Experiment & parent guide

How do insulation and refrigerators work?

Build an insulated box and save Nallo’s ice. Then turn the box into a refrigerator, one part at a time.

What you can build in this workshop

Insulation slows heat entering from the warmer surroundings. An active cooling circuit absorbs heat inside and releases it outside. The compressor needs electrical energy, so the warm side releases both the removed heat and the electrical input.

Follow the next step in the workbench. You can also tap the panels in the picture.

Four research missions

1 · Save the ice

Keep at least 75% of the ice after 30 minutes, without active cooling.

Build the floor, walls and lid. Use insulated-box mode, a room temperature of 26 °C and a starting temperature of 8 °C.
Predict which panel will slow heat best, then test 30 model minutes.
Read the ice percentage. Change only one panel and test again.

Insulation does not create cold. It slows heat entering from warmer surroundings. Better insulating materials and thicker panels can preserve ice for longer.

2 · Add a layer

Compare the same build with and without a second insulating layer.

Test without a second layer, then select “Save A” after the result.
Add a second layer under “Fine adjustments”. Keep the original panels and all other settings unchanged.
Test again and compare heat entering with A. Less incoming heat is better.

Each insulating layer adds resistance to heat flow. The model adds the thermal resistances of the layers. Keep the first layer unchanged for a fair comparison.

3 · Save electricity

Reach at most 6 °C after 30 minutes using no more than 10 Wh; set the target to 5 °C.

Replace the metal panels with insulating panels. Fit all four cooling parts and connect every pipe.
Keep room temperature at 26 °C, starting temperature at 8 °C and target temperature at 5 °C. Test 30 model minutes.
Compare the inside temperature and electricity use. Change one insulation, heat-exchanger, ventilation or power setting and test again.

The evaporator absorbs heat inside. The compressor uses electricity, and the condenser releases heat outside. Good insulation reduces the heat that enters again.

4 · Warm supplies

Show that more supplies starting at 24 °C cool more slowly with the same equipment.

Test the prepared refrigerator with 0.5 kg of supplies, then select “Save A”.
Increase only the supply mass under “Fine adjustments → Wall layers, size and supplies”.
Test again and compare temperature after 30 minutes. Keep the room at 26 °C and the starting temperature at 24 °C.

More supplies at the same temperature have a larger heat capacity. The same cooling machine must remove more heat to produce the same temperature drop.

Build and test your idea

Understanding the readings

Inside · °C

The temperature inside the box. Lower means colder. The ice can have a different temperature from the inside space.

Ice left · %

100% means the cube is still fully frozen; 0% means it has completely melted.

Electricity use · Wh

Electrical energy used over the whole trial. A smaller value means the compressor used less electricity.

Cooling power · W

Heat removed from inside per second at this moment. This is not accumulated electricity use. It is zero during a thermostat pause.

Getting started together

Follow the workbench: fit the floor, walls and lid, then test the box. Compare two equally long trials, changing one panel. Add the four cooling parts and connect their pipes to make a refrigerator. Individual parts and settings remain available in the expanded workbench. The yellow Nallo band shows the mission and goal; the workbench gives the next step. “How the experiment works” contains three instructions for each mission.

What happens in the cooling circuit?

At low pressure, refrigerant in the evaporator absorbs heat from inside. The compressor compresses the vapour and needs work. The outer heat exchanger, the condenser, releases heat to the surroundings. After the expansion restriction, pressure and temperature drop again. Moving marks follow the closed circuit; they do not represent air circulating through the refrigerator.

What can you build?

The floor, walls and lid are independent panel regions with their own material and thickness. A region may remain open. The heat model assigns 20% of the area to the floor, 60% to the walls and 20% to the lid. Open regions are simplified strong thermal bridges. Active cooling requires all four parts and all four pipes. Compatible sockets define the circuit; this is not an assembly guide for a real refrigerant system.

Layers, size and supplies

The thermal resistances of two layers add in this simplified model. Reversing layer order while keeping each material’s thickness does not change steady heat conduction. A larger box has more surface area. More supplies have more heat capacity. Change only supply mass to investigate that effect. The second layer applies to all fitted panels; an open region stays open. Material and thickness of the first layer affect only the selected region. A zero-thickness second layer has no effect.

Making a fair comparison

Predict which panel insulates better. Save a completed trial as A and change only material or thickness. Keep room temperature, door and starting temperature equal. Both operating modes normally start at 8 °C. Increase starting temperature deliberately for warm supplies. Compare the same target temperature with clear and obstructed ventilation behind the outer heat exchanger.

A common misconception

A thick wall does not create cold; it slows heat transfer. A refrigerator does not destroy heat. It transports heat and releases additional heat from its electrical input. Cooling power in watts is different from accumulated electricity consumption in watt-hours.

Away from the screen

Compare equal ice cubes in two equal closed containers, with and without added insulation. Put them in the same place and observe after the same time. An adult can show where a real refrigerator releases heat. Do not open covers or alter pipes.

Model and limits

The model balances wall conduction, simplified door heat input, heat capacity and the latent heat of 120 g of ice. An idealised temperature-dependent coefficient of performance includes an efficiency factor. Larger heat exchangers and better ventilation reduce the modelled temperature difference of the cooling cycle. Refrigerant-specific pressures, humidity and three-dimensional airflow are not simulated. Values are for learning, not refrigerator design. Red heat-flow marks show power, not molecular speed. Box volume changes area and heat capacity. Wall layers do not have separate temperature histories. The ice and inside space start with the same conditions in both modes; warm supplies may also release heat outward.

Keep investigating

Write a prediction before starting. Save a completed trial as A, change one thing and test again. The result keeps your prediction and names the changed parts. Mission feedback identifies conditions that must match. Free building is always available.