Can it handle the heat?
Thermal Modelling Based on Melbourne’s IceBox Challenge
By Abanoub Mina, Mechanical & Environmentally Sustainable Design (ESD) Engineer
Is Insulation Everything?
Insulation is designed to act as a barrier to keep your home warm in winter and cool in summer.
Potentially, this means it could keep occupants more comfortable throughout the year, as well as reduce the demand for air conditioning.
Does that mean the more insulation I have the more I’ll be able to save on my cooling and heating bills?
As a training exercise to improve my researching, energy modelling and critical thinking skills, I was given the task by my team leader to recreate the IceBox Challenge in Melbourne using the thermal simulation software, Integrated Environmental Solutions (IES).
My challenge was to create an energy model of the IceBox Challenge as accurately as possible.
The only difference is, instead of having ice inside the box, internal gains were added to the energy models to better represent real-life conditions i.e. simulating heat from people, lighting, equipment etc.
The questions that I’ll try to address with this analysis include:
- In passive mode, which box will result in a higher maximum temperature and a lower minimum temperature?
- In active mode, which box will require more heating energy to maintain a comfortable temperature (above 20°C) throughout the year? And which box will require more cooling energy to maintain a comfortable temperature (below 24°C) throughout the year?
- Based on these results, in what climate is the “super insulated” design suitable for, and in what climate could it be potentially unsuitable? Why?
- What are some potential risks of “super insulated” design? What are some ways to overcome these risks?
- Is this experiment a fair representation of real-life scenario? What are some additional factors we should be considering if we wanted to make the experiment better?
The #IceBoxChallengeMelbourne is a public demonstration intended to show how the building fabric impacts comfortable living as well as energy costs in a home.
Running from 20th February until 3rd March 2019 in Melbourne CBD, the challenge is made up of two identical structures; however, they differ in insulating properties of the walls, roof, floors as well as windows.
One structure is built according to the energy efficiency requirements of the Australian Building Codes, and the other is built to the Passive House Standard.
Both structures were left for 12 days in the summer sun with 720kg of ice inside of it. The public is challenged to guess the amount of ice remaining in each box at the end of the 12-day period.
Image source: https://greenmagazine.com.au/ice-box-challenge-melbourne/
Does the IceBoxChallenge Simulate Real-Life Conditions?
In a typical home, it isn’t common to find a large block of ice in your living room.
A typical home has occupants, lighting and miscellaneous equipment e.g. kitchen appliances. These are known as internal heat loads, which are more realistically found inside the home.
Assessing the performance of the boxes in more realistic conditions, i.e. with internal loads added, can yield some interesting results.
Modelling Details and Thermal Specifications
Through research, I was able to find the building fabric breakdown and insulation properties on the Australian Passive House Association website.
However, it was very difficult to find the dimensions and orientation of the boxes.
To accurately find the dimensions I used images from the Melbourne IceBox Challenge website.
With close inspection of the images, I was able to scale my drawing via a T-Top Bollard (standard height of 1150mm) and hence measure the boxes’ dimensions.
I used Google Maps and Google street view to accurately determine the orientations of the facades.
Image source: https://www.thefifthestate.com.au/events-tfeevents/event-news/passive-house-debate-heats-up-with-ice-box-challenge/
- Floor Dimensions = 2.5m x 2.5m
- North Facade Height = 3.2m
- South Facade Height = 4m
- Window Dimensions = 0.9m x 1.2m
- Overhang = 0.5m (all 4 sides)
A comparison of each structure’s building fabrics are shown below:
To represent the internal loads, I assigned a total of 150W to each box, which I believe is a reasonable representation of the internal loads in a typical dwelling:
- Occupancy = 10 m2/person
- Lighting = 10 W/m2
- Equipment = 5 W/m2
For the purposes of this exercise the infiltration was set to zero.
I used the available online data and multiple engineering methods to determine the inputs for the buildings’ fabric makeup, orientations and dimensions as well as the internal loads. I felt that by placing my model in the Melbourne CBD, I had accurately replicated the IceBox setup.
I am now ready to test their performance under different scenarios.
