Complete Chiller Systems: Chapter 3
Chiller System Parameters
In this module, we will learn about pump head and delta T. We will also learn about cold water flow. Skip to quiz!
Discharge Head
Recall that the water pumps circulate cold water from the chiller system and return it to the chiller system. Water pumps should circulate cold water to the total height of the building. The maximum height that the pump can circulate is the pump head.
The pump head is the height to which a pump can raise water straight up. It is measured meters or feet. The pump head is useful because it tells a pump capacity to do a job.
If we have to pump cold water up to 50 meters in the height of the building, but the pump has 30 meters pump head, it will not circulate the cold water. We have to select a pump of more than 50 meters discharge head or use two pumps of 30 meters head.
If we select a large discharge head than required, it will consume more energy. It can even cause damage to the cold water piping.
Delta T
Delta T is the most common word in the HVAC industry. It means the temperature difference between two points. For example, if the water enters the evaporator at 12°C and leaves at 7°C in the chiller system, then the Delta T is 5°C.
For example, a chiller system’s design delta T is 6°. During the operation of the chiller, the water enters the evaporator at 13°C and leaves at 6°C in the chiller system. Then the delta T is 7°C. Chiller’s operation delta T is higher than design delta T. This is called high delta T.
If the chiller system has a high delta T, this means that it is working properly. The efficiency of the chiller system is also good.
For example, a chiller system’s design delta T is 6°. During the operation of the chiller, the water enters the evaporator at 10°C and leaves at 7°C in the chiller system. Then the delta T is 3°C. Chiller’s operation delta T is lower than design delta T. This is called low delta T.
If the delta T is lower than the manufacturer’s specified value, then it is low delta T. It is usually called low delta T syndrome because it causes problems to the chiller system.
Every chiller system will experience low delta T at some point during its continued operation. Low delta T causes cold water pumps to operate at more speed to increase the flow rate. Low delta T reduces the efficiency of the chiller system and consumes more energy.
Low delta T syndrome is the result of insufficient use of cold water at AHU/FCU. Reasons for low delta T can be:
oversized chillers, pumps, coils, control valves, and cold water piping
dirty air filter or cooling coil which does not allow air to pass through it
Water Flow
Recall that cold water is circulated through water piping throughout the building. The water flow rate in the piping is measured in GPM. GPM is abbreviated as gallons per minute.
GPM tells how many gallons of water flows through a pipe in a minute. It is largely determined by the rotational speed and size of the pump.
The ton of refrigeration is the measure of the cooling capacity of chiller systems. TR is the short form of a ton of refrigeration. In chiller systems, one ton of refrigeration equals 2.4GPM. To provide one ton of refrigeration, we need a water flow of 2.4 gallons per minute.
The maximum height that the pump can circulate is the pump head. The pump head is useful because it tells a pump capacity to do a job. Delta T means the temperature difference between two points.
The water flow rate in the piping is measured in GPM. In chiller systems, one ton of refrigeration equals 2.4GPM. To provide one ton of refrigeration, we need a water flow of 2.4 gallons per minute.
Electricity and Controls
In this module, we will learn about the main electrical components of chiller and how they work. We will also learn about the controls of the chiller system. Skip to quiz!
Controls
Recall that HVAC control systems are used to control the operations of HVAC equipment. Control systems use a small amount of control voltage to control larger voltage-connected equipment. In the chiller systems, we use 120V AC and 24V DC for control purposes.
In the chiller systems, control systems can be divided into
Safety controls, and
Flow controls.
Let us learn more about both types of controls in chiller systems in detail
Safety Controls
Safety controls prevent a hazard from occurring. Recall that safety control circuits are always in closed condition. If any abnormality happens, these will open and turn off the chiller system.
Safety controls present in the chiller system are:
Overload relays,
LPCO switch,
HPCO switch,
Water flow switch,
Antifreeze thermostats, and
Motor winding thermostats.
Let us learn more about these safety controls in detail.
In chiller systems, overload relays are found in compressors, fan motors, and water pumps. Recall overloading is a condition when the motor draws more current than the specified range.
The overload relay detects the overloading of the motor and stops the electric supply to the compressor. It protects the motor from overheating and winding damage.
LPCO switch means low-pressure cutout switch. Recall that it detects pressure on the inlet of the compressor. It stops the control signal and shuts off the system if the refrigerant pressure from the compressor is lower than the set value.
