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# Chapter 4: Energy Efficiency and Sustainability
4.1
Scope
The purpose of including this Chapter in the Code is to enhance the design and
construction of buildings through the use of building concepts having a positive
environmental impact and encourage sustainable construction practices, allowing
efficiency and conservation of energy, water and building materials, and to promote
resource efficiency.
In addition to the clauses stipulated here, all Codes and standards relevant to a building
occupancy as set forth in other Sections of this Code will be applicable during
implementation.
Design and drawings will be submitted to indicate the location, nature and scope of the
proposed energy efficient/sustainable feature. These shall indicate compliance to the
provisions of this Code, and will be supplied by the relevant design professionals, e.g.
electrical engineers, mechanical engineers, plumbing engineers, etc., supporting
architectural drawings.
4.1.1
Rationale for Sustainable/Green Buildings
Climate change is an established phenomenon affecting the environment globally and it is
recognized that buildings and the built environment play a vital role in the process,
impacting on the natural environment and the quality of life. Sustainable development
concepts and approaches applied to the design, construction and operation of buildings or
to any built environment can enhance both the economic and environmental benefits of
the community in Bangladesh and around the world. Energy efficiency and sustainability
is not an individual issue rather an integrated and inseparable part of the building design
and construction process. The benefits of sustainable design principles include resource
and energy efficiency, healthy buildings and materials, ecologically and socially sensitive
land use and strengthened local economics and the communities, objectives vital for
future development of Bangladesh.
4.2
Definitions
DAYLIGHT ZONE
An area with a depth of 5m parallel to any glazed external
wall.
EMERGENCY
LIGHTING
Lighting used for emergency spaces and functions, e.g. in fire
stairs, for egress path signage.
GREY WATER
Waste water generated from wash hand basins, showers and
baths, Grey water often excludes discharge from laundry,
dishwashers and kitchen sinks due to the high nutrient levels.
It
differs
from
the
discharge
of
WC's
which
is
designated sewage or black water to indicate it contains human
waste.
REGULARLY
OCCUPIED SPACE
All the main areas in the buildings that are used on a frequent
basis, such as living rooms, bedrooms, classrooms, lobbies,
meeting rooms, hall rooms and office spaces. Service spaces
like toilets, bathrooms, corridors and stores will not be
considered as frequently occupied areas.
WINDOW TO
WALL RATIO OF
BUILDING
(WWRB)
The window-to-wall ratio of a building is the percentage of its
facade taken up by light-transmitting glazing surfaces,
including windows and translucent surfaces such as glass
bricks. It does not include glass surfaces used ornamentally or
as cladding, which do not provide transparency to the interior.
Only facade surfaces are counted in the ratio, and not roof
surfaces.
LIGHTING POWER
DENSITY (LPD)
Average total lighting power installed divided by the total
occupied area.
SHADING
COEFFICIENT (SC)
The ratio of solar heat gain at normal incidence through
glazing to that occurring through 1/8 inch thick clear, double-
strength glass. Shading coefficient, as used herein, does not
include interior, exterior, or integral shading devices.
SOLAR HEAT GAIN
COEFFICIENT
(SHGC)
An indicator of glazing performance is the amount of heat
admitted through the glass vis-à-vis the total heat incident on
the glass by virtue of direct solar radiation. The unit is a
simple fraction or percentage.
| Waste water | Col2 | generated from wash hand basins, showers and | Col4 | Col5 | Col6 | Col7 |
| -------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------- |
| baths, Grey water often excludes discharge from laundry, | baths, Grey water often excludes discharge from laundry, | baths, Grey water often excludes discharge from laundry, | baths, Grey water often excludes discharge from laundry, | baths, Grey water often excludes discharge from laundry, | baths, Grey water often excludes discharge from laundry, | baths, Grey water often excludes discharge from laundry, |
| dishwashers and kitchen sinks due to the high nutrient levels. | dishwashers and kitchen sinks due to the high nutrient levels. | dishwashers and kitchen sinks due to the high nutrient levels. | dishwashers and kitchen sinks due to the high nutrient levels. | dishwashers and kitchen sinks due to the high nutrient levels. | dishwashers and kitchen sinks due to the high nutrient levels. | dishwashers and kitchen sinks due to the high nutrient levels. |
| It
differs
from
the
discharge
of
WC's
which
is | It
differs
from
the
discharge
of
WC's
which
is | It
differs
from
the
discharge
of
WC's
which
is | It
differs
from
the
discharge
of
WC's
which
is | It
differs
from
the
discharge
of
WC's
which
is | It
differs
from
the
discharge
of
WC's
which
is | It
differs
from
the
discharge
of
WC's
which
is |
| designated | sewage | sewage | or | black water | to indicate it contains | human |
| REGULARLY | Col2 |
| -------------- | -------------- |
| OCCUPIED SPACE | OCCUPIED SPACE |
U-VALUE
(THERMAL
TRANSMITTANCE)
Heat transmission in unit time through unit area of a material
or construction and the boundary air films, induced by unit
temperature difference between the environments on each side.
