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Parents Pricing Home Leaving Cert Construction Studies Heat & U-Value Calculations Using the following data, calculate the U-value of the external wall of a new dwelling house
Using the following data, calculate the U-value of the external wall of a new dwelling house - Leaving Cert Construction Studies - Question 5 - 2015 Question 5
View full question Using the following data, calculate the U-value of the external wall of a new dwelling house. The wall is of concrete block construction, with a 250 mm cavity. The c... show full transcript
View marking scheme Worked Solution & Example Answer:Using the following data, calculate the U-value of the external wall of a new dwelling house - Leaving Cert Construction Studies - Question 5 - 2015
Calculate the U-value of the external wall Only available for registered users.
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To find the U-value, use the formula:
U = 1 R t o t a l U = \frac{1}{R_{total}} U = R t o t a l 1
R t o t a l = R e x t e r n a l + R b l o c k e x t + R c a v i t y + R b l o c k i n t + R i n t e r n a l R_{total} = R_{external} + R_{block_{ext}} + R_{cavity} + R_{block_{int}} + R_{internal} R t o t a l = R e x t er na l + R b l oc k e x t + R c a v i t y + R b l oc k in t + R in t er na l
Given the resistances:
R e x t e r n a l = 0.048 R_{external} = 0.048 R e x t er na l = 0.048 R b l o c k e x t = 100 1.440 = 0.069 R_{block_{ext}} = \frac{100}{1.440} = 0.069 R b l oc k e x t = 1.440 100 = 0.069 R c a v i t y = 250 0.250 = 1.000 R_{cavity} = \frac{250}{0.250} = 1.000 R c a v i t y = 0.250 250 = 1.000 R b l o c k i n t = 100 1.440 = 0.069 R_{block_{int}} = \frac{100}{1.440} = 0.069 R b l oc k in t = 1.440 100 = 0.069 R i n t e r n a l = 0.122 R_{internal} = 0.122 R in t er na l = 0.122
Calculating R t o t a l R_{total} R t o t a l R t o t a l = 0.048 + 0.069 + 1.000 + 0.069 + 0.122 = 1.308 R_{total} = 0.048 + 0.069 + 1.000 + 0.069 + 0.122 = 1.308 R t o t a l = 0.048 + 0.069 + 1.000 + 0.069 + 0.122 = 1.308
Thus,
U = 1 1.308 ≈ 0.765 W/m² °C U = \frac{1}{1.308} \approx 0.765 \text{ W/m² °C} U = 1.308 1 ≈ 0.765 W/m² °C
Calculate the cost of heat loss annually through the external walls for the new house Only available for registered users.
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Using the U-value calculated above, apply the formula:
Heat loss = U × A × Δ T × t \text{Heat loss} = U \times A \times \Delta T \times t Heat loss = U × A × Δ T × t
Where:
U = 0.765 U = 0.765 U = 0.765 A = 150 A = 150 A = 150 Δ T = 20 − 6 = 14 \Delta T = 20 - 6 = 14 Δ T = 20 − 6 = 14 t = 35 weeks = 35 × 7 × 8 hours = 1960 hours = 7056000 seconds t = 35 \text{ weeks} = 35 \times 7 \times 8 \text{ hours} = 1960 \text{ hours} = 7056000 \text{ seconds} t = 35 weeks = 35 × 7 × 8 hours = 1960 hours = 7056000 seconds
Calculating heat loss:
Heat loss = 0.765 × 150 × 14 × 1960 ≈ 1639062 joules \text{Heat loss} = 0.765 \times 150 \times 14 \times 1960 \approx 1639062 \text{ joules} Heat loss = 0.765 × 150 × 14 × 1960 ≈ 1639062 joules
Substituting into cost calculations with given prices, total cost is approximately €44.60.
Calculate the cost of heat loss annually through the external walls for the existing house Only available for registered users.
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For the existing house with a U-value of 0.21 W/m² °C, use the same formula:
Cost = 0.21 × 150 × 14 × 1960 \text{Cost} = 0.21 \times 150 \times 14 \times 1960 Cost = 0.21 × 150 × 14 × 1960
Performing the calculation:
Cost ≈ 79.13 € \text{Cost} \approx 79.13 € Cost ≈ 79.13€
Design detailing to prevent the ingress of water Only available for registered users.
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To detail the window head:
Ensure the window sill extends outwards to divert water.
Implement a flashing above the window to shed water away from the wall.
Use a drip edge at the bottom of the flashing to redirect water.
Incorporate weep holes in the masonry to allow moisture drainage.
Freehand sketches should illustrate these elements effectively.
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