Ventilated Slab Cooling Systems: Improving Building Energy Efficiency

This report provides an overview of energy consumption in the building sector, focusing on heating and cooling systems. It highlights the increasing energy demands due to population growth and urbanization, leading to a significant carbon footprint. The report emphasizes the importance of energy-efficient building designs and technologies, particularly ventilated slab cooling systems, to reduce energy consumption and promote sustainability. It explores different designs of ventilated cooling systems, including thermo-active tubing, and discusses the use of hollow-core slabs for efficient heat transfer. The report also touches upon the impact of various parameters, such as surface insulation and airflow rate, on the thermal efficiency of buildings, citing a case study in Montreal that shows significant improvements in cooling load with optimized slab configurations. Desklib offers a platform to explore similar documents and study resources.

Name of student:
Institutional Affiliations:

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.