Uses for air-to-air heat exchangers (AAHXs), types, processes, and manufacturers
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Air-to-air heat exchangers (AAHX) are part of a balanced ventilation system where hot extracted air is recovered and transferred to the incoming air supply. The process allows the heat in the extracted air to be recovered to heat cold fresh air drawn from outside. Air-to-air heat exchangers use a mechanical ventilation system that consists of two fans, with one fan being a supply fan while the other fan is an extraction fan with each fan having its own duct. A heat transfer unit and air flow remove heat.
The major function of air-to-air heat exchangers is to dissipate heat from various types of equipment and replace it with cooled air. It is a closed loop system that is capable of cooling a wide range of equipment without contaminating the air around equipment. Heat exchangers take several forms with the majority of heat exchangers being either plate type or shell and tube type. The closed loop design of air-to-air heat exchangers, with tubes or plates, makes them different from the other forms of heat exchangers.
Air-to-air heat exchangers are an inexpensive method for cooling an area and can be used as a replacement for air conditioning systems. The closed loop cooling system of an air-to-air heat exchanger is ideal for applications where the use of fans is undesirable and air conditioners are too large to be practical. They can be used in sealed enclosures due to their closed loop design.
Air-to-air heat exchangers are a unique and economical method for quietly cooling enclosures. They serve as a viable alternative to air conditioning. The key to the process of an air-to-air heat exchanger is its heat pipe that transfers heat from an enclosure to cooler ambient air. The heat pipe is filled with a special form of refrigerant that boils as the heat pipe absorbs heat.
As with all forms of heat exchangers, there are different types of air-to-air heat exchangers that vary in accordance with the types of elements used to construct them. Industries that rely on air-to-air heat exchangers use them to collect heat energy that is lost during heating applications. The recovery of heat energy helps save on energy costs and increases operational efficiency.
The method used to classify air-to-air heat exchangers is by the way air moves through an air-to-air heat exchanger. The three primary types of air-to-air heat exchangers are plate, tube, and wheel, each of which has advantages and disadvantages and are adaptable to different applications and environments.
With plate type air-to-air heat exchangers, the supply and exhaust air flows are separated by plates, with the supply air flow on one side of the plate while the exhaust air flow moves on the other side of the plate. The exhaust air preheats or pre-cools the incoming air supply and does not allow the airstreams to mix.
Plate air-to-air heat exchangers are divided into cross air flow and counter air flow. The cross form of plate air-to-air heat exchangers transfers heat from one airstream to the other airstream. They have thin aluminum panels that exchange the thermal energy at a thermal efficiency of 40% to 65%. The popularity of cross flow plate air-to-air heat exchangers is due to their low cost. They are normally used in hygienic conditions that require airstreams to be kept separated.
Plate counter air flow air-to-air heat exchangers have the exhaust air flow and fresh air flow passing each other in separate channels. The temperatures of the air flows are interchanged as the incoming and outgoing volume flow is in proportion to one another. As the air flows across one another, cold air is heated to room temperature, as the temperatures in the separate channels equalize. Plate counter air flow air-to-air heat exchangers are exceptionally efficient and have greater recovery as the size of the air-to-air heat exchanger increases. The principle of the process makes them suitable for very large ventilation systems.
Another variation in plate air-to-air heat exchangers is the types of plates, which can be dimple plates or wave plates. The dimple plate form of air-to-air heat exchanger is a very sturdy and rugged form of air-to-air heat exchanger that is used for heavy duty applications. The dimples on the plates make it possible for the heat exchanger to handle low pressure drop and help improve turbulence. The consistent dimple pattern and flatness of the plates make them easy to clean and maintain.
Wave plate air-to-air heat exchangers combine the dimple pattern with a wave pattern, a combination that allows the heat exchanger to have higher turbulence with structural integrity while maintaining low pressure drop. The design of wave plate air-to-air heat exchangers removes the need for gaskets between the plates, makes heat transfer three to four times more efficient, and enables air-to-air heat exchangers to make use of corrosion resistant metals. Wave plate air-to-air heat exchangers are heavy duty with a welded plate type that eliminates cross contamination between gases with a high percentage of heat transfer effectiveness.
Tube type air-to-air heat exchangers have a heat pipe that is an evacuated tube filled with a special type of refrigerant that boils when absorbing heat. Vapors inside the tube rise to the top of the tube to be condensed by cooler air, a process that constantly repeats. Although the process does not require any energy, small fans are used to circulate air inside an enclosure and blow air over the heat pipe. Tube air-to-air heat exchangers are able to handle higher pressures and temperatures than other forms of air-to-air heat exchangers.
