Good Example of Your Project Micro Climate and Heat Gain

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GOOD EXAMPLE OF YOUR PROJECT FOR

MICRO CLIMATE AND HEAT COMFORT

2.0 - Climate and Built Environment

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2.1 - WEATHER PATTERNS

Trinidad lies between 10˚N to 11˚N latitude and 61˚W to 62˚W longitude. It is situated just 15 km

(9 miles) off the Venezuelan east coast.

This results in two distinct seasonal climate types: (i) Tropical Maritime and (ii) Modified Moist

Equatorial (Trinidad and Tobago Meteorological Service 2011). Tropical Maritime climate occurs

between the months of January to early May, and is characterised by warm days and cool nights,

with occasional rainfall due to convective showers. Modified Moist Equatorial climate occurs

between the months of late May to December and is characterised by hot, humid days and nights,

low wind-speeds and significant rainfall. These two seasons are generally known as the dry and wet

seasons.

Some of the main influences on Trinidad’s climate include: The Inter-tropical Convergence Zone

(ITCZ), the Mid-Atlantic trough of low pressure, and the sub-tropical ridge of high pressure

(Bermuda-Azores High).

2.2 - SUN PATH

Fig. 2.1 – Sun path diagram

Sun path

Today

June 21

December 21

Annual variation

Equinox (March and September)

Sunrise/sunset

Sunrise

Sunset

Time

00-02

03-05

06-08

09-11

12-14

15-17

18-20

21-23

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The solar azimuth angle runs from left to right, while the elevation angle runs from top to bottom as

illustrated in Fig. 2.1. So, for example, on June 21st, the sun rises from the North-East (azimuth=65˚)

at 5:41 am. Sunset occurs when the sun is at North-West (azimuth=290˚) at 6:28 pm. On that day,

the elevation angle is approximately 85˚ at noon.

Using these sun path diagrams, together with standard calculations of solar heat gain, one can

produce a fairly accurate prediction of the amount of solar heat a building envelope will be subjected

to, throughout an annual period. A similar type of study was done by Dr. Tawee Vechaphutti in

1987, who produced a table listing estimated solar heat gains of buildings situated in Thailand.

This is shown in Table 2.1 below.

Wall/Window

Ratio (%)

HEAT GAIN PER UNIT WALL AREA (W/m2)

hnorth hsouth heast hwest hnorth-east hsouth-west hsouth-east hnorth-west

0 21.76 27.20 27.20 27.20 24.48 27.20 27.20 24.48

20 39.898 51.642 49.266 52.17 43.526 53.226 50.718 45.242

40 58.036 76.084 71.332 77.14 62.572 79.252 74.236 66.004

60 76.174 100.526 93.398 102.11 81.618 105.278 97.754 86.766

80 94.312 124.968 115.464 127.08 100.664 131.304 121.272 107.528

100 112.45 149.41 137.53 152.05 119.71 157.33 144.79 128.29

Table 2.1 – Average Solar Heat Gains (Tawee Vechaphutti 1987)

2.3 – BUILDING ORIENTATION

In order to provide optimum comfort in terms of building orientation, one of the fundamental energy

equations should be considered:

⁄ [1]

So, the larger the surface area of wall that the sun’s radiant heat shines on, the smaller the energy

received within the building.

However, if there are windows located in the wall receiving direct sunlight, then the heat entering

through the window will be far greater than the energy reduction achieved by the larger wall surface

area. This situation will be discussed in detail under “Thermal Comfort”, but for the purpose of

orientation, the thermal transmittance (u-value) of a double-glazed window is 2.80 W/m2K, while

the u-value of the wall is 0.32 W/m2K (which means less heat transmitted through the walls).

The above-mentioned factors, as well as the measures taken to create optimum comfort in the one-

room mansion, in the context of orientation, are illustrated on pages 3 and 4.

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Since the prevailing winds in Trinidad come from the North-East, and since the most advantageous

position for cool breezes is on gentle slopes, the one-room mansion is positioned accordingly.

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Concrete Blocks Back-fill/Hardcore

Sand Blinding Polyethylene Membrane (d.p.m.)

