Pros and Cons of Air-to-Air Heat Exchangers
Air-to-air heat exchangers are common in various industries, effectively carrying out heat transfer and recovering wasted heat from exhaust air for use in other equipment. Managing thermal energy is particularly important for technological, power, and other utility installations, though it has specific benefits and drawbacks for any application. Before integrating an air-to-air heat exchanger into your systems, learn more about this equipment and its ideal uses.
What Are Air-to-Air Heat Exchangers?
When energy transfers from one piece of equipment to another, or even from one kind of energy to another, at least a portion of that energy transitions to heat. Air-to-air heat exchangers enable thermal energy transfer, exchanging heat between a minimum of two environments of different temperatures. These exchangers use a working fluid like liquid or gas as well as a working surface, with heat transfer occurring between them through a crossflow or a cross-counterflow air stream movement without actually mixing them.
Heat exchangers recover wasted heat from equipment like ovens, dryers, and incinerators and circulate it around tubes containing fresh, cool air. The tubes have thin walls, facilitating heat transfer between the exhaust air and the cooler air, efficiently preheating the cooler air for use elsewhere in a system for more environmentally friendly operations.
Advantages of Air-to-Air Heat Exchangers
There are many benefits of an air exchanger, including:
Cleaner indoor air quality
Regarding ventilation, the air-to-air heat exchanger core uses high-performance filters to ensure healthy, breathable air and pleasant indoor temperatures. In addition to removing pollutants and excess moisture from the air, heat exchangers also effectively eliminate foul smells.
Energy efficiency
Air-to-air heat exchangers recover energy by capitalizing on exhaust airstreams, wasted or latent heat, and passive cooling, lowering your operation’s carbon footprint. These heat exchangers do not utilize any power, which equals lower energy consumption. This makes them ideal for locations in which electricity is inaccessible.
Cost efficiency
Compared to other cooling equipment like air conditioners, heat exchangers are more cost-efficient for thermal management in an enclosed space. Their only moving components are their circulation fans, which leads to energy bill savings.
Disadvantages of Air-to-Air Heat Exchangers
Conversely, there are potential disadvantages to air-to-air heat exchangers as well, such as:
Leaks and pressure drops
When leaks do develop, allowing two airstreams to mix through a hole in the exchanger, they can be hard to fix, often requiring a full deconstruction. Similarly, when system pressure drops off within a plate heat exchanger, technicians typically have to inspect each plate individually to locate the source of the problem.
Temperature limitations
Air-to-air heat exchangers are only capable of functioning in environments where the external air temperature is less than that of the system’s internal maximum operational temperature. Also, they cannot effectively cool spaces that are already overheated. This can be remedied, however, by using them in combination with other machinery.
Applications of Air-to-Air Heat Exchangers
Air-to-air heat exchangers have applications in numerous industries, including:
Automotive
Corrosion-resistant stainless steel heat exchangers can handle exhaust flow from automotive applications, despite its contaminants. They have applications in incinerator heat recovery for dryer usage, as well as preheated air for ovens that cure paint or other coatings
Air pollution control
Using a heat exchanger can save energy in an air pollution control system by preheating air streams containing volatile organic compounds (VOCs) or precooling air before its introduction into a baghouse. This cuts down on the amount of fuel that incinerators would otherwise use to maintain specific temperatures.
Food and beverage processing
Safety is always a priority in the food and beverage sector. Heat exchangers provide greater control over temperature than other thermal management techniques, facilitating sanitizing. Also, they keep refrigerants like freon separate from consumable goods to safely cool equipment and control panels during manufacturing.
Medical
Medical equipment can generate a fair amount of heat in sealed areas. To solve this, the industry can integrate heat exchangers into healthcare equipment to promote operational efficiency and accuracy, as well as extend the life span of medical devices.
Customized Solutions From PRE-heat, Inc.
Air-to-air heat exchangers are viable options for improving heating and cooling efficiency. By understanding the benefits and drawbacks, you can decide whether or not a heat exchanger is the right solution for your needs.
The team at PRE-heat, Inc. can help. For over four decades, PRE-heat has designed and manufactured customized air-to-air heat exchangers as well as packaged heat recovery systems. If you’re interested in learning more about air-to-air heat exchangers or would like to request a quote for your operation, contact us today.
