Ventilated Slab Cooling System and Energy Efficiency in Buildings

This article discusses the need for energy efficiency in the building sector and how the design of the building can play a role in achieving this. It focuses on the ventilated slab cooling system, its design criteria, construction methodology, and the use of phase-changing materials. The article also highlights the importance of coupling the ventilation potential of the piping system and the hollow core slab to improve thermal comfort within the room or any other enclosed space.

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Overview: Introduction to building heating and cooling
The building sector is highly dependent on energy. This by itself is not bad, but with increased
energy consumption there is an increase in the carbon footprint of the building sector. The
increase in population growth and an increase in the time that people spend indoors tend to
aggravate the need for more power. Over the past couple of decades, the total earthly space
occupied by buildings has increased by over 60% (iea, 2019), necessitating the need for energy
efficiency measures.
The increase in building energy requirements has translated consumption of about 40% of the
total global energy by the building sector (Büyükalaca, Bulut, & Yılmaz, 2011). This is mainly
in developing countries around the European Union and the United States of America. This may
be translated to a carbon emission that is 36% of the worldwide carbon emissions (Cao, Xilei, &
Liu, 2016). In essence, the Energy Information Administration indicated that the increase in the
carbon dioxide emission has increased in the ranges between 75% and 85% between the years
1980 and 2012 (Cao, Xilei, & Liu, 2016). What is more significant in these studies is the fact that the
primary source of energy production is the combustion of coal (Chan, Riffat, & Zhu, 2010). Not
only is this the depletion of non-renewable source, but the combustion of these resources also
tends to be associated with the production of an enormous amount of greenhouse gases
Therefore, building end-use plays a big role in energy conservation and energy-conscious
practices. As research has indicated, people usually spend about 10% of their lifetime outdoors
(Echenagucia, Capozzolie, Cascone, & Sasson, 2015), meaning that optimizing the indoor air
quality and the temperature is usually done through mechanical HVAC. It is a significant end-

use in the building sector, increasing by over 2% between the years 1980 and 2012 (Cao, Xilei, &
Liu, 2016).
Energy End-use in Buildings
Understanding the building design is an integral aspect of the net-zero building design. In the
HVAC design systems, the increased need for internal air cooling has resulted in an increase in
energy consumption by between 1.5% and 6% between the years 1990 and 2015 (Joustra, 2010).
Between the years 2000 and 2019, cooling energy consumption has increased by over 36%,
moving from 3.6EJ to 7EJ. However, heating presents the major consumption point of building
energy. As compared to the 7EJ of cooling, heating consumed a staggering 42EJ, meaning that it
consumes about 36% of the total building energy. The current building practices have saved
about 7EJ and there is a need to reduce the building heating energy to about 39EJ (Ghoubali,
Byrne, Miriel, & Bazantay, 2014). In line with this, there is an increased consensus on the need
to increase the amount of floor and space area that may be heated from an efficient heating
appliance. There is also the aspect of lighting that has had a profound effect on the energy
consumption of the building. However, standing at 7% of the total energy consumed by
buildings, this end-use is relatively smaller as compared to heating and cooling (Voss, Musall, &
Lichtmeß, 2011). This has mainly been associated with the increased use in energy-efficient
lighting appliances such as LED.
Looking at the facts that have been mentioned, it is clear that there needs to be a framework that
tames the increased use of energy in cooling and heating. It has been projected that despite the
use of energy-saving techniques in energy consumption, the increased rate of urbanization and
growth will always translate to an increase in the use of energy. Therefore, the building design

