Passive Cooling Methods For Energy-efficient Buildings

The impacts of conventional cooling systems on the environment

Question:

Describe The Low Carbon Cooling in Tropical and Semi-Tropical Climates?
 

The global warning is an alarming issue in present days. The increment in the global temperature created an excessive temperature increment in the tropical and the semi-tropical regions. This increment in the temperature has increased the use of the conventional cooling system in these regions. This has increased the carbon emission from the conventional cooling systems that is creating an adverse effect on the global environment (Lübken, 2013).

Most of the global countries are trying to reduce the carbon emission from the conventional cooling system through implementing a passive cooling system in the buildings. Recently QGBC- Qatar Green Blinding Council and the SIJ- Solar Institute Julich have shaken the hands to create an environment friendly sustainable housing project (Qf.org.qa, 2014).

The Qatar government cleared their intention to implement the environment friendly passive cooling through taking decision in implementing the passive cooling through solar cooling systems in all the stadiums for the world cup (Marsh, 2014). Therefore, throughout this report the analysis of the available passive cooling methods will be discussed in accordance with the cost and the effectiveness of the methods for the home and industrial purpose.        

Figure 1: The High Temperature Zone

(Source: Sciencedirect.com, 2014)

The tropical and the semi-tropical region geographically positioned within the cancer 23º27´N to the Capricorn 23º27´S (Sciencedirect.com, 2014). The regional temperature in this area is much higher than the other areas across the globe. According to the study by Chaussinand (2014) the average temperature difference ranges within 10º C 15º C. Therefore, the use of the conventional cooling system is very much wide in this section.

The emerging economic condition has increased the construction of the individual and the industrial building in these areas especially in India, Singapore, Malaysia and Qatar Li et al. (2013). This economic growth has increased the use of the cooling system within this region. This increment in the conventional cooling system increased the demand of the power generation. The cumulative effect of these two has increased the higher carbon emission in the environment. This higher carbon emission has worked as a catalyst for the warming of the temperature in these areas (Fang, 2014).

In Qatar according to the study by Suljic (2014) the power consumption has increased by approximately 9.30%. However, according to the majority portion of this higher incremental demand has come from the higher installation of the conventional cooling system.

According to the study by Biswas (2014) clearly demonstrated that the structure and the materials used for the development of a building majorly increases the inside temperature. This study has also showed that the faulty design and the selection of the wrong material contributed in the 70% growth of the internal temperature. Therefore, the main issue is that to deliver such a design that will help the houses to decrease the inside temperature and this decrement in the temperature will slow down the use of the conventional cooling systems in the houses.       

Available passive cooling methods and their cost-effectiveness

Figure 2: Passive Cooling Methods for Energy Efficient Buildings

(Source: Sciencedirect.com, 2014)

The concept of the passive cooling says that, it is a preventive measure that will help in the overheating of the interior sections inside the building. According to Liu et al. (2013) the passive cooling strategy involves a three step cover up in the structural aspect of the building. These three aspects are:

1. A mechanism should be developed so that the inside temperature does not increase. In doing this, the measures that can be taken are solar shading of the roof, use of the reflective elements in the construction of the building and use of color that helps in reducing the generation of the heat.

2. The structure should be constructed that it remains able to keep the balance within the heat generation and heat emission for the building. In doing this, the structure should provide ample space for the airflow and incoming of the sunlight during the daytime.

3. The implementation of the air infiltration mechanism to reduce the interior heat generation. To achieve this energy efficient material should be used and should use such interior color that reduces the heat generation (Ni and Zhao,2013).  

According to S.K. Ng et al. (2013) the most acclaimed and the most practical designs that are available recently are the:

1. ZCB- Zero carbon building

2. ZEB- Zero energy building

However, in recent days a hybrid system has been developed that uses the renewable energy to run the cooling systems installed in the building. However, according to Gholami et al. (2014) the development of the captive house has larger potential to implement the passive cooling but the implementation cost is very high.

In UK and USA the implementation of the ZCB and ZEB, based building has evolved very smoothly. However, in Qatar and in the Asian countries the initiative is very low. According to the MoU between the Qatar Green Blinding Council and the Solar Institute Julich will help to implement the lower carbon emission buildings in Qatar (Qf.org.qa, 2014).     

Figure 3: The ZCB Design (Sample Only)

(Source: Ng et al. 2015)

According to Chávez and Melchor (2014) ZCB is the most suitable strategy for the construction of the Zero carbon building. However, according to him the designing of this kind of building is very much complex. The main theme of this construction is to construct such a kind of house that is capable of response to the climate.

According to Halirova et al. (2014) the cooling season difference in Qatar and London is very much high and due to it the fundamental designing of this king of building is to block the direct heat coming from the sun and letting the air flow freely within the building. Moreover, it develops a natural ventilation system that keeps the balance between the optimum temperature and the inside heating. The natural ventilation has the ability to reduce the overheating more efficiently than the mechanical ventilation system.