Test 1 – Air Conditioned 24/7/365 (Heating Only)
In the first test, both rooms were modelled with an Air Conditioning system that would stop the rooms dropping below 20°C.
The energy required to provide sufficient heating throughout the year is displayed in the column graphs below.
Figure 1A – No Internal Loads (Heating Only)
Figure 1B – With Internal Loads (Heating Only)
In active mode, which box will require more heating energy to maintain a comfortable temperature (above 20°C) throughout the year?
Looking at Figure 1A (graph to the left), the Compliant Code Box required more energy to heat the box above 20°C throughout the year.
This means that when there are no internal loads in the box, the Compliant Code Box may be less cost-effective.
In comparison, the results for the Super-insulated Box in Figure 1B (the graph on the right) did not require heating from the air conditioning system to keep the box above 20°C. This demonstrates how efficient the Super-insulated Box may be in winter conditions.
Test 2 – Air Conditioned 24/7/365 (Cooling Only)
For the next test, both rooms were modelled with an Air Conditioning system to maintain the rooms to a maximum of 24°C.
The energy required to provide sufficient cooling throughout the year is displayed in the column graphs below.
Figure 2A – No Internal Loads (Cooling Only)
Figure 2B – With Internal Loads (Cooling Only)
In active mode, which box will require more cooling energy to maintain a comfortable temperature (below 24°C) throughout the year?
Looking at the results above, the Super-insulated Box performed better than the Code Compliant Box when there are no internal loads.
Once internal loads are considered, the Air Conditioning and cooling energy demand of the Super-insulated Box is higher than the Code Compliant Box.
Evidently, this indicates the “super insulated” design is trapping internal heat gains indoor.
Test 3 – No Air Conditioning for a full year
In test 3, the boxes were left for a full year without an Air Conditioning system to observe how they behave. The results for both boxes are shown below:
In passive mode, which box will result in a higher maximum temperature and a lower minimum temperature?
Looking at the table below, the Super-insulated Box will result in a higher maximum temperature and the Code Compliant Box will achieve a lower minimum temperature.
In passive mode, what is the number of hours above 28°C and below 18°C?
Based on these results, in what climate is the “super insulated” design suitable for and in what climate could it be potentially unsuitable?
From the results above, the “super insulated” design has a higher peak and mean temperature throughout the year. This indicates that the heat is being trapped inside the heavily insulated box, which means the Super-insulated Box will be more suitable for winter conditions and cooler climates.
When internal loads were applied, the Super-insulated Box had temperatures above 28°C for 7,563 hours in a year (86% of the year). The results suggest that this design may not be ideal for summer conditions and hot climates.
What are some potential risks of “super insulated” designs?
What are some ways to overcome these risks?
In a situation where the Air Conditioning system is failing or in the event of a power outage, the temperatures inside the “super insulated” design can potentially become high.
If the room has not got access to good ventilation to help expel the heat trapped in the room, then the temperatures inside can potentially be intolerable for the occupants.
This highlights the importance of coupling ventilation with the appropriate building fabric insulation.
Is this experiment a fair representation of real-life scenario?
Obviously, this is a simplified model that does not account for the complexities of an actual building, nor is it intended to.
It does, however, highlight the potential benefits and risks of “super-insulated” design.
In my opinion, the IceBox Challenge can better represent a real-life scenario by having internal loads inside the room, instead of ice.
Normally, internal heat is generated from the occupants of the house, as well as equipment and lighting heat. To represent a real-life house, internal heat gains must be considered.
In addition, as it is near to impossible to have a completely sealed house. There will be some infiltration air from the outside, as well as leakage from the room exiting to the atmosphere. This will change the results from the thermal simulation software slightly.
It is evident that the “super insulated” design will still favour cooler climate conditions.
Is it actually more cost-effective to use the “super insulated” design?
From the results, it does not appear to be more cost-effective.
Depending on the climate, the “super insulated” design may require a higher amount of energy to cool the space (when internal loads are applied).
When the room was cooled to below 24°C the heavily insulated box actually required 60% more cooling energy over a year, compared to the Code Compliant Box.
These results may change once a tuned ventilation strategy is introduced. Now that could be an interesting follow up study…….