HVAC control system

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HVAC (Heating, Ventilation and Air Conditioning) equipment needs a control system to regulate the operation of a heating and/or air conditioning system. Usually a sensing device is used to compare the actual state (e.g. temperature) with a target state. Then the control system draws a conclusion what action has to be taken (e.g. start the blower).

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Direct digital control

Central controllers and most terminal unit controllers are programmable, meaning the direct digital control program code may be customized for the intended use. The program features include time schedules, set points, controllers, logic, timers, trend logs, and alarms. The unit controllers typically have analog and digital inputs that allow measurement of the variable (temperature, humidity, or pressure) and analog and digital outputs for control of the transport medium (hot/cold water and/or steam). Digital inputs are typically (dry) contacts from a control device, and analog inputs are typically a voltage or current measurement from a variable (temperature, humidity, velocity, or pressure) sensing device. Digital outputs are typically relay contacts used to start and stop equipment, and analog outputs are typically voltage or current signals to control the movement of the medium (air/water/steam) control devices such as valves, dampers, and motors.

Groups of DDC controllers, networked or not, form a layer of systems themselves. This "subsystem" is vital to the performance and basic operation of the overall HVAC system. The DDC system is the "brain" of the HVAC system. It dictates the position of every damper and valve in a system. It determines which fans, pumps, and chiller run and at what speed or capacity. With this configurable intelligence in this "brain", we are moving to the concept of building automation. [1]

Building automation system

More complex HVAC systems can interface to Building Automation System (BAS) to allow the building owners to have more control over the heating or cooling units. The building owner can monitor the system and respond to alarms generated by the system from local or remote locations. The system can be scheduled for occupancy or the configuration can be changed from the BAS. Sometimes the BAS is directly controlling the HVAC components. Depending on the BAS different interfaces can be used. [2]

Today, there are also dedicated gateways that connect advanced VRV / VRF and Split HVAC Systems with Home Automation and BMS (Building Management Systems) controllers for centralized control and monitoring, obviating the need to purchase more complex and expensive HVAC systems. In addition, such gateway solutions are capable of providing remote control operation of all HVAC indoor units over the internet incorporating a simple and friendly user interface. [3]

Cost and efficiency

Many people do not have a Heating, Ventilation, and Air Condition (HVAC) system in their homes because it is too expensive. However according to this article Save Money Through Energy Efficiency, HVAC is not as expensive as one may think it is.[ citation needed ]

This article Save Money Through Energy Efficiency tells us that the main thing to look for when shopping for a HVAC system is to make sure it runs efficiently. One thing to always look for when in the market of a new HVAC system is the energy guide sticker on the machine.[ citation needed ]

Although many might choose to not believe that sticker and that it is just there to help with the sales, history shows that many of the newer HVAC systems with the yellow energy guide stickers help save customers hundreds to thousands of dollars depending on how much they use their HVAC system.[ citation needed ]

On the yellow energy guide sticker on many of the newer systems, it displays the average cost to run that machine. Once a customer has found the perfect HVAC system, the customer should run it monthly if it is only put into use during specific times of year. It is recommended that if an HVAC system is not being used each month, that it should be turned on and left running for ten to fifteen minutes.[ citation needed ]

On the other hand if the customer is somebody who runs their HVAC system frequently, it is really important to maintain it. Maintenance on an HVAC system includes changing out the air filter, inspecting the areas where air intake takes place, and check for leaks.[ citation needed ]

Doing these three steps are super essential and is the key to keeping an HVAC system running for a long time. A customer should do these three steps every couple of months or when it is suspected problem with the HVAC system.[ citation needed ]

Some signs that could lead to a potential problem is if the HVAC system does not provide air cool enough.[ citation needed ]

That could be due to a leakage in the cooling fluids. Another sign that could mean that the HVAC system is not running perfectly fine is if there is a bad smell to the air that it is providing. That often means that the air filters need to be replaced. Changing the air filters on an HVAC system is really important because they are exposed to a lot of dust depending on where your HVAC system is and it could build up dust from simply just sitting in one's home.

Goals HVAC system installation

Source [4]

Goal 1: Keep HVAC equipment and materials dry during construction and provide temperature and humidity control as required during the close-in phase of construction. HVAC System Installation

Goal 2: Install HVAC systems to effectively implement moisture control as specified in the design drawings and specifications. HVAC System Installation

Goal 3: Prepare operation and maintenance materials for continued performance of HVAC system moisture control.