has been identified as one of the strategies that may be used to improve the energy efficiency of
buildings. The design of the floor slab, the design of columns, and the design of other aspects of
the building structure are of fundamental importance for the general energy-saving measures
(Corgnati & Kindinis, 2007).
It has been indicated that energy heating and cooling efficiency (Romani, Draoui, & Allard,
2015) measures may be the best platform for maintaining the building energy use. Innovations
that surrounding heating and cooling a building envelope plays a fundamental role in the design
of energy-efficient buildings. It is this concept that has led to the development of the ventilated
slab cooling system.
Introduction to the ventilated Slab cooling system
There is an increase in awareness that surrounds these types of slabs, mainly due to their high
energy efficiency. These are among the natural cooling and heating systems that have come to be
widely adopted because of the NetZero framework (Zmeureanu & Fazio, 1998). Not only are
these panels efficient in terms of energy savings, but they are also comfortable, making the
conventional cooling and heating systems obsolete.
Nevertheless, these systems have been described as those whereby almost half of the total heat
movement on the surface occurs as a result of thermal radiation (Barton, Beggs, & Sleigh, 2002).
Furthermore, these systems use radiation and convection in order to heat and cool the building
surrounding and space. Various forms of this design may be used to provide a basis in which
there is an exchange of heat among the various building elements and the environment. Heat
exchange takes place between the ventilation air and the core of the slab. They utilize the
principles of ventilation cores (You-Jie & Fox, 2012) in order to ensure that the indoor

temperature is at an optimum. In line with this, it has been described as a system that utilizes the
principles of natural cooling in temperature regulation.
This is just one of the thermal energy storage that has gained significant attraction over the past
couple of years because of the need to optimize the indoor air quality (Bauer & Scartezzini,
1998). The methodology that is used in the overall design of these systems pertains the thermal
and sensible heat gains and losses. In the first scenario of sensible heat gain, the temperature is
maintained at an optimal through the exchange of heat by the medium (Sartori, Napolitano, &
Voss, 2012), in this case, masonry and the slab. On the other hand, the latent heat methodology is
extensively used in phase change material where heat is modified through changing the
temperature between its different phases (Jamil, Alam, & Sanjayan, 2019). This, as such, means that
the construction activity has to be intense with particular emphasis on how the system will fit
into the overall system.
It has been indicated that there are four particular ways in which the design of the ventilated
cooling system can be done (Rinaldi, 2009). The first aspect considered in the overall design
criteria is the factor of integrating the tubing into the concrete. This has come to be known as the
thermo-active tubing system. Nevertheless, this affects the final building design since it
considers various aspects of the final building use, the type of occupancy, the arrangement of the
furniture and even the capacity of the building, just to mention a few. This means that the
designers have to pay special attention to the very minute details. The layout of the tubing
system has an effect on the general indoor atmosphere because of the aspect of solar radiation
and shade. It has been indicated that there are various layouts that may be used in line with the
tubing system. The full-coverage system implies that the tubing material has to be distributed
over the whole floor mainly because of high heat exchanges that may be experienced in the

building interior hand, the perimeter tubing is done along the perimeter walls, mainly in
industrial buildings (Ren & Wright, 1998). This is because of the efficiency of such systems is
dependent on the perimeter heat transfer. Thirdly, there is a varied tubing system. This is done
when the building design anticipates that there is going to be a major heat load at the perimeter
walls but the interior of the building is likely to experience significant heat loads too. Finally,
there is minimal coverage. This is mainly done in buildings where there is no significant impact
of the heat load, with the interior of the building not significantly affected because of changes in
external and indoor temperatures.
As with the construction methodology used, there are two systems that have become profound in
the industry. Floor slab on either the deck or over a steel deck are the most common
methodologies that have been used in the construction of this system In order to maintain the
structural integrity of the building (Koroneos & Tsarouhis, 2012), embedding the piping in the
rebar has become more of a necessity.
It has often been discussed that these systems usually require a properly designed system for
ventilation purposes (Ngata, 2012). In line with this, research into the system has indicated that
they are able to handle the entire sensible heat load but that is not the same case when it comes to
the sensible heat load. In essence, it has been discovered that designing the system using a
mechanism in which the sensible heat load, as well as any residual heat load, maybe the best
option for the effective administration of an optimal indoor environment.
The Hollow-core slab
Hollow core slabs have been identified as one of the ways through which the heat that is
transferred between the indoor environment and the fluid may effectively be used to optimize the

