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The architectural implications of adopting low exergy cooling strategy: separation of sensible and latent cooling

Authors:
12th International Conference on Sustainable Energy technologies (SET-2013)
26-29th August, 2013
Hong Kong
Paper ID: SET2013-197
The architectural implications of adopting low exergy cooling strategy: separation of sensible and
latent cooling
Chen Kian Wee1,*, Arno Schlueter2 and Patrick Janssen3
1Future Cities Laboratory, Singapore-ETH Centre for Global Environmental Sustainability, Singapore
2 Ass. Professorship of Architecture and Sustainable Building Technologies (SuAT),
ETH Zurich, Switzerland
3 Department of Architecture, National University of Singapore
*Corresponding email: kian.chen@arch.ethz.ch
ABSTRACT
The Separation of Sensible and Latent Cooling Load (SSLC) is an appropriate low exergy cooling strategy for the tropical
climate. The cooling process consists of two main components; the latent and sensible cooling. Latent cooling is exergy intensive
where 8ͦC is used for the removal of moisture from the air by condensation. For sensible cooling only around 18ͦC for the removal
of heat from the space are required. However, in conventional practice these two processes are often combined as part of an air-
based cooling system. As a result 8ͦC is used for both processes resulting in a higher exergy consumption. This paper proposes the
implementation of SSLC as an alternative cooling method. Alongside this, promotes the change from an air-based to a hydronic,
high temperature cooling system for the delivery of sensible cooling. Furthermore, to reduce exergy losses due to the transport of
dehumidified air within the building, decentralized ventilation is advocated. This work addresses potential architectural
implications of employing such a strategy and the related technologies to achieve exergy efficient buildings. A series of design
scenarios using a sample building shows that it is essential for the architect to consider the related system parameters in the early
design stage where adjustments to the design can still be easily made.
KEYWORDS: Sustainable Building, Low Exergy, Integrated Design, Separation of Sensible and Latent Cooling, Architectural
Design Process, Environmental Simulation
1 INTRODUCTION
The concept of exergy describes the quality of an energy flow. The concept was originally used for the assessment of power stations
to maximize the power output. Recently, it was used for the analysis of cooling and heating in buildings (Shukuya and Hammache,
2002). In the case of cooling a building, the main aim is the removal of heat from an interior space. This can be achieved using
different mediums at different temperatures. Exergy efficiency in this context is related to the temperature difference between the
supplied medium to cool down the space, dehumidify the supply air and the heat rejection; the smaller the temperature difference
the higher the performance of the chiller and the less exergy is required for running the chiller (see Equation (1) and (2)). To
exergetically assess the cooling process, one needs to investigate the two main components of cooling, sensible and latent.
The latent cooling is the dehumidification of the fresh air supply, while the sensible cooling is the removal of heat from the occupied
space. Latent cooling is an exergy intensive process since a temperature of C is required to remove the moisture from the air
through condensation. Given sufficient large cooling surfaces, sensible cooling only needs about 18ͦC to keep the occupied space at
25C.
The Separation of Sensible and Latent Cooling Load (SSLC) is a very appropriate low exergy strategy in the tropical climate
(ECBCS, 2011). Research had been conducted to assess the feasibility of SSLC through simulation models (Hwang et al., 2010;
Ling et al., 2008) and SSLC had been implemented in buildings such as the ST Diamond building in Kuala Lumpur (Reimann,
2012). In Singapore the minimum fresh air supply for an office space is 5.5 l/s per person (SS553, 2009), the latent load can amount
to about 30%~40% of the total cooling load, thus by separating the two processes bears the potential for significant energy savings.
The performance of a chiller (heat pump) is limited by its Coefficient of Performance (COP); the COP is dependent on the
temperature lift between the supply temperature and the heat rejection temperature. The supply temperature is the temperature
needed to perform the cooling task; where it is 8C for latent and 18C for sensible cooling. The heat rejection temperature is equal
to the surrounding air temperature and can be assumed to be 32C in Singapore. This relationship is reflected in equation (1).
sr
s
eal TT T
gCO
rP
(1)
Where g is the Carnot factor, it is usually around 0.4~0.5. Tr is the heat rejection temperature and Ts is the supply temperature in
(K). In equation (1) the minimization of the temperature difference between Tr and Ts will improve the COP of a chiller. According
to equation (2) the exergy input is reduced by increasing the COP of the chiller.
