# Refrigerator Energy Use and Cost Analysis Let's break down each question step by step. --- ## a. **Energy Use in "D" Units for a New Refrigerator** ### Step 1: Understanding "D" Units - **"D" unit** = average daily energy use by a human (about **2.2 kWh/day**). - To convert annual kWh to D units: \[ \text{D units per year} = \frac{\text{Annual kWh}}{2.2} \] ### Step 2: Calculate for New Fridge - **Annual usage:** 422 kWh/year \[ \text{D units per year} = \frac{422}{2.2} \approx 192 \text{ D units per year} \] - **Daily D units:** \[ \text{Daily D units} = \frac{422}{365 \times 2.2} \approx 0.52 \text{ D units/day} \] **Final Answer:** - **Annual:** ~192 D units - **Daily:** ~0.52 D units --- ## b. **Daily D Units for a 20-Year-Old Fridge** - **Annual usage:** 1700 kWh/year \[ \text{D units per year} = \frac{1700}{2.2} \approx 773 \text{ D units per year} \] - **Daily D units:** \[ \text{Daily D units} = \frac{1700}{365 \times 2.2} \approx 2.12 \text{ D units/day} \] **Final Answer:** - **Daily:** ~2.12 D units --- ## c. **Payback Period Calculation** ### Step 1: Annual Cost for Each Fridge - **Electricity cost:** \$0.18/kWh #### New Fridge: \[ 422 \text{ kWh/year} \times \$0.18 = \$75.96 \text{ per year} \] #### Old Fridge: \[ 1700 \text{ kWh/year} \times \$0.18 = \$306 \text{ per year} \] ### Step 2: Annual Savings \[ \$306 - \$75.96 = \$230.04 \text{ saved per year} \] ### Step 3: Payback Period \[ \text{Payback Period} = \frac{\$1500}{\$230.04} \approx 6.52 \text{ years} \] **Final Answer:** - **Payback period:** ~6.5 years --- ## d. **Should You Replace the Old Fridge?** - **New fridge lasts:** 12 years - **Payback period:** 6.5 years ### Analysis - **You break even** after 6.5 years. - For the remaining \(12 - 6.5 = 5.5\) years, you **save money** on electricity. - **Conclusion:** Yes, it makes financial sense to replace the old fridge if you expect it to last 12 years. --- ## e. **Other Decision Factors** ### 1. **Future Cost of Energy** - If electricity prices **rise**, savings increase, reducing payback time. - If prices **fall**, savings decrease. ### 2. **Other Factors** - **Environmental impact:** Newer fridges use less energy, lowering carbon emissions. - **Reliability:** Old fridges may require costly repairs. - **Features:** New fridges may have better insulation, more space, or smarter controls. - **Disposal:** Properly disposing of an old fridge has costs and environmental considerations. --- ## **Summary Table** | Fridge | kWh/year | Daily D units | Annual Cost | Payback Period | |---------------------|----------|:-------------:|:-----------:|:--------------:| | New (efficient) | 422 | ~0.52 | \$75.96 | 6.5 yrs | | Old (20 yr) | 1700 | ~2.12 | \$306 | — | --- **Image suggestion:** *Bar chart comparing annual energy use of old vs. new fridge, showing D units and cost differences.* _Alt text: Bar chart showing new fridge uses about 25% of the energy and cost compared to a 20-year-old fridge._