indoor air temperature. This is to mean that the slab fabric needs to have a phase material that
has been designed in the form of hollow cores. In this arrangement, the hollow cores are
interconnected in such a way that there is the efficient transfer of air between the general fabric
and the moving fluid. However, the air has been the predominant means through which air is
transferred in these systems. Utilizing the increased area between the hollow cores enables the
air transfer medium to efficiently utilize all the heat (Marszal, Heiselberg, Bourrelle, & Musall,
2011) in ensuring that the indoor temperature is at a suitable level. These modifications may be
useful especially during the summer when the daytime temperature is very high while at night
the temperatures are low. In such a scenario, the air in the piping system moves the warm
temperature from the slab and distributes it in the building fabric, elevating the internal
temperature. On the other hand, during the daytime when the temperature is at a high, the air
circulates through the slab and as such, is lowered before it is dissipated into the living area.
Therefore, the air supply system has to run parallel to the slab width in order to maximize the
floor area if efficient cooling is to be done.
With all that in mind, designers have tried to simulate the effect of the various slab parameters on
the efficiency of the system when it comes to the control of the ambient heat load and sensible
heat load (Lechner, 2014). Some of the parameters that have been considered in a recent study
are the surface insulation properties, the airflow rate, and the slab’s thermal conductivity, just to
mention a few. With proper control of these parameters, as one study indicated, there is a very
high possibility that any building structure may achieve a thermal efficiency of between 50 and
70 kW/h2. This may be more important in an n office setting where there is a need to maintain
the indoor temperature because of the need for personnel comfort. Such studies indicated that the
office indoor temperature can be effective in ensure that the cooling load is dramatically

improved. A study conducted in the city of Montreal revealed that the cooling load is improved
from 28.4 W/M2 to 44.2W/m2.
Therefore, it has been understood that there is a big correlation between the slab temperature, the
indoor ambient temperature, and the slab configuration. This correlation has been identified as a
very crucial aspect when it comes to understanding how the core air temperature affects the
cooling potential of the slab and the overall effects on the surface condensation. This has been
identified as one of the most crucial aspects that affects the thermal comfort in an enclosed
space.
In line with the studies in this platform, it has come to be understood that coupling the ventilation
potential of the piping system and the hollow core slab may have an effect on the operative
temperature which may have an effect on the thermal comfort within the room or any other
enclosed space. This has led to various developments even into the aspects concerning how the
phase change material functions. This is not in line with the conventional hollow slab system
because of its profound and considerable effects on various aspects of the functionality such as
the minimal variations in the temperature and the high capacity heat changes. It has often been
discovered that the phase change material can be categories into predominantly three categories
depending on how their function. It has been discussed that there is a passive system, an active
system, and the free cooling system.
The phase changing material
The first category of the passive system has found extensive use in various materials which may
include the ceilings, the plasterboards, brick walls, and even concrete floors, just to mention a
few. With the increase in the concrete jungle and the fact that concrete is becoming one of the

most extensively used construction materials, using this type of phase-changing material may
have a profound effect on the construction industry. Nevertheless, it has been discovered that the
use of this material may be dependent on various aspects that pertain the building configuration
such as the location properties, the climatic conditions, and the thermophysical properties
(Loosemore, Danity, & Lingard, 2011), just to mention a few. Depending on these stated
properties, there is usually a varying level in the thermal comfort offered as well as the reduction
in the energy consumed for the sole purpose of optimizing the internal temperature.
On the other hand, there is the prospect of using conventional HVAC systems when it comes to
active phase-changing materials. Pumps and other floor heating systems may be used to ensure
that the thermal comfort associated with these types of flooring systems can ensure that the
internal thermal comfort is improved in extreme weathers such as extreme winters and extreme
summers. According to one study aimed at understanding how thermal comfort can be improved
using heat-pump-systems whereby two tanks were used, it was discovered that there is a
significant reduction in the amount of electricity used in ensuring the thermal comfort. It was
discovered that these systems could ensure that energy savings are approximately 3.09kWh/day.
It was translated that such a system would ensure thermal comfort by reducing the amount of
money spent. It was discovered that using such a configuration may lead to a saving of about 170
USD on an annual basis. This, as such, indicates that there may be a reduction in the carbon
footprint of the building sector, improving the environment.
Finally, the free cooling system may be associated with increased thermal comfort because of the
fact that they store the ambient cool temperature available in the night and they can use it during
the daytime to cool the indoor air temperature. Availability of a phase-changing material storage
unit ensures that the temperature stored during the night can be released through the daytime,

