17.2.1 Assignment No. 1
Introduction
Midlands Institute of Engineering and Technology have proposed to construct a single-storey
conference centre as an extension to the main building. The size of the extension and other
details are given in the datasheet. Although the main use of this extension will be for
conferences and seminars, it may also be used for other events like lectures, open days etc.
The choice of materials, components and construction techniques should ensure that the new
construction conserves energy and creates a comfortable environment in the conference
room. The constructional details of the extension are:
Roof: RC slab
Ground floor: Solid concrete floor
Walls: Cavity construction using bricks and dense concrete blocks.
Your assignment, as a trainee technician, is to complete the following tasks and present your
findings in the form of a written report/power-point presentation. Use tables, images, graphs,
wherever appropriate.
DATASHEET
Plan area of the extension (internal): 20.0 m x 15.0 m
Height of the building: 4.5 m (floor to ceiling)
Number of 1.5 m x 1.2 m high double-glazed windows: 12
Number of 2.0 m x 2.0 m high doors: 3
Internal temperature = 21 ºC; External temperature = 0 ºC
Ground temperature = 5 ºC
Number of air changes: 2 per hour
U-values (W/m2 K)
Floor: 0.50;
Roof: 0.50;
Windows: 1.70;
Doors: 2.0
(Refer to Chapter 9 for any other information)
TASK 1
a) Identify and describe the factors (temperature, humidity, ventilation, acoustic
environment and visual environment) that could affect human comfort in the
conference room.
Answer:
Read Chapter 15 of the book to answer this question.
b) Describe, with diagrams of appropriate instruments, how each factor is measured and
state the acceptable values of each identified factor.
Answer:
i) Temperature: Two types of thermometers are described and illustrated in chapter 8.
ii) Relative humidity: Whirling hygrometer, Regnault’s hygrometer and an electronic
hygrometer are described and illustrated in chapter 9.
iii) Sound: digital sound level meter is described in chapter 13.
iv) Light: digital light meter is described in chapter 14.
TASK 2
a) Use the information given in the datasheet and calculate the fabric heat loss and the
heat loss due to ventilation from the conference room.
Answer:
Area of the windows = 1.5 × 1.2 × 12 = 21.6 m2
Area of the doors = 2 × 2 × 3 = 12 m2
Area (gross) of the walls = (20 + 20 + 15 + 15) × 4.5 = 315.0 m2
Net wall area = 315.0 – 12.0 – 21.6 = 281.4 m2
Area of the floor/roof = 20 × 15 = 300 m2
Since the cavity wall details are not given, let us assume 103 mm brickwork, 100 mm thick
mineral wool in 100 mm wide cavity, 100 mm thick medium density blocks and
12 mm thick lightweight plaster. Assuming the standard λ values, the calculations for its Uvalue are:
R = 0.12 +
0.012 0.100 0.100 0.103
+
+
+
+ 0.06 = 3.509
0.16
0 .2
0.038
0.84
U – value of the external walls =
1
= 0.285 W/m2 K
3.509
FABRIC HEAT LOSS
Element/component U-value (U)
Area (A)
Temperature
Heat loss =
difference (T)
U×A×T
Walls
0.285
281.4
21 – 0 = 21
1684.18
Doors
2.0
12
21
504.0
Windows
1.7
21.6
21
771.12
Floor
0.5
300
21 – 5 = 16
2400.0
Roof
0.5
300
21
3150.0
TOTAL
VENTILATION
Heat loss due to ventilation =
=
cv  V Nθ
3600
1212  (20 15  4.5)  2  21
= 19 089.0 W
3600
Total heat loss = 8 509.3 + 19 089.0 = 27 598.3 W
8509.3 W
b) Three vehicles, parked in the car park, started at the same time and produced noise
levels of 76 dB, 80 dB and 83 dB. Use either the analytical or the graphical method to
calculate the overall noise level.
Answer:
Consider 76 dB and 80 dB first. The difference between these noise levels is 4 dB.
Refer to chapter 13 and Figure 13.2. Locate 4 dB difference on the upper scale.
Correction (from the lower scale) = 1.45 dB
Overall noise level of 76 dB and 80 dB = 80 + 1.45 = 81.45 dB
Now consider 81.45 dB and 83 dB. The difference is 1.55 dB; locate this difference on the
upper scale.
Correction = 2.4 dB
Overall noise level = 83 + 2.4 = 85.4 dB
(The accurate answer can only be found by the analytical method, which gives 85.31 dB)
c) A street lamp (point source), having a luminous intensity of 1200 cd, is suspended 6 m
above the edge of the road leading to the car park. If the road is 8 m wide, calculate:
i) the illuminance at point A on the road surface, which is directly under the lamp.
ii) the illuminance at a point, on the other edge of the road, directly opposite to point A.
Answer:
i)
I = 1200 cd, h = 6 m
Illuminance, E =
b)
1200
I
= 2 = 33.33 lx
2
h
6
d2 = 62 + 82 = 100
d = 100 = 10.0 m
cos  =
6
= 0.6
10
Illuminance, E =
=
I
cos3 
h2
1200
 (0.6)3 = 7.2 lx
2
6
TASK 3
a)Explain how the human thermoregulatory system is affected by air temperature, air
movement, humidity, clothing and level of activity. Give acceptable values of these
factors for the conference room.
Answer:
Refer to chapter 15 of the book for answering this question.
b)Discuss how the NC/NR curves and the speech interference criteria may be utilized to
analyse noise and achieve acoustic comfort in the conference room.
Answer:
Refer to chapter 15 of the book for answering this question.
c)Discuss the reasons why designing for high levels of daylight in the conference room
may impact upon levels of visual and thermal comfort. Give acceptable values of
illuminance for the conference room.
Answer:
For psychological reasons, some daylight is important in buildings especially in dwellings. In
the conference room however, excessive daylight could cause discomfort glare which may
put strain on the eyes and cause loss of concentration. Direct sunlight could be acceptable in
winter but in summer it will cause thermal discomfort by raising the internal air temperature.
Larger windows would add to this problem and also cause heat loss in winter.
The acceptable level of illuminance is 500 lx.