COP
Q
Ex r
in
(2)
Where Exin is the exergy input to remove the heat, which is usually supplied in the form of electricity. Qr is the amount of heat
removed also called cooling energy in (J). Conventional practices delivers the cooling through an air-based system, due to this a
temperature of 8C is used for both latent and sensible cooling. For SSLC two chillers are used; one responsible for sensible and the
Paper ID: SET2013-197
By Chen Kian Wee, Arno Schlueter, Patrick Janssen
other for latent cooling. For the provision of sensible cooling the COP of a chiller is significantly increased due to the lowering of
the temperature difference between the supply and heat rejection temperature, which in turn, significantly reduces the exergy input.
This paper briefly describes the building systems necessary to implement SSLC strategy in the tropical climate. The focus is on the
resulting influences on architectural design and the impact of the prevalent architectural design process by considering active system
already in the design stage. A case study inspired by the design of the SANAA Zollverein School of Management and Design
(Basulto, 2010) is employed to illustrate the benefit of SSLC. Lastly, the challenges of such a design process and how it is a step
towards an integrative design approach will be discussed.
Building Systems
The two main building systems that are used in practice and considered in this work are radiant panels and decentralized ventilation
units (Figure 1). The radiant panels are responsible for the sensible cooling and belong to the category of high temperature cooling
systems. It is a hydronic system where 18C water is supplied to the panels to create a cool surface. The cool surface cools the
occupants through radiant exchange and air convection. Water of 18C provides a heat removal rate of 50W per cooling surface area
(ASHRAE, 2002). The cooling capacity of the radiant panels is dependent on the amount of surface area available, the heat removal
rate and cooling load as described by equation (3).
cc qAc
Q
(3)
Where
c
Q
is the cooling capacity of the radiant panels in (W). Ac is the area of the cooling surface in (m2) and qc is the heat
removal rate in (W/m2). According to equation (3) the cooling capacity is dependent on the cooling surface available which is
usually the ceiling area. First of all, the sensible cooling load needs to be within the cooling capacity. It is influenced by the
envelope quality, orientation, shading and the Window Wall Ratio (WWR) of the building. In order to meet the cooling load,
enough surface area needs to be allocated to have enough cooling capacity. The architect has to balance the cooling load and the
cooling capacity at the architectural design stage where alterations can still be easily made.
Due to the high humidity in the tropical climate, condensation on the radiant panels is an issue of major concern. The air tightness of
a building envelope comes into question when such a system is proposed. The use of similar systems such as the cool slab has been
successfully implemented in the ST Diamond building, the Green Energy Office (GEO) building (“Green Energy Office (GEO),”
2007, “ST Diamond Building,” 2010) and “Gardens by the Bay” in Kuala Lumpur and Singapore respectively. The architectural
concern is that a space that is conditioned by radiant panels should not be directly exposed to an unconditioned space, as the
moisture from the unconditioned air will condense on the panels due to the cold surface.
Dehumidified fresh air is provided by the decentralized ventilation unit. Decentralization reduces the pressure loss within the air
distribution system, which is achieved by placing the unit close to the façade to draw air from the outside and directly deliver it to
the occupants. The ventilation unit can be integrated into building elements such as the floor slab or placed under a raised floor.
While providing dehumidified fresh air, 40-50% of the sensible load is already removed from the space. This percentage of the
sensible load is dependent on the amount of fresh air needed, which is determined by the occupancy. For some usages such as an
auditorium, SSLC is not beneficial as the amount of required fresh air already provides adequate sensible cooling. In this paper, the
requirements of office spaces are used.
Figure 2 is a schematic diagram showing one of different options of how the building systems can be integrated into the
architectural design. The decentralized ventilation unit and the ducting are embedded into the floor slab. The air intake and
exhausts are located at the window sill, where it is not visible from the elevation of the façade.
Figure 1(a) radiant panels (b) decentralized ventilation unit
The implementation of SSLC needs a holistic design approach, where architecture elements such as building envelope, orientation,
shading, WWR and program of a space have a direct impact on the feasibility of the cooling strategy. Active systems need to be
factor into the design process, so that an architect is aware of the impact of his design actions on the cooling strategy and vice versa.