improving the general thermal comfort within the indoor environment. Therefore, it stores
daytime temperature and nighttime cooling in order to ensure that the internal comfort is
maintained. According to studies, it has come to be understood that this system may improve the
applicability of the passive systems by reducing the effects of solidification and those that are
experienced during thawing, especially in regions with alternating summers and winters. As
such, it may be used to improve the overall efficiency of the phase changing materials.
Phase Changing Material and the Hollow Core Slab
The two systems have been identified to have numerous advantages when it comes to improving
the thermal comfort of the indoor environment. As such, recent studies have focused on how the
two systems can be integrated to create a super system that may improve the thermal comfort and
at the same time reduce the energy consumption of buildings. In line with this, various laboratory
designed prototypes were used to understand these effects.
Nevertheless, when the hollow core is integrated into the PCM, it was discovered that there was
an additional saving on the energy consumed. On a daily basis, the use of this combination may
lead to a saving of about 0.1kWh. Moreover, there is an additional reduction in the temperature
of the room by about 1.0 degrees Celsius, which may also mean that the thermal delay may be
approximated as 1.2 h. In essence, it has been discovered that these systems pose great energy-
saving measures which may be in the range of 15% and 20% when it comes to severe conditions
while the mild conditions may lead to savings which may be in the range of 30% and 50%.
When it comes to the heating applications of these systems, the savings may be approximated as
25% and 40% when it comes to the extreme conditions and the mild conditions respectively
(Mateus & Oliveira, 2009).

Looking at the initial descriptions, it may be wise to consider using the floor system because of
the numerous benefits associated with them. The building sector has continually advocated for
green building and as such, these systems present one of the most innovative solutions aimed at
ensuring thermal comfort while reducing the carbon footprint of the building sector. It has
extensive use in ensuring that the end-use of the building, especially accommodation, is in line
with the LEED requirements.
The conventional Method of Air conditioning
When it comes to the conventional HVAC systems, there is usually the aspect of handling the
heat mass and ensuring that there is proper circulation of warm air and cool air. Therefore, these
systems are used in order to satisfy the internal thermal requirements by mainly adjusting and
altering the outdoor temperature and conditions with internal conditions and temperatures. These
systems are mainly mechanical and work by drawing in the external cool air into the building
before heating it and distributing it in the indoor environment. The air may be reused or extracted
through the ambient air available in the building atmosphere. Nevertheless, the design of the
HVAC system is usually dependent on various factors such as the preferences, the architectural
design and the location of the building, just to mention a few. In essence, these systems may
have more control of the building internal atmosphere mainly because they use mechanical
systems.
In essence, the design of the HVAC system may be predominantly dependent on the heating load
requirements of the building structure and the budgetary strain. This may mean that there is a
need to ensure that there is a proper budgetary allocation to the HVAC systems of the building
design if the designer intends to improve the energy-saving measures of the building. However,

this constraint still limits the design and selection of the HVAC system because they tend to be
expensive and may increase the overall cost of the building g structure.
As such, it has been discovered that the HVAC systems may be the largest end-users of the
building energy. They account for approximately 60% of the total building energy use. This is
very unconventional considering that the building industry has continually emphasized the need
to reduce the energy consumption of buildings. This means that, in order to reduce the carbon
footprint of the building sector, considerable attention has to emphasize on the HVAC systems
design. It is very high as compared to the building lighting requirements which may be in the
range of between 11% and 20% of the total building energy demand.
According to a recent study conducted in the United Kingdom, it was discovered that space
heating has a humongous strain on the building energy requirements. The IEA indicated that this
aspect of the HVAC system may consume about 50% of the total service energy, especially in
regions with extreme winters. In China, this figure was comparatively higher with the heating
requirements approximated to consume about 69% of the total building energy requirements. In
the United States, it was indicated that the HVAC systems may consume about 35% of the total
building energy requirements, meaning that this sector tends to consume a considerable amount
of the total building energy.
Studies have indicated that these mechanical HVAC systems, mainly associated with cooling and
ventilation, tend to consume building energy in the ranges of between 30% and 50% of the total
building energy demand (Pinang & Mardiana, 2015). In a recent study in the European region, it
was discovered that the energy demand associated with the heating requirements of the
ventilation air may be in the excess of 70% of the annual energy demand for the building.

