A Typical Home and Passivhaus compared


Let's compare the information we have gathered:

  • A typical UK home uses circa. 226kWh/m²

  • A typical Passivhaus uses circa. 40kWh/m²

  • In monetary terms, using a similar split of gas/electricity to typical households (81% gas, 19% electricity):

  • A Typical UK home will use £33.71/m²

  • A Passivhaus building will use £5.93/m²

If we applied these figures to a typical 2-3 bedroom house this would cost:

  • £2,056.31 a year for a typical home

  • £361.73 a year for a Passivhaus home

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