Compliance with H1 using AccuRate NZ
Using the building performance index (BPI) is one way to show compliance with the house insulation requirements of Building Code Clause H1 Energy Efficiency. A house complies with the insulation requirements of H1 if the BPI ≤ 1.55. The BPI is calculated as follows.
BPI = heating energy / heating degrees total x (floor area + total wall area)
The heating energy can be calculated using either the Annual Loss Factor method (ALF) (refer to www.branz.co.nz 
) or another method that can be correlated with ALF (see the H1 Compliance Document for more details).
In December 2007 the Energy Efficiency and Conservation Authority (EECA) launched a Home Energy Rating Scheme (HERS). The scheme uses a thermal simulation tool called AccuRate NZ to determine the heating and cooling energy of a house or a proposed house design.
The Department has worked with EECA to determine the heating energy use of 14 different house designs using both AccuRate NZ and ALF to see if the calculated energy use correlates.
The energy use was calculated for each design in 16 different climate zones using both ALF and AccuRate NZ. The results are shown in the graph pictured. Note that while AccuRate NZ calculates both heating energy use and cooling energy use, ALF calculates only heating energy use (this difference has a negligible impact for the 14 houses simulated).
The graph shows a very good correlation between the two different programmes, demonstrated by an R2 value of 0.9 (R2 is a statistical term measuring how closely the equation fits the actual results - a perfect correlation would have an R2 of 1). Therefore AccuRate can be used to calculate heating energy and BPI as follows.
Heating energy = (total energy from AccuRate NZ x 1.45)
This heating energy figure is then used with the following BPI formula:
BPI = heating energy / heating degrees total x (floor area + total wall area)
where:
Heating degrees total can be taken from Table 1 Floor area, in relation to a building, means the floor area (expressed in square metres) of all interior spaces used for activities normally associated with domestic living.
Total wall area, in relation to a building, means the sum (expressed in square metres) of the following:
(a) the wall area of the building, and
(b) the area (expressed in square metres) of all the vertical glazing in external walls of the building.
Heating degrees total for Home Energy Rating Scheme Climate
| Table 1: Heating degrees total for Home Energy Rating Scheme Climate Zones |
| Region |
Climate station |
Heating degrees total |
| Northland |
Kaitaia |
12.0 |
| Auckland |
Auckland |
13.0 |
| Hamilton |
Ruakura/Hamilton area |
19.7 |
| Bay of Plenty |
Tauranga |
11.2 |
| Rotorua |
Rotorua |
26.3 |
| Taupo |
Taupo/Turangi |
33.0 |
| New Plymouth |
New Plymouth |
15.8 |
| East Coast |
Napier |
17.1 |
| Wellington |
Paraparaumu |
22.7 |
| Nelson |
Nelson |
30.3 |
| West Coast |
Hokitika |
32.2 |
| Christchurch |
Christchurch |
32.4 |
| Queenstown |
Queenstown |
46.4 |
| Central Otago |
Lauder |
59.1 |
| Dunedin |
Dunedin aero |
37.4 |
| Invercargill |
Invercargill |
49.8 |
Changes are now planned to revise the H1 Compliance Document to include the use of AccuRate NZ to calculate heating energy and the BPI.
Example
| House location: |
Napier |
| Floor area: |
130 m2 |
| Wall area: |
110 m2 |
| Heating degrees total (from Table 1) |
17.1 |
| ALF calculated heating energy: |
6330 kWh/year |
BPI = 6330 / 17.1 x (130 +110) = 1.54 < 1.55
Therefore the house complies with the insulation requirements in H1.
Alternatively, AccuRate NZ calculated energy = 4365 kWh/year
BPI = 4365 x 1.45 / 17.1 x (130 +110) = 1.54 < 1.55
As above, the house complies with the insulation requirements of H1.