However, it has been discovered that the energy demand associated with this may be on the
increase because of the increased tightness associated with the building envelope and the
increasing ventilation air heating requirements.
The conventional air conditioning system
The selection of the components of the HVAC system depends on various factors such as the
preferences of the designer and the architectural design, just to mention a few. However, there
are various components of the HVACs system that need to be considered prior to the actual
design process since these are the fundamental components when it comes to air circulation,
heating, cooling, and the ventilation mechanism. Nevertheless, the HVAC system has been
described to be dependent on four very crucial components which include the space, the piping
system the air distribution and the primary equipment.
When it comes to the primary equipment, the designer may have an array of choices when
selecting the heating equipment. This may include the steam boilers or the hot boilers. The
selection is dependent on the building space, the air delivery equipment, and the refrigeration
systems. Other primary equipment are those that are required in cooling such as the cooling coils
and the fans, just to mention a few. This means that the shape requirements of the building play a
vital role in the selection of this primary equipment. The study has shown that for the efficiency
in the heating and cooling requirements of the building structure, this primary equipment may
either be local or central. All this depends on the configuration of the building structure. In
essence, a study has shown that this primary equipment may have five primary needs which

include the equipment rooms, the facilities, the fan rooms, the vertical shaft, and the equipment
access, just to mention a few.
To begin with, there is a need to consider the space required for the storage of the various HVAC
equipment. It has been estimated that the total space required for these systems is between 4%
and 9% of the total building are requirements. In line with this, it has been indicated that between
the two location requirements, the central configuration may be the most convenient. This is
because it reduces the amount of ductwork required, the piping needs and the runs. On the other
hand, the HVAC facilities that required in every building configuration usually need secondary
facilities which improve the functionality of the primary equipment. Boiler exchanges, heat
pumps, and air gauges are some of the secondary equipment required in the control of the
building heating equipment while cooling towers and condenser pumps are some of the
requirements when it comes to the cooling needs of the building. The fan room is the other
necessary input in the HVAC systems and this is used for the storage of other equipment such as
the fan shaft as well as the coils. Equipment access should also be provided in order to ensure
that there is ease of access to the equipment. Finally, there is a vertical shaft that is required
because there is a need to ensure the efficient distribution of air, steam, and water.
Conventional ventilation and cooling
It has often been discussed that the conventional cooling ad heating requirements of a building
may be the most common. However, they are associated with high energy requirements.
This can be demonstrated through the building design incorporating the conventional
methodology.
In calculating the cooling loads, there is need to estimate the balance point.

This can be calculated through the following equation:
(Qsolar+Qinternal)sensible= UA( indoor temperature-outdoor temperature)
The overall heat transfer coefficient may be estimated as: 5.32 W/m2
External heat loads;
Opaque structures= UA. Cltd
Looking at the various elements provided, all of them are opaque. This means that the total heat
load from external environment is 5722 W/m2
This is primarily based on the solar radiation received. Looking at it, the use of photovoltaic cells
to harness this energy may be of immense importance when it comes to ensuring that there is an
optimal indoor temperature.
Nevertheless, it has been indicated
This is based on the assumption that all the units will play an important role in the internal heat
loads of the building.
The area may be approximated as 202.2 square meters
The internal temperature is approximated as 300 degrees Fahrenheit while the internal
temperature may be approximated as 273 degrees Fahrenheit
Therefore, the sensible heat gain is approximated through: 5.32*202.2*27=5722
The Design

