HVAC System And Controls | HVAC Controls | Control Strategies

HVAC System

Heating and cooling are the purpose of an HVAC system in both residential and commercial buildings. As a result, you can spot several HVAC systems in several places, from single-family houses to submarines, and provide environmental comfort.

These systems, which are becoming increasingly common, utilize fresh air from the outside to produce the best indoor air quality.

What does an HVAC control? The HVAC system is responsible for providing indoor air comfort and influencing energy consumption. It has a control system that regulates temperature, humidity, and ventilation. The control also has various components in an electronic HVAC system.

Many people understand how an HVAC system works, but only a few are aware of the controls. This post can assist you regardless of whether you are new to the HVAC sector or want to learn more about energy usage.

This article will be your starting point for understanding more about these systems and how they operate.

HVAC System And Controls

Heating, Ventilation, and Air Conditioning include everything from your home’s air conditioner to large systems found in industrial complexes and apartment buildings.

The goal of the best HVAC system is to provide temperature management and indoor comfort. Furthermore, it should utilize thermodynamics, fluid mechanics, and heat transfer concepts.

The large air conditioner boxes on top of apartment buildings or workplaces are examples of (the visible component) HVAC systems.

Large industrial structures, skyscrapers, apartment towers, and large interior spaces are the usual places to find them. They’re also necessary for locations where health standards mandate proper stability in temperature and humidity at specific levels.

Your home’s heating and cooling systems, however, are also HVAC systems. Therefore, they may take diverse forms. However, many fundamental principles governing how they work apply from small personal devices to large commercial installations.

Among the most crucial parts of an HVAC system is the control. And since this is not discussed more often than the other components, only a few know about it.

Most large HVAC systems use system controls to make indoor temperatures more suitable. It also plays a role in the ease of overall system control.

Furthermore, controls are also known as building automation or energy management systems. But this term is only applicable to huge facilities, businesses, or houses.

How Does An HVAC System Work

Your HVAC is likely one of the most intricate and extensive in your home. Furthermore, you’ll know when it breaks down quickly! In terms of delivering adequate indoor air quality and thermal comfort, the three major tasks of an HVAC system are intertwined.

You have to be aware of at least the most fundamental HVAC system components to understand controls.


Coils cool the air as it goes through with the help of the refrigerant. These are often outside of the unit. Check your HVAC coils at least once a year. In addition, you should check your filter or refrigerant levels if they freeze.


Warm air is drawn into the main section of the unit by the blower. The more effectively this air moves through your system, the longer it will last.


Ducts are air delivery and removal conduits or passageways used in heating, ventilation, and air conditioning (HVAC). Return air, supply air, and exhaust air are examples of required airflows.

In addition, as part of the supply air, ducts frequently deliver ventilation air. Here is a tip. To maintain everything in working order, have your ducts cleaned every 2 to 5 years.

Electrical Elements

This section of your system can be a little tricky, but it’s where most problems start. Check for dead batteries or a tripped breaker in your thermostat if something isn’t operating the way it should be.

Air Return

The portion of your system that signals the start of the ventilation cycle is your air return. This return takes in air, filters it, and then discharges it into the system. Dust your returns regularly since debris and dust can readily accumulate on your filters.


The filter draws the air, which is the second stage of the air return. To keep your system in peak form, make sure to change your filters regularly.

Exhaust Outlets

The exhaust outlets, where the exhaust created by the heating system is released, are another component of your system. Check your chimney flue or vent stack at least once a year, and tune it up if necessary.

Outdoor Unit

When someone discusses an HVAC system, this is most often the part of your system that comes to mind. The fan that generates airflow is in the outdoor unit. Keep your HVAC unit clean of garbage and grass, as plants sucked into your fan can create difficulties.


The compressor is responsible for turning refrigerant from a gas to a liquid. It is also responsible for sending it to the coils as part of the outside unit.

Check your compressor if something doesn’t seem to be working the way it should be. Many system failures are often a result of a broken compressor.

HVAC Controls

Building Automation Systems

Mechanical systems at huge facilities are frequently complex, and they must operate efficiently to be effective and not waste energy. HVAC, lighting, fire alarm, and access/security systems are examples of equipment managed by building automation systems (BAS).

