Performance Metrics

HAYFIELD HOUSE PERFORMANCE METRICS

• EUI of 15.6 (measured from Feb 2021 to Feb 2022)
• 0.98ACH@50 (measured by a blower door test in May 2019)

EUI is the Energy Use Index which is the key metric used to measure the performance of a building. It is calculated by dividing the total annual energy consumed by the house by the gross square footage of the house’s conditioned floor space. Typically (in the US) the energy used in this calculation is measured in kBtu. For an all-electric house with solar panels (such as THE HAYFIELD HOUSE) this figure is easily obtained by taking an annual beginning and ending reading from the solar production meter which measures the amount of kWhs produced by the solar array. This figure needs to be adjusted to account for the annual change in the net-meter reading. This adjustment is necessary to account for either (1) the net annual surplus production sent back into the grid or (2) the net annual power pulled from the grid. From the resulting adjusted kWh figure, multiply kWh times 3.412 to obtain annual kBtu used. This kBtu figure becomes the numerator in the EUI calculation. The denominator for this calculation is your home’s gross square footage, which typically is measured for your conditioned floor spaces using exterior wall dimensions. THE HAYFIELD HOUSE’s measured EUI of 15.6 (in hindsight) is too high. A better target would have been closer to 10.

ACH@50 represents Air Changes per Hour at 50 pascals (Pa) pressure differential between the inside and outside of your house. This figure is obtained from a blower door test that uses a fan to artificially create the required pressure differential between the inside and outside of your house. Lower ACH@50 values are better than higher values as lower values mean less air exchanges per hour, hence a tighter house. Zero net-energy houses typically have ACH@50 values less than 1.0. Houses built to the Passive House standard have an ACH@50 value of 0.6 or less.