The design of tube air-to-air heat exchangers is ideal for dusty environments with high concentrations of particulate matter in the air. Tube air-to-air heat exchangers are commonly used to recover heat from dryers, ovens, kilns, and furnaces and are used with fume incinerators and volatile organic contamination (VOC) abatement systems. The different patterns of the tubes include rotated squares, triangles, squares, and other forms of triangular patterns. Multiple tube side passes and shell side passes can be added to enhance the performance of a tube air-to-air heat exchanger.
Thermal wheel air-to-air heat exchangers, also known as rotary heat exchangers, rotary air-to-air heat exchangers, energy recovery wheels, and heat recovery wheels, are a form of heat exchanger that uses a rotating metal wheel to transfer thermal energy from an airstream to another airstream. The two types of wheel air-to-air heat exchangers are heat wheels and enthalpy wheels, which have a similar appearance but operate differently.
The exchange process for enthalpy air-to-air heat exchangers includes the use of silica gel and molecular sieves with desiccants that transfer moisture through the absorption process created by the difference in pressure of vapor in the opposing airstream. The enthalpy air-to-air heat exchanger has a rotating cylinder that is filled with air permeable materials, such as a polymer, aluminum, or synthetic fibers that provide a large surface area. As the wheel rotates between the airstreams, it picks up heat energy and releases it into the colder airstream. The driving force of the process is the different temperatures between the airstreams.
Heat recovery wheel air-to-air heat exchangers transfer heat between the airstreams as the exhaust airstream removes air and the supply airstream brings in fresh air. Heat transfer happens through the use of a heat absorbing metal. The captured heat energy is transferred to the incoming airstream as the wheel of the heat exchanger rotates. The airstream entering a building is preheated while the exiting airstream is cooled. It is an excellent method for reducing cooling costs. Heat wheel air-to-air heat exchangers can work as a separate piece of equipment or be included in an air handling system.
As with all forms of air-to-air heat exchangers, run around air-to-air heat exchangers have separate air flows. They consist of one heat exchanger in the supply air flow and one in the extract air flow, which are connected by a hydraulic circuit. A mix of glycol and water are used as the transfer fluid.
Known as a coil energy recovery system, run around air-to-air heat exchangers have finned tube water coils in the supply and exhaust airstreams that are connected in a closed loop by counterflow piping through which the heat transfer occurs. A three-way temperature control valve is installed to prevent the coil on the exhaust air flow from freezing. This design enables run around air-to-air heat exchangers to be installed in a wide range of applications. They are particularly suited for large industrial and manufacturing applications due to their high efficiency.
Energy recovery ventilators is a term that is used to refer to air-to-air heat exchangers (AAHX) and ERV systems, which are designed to be connected to HVAC systems in factories, buildings, homes, and offices. ERVs are a complex and complicated air recovery system that removes dirty contaminated air and replaces it with cleaned and refreshing air. A properly designed ERV will remove large amounts of humidity along with dirt air.
Heat recovery ventilation (HRV) is another term that is used to describe an air-to-air heat exchanger that reduces heating and cooling needs, like an AAHX system, of a building or structure. ERV and HRV are terms that are used to identify thermal wheel, plate, tube, and run around air-to-air heat exchangers.
The wide use of air-to-air heat exchangers is due to their low cost and efficiency. They are commonly used in tightly sealed enclosures as a means of cooling electrical systems and not contaminating the air of a system. Air-to-air heat exchangers are essential when heat is generated in an environment, or a system needs protection from external factors.
Control panels and enclosure are designed to protect sensitive technologies. They trap waste heat that is produced by electrical circuits. Air-to-air heat exchangers are an effective and efficient method for collecting the heat that is trapped and releasing it. The use of air-to-air heat exchangers for enclosures and electrical panels helps reduce energy costs and prevents damage to electrical circuits. Air-to-air heat exchangers cool electrical circuits without needing to chill the air in the enclosure.
Paint booths require high quality ventilation systems due to their high temperature air, which can be lost as waste heat. One car can take two or more days to prime and paint. A normal paint booth can paint up to six cars per day, a factor that necessitates a heat recovery solution. Air-to-air heat exchangers are capable of recovering the air from a paint booth and sending it back to sections that require heating. The simple installation and maintenance of air-to-air heat exchangers make them an ideal low cost method for recovering potentially wasted heat.
