mpare the rate of heat loss per unit area through the original and new window.

You have joined a building construction company as a mechanical engineer. Your company is working on refurbishment of an old building at the Liverpool University campus. Your manager has assigned you to work on heat transfer throughout windows and how much money can be saved if single-glazed windows of that building is replaced with double-glazed units. Cross-sections through the old and new windows are the same. The heat transfer coefficient on the room side surface of the glass (h_r) is 8 Wm^-2K^-1; on the glass surface exposed on the outside ambient, the heat transfer coefficient (h_o) is 15 Wm^-2K^-1. The original glass plane and the two glass planes in the double-glazed unit are each 7 mm thick and have a thermal conductivity of 0.8 Wm^-1K^-1. Air fills the gap between the planes of the double-glazed unit and the convective heat transfer co-efficient for these surfaces is 5 Wm^-2K^-1.

1. If room temperature in the building is maintained at 20 °C and outside air temperature is 0 °C, compare the rate of heat loss per unit area through the original and new window. [25 marks]
2. Surface area of a window expose to the outside ambient is 3 m². How much money can be saved from heat energy by replacing a window? (consider a time of 30 days and ignore temperature changes over the time period, unit energy price is 0.15 GBP) [15 marks]
3. Briefly explain the difference in heat transfer between a central heating radiator and electric fan heater. Use schematic diagrams.