The challenge for the architects lies in the acquisition of all the necessary information for making design decisions in the early
design stage.
Paper ID: SET2013-197
By Chen Kian Wee, Arno Schlueter, Patrick Janssen
Figure 2 Integration of building sytems
Architecture Design Process
The prevalent architectural design process for energy efficient buildings is primarily focused on optimizing the passive aspect of a
building. However, according to the Building Construction and Authority (BCA) Green Mark assessment scheme in Singapore
(BCA Singapore, 2013), to achieve a Green Mark Platinum building one needs to satisfy an Envelope Thermal Transfer Value
(ETTV) (Chua and Chou, 2010a, 2010b) of 40W/m2 and a chiller COP of about 5.4. Therefore, if an architect wants his building to
be accredited it would be beneficial for him to also consider the active systems. Instead of leaving everything to the mechanical
engineers, architects should assume a certain responsibility to ensure an efficient cooling strategy for the building. Although the
COP of a chiller is dependent on many systems variables, an architect can contribute by reducing the temperature lift and designing
a favorable environment for the cooling system to achieve a high COP.
Furthermore, looking at only the passive systems greatly limits the architectural expression of a design as the building envelope is a
main component of the building aesthetics (Ritter and Meggers, 2010). By also paying attention to the active systems in the
architectural design stage, the architect is able to control and balance his architecture intention while realizing an energy efficient
building. Usually architects are more comfortable with the manipulation of geometry, material and space in a design process and are
unfamiliar with active systems. In order to facilitate the consideration of active systems in the architecture design stage, the use of
energy simulation programs would be necessary to offer feedback to an architect’s design decision.
The use of environmental simulation programs in the design process has been extensively studied in the architecture field
(Augenbroe et al., 2004, 2003; Citherlet et al., 2001) and tools are readily available to facilitate this design process. A few examples
include Rhinoceros3D/grasshopper with Energyplus and Radiance (Lagios et al., 2010), Houdini3D with Energyplus and Radiance
(Janssen et al., 2011) and Revit Architecture with EnergyPlus (Sanguinetti et al., 2012; Schlueter and Thesseling, 2009). The
environmental simulation programs used in these examples are energy simulation and daylighting simulations.
For implementing SSLC the architect needs to obtain the cooling loads of his design using an energy simulation program. For the
cooling load, the heat removal rate for the radiant panels can be derived from equation (3) and from the heat removal rate we can
obtain the supply temperature. The permissible temperature range is about 16C to 20C. If a temperature below 16C is used there
is a high possibility of condensation on the panels and the high temperature difference between the panel and the occupant’s body
temperature will cause discomfort to the occupants. If the temperature is higher than 20C there might not be enough cooling
capacity to keep the space at 25C. The COP of a chiller can then be calculated using equation (1). Lastly, according to equation (2)
the exergy input for sensible cooling can then be calculated. These steps are repeated for calculating the exergy input for latent
cooling, where a supply temperature of 8C is used.
The low exergy design process introduces a new layer of complexity by including the active systems in the architecture design
process. The various parameters of passive and active systems are illustrated in Figure 3. According to equation (3) if the sensible
cooling load exceeds the cooling capacity that is available from the panel surface area then it is not possible to implement SSLC.
The sensible cooling load is related to the thermal properties of the wall constructions and glazing, WWR, shading and the
orientation of a design, so the passive aspects still plays a major role in the low exergy design process. The low exergy design
process offers strategies that do not directly affect the building envelope, however this is only possible if the sensible cooling load
stays within the cooling capacity of the panels. One can increase the supply temperature by increasing the panel surface area or
reduce the heat rejection temperature by using cooling towers, which will reduce the temperature lift and increase the COP and in
turn decrease the exergy input. The dependency of the active system on the passive system further complicates the design process as
compared to the more straightforward prevalent design process.
Paper ID: SET2013-197
By Chen Kian Wee, Arno Schlueter, Patrick Janssen
Figure 3 Active and Passive System Components
2 DEMONSTRATION
Design Scenario
A design scenario based on SANAA Zollverein School of Management and Design (Basulto, 2010) was used to demonstrate the
low exergy design process. For the demonstration, the building was placed in Singapore. The Zollverein School is a 35x35x35 meter
cube, the façade consisting of windows of four different dimensions. The initial design punctured the concrete exterior wall with
numerous apertures and it consisted of hundreds of windows, but had to be altered to the current design due to cost and structural
considerations.