The two forms of air-to-air heat exchangers for paint booths are plate air-to-air heat exchangers and rotary air-to-air heat exchangers
The process of wood drying is complex and complicated and requires an adaptable heat exchanger capable of meeting the challenges of the wood drying process. The main difficulty with wood drying is the considerable amount of energy the process requires, which is due to the high volume of water that is retained in pieces of wood. The various types of drying kilns produce a great deal of thermal energy that can be wasted if not properly recovered. The use of a heat recovery system can significantly affect the cost of the wood drying process.
The problems associated with wood drying are its high humidity and substantial particle content, each of which has to be carefully considered in the design of a heat recovery system. The ideal solution for wood drying is a crossflow air-to-air heat exchanger, which is capable of extracting the accumulation of wood particles from the wood drying process.
Dehumidifiers are normally used to regulate room temperatures and condensation for various types of conditions. Operational process dehumidifiers have to be more robust and capable of providing controlled and specific humidity levels to ensure the efficient completion of an application. Warehousing and food production necessitate air humidity control to ensure the quality of stored and produced products, with colder climates requiring greater moisture control.
Curtains and doors create energy loss and are major hurdles for the humidity control process. Regardless of the need for a dehumidification system, the energy consumption of a system is a concern due to the cost of the system. A unique approach to the dehumidification problem is to combine a dehumidifier with an air-to-air heat exchanger where captured heat from an air-to-air heat exchanger is fed back into the dehumidification system. The heat from the air-to-air heat exchanger occurs without the presence of moisture. Heat remains in the regeneration process of the dehumidifier, and energy usage is lowered by the air-to-air heat exchanger.
Greenhouses and indoor farms require a strictly controlled environment for the growth of crops, which is a costly energy intensive process. Although HVAC systems are the solution to controlling such conditions but are an expensive high energy solution. Controlled environment agriculture (CEA) has developed technologically advanced methods for caring for crops and maintaining productivity.
A critical aspect of CEA farming is ventilation, which needs to be maintained, controlled, and dependable for optimal growing and acceptable efficiency. The management of temperature, humidity, and CO₂ levels is an essential component since poor and irregular air circulation reduces plant growth and can lead to diseased plants.
HVAC systems that work with air-to-air heat exchangers radically reduce the load placed on the system, which saves energy for cooling and dehumidification and increases system efficiency and effectiveness. As with other forms of air-to-air heat exchangers, common ones that are used for CEA farms are rotary and plate air-to-air heat exchangers that reduce the stress placed on HVAC systems and help lower overall costs.
All commercial buildings require a ventilation system that will maintain healthy indoor air quality (IAQ). As with all forms of modern buildings, the quality of air in a building is dependent on an air handling system and heat exchanger that serves as a heat and energy recovery unit. Contaminants that contain dust, pollen, dirt, and pollutants can lead to disease and breathing problems as well as damage to a building.
Air-to-air heat exchangers provide efficient air quality control by using the temperature difference between the supply and exhaust air. The type and design of an air-to-air heat exchanger for commercial ventilation depends on the application for which it will be used. Air-to-air heat exchangers work with air handling units (AHU) that remove contaminants and particulate matter from the airstream. The combination of an AHU system and AAHX system creates a high air quality.
One of the factors that became apparent at the beginning of the computer era was the need for an environment that had exceptional temperature control with minimal moisture and the absence of any forms of dirt, dust, or particulate matter that could interfere with the function of the computing equipment. The initial solution was a variety of huge HVAC systems that were costly and high energy. As technological advances have been made, the need for an efficient HVAC system has become increasingly important.
Data centers of the 21st century are highly complex and technologically advanced. Keeping such centers operating smoothly requires close monitoring, management, and oversight to ensure they run safely, continually, and efficiently. Air-to-air heat exchangers have become a vital part of the cooling process for data centers by providing indirect cooling using external air that is kept in a separate loop such that it provides cooling without contaminating the server room.
One of the issues facing modern society is the number of pollutants to which citizens are exposed. With the rise of technology, the majority of work performed is completed in enclosed offices and buildings that can contain dangerous VOCs, such as bacteria, viruses, mold, pollen, carbon dioxide, smoke, and formaldehyde. These materials can come from outside or be from furniture, paint, cleaning chemicals, the operation of office equipment, personal care items, air fresheners, pesticides, and personnel.
The results of the presence of VOCs can be sick building syndrome, which can range from personal discomfort to very serious diseases or cancer. Improperly vented and maintained air conditioning equipment can spread different types of damaging and harmful pollutants. When an office space is occupied by hundreds of people for extended periods of time, contaminated air can create unpleasant odors, moisture formation, and different diseases.