Qi et al. (2013) the development of the large open area helps in reducing the temperature very efficiently along with the proper airflow provisions. The south facing design development allows the flow of the air more freely than the other structures. The following figures will demonstrate some of the most widely used airflow maintenance system within the buildings.

The implementation of renewable energy-based cooling systems

Figure 4: Open Plan layouts

(Source: Yourhome.gov.au, 2014)

The open plan layout allows the free flowing of the incoming air through the open space. This free flow of the air helps in reducing the interior heat of the building (Ogunbiyi et al. 2014). If the design is constructed through keeping the side of the building in the southend, the air will be flowed through the windows and will reduce the interior temperature.    

Figure 5: Convection air Movement

(Source: Yourhome.gov.au, 2014)

According to Velasco et al. (2014) the convective air movement allows the warm air to gets ventilated through the upper panel where as it allows the cool air to come in through the lower panels. The cool air comes inside the building through the open spaces and it circulates to the upper floor and is ventilated through the upper floor, as it gets warm. The south facing buildings with evaporating cooling options get the most of the benefit from this type of design (Henry and Kato, 2014). 

Figure 6: Earth coupling cooling mechanism

(Source: Yourhome.gov.au, 2014)

According to Shari and Soebarto (2014) the earth coupling is the most sustainable solution for the passive cooling of the buildings. Through this mechanism the house, remain able to keep the ground temperature low that helps in cooling of the interior section during the nighttime. However, according to if the shading is done through unstructured way it can exceed the level of comfort in the interior section. The study by Waris et al. (2014) has shown that the ground temperature varies therefore the earth coupling will be very much effective for the country.     

Figure 7: Concept of Life Cycle for ZCB

(Source: Ng et al. 2015)

According to Tsukiyama et al. (2014) the ZCB does not have any standardized framework for the construction or setting benchmark. Therefore, it becomes tough to calculate the life cycle of the ZCB. However, considering the lower use of the conventional cooling system and the other electrical equipments in the daytime the building could have a life cycle of 50 years (Ng et al. 2015). To attain the zero carbon building the owner of the building and the constructor of the building needs to put focus on the development of the renewable energy sources within the premise of the building. On this context, the roof of the building could be used as the source of unconventional power. The installation of the solar panel will help to develop a self-sustainable power resource for the building (Waris et al. 2014). Therefore, through this development the demand for the power extraction from the national grid will be decreased for that building. This will also help to reduce the carbon emission from that building.

According to Zhai et al. (2014) the carbon neutrality is the summation of couple of factors. Therefore, the carbon neutrality is:

Carbon Neutral= Emission associated with electricity supplied to the building+ Emission reduced through adopting the renewable energy + Emission related with the biodiesel.

The design and implementation of zero-carbon and zero-energy buildings

Therefore, to achieve the zero carbon building the source of the renewable energy should be developed within the premise of the building. In the case of the industrial buildings, it is possible to develop a captive renewable power plant but it becomes very tough for the residential areas. In the residential areas, the implementation of the solar panel will be the best fit (Hu et al. 2014). The bio diesel could be used for the burning propose inside the building. The use of the bio diesel will help to reduce the carbon emission happened due to the burning of the natural gases and other resources.

Figure 8: PV and CCHP operation system

(Source: Ong, 2014, pp.106)

On the other hand, use of the sun reflective glasses and the large windows with proper outside painting and the inside ventilation will reduce the inside temperature. This structure will help to reduce the use of the conventional cooling system. Moreover, the use of the bio-diesel and the renewable energy will generate surpluses in the national grid and that could be used in somewhere else. The captive electricity that will be generated through the solar panels will be used for the electrification of the ground areas and the CCHP will help to reduce the heat generated by the cooling instruments. The surplus energy will be redirected to the CCHP section (Wongvisanupong and Hoonchareon, 2013).

At the early design stage, the energy simulation of the whole building can be conducted and it can help in predicting the energy consumption by the ZCB. Then the renewable energy system and building energy system were rebuilt by using the results for the neutralization. The effectiveness of the different design strategy can be evaluated at the design phase and in that phase the energy demand and the loads can be strategically reduced as well. Thus it can help in using the standard cost-benefit analysis for making the decisions regarding the design in architecture and engineering of the design. Here the simulation tool can be used for building the energy simulation. The main inputs that are required are ZCB building designs (building systems and architectural elements) and hourly weather databases. Here the Typical Meteorological Year can be used as well for the determination of the weather years.

It is evident that the base design of the building is very important in order to make it more energy efficient. In order to make the buildings energy-efficient, it is very important to take into consideration the Building energy Codes (BEC) for the new buildings. The code can implement the designs of best practices for all the building developments in the region. The Overall Thermal transmittance value is regulated by the BEC regulations and it can also provide the guidelines for the use of escalators, lightings, electricity usage, air-conditioning etc. thus the design targets and the baselines are formed for the practitioners by using the regulations.  This can also help in achieving the main aims and objectives of the use of ultra-low energy and the baseline performance can be surpassed by such designs of the low energy and ZCB design.