Design, modeling, and marketing

Most HVAC systems are used for the same purpose but designed differently.[ citation needed ]

All HVAC systems have an intake, air filter, and air conditioning liquid. However, when designing HVAC systems, many engineers design it for a specific setting and/or purpose. When engineers are designing an HVAC system, they try their best to make it compact while still being able to perform at the highest level and experiment with different ways to make HVAC systems as efficient as possible. Even through all the hardships that come from designing a HVAC system, many Mechanical Engineers in particular have a passion for doing. Although it may be hard to get your sales after designing a new HVAC system, marketing the product is very important. The biggest concern that customers have when in the market looking for a new HVAC system is price and reliability.[ citation needed ]

History

The first HVAC controllers utilized pneumatic controls since engineers understood fluid control. Thus, the properties of steam and air were used to control the flow of heated or cooled air via mechanically controlled logic.

After the control of air flow and temperature was standardized, the use of electromechanical relays in ladder logic to switch dampers became standardized. Eventually, the relays became electronic switches, as transistors eventually could handle greater current loads. By 1985, pneumatic controls could no longer compete with this new technology although pneumatic control systems (sometimes decades old) are still common in many older buildings. [5]

By the year 2000, computerized controllers were common. Today, some of these controllers can even be accessed by web browsers, which need no longer be in the same building as the HVAC equipment. This allows some economies of scale, as a single operations center can easily monitor multiple buildings.

See also

Related Research Articles

<span class="mw-page-title-main">Heating, ventilation, and air conditioning</span> Technology of indoor and vehicular environmental comfort

Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR.

<span class="mw-page-title-main">Thermostat</span> Component which maintains a setpoint temperature

A thermostat is a regulating device component which senses the temperature of a physical system and performs actions so that the system's temperature is maintained near a desired setpoint.

<span class="mw-page-title-main">Damper (flow)</span> Valve or plate for regulating airflow inside a duct, chimney, vent, etc.

A damper is a valve or plate that stops or regulates the flow of air inside a duct, chimney, VAV box, air handler, or other air-handling equipment. A damper may be used to cut off central air conditioning to an unused room, or to regulate it for room-by-room temperature and climate control -- for example in the case of Volume Control Dampers. Its operation can be manual or automatic. Manual dampers are turned by a handle on the outside of a duct. Automatic dampers are used to regulate airflow constantly and are operated by electric or pneumatic motors, in turn controlled by a thermostat or building automation system. Automatic or motorized dampers may also be controlled by a solenoid, and the degree of air-flow calibrated, perhaps according to signals from the thermostat going to the actuator of the damper in order to modulate the flow of air-conditioned air in order to effect climate control.

<span class="mw-page-title-main">Air handler</span> Device used to regulate and circulate air as part of an HVAC system

An air handler, or air handling unit, is a device used to regulate and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. An air handler is usually a large metal box containing a blower, furnace or A/C elements, filter racks or chambers, sound attenuators, and dampers. Air handlers usually connect to a ductwork ventilation system that distributes the conditioned air through the building and returns it to the AHU, sometimes exhausting air to the atmosphere and bringing in fresh air. Sometimes AHUs discharge (supply) and admit (return) air directly to and from the space served without ductwork

Building automation(BAS), also known as building management system (BMS) or building energy management system (BEMS), is the automatic centralized control of a building's HVAC (heating, ventilation and air conditioning), electrical, lighting, shading, access control, security systems, and other interrelated systems. Some objectives of building automation are improved occupant comfort, efficient operation of building systems, reduction in energy consumption, reduced operating and maintaining costs and increased security.

Direct digital control is the automated control of a condition or process by a digital device (computer). Direct digital control takes a centralized network-oriented approach. All instrumentation is gathered by various analog and digital converters which use the network to transport these signals to the central controller. The centralized computer then follows all of its production rules and causes actions to be sent via the same network to valves, actuators, and other heating, ventilating, and air conditioning components that can be adjusted.

<span class="mw-page-title-main">Variable air volume</span> Heating or air-conditioning system

Variable air volume (VAV) is a type of heating, ventilating, and/or air-conditioning (HVAC) system. Unlike constant air volume (CAV) systems, which supply a constant airflow at a variable temperature, VAV systems vary the airflow at a constant or varying temperature. The advantages of VAV systems over constant-volume systems include more precise temperature control, reduced compressor wear, lower energy consumption by system fans, less fan noise, and additional passive dehumidification.

<span class="mw-page-title-main">Duct (flow)</span> Conduit used in heating, ventilation, and air conditioning

Ducts are conduits or passages used in heating, ventilation, and air conditioning (HVAC) to deliver and remove air. The needed airflows include, for example, supply air, return air, and exhaust air. Ducts commonly also deliver ventilation air as part of the supply air. As such, air ducts are one method of ensuring acceptable indoor air quality as well as thermal comfort.