Units of U-value are W/m2/ok
VISIBLE LIGHT
TRANSMITTANCE
(VLT)
Amount of light transmitted through glazing, expressed as a
simple fraction or percentage
4.3
Site Sustainability
This Section deals with sites to ensure energy efficiency through passive and low energy
architectural features and management of resources.
4.3.1
Mandatory Unpaved Area
Fifty (50) percent of mandatory open space shall be permeable on sites of all occupancy
categories. The permeable area shall not remain bare generating dust, but will have green
cover or be treated with perforated paving (≥ 50%), organic mulch, charcoal, etc.
4.3.2
Site Drainage and Run-Off Coefficient
Designs shall indicate site drainage considerations along with flash flooding and erosion
prevention measures for sites above 1340 m2 in area. As excessive paving is largely
responsible for fast water run-off and flash flooding, design shall indicate measures taken
to make paving permeable. The net run-off from a site shall be a maximum of sixty (60)
percent. The following method will be used for the calculations, in conjunction with
Table 3.4.1:
Total Perviousness on Open Area of Site (Ap) = A1 x C1 + A2 x C2 + . . .
(3.4.1)
Where, A1, A2, etc., being the areas of various surfaces, e.g. Pavements, roads,
vegetation, etc., with different run-off coefficients C1, C2, C3 etc., shown in the Table
3.4.1.
4.3.3
Vegetation Plan
For sites above three (3) acres, it is mandatory for a vegetation plan to be submitted along
with the site plan and Irrigation Plan, where priority shall be given to native plants in the
selection for planting.
4.3.4
Irrigation Plan
##### 4.3.4.1 For sites above ten (10) acres, an irrigation plan with construction details shall
be submitted with the site plan, where considerations shall include for management of
rainwater.
##### 4.3.4.2 For these sites a retention pond of ≥ 3% of site area shall be provided. This shall
include any existing natural water body within the site.
Table 3.4.1: Run-Off Coefficients of Various Surfaces
Surface Type
Run-Off Coefficient, C
Roofs, conventional
0.95
Green Roofs (soil/growing medium depth ≥ 300 mm)
0.45
Concrete paving
0.95
Gravel
0.75
Brick paving
0.85
Vegetation:
1-3%
3-10%
> 10%
0.20
0.25
0.30
Turf Slopes:
0-1%
1-3%
3-10%
> 10%
0.25
0.35
0.40
0.45
4.3.5
Rain Water Harvesting System
##### 4.3.5.1 Buildings of total floor area > 4000 m2 shall have its own rain water harvesting
system as discussed in Chapter 7 Part 8 and installed complying with Section 7.13 Part 8,
of this Code. The reservoir capacity shall be a multiple of the area of Ground Coverage of
the building and a rain collection coefficient of 0.073.
##### 4.3.5.2 The rainwater reservoir may be placed under the roof or at lower levels,
including underground.
4.4
BUILDING ENVELOPE
4.4.1
Window to Wall Ratio
##### 4.4.1.1 For mechanically ventilated and cooled buildings of all occupancies, other than
Hazardous and Storage, the Window to Wall ratio of building (WWRB), will be
determined in conjunction with the glazing performance, as indicated by the Solar Heat
Gain Coefficient (SHGC) or Shading Coefficient (SC) of the glass used. The relationship
is given in Figure 3.4.1 and Table 3.4.2.
