ASHRAE Journal - February 2015 - S13

simultaneously reducing cooling load by 25% and saving 1,228
tons of carbon emission every year (Figure 7).

Shading Devices Optimization
An external sunshade can often be used as a design feature,
but its primary purpose is to reduce solar heat gains. Besides,
shades also serve the purpose of controlling views into and
out of a building, reducing solar glare, providing rain protection for openable windows and serving as a part of the maintenance strategy. Thus, sunshade design should always be
influenced by solar geometry and sun-path studies to ensure
its effectiveness.
Keeping in mind the above considerations, shading devices
with varying widths were simulated for analyzing their effectiveness in cutting down direct solar radiation into the habitable zone. This helped in cutting down the direct solar radiation, reducing solar ingress and allowing the diffused component of light to enter the building, illuminating it uniformly.
Optimized building designed with shades extending nearly 600
mm demonstrated reduction in energy demand from 7,590 to
7,099 mWh, shaving off 7% annual energy consumption (Figure 8).

Fenestration Optimization
Fenestration refers to openings in a building envelope, primarily windows and doors. Fenestration plays a vital role in
providing thermal comfort and optimum illumination levels

Figure 8: Graph highlighting impact of shading device width on energy consumption.

Figure 9: Graph highlighting impact of glazing unit assembly on energy consumption.

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in a building. Glass performance can be indicated through
a number of properties, such as Visible Light Transmittance
(VLT), Shading Coefficient (SC) and Thermal Conductivity
(U-value). In recent years, there have been significant
advances in glazing technology that include solar control
glasses, insulating glass units, low emissivity coatings, double
glazed units, etc.
For the selected case study, simulation was carried out for
three glazing types including single glazed units, double glazed
units and double glazed unit with low e-coating wherein a low
U-value glass with a low SC (to negate the harsh effect of direct
sunlight) provided best results, fetching another 6% reduction
in the annual energy demand of the building (Figure 9).

Wall and Roof Assembly Optimization
Walls are generally a predominant fraction of a building envelope and are expected to provide thermal and acoustic comfort
within the spaces, without compromising the aesthetics of the
building. The thermal resistance (R-Value) and thermal conductivity (K) of the wall/roof is crucial as it influences the building
energy consumption heavily, especially in high rise buildings,
where the ratio between wall and total envelope area is high.
Wall and roof assembly consisting of building material with
high thermal mass and thermal insulation plays a vital role
in energy savings and thermal comfort in composite climate
conditions. Thermal insulation plays an important role in
reducing the conductance or U value of walls/roofs, while
high thermal mass helps in achieving thermal comfort conditions by providing a time delay. It is important to note that
thermal mass is not a substitute for insulation; in fact, a high
thermal mass material is usually not a good thermal insulator.
Buildings should, therefore, employ insulation in combination with heat storing materials. The insulation should preferably be placed on the hotter side of the surface.
Therefore, maximum saving was achieved by using wall and
roof assembly with R24 (U Value=0.23 W/m²K) resulting in
another 3% savings on the annual energy consumption (Figure 10).
Thus, the combination of these five basic steps, i.e. optimized orientation, window wall ratio, shading devices, glazing type and insulation in wall/roof resulted in 34% saving
in annual energy demand, and up to 45% saving in the peak

Figure 10: Graph highlighting impact of wall assembly on energy consumption.

FEBRUARY 2015

ASHRAE Journal - February 2015

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