# Notes for P1b (OCR Gateway Science)

Teacher recommended

?- Created by: Alfiya
- Created on: 25-12-12 21:07

**Keeping homes warm**

**Efficiency and payback time**

**Efficiency:**

- The efficiency of a device is the **proportion** of the energy supplied that is **transferred** in **useful ways **

- Energy efficiency is not just about heating homes. Everything that transfers energy **wastes** some of the energy as **heat** to the **surroundings**

- Energy can be **transferred** usefully, stored or dissipated. **It cannot be created or** **destroyed**.

- You must know this **equation** in order to be able to work out efficiency

**efficiency = useful energy output (x100) ÷ total energy input**

**Sankey Diagrams:**

**-** It looks like the one below which is for an filament lamp, sankey diagrams show **energy transformation**, therefore the energy efficiency is shown

- The **width** of each arrow depends on the **amount** of energy transferred to each element

- The energy transfer to light energy is the **useful** transfer, the rest is **‘wasted’**

**Payback time:**

**-** To be able to calculate the **payback time** you must know this **equation**

**payback time (years) = cost of insulation (£) ÷ annual saving (£)**

**-** As we know homes lose energy so to reduce the energy loss the uninsulated homes need to be **insulated** which could be quite **expensive **

- This means that it will **cost** you money in order to save money thus the equation helps you workout the in how many **years** you will be given back the money you spent on the insulation

- Payback time calculation helps us to work out the most **cost-effective** type of insulation.

**Energy Transfer**

- Heat energy can be **lost** from homes in many different places but there are ways of **reducing** these losses.

- **There are three**…

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