A300CAW (AWS3): Optimizing Chiller Performance in Singapore Buildings

This report delves into the critical topic of chiller performance optimization within building automation systems, focusing on energy efficiency and sustainability. It begins by highlighting the significance of chiller optimization in reducing energy consumption, especially in the context of global green building initiatives. The report then explores various techniques and methodologies for optimizing chiller performance, including variable speed drive strategies and maximizing chilled water delta T. It examines the chiller control process, the use of variable speed design strategies, and the importance of maintaining a high chilled water delta T. Furthermore, it investigates standard grading systems, with a particular emphasis on ASHRAE standards, and compares them to Singapore standards. The report concludes with case studies from Singapore and Australia, analyzing performance visualization, energy management, and real-time building cooling load prediction using artificial neural networks. The overall aim of this report is to offer insights into the enhancement of chiller plant efficiency and energy conservation.

A300CAW ACADEMIC WRITING SKILLS 3 (AWS3)
How the performance of a chiller optimized? Are the buildings in Singapore subject to a
standardized grading?
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Table of Content
1. Abstract
2. Justification
3. Why the optimization of chiller performance is important?
4. Chiller Control Process
4.1 Technique and Methodologies for Performance Optimization
4.1.1 Variable Speed Design Strategy
4.1.2 Maximizing High Chilled Water Δ T (Delta)
5. Standard Grading Systems
5.1 Comparison of Standard Grading Systems with Singapore Standards
6. Case Study
7. Conclusion
8. Recommendations
9. References
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1. Abstract
Maintaining and managing optimal energy efficiency in a building is a huge challenge
that all engineers in Building Automation Systems (BAS) and Heating, Ventilation and Air
Conditioning (HVAC) industry work extremely hard to overcome. Chiller plant consumes the
majority of energy consumption in a building thus it is vital to optimize the performance of the
chiller plant and achieve desired thermal comfort at the same time. This report looks into the
technique and methodologies of chiller plant performance optimization and common challenges
that arise during the implementation of the optimization process. It also explores the standard
international standards of chiller optimization and compares that with current approaches in
Singapore buildings and concludes with recommendations to close necessary gaps in
standardizations.
2. Justification
As a Building Automation Engineer in this industry, this topic is very interested in me
since it plays a significant role in saving energy in a building. At the same time, I am concerned
about the global green building concept, which enhances the sustainability and efficiency of a
building (Burrows, 2017). A chiller plant consumes a huge amount of energy thus optimization
of chiller is very important since energy costs a lot of money as well as huge environmental
impacts as energy is mostly produced by using natural resources. Thus this research report would
address the importance of chiller optimization and different kind of methods and technique to
achieve standard grading in a building to save energy consumption.
3. Why the optimization of chiller performance is important?
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Chiller plant is often considered the "heart" of a building's HVAC system, thus it is
massively important to optimize the chiller plant in order to achieve the improved building
performance (Taylor, 2010). Not only is the chiller plant the main source of cooling, but also its
power requirements make up a large amount of a building's energy needs. For an example, the
HVAC system can equal an average of 60 per cent of the total electrical load in a building and
plant represents a major portion of that HVAC load.
According to Energy Information Administration, DC, USA, (2003), "The building sector
is responsible for a significant share of energy-related carbon emissions across the world".
Greenhouse Gases (GHG) in the atmosphere block radiated heat returning from earth surface,
which would lead to global warming and various climate changes. Water vapors (H2O), Carbon
dioxide (CO2), Methane (CH4) and Chlorofluorocarbons (CFC) are some of the major GHGs
that could be found during the operation of a chiller plant. By optimizing a chiller plant it is
viable to reduce the emission of those Greenhouse Gases and achieve the Global Green Building
status (Bell, 2013).
In an optimized chiller system condenser water pumps, chilled water pumps and cooling
tower fans are often controlled by Variable Speed Drives (VSD) and they run according to
required speed calculated by different designed set points. So such equipment does not function
at a constant speed or maximum speed for a long time and it will lead to have a higher life
expectancy for equipment and reduce the ratio of breakdowns in the plant. Thus this would lead
to having a more reliable system with higher durability (Le, 2018). The diagram below
illustrates the chiller;
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Figure 1: Showing a chiller (Bell, 2013)
4. Chiller Plant Control Process
In most cooling process application, the pumping system will circulate a solution of a cool
glycol/water from the chiller to the process. The cold liquid will remove heat energy from the
process and then warm fluid before it returns to the chiller. The heat transfers from the process to
the chiller through process water. Chiller process has refrigerant as the compound chemical
(McDowall, 2010). There are several kinds of refrigerant as well as their application depends on
the temperature needed. Even though there are several types their principle of operation remains
the same which is phase change and compression. The refrigeration cycle is the process of
cooling and heating refrigerant and changing it from liquid to gas and back again.