Reinforced Concrete Bamboo Flooring

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Hollow Clay Block Coconut Fibre

Masonry Plaster R.C. Ring Beam

Timber Doors Steel Windows

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Glu-Lam Joists Metal Decking Sheets

Foam Concrete Geomembrane

Stone-Wool Ceiling Roof Grass

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2.11 – EFFECT OF MATERIALS ON THE ENVIRONMENT

Most building construction materials are users of non-renewable energy and emitters of greenhouse

gases and other gaseous wastes (Kospomoulos, 2004). According to data from the Worldwatch

Institute, the construction of buildings consumes 40% of the stone, sand and gravel, 25% of the

timber and 16% of the water used annually in the world (Arena and de Rosa, 2003). Moreover, the

International Energy Agency estimates that $16 trillion of investment will be needed to meet the

world energy requirements from 2003 to 2030 (James Chalker, 2006).

In this section, the materials chosen to construct the one-room mansion will be assessed in terms of

their energy consumption or embodied energy, and their impact on natural resources. Embodied

energy can be split into (i) Energy consumed during production (ii) Energy needed for transportation

(iii) Energy required for installing onto building (B. V. Venkatarama Reddy, 2001).

The data in Table 2.2 was obtained from the international literature (SIA, CBPR) as presented in

Bikas, 2001.

Material Embodied Energy

(MJ/kg)

Equivalent CO2

(gCO2/kg)

Equivalent SO2

(gSO2/kg)

Concrete 0.7 123 0.4

p.v.c. membrane 51.6 2043 14.27

Clay block 2.7 247 0.94

Masonry plaster 1.4 181 0.61

Reinforcement steel 9.9 474 1.79

Aggregate (general) 0.1 - -

Aluminium 312.7 11815 94.83

Glu-lam 4.6 - -

Polyethylene membrane 103 - -

Light concrete 0.4 68 0.25

Glass 15.9 - -

Table 2.2 – Embodied energy of finite construction materials

Aluminium has the highest embodied energy, followed by the polyethylene and p.v.c. materials.

Obviously, the aggregates would have the lowest energy requirement although quarrying does have

significant negative impacts on the environment if it is not controlled.

In the context of the renewable materials chosen, the Coconut fibre has a significantly low embodied

energy value of 0.09 MJ/m3. Bamboo flooring has an embodied energy of 0.02 MJ/kg, and the

Softwood timber has an embodied energy of 0.3 MJ/kg. These values were obtained from

manufacturers and industry data.

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2.12 - SICK BUILDING SYNDROME

Sick Building Syndrome has been defined as “a generic term used to describe common symptoms

which, for no obvious reason, are associated with particular buildings” (TSSA 2010).

Cases of this phenomenon may include: employees working

in an enclosed environment, students and teachers attending

schools, or any occupant who spends a considerable amount

of time within a building.

The indoor environment of a building is affected by its

ventilation, thermal insulation, acoustic comfort, lighting,

room and furniture layout, and ergonomic factors.

Ventilation – Indoor air quality, which is determined by the number of air changes per hour, is

important to all occupants in buildings. Occupants of buildings with poor ventilation systems have

reported experiencing sore eyes, dry throats, coughing, burning lips, nausea and other symptoms of

sick building syndrome (Roy 2010).

Thermal Comfort – An indoor building temperature above 25ºC can cause headaches and fatigue

while indoor temperature below 18ºC can cause chills and influenza like symptoms (Janis Jansz

2011). Excess indoor air humidity can result in fatigue, growth of fungi, and increased “off-gassing”

from building materials (Property Council of Australia 2009).

Acoustic Comfort – “Too much distracting noise interferes with short term memory processes, can

cause headaches and even personality changes as the building occupant becomes increasingly

frustrated and irritated with their inability to concentrate” (Janis Jansz 2011).

Lighting – Adequate natural lighting and proper artificial lighting configuration significantly

improves the occupants’ comfort and health. Inadequate lighting may cause headaches, eye strain

and other symptoms of sick building syndrome.

Other factors that have been identified as causes of sick building syndrome include: Office work,

Psychosocial factors, Building maintenance, Biological hazards, Fibre pollutants (e.g. formaldehyde

from chip board), Poor sanitation and poor management practices.

Serious legal implications can arise from sick building syndrome occurrences. Engineers, architects,

contractors, building owners, manufacturers, distributors and real estate brokers are all liable to be

sued when occupants of buildings can prove that they suffer from sick building syndrome.