Figure 3.4.1 Selection of glazing SHGC based on WWR
Table 3.4.2 Selection of Glazing SHGC Based on WWR in Tabular Format
WWR
SHGC
SC
0.85
0.98
0.6
0.69
0.5
0.57
0.4
0.46
0.35
0.4
0.33
0.38
0.31
0.36
0.3
0.34
0.27
0.31
##### 4.4.1.2 In all of the above cases, the Visible Light Transmittance (VLT) of the glazed
element shall not be lower than thirty five (35) percent.
##### 4.4.1.3 For Air-conditioned buildings with external shading, permitted SGHC limit may
be adjusted, but the increase shall not exceed values determined by Eq. 3.4.2 below:
= +
(3.4.2)
Where,
is the adjusted solar heat gain coefficient limit for windows with shading
SHGC is the solar heat gain coefficient from Table 3.4.2
A is the SHGC correction factor for the external shading as per Table 3.4.3 or Table
3.4.4: For a window with overhang and fin, the value of A can be only used either from
overhang or from fin.
##### 4.4.1.4 For naturally ventilated buildings, window size shall be based on Sec 4.4.2.
Window Openings of this Code and shading shall be provided as per Sec 4.4.3.
##### 4.4.1.5 Window size shall under no circumstances be less than as stipulated under Part
3: Chapter 1, Section 1.17 of this Code.
| Col1 | WWR | Col3 | Col4 | SHGC | Col6 | Col7 | SC | Col9 |
| ---- | --- | ---- | ---- | ---- | ---- | ---- | -- | ---- |
Table 3.4.3: Correction Factor against Overhang Shading Projection Factor
Overhang Projection Factor
SHGC Correction Factor(A)
0.0
0.00
0.1
0.05
0.2
0.09
0.3
0.14
0.4
0.19
0.5
0.24
0.6
0.28
0.7
0.33
0.8
0.38
0.9
0.43
1 or higher
0.47
Projection factor for overhang is the depth of the overhang divided
by the height of the window
Table 3.4.4: Correction Factor against Vertical Shading (fins) Projection Factor
Vertical Shading (Fins) Projection Factor
SHGC Correction Factor (A)
0.0
0.00
0.1
0.04
0.2
0.08
0.3
0.12
0.4
0.16
0.5
0.20
0.6
0.24
0.7
0.28
0.8
0.32
0.9
0.36
1 or higher
0.40
Projection factor of fins is the depth/length of fin divided by the width of the window.
| Overhang Projection Factor | SHGC Correction Factor(A) |
| ----------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------- |
| 0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1 or higher | 0.00
0.05
0.09
0.14
0.19
0.24
0.28
0.33
0.38
0.43
0.47 |
| Vertical Shading (Fins) Projection Factor | SHGC Correction Factor (A) |
| ----------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------- |
| 0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1 or higher | 0.00
0.04
0.08
0.12
0.16
0.20
0.24
0.28
0.32
0.36
0.40 |
4.4.2
Window Openings
Mechanically ventilated and cooled buildings of all occupancies, other than hazardous,
retail and storage, shall have the provision of using natural ventilation for cooling and
fresh air, in frequently occupied areas , with a fraction > 4% of the floor area being
specified as openable windows. Openable balcony doors can be counted in this
calculation. Note if the window area defined under Sec 4.4.1 is less than openable area,
then fifty (50) percent of window area should be openable.
##### 4.4.2.1 Naturally ventilated buildings of all occupancies, other than hazardous and
storage, shall provide for fifty (50) percent of its window area to be openable.
##### 4.4.2.2 All the openable windows above ground should be designed with safety
measures in place such as protection hand rails for child safety.
##### 4.4.2.3 Windows to any regularly occupied space on exterior walls in naturally
ventilated buildings shall be shaded conforming to Sec 4.4.3.
4.4.3
Shading
##### 4.4.3.1 For naturally ventilated buildings of all occupancies, horizontal sunshades shall
be provided over windows on South, East and West, the depth of which shall be
calculated by multiplying the window height with a factor of 0.234 (Figure 3.4.2).
Horizontal louvers can be used instead of sunshades, in which case, depth of louver shall
not be less than 0.234 times the gaps between the louvers (Figure 3.4.3).
##### 4.4.3.2 Vertical Shading devices shall be provided on the West, depth of which shall be
calculated, by multiplying the gaps between the vertical fins, or the window width if the
shades border the window width, with a factor of 0.234 (Figure 3.4.4).
Exceptions:
(a)
The above rule shall be relaxed if it can be demonstrated that shading is
achieved by existing neighbouring structures.