The chiller plant is comprised of two main circuits, that is refrigeration and fluid circuit. All
these circuits become more complicated as the temperatures go down to below 40 0 C. At that
low temperature, the plant incorporates additional cooling circuits as well as the refrigerant
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(Publication, 2015). The heat will be transferred in the plant from the process to the fluid. After
that, it moves to the refrigeration circuit and then to the condenser. At the condenser, the heat
accumulated will be removed. A water-cooled condenser removes heat through circulation of
cool water with the help of lines in the condenser. The heat is moved by the help of water to an
external cooling apparatus.
Figure 2: Showing the working principle of a chiller (Publication, 2015)
4.1. Technique and Methodologies for Performance Optimization
The conventional supervisor control basically fixes the water condenser temperature at the
setpoint given as TCW, SET. This results to cooling tower cool the water at the condenser at a lower
temperature than TCW, SET in almost every time. The efficiency of the chiller increases at that point
when the water entering the chillers TCW, SET reduces. Hence there is TCW, SET optimum where the
total consumed energy Etot of the cooling tower and the chiller is least. The optimization can be
illustrated using the below function;
j= min (Etot) = min ( Ech+Etw)
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Where Etw and Ech = consumed energy by cooling tower and chiller respectively
Current vapor-compression chiller technology is based on the "reverse-Rankine" cycle known as
vapor-compression. See the attached diagram which outlines the key components of the chiller
system. This can be illustrated mathematically as below;
COP = Cooling Power
Input Power
4.1.1. Variable Speed Design Strategy
There are two basic types of chilled water flow systems.
1. Constant flow
2. Variable Flow
A constant flow will mostly be used for smaller scale chillers with domestic use while
variable flow systems are vastly being used in large systems like commercial and healthcare
buildings (III, 2016). Usage of variable chilled water flow systems reduces the energy
consumption on most of the equipment in a chiller plant. Thus variable speed control is one of a
very important design strategy that used in chiller plant optimization. It is specially used in
chilled water primary and secondary pumps and cooling tower fans using a Variable Speed Drive
(VSD) to control the motor speed according to required demand.
Induction motors are used for chilled water primary, secondary and cooling tower fans and
those are sized to handle the maximum demand load under any circumstance and the letting them
and at a constant speed at full power. Those are known as fixed speed motors where their speed
is determined the constant frequency of the power supply that is typically 50Hz. Variable Speed
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Drives (VSDs) are frequency converters which rectified the 50Hz input voltage to DC and
converted back to variable frequency AC voltage. In VSDs power demand of motor is
proportional to the cube of speed (speed) 3. Thus it enables pumps and fans in the chiller plant to
function according to required demand at a required speed instead of full speed. Reduction of
motor speeds will result in less power consumption and it leads to achieving significant energy
savings (M. Anson, 2012). The diagram below shows a chiller plant and its basic component in
its operation.
Figure 3: Showing the diagram of a chiller plant and its basic component in its operation
(McDowall, 2010)
4.1.2. Maximizing High Chilled Water Δ T (Delta)
Chiller optimization is carried out based on cooling load and chilled water temperature threshold
(Hyman, 2011). Cooling load is the amount of heat energy that needs to be removed from a
building to maintain an acceptable temperature for the occupants of the building.
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The simplest form of calculation for the cooling load is,
Cooling load = 4.2 * chilled water flow rate (chilled water return temp - chilled water
supply temp)
Difference between the chilled water supply and return (chilled water return temp - chilled water
supply temp) is called Δ T (Delta) (M. Anson, 2012). The chilled water flow rate is inversely
proportional to Δ T (Delta) which means that when the Δ T (Delta) drops flow rate must be
higher in order to meet the required cooling demand capacity. To achieve higher flow rates
pumps should run at a higher speed using more power that increases energy usage in the plant.
