Introduction to Commercial Systems: Chapter 3
Residential vs Commercial: Controls and Electricals
In this module, we will take a look at the controls of commercial HVAC systems.
We’ll also learn about electrical components present in common commercial HVAC systems. Skip to quiz!
Controls
Recall that HVAC control systems are used to control the heating, ventilation, and air conditioning processes in equipment. Control systems gather information in the form of inputs, process this information, and control an output. They are essential for systems to remain stable and within safe working limits.
The most common control components are:
Thermostats,
Sensors,
Solenoid valves,
Fan speed controls, and
Control Boards.
Apart from basic controls, commercial systems have additional control components in them for more precise control. These include:
Humidity controls,
Building Automation Systems,
Air volume controls, and
Economizer controls.
In commercial systems, we need to control the heating or cooling load of multiple places. For that, we need a thermostat and sensor installed at each location.
Recall that economizers are used in commercial systems to provide cooling by way of outside air. We need to control the economizer as per the cooling or heating load demand of a commercial system. Similarly, we control humidity and airflow in a commercial system.
Commercial systems need control components that can control system operations automatically. Building Management Systems (BMS), also called Building Automation Systems (BAS), automatically control commercial systems. We’ll learn about the control components of commercial systems in later courses.
Electricals
Recall that electric components are connected in a circuit. Different power sources power the circuit of an HVAC system. We also make use of different electrical components in HVAC systems.
Recall that the electrical components used in a common residential HVAC system are:
Circuit Breaker,
Relay,
Transformer,
Contactor,
Starter,
Capacitor, and
Solenoid valves.
Recall that we need to control the heating and cooling of more than one room in a commercial system. We require more electrical components to regulate the operations of heating, ventilation, and air conditioning equipment.
Along with the primary components of a residential system, the following components are present in commercial systems:
Busbar,
Switch gears,
Motor Control Center, and
Ring Main Unit.
These are mainly used to handle the high amount of power required by these systems.
In the USA, homes are powered by 120-volt electricity. This is why electric wires for a residential system can be made thinner. A commercial system is powered by 240 volts. These high-voltage cables are thicker than the wires of a residential system.
We use single-phase power for a residential system, since the load requirement is less in residential units. A three-phase power supply is used to power commercial systems. We will go over each of them in the next presentation.
Commercial systems need control components that can control system operations automatically. Electrical components that can handle high power are essential in commercial HVAC systems to heat and cool.
Three-Phase Power
In this module, we will learn about three-phase power supply. We’ll also discuss the application of three-phase power and its advantages. Skip to quiz!
Single Phase Vs Three Phase
Home appliances are small household electrical machines like washing machines, air-conditioners, and refrigerators. Commercial appliances are heavy-duty machines built specifically to handle high loads. They assist in tasks like cooking, cleaning, and food preservation on a larger scale.
The power supply needed to run any electrical appliance can be classified as:
Single-phase power, or
Three-phase power.
Residential appliances generally use single-phase power. Commercial appliances mostly use a three-phase power supply. As commercial appliances are built to provide high output, they need a high power supply and better control systems.
Recall that there are two types of current: AC and DC. DC circuits use a constant value of current, and AC circuits use waves of current.
“Phase” comes from studying the sine wave. Current flows in a sine wave in an Alternating Current (AC) circuit. The phase of a sine wave is the distance between its actual starting point shown in blue and the ideal starting point shown in red in the image.
A single-phase power uses a single current source of AC power. The power output of a single-phase is constantly fluctuating. The image to the right shows the fluctuating sine wave of a single-phase power supply.
A three-phase motor uses three current supplies. Instead of a single sine wave, we now have three sine waves, and all spread out to reach peak current at three times the single rate. That’s why the power output of a three-phase power remains constant, and it never drops to zero.
A three-phase motor is a rotating machine that is designed to operate on a three-phase supply. A three-phase power supply can transmit consistent and higher power than a single-phase power supply. This makes them suitable to handle the higher loads required for commercial appliances.
Three-phase motors are used in all commercial HVAC applications. For example, water pumps used for commercial chiller systems run on a three-phase motor.
Most home appliances, including fans, heaters, televisions, refrigerators, and lights, require only a small amount of power to function. That’s why we prefer single-phase supply over three-phase to run household appliances.
A single-phase uses two wires, while a three-phase power requires four wires. Because of this, a single-phase power supply requires fewer conducting materials and wires to transmit and distribute electrical power.
A single-phase power supply is easier to get and install. Single-phase connections are easy compared to three-phase power connections.
Since single-phase systems deliver fluctuating power, motors tend to experience more vibration. The constant supply of three-phase systems results in a more stable performance.
Single-phase motors cannot start by themselves and require external devices. For example, a capacitor is needed to start a single-phase motor in a fan. On the other hand, a three-phase motor can start with the power supply alone.
The power output of a three-phase power remains constant, and it never drops to zero. A three-phase motor is a rotating machine that is designed to operate on a three-phase supply. Three-phase motors are used in all commercial HVAC applications.
Question #1: Which of the following is not a control component of HVAC?
Thermostat
Sensor
Compressor
Solenoid Valve
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Answer: Compressor
Compressors are one of the primary components of the refrigeration cycle.
The most common control components are thermostats, sensors, and solenoid valves.
Question #2: Which of the following control component is not present in a residential system?
Thermostat
Building Automation Systems
Sensors
Solenoid Valve
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Answer: Building Automation System
Building automation system is only present in commercial unit for automatic control.
Question #3: A commercial system requires only one thermostat to monitor the temperature of commercial space.
False
True
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Answer: False.
The temperature in each room is monitored in commercial system.
We require multiple thermostats for this purpose.
Question #4: A commercial system can be controlled automatically.
False
True
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Answer: True
Building automation systems are present in commercial units for automatic control.
Question #5: Low voltage, thin wires are used for both residential and commercial systems.
False
True
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Answer: False.
Thin wires are only used in a residential system. A commercial system is powered by 240 volts. These high-voltage cables are thicker than the wires of a residential system.
Question #6:Commercial appliances require less power to operate than residential appliances.
True
False
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Answer: False.
As commercial appliances are built to handle high output, they are readily equipped with robust controls and a high power supply.
Question #7:A three-phase power supply can transmit fluctuating power.
True
False
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Answer: False.
The power output of a three-phase power remains constant, and it never drops to zero.
Question #8:Where do we use three-phase motor?
Commercial HVAC system
Home appliances
Both commercial and home appliances
Capacitors
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Answer: Commercial HVAC system
Three-phase motors are used in all commercial HVAC applications.