HVAC mostly involves moving heat and humidity around in the most efficient and appropriate way possible. Sometimes you need more heat and humidity inside. Other times you want to get rid of as much as possible. The second case is what we’ll discuss in this article. When you need to cool some kind of enclosure, you need to take the heat from the inside and send it outside. There are many ways to do this. All involve some kind of heat exchanger (HEX) cooling system. Heat exchangers transfer heat, and sometimes humidity, from one fluid to another. Many kinds of different HVAC systems use heat exchangers, heating and cooling liquids, gases and solids for diverse applications. In this article, we’re particularly interested in the case where both fluids are air (because technically speaking, gases like air are fluids too).


How air-to-air heat exchangers work

Air-to-air heat exchangers rely on a temperature difference between two air sources, heating one source and cooling the other. For example, in an air-to-air HEX cooling system, that could mean pulling in warmer outside air and cooling it with the air leaving the building. This allows you to pull in fresh air to meet indoor air quality standards and keep those in the building comfortable. You can accomplish this without a huge input of energy to maintain the desired internal temperature. Such a system could also pull in cooler air, but we’ll get into all the possibilities later. In any case, air-to-air heat exchangers are energy-efficient. A fan is needed to pull air through the heat exchanger, but that’s it. It’s also important to note that there are several different kinds of air-to-air heat exchangers. Some perform energy recovery ventilation (ERV), exchanging both heat and humidity. Others only do heat recovery ventilation (HRV), where no humidity is exchanged between the two airflows.

There are many ways to exchange heat and humidity between airflows. When it comes to air-to-air heat exchangers, there is a crossflow and counterflow method. Each has a different physical configuration. Crossflow heat exchangers mix the two airflows. In counterflow heat exchangers, the airflows remain separate at all times. The materials used for heat exchange also differ between designs. Two common choices are aluminum and polymers. To learn more about it, read about the Benefits of Aluminium and Polymer Counterflow Heat Exchangers. Lastly, heat exchangers come in all shapes and sizes. For example, Swiss Rotors produces counterflow heat exchangers in many sizes, with polymer and aluminum cores, and as part of a larger HexWall system.

For more information, be sure to read the article where our experts answer common questions about air-to-air heat exchangers.

Possible scenarios for air-to-air HEX cooling systems

Since air-to-air heat exchangers come in so many varieties and sizes, they can be used for all sorts of different applications. Here are some of the most notable.

New construction and replacement systems – The different sizes are made to fit all kinds of different standards, both new and old.

For small-scale and large-scale applications – You can scale HEX cooling systems to meet all kinds of demands, from small to very large enclosures for residential, commercial and industrial applications. See the benefits and scenarios sections below for more details.

Without an additional cooling system – In some climates, it’s possible to just pull in outside air to satisfy needs for cooling an enclosure. This would mean that year-round, or in some seasons, no extra input of energy would be needed to further cool the enclosure.

With an additional cooling system – It’s not always possible to do without additional cooling. In hot and humid climates, it’s a good bet that fresh air will need more cooling than HRV and ERV alone can provide. But even in those systems, air-to-air HEX cooling is still useful. Precooling the outside air, and possibly removing humidity, will help the other cooling systems operate more efficiently and make it easier to get in enough fresh outside air.

For heating systems – We’re talking about cooling in this article, but it’s worth mentioning that air-to-air HEX systems can also be used in all kinds of situations where enclosures need to be heated.

The main benefits of air-to-air HEX cooling systems

Energy efficiency – Air-to-air heat exchangers can achieve up to 90% heat recovery. They take advantage of energy that is already in the system to reduce or eliminate the need for other less efficient cooling and heating systems.

Lower energy costs – Only the fans need power in an air-to-air HEX cooling system. This means a big reduction in energy costs versus other kinds of cooling systems.

Efficient ventilation – The introduction of fresh air helps meet indoor air quality standards. It also makes the interior much more comfortable for anyone living or working there.

Quiet operation – Energy-efficient operation with just fans to move the air around means these systems generate very little noise.

Elimination of odours and harmful pollutants – The systems can be configured to keep fresh and exhaust air separate and you’ll be able to easily expel unwanted elements from the enclosure.

Moisture removal – The dehumidification of airstreams helps meet enclosure standards, such as for drying rooms.

Decreased potential of structural damage – Better control over interior air conditions helps stay within standards for which the structure was designed.

Suitable for use in harsh and dirty conditions – The systems can be designed to both withstand harsh conditions and keep contaminants out of the enclosure.

Use cases for air-to-air HEX cooling systems

Residential buildings – The old method of opening the window has a lot of problems. It’s inefficient, can let in outside noise, and doesn’t do a good job of circulating air. At the same time, powered cooling systems generally use a large amount of energy. Air-to-air HEX cooling solutions improve efficiency by using energy already in the system. They can cool incoming air, and possibly remove humidity as well. You can also design the system to efficiently circulate air around the building, getting fresh air in and removing stale indoor air.

Telecom electronics – The equipment generates heat, so cooling is almost always required. In situations where the outside air is cool enough, an air-to-air HEX cooling system is a good choice that will save on energy costs.

Electrical enclosures in dirty or dusty environments – Adapt the system to be closed-loop and keep those external contaminants out while still keeping the equipment within acceptable operating temperatures. A similar solution could also be used for production line control cabinets.

Sealed enclosures in hazardous environments – The system can withstand harsh conditions when equipped with a proper NEMA enclosure.

Hospital labs with sterile environments – Sterile environments have long lists of requirements, including good ventilation, removing contaminants and maintaining proper temperature and humidity. Air-to-air HEX cooling systems have a role to play there, especially airtight designs such as Swiss Rotors EN308-compliant counterflow heat exchangers and HexWall solutions. Read more about how HVAC systems can help in hospital settings in the article about ventilation systems and COVID-19.

Food processing plants – Food processing has a similar, but different, set of requirements from those of sterile zones in labs and hospitals. Good ventilation and removal of contaminants are key.

Flexible and efficient cooling systems

It’s easy to tell from the long list of use cases above that air-to-air HEX cooling systems are useful in a wide variety of HVAC applications. Improved manufacturing techniques have also made these systems more energy-efficient and cost-effective than ever. 

It’s a good moment for those improvements. All over the world, standards for the energy use of HVAC systems are becoming stricter. For example, Gulf News reports that Dubai is aiming to reduce its energy use by 30% by 2030. Currently, 80% of electricity use in the United Arab Emirates goes to buildings for essentials such as air conditioning. The story looks similar in Europe, where the European Commission is moving towards new standards for energy-efficient heating and cooling.

Are you considering a cooling system using products such as counterflow heat exchangers, HexWall solutions, and energy recovery wheels? Get in touch with Swiss Rotors. We’d be happy to answer any further questions you have.