Using the realized design, a 3D model was constructed for energy and daylighting simulations. The wall and glazing was assigned
with typical construction properties of a Singapore office building. The insulated concrete wall has a U-value of 2W/m2K and the
double-glazing window without any LowE coating has a U-value of 2.8W/m2K and a shading coefficient of 0.81. The solar heat
gain was calculated using the ETTV and the typical occupancy, plug and lighting load were added to get an estimation of the
cooling load. The exergy input for cooling was then calculated. A Radiance lighting simulation (Ward, 1994) was conducted with
cloudy sky settings to obtain the daylight levels of the interior. The daylighting performance was expressed as the ratio of the floor
area receiving more than or equal to 300 lux over the total floor area. This configuration has been used as the base case scenario for
comparison as the design was improved gradually.
Passive Improvements
In a first step, the performance of the design was improved through alterations of its passive systems, namely the improvement of
the building orientation, the wall and glazing construction and the addition of shadings. The addition of shadings to the glazing is a
highly effective strategy to reduce solar heat gain in the tropics and the increase in thickness of the wall construction to have better
thermal performance reduces the heat transmitted into the space through conduction. Most of these improvements have a large
impact on the aesthetics of the building.
Five designs have been simulated for their performance. A summary of the designs is provided in Table 1. The cooling load was
obtained as mentioned in previous section and using equation (1) to (3) the exergy input for cooling was calculated using a supply
temperature of 16C(70W/m2) to 18C(50W/m2) depending on the cooling capacity required for the sensible load and 8C was
used to calculate the exergy input for the latent load. Design 1 is the base case scenario with a daylighting performance of 42% and
a cooling exergy input of 55.7kWh/m2/yr. For Design 2 the passive system was optimized with a better construction, a different
orientation and the addition of 1.5m deep horizontal shadings at each window. Design 2 performed significantly better with about a
12.7kWh/m2/yr reduction in cooling exergy input. A comparison between the two designs is shown in Figure 4. However, due to
the addition of shadings the daylighting performance dropped drastically to 27.4%. This is a common dilemma faced by architect in
design, where the increase in performance of one aspect leads to the decrease in another. A conventional air-based cooling system
was used for both the design and a COP of 4.6 was achieved.
Active Improvements
Design 3 is similar to Design 1 but uses a SSLC system. The cooling exergy input decrease from 55.7 kWh/m2/yr to 36.4
kWh/m2/yr (Figure 5). This is due to the much higher efficiency of the SSLC system as compared to a conventional air-based
system. The overall COP increase from 4.6 to 6.3. The building envelope does not need to be altered to improve the exergy
performance and the original architecture intention remains unchanged. However, the implementation of SSLC does requires
attention to the construction details in order to integrate the cooling system into the building. This is shown in Figure 2.
Paper ID: SET2013-197
By Chen Kian Wee, Arno Schlueter, Patrick Janssen
Table 1 Design Scenarios
Description
(W/m2K)
Glazing U-
value (W/m2K)
& Shading
Coefficient
Orientation
(ͦ anti-
clockwise)
Shading
(m)
Window
Wall Ratio
Cooling
system
Design 1 (base
case)
2
2.8, 0.81
0
0
0.22
Air-based
Design 2
1.11
1.55, 0.54
225
1.5
0.22
Air-based
Design 3
2
2.8, 0.81
0
0
0.22
SSLC
Design 4
2
2.8, 0.81
225
0
0.25
SSLC
Design 5
1.11
1.55, 0.54
225
0
0.25
SSLC
Figure 4 Comparison of Design 1 and Design 2
In an attempt to further improve the daylighting performance, in Design 4 the WWR is increased from 0.22 to 0.25 and is orientated
225 anticlockwise to receive better daylighting. The daylighting level is increased to 50.3%, while the cooling exergy input
increased by 1.3kWh/m2/yr as compared to Design 3. The increase was dampened by the efficiency of the cooling system, thus
giving an advantage for the architect to balance the performance of two contradicting aspects of design. Even without the high
performance constructions and shadings, Design 4 is able to outperform Design 2 both concerning daylighting and cooling exergy
input (Figure 6).