In the following diagram the distribution of energy that is predicted for the baseline model is shown. The energy use intensity (EUI) is between 25-350 kWh/m2 for a typical existing building and the BEC is around 157 kWh/m2 for a typical building. Thus it can be said that the energy can be effectively reduced in a building by adopting the BEC requirements.

Figure 9: The base design for ZEB

(Source: Ng et al. 2015)

In the following table, the key parameters of ZCB and the design values has been summarized. As one of the design cases, the energy model was used here. The predicted ZCB and EUI is 45% lower than the compliant baseline building as it is 86 kWh/m2. As a result of intensive application and mixed uses the CIC ZCB is more energy intensive. Thus it can be said that the energy performance of the building structures in the country can be significantly improved by using the specific design.

Figure 10: The Energy Analysis

(Source: Ng et al. 2015)

Now the effectiveness of the design can be discussed as well. It is known that the energy simulation can predict the effectiveness of the strategies of energy savings in the active and passive system settings. In the following figure the relative effectiveness can be summarized. The performance and effectiveness of the design can be evaluated through various measures. These are discussed here.

Figure 11: Energy Efficiency Level

(Source: Ng et al. 2015)

It is very important to minimize the envelope loads for lowering the build-up heat. It is calculated that the approximately 163 W/m2 is the value of the peak load cooling but mostly the cooling load is approximately 80 w/m2.

It is evident that the solar heat can be gained nearly ten times more through the windows compared to the opaque facades. There can be a dramatic impact of the solar heat gain due to the minimization of the extent of glazing. It is very important to consider the angle of the sun in various times of the day and how it can maximize or minimize the requirement of heat and light at home during those times. It can help in optimizing the benefits and can help in deciding on the position of the windows.

It is important to minimize the heat flow with the help of opaque walls. There are mainly two steps that can help in reducing such effects. First, the flow of heat through the walls can be stopped by adding insulation in the walls. Secondly, the surface temperature can be reduced as wall by reducing the absorption of the façade which can help in reflecting the heat away. Here the absorptivity can reduced below 0.3 by using the glazed finishes and the white walls.

The solar penetration of the building can be minimized by maximizing the daylight, if the building is tilted to the North. It can be integrated into the design of the building and it can provide the desirable results.

Figure 12:Optimum use of Daylight

(Source: Ng et al. 2015)

In a hot and humid climate it is very important that air-tightness is implemented as a disproportional impact can be can be seen for the high humidity. The risk of condensation can be reduced as well with the air tightness.

The energy load can be reduced by enhanced natural ventilation. In the following diagram, the modeling technique is shown with the help of computational fluid dynamics. It can help in optimizing the natural air flow availability

The radiation heat transfer helps in radiant cooling system. The circulated chilled water help in reducing the heat from the circulation and this system is more energy-efficient. Thus the radiant cooling system can help in reducing the use of energy on the design.

The renewable energy needs to be generated on-sight. The landscape and the building energy consumption can be significantly reduced after the application of active and passive design measures for the efficiency of energy. The energy demand needs to be met through the means of renewable energy in order to achieve net zero carbon. A bio-diesel design system can be installed as well in order meet with the requirements of renewable energy. A CCHP energy system can be used as well for the reduction of the electrical energy used for the cooling process.

Figure 13: Main components of the CCHP bio diesel generator and the absorption chiller

(Source: Qingyuan and Yu, 2014, pp.1728)

The main theme is this system is to use the CCHP system and bio fuel as the fuel for the operation. According to Qingyuan and Yu (2014) the use of the bio fuel will help to reduce the carbon emission into the environment. However, the most of the complex situation is the designing of the absorption chiller and the generator. According to Leydecker (2013) while designing the CCHP system, four key considerations are required. The considerations are:

1. Optimization of the operational cost

2. Plant size is short

3. System designed to fulfill the instantaneous cooling demands

4. PV panel position inside the house

In the combination system, the water from the chiller helps to absorb the excess heat generated from the cooling system. However, currently the highest capacity of the combination system is the 100 kWe (Cameron and West, 2013).   

Conclusion

The global warming has increased the temperature of the tropical and the semi-tropical regions. This increment in the temperature has increased the demand for the conventional cooling systems. However, due to the excessive use of these conventional cooling system the Carbon emission has increased that affected the environment adversely. Therefore, to maintain the balance between the comfort and the environmental safety the implementation of the ZCB and the ZEB will be much effective for the residential buildings. On the other hand, for the industrial buildings the implementation of the combination system will help to reduce the carbon emission from the cooling system. However, the implementation of the solar panel and the use of the bio diesel will help to reduce the carbon emission largely.

On the other hand, while developing the projects through the ZCB and ZEB approaches the cost estimation affordability needs to be taken care of. Otherwise, the project popularity could lows down. On the promotion issue, the government needs to take the initiative through developing separate plans for the companies and customers.

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