<span class="mw-page-title-main">Programmable thermostat</span>

A programmable thermostat is a thermostat which is designed to adjust the temperature according to a series of programmed settings that take effect at different times of the day. Programmable thermostats are also known as setback thermostats or clock thermostats.

Constant air volume (CAV) is a type of heating, ventilating, and air-conditioning (HVAC) system. In a simple CAV system, the supply air flow rate is constant, but the supply air temperature is varied to meet the thermal loads of a space.

A control valve is a valve used to control fluid flow by varying the size of the flow passage as directed by a signal from a controller. This enables the direct control of flow rate and the consequential control of process quantities such as pressure, temperature, and liquid level.

oBIX is a standard for RESTful Web Services-based interfaces to building control systems. oBIX is about reading and writing data over a network of devices using XML and URIs, within a framework specifically designed for building automation.

<span class="mw-page-title-main">Fan coil unit</span> HVAC device

A fan coil unit (FCU), also known as a Vertical Fan Coil-Unit (VFC), is a device consisting of a heat exchanger (coil) and a fan. FCUs are commonly used in HVAC systems of residential, commercial, and industrial buildings that use ducted split air conditioning or with central plant cooling. FCUs are typically connected to ductwork and a thermostat to regulate the temperature of one or more spaces and to assist the main air handling unit for each space if used with chillers. The thermostat controls the fan speed and/or the flow of water or refrigerant to the heat exchanger using a control valve.

HVAC is a major sub discipline of mechanical engineering. The goal of HVAC design is to balance indoor environmental comfort with other factors such as installation cost, ease of maintenance, and energy efficiency. The discipline of HVAC includes a large number of specialized terms and acronyms, many of which are summarized in this glossary.

Variable refrigerant flow (VRF), also known as variable refrigerant volume (VRV), is an HVAC technology invented by Daikin Industries, Ltd. in 1982. Similar to ductless mini-split systems, VRFs use refrigerant as the primary cooling and heating medium, and is usually less complex than conventional chiller-based systems. This refrigerant is conditioned by one or more condensing units, and is circulated within the building to multiple indoor units. VRF systems, unlike conventional chiller-based systems, allow for varying degrees of cooling in more specific areas, may supply hot water in a heat recovery configuration without affecting efficiency, and switch to heating mode during winter without additional equipment, all of which may allow for reduced energy consumption. Also, air handlers and large ducts are not used which can reduce the height above a dropped ceiling as well as structural impact as VRF uses smaller penetrations for refrigerant pipes instead of ducts.

Airflow, or air flow, is the movement of air. The primary cause of airflow is the existence of air. Air behaves in a fluid manner, meaning particles naturally flow from areas of higher pressure to those where the pressure is lower. Atmospheric air pressure is directly related to altitude, temperature, and composition.

<span class="mw-page-title-main">Air-mixing plenum</span>

In building services engineering and HVAC, an air-mixing plenum is used for mixing air from different ductwork systems.

<span class="mw-page-title-main">KMC Controls</span>

KMC Controls has designed and manufactured HVAC control system products and building automation systems since 1969. KMC was one of the early privately held controls manufacturer with a full line of digital, electronic, and pneumatic products in the United States. The latest products include BACnet digital controllers and thermostats.

In air conditioning, an inverter compressor is a compressor that is operated with an inverter.

<span class="mw-page-title-main">Register (air and heating)</span>

A register is a grille with moving parts, capable of being opened and closed and the air flow directed, which is part of a building's heating, ventilation, and air conditioning (HVAC) system. The placement and size of registers is critical to HVAC efficiency. Register dampers are also important, and can serve a safety function.

References

  1. ↑ "Role on DDC Systems in Building Commissioning". Archived from the original on 2020-05-06. Retrieved 2009-05-19.
  2. ↑ KMC Controls. "Understanding Building Automation and Control Systems". Archived from the original on 19 May 2013. Retrieved 12 March 2017.
  3. ↑ "CEDIA Find: Cool Automation Integrates Smart Air Conditioners with Third-Party Control Systems". CEPro. Archived from the original on 17 June 2015. Retrieved 16 Jun 2015.
  4. ↑ Moisture Control Guidance for Building Design, Construction and Maintenance. U.S. Environmental Protection Agency. December 2013.
  5. ↑ KMC Controls. "Pneumatic to Digital: Open System Conversions" (PDF). Retrieved 5 October 2015.
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