(b)
The north side of all buildings are exempt from the above rules.
Figure 3.4.2 Horizontal shade: x ≥ 0.234y
Figure 3.4.3 Horizontal Louvres: relationship between depth (x) and gap (y): x ≥ 0.234y
Figure 3.4.4 Vertical shading or louvres: relationship between depth (x) and
gap (y): x ≥ 0.234y
4.4.4
Roof Insulation and Green Roofing System
##### 4.4.4.1 Fifty (50) percent of horizontal exposed roof slabs of Buildings of Occupancy
B, C, D and E, shall have green roofing system, to manage water run-off from roof tops,
to control internal temperatures within the top floors and to reduce the carbon footprint of
the building. This shall not include any covered roof surface, e.g. solar panels, solar
thermal heaters, machinery for mechanical or electrical systems, water tanks, etc. Stair
loft or machine room tops will be exempt from this rule.
(a) The roof slab design shall consider structural support of the green roof system,
with growing medium of minimum 300 mm.
(b) The design will indicate protection from dampness and provide a drainage
system
##### 4.4.4.2 Horizontal roof slabs, which are not covered by green roofing system, will have
roof slabs with insulation, so that the time lag and decrement factor is greater than the
other floor slabs of the building.
4.5
Energy Efficient Building Systems
4.5.1
Daylighting and Supplementary Lighting System
##### 4.5.1.1 Window area shall not be less than 14 percent or 1/7th of the total floor area of
the building.
##### 4.5.1.2 Every regularly occupied space shall contain a minimum percentage of day-lit
area along the building perimeter zones, with no window less than an area of 1 m2 and
will ensure the appropriate stipulations given below.
(a) for rooms that measure less than 8 m in depth, window area shall be at least 20
percent of the area of the external wall of the room.
(b) for rooms that measure between 8 to 14 m in depth, window area shall be at
least 30 percent of the area of the external wall of the room and 35 percent of the
external wall.
(c) for rooms that measure more than 14 m in depth, window area shall be at least
35 percent of the area of the external wall of the room.
##### 4.5.1.3 For Buildings of Occupancy A5, B, C, E1 and E2, photoelectric sensors shall be
connected to luminaires, to enable dimming or switching off lamps that do not require to
be operated, due to the presence of adequate daylight. The photoelectric sensor shall be
located approximately at half (½) the depth of day-lit zone.
##### 4.5.1.4 If occupancy sensors are installed in the daylight area, the occupancy sensor
shall override the daylight sensor during non-occupancy period.
Exceptions:
(a)
Zones with special requirements are exempt from the stipulation of Sec
4.5.1.3. The designer shall justify the reason for exemption.
(b)
Hotel guest rooms are exempt.
4.5.2
Lighting Power Density
##### 4.5.2.1 Lighting Power Density (LPD) of the values set in Table 3.4.5 shall be provided
for the respective functions within all building occupancies, or as specified.
##### 4.5.2.2 In addition to Sec 4.5.2.1, Illumination values (Lux) as specified in Tables 8.1.5
to 8.1.14 of Part 8 of this Code shall be provided for buildings of the respective
occupancies.
4.5.3
Occupancy Sensors
##### 4.5.3.1 In order to limit the use of electricity in the unoccupied areas of buildings,
occupancy sensors linked to lighting (except for emergency and security lighting) shall be
installed in the public areas of buildings of occupancies specified in Table 3.4.6.
Table 3.4.5: Maximum Allowable Lighting Power Density for Different Occupancies
Occupancy
Maximum LPD (W/m2)
E1 and E2
Offices
F1 and F2
Retail/Mercantile
A5
Hotels
D1
Hospitals
A1, A2 and A3
Apartments/residences
B
Educational
All occupancies
Covered parking\*
All occupancies
Open/outdoor parking
1.6
* LPD for car parks shall calculated from the total lighting power divided
by the total car park area
Table 3.4.6: Applicability of Occupancy Sensors
Occupancy
Applicability
E1 and E2
Offices
Meeting rooms and corridors
A5
Hotels
Meeting rooms and corridors
A3
Apartments
Covered car parks and corridors
B
Educational
Covered car parks and corridors
##### 4.5.3.2 For car parks a minimum 2/3rd of the lighting shall be controlled by occupancy
sensors.
