Temperature Air Movement Humidity Ventilation Engineering Essay

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The metabolic rate of a person depends on his/her level of activity. Metabolism can be classified as the sum of all chemical reactions that go in the human body for producing energy by means of converting consumed food. The metabolic rate and the heat created by a person increases as the rate of expenditure of physical energy increases. Therefore, he/she will be comfortable at a slightly lower resultant temperature. Sedentary people lose body heat at a rate of about 120 W at a temperature of 21 °C. The rate of body heat loss will increase to about 240 W on taking up light physical activity. The room temperature may be reduced slightly to maintain the thermal comfort.

Clothing

Clothes provide thermal insulation due to the low thermal conductivity of the clothing material and the air layer trapped between the clothing and the skin. The thermal resistance of clothing is expressed in terms of a unit known as the clo-value; 1 clo being the insulation provided by men's business suit. In winter people wear thicker and heavier clothing to get better insulation and hence more comfort. In summer people need to lose more heat from their bodies, therefore, lightweight clothing like shirt/blouse and trousers/skirt may provide the necessary comfort. Women, generally, wear lighter clothing as compared to men and hence prefer slightly higher temperatures.

Air movement

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Air movement in a building is usually due to ventilation and draughts. The draughts could be due to gaps around openable parts of doors and single-glazed windows. Air movement creates freshness in a building and is more desirable in summer than in winter. Air movement increases heat loss from human body and causes chilliness and discomfort in winter. In domestic buildings, an air velocity of 0.1 - 0.2 m/s is considered to be reasonable. As draught increases and air velocity of 0.2 m/s or more is achieved, an increase in the dry resultant temperature is required to compensate for the cooling effect produced by air movement.

Humidity

The effect of humidity on human comfort is studied by considering the relative humidity (RH) of air. Its effect is considered to be very small when the resultant temperature is close to the recommended value. At temperatures above 25 °C (approx.) and higher activity level, heat is lost from the body by sweating. If the RH of the air is high, i.e. > 70%, the evaporation of sweat is very slow and people feel uncomfortable. The comfortable range of relative humidity is about 40 - 70%. If the RH of air is below 40%, some people may suffer from dry throat and dryness of skin and eyes.

Ventilation

Ventilation is the process by which clean air is brought into a building to remove the stale air. It is essential in buildings to remove carbon dioxide gas, body odours, bacteria, cooking smells and humidity. In crowded rooms the humidity may increase due to respiration and perspiration of the occupants, and there will also be an increase in the air temperature. Adequate ventilation will bring in fresh air to maintain the supply of oxygen for breathing, remove smells and excess water vapour, and lower the air temperature. See below table 'Extract ventilation rates' for a selection of ventilation requirements.

Extract ventilation rates

Room

Extract rate

Rooms containing printers and photocopiers in substantial use (greater than 30 minutes per hour)

Air extract rate of 20 l/s per machine during use. Note that, if the operators are in the room continuously, use the greater of the extract and whole building ventilation rates

Office sanitary accommodation and washrooms

Intermittent air extract rate of:

15 l/s per shower/bath

6 l/s per WC/urinal

Food and beverage preparation areas (not commercial kitchens)

Intermittent air extract rate of:

15 l/s with microwave and beverages only

30 l/s adjacent to the hob with cooker(s)

60 l/s elsewhere with cooker(s)

All to operate while food and beverage preparation is in progress

Whole building ventilation rate for air supply to offices

Air supply rate

Total outdoor air supply rate for offices (no smoking and no significant pollutant sources)

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10 l/s per person

Noise

Noise can be defined as unwanted sound. Noise in a building may be produced by a multitude of sources like printers, photocopiers, air-conditioning systems, people in a room and people in adjoining rooms. Whatever the source, noise may interfere with our hearing of speech, distract us from what we are trying to do or it may just be annoying. Various criteria have been developed to analyse noise and hence minimise or avoid disturbance and speech interference. Two of these criteria are:

speech interference criteria

noise criteria curves

b) State the acceptable values of each factor.

