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# Energy - You are considering to replace the single glass in your house

CFL - IS AN ENERGY-EFFICIENT LIGHT

You are considering to replace the single glass in your house with double insulated glass.
The single glass has an R value of 0.91 m2-K/W and the double glass has a R value of 2.04 m2-K/W.

Calculate the heat loss for each type of glass from a room through a 2 m by 3 m window if the indoor temperature is 20 °C while it is 5 °C outdoors. [3]
How many 60 W incandescent bulbs must be replaced by 17 W CFLs before you get a MW saving? Assume all is switched on at the same time. [2]

Assuming 80 % of these lights are utilised during peak times and that Eskom is willing to pay R 3 million per peak MW saved. Further assume that Eskom is distributing these CFLs for free. What is the cost of each CFL to make such a rollout worth the effort? [3]

If each CLF cost R11 (bulk price) and the total project cost for distribution is R100,000. Is a CFL rollout worth the effort? [2]

#### Solution Preview

(a) - Glass --
As nothing is said about convective heat conductivity, we assume that it is to be disregarded.

The heat loss for a single glass is

2m * 3m * (20 °C - 5 °C) / (0.91 m2-K/W) = 98.9 W

And for the double glass it is

2m * 3m * (20 °C - 5 °C) / (2.04 m2-K/W) = 44.1 W

(b) CFL bulbs

Each bulb ...

#### Solution Summary

You are considering to replace the single glass in your house with double insulated glass.
The single glass has an R value of 0.91 m2-K/W and the double glass has a R value of 2.04 m2-K/W.

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