Understanding Internal Temperatures and Their Impact on Energy Efficiency
The National House Energy Rating Scheme (NatHERS) is used to assess energy efficiency levels of homes throughout the country. NatHERS uses an underlying calculation engine which produces a star rating by calculating the total energy required to bring a home into or within a comfortable temperature range.
This is important to consider because it means that; if we are able to understand the dynamics of a home’s internal temperature fluctuations, we are able to determine effective strategies that reduce the need for excess energy consumption, because for every 1 degree of heating or cooling required, an increase in energy consumption by 5-10% (1) can be expected.
Internal temperatures have a huge impact on the energy efficiency of a home with internal temperatures corresponding with how comfortable and healthy a space can be.
Imagine a home that fluctuates in line with the temperature outside, it wouldn’t be much of a home and would be more like living in a tent!
By conducting a temperature analysis we can visually see whether this is happening or whether the home is effectively insulating the occupants from the volatility of the weather outside.
It’s important to note that when it comes to energy efficiency, climate is everything. No two places are going to act the same and each jurisdiction requires slightly different approaches. NatHERS does a great job of identifying climate zones, but it is then up to the assessor to determine the strategies to increase energy efficiency and reduce the impacts of extreme weather on the occupants.
Let’s walk through an example.
Figure 1 shows temperature fluctuations during a cold week in winter. The separation between the outside and inside is how we measure the impact and effectiveness of the wall, roof and floor construction (including all insulation and glazing).
Figure 1: Temperature fluctuations during a cold week in winter.
Taking the above graph a little further we can start to layer on further evidence of a home performing very well throughout a cold week in winter.
Everyone experiences comfort at different temperatures, so it is important to ask each client what temperatures they feel comfortable at and optimising a home to reflect this. However, a generally comfortable temperature range during winter for most is between 18 and 22 degrees.
Shown in Figure 2, we can see that as we move towards 8.2 stars, the homes internal temperature becomes less volatile and starts to fit within an 18 to 22 degree Celsius band more consistently.
This is then further evidenced when we interrogate the numbers we get from the NatHERS assessment.
We are able to conclude that by going from 6.1 to 8.2 stars:
The frequency at which the internal space is naturally between 18 and 22 degrees Celsius increased by 43.8% from 28.5% (at 6.1 stars) to 41.0% (at 8.2 stars).
The absolute lowest temperature went from 14 to 16 degrees Celsius. A 14.3% increase and 10-20% reduction in energy required to bring the space into a comfortable temperature.
Figure 2: 18 to 22 degree range - temperature fluctuations during a cold week in winter.
When we compare the winter performance against the summer performance, we are able to compare the extremes and recommend a suitable energy efficiency strategy for each home.
In this instance, as shown below in Figure 3, we can see that during a hot week in summer the home fluctuates closely with the outside temperature, however, we note that the extreme increases in outside temperature are made more bearable at 8.2 stars.
In our experience very few homes are completely disconnected from the outside temperature during summer (due to a wide variety of factors) which makes crossflow ventilation and purging of summer heat critical across Australia. Designing for Australian summers will require its own article around the growing implementation of Passive House, over-heating homes and the importance of passive and active ventilation in the design and construction of a healthy energy efficient home.
Figure 3: Temperature fluctuations during a cold week in winter.
By conducting a thorough temperature analysis, a home's tendencies are unveiled, allowing a targeted focus on its potential problem areas. This data is then utilised in conjunction with the homeowner's comfort preferences and goals, culminating in a recommended strategy to minimise the impact of extreme weather patterns on occupant comfort and health.
To note: this particular project began with a client wanting to understand their heating needs and exploring the cost-effectiveness of an in-slab heating system. Following this investigation, heating needs were reduced and eliminated. It made sense to reallocate this budget to invest in high efficiency split systems for summer which can be powered by the on-site renewable energy generation the site enables.
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