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3.0 - Thermal Comfort

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3.1 - THERMAL COMFORT PARAMETERS – ASHRAE Standard 55-2010

Thermal comfort in the one-room mansion will be affected by the following factors:

Personal variables – Activity, Clothing, Age and Gender

Physical variables – Air temperature, Ventilation, Humidity and Surface temperature.

ASHRAE’s Thermal Comfort Tool software enables users to calculate acceptable comfort

parameters in accordance with USGBC’s LEED (http://www.ashrae.org/resources--

publications/bookstore/thermal-comfort-tool). The following values can be obtained using this

software.

Building Type Design Temperature

(ᵒC) Air Change/hour

Living room 21 1

Bedroom 18 1/2

Bathroom 22 1/2

Offices (general) 20 1

Classroom 18 2

Shops 18 1/2

Restaurant 18 1

Hotel room 22 1

Factory 16

Table 3.1 – Typical Design Temperatures

Table 3.2 – Fresh Air-Supply Rates

Fig. 3.1 – ASHRAE Standard 55-2010 User Interface

Building Type Air-Supply

(litres/second per person)

Residence, office, shop

8

Restaurant 18

Kitchen 10 l/s per m2 floor

Toilets 10 l/s per m2 floor

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3.2 - THERMAL PROPERTIES OF MATERIALS

Table 3.3 indicates the thermal properties of the materials used in the one-room mansion. These

values would provide fairly accurate results when calculating the temperature gradients, dew

points, fabric heat gain, and the overall cooling load requirement of the one-room mansion.

Material k - value

(W/mK)

rv - value

(GNs/kgm)

u - value

(W/m2K)

Rv -

value

Source

obtained

Hardcore fill / Earth 1.500 Industry

Sand 1.700 Industry

Polythene Sheet (0.06mm)

membrane 125 Manufacturer

Reinforced Concrete - 2% Steel 2.500 30 - 100 L 1 & L 2

Steel (Mild Structural) 60.000 Manufacturer

Coconut Fibre 0.045 Industry

Expanded Polystyrene Board

(EPS) 0.040 100 - 600 L 1 & L 2

Medium Density Concrete (inner

leaf) 1.130 30 - 100 L 1 & L 2

Clay Block 0.160 25-100 Manufacturer

Plaster (Lightweight) 0.180 60 L 1 & L 2

Double Glazing (air-filled)

Window - p.v.c. or wood (12mm) 2.8 L 1 & L 2

Double Glazing (air-filled)

Window - metal (12mm) 3.4 L 1 & L 2

Solid Wooden Door (25mm) 3.0 L 1 & L 2

Glue-lam - Timber Plywood 1.200 1500 -

6000 CIBSE

Galvanized Steel 18.000 100 Manufacturer

Foamed Concrete or Fly-Ash

Concrete 0.340 Manufacturer

Asphalt Coating 0.750 11 Industry

Mineral Wool Quilt 0.042 5 L 1 & L 2

Drainage layer 0.190 930 Manufacturer

Polymer based Geotextile 0.500 167 Manufacturer

Soil with organic matter / Coconut

Fibre 0.15 - 2.0 454 Industry

Table 3.3 - Thermal Properties of Materials used in the building

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3.6 – THERMAL BRIDGING

In the one-room mansion, thermal bridging occurs along the walls at the wall stiffeners and ring

beam locations as illustrated in Fig. 3.2. Both of these members are constructed using reinforced

concrete, with cement plaster on both sides.

Fig. 3.2 - Thermal Bridge Location 1

Calculating Structural Temperatures:

Layer k

(W/mK) L (m)

R

(m2K/W)

Δθ = R/Rt x Δθt

(ᴼC)

Boundary

Temp. (ᴼC)

Outside Air - - 0.189 3.200

Boundary - - - - 32.00

Lightweight plaster 0.18 0.025 0.139 2.351

Boundary - - - - 29.65

Reinforced concrete 2.50 0.150 0.060 1.016

Boundary - - - - 28.63

Lightweight plaster 0.18 0.025 0.139 2.351

Boundary - - - -

26.28

Internal Surface - - 0.123 2.082

Inside Air - - - - 24.20

Rtotal 0.650

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Hence, the Thermal transmittance of Thermal Bridge: ⁄

3.7 - CALCULATION OF TOTAL HEAT GAIN IN THE ROOM

U-VALUE OF GROUND FLOOR

Using Formula:

Area of Floor = 35.812m2

Perimeter of Floor = 25.146m

Using Formula:

Wall thickness = 0.2m

Thermal conductivity of ground = 1.5W/mK

Rsi = 0.123m2K/W Rf = 1.057m

2K/W Rse = 0.189m

2K/W

Since dt < B' use formula:

U-VALUE OF WALLS

Overall Areas

Wall Orientation Blockwork Area (m

2) Window Area (m

2) Door Area (m

2)

North 10.339 2.88 1.89

South 12.949 2.16 -

East 11.818 - -

West 11.818 - -

46.924 5.04 1.89

Using Formula:

Calculating Uwall

Component Area (m2)

u-value

(Wm2/K)

A*u

Blockwork 46.92 0.32 15.02

Window 5.04 2.80 14.11

Door 1.89 3.00 5.67

53.85

34.80

Uwall = 34.80 ÷ 53.85 = 0.646 Wm2/K

U-VALUE OF ROOF

= 2.85

( )

( )

(

)

(

)

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Note:

Very little to no heat passes through a Green Roof so heat gains through the roof

are negligible

THERMAL BRIDGE

Wall stiffeners and Ring beam made of reinforced concrete which has a U-value = 1.538 Wm2/K

FABRIC HEAT GAIN

Using Formula: Pf = UAΔt

Component U-value (Wm2/K)

Area

(m2)

Δ temp.

(ᴼC) Pf (W)

Floor 0.358 35.812 11 141.03

Wall 0.646 53.854 11 382.69

Roof 0 35.812 11 0.00

Thermal bridge 1.538 13.669 11 231.25

754.97 Watts

VENTILATION HEAT GAIN

Using Formula: Pv = 0.33NVΔt

Number of air changes per hour = 1

Volume of room = 86.751m3

Δt = 11ᴼC

Pv = 0.33 x 1 x 86.751 x 11 = 314.906 Watts

SOLAR HEAT GAIN

Using Table 2.1 from Page 3

Hnorth Hsouth Heast Hwest

Wall/Window Ratio 0 0 0 0

Heat gain / unit area 21.76 27.2 27.2 27.2

Wall area (m2) 15.11 15.11 11.82 11.82

Total heat gain (W) 328.77 410.96 321.45 321.45

Psolar = 1,382.64 Watts

CASUAL HEAT GAIN

Source Heat gain (W)

2 avg. adults 240

Flourescent lamps over 29.73m2 594.6

Computer & printer 250

Stove 3500

Refridgerator 150

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Television 100

Total 4834.6 Watts

Note:

An incandescent lamp system over the same area would have an emmision of 1,189.2W

This would have increased the total Heat Gain to 5,429.2W !

3.8 - COOLING LOAD DESIGN

Total Heat Gain of room = Hfabric + Hventilation + Hsolar + Hcasual

= 754.97 + 314.91 + 1382.64 + 4834.6

= 7,287.12 J/s

= 7,287.12 x 60 x 60 J/h

= 26,233.63 kJ/h

Now: 12,000 Btu/h = 12,661 kJ/h

26,233.63kJ/h would require -

26,233.63 ÷ 12,661

= 2.072003001

= 24,000 Btu Air conditioning unit

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3.9 – HEAT MEASURING DEVICES – Thermal Imaging Cameras

A thermal imaging camera, or infrared camera, can provide valuable information during moisture

assessments, mitigation work, energy audits, roof and electrical system inspections and water damage

investigations (www.professionalbuildinginspector.com 2012).

Fig. 3.3 – Thermal Imaging Camera

Since the human eye cannot see all the heat energy emitted by materials, thermal images help us ‘see’ this

heat emitted from materials, allowing detection of any abnormalities in the building. The device works by

measuring the amount of radiation emitted by materials into the atmosphere and representing the

measurements graphically in a coloured image. Hot/warm objects will usually appear as bright yellow,

red or white colours on the camera, while colder objects will usually appear as dark blue, purple or green.

This technology can reveal the most significant amount of beneficial information pertaining to a building,

some of which are indicated in Fig. 3.4

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Fig. 3.4 – Infrared Images of Building defects

Through the use of an infrared camera, or thermal imaging device, one can easily identify and fix

heat related building problems. Without the use of this advanced technology, it would have

indeed been costly and time-consuming to conduct these exercises.