Active and Passive Improvements
When only one system is optimized at a time, none of the design was able to satisfy the Green Mark Platinum criteria. Design 2
performed well in terms of the ETTV requirement with a 27.7W/m2 but badly in terms of COP at 4.6, Design 3 had a high COP of
6.3 and an ETTV of 57W/m2, while Design 4 had a high COP of 6.4 and an ETTV of 62W/m2.
Design 5 is optimized passively and actively (Figure 7). The building envelope is constructed of insulated concrete wall of U-value
1.11 and LowE double-glazing of U-value 1.55 and Shading Coefficient of 0.54. The architectural intention was preserved, while a
high level of performance was achieved for both daylighting level and cooling exegy input. The cooling exergy input was the lowest
of the five designs, while the daylighting level performed 2.5% lower than Design 4 due to the use of LowE double-glazing glass.
The ETTV was 39.7W/m2 and the COP was 6.3. Design 5 satisfies the Green Mark Platinum criteria, at the same time it preserves
the architectural intention and improved the daylighting performance of the design.
Some may argue that the systems could still be optimized individually by the architect and the engineer. However, the dependency
between the active and passive systems will cause conflict to arise. For example, if an architect would like to further improve the
daylighting performance, he will increase the WWR. This inevitably will increase the cooling load and affect the COP. By
designing with the cooling system in consideration, he will be able to know how much more cooling load is permissible before his
design actions will impede the implementation of the cooling systems.
In addition, the implementation of the radiant panels and decentralized ventilation units requires certain spatial consideration such as
the cooling surfaces area and the program of the spaces. By considering the cooling strategy at the architectural design stage, the
architect greatly facilitates the implementation of the cooling systems and at the same time ensures his design intention goes hand in
hand with the cooling strategy
Paper ID: SET2013-197
By Chen Kian Wee, Arno Schlueter, Patrick Janssen
Figure 5 Comparison of Design 1 and Design 3
Figure 6 Comparison of Design 2 and Design 4
Figure 7: Design 5
Paper ID: SET2013-197
By Chen Kian Wee, Arno Schlueter, Patrick Janssen
Sensible Cooling Load and Radiant Panels
The cooling exergy input can be further reduced by adjusting the heat removal rate; which is related to the supply temperature, or
the cooling surface area of the radiant panels. The parameters involved are shown in equation (3). This can only be achieved if there
is sufficient cooling surface area available. In the example, the sample building had a ceiling area of 4900m2. As the panels are
mounted on the ceiling, the area of the ceiling will restrict the amount of surface area available for installing the panels.
The supply temperature used in Design 5 is 18 ͦC. For Design 6, the supply temperature is increased to 19 ͦC, thus increasing the
COP of the chiller according to equation (1), in turn reducing the sensible exergy input. The amount of cooling area needed in
Design 6 will then be 4405m2, which is still within 4900m2 and the COP will increase to 9.4. To further reduce the sensible exergy
input the supply temperature is increased to 20 ͦC in Design 7, which leads to a required cooling surface area of 5662m2 and a COP
of 10. Since this exceeds the ceiling area available, one could improve the quality of the building envelope construction in order to
reduce the cooling load.
Table 2 Parameters determining the implementation of radiant panels
Description
Supply
temperature
(ͦC)
Heat removal
rate
(W/m2)
Cooling surface
area
(m2)
Sensible load
to be removed
by the panels
(kW)
COP
(Sensible)
Design 5
18
50
3964
198.2
8.7
Design 6
19
45
4405
198.2
9.4
Design 7
20
35
5662
198.2
10.1
3 DISCUSSION AND CONCLUSION
The design scenario used in this work is a conceptual implementation of SSLC, so the results from the simulations are only
indicative of an actual building. Further studies need to be conducted to validate this design approach. The BubbleZERO laboratory
at the Future Cities Laboratory is a result of the low exergy design process. Currently, experiments are being conducted to measure
the effectiveness of such an approach. The results from the experiments will feedback into the design process to strengthen the
performance claims of the low exergy design method.