So it is better to maintain the Δ T (Delta) in a higher range and recommend to maintain around 4-
6 degrees in order to reach optimal performance.
5. Standard Grading Systems
The standard Grading system is very crucial in Chiller plant operation, the most common
standard grading system for a chiller is the American Society of Heating, Refrigerating and
Air Conditioning Engineers ( ASHRAE). Basically this standard deals with setting the design
standards and maintain ace of the indoor environments. Basically, ASHRAE standards deal with
three main issues in the optimization of the chiller plants. These includes Standard design of
chillers, testing chillers and standard practice of chiller plants. In other words, the Standard
grading systems help in monitoring, construction, and operation of chiller plants to ensure that
the chiller plants perform in accordance with the standard requirements.
5.1. Comparison of Standard Grading Systems with Singapore Standards
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The grading of chiller system in Singapore’s standard in a tropical climate, as well as air
condition, is a necessary building which meets the high cooling demand in these building. And
for Singapore there is a large portion of electricity savings is as a result of replacement or even
upgrading to a more efficient centralized air condition system. This is actually the same as the
standard grading system of chiller which also saves a lot of electricity as they operate (Cheung,
2015). But when the efficiency of the chiller was compared between standard grading with
Singapore standard, it is confirmed that the efficiency of the standard grading is higher than
Singapore standards.
6. Case Study
The BCA standard on Singapore chiller is a case study which analyzed performance
visualization and energy management. This is where chiller standard monitoring interfaces. The
energy consumption system used for monitoring has a relatively higher efficiency with lower
power consumption. There is a power monitoring interface employed for this case study
(Eugene E. Drucker, 2010). There is also an optimization suggestion interface for this case study.
From ASHRAE journal the building cooling load prediction, the traditional modeling approach
by the use of the predefined profile of weather operates scheduled, occupancy among others.
There is also a real-time building cooling load which is made possible for this case study. The
standard of operation from this case study involves very low power consumption and higher
efficiency of the chillers.
Another case study is from Australia, it is true from ASHRAE journal that there is a real-time
prediction of the load which is mostly done by the model of Artificial Neural Network (CHOW,
2009). This illustrates the correlation between the weather and the building conditions as well as
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the building load in the historical data of the building system (Hyman, 2011). With the ANN the
prediction can be amplified after a given period of time when several data of the building system
is put into it.
7. Conclusion
As seen above the Singapore Buildings chiller plant optimization has almost the same
standards as those of the international standards and this makes them be as effective as those of
the international chiller plants. There are some standards of grading for the chiller plant which
ensures it operates within standards required. The standard grading like the ASHRAE makes the
chiller designers and operators to follow the standard required in the operation, design and test
these in general increases the efficiency of operation of the chiller plant.
Singapore has made significant improvements with regards to the attainment of
optimized chillers as has been observed in the case study above. The optimized chiller whose
analysis was based on energy management and performance visualization established a low
power consumption chiller that is accompanied by high energy efficiency. While there are
remarkable steps towards the realization of the standards of the Standard Grading Systems,
Singapore has not hit the mark yet and needs to work on a few areas to enhance full attainment
of the expected standards. The mainly underlined issues as per the ASHRAE standards revolve
around the standard design of chillers, testing chillers and standard practice of chiller plants, all
of which is incorporated in the Singapore standards will serve to meet the required standards. To
this extent, Singapore has not successfully managed to address the ASHRAE standards with
regard to the standard design of chillers owing to the climate of the country which is mainly
tropical and in some way influences the nature, size, shape, and form of the chillers that are
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applicable within the geographical boundaries. Designing of the chillers as per the ASHRAE
standards would thus call for greater knowledge and innovation to be brought on board to ensure
that all the factors at play are taken into consideration.
8. Recommendations
The chiller plant optimization in Singapore is almost a few steps to the international set
standards and only calls for slight if not minor adjustments so as to be at par with such standards.
In order to get to the international levels, it is recommended that the design of the chillers be
done in such a way that they meet the design requirements of the international standards. This
should be done taking into consideration the tropical climate of the country. By considering the
climate as well as other determinant environmental factors, the chillers will not only be efficient
in terms of energy management and consumption but also be highly ideal for the country. There
would need to be a link and harmony between the HVAC systems and BAS systems and the
chillers in order to attain maximum performance in the various buildings and structures.
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