Recommended comfort criteria for specific applications

Building/room type

Winter operative temp. range for stated activity and clothing levels

Summer operative temp. range (air conditioned buildings) for stated activity and clothing levels

Suggested air supply rate / (L.s-1 per person) unless stated otherwise

Filtration grade

Maintained illuminance

/lux

Noise rating

(NR)

Temp

/°C

Activity

/met

Clothing

/clo

Temp

/°C

Activity

/met

Clothing

/clo

Conference/board rooms

22-23

1.1

1.0

23-25

1.1

0.65

10

F6-F7

300/500

25-30

Source: (CIBSE, 2006, p.16)

Temperature

The acceptable value for temperature in the conference room can be broken down in to winter and summer:

Winter ideal range is 22-23°C.

Summer ideal range is 23-25°C.

Activity

The acceptable value for activity in the conference room is 1.1 met.

Clothing

The acceptable value for clothing in the conference room can be broken down in to winter and summer:

Winter ideal range is 1 clo.

Summer ideal range is 0.65 clo.

Air supply rate

The acceptable value for air supply rate in the conference room is 10 L.s-1 per person.

Illuminance

The acceptable value for illuminance in the conference room is 300-500 lux.

Noise

The acceptable value for noise in the conference room is 25-30 NR.

Task 2 (Assessment Criteria 3.2)

Explain the provision of services for the building and for the safe disposal of waste products. Discuss how you would expect the services to be incorporated into the overall design of the building.

The Offices, Shops and Railway Premises Act require buildings in use to have suitably located accommodation for sanitary appliances.

In general, the following minimum necessities apply:

Sufficient ventilation

Regular cleaning plan

Cold and hot running water, or mixed warm water

Way for cleaning (soap) and drying (warm air or towels)

Shower, if the type of work gives good reason for it

Toilet paper and coat hook in the WC cubicle

Privacy, if possible with separate male and female accommodation unless each facility is separated with a lockable door for use by one person at a time

Ease of access - not necessarily in the workplace but within the vicinity

Minimum facilities:

Mixed use or female use only -

Persons

WCs

Washbasins

1-5

1

1

6-25

2

2

Source: (Hall, F and Greeno, R, 2011, p.391)

Thereafter, 1 additional WC and 1 additional washbasin per 25 persons

Male use only -

Persons

WCs

Urinals

Washbasins

1-15

1

1

As above

16-30

2

1

As above

31-45

2

2

As above

46-60

3

2

As above

61-75

3

3

As above

76-90

4

3

As above

Source: (Hall, F and Greeno, R, 2011, p.391)

Thereafter, allocated on the same proportional basis

Sanitary accommodation design

It is estimated that the conference room will have capacity for up to 100 persons. For the purpose of sanitary accommodation design is has been assumed that 50% of the capacity will be male and the remaining 50% will be female.

Both female and male use only WCs should be provided and include for the following sanitary accommodation:-

Male WC (see sketch SK01)

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Three WCs

Two urinals

Three washbasins

Female WC (see sketch SK02)

Three WCs

Three washbasins

Male WC.bmp

Female WC.bmp

Task 3 (Assessment Criteria 3.3)

a) Calculate the coefficient of thermal transmission (U-value) of the external wall. Refer to the data sheet for the 𝝀-values. If you need additional information, reference should be made to text books on construction science.

Thermal conductivity of some building materials

Material

Thermal conductivity (𝝀) W/m K

Brickwork (external)

0.84

Aerated concrete blocks

0.11

Mineral wool batt

0.038

Plaster - lightweight

0.16

Source: (Virdi, 2012, p.101)

Standard thermal resistances

Type of resistance

Construction element

Heat flow

Surface emissivity

Standard resistances (m2 K/W)

Inside surfaces

Walls

Horizontal

High

0.12

Outside surfaces

Walls

Horizontal

High

0.06

Source: (McMullan, 2007, p.23)

Total thermal resistance

For a cavity wall consisting of 12 mm thick lightweight plaster, 100mm thick aerated concrete blocks (inner leaf), 100mm wide cavity filled with 100mm thick mineral wool insulation, 103mm thick brickwork (outer leaf), the total thermal resistance is given by:

Where

is the total thermal resistance of an element

is the resistance of the inside surface

is the material resistance

is the material resistance

is the material resistance

is the material resistance

is the resistance of the outside surface

Alternatively, in tabular format

Total thermal resistance

Layer

Thermal conductivity (𝝀) W/m K

Thickness d (m)

Thermal resistance R (m2K/W)

Inside surface

n/a

n/a

Standard

0.12

Plaster - lightweight

0.16

0.012

0.012/0.16

0.075

Aerated concrete blocks

0.11

0.100

0.100/0.11

0.909

Mineral wool batt

0.038

0.100

0.100/0.038

2.632

Brickwork (external)

0.84

0.103

0.103/0.84

0.123

Outside surface

n/a

n/a

Standard

0.06

Total thermal resistance, Rtotal

3.918

Calculation of U-values

The U-value is calculated as the reciprocal of the total thermal resistance using the following formula.

