Hot houses

What the Activity is for

This activity looks at the energy losses in a model house and provides an environment where several explorations are possible. Sensible actions rely on reasoning based in convection, conduction and radiation in trying to achieve a chosen goal for the house. There are several possible goals and you need to be clear about what these are. You could set this up as an investigation to find the factors affecting how successfully a particular goal can be reached. Or you could leave it as a relatively open exploration.

What to Prepare

• heater bases (1 ohm, 10 watt rated resistors on a hardboard base, protected by gauze to prevent burnt fingers. Mark these with the power outputs for the different voltage values on the power supplies that you intend to ask the pupils to use (you can calculate these using power is voltage supplied squared and then divided by the resistor's resistance.)
• cardboard houses to fit heater bases – here 10 centimetre by 5 centimetre
• supply of material to insulate (Thin layers are better. You might aim to have some aluminium foil, some bubble wrap, some cling film, a supply of corrugated card, and thin foam (the foam provided for going under wooden flooring is suitable.)
• sticky tape, glue, scissors
• datalogger plus two temperature probes
• stepped power supply

Support sheet

Safety note: The heater does get hot. Warn pupils not to touch it.

What Happens During this Activity

You want pupils to use ideas of radiation, convection and conduction to keep a house warm. There are several ways they could tackle this. The house could be warmed to 30 degrees above ambient temperature, fully insulated, and then the pupils find how long it takes for the temperature to drop by 20 degrees Celsius. Alternatively, the challenge might be to insulate the house so that it stays at a certain temperature above ambient.

Some things to vary include where the insulation goes, how much of it there is, whereabouts in the house the temperature probes go, which windows are open and whether there is an internal floor. Pupils will be inventive, perhaps even replacing the roof with cling film and asking for a sun lamp!

In all reasonable cases they can be encouraged to build and modify a house as they suggest, showing how it compares to a standard (card) house, and how it improves on this standard for the purposes of the challenge that they are trying to answer. This is a very good opportunity for them to articulate their reasons.

Greater progress can be made by each group having access to a pair of houses and heater bases, plus three temperature probes. This allows them to compare a change to the standard set-up simultaneously. In this case each experimental run takes about twenty minutes. You'll want to ensure that the pupils are constructively engaged in this time, perhaps laying out their reasoning for the experiment. A competitive challenge can help focus the goals. Don't forget that hi-tech building materials are expensive, so encourage them to think and not to be wasteful!