December 13, 2021
Your heating, ventilation, and air conditioning (HVAC) system consists of many parts, but perhaps none carries more importance than your system’s heat exchanger. The heat exchanger transfers thermal energy from one area or medium to another area or medium. In plain English, that means it takes the hot air from the home and forces it outside in summer; in winter, it takes cold air from the home and forces it outside. This exchange keeps your home warm in the winter and cold in the summer.
Heat Exchanger Defined
Many pieces of equipment have heat exchangers built into them. In a gas furnace or boiler, the heat exchanger absorbs the heat energy. By doing so, it heats up, which heats the water that travels to the radiators. The heat exchanger ensures the heat liquid or gas from a fluid can pass to a second gas or fluid without mixing together or directly contacting one another. So, this device transfers heat without transferring the heat-generating fluid.
Devices That Use a Heat Exchanger
Many common devices use a heat exchanger. Air conditioners and refrigerators use heat exchangers, but they use them to remove heat from a room and to expel it to another area, typically outdoors. The coolant remains sealed inside the pipes and never comes in contact with the air.
You can also find heat exchangers inside power plants, engines, buses, and other motor vehicles; they’re even used in wastewater exchanges. The exchanger helps reduce lost energy that would be uselessly expelled into the open air. This makes each system that uses this device work more efficiently.
In a power plant, the exchanger captures hot exhaust gases traveling through smokestacks to cool them and redirect them back into the plant. This recycles the energy. The air passes over copper fins with water flowing through them. These fins handle the redirection. Once returned to the building, the air gets put to good use to heat offices or to feed a furnace or engine.
Since the two fluids never touch, heat exchangers also contribute to more efficient heating of liquids for equipment. In a shower wastewater system, the device uses outgoing waste to warm incoming cold water. This exchange of heat reduces the energy needs of the power plant. In motor vehicles, the heat exchanger cools down an engine, and the vehicle’s system can reclaim the heat to use in the passenger compartment. A car radiator also counts as a heat exchanger.
What you need to know is that you cannot switch out these different types of heat exchangers. The type used in your HVAC system only works in an HVAC system. These systems contain either a plate/fin system or a shell-and-tube system.
Plate/Fin Heat Exchangers
Plate/fin heat exchangers use a large surface area to quickly exchange heat. These large areas consist of thin metal fins or plates, hence their name. Gas boilers and furnaces typically use this type of exchanger.
Shell-and-tube heat exchangers use a set of metal tubes to exchange the heat. The two fluids each pass through a different set of tubes so that they never touch. They can flow in the same or a different direction or with crossflow.
The Utility of Heat Exchangers
Heat exchangers go a long way to reducing energy bills. They contribute to the minimization of heat loss from buildings, machinery, and vehicle engines. You might also refer to them as recuperators or regenerators, but they aren’t the same thing. The term “recuperator” refers to a device that captures heat that the system would otherwise lose.
Using a heat exchanger ensures that each of the fluids flows through its own channel, thus remaining separate. The two fluids never mix. The incoming fluids and the outgoing fluids flow in opposing directions. The heat exchanger in a heat-recovery ventilation (HRV) system provides a common example of a recuperator, which moves stuffy, warm, or hot air out of a room or structure while it pulls in fresh air from outside. This ensures building ventilation with no heat loss.
It is similar to a regenerator but differs in the separation of fluids. In a regenerator, the incoming and outgoing fluids use the same channel but travel in opposing directions. They also travel at different times. First, the warm fluid flows out, releasing some heat. At a later time, the cold fluid flows in using the same channel and picks up some stored heat. You can find one common example of a regenerator in a Stirling engine.
What Are the Best Materials for a Heat Exchanger?
Heat exchangers use numerous materials in their constructions, including:
- Metal
- Ceramics
- Composites combining ceramics and metals
- Plastics (also called polymers)
For a system with high-temperature heat exchangers, look for construction using metal, which quickly absorbs and conducts heat. Conversely, any low-temperature heat exchanger can use plastics. Their lightweight nature and low cost make them perfect for applications like swimming pools and showers. They resist fouling and corrosion best but are mechanically weak.
Ceramics work best with high-temperature applications of more than 2,000 degrees Fahrenheit. These applications typically melt metals such as iron, steel, and copper. Ceramics also make the best choice for use in abrasive or corrosive fluids applications in either temperature range. With composite heat exchangers, you get the best of metal’s thermal conductivity with plastic’s reduced weight and corrosion resistance. While they aren’t yet ready for dissemination, you could soon see heat sinks created from carbon nanotubes, a material that wraps carbon around itself in thin hexagonal sheets.
What Is Not a Heat Exchanger?
From its essential explanation of moving hot air out and cool air into the room or system, you might think that a bathroom or kitchen fan qualifies. It does not qualify. This type of fan is designed to remove moist, hot air from the room, which reduces internal humidity. The utility fan does not bring outside air in; it just dumps the indoor air out. This makes this system a heat extractor.
Signs That Your HVAC System’s Heat Exchanger Is Broken
It is important to have your HVAC system inspected to spot problems in the heat exchanger and other furnace parts. Your certified HVAC technician will look for problems like cracks in the metal, ceramic, or plastic. They will also look for discolored metal and soot buildup, carbon monoxide in the air, and a difference in the furnace’s flame from its normal firing, which can all indicate a heat exchanger problem.
When you notice any of the above signs, immediately call Bardi Heating, Cooling, Plumbing. We offer around-the-clock service, and we’ll respond quickly to repair your system. Our team also maintains and installs heating systems, and we provide a full range of air conditioning services as well. Our other services include plumbing repair, drain cleaning, pipe replacement, and leak detection. We service Norcross and all surrounding areas. We help Georgia stay comfortable all year long, so call us with any HVAC problem, and we will come to help you fix it.