In this design, the plans are used in the design of ventilated floor cooling system. In this analysis
and as initially stated, it is important to consider the various aspects of the building fabric. As
such, the U value, among other building material properties is very important in identifying the
thermal comfort associated with the internal building atmosphere. The use of HAP and the IES
VE software presents a more detailed analysis into the building structure and as such, may be
used as the platform in which the provided building may be analyzed.
Using the IES VE software
The software has been designed for a detailed analysis of the indoor environment. It presents
one of the best forms for the analysis of the indoor environment due to the use of the ventilated
slab cooling system.
The screenshot provided below indicates that the building structure has mechanisms which
enable the extraction of the internal warm air during the day. This, at the same time, means that
the external cool air will be drawn into the building for the purposes of moderating this
temperature. In the hollow slab system, the fluid is used as the main temperature-regulating
agent, ensuring the proper transfer of heat from the different mediums.

The plan view of the building structure
The side view of the building

Nevertheless, it is important to consider the various properties of the building fabric. In line with
this, it has been indicated that the U values, the thermal conductivity of the building in ensuring
that there is thermal comfort within the building structure. This means that in order to properly
analyze the thermal comfort offered to the indoor environment, the properties of the building
fabric need to be considered.
Nevertheless, it is important to first consider the heat load calculations using the manual
methodology
In the analysis, it is first important to consider that area of the rooms available in the building
and the total area covered.
Looking at the drawings, it can be seen that the building is composed of two floors.
The first floor has an area of approximately 202.2 square meters
This may be approximated as the total area for the ground floor too.
This may be used to calculate the area required for cooling. In essence, the cooling load required
for each building, assuming that the height is 2.0 m, can be estimated as
202.2*31.2=6309 square meters BTU.
Based on the assumption that all the floors have the same occupancy level, it may be assumed
that the area BTU on the first floor is equal to the area BTU on the ground floor.
Windows tend to affect the heat gain by allowing solar radiation into the room. In this, it has
been indicated that the area of the window is of impeccable need when there is a heating need to
the building structure.

It may be assumed that each of the windows has an area of approximately. 0.9 square meters.
Moreover, it may be assumed that the windows face the north and south side of the buildings
only.
There are factors that are used when it comes to identifying the heat gain associated with the
windows and this may be summarized as below:\
The windows that face the northern side are 2. Therefore, the BTU of the windows
Nevertheless, this is based on the assumption that there is no shading on the windows.
The north-facing windows can be calculated to have a heat gain of
1*164=164BTU /m2
As with the southern facing windows, and assuming no shading, it can be calculated as:
1*868=868 BTU/m2
The occupancy BTU can be calculated as the number of occupants*600
Assuming that the building has 10 occupants, the calculations indicate that the results give \
6000 BTU
All these indicate the heat gains and losses in the building.
However, it has been indicated that the building design is to incorporate the use of the ventilation
hollow slab system.
In line with this, it has been indicating that in order to find the heat gains and losses of the walls,
the columns and the windows, the following calculation may be used

Q=A*U*(T1-T2)
The analysis is dependent on the difference in temperature between the outside and the inside of
the building.
Therefore, the analysis has to be dependent on the daytime temperature and the night time
temperature. The night time temperature in Dubai tends to go very low due to the shortage of
cloud cover and during the day, the temperature is usually at a maximum.
In line with the analysis, research has indicated that the room temperature cannot exceed 65
degrees Fahrenheit. As with the external temperature, this is dependent on the location of the
building. Being in Dubai, the environmental temperature can be estimated as 300 degrees
Fahrenheit. This is especially during the day time but at night, the inverse may be true.
Working on this assumption, the difference in temperature has been estimated as 27 degrees
Fahrenheit.
Therefore, the overall design will be based on the materials used in the building fabric
It has been indicated that the external wall has a U value of 0.38 W/m2
The external column has a U value of 1.62 W/m2k
The roof has a U value of 0.21 W/m2K
The partition has a U-value of 2.29 W/m2k
The typical flooring has a U value of 0.82 W/m2k
The wall heat gains and losses can be estimated as:

During the day, the heat losses=(2*10*0.38*2.7)*4
164.2 BTU for the two-building floors. This is also the heat loss during the night for the whole
building structure assuming that all the walling units are made from the same material and the
changes in temperature occur in an inverse manner during the day and the night.
When it comes to the column, it may be assumed that the total number of external columns is 4.
Therefore, the heat loss and gain from the columns, assuming that they occur in an inverse
manner can be estimated as :
2*5*1.62=162 BTU for the number of columns present in the building structure. This means that
during the day, the internal heat losses are approximately 162 Btu while during the night, the
internal heat gain will be the same. This may be important in ensuring that there is no significant
deviation in the temperature between the inside and the outside of the building structure.
As with the internal partitions, they are maybe approximated to be equal to that of the external
wall units. This means that the heat gains and losses from the partitions will be the same as the
heat gains and losses from the walling units. However, it is important to consider that the heat
changes in the rooms will directly affect the heat transfer in the partitions which will eventually
affect the amount of heat gained and lost through the walling units.
The flooring unit is highly considered in the heat losses and gains since this is the primary unit
through which the hollow slab ventilation system maintains the ambient room temperature.
It has been calculated and the total plan for the building area has been estimated as 202.2 square
metes. Therefore, it may be assumed that the heat gain and losses are inversely proportional
during the day and during the night.

Nevertheless, this may be calculated from
0.82*202.2*27= 4476 BTU.
Therefore, during the day, the building has a heat gain of 4476 BTU but during the night and
considering the inverse changes in temperature, the building loses the same amount.
Hollow slab thermal comfort calculations
In order to fully comprehend the capabilities of this system, some proper evaluation strategies
have to be defined. One assumption is that the rate of ventilation is controlled by a system made
up of fans, a heat exchanger and the ducts, as has been described during the literature review of
the whole system.
The efficiency of the exhaust fan may be estimated as 0.9, the heat exchanger also has an
efficiency of 0.9 while the changes in temperature due to the fan system can be approximated as
374 degrees Fahrenheit.
Nevertheless, it has been indicated that the normative temperature required to maintain the
thermal comfort of the building during the summer and the winter period is 20 to 24 degrees
Fahrenheit and 23 to 26 degrees Fahrenheit. Moreover, there are different levels of thermal
comfort that may be offered to the occupants of a building structure. In this regard, it has been
indicated that the level 2 thermal comfort has been identified as that which is
A maximum=18.8+0.33 with the transient temperature +3
At a minimum=18.8+0.33 with the transient temperature-0.3 degrees Celsius

In this, line of thinking, it has been proposed that there are two methodologies that may be used
to identify the thermal comfort of the occupants of a building.
When it comes to the heating and cooling evaluation criteria of the energy requirements, the first
consideration is the external weather and its correlation to the internal weather. This means that
the air handling apparatus needs to provide variable temperature for the purpose of cooling the
interior. It has been indicated that the maximum ACH is usually 8 and the building has an
assurance of 2 ACH. On the other hand, at night when the temperature outside is cool as
compared to the interior temperature, the air handling unit needs to be turned off in order to
improve the internal atmosphere.
The hollow slab ventilation system well in line with the night cooling strategy tends to focus on
the operative temperature. This may mean that there is no need for thermal mass activation since
the strategy works with the requirements of the night cool temperature and the requirements of
the daytime warm temperatures. In this, the cool air may flow through the slab into the ceiling
void which in turn ensures that there is thermal storage. With such a strategy, there is an
improvement in the thermal capacity of the building, which tends to ensure that there is thermal
comfort (Rinaldi, 2009).
Net Zero Building Design
It has been indicated that Energy performance of building directive has been developed in order
to ensure that building design incorporates the use of renewable resources in the design of a
building. Solar energy has been described as the ideal renewable source mainly due to its
availability and the fact that it does not pollute the environment.