##### 4.5.3.3 Emergency lighting shall not be connected to occupancy sensors.
4.5.4
Ceiling/ Wall Mounted Fans
##### 4.5.4.1 For naturally ventilated buildings of occupancy A, ceiling/wall mounted fans
shall be provided in each regularly occupied space.
##### 4.5.4.2 For buildings of occupancy B, C, D, E and I, ceiling/wall mounted fans shall be
provided in each room larger than 25 m2, with a minimum of one fan every 25 m2.
Exceptions:
(a)
Corridors of buildings of all occupancies
(b)
ICU, CCU, operating theatres of Hospitals and Clinics
4.5.5
Lift and Escalator Efficiencies
##### 4.5.5.1 Escalators, in buildings of all occupancies, shall be fitted with controls to reduce
speed or to stop when no traffic is detected.
##### 4.5.5.2 Such escalators shall be designed with one of the energy saving features as
described in i or ii below:
(i)
Reduced speed control: The escalator shall change to a slower speed when no
activity has been detected for a period of a maximum of three (3) minutes.
Detection shall be by photocell activation at the top and bottom landing areas.
(ii) Use on demand: The escalator shall shut down when no activity has been detected
for a period of a maximum of fifteen (15) minutes, designed with energy efficient
soft start technology. The escalator shall start automatically when required;
activation shall be by photocells installed in the top and bottom landing areas.
##### 4.5.5.3 Elevators (lift) in buildings of occupancy A5, D1, E1, E2, F1, F2, I1 and I3
occupancies shall be provided with controls to reduce the energy demand, using the
following features in traction drive elevators:
(a)
AC Variable-Voltage and Variable-Frequency (VVVF) drives on non-
hydraulic elevators.
(b)
An average lamp efficacy, across all fittings in the lift car, of >55 lamp
lumens/circuit watt, with provision for switching off, when lift is inactive for
a period of a maximum of five (5) minutes.
(c)
The provision to operate in stand-by condition during off-peak periods, when
the lift has been inactive for a period of a maximum of five (5) minutes.
4.5.6
Renewable Energy Options
##### 4.5.6.1 Buildings of occupancy A shall use Solar or other renewable sources of energy
to power 3% of the total electric load of the building, applicable to the uses in Sec
4.5.6.3.
##### 4.5.6.2 Buildings of all occupancies other than A, shall use Solar or other renewable
sources of energy to power 5% of the lighting and fan loads of the entire building,
mandatory to uses in Sec 4.5.6.3.
##### 4.5.6.3 For all occupancies, the solar or other renewable energy connection shall power
spaces in the following order of priority: lighting in underground/basement spaces, dark
corridors, supplementary lighting, fans, emergency lighting like fire stairs, emergency
signage egress path lighting, etc.
4.5.7
Heating Ventilation and Air-conditioning (HVAC) System
For conditioned buildings, any Heating Ventilation and Air conditioning (HVAC) system
planned for installation will meet energy efficiency standards specified in Part 8 of this
Code.
4.6
Internal Water Management
4.6.1
Reuse of Grey Water
Buildings of occupancy A5, E1 and E2 and I shall reuse grey water for water efficiency
and management.
Grey water from wash basin shall be reused in toilet flushing and/or irrigation after
filtration to ensure a BOD (Biochemical Oxygen Demand) level \<50. Such water shall
not be considered potable.
4.6.2
Efficient Fittings in Toilets
Water efficient fittings, including faucets, showerheads and flushes, that use less water
for the same function as effectively as standard models, shall be used in buildings of all
occupancies. The low flow fixtures shown in Table 3.4.7 shall be used.
Table 3.4.7: Fixture Ratings
Type of Fixtures
Quantity (max)
Unit
Water closets
Dual Flush (6/4)
liters/flushing cycle (full/low)
Shower
9.5
liters/min at 551 kPa
Urinals
liters/flushing cycle
Hand wash taps
liters/min at 417.7 kPa
Kitchen/pantry faucets
liters/min at 417.7 kPa
4.6.3
Service Hot Water and Pumping
In order to reduce the energy used for water heating, buildings of occupancy A5 and D1
shall use solar hot water system to supply a minimum of thirty (30) percent of the total
building hot water requirements. The solar hot water system can be flat plate solar
collectors or vacuum tube solar system, this system must be designed and installed with
the backup system or as a per heating for the main hot water system.