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# ETG002 Building physics Assignment

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1.Here is speech number 1. Write this on the first page of the exam.

"I certify with honor and conscience that I,First Name Last Name, not during the examination period  and subsequent reporting period shared or received information from another examinee or person  that could affect study performance"Signature.

2.Nisse lives in a two-story house that consists of wooden block walls, flat ground and a ventilated attic space.  The house is rectangular and has floor dimensions of 7 x 12 m?2;. Each floor has a room height of 2.5m.  The ventilation covers approx. 0.5 oms/hi throughout the house and is of the self-draft type.

Nisse, who is an electrician, wants electric heating of the house (perhaps expensive, but convenient he  thinks). Help Santa perform this calculation!

a) Start by calculating the U-value of the outer walls. The outer walls consist of the following layers, counting from the  inside:

* The mineral wool's thermal conductivity is assumed to be 0.039 W/(m?K) as it is of lower  quality

Calculate the U-value of the outer wall using the --value method. (3p)

b) Estimate the building's heating power requirement if the DVUT is -17 °C. Nisse wants an indoor temperature of  21 °C. The total window area is 22 m?2; and these have a U-value of 2.8 W/(m?2;?K). The ground structure  (including ground) has a U-value of 0.283 W/(m?2;?K) and the roof a U-value of 0.118 W/(m?2;?K). Express the power  requirement in the form Watts per square meter of floor area. Ignore thermal bridges and air leakage. (5p)

c) Nisse intends to put electric underfloor heating in the ground floor of the house (he keeps the old electric  radiators upstairs). He has found a so-called underfloor heating foil that is energized with 230 V and has  the capacity to emit up to 80 W/m?2;. The system is regulated with a thermostat, so that the spaces that  are heated do not become too hot. The low construction height of the system (0.3 mm) means that he  does not have problems with thresholds, bench heights, etc., when the system is placed on the existing  ground plate. He will lay the system according to Figure 1, see below.

Nisse begins by placing a heat-insulating reflector board (6 mm, thermal conductivity 0.036 W/(m? K)) on the existing concrete slab. On this disc is placed the heating foil (0.3 mm, the thermal  resistance of the foil is neglected because it generates heat). According to industry regulations, an  age-resistant PE foil is then laid on top and then, according to Nisse's wishes in most rooms, a  wood-based laminate floor (10 mm, thermal conductivity 0.14 W/(m?K)).

Determine what temperature the foil gets if it is to emit the effect (heat demand directed upwards) according  to what was calculated in part task 2.b! The heat transfer resistance between the floor surface and the air is  assumed to be 0.1 m?2;?K/W. Disregard that some surfaces are not covered with underfloor heating (e.g. under  kitchen counters). If answer for part task 2.b is missing, calculate 50 W/m ?2; (3 p)

d) Assume that the ground's previously stated U-value assumed that there was a plastic mat on the  ground plate before the underfloor heating system was installed (Nisse removed this) and that its  heat resistance is negligible. How big is the heat loss if the ground temperature is assumed to be +5  °C (DVUT prevails but the cold has not been transmitted deep into the ground)? If there is no answer  in 2.c., assume 31 °C. (3p)

e) Make a more accurate calculation of the heat transfer resistance above the floor. First calculate the  surface temperature of the floor using the given value of 0.1 m?2;?K/W (according to building regulations  the surface temperature should not be higher than 26 °C). Then calculate, using the Nu number, which  convective heat transfer coefficient and heat transfer coefficient for long-wave radiation can be  expected. Do these provide the heat transfer resistance originally assumed ie 0.1 m?2;?K/W? Assume that  the characteristic length of the room is 3 m and that the temperature of the room air is 21 °C and the  surrounding room surfaces 22 °C. (6p)

3.Santa and his wife usually lie down in the bedroom and sleep soundly; usually 8 hours per night. The bedroom  has floor dimensions of 4 x 5 m?2; and room height of 2.5 m. In the old house in which they live, it can be  estimated that the air circulation in the bedroom corresponds to 0.4 rpm where 75% of the supply air comes  from outside and 25% from the adjacent hall ( they sleep with the bedroom door ajar so the cat can run in  and out).

The air temperature of the hall and bedroom is 20.5 °C. The hall's air has a relative humidity of about 40%. It  has been around -10 °C outside during the night for a month and the relative humidity is 85%.

In the bedroom there is a double-glazed window, which has a U-value of 2.8 W/(m?2;?K). Nisse usually pulls down a  roller blind which consists of a thin dark fabric (the fabric is open to diffusion but prevents light from entering the  room). An air gap is formed between the roller blind and the window's inner glass, which has a heat resistance of  approx. 0.16 m?2;?K/W.

a) Estimate the vapor content that the bedroom air reaches at stationary conditions if Santa and his  wife each emit moisture equivalent to 40 g/h. Ignore moisture in the air that can be absorbed by  furnishings, fabrics, structures, etc. (4p)

b) What temperature does the inner glazing of the window get? (2p)

c) Will there be condensation on the inner glazing when Santa pulls up the blinds in the morning?  Show calculations and justify them! (2p)

d) How much is the energy loss reduced by pulling down the blinds at night during a month with  the prevailing conditions? The area of the window is 1.6 m?2;. (2p)

4.Dog food is produced in an old industrial building. Because the neighbors have complained about odors from the business,  a powerful ventilation system with exhaust air filters has been installed. The ventilation system creates a negative  pressure of 10 Pa so that indoor air does not leak out to the surroundings. The reason for this severe underpressure is  based on a calculation that a consultant has carried out. She means that if the desired temperature in the room is 19 °C  and the outside temperature falls to a lower temperature in the town,

- 15 °C, the negative pressure will ensure that indoor air does not leak out through the roof of the building, which has  gaps between roof elements. The room's ceiling height is 7 m and the majority of openings (doors, windows, air  intakes, etc.) in the climate screen are at or near ground level.

a) Reason about what happens if there is a cold snap so that the outside temperature drops to -20 °C. How is  the pressure pattern in the building affected and what air pressure can be expected directly under the  roof? (2p)

b) The roof consists of lightweight concrete elements (see figures 2 and 3 below), which have been covered with an outer roof  (so-called up-posted roof).

The problem is that due to subsidence of the building, two roof elements have separated so that a gap has  formed. The length of the roof elements is 6 m and thickness 250 mm. How much air (m?3;/h) risks flowing if the  conditions in 4.a prevail? The width of the gap is 2 mm (disregard the groove and tongue on the edges - i.e. the  "grooves"). (4p)

c) Will there be condensation on the current occasion and if so, how much, assuming the cold snap lasts for  three days? The air in the room has a relative vapor content of 70% and outside 90%. Assume that the  attic air has the same condition as the outside air. If answer in 4.b. missing, use flow 15 m?3;/h (2 p)

d) The roof's old moisture barrier (roofing paper) is at risk of cracking. In case of long-term and recurring  rain, rainwater can drip/run down on a roof element and form a puddle that is filled up every time it  rains (this does not mean that the water flows through the joints between the elements - these are 60  cm wide). How long from the start of rain does it take before staff notices that the roof is leaking? (2p)

• Uploaded By : Katthy Wills
• Posted on : February 20th, 2023
• Views : 179

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