Most people nowadays desire to design sequences of processes to make advanced buildings. Having these consolidated under one software platform might be beneficial.

Yet, some building operators see this as putting “all their eggs in one basket.” Therefore, we’ll stick to stand-alone HVAC control systems for this essay.

To make things simple, we’ll divide a typical BAS into four primary categories:

  • Head-end computer/software
  • Network Infrastructure
  • Controllers
  • End Devices

As you learn more about HVAC controls, you’ll see that many pieces of equipment fall into more than one of these categories. Nonetheless, we’ll try our best to stick to simple examples for each.


A device that connects to the network infrastructure and allows end-users to monitor and control their devices.

End Devices

Examples of the end devices:

  • Sensors that measure the value of a variable like a temperature or humidity
  • Relay switches that open and closed circuits
  • Actuators that turn energy into mechanical force

There are many different types of end devices. These are only a few examples.

Head-End Computer/Software

A workstation, the front-end, or energy management software describes the head-end computer/software. i is the main user interface. It lets an operator see what’s going on in the field and transmit commands as needed.

Based on monitoring the system inputs, users can see the effects of the control signals delivered.

For example, the zone temperature will drop if an air duct damper was previously closed and commanded to open. This is because it reacts that way as a result of the control command.

Network Infrastructure

The network architecture of a modern HVAC control system is from CAT-5/6 Ethernet and RS-485 twisted pair wires. The CAT 5/6 uses an ethernet line to send and receive messages from the controllers.

On the other hand, the RS-485 cables are responsible for the communication between the controllers and field equipment.

These four components work together to create an HVAC control system. Its purpose is to assure occupant comfort and safety while consuming as little energy as feasible.

HVAC Control Strategies

To satisfy part-load situations, it uses the simple control of an HVAC on/off control. The system runs for around ten minutes, turns off for ten minutes, and cycles on again.

However, it only does that if the building requires half of the energy that the system is supposed to deliver. Therefore, the system runs longer and has a shorter off period as the building load grows.

Short-cycling is an issue with this form of control. It keeps the system running inefficiently and wears out the component quickly. For example, it takes several minutes for a furnace or air conditioner to reach steady-state operation.

You may wonder why not merely prolong the time between starts to avoid short-cycling? This cycle is doable, albeit at the cost of some temporary discomfort. The more the temperature changes in space, the longer the period between cycles.

Modulation or capacity of the chiller establishes a compromise. This compromise provides enough comfort without excessive wear on the equipment.

For example, in a heating furnace, fuel is delivered to the HVAC furnace at half the design rate. Thus, the amount of energy delivery is proportional to the amount of energy demanded.

While this system is superior to cycling, it is not without flaws. The turn-down ratio of equipment is limited. Only 20% of the rated capacity of a furnace with a 5:1 turn-down will be available for use.

Cycling would still have to be employed if the building demand was low. Staging is an alternative way of control in part-load situations. Instead of one large unit, owners install several small ones.

When the situations only intend half of the capacity, installers only use two units. Two units are base-loaded (run constantly) at 60 percent load. And a third unit swings as needed – it can either be cycled or modulated.

Sequencing usually occurs to alter the unit cycle to prevent excessive wear. For example, assume Unit 3 has just cycled on to continue the scenario at 60% load and Units 1 and 2 are base-loaded.

Unit 1 cycles off when the cycling load portion is satisfied, while Units 2 and 3 become base loaded. Unit 4 comes on when more capacity is required, and so on.

Types Of HVAC Controls

Direct Digital Controls (DDC)

Large buildings require complex controls to maintain pleasant temperature and humidity levels while being efficient and dependable. Many industrial, commercial, and other structures, including schools, residential complexes, and office spaces, use DDC systems for this purpose.

DDC systems allow you to define distinct temperature zones, plan and automate system operation, and track performance over time. This system is best in giving you more exact control over HVAC and lighting operation.

Installing a DDC control system if your building doesn’t already have one could be a good investment.

Allow the SitelogIC team to assist you in determining what would work best for your needs. It will help you develop a plan that will meet your operational needs.

Operating Principles Of DDC

DDC systems have a central computer workstation that uses several sensors to monitor HVAC, lighting, and other system functions.

These sensors send data back to the workstation, where sophisticated software keeps track of performance and makes modifications as needed.

