Question 1

a) Calculate the U-value of a proposed wall construction for a new house. The proposed construction from outside to inside is 102.5 mm bricks, 75 mm mineral wool, 140 mm mediumweight concrete blockwork and 12.5 mm plasterboard. The conductivities for these four materials can be taken to be 0.84, 0.04, 0.80 and 0.16 W/m.K respectively. Assume inner and outer surface resistances of 0.13 and 0.04 m2 .K/W. Thermal bridging can be ignored for the purposes of this calculation. (2 marks)

b) If you were to improve the U-value to Passivhaus levels by increasing the depth of insulation, what is the minimum thickness of mineral wool that would be needed? (1 marks)

c) What might be the practical implication of this change, and quantitatively demonstrate how this could be mitigated? (2 marks)

d) The original specification wall is to be used in a flat-roofed building that is 5 m wide, 8 m deep and 10 m high. The building will have glazing that occupies 30% of the wall area. The U-values of the floor, roof and glazing have been stated to be 0.25, 0.28 and 1.8 W/m2 .K respectively. The building will have a ventilation air exchange rate via openable windows of 1 air change per hour (note: an air change per hour is a measure of the air volume added to or removed from a space divided by the volume of the space). What fraction of the buildingstotal heat loss is due to air exchange (you can assume air density is 1.2 kg/m3 and specific heat capacity is 1012 J/kg.K)? (3 marks)

e) Now uprate the specification of the fabric and ventilation of the building to the minimum allowable standards for Passivhaus based on the information contained in the lecture slides. Ignore (assume zero for) thermal bridging and air leakage due to air-tightness i.e. assume the only air exchange is via ventilation at 1 air change per hour. What is the percentage saving in heat loss for the Passivhaus specification over the original design? (2 marks)

Preferably D using the specs given in A

Thanks