Energy efficiency assessments can be performed in several different ways – each with their own strengths & weaknesses. Firstly, there is the Deemed-To-Satisfy (DTS) Energy Efficiency Building Solution. To achieve compliance through a DTS assessment, every individual element of the building must comply with the National Construction Code Section J (Energy Efficiency).
An alternative assessment method is the Verification Method (JV3) to find a Building Solution, which is more complex.
So what’s the difference?
While the DTS method requires all components to individually meet the Code, the JV3 method instead checks that the whole building complies with the NCC Objective JO1 “…to reduce greenhouse gas emissions”. This is done by first creating a computer simulated three-dimensional model of the building – everything from the interior wall cavities to the individual blades on a window shading device are replicated in the 3D model.
Once that’s done, we run a simulation that uses actual historical weather data from a nearby weather station to determine the building’s temperature for every hour of a whole year. In addition to calculating the transfer of heat through the building, the simulation includes the extra heat load created by the building’s occupants and electrical equipment according to JV3 modelling conditions.
The simulated building must also contain Section J-compliant HVAC and Artificial Lighting to calculate the building’s total Annual Energy Consumption (kWh). The “verification” of the building then occurs through the simulation of a Reference Building that complies with all the DTS elemental Requirements.
The calculated Annual Energy Consumption (kWh) of the Proposed Building must be less than the kWh of the Reference Building to achieve a Building Solution according to JV3. If this is all getting a bit confusing or you’d like to know more about the JV3 Assessment Method, check out our more in-depth article explaining Verification Method JV3.
Meanwhile, a DTS-compliant building doesn’t require the above complicated simulation. Every element of the building must comply independently, and there is no trade-offs between areas or any wiggle-room. Fantastically high-performing quadruple-glazed low-e tinted windows won’t do anything for your insulation requirements, and increasing the total insulation can’t be used to avoid installing roof raisers or spacers to prevent your insulation being squished by purlins.
DTS assessments are quick & easy to calculate but in almost every case, a DTS-compliant building will cost more and won’t be as efficient as a JV3-compliant building.
A DTS-compliant building must include all of the following:
- Insulation complying with Part J1.2 as a “continuous barrier” including under box gutters, walls above uninsulated ceilings, colour-backed glass or fascias, and internal walls to non-conditioned areas.
- Reflective foil insulation, if used in your design, must be installed with the manufacturer’s specified airspace gap.
- Roof or wall bulk insulation must be uncompressed, so roof raisers or spacers will be required if your insulation will be squished.
- Roof and Ceiling insulation (complying with Part J1.3) must have added internal ceiling insulation to an unconditioned space above.
- External and internal wall insulation must comply with Part J1.5 which gives you a limited ability to benefit from the passive cooling of thermal mass walls, and no ability to reduce or avoid adding insulation to envelope walls.
- Floor insulation must comply with Part J1.6 which means there is no ability to maximise the thermal mass benefit of concrete floors, nor the ability to reduce or avoid adding insulation to envelope floors including soffits to conditioned spaces.
- Glazing for each orientation façade must comply with the DTS glazing allowances, which depend on Climate Zone, façade area, glazing type (Uw and SHGCw) and shade.
- Roof Lights may need better thermal specifications, and the total amount must be no larger than 5% of floor area.
All of these DTS requirements will add significantly to the overall construction costs. Many of these restrictions become irrelevant in a JV3 assessment since the building’s elements can instead be modelled exactly, with their benefit or detriment calculated exactly for each specific project.
In short, because the Annual Energy Consumption is calculated to be less than the DTS-compliant Reference Building, a JV3-compliant building will always be more energy efficient than a DTS-compliant Reference Building. Yes, really – always!
What’s more, a JV3 Building Solution is able to take the increased information into account to optimise the building’s design by trading between elements, reducing the construction costs with less insulation than a DTS assessment requires. We won’t say “always” for this one because there can be the very rare outlier case, but almost always, a properly-optimised JV3-compliant building will be cheaper to build than a DTS-compliant building.
It might not seem possible, but you achieve both of these things at the same time. For more information about thermal trading between building elements, check out our presentation to the Australian Institute of Building Surveyors 2013 annual conference where we covered some Energy Efficiency Case Studies.
So why would anyone ever pick the Deemed To Satisfy assessment method?
A DTS-compliant building is much easier to spec out in the early design phase, since it’s an easy way to make sure a design will comply with the Code’s energy efficiency requirements. This makes it easier to estimate the total project cost too, since you already know what quantity of insulation you’ll be using before you’ve even locked down the floor plan. Some HVAC consultants also prefer a DTS building, because it’s straightforward to calculate the maximum heating & cooling loads based on the thermal conduction of different building elements.
They are skilled at calculating the required temperature/humidity conditions (summer and winter), which is similar but not quite identical to our calculations. Calculating the Annual Energy Consumption accounts for the thermal mass, the effects of solar radiation, as well as heat transfer on an hourly basis.
There’s a lot of debate over which method is more accurate & that’s a topic for another article. However, since the sizing of heating & cooling devices is part of our thermal simulations, we include our calculated kW in our Energy Efficiency Reports – you can use these to compare with the HVAC designer’s calculations if you like. Curious about what else we include in our reports? Have a look at our article showing how to understand your Energy Efficiency Report.
Are the NCC Section J DTS measures wrong?
Absolutely not – the Code is never wrong! We don’t mean that in a head-in-the-sand way either, since we’ll be the first to say something when we think the Code isn’t right and we regularly submit changes for review. We think the DTS assessment method is valuable & its requirements are at the levels where they should be.
However, like most other experts in the industry, we don’t think the DTS method should be relied upon as a design tool for a highly energy efficient building. Doing that requires optimisation of the total building using a thermal simulation. The reason for Section J in the first place was to overcome a “market failure” where the people who pay for energy consumption were not adequately encouraged to improve the building to achieve energy savings & reduce their greenhouse gas emissions. Hence the Code stepped in to address this imbalance.
A building that complies under JV3 is not “inferior” to a building that complies under DTS. True, a JV3 assessment can achieve a Building Solution without complying with all the strict DTS elemental Requirements – but that’s exactly the point of JV3 assessments.
Are all the DTS Requirements needed, and are they cost effective? If you ask the question “is a DTS-complying building a highly energy efficient building?” our answer for most projects is no, with the rare exception for a few number of projects in Climate Zones 6 & 7 (Canberra, Melbourne & Tasmania) which have a higher demand for heating energy. However, in these climates it is still possible to avoid some of the DTS-required insulation while achieving a Building Solution using JV3 that lowers the total construction cost.
Our clients have reported savings of tens of thousands of dollars in construction cost with our JV3 assessment reports, compared to a DTS-compliant building. In fact, it’s not uncommon for us to save a client over a hundred thousand dollars on a large project. Here’s an example similar to past jobs.
Example Calculation of Potential Construction Cost Savings
Construction: Tilt concrete walls with metal-deck roof
Wall Saving: no steel battens, plasterboard or added insulation
Roof Saving: less material R-value, no insulation spacers
Building size: 60m × 60m, floor area = 3600m²
Average floor to roof height = 4.2m
Estimated Wall Saving = $59.00/m²
Estimated Roof Saving = $11.75/m²
Total Potential Construction Cost Saving = $101,772
A JV3 assessment might cost more than a DTS assessment but it well and truly pays for itself. The savings are worth several times the investment in our Energy Efficiency consulting expertise, resulting in an incredibly quick return on investment.
If you are interested in reducing the cost of construction on your project compared to a DTS assessment while still maintaining a highly energy-efficient design, then the JV3 Method is right for you! Contact us for a competitive fee proposal.