Its function is building automation and systems integration. For example, staff may monitor HVAC system performance in real-time and make manual program modifications as needed from the central workstation.

Furthermore, DDC systems also allow personnel to respond to unusual conditions, fix faults, and perform simple maintenance. All from a single point with system-wide visibility.

Benefits Of Direct Digital Control Systems

Building owners, maintenance workers, and facility managers benefit from DDC and other building automation systems. For example, a well-designed DDC system will do the following:

  • Respond rapidly to changes in the environment, resulting in more consistent temperatures and, ultimately, better occupant comfort all year.
  • Increase energy efficiency by implementing programmed operation sequences.
  • Maintain low operating expenses by ensuring that HVAC systems are operating at maximum efficiency.
  • Automate simple lighting and HVAC activities on a set timetable to reduce workloads.
  • Assist with diagnostics, saving downtime, and informing you when maintenance is required.
  • Retro-commissioning becomes easier since each piece of equipment and system is available for swapping without costly infrastructure modifications.

Pneumatic HVAC Controls

The pneumatic control HVAC system is vastly not appreciated in the engineering world. However, they are utilized in several applications globally, some of which we wouldn’t be without today.

Pneumatics is a branch of engineering that involves compressed air or gas to conduct and control energy. These work like hydraulic systems.

However, instead of moving water, they move compressed air and gases. Regular practice uses these complex pneumatic devices, and it uses pressurized air to operate HVAC systems.

Many industries use pneumatics controls, from big manufacturing warehouses to factory applications. These industries perform a variety of duties and are easy to modify for small and easy chores.

Due to the repeating motion that the device performs, these devices are ideal for use in heavy machinery.

Principles Of Pneumatic Controls In HVAC Systems

Pneumatic control systems use gas or pressurized air to regulate HVAC systems. The pressurized air from a controller is carried to the control device.

It is usually a valve actuator or damper via plastic tubes and copper. This control also uses thermostats and sensors that hold or leak the line pressure from the sensors to the actuator and control device.

Each sensor responds to humidity changes, temperature, and static pressure and feeds data back to the control loop.

Then, it opens or closes the actuator to meet the controller’s set point. Thus, spring and diaphragm actuators work in specified order without the usage of control signals.

This technology uses compressed air for communication. Multiple airlines from the main supply of compressed air and valves have connections to every pneumatic control system.

Benefits Of Pneumatic Control System

There are numerous advantages of a pneumatic instrument, which the modern world still uses with several applications.

  • Pneumatic systems are excellent for working situations exposed to radiation and high temperatures. They are also resistant to the majority of natural elements.

  • Other compressed gases are also part of a pneumatic system. This one is advantageous in applications that use natural gas as a power source. For pneumatic devices, compressed natural gas can create a way for an alternate power source.

  • Pneumatic systems are also viable due to their fast transmission speed and efficient power supply.

  • Because atmospheric air is copious and freely available, it may be used as a power source indefinitely.

  • A pneumatic system automatically purges compressed air. It keeps the instrument clean and free of pollutants that could damage or prevent the system from working.

  • A pneumatic system is simple to operate and maintain.

  • The intrinsic safety of a pneumatic system is one reason why industrial equipment uses this control system. In addition, a pneumatic system will not generate sparks that ignite gases because it does not rely on electricity for power or energy.

    As a result, pneumatic systems are beneficial in mining equipment, factory equipment, and other hazardous working settings.

Overall Benefits Of HVAC Control System

The purpose and advantage of HVAC controls are to provide a comfortable atmosphere for building occupants. You can practically remove hot/cold spots by combining input data with the precise management of a DDC system.

The operation of a business facility’s HVAC system accounts for roughly half of its total energy consumption.

Facility managers can dramatically reduce their energy expenditures and overall environmental impact by implementing management systems that reduce energy consumption.

Another significant benefit that these systems bring that has traditionally gone unnoticed is safety. People seek to provide a healthy atmosphere for all building inhabitants. So, being able to control the air quality of a facility is more vital than ever.


Understanding the building, HVAC systems, room utilization to be conditioned and regulated is the first step in using HVAC controls. And the only way to determine the control sequencing is through the HVAC system type.

The simple control sequence can then be performed by several control products, including pneumatic, electric, analog electronic, and electronic direct digital control (DDC).

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