For more than 40 years, the team at PRE-heat, Inc. has focused on high-performance industrial air-to-air heat exchangers as well Read more
Process heating is critical to a variety of industrial processes, from food manufacturing to pollution control systems. Indirect-fired heaters heat Read more
Every facility loses heat to the atmosphere. In industrial settings, this loss is a significant source of wasted energy and Read more
Many industrial processes create heated air as some type of exhaust or byproduct. Typically, this heated air gets vented outside Read more
- Published in Air to Air Heat Exchangers, Featured
A Look at Heat Recovery Systems
Every facility loses heat to the atmosphere. In industrial settings, this loss is a significant source of wasted energy and money. Recovering even a portion of lost heat allows companies to improve their energy efficiency, save money, and reduce their carbon footprint without altering existing workflows.
In this post, we will cover topics such as important qualities of heat recovery equipment and how to select the right one for your situation and application, including indirect heaters and heat exchangers.
What Is a Heat Recovery System?
Heat recovery systems use the heat energy from outgoing exhaust air to heat fresh incoming air. They typically consist of a heat exchanging unit, blower fans, and separate air flow channels (e.g., ducting or piping). The heat exchanging unit facilitates the extraction and transfer of heat from the outgoing air to the incoming air, the blower fans move the outgoing and incoming air through the channels, and the separate channels prevent cross-contamination between outgoing air and incoming air.
PRE-Heat Offers Several Systems
Dimple-Plate Heat Exchangers
The most versatile, sturdy, and cleanable plate heat exchanger is the Dimple-Plate (DPL) unit. The DPL uses dimples on each plate to maintain plate spacing and increase turbulence while operating at lower pressure drops. Our DPL is an all-welded, plate-type heat exchanger with the strongest primary-seal weld in the industry.
The welded design eliminates cross-contamination (leakage) between the gases. DPL also has a high percentile heat transfer efficiency. Variable plate thickness, spacing, and size are chosen to satisfy system needs while further optimizing performance and cost. Cleaning and inspecting accessible ports are possible.
Shell and Tube Units
All types of VOC abatement or fume incineration, including catalytic, thermal recuperative, and thermal regenerative incinerators, make use of our high quality shell and tube heat exchangers as their primary and secondary heat exchangers. They are also utilized to take away the heat energy from industrial furnaces, kilns, ovens, and dryers of all kinds.
Shell and tube heat exchangers are used for many different applications. They can be placed in the exhaust of the object to be heated, or they can also be placed in the input of the object to be cooled. Shell and tube heat exchangers are available in vertical or horizontal design. When the exhaust air is very dirty, shell and tube heat exchangers are recommended because they don’t need frequent cleaning.
Indirect Heaters
Indirect heaters are most suitable for lower volumes of hot gases being expelled from the facility or if gas temperatures are too low to be used directly in a heat exchanger. Depending on design specifications and operating conditions, they can also achieve higher thermal efficiencies than direct systems at certain flow rates.
Benefits of Heat Recovery Systems
The ever-increasing operating expenses of heating, air conditioning, and ventilation can be significantly reduced by heat recovery from exhaust air.
The advantages of air-to-air heat exchangers are:
- Almost complete segregation of the air streams
- No moving components
- No wear, thus no maintenance required
- Long life and resistance to breakdowns
Who Needs a Heat Recovery System?
Heat recovery equipment is an integral part of the heating, ventilation, and air conditioning systems in buildings. As structures are being built for energy efficiency, they have become more tightly sealed so that natural pollutants cannot escape these structures over time. These natural pollutants can lead to poor air quality inside your building if not expelled from time to time through installing well-thought-out equipment such as the heat recovery system or indirect heater.
Heat recovery systems are important in any industry that uses (or needs) heating, ventilation, or air conditioning systems, such as in car manufacturing and food and beverage processing. The purpose of the heat recovery system is thus two-fold: first, it ensures those natural pollutants can leave the structure, and secondly, it allows companies to achieve their goal of improved energy efficiency as well as a reduced carbon footprint by recovering lost excesses.
Heat loss represents a significant source of wasted energy and money in industrial settings. Recovering even a portion of lost heat allows companies to improve their energy efficiency, save money, and reduce their carbon footprint, all without altering existing workflows.
The end goal of the heat recovery system is to provide the most efficient use of energy possible. When designing a heat recovery system, it’s important to establish these goals upfront to properly reflect what is required. The end-state of a heat recovery system is ultimately determined by the building’s final use and what the people who will live or work in it require. When designing the heat recovery system, be sure to consider these variables.
How We Can Help
Do you need help with designing an indirect heater, heat recovery system, or other industrial heating equipment? Or do you have questions about how to correctly size/configure your components so that they work together seamlessly for maximum energy savings and efficiency? PRE-heat is on hand to answer all of your questions!
Don’t forget to grab your free eBook to gain access to expert information that has helped prior clients choose the perfect heat recovery system for their industry.