The main aim of this research is to bring forth this new approach in architectural design in the tropics and outline its related
principles and building systems. This example shows the advantage of factoring in active systems considerations in the architecture
design stage. The architect can incorporate cooling strategy into his design and create a favorable environment for the
implementation of high performance active systems. Moreover, in order to satisfy the Green Mark Platinum criteria it is essential to
consider the cooling systems in the design process, as it allows the architect more negotiation power in balancing between the
architecture intention, the daylighting and energy performance. It also shows that the orientation, constructions and shading of a
building are of far less importance in the reduction of cooling exergy input as compared to the usage of a more efficient cooling
strategy. Although the cooling load is directly link to the passive systems, the extra cooling load induced by a lower quality building
envelope can be compensated with an effective cooling strategy such as SSLC.
Low Exergy Design Support Tool
The challenge for an architect to adopt the low exergy design approach lies in the lack of information and data about the cooling
systems of a design at the schematic design stage. This is addressed with the use of energy simulation programs. The topic of design
and energy simulation has been extensively studied and there are commercial software packages in the market. However, the
running of an energy simulation is still a difficult task especially in the schematic design stage, where a great amount of information
about the building is still not available.
In order to support the low exergy design approach, including the relevant systems parameters; such as the supply temperature for
the radiant panels, the required cooling surface and the number of ventilation units, digital design tools are being created to support
integrated design decision-making. Various 3D modeling, lighting simulation and energy simulation programs are linked together in
a workflow management program to ensure a smooth exchange of information (Chen et al., 2012a). An initial workflow was created
(Chen et al., 2012b), but it needs to be further refined and validated alongside the low exergy design method. Such an environment
will allow architects to test out various design options and obtain essential systems information for implementing SSLC. Through
this the architect will be able to understand the relationship between the various parameters, envelope, structure and building system
to the cooling exergy input.
ACKNOWLEDGMENT
We thank the entire team of the Low Exergy Module of the Future Cities Laboratory for their contribution on the different system
components and Dr. Matthias Mast for the feedback on the paper. This work was established at the Singapore-ETH Centre for
Global Environmental Sustainability (SEC), co-funded by the Singapore National Research Foundation (NRF) and ETH Zurich
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Chapter 1 describes the characteristics of a thermodynamic concept, exergy, in association with building heating and cooling systems. Exergy is the concept that explicitly indicates 'what is consumed'. All systems, not only engineering systems but also biological systems including the human body, work feeding on exergy, consuming its portion and thereby generating the corresponding entropy and disposing of the generated entropy into their environment. The whole process is called 'exergy-entropy process'. The features of 'warm' exergy and 'cool' exergy and also radiant exergy are outlined. General characteristics of exergy-entropy process of passive systems, which would be a prerequisite to realize low exergy systems, are discussed together with the exergy-entropy process of the global environmental system. Chapter 2 introduces the various forms of exergy and the mathematical formulations used to evaluate them. The exergy balance on an open steady state system, which is much more relevant to thermodynamic analysis of energy systems, is also described, as well as the different exergetic efficiency factors introduced in the thermodynamic analysis of energy systems. Next, an exergy analysis example is outlined through an air-conditioning application. Air-conditioning applications are widely used in heating and cooling of buildings. Chapter 3 introduces an example of exergy calculation for space heating systems. The issues to have a better understanding of low-exergy systems for heating and cooling are raised. It is suggested that a prerequisite for low exergy systems would be rational passive design of building envelope systems.
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The performance of desiccant wheel (DW)-assisted separate sensible and latent cooling (SSLC) air-conditioning systems has been greatly improved by the application of divided heat exchangers, resulting in 7% and 46% increases in COP for R410A and CO2 systems, respectively. The paper simulated new performance-enhancing options that include evaporative cooling, a sensible wheel (SW) and an enthalpy wheel (EW) to the SSLC systems. The application of evaporative cooling to the SSLC system further improves the system COP by 7% and 14% respectively. By applying an EW to the SSLC systems, the COP is improved by 39% and 40% respectively. The DW-assisted SSLC technology also can be adopted for the dedicated outdoor system (DOS). It is concluded that only the EW is effective for enhancing the DW-assisted SSLC DOS systems because it lowers not only the cooling requirement of the vapor compression cycle, but also the heat requirement for DW regeneration.
