An update to Aotearoa/New Zealand Design Temperatures
Richard Turner, Meteorologist at NIWA
With marine heatwaves, La Nina’s, and the general warming temperatures from climate change in the news NIWA has recently received several enquiries around what changes would be appropriate to design dry-bulb and wet-bulb temperatures for heating, cooling and ventilation systems across the Nation. In this short note we provide an update to previous tables calculated nearly 30 years ago as well as providing some aid to interpretation.
Aotearoa/New Zealand is a long skinny country with several different climate zones, where Foehn Nor’wester conditions can cause blistering hot summer conditions in eastern parts, contrasting with cold damp alpine conditions at high inland locations to the warm and humid climes of the far north, so it is important to have the correct settings for specific locations to ensure the optimal operation of heating and cooling systems and the comfort of inhabitants.
Note that for the previous 1986-1995 table values were provided to the nearest degree, but the updated table has values rounded to 0.1 degree °C.
Additionally, some observing stations used in 1986-1995 no longer exist, so either data from a new nearby station was used or if no suitable nearby records were available the location was removed, those locations were Ponsonby, Te Teko and Lower Hutt. However, some new locations have been added, i.e., Hicks Bay, Waiouru, and Lincoln Road, Auckland.
The ASHRAE website (http://ashrae-meteo.info/v2.0/help.php#annual_cooling) is a useful resource. It does have some information for some Aotearoa/New Zealand locations, but uses slightly different periods and thresholds to the NIWA derived tables (e.g., instead of 1%, 2.5%, and 5% for Nov-May, it specifies 0.4% for the whole year, etc.).
Often times HVAC engineers require more detailed information about the temperature and humidity climate for a location and tin these instances psychrometric charts for an appropriate observing site can be generated upon request (see Figure 1).
Below are the new tables for Te Waipounamu / South Island and Te Ika-a-Māui / North Island respectively.
Design Temperatures for Air Conditioning (°C)
Data Period: 2011-2020
d.max/day: Maximum dry-bulb temperature (°C) which will not be exceeded more than 1.0%, 2.5%, or 5.0% of the time (as specified) between 0800 to 1800 NZ Local Time from 1st November to 30th April.
w.max/day: Similarly, for wet-bulb temperature (°C) for the same thresholds and period as d.max/day.
d.min/day: Minimum dry-bulb temperature (°C) which will not be subceeded more than 1.0%, 2.5%, or 5.0% of the time (as specified) between 0800 to 1800 NZ Local Time from 1st May to 30th October.
d.min: Similar to d.min/day except the period is for the whole 24-hour period and from 1st May to 30th October.