One of the challenges that all companies have had to face is forced air ventilation in well insulated buildings. In order to provide a comfortable and pleasing work environment, companies use various forms of HVAC systems that can be helpful when properly installed. Air-to-air heat exchangers are designed to provide safe and reliable ventilation by removing stale contaminated air with its odors, moisture, dust, and bacteria and replacing it with filtered fresh air.
The installation of an air-to-air heat exchanger system resembles that of an HVAC system with the ability to effectively collect and distribute fresh air using a four duct system. The higher efficiency and effectiveness provide a comfortable working environment with uncontaminated high quality clean air.
The few examples of air-to-air heat exchangers is a small sampling of the many ways these highly efficient and economical heat exchangers can be used. Their durability, flexibility, and exceptional performance has made them a reliable form of heat recovery unit that can be used domestically and commercially.
There are many benefits associated with the installation of an air-to-air heat exchanger system, with the cost being the primary one. The goal of many organizations is to provide a staple and clean working environment at an acceptable cost. There are several challenges that organizations face as they work to meet these goals. The typical solution is to install a HVAC system, which is costly due to the system's use of energy. Air-to-air heat exchangers have been found to be instrumental in supplying an efficient solution.
When an air-to-air heat exchanger is performing at peak efficiency, it can transform heat energy from stale air into 99% clean, high-quality air. The process provides an energy efficient solution to ventilating a workspace, office, factory, or home. Energy costs are lowered as a comfortable and controlled temperature is provided.
The addition of an air-to-air heat exchanger to a HVAC system has several benefits. The first noticeable difference is cleaner ductwork and filters, which keeps the HVAC system cleaner. Less maintenance is required and a HVAC system lasts longer. The result of these benefits is lower cost and more efficiency.
As has been emphasized, air-to-air heat exchangers remove contaminants and particulate matter that can be unhealthy and lead to serious diseases. The build up of stale air in a workspace allows for the growth of contaminants and allergens that can irritate airways and drastically lower air quality. The use of an air-to-air heat exchanger removes foul odors and helps circulate clean fresh air.
Moisture can cause the growth of mold and mildew that greatly affect nasal passages and allergies. Air-to-air heat exchangers as energy recovery ventilators significantly lower the presence of moisture by 30% up to 50%, which helps keep a living space comfortable and prevents potential damage.
Whenever a designer is planning a building, their solution to air flow and air handling usually involves the use of a HVAC system. This dependency on HVAC systems has been a necessity for many years and has become a common practice. The use of an air-to-air heat exchanger removes the need for a HVAC system and provides a lower cost solution to providing high air quality.
The simple operational process of an air-to-air heat exchanger removes the need for regular maintenance. In many cases, once an air-to-air heat exchanger is installed, it may require monitoring and management, but, most likely, will not require regular maintenance and repair.
An understanding of the various components of an air-to-air heat exchanger can assist in determining any problems that may arise during its use. The cooling process for an air-to-air heat exchanger is rather simple and includes transferring heat away from a warm area to a cool area. By definition, the process of an air-to-air heat exchanger is heat transfer being the movement of thermal energy from one object to a different object with a different temperature. Included in the process are sealed tubes, normally made of copper, that contain a heat absorbing liquid.
The heat recovery core transfers heat to the supply airstream without mixing it with the exhaust airstream. The warmed air is distributed in an enclosure or space using ducts and circulating fans while the exhaust air is vented. The heat recovery core is the heart of an air-to-air heat exchanger. It can get clogged with dirt or dust and may need to be cleaned.
Fans are responsible for the movement of air in an air-to-air heat exchanger. Depending on the design of an air-to-air heat exchanger system, fans can be placed indoors or outdoors. With air-to-air heat exchangers for enclosures, fans for the system are encapsulated and sealed in the enclosure.
The purpose of filters for air-to-air heat exchangers is to protect the core from the build up of dirt or dust. Hot air that is collected is filtered before it passes through an air-to-air heat exchanger. The incoming outdoor air is filtered as it passes through the heat exchanger. The filtration process assists in ensuring an air-to-air heat exchanger system works smoothly and reduces potential damage to components. Filters for air-to-air heat exchangers take several forms and vary in accordance with the design of the air-to-air heat exchanger unit.
The ventilation system for an air-to-air heat exchanger spreads the supply airstream throughout an enclosure or living space. The system fans push clean air through the ducts of the ventilation system to spread the clean air evenly and uniformly. The ventilation system consists of separate ducts with one set of ducts used to extract air that passes through the air-to-air heat exchanger where energy transfer takes place with fresh filtered air being returned to the enclosure or living space.
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