For more than 40 years, the team at PRE-heat, Inc. has focused on high-performance industrial air-to-air heat exchangers as well Read more
Process heating is critical to a variety of industrial processes, from food manufacturing to pollution control systems. Indirect-fired heaters heat Read more
Air-to-air heat exchangers are common in various industries, effectively carrying out heat transfer and recovering wasted heat from exhaust air Read more
Many industrial processes create heated air as some type of exhaust or byproduct. Typically, this heated air gets vented outside Read more
- Published in Air to Air Heat Exchangers, Featured
The Top Uses for Indirect-Fired Air Heaters
Process heating is critical to a variety of industrial processes, from food manufacturing to pollution control systems. Indirect-fired heaters heat air for applications where direct contact with combustion products is detrimental to the process or product. Unlike direct heaters, indirect-fired heaters heat process air without contaminating the product with combustion products.
Like a boiler, indirect-fire air heaters create energy by combusting liquid or gaseous fuel in a combustion chamber. The resulting combustion products heat the process air to the desired temperature but are kept separate from the process air by an air-to-air heat exchanger.
Purpose of Indirect-Fired Air Heaters
Single Hot Pass Design
This indirect-fired heater design uses a burner and high-temperature chamber to heat process air as it passes over the heater. Heat is generated by a burner firing into a specially designed high-temperature chamber, which is engineered to radiate. The process air is pulled, or blown, over the heater and heated to the desired temperature. This system is ideal for recirculated air processes like paint booths and smokers. This type of indirect-fired heater is approximately 60-70% efficient.
Multiple Hot Pass Design
These indirect-fired heaters consist of a burner, a combustion chamber, an air-to-air heat exchanger, and high-temperature fans. In this type of heater, the high-temperature fans pull the hot products of combustion, produced by the burner, through an air-to-air heat exchanger heating the process air passing through the other side of the heat exchanger. The hot gasses then reenter the system to create a continuous heating loop. As the process air is separated from the hot gases by the heat exchanger, they are free from products of combustion providing hot, clean air to the process.
This design can heat high volumes of air with more than 90% efficiency. The heater’s efficiency can be further enhanced by installing an air-to-air heat exchanger in the process exhaust system, so clean air can be heated before it enters the main heating chamber. This type of heater is ideal for use in food-grade spray dryers and mineral drying applications.
Applications of Indirect-Fired Air Heaters
Indirect-fired heaters are valued for their ability to rapidly and efficiently heat process air without contaminating processes through direct contact or the diffusion of combustion byproducts into the process. Applications that benefit from indirect fire heaters include:
- Food Manufacturing: Perfect for food-grade applications such as spray dryers for dairy products, produce, and other food products.
- Pharmaceuticals: Incorporated into pharmaceutical manufacturing for heating and drying products.
- Chemical Manufacturing: Used to heat and dry chemicals while preventing the intrusion of contaminants from combustion processes.
- Automotive Paint and Detailing: Used in recirculating systems for painting, lining, coating, and detailing.
- Pollution Control Systems: Heats downstream exhaust to eliminate pollutants without adding additional contaminants to the stream.
- Iron Industry: Used to heat pellets and other products without introducing contaminants that can cause unwanted chemical impurities.
- Printing Presses: Used to quickly and efficiently dry ink on paper products, labels, and other high-volume products.
- Heating Industrial and Commercial Buildings: Ensures clean heated air is circulated in commercial and industrial facilities for a healthier work environment.
Direct vs. Indirect Air Heaters
While direct-air heating is the most common method of industrial heating, it does introduce products of combustion into the process air stream. In applications where the product cannot be exposed to the CO2, CO, NOx, H2O, SOx, or particulate produced during the combustion process, an indirect air heater is the only option.
Cutting-Edge Air-to-Air Heating Solutions by PRE-heat, Inc.
PRE-heat, Inc., is a leading provider of air-to-air indirect heating solutions for our customers in commercial and industrial sectors. As experienced fired-heater manufacturers, we leverage our expertise to create economical, efficient, and effective solutions to meet a variety of process heating needs. To learn more about our extensive selection of indirect-fired heaters and custom heating solutions, contact our experts today or request a quote.
For more than 40 years, the team at PRE-heat, Inc. has focused on high-performance industrial air-to-air heat exchangers as well Read more
Every facility loses heat to the atmosphere. In industrial settings, this loss is a significant source of wasted energy and Read more
Air-to-air heat exchangers are common in various industries, effectively carrying out heat transfer and recovering wasted heat from exhaust air Read more
Many industrial processes create heated air as some type of exhaust or byproduct. Typically, this heated air gets vented outside Read more
- Published in Air to Air Heat Exchangers, Featured
How Do Shell & Tube Heat Exchangers Work?