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The advantage of separating sensible and latent cooling (SSLC) via the use of separate cycles is saving energy by raising the evaporating temperature of the sensible cooling process. In this study, the pertinent characteristics of the SSLC system using two parallel vapor compression cycles were investigated. The requirement for high air flow rate through the sensible evaporator was the most important hardware design issue, since it might lead to a high air-side pressure drop. To address this issue, a new air distribution method, which could significantly reduce the pressure drop, was proposed to replace the conventional one. The heat exchanger modeling results demonstrated that sensible evaporators of the SSLC system could provide the equivalent cooling capacity at reduced air-side pressure drop to that of the conventional system without increasing the total heat transfer area. Although initial investment of the SSLC system is projected to be higher than the conventional system, the estimated operating cost of the SSLC system is lower than the conventional one because of the low energy consumption.
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This paper aims to study the various parameters that affect the energy performance of commercial buildings in Singapore. The parameters are diverse, ranging from characteristics of construction of the walls and windows, to the various system settings and types within the building. Building energy performance is measured via two key indexes, namely, the Envelope Thermal Transfer Value (ETTV) and the annual cooling energy requirement (Ec). Parameters related to these two indexes are identified. An additional parameter, the solar absorptance of the wall, is further incorporated to calibrate the ETTV equation. A relative ranking on the functional parameters of ETTV has been performed to evaluate their effectiveness in lowering the ETTV of buildings. In addition, the impact of using cladding on ETTV is also studied. A correlation for Ec, expressed in the form of a simple linear equation, has been developed. This correlation accounts for the internal building loads, envelope loads, operating schedules and efficiency of the cooling equipment. Finally, ETTV and Ec have been employed to study the effects of chiller over-sizing and ventilation rates on building cooling energy. In the pursuit for better energy-efficient buildings, the approach presented in this paper contributes to the construct of sustainable energy-efficient built-environment.
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One of the significant benefits of Building Information Modeling (BIM) is the ability to effectively use analysis and evaluation programs during design, as feedback. However, the current dominant approach to analysis and evaluation of design proposals requires the creation of a separate building model for each kind of evaluation. This typically involves using a BIM tool to prepare the data for a specific type of anal-ysis to obtain design feedback. Most of the effort lies in modifying the building model to support the anal-ysis required. When dealing with multiple evaluations, this process is time consuming, greatly reducing the design benefits of BIM. We propose a system architecture to facilitate analysis and feedback in archi-tectural design, based on post-processing design-oriented building models. The post-processing automat-ically adapts the building model to the needs of the specific analysis, where multiple analyses can be run from the same building model. We outline the methods for realizing such design interoperability. By uti-lizing geometric and attribute relationships and semantics, data subsets are identified and aggregated. We present an example where the design of a class of buildings – federal courthouses, is evaluated in terms of multiple analyses: programmatic spaces, building circulation, energy consumption, and preli-minary cost. These analyses are performed by post-processing a single BIM model. The method is appli-cable to both API-based direct interfaces as well as open-standard building models.
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Due to the rising awareness of climate change and resulting building regulations worldwide, building designers increasingly have to consider the energy performance of their building designs. Currently, performance simulation is mostly executed after the design stage and thus not integrated into design decision-making. In order to evaluate the dependencies of performance criteria on form, material and technical systems, building performance assessment has to be seamlessly integrated into the design process. In this approach, the capability of building information models to store multi-disciplinary information is utilized to access parameters necessary for performance calculations. In addition to the calculation of energy balances, the concept of exergy is used to evaluate the quality of energy sources, resulting in a higher flexibility of measures to optimize a building design. A prototypical tool integrated into a building information modelling software is described, enabling instantaneous energy and exergy calculations and the graphical visualisation of the resulting performance indices.
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Energy consumption of buildings takes up about a third of Singapore's total electricity production. In this paper, we present a pioneering study to investigate the energy performance of residential buildings. Beginning with an energy survey of households, we established the air-conditioning usage patterns and modelled residential buildings for computer simulations. An ETTV equation for residential buildings was developed. Employing this equation, we demonstrated how to achieve improved energy efficiency in residential buildings. Two types of residential buildings, namely, point block and slab block, were modelled and parametric runs performed. ETTV impacts the energy consumption of residential buildings and thus lowering the ETTV will result in reduced building heat load. Results from the developed equation showed that a unit decrease in ETTV resulted in 4% and 3.5% reduction in annual cooling energy for point block and slab block residential buildings, respectively. In addition, a set of simple energy and load estimating equations were developed using computer simulation and local climatic data. These equations provided a means of estimating the annual cooling energy consumption of residential buildings in Singapore.