Question 3 (12 marks) a. i.Explain in your own words what is meant by the U-value of a piece of building fabric. (2 mark

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Question 3 (12 marks)
a.
i.Explain in your own words what is meant bythe U-value of a piece of building fabric.
(2 marks)
ii.An insulated wall in a new house consists of four layers.Table 1 gives their thicknesses and thermal conductivities.
Table 1
For each layer, calculate the thermal resistance inm2 K W–1.
(4 marks)
iii.If the thermal resistance of an outside layer of air is0.04 m2 K W–1 and of aninside layer of air is0.13 m2 K W–1, show that theoverall U-value of the wall is just under0.18 W m–2 K–1.
(3 marks)
b.Explain briefly how the design of a condensing gas boilerdiffers from a non-condensing one. Why is the difference betweenthe higher and lower heating value of a fuel such as natural gasimportant in determining the increased boiler efficiency?
(3 marks)