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27 October 2020

The Need for Embodied and Operational Carbon Reduction

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With our governing political party not having been changed at the recent election, it can be expected that government’s climate change work of the past three years will be continued along a similar path. Some readers will know that MBIE’s Building System Performance Branch has set up the Building for Climate Change (BfCC) programme to undertake the work to reduce carbon emissions, be they in the form of CO2 or other greenhouse gases. The carbon emissions have been divided into two broad categories, namely Embodied Carbon and Operational Carbon. Carbon emissions are used as the basic measure of energy consumption because they are the common factor for all energy usage which influences climate change.

Embodied Carbon is a simple over-arching term to describe the ‘whole-of-life’ carbon used and emitted, in the case of the building industry, in the gaining of raw materials, transportation, manufacturing, construction, maintenance/repair/replacement of products during the building’s life, and the final re-cycling/disposal of the construction. The subject of embodied energy is much too extensive to begin to discuss here, but the reader can make a useful start with MBIE’s ‘Whole-of-Life Carbon Emissions Reduction Framework’.

Operational Carbon is produced by the use, (as widely defined), and operation of a building during its lifetime. They are the obvious emissions associated with heating, cooling, lighting and hot water, plus the electricity needed for appliances, machines and lifts etc. An example of the less obvious is the whole and diverse chain of energy required to provide potable water and to then dispose of the waste generated. There are many more aspects to Operational Carbon than these few common examples. Again, the subject is too broad to discuss here, but MBIE’s ‘Transforming Operational Efficiency’ introduces the complexity of the issue.

While the Building System Performance Branch of MBIE is taking a long-term look at the country’s energy usage at the basic level of carbon emissions, another branch of government, Tenancy Services appears to sometimes be taking a limiting and contrary approach to emissions when introducing some aspects of their regulations. These will be ‘unintended consequences’ but even so they will have significant effect on our carbon emission reduction efforts.

The Healthy Homes initiative of Tenancy Services is very laudable and necessary given the poor thermal performance of our historic housing stock, and in my opinion, must be continued. In the 2000s, government began taking notice and since then has actively and continually worked to make significant improvements. Despite this there are some hiccups regarding the reduction of emissions which I have recent specific experience of. This is the application of Tenancy’s Heating Standard. The supply of heating is a substantial proportion of carbon emissions, and dwellings probably make up the major portion of our non-industrial heating (plus cooling) energy use. Given the growing share of rentals in the housing market, any energy regulatory requirements of Tenancy Services must be taken into account when Net Zero Carbon Emission targets are being considered by Government.

Early in this decade, I was asked by architects and developers in Auckland and Wellington, and regionally, to demonstrate that their apartment buildings complied with the NZ Building Code-clause H1 (Energy Efficiency) by the Modelling Method of the Code. I used sophisticated AccuRateNZ thermal simulation software which was brought to New Zealand, (from Australia’s CSIRO), by EECA for Government’s Home Energy Rating Scheme (HERS). The software was adapted from the ‘AccuRate’ programme which has been in development in Australia since the 1960s specifically for assessing the energy usage of their housing and is the software for their current NatHERS rating scheme. (At the turn of this decade, the NZ public was not ready for a home star-rating scheme, and there was a change of political attitude, so the HERS scheme was put into abeyance). The software was accepted for Building Consent compliance by BRANZ, the then Department of Building and Housing, (now MBIE), and local authorities to calculate the passive solar performance, and heating appliance requirements, for dwellings from standalone houses to multi-storey apartment blocks.

Recently I have been asked by the property manager of two of these apartment blocks to assist with their checking for compliance with the Heating Standard of the Residential Tenancies (Healthy Homes Standards) Regulations 2019. I am not a lawyer, (and so am happy to be corrected), but my layman understanding of the regulation is that the calculation of the Heating Capacity of the Main Living Room is to be undertaken using only the regulation’s Schedule 2 formulae, or Tenancy Services’ Heating Assessment Tool. I checked with the Tenancy Services call centre and was told that only these two methods can be used, and when I asked if calculations from a professional mechanical engineer would be acceptable, I was told that they would not be.