The first step pertains the integration of the photovoltaic cell into the building envelope. The
photovoltaic cells may be used as a replacement for the roof shingles or in other cases, may be
used to clad the building structure. In line with this, it has been indicated that the concept of
replacement may be the most suitable considering that this reduces the overall cost of the
building. Moreover, this concept means that the envelope of the building is maintained to ensure
that heat is sufficiently distributed durig the cool periods. Nevertheless, it has been indicated that
this peart of photovoltaic cell arrangement may require good architectural and aesthetic planning.
It has been described as a methodology that improves both the overall performance and the
durability of the building.
Secondly, there is the concept of an integrated photovoltaic cell. This concept is important since
it has been indicated that it is able to capture about 18% of the total incoming solar radiation.
Therefore, this concept improves the heat capacity of the building and moreover, ensures that
there is available electricity. This is a double edged strategy that ensures that the heat cost of the
building is maintained at a minimal, without affecting the efficiency of the building.
Nevertheless, in its working, there is need to ensure that there is a fluid or coolant behind the
panels in order to ensure that there is heat collection. This fluid may be used in conjunction with
the ventilation slab since it will ensure proper heat distribution throughout the building structure.
The flexibility of the system means that the use is extended in both the closed loop adnd open
loop system, improving its viability in the project. Moreover, ensuring that the photovoltaic cell
has a coolant at the back is one of the ways through which its efficiency can be maintained. The
coolant improves the efficiency by decreasing the temperature, a detrimental factor in the panels’
efficiency This nevertheless, depends in the suitability of the designer. Other designers may opt
to integrate the panel onto the façade while other may opt to use the roof as the best option. .

Using the panel for other purposes such as the integration of a transmission channel may bring
about extra advantages. Nevertheless, the panels used in this case are specially designed for the
multiple purposes. The panels used need to be semitransparent in nature in order to ensure
efficiency in sunlight transmission. However, in line with the design strategy of ensuring proper
ventilation and heating, it has been indicated that only a portion of the power generated need to
go to electricity. Considering that these panels are integrated into the window design, they may
be very effective.
Advantages of the hollow core slab system
The major advantage is the fact that it is able to regulate the internal air at a very minimal cost.
As compared to the conventional system whereby mechanical equipments are used, this
methodology tends to be more efficient at a relatively lower cost.
Moreover, there is the aspect of reduction in the building energy requirements. The system tends
to minimize the energy requirements mainly because it uses the natural ventilation
methodologies to ensure optimal indoor air quality. This is a move away from the conventional
systems which tend to increase the energy requirements.
Disadvantages
The system tends to be expensive. This mainly pertains the building design. Because of the
complexity in design, some developers may design to use the conventional system. This has
further been reinforced by the fact that there is no awareness towards its use.

The use of a hollow core slab tends to compromise on the integrity of the building. This is
mainly because it is a move away from the conventional slab system. Checking the
reinforcements is an important aspect of this design.
Conclusion
Looking at the various aspects of building design, it is clear that the hollow slab ventilation
system presents a more viable alternative to the conventional ventilation system. Unlike
conventional systems, hollow slab ventilation systems tend to have very little energy
requirements. This is mainly because of the transfer of energy between the slab and the indoor
environment. It has come a long way mainly because of the increase in indoor electricity use.
However, the use of this system may be more pronounced in regions that have extreme summers
and winters as compared to those which have less pronounced seasons.
The fluid that is contained in the hollow slab system plays a big role in this transfer of energy
between the building fabrics. Therefore the U- value of the building fabric is very important
when it comes to ensuring that there is effective and efficient heat transfer through the slab,
column, and all the other building elements. Higher U values may mean that there is an increase
in heat gain and loss through the building fabric while lower U values may mean that the inverse
is true. Brick, cement and all the other building elements have different u-values meaning that
the design has to be specific on the type of construction materials to be used.
In this analysis, the manual method of calculation, as well as the use of the IES VE software
have been imperative in identifying the thermal comfort of the building whose location is Dubai.
The building simulation provides an overview of the type of internal environment created

through the use of the hollow slab system and as such, the thermal comfort that may be accorded
to the occupants. This has been backed up with the manual method of calculation.
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