HPCO switch means high-pressure cutout switch. Recall that it detects pressure on the outlet of the compressor. It stops the control signal and shuts off the system if the refrigerant pressure from the compressor is higher than the set value.
The water flow switch is a device used to control the flow of water in piping. The water flow switch operates through the use of a paddle which moves due to the force of water through the pipe. It ensures that the water is flowing through the piping within set parameters.
The switch will close when the flow is present and open when there is no flow. These devices are used with the purpose of protecting a pump. These are capable of stopping a pump when there is no flow as well as turning it on once the flow starts. Let us a video to understand the working of it.
Antifreeze thermostat is installed cold water piping. It prevents the temperature of water from falling below a set safety value by switching off the chiller. It prevents cold water in the piping from freezing.
The motor winding thermostat is installed in motors to protect them. It is a thermostat for monitoring the temperature of motor winding.
It stops the control signal and shuts off the motor if the temperature rises above the set temperature. It protects the motor from the excessive winding temperature that could lead to damage.
Flow Controls
Flow controls regulate the flow of refrigerant or water in the chiller system. They are installed in the refrigerant or water piping.
Some of the flow controls present in the chiller system are:
Solenoid valve,
Hot gas bypass valve, and
Back pressure regulating valve.
Let us learn more about these flow controls in detail.
Recall that a solenoid is a type of valve that works on control signals. A solenoid valve opens or closes whenever it receives control signals. Let us see a video to understand the working of the solenoid valve in chiller systems.
The hot gas bypass valve is also called the discharge bypass valve. It is usually installed at the outlet of the metering device. Let us see a video to understand the working of it.
Back pressure regulating valve is a spring loaded non-return valve. It is fitted at the outlet of the evaporator. It prevents the evaporator pressure from falling below a set value. Let us see a video to understand the working of it.
Electricity
The main electrical components of the chiller system are:
Compressor,
Primary pumps, and
Secondary pumps.
Additionally, the air-cooled chiller will have condenser fan motors, and the water-cooled condenser will have a condensing water pump and cooling tower fan motor.
All main components of chiller like compressor, water pumps, and fan motor work on the 3-phase power supply. All the above components have a 3-phase electric motor as an integral component in them. The compressor is the main electrical component that consumes most electricity in the chiller systems.
3-phase electricity supply is connected control panel of the chiller. From the control panel, electrical cables are connected motor starter or VFD. From the motor starter or VFD, electrical cables are connected to the terminals of motors.
3-phase electricity is supplied to chiller systems. Fan motors and water pumps run with 420 volts. The compressor may run 420V, 4120V, or even higher voltages depending on size.
Recall that a motor starter is an electrical device used to start and stop a motor safely. It is similar to a contactor, but it provides low voltage and overcurrent protection. Let us see a video to understand the working of it.
VFD stands for variable frequency drive and also is known as variable speed drive. It is also used to control the electrical motor as the motor starter. It controls the speed of the motor by varying the frequency and voltage supplied to it.
If the motor runs in constant speed, motor starter is best choice. If motor speed control is required, installing VFD is a must. Let us see a video to understand the difference between both of them.
Recall that primary pumps are constant speed pumps. We use motor starters for these pumps. Recall that secondary pumps are variable speed pumps. We use VFDs for these pumps. The motor starter has fewer applications, and the price is lower than VFD.
Recall that 3 phase motor is a rotating machine that is designed to operate on a three-phase supply. In the chiller systems, compressor, water pumps, and fan motor have 3 phase motor has an integral part of them. 3 phase motor of the compressor is sealed inside it.
In the chiller systems, we use 120V AC and 24V DC for control purposes. In the chiller systems, control systems can be divided into
Safety controls, and
Flow controls.
The main electrical components of the chiller are are:
Compressor,
Primary pumps, and
Secondary pumps.
They all have 3 phase motor has an integral part of them.
Vapor Absorption Chiller Systems
In this module, we will learn about a vapor absorption chiller. We will also discuss the basic working of a vapor absorption chiller. Skip to quiz!
Introduction
Recall that chiller systems produce cold water using a basic refrigeration cycle. There are also chillers that do not run on a basic refrigeration cycle. These are called vapor absorption chillers.
In vapor absorption chillers, vapor refrigerant is absorbed instead of compressed. These systems contain all the main components of the basic refrigeration cycle other than a compressor.