For more than 40 years, the team at PRE-heat, Inc. has focused on high-performance industrial air-to-air heat exchangers as well as packaged heat recovery systems, with a specialization in customized builds and designs. Shell and tube heat exchangers, part of PRE-heat’s extensive product line, are available in several options to effectively carry out heat transfer. Learn more about what these heat exchangers do and how they do it.
What Is the Purpose of Shell & Tube Heat Exchangers?
Shell and tube heat exchangers recover energy from the heat of equipment like furnaces, ovens, kilns, and dryers. They also serve as primary and secondary systems for heat recovery with volatile organic compound (VOC) abatement systems or fume incinerators. In furnaces, properly functioning heat exchangers prevent unsuccessful fuel combustion, which would lead to harmful levels of carbon monoxide in the air. They’re also helpful in industries like pharmaceuticals, food and beverage, and petrochemical for offering thermal control in things like tank heaters, condensers, process coolers, and more.
Among their strengths is the fact that their design allows them to accommodate higher levels of pressure as well as extreme temperatures, particularly as compared to other varieties like plate and wheel exchangers. They also maintain reliable performance in environments that might challenge other systems, such as locations with high volumes of dust in the air. These heat exchangers are easy to clean and maintain, all while providing superior thermal transfer.
Types of Shell & Tube Heat Exchangers
It is typically simple to build various tubular heat exchanger subtypes because of the versatility of available shell, tube, and front and rear header arrangements, making these exchangers a common choice for design engineers in the process industry. Some exchanger options include:
Fixed tube sheet exchanger.
The economical structural design of this exchanger is simplistic with the tube sheet fused to its shell. This makes chemical or mechanical cleaning of the tubes possible, though the external surface of the tube is inaccessible for all except chemical cleanings.
Free Floating Tube heat exchanger
Unlike the design of fixed tube sheet exchangers, Free Floating Tube heat exchangers are structured so that each tube within the exchanger can grow separately from the rest.
U-tube heat exchanger
The U-tube design in this exchanger enables limitless thermal expansion. The tube is straightened or bent into a U configuration, hence the name. The front header can have any design, but the rear header is M-shaped. Cleaning can be challenging, so these heat exchangers are ideal for tasks with clean tube-side fluid. Like floating heat exchangers, U-tube heat exchangers have the option for removable bundles.
How Do Heat Exchangers Work?
Shell and tube heat exchangers are made up of a metal enclosure, or shell, acting as a pressure vessel with hollow, bundled metal tubing passing through it as part of a compact design. They work by transferring heat safely from point A to point B. To achieve this, they utilize thermal exchange and transmit warmth between two working media like liquids, gases, or a combination of both through tubes installed in the cylindrical case. The temperatures of the two materials are different than each other, and this variation is what drives the transfer of heat.
Using furnaces as an example, while burning propane fuel or natural gas, a furnace exhaust’s by-product, or its flue gas, passes through the heat exchanger. Since the flue gas is hot, it warms the metal as it moves through the system and, ultimately, a furnace’s exhaust outlet. While this is occurring, the metal’s heat warms the air surrounding the heat exchanger’s exterior surface. In high-efficiency furnaces, there will also be a secondary heat exchanger, in which the heat from the flue gas helps to generate water vapor which is a catalyst for greater latent heat release. This will make the furnace more efficient.
Shell & Tube Heat Exchangers From PRE-heat
Among its many offerings, PRE-heat’s product line includes our rugged air-to-air industrial shell and tube ALT-imate heat exchanger for excessive temperatures and dirty exhaust air streams as primary and secondary heat exchangers. In vertical or horizontal options and a variety of other configurations, they have applications in furnaces, ovens, kilns, and dryers of virtually all kinds.
Our company uses square, triangular, and rotated square and triangular tube patterns, among others. With partial or full baffles, we also utilize multiple shell side flow and tube side passes. This gives our team the flexibility to custom design an exchanger for your specific space and performance needs. PRE-heat’s quality systems can withstand temperatures and air pressures of as much as 1,800° F and 25 psi, respectively.
Contact us today or request a quote to learn more about how the PRE-heat team can develop and construct a shell-and-tube heat exchanger that complies with your unique specifications.
Process heating is critical to a variety of industrial processes, from food manufacturing to pollution control systems. Indirect-fired heaters heat Read more
Every facility loses heat to the atmosphere. In industrial settings, this loss is a significant source of wasted energy and Read more
Air-to-air heat exchangers are common in various industries, effectively carrying out heat transfer and recovering wasted heat from exhaust air Read more
Many industrial processes create heated air as some type of exhaust or byproduct. Typically, this heated air gets vented outside Read more
- Published in Air to Air Heat Exchangers, Featured
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