PURPOSE: To provide an indicative range of potential savings for preliminary consideration of using COLORBOND® Coolmax® steel for your project and inclusion in energy modelling to estimate savings specific to your building. This guide is not designed or intended for use by people considering COLORBOND® Coolmax® steel for residential applications

BASIS: Independent studies† of energy savings from real buildings as a consequence of having a cooler roof. This calculator scales the range of possible savings observed from studies of real buildings and provides a guide to whether high, medium or low range savings might be achievable on the basis of insulation, air conditioner position and climate. These are not the only factors that might affect potential energy savings*.

NOTE: Conventional energy modelling often has been found to underestimate savings for large commercial roofs. Current energy models typically do not recognise the local warming impact of the roof on the air temperature above the roof leading to underestimation of the benefit of cooler roofs, see reference for further details^.

If you would like one of our Specification Team members to take you through the online calculator please call Steel Direct on 1800 064 384.

Project Details

Conditioned Floor Area (m2)

Note: For multi storey construction use the upper storey air-conditioned area only.

Comparison to

Guiding Factors

Insulation Low insulation tends to higher potential savings
HVAC air delivery Air delivery near roof tends to higher potential savings
Location Location tends to higher potential savings

Guide to range of cooling savings

High and low cooling savings are predicted based on independent building studies and assumptions noted below.

Based on the input parameters above a saving in the vicinity of a high result is predicted. Note that due to the simplicity of this model and complexity of buildings* your cooling savings could lie anywhere within the low to high range.

Total Predicted Cooling Savings*
Year 0
Upfront cooling
equipment
Year 5 Year 10 Year 20
Low Saving
High Saving
Calculation Details

Cooling Energy Savings

Several independent studies† have shown cooling energy savings ranging from around 10 to 50% (low to high), with an average saving of about 20%; when changing the solar reflectance of a roof from dark and absorbent to light and reflective, representing a total solar reflectance change (TSR) of about 60% (or 0.60).

You are comparing COLORBOND® Coolmax® steel (TSR 77%) with (TSR %). This will result in a TSR that is % () higher.

Scaling the independent studies based on TSR change:

Low Saving % (/60 x 10)
Average Saving % (/60 x 20)
High Saving % (/60 x 50)

It has been assumed that on average a commercial building consumes 42 kWh/m2.pa at 0.25 c/kWh resulting in an annual cooling bill for the building of $10.44/m2.

The range of predicted savings is:

Low Saving $/m2.pa (% x 10.44)
Average Saving $/m2.pa (% x 10.44)
High Saving $/m2.pa (% x 10.44)

Cooling Equipment Saving

The cooling equipment saving is calculated based on a reduced cooling load and an assumed cooling equipment value of $930/kWr. (Reference Ecolibrium December 2010)

The reduced load is calculated using a steady state model based on thermodynamic fundamentals.

The reduced load is calculated for a representative hot sunny day (I=1000 W/m2, Tin=22C, Tout = 34C, wind = 0.5m/s) assuming an roof insulation value of

The reduced cooling load from COLORBOND® Coolmax® steel compared to is predicted to be Wr / m2.

Potential predicted cooling equipment saving = $ / m2 (/1000 x 930)

Total Predicted Cooling Savings

Total Saving = Upfront cooling equipment + Cooling saving x Years

10 Year Saving $/m2 x conditioned floor area ( m2)
Low $/m2 ( + x 10) $
Average $/m2 ( + x 10) $
High $/m2 ( + x 10) $

Based on the input parameters:

Insulation HVAC Air Delivery Location

Your indicative saving is predicted to be in the result.

The refined 10 year savings range is predicted to be between:

Predicted Saving $/m2 to $/m2
Total 10 Year Saving $ to $

This refined range is intended to provide a guide for consideration of using COLORBOND® Coolmax® steel for your project and inclusion in further energy modelling to obtain more accurate predictions specific to your building. Note that due to the simplicity of this model and complexity of buildings your cooling savings could lie anywhere within the low to high range.

Assumptions
  • Total Saving for 5, 10, 20 years includes simple addition of potential upfront cooling equipment saving and potential annual cooling energy savings.
  • light to dark roof (solar reflectance change of 60%) provides cooling savings ranging from 10 to 50% (20% average)
  • electricity priced at 25 c/kWh to include blending of consumption and a demand charge reduction
  • annual cooling cost of $10.44 / m2 (42 kWh/m2/year @ 25 c/kWh)
  • includes cooling equipment saving valued at $930 / kWr, reference Ecolibrium December 2010
  • cooling equipment saving is calculated based on peak load reduction on a representative hot sunny day (steady state conditions: I=1000 W/m2, Tin=22C, Tout=34C, wind=0.5m/s)
Additional Supporting Material

BlueScope Steel have conducted an controlled air conditioning experiment of Coolmax® steel roofing versus alternative roofing. In this study a medium level of roof insulation (R3) was used and did not have an air delivery system in or near the roof leading to conservative results. An estimate of savings from this study is shown below

5 years 10 years

Further details of study

† Report documenting the independent study results can be viewed here. (P9 Table 1)

* Cooling energy savings will vary considerably as each building is unique in its construction and operation. Factors such as the amount, quality and installation of roof insulation, the roof size, the type of cooling equipment and presence of ducting within or near the roofspace will also influence potential savings. When air conditioning is not used the building will be cooler in hot weather.

^ Ecolibrium February 2016 and Carter G and Kosasih B. (2015) Not So Cool Roofs, AIRAH’s Future of HVAC 2015 Conference, Melbourne, August 18-19, 2015.