Vapor absorption chiller systems are named after the cycle which they work on. In these systems, the compressor is replaced with an absorber, pump, and generator.
The main components of the vapor absorption chiller system are:
Evaporator,
Absorber,
Pump,
Generator,
Condenser, and
Metering device,
Let us see a video to understand the working of these components briefly.
Recall that refrigerant is a substance that changes from liquid to vapor and vapor to liquid to provide cooling. An absorbent is a substance that absorbs the vapor refrigerant.
Vapor absorption chiller systems most commonly use ammonia as refrigerant and water as absorbent. In large commercial applications, they may use water as a refrigerant and lithium bromide as an absorbent.
The refrigerants used in vapor absorption chillers do not contribute to global warming and ozone depletion. They do not consume electricity to produce cold water. They do not make much noise and vibration since there is no compressor.
Vapor absorption chillers’ initial cost is high. These are too large as they consist of an absorber, pump, and generator. The efficiency of these chillers is less compared to air-cooled and water-cooled chillers of the same capacity.
Vapor absorption chiller systems do not run on a basic refrigeration cycle. In vapor absorption chillers, vapor refrigerant is absorbed instead of compressed. In these systems, the compressor is replaced with an absorber, pump, and generator.
Vapor absorption chiller systems most commonly use ammonia as refrigerant and water as absorbent. The refrigerants used in them do not contribute to global warming and ozone depletion. Vapor absorption chillers’ initial cost is high.
Question #1: The pump head is measured in ______.
Meters
Liters
Kilograms
Volts
Scroll down for the answer...
Answer: Meters
The pump head is the height to which a pump can raise water straight up. It is measured in meters.
Question #2: Delta T means the _________ difference between two points.
temperature
pressure
humidity
voltage
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Answer: temperature
Delta T means the temperature difference between two points.
Question #3: Which of the following condition indicates the proper working of the chiller system?
High delta T
Low delta T
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Answer: High delta T
High delta T condition indicates the proper working of the chiller system.
Question #4: Low delta T increases the efficiency of the chiller system.
True
False
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Answer: False
Low delta T reduces the efficiency of the chiller system and consumes more energy.
Question #5 GPM tells how many gallons of water flows through a pipe in ______.
a second
a minute
an hour
a day
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Answer: a minute
GPM is abbreviated as gallons per minute. It tells how many gallons of water flows through a pipe in a minute.
Question #6: Which of the following component protect the motor from excessive winding temperature?
Antifreeze thermostat
Motor winding thermostat
Water flow switch
LPCO switch
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Answer: Motor winding thermostat
The motor winding thermostat is installed in motors to protect them. It protects the motor from the excessive winding temperature that could lead to damage.
Question #7: Which of the following component is attached to the variable speed motors like secondary pumps in cold water piping?
Motor starter
VFD
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Answer: VFD
Secondary pumps are variable speed pumps. We use VFDs for these pumps.
Question #8: Where can we find 3 phase electrical motor in chiller systems?
Chiller’s compressor
Water pumps
Fan motors
All the above
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Answer: All the above
In the chiller systems, compressor, water pumps, and fan motor have 3 phase motor has an integral part of them.
Question #9: The vapor absorption chiller systems run on a basic refrigeration cycle.
True
False
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Answer: False
This statement is false. The vapor absorption chiller systems do not run on a basic refrigeration cycle.
Question #10: Which of the following component is not present in the vapor absorption chiller system?
Evaporator
Condenser
Compressor
Absorber
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Answer: Compressor
The compressor is not present in the vapor absorption chiller system.
Question #11: Vapor absorption chiller systems most commonly use _________ as refrigerant, and _________ as absorbent.
lithium bromide, water
water, lithium bromide
ammonia, water
water, ammonia
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Answer: ammonia, water
Vapor absorption chiller systems most commonly use ammonia as refrigerant and water as absorbent.
Question #12: Vapor absorption chiller systems do not make much noise and vibration. What is the reason for it?
They do not have a compressor
They do not use refrigerant
They do not generate cold water
All the above
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Answer: They do not have a compressor
Vapor absorption chiller systems do not make much noise and vibration since there is no compressor.
Question #13: Which of the following is not the disadvantage of the vapor absorption chiller system?
The initial cost is high
Too big in size
Less efficiency
Consume more electricity
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Answer: Consume more electricity
Vapor absorption chiller systems use a heat source to produce cold water. They do not consume more electricity.