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Heat Exchangers: What They Are and How They Work

Heat exchangers are integral to modern life, but unless you work in an industry that relies on them, you probably spend little time thinking about them despite the fact that you likely have a heat exchanger in your car, furnace, refrigerator, and even computer. Heat exchangers do exactly what the term suggests: they exchange heat. They can be used to exchange heat in order to make something warmer but also to make it cooler. A heat pump is an example of a common residential AC/Heat technology that requires multiple heat exchangers in order to both heat and cool.

How Heat Exchangers Work

There are various styles of modern heat exchangers in use. In this initial section, we will explore how the concept works in a more general sense without getting into specifics.

From a scientific perspective, heat exchanging is the transferring of heat energy from one medium to another. Heat exchangers are often used to transfer that heat to or from a liquid or a gas. A traditional heat pump transfers heat from the outside air to inside the home. It is also able to transfer heat from inside the home to the outside. This kind of equipment is called an air-source heat pump. An alternative is a ground-source — also known as geothermal — heat pump, and this type does not use a liquid or a gas. A geothermal heat pump exchanges heat with the earth as opposed to the ambient air.

Uses for Heat Exchangers

Heat exchanges are used to exchange heat, a process that has a wide range of applications. Your furnace includes a heat exchanger that it uses in the process of generating heat. If it is a high-efficiency model, it may have a second heat exchanger to recapture energy that would otherwise be lost. But as mentioned in the introduction, heat exchangers are not only used in the process of providing heat but in taking it away. An air conditioner often has two heat exchangers — an evaporator and a condenser — that it uses to cool. Your refrigerator has a heat exchanger as well. All of your computing devices have heat exchangers, too. They tend to be more basic and passive, but they are a type of heat exchanger.

Types of Heat Exchangers

One of the most prevalent types of heat exchangers is shell and tube. These heat exchangers transfer energy between tubes that are contained within an enclosure. The basic design is rather simple, but there are also shell-and-tube designs that are quite advanced with multiple stages.

Plate and frame heat exchangers are highly efficient and very prevalent. In this approach, hot fluid is passed over a plate. This is the type of heat exchanger used in a furnace, but there are also more advanced versions of this approach, such as those use in the pasteurization process.

Heat Exchanger Materials

A wide range of materials can be used for heat exchangers, and the optimal material often depends on the application. Metal is often used because it can absorb and conduct heat quickly. Ceramic is a popular choice and is often used when there are temperatures that would melt metal or when the process must employ abrasive or corrosive fluids that would undermine the metal. Heat exchangers can be made from polymers in addition to composite materials that can be based on either ceramic or metal. The heat exchanger that you will find in most furnaces is made from stamped sheet metal.

Health Risks Associated With Heat Exchangers

The process of exchanging heat does not inherently pose health risks. However, heat exchangers often contain fluids that do present health risks. The heat exchanger in a home furnace, for instance, contains flue gases, and a component of flue gas is carbon monoxide. If the heat exchanger is compromised, it could release carbon monoxide into the home, which can lead to poisoning. This is why most local ordinances require carbon monoxide detectors to be installed in a home with a new furnace.

Primary Heat Exchangers

Within the context of furnaces, the primary heat exchanger contains the hottest flue gas. It is often positioned close to the burner. It is also subject to intense flame and heat and thus a great deal of stress. This stress is why holes can form and heat exchangers can even crack over time. Furnaces that have an AFUE rating lower than 90 will generally have a primary heat exchanger only.

Secondary Heat Exchangers

High-efficiency furnaces are becoming more prevalent. These units have an AFUE rating of at least 90, and a couple of manufacturers recently released models with an AFUE of 98. A key way that these higher-efficiency ratings are reached is by having a secondary heat exchanger. Combustion is the process through which inefficiency occurs in a furnace. In a high-efficiency model, combustion exhaust flows into a secondary heat exchanger that converts water vapor into a liquid, and that process releases latent heat. This process is, in effect, recapturing some of the energy that would typically be lost in combustion.

Heat Exchanger Maintenance

There are a number of excellent reasons to schedule seasonal heating maintenance. Your warranty requires it. The technician will clean your unit, correct any wear and tear, and identify issues before they manifest into serious problems. The industry estimates that a comprehensive furnace tune-up can improve efficiency by as much as 30%. This can actually save you money over the course of a heating season. Cleaning a heat exchanger requires specialized tools and is essential to maximizing your equipment lifespan. Be mindful that if a heat exchanger fails, it is often necessary to replace the entire unit. Therefore, any money you spend in maintenance will be well worth it in terms of identifying correctable heat exchanger issues before that unit actually fails.

Common Heat Exchanger Problems

A dirty heat exchanger is the most common problem because it puts the heat exchanger under additional stress. Another issue is excess condensation that can result in rust and corrosion. There is also the matter of age-related deterioration. The bottom line is that a heat exchanger will eventually fail due to the intense stress that it is under throughout a heating season. However, basic maintenance like having it cleaned will extend that lifespan.

Your Local Heating Pros in Tucson

Rite Way Heating, Cooling and Plumbing is a locally owned and operated AC/Heat and plumbing company that has served Tucson and the surrounding areas since 1959! Our company has been established in this region for more than 60 years, and many of our customers have been with us for decades. Our certified technicians install, maintain, and repair furnaces, heat pumps, and other heating equipment. We also install, maintain, and repair air conditioners. Our team works with ducted and ductless systems in addition to units that use electricity and natural gas. We perform energy audits. We clean ducts and install indoor air quality equipment, and our plumbing services range from clog repairs to whole-home re-piping. Call us today or contact us online to schedule an appointment.