Do I hear you ask, “what have the above paragraphs got to do with Net Zero Carbon Emissions?” The answer is: “A lot.” The property manager asked if the earlier AccuRateNZ analysis could be used to calculate the Heating Capacity of the Residential Tenancies (Healthy Homes Standards) Regulations. For AccuRateNZ to calculate the annual heating and (sensible and latent) cooling HERS result, it uses an interim step within itself which calculates for each space, (including the roof and sub-floor spaces), the temperature at the end of each hour of each day of the year — over 8,700 temperatures for each room. In the depths of the HERS report, there is a panel tabulating the ‘Heating Shortfall’ for each of the rooms. This has the ‘Peak Shortfall’ (kW), ‘Annual Energy Consumption’ (Mj), and ‘Annual CO2 Emissions’ listed for the individual rooms. The ‘Peak Shortfall’ is the calculated heating requirement for the room for the coldest hour of the coldest day of the year; ie for the rest of the year, less energy will be needed. This Peak Shortfall (the passive thermal performance before heaters are turned on) is the maximum ‘Heating Capacity’ as defined in the Tenancy Regulations.

By my layman interpretation of the Heating Standard of the Residential Tenancies (Healthy Homes Standards) Regulations, the degree and precision of the AccuRateNZ HERS analysis could not be used to demonstrate compliance with the Tenancy Regulations should the matter be put before a Tenancy Tribunal Adjudicator who would have to follow the strict wording of the regulations. Presumably, the negative outcome for the landlord would be the same if similarly precise calculations from a registered professional mechanical engineer were to be presented as evidence. It would be simple to allow recognised energy usage software to be used.

I recently completed the analysis of the two eight-storey apartment building using the Assessment Tool, the Schedule 2 formulae, and revisited the original HERS analysis. All three methods used the same living room dimensions and R-values. The Heating Capacity calculated by the HERS analysis were between 69% and 54% of the Tenancy and Regulation methods. Apart from the simplifications of the Assessment Tool and the Schedule 2 formulae methods, the primary reason for the difference is that HERS takes account of actual orientation and the thermal mass of the building elements whereas the regulation methods ignore these essential factors.

In the past week, I have been approached by another owner of two apartment blocks, (with thermal mass), regarding the assessment of the Living Room Heating Capacity of his units. He has undertaken extensive data-logging of a range of the apartments and cannot relate the results with the regulation requirements, especially as the tenants report the units to be warm and comfortable. The results of the ‘Tool’ and ‘Schedule 2’ calculations will be interesting to compare. He has been quoted around $150,000 for heat pumps and only a third of this for electric panel heaters.

My reason for setting-out the information above is that the narrow-focused regulations are requiring the willy-nilly installation of heat-pumps. By allowing the option of more sophisticated thermal capacity analysis methods, a dwelling could be shown to meet the 18°C minimum temperature, (the base temperature for the Schedule 2 formulae), without the excessive expense of a heat-pump.

From the wider Government viewpoint of the need to reduce carbon emissions, being more clever with the distribution of heat-pumps would reduce both embodied and operational carbon. There is far more embodied carbon associated with the manufacture, transport, installation, maintenance, repair and disposal of heat-pumps than for electric panel heaters. While heat-pumps heat a room in cold times, on hot days they can also be run to cool the room’s air. Unfortunately, occupants will tend to open the windows and doors first and then not close these before turning on the heat-pump ‘air-conditioning’. On the other hand, a panel heater is no longer active once the days become warm. Over a year, the panel heater will use less operational carbon, both for maintenance and operation.

If MBIE is serious about embodied and operational carbon emissions, then I believe they could look at the Healthy Homes requirements as an example of not knowing what the other hand is doing.

Through EcoRate Ltd – Architect I provide objective independent passive solar thermal performance analysis and advice on sustainability matters, to architects, designers, builders, manufacturers, and others in the construction industry, including those proposing to build a new home. I am also a Homestar Assessor.
For more information feel free to contact Keith at EcoRate Ltd on 021 890 251,, or our website

Photo by Malcolm Lightbody on Unsplash

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