Reply To: Heating Assessment Tool

[Vicki Cowan]

Hi Adam,
Richard Popenhagen, Nelson City councils EDA has kindly had a little look through.
Here’s his email to me (happy for me to re-post here!).
Vicki

Hi Vicki

I haven’t had cause to use the tool to date, so I took a look today to familiarise myself with it, in an attempt to understand the questions raised.

Regarding the temperatures to be used for different districts, these are set in Schedule 2, Clause 5: Assumed external temperature, in the Residential Tenancies (Healthy Homes Standards) Regulations 2019: http://www.legislation.govt.nz/regulation/public/2019/0088/latest/LMS160629.html#LMS160629

As to how these figures are derived, this question should be addressed to the Ministry of Housing and Urban Development: healthyhomes@hud.govt.nz. I am sure there will be a metrological basis these are derived from, maybe the coldest temperature that district is likely to experience in winter? Bear in mind that in every district there can be quite varying micro-climates and temperatures across relatively short distances (north side of a hill verses shaded southern valley), so the temps in schedule 2 are a fairly blunt instrument. As a precaution, maybe anyone doing the calculation should err on the side of caution and use the worst case scenario? (refer to comments below about what temp to heat too).

Whether the required heating calculation output is higher than people believe it should be is subjective (and somewhat irrelevant). It is what legislation states you must achieve, and unless/until someone is going to effect a change to the regulations, that is what the law sets as the minimum level of heating that must be provided.

The other point I would make is that the calculation is to only take that living area to 18oC. Try living in your home at only 18oC all winter, most people would find this still too cold. WHO recommends a minimum living room temperature of 20oC for homes with young children, elderly or unwell people. 20oC to 24oC is the temperature most people find comfortable for their living room in winter. Having a little bit of extra capacity to give people a choice of what temperature they want to heat their house to in winter is not a bad thing. Indeed, as I search further into this I found this statement: It is important to note that devices capable of heating a living room to 18˚C on the coldest days, which is the requirement under the heating standard, will be able to heat a living room to higher temperatures most days in the year. https://www.hud.govt.nz/assets/Healthy-Homes/765404e8a3/Healthy-Homes-Standards-Common-Questions-and-Answers-13052019.pdf

In regard to heat pump capacity:
To reflect a variation in capacity depending on outside temperatures, heat pumps can have three heat capacity ratings. These are based on standardised testing under laboratory conditions.
• H1 rates the unit’s heating output when the outside temperature is 7°C.
• H2 rates the heating output at 2°C ambient temperature.
• H3 rates the heating output at -7°C ambient temperature.
These ratings allow you to select the appropriate heat pump for the climate and household requirements (i.e. the design temperature and heating load) of individual situations. (From: http://www.level.org.nz/energy/space-heating/heat-pumps/)
So, although most heat pump capacities (and COP) are published using the H1 figure, in colder districts you need to ask the manufacturer what are the H2 or H3 figures that match the climate you are installing into.

A quick review, come back to me if you want any further comment

Cheers
Richard

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