Where

U-value (W/m2 K)

sum of the thermal resistances (R-values) of all the components in the

element

Task 3 (Assessment Criteria 3.3)

b) Calculate the heat loss from the building and the heat gain over a heating season of 33 weeks.

Heat loss from the building over a heating season of 33 weeks

Fabric heat loss

Limiting fabric parameters

Windows, roof windows, rooflights, curtain walling and pedestrian doors

2.2 W/m2 K

Source: (HM Government, 2010, p.18)

The inside measurements should be used in this question:

Walls:

Door(s):

Window(s):

The rate of heat loss through the fabric of the building may be calculated by using the following table:

Total rate of fabric heat loss

Element

U-value, U

(W/m2 K)

Area, A

(m2)

Temperature difference, T

(K)

Rate of heat loss,

U x A x T

(W)

Windows

2.2

3.1.5

19

1316.70

Door

2.2

2.0

19

83.60

Walls

0.26

221.65

19

1094.951

Roof

0.45

284.94

19

2436.237

Floor

0.25

284.94

16

1139.76

Total rate of fabric heat loss

6071.248

Heat loss due to ventilation

The rate of heat loss due to ventilation is given by the formula:

Where

is the volumetric specific heat capacity of air (J/m2 K)

is the volume of room (m3)

is the number of complete air changes per hour (each)

is the difference between the inside and outside air temperature (K)

Seconds in 1 hour = 3600

The total rate of heat loss from a building is determined by adding the fabric heat loss and the ventilation heat loss.

Or

Heat gains over a heating season of 33 weeks

Solar heat gains from the sun

Seasonal solar gain through windows

Type of window

(vertical unobstructed)

Average solar flux

Seasonal total heat gain

South-facing windows

72 W/m2

680 MJ/m2 glass

East and west-facing windows

48 W/m2

410 MJ/m2 glass

North facing windows

29 W/m2

250 MJ/m2 glass

Source: (McMullan, 2007, p.58)

Casual heat gains from occupants and equipment in the building

Heat emissions from casual sources

Type of source

Typical heat emission

Adult person (for 20°C surroundings)

Seated at rest

90 W

Lighting

Fluorescent system giving 400 lux (e.g. classroom)

20 W/m2 floor area

Source: (McMullan, 2007, p.59)

Or

Or

Find the number of radiators required

Heat output of compact radiators

Output based on a mean radiator water temperature of 70°C and a room temperature of 20°C

Nominal

Length

Single convector

Double panel plus

Double convector

height

mm

btu/h

watts

btu/h

watts

btu/h

watts

400 mm

500 mm

1244

365

1066

521

2372

695

Source: (Virdi, 2012, p.129)

Try 500 x 400mm double panel plus radiators.

Provide FOURTEEN 500 x 400 high double panel plus radiators (see sketch SK03).

Drawing1.bmp

Reference list

Hall, F. and Greeno, R. (2011) Building Services Handbook. 6th Ed. Oxford: Elsevier Butterworth-Heinemann.

HM Government. (2010) The Building Regulations 2010: Approved Document L2A: Conservation of fuel and power in new buildings other than dwellings. London: NBS.

HM Government. (2010) The Building Regulations 2010: Approved Document F1: Means of ventilation. London: NBS.

McMullan, R. (2007) Environmental Science in Building. 6th Ed. Basingstoke: Palgrave Macmillan.

The Chartered Institution of Building Services Engineers. (2006) CIBSE Guide A: Environmental design. 7th Ed. London: CIBSE Publications.

Virdi, S. (2012) Construction Science and Materials. Chichester: Wiley-Blackwell.