Experts answer your questions about air-to-air heat exchangersWe want to look at some of the key concepts around air-to-air heat exchangers and answer the questions most commonly asked about these systems. Air-to-air heat exchangers recover heat from one airstream and transfer this heat to a second airstream. The benefits of these systems include reducing energy costs, lowering your building’s carbon footprint and their ability to remove bad smells, odours and pollutants. They can also help address excessive moisture levels, reducing the risk of potential structural damage.

Expert answers

Our team of experts has looked at the issues you face when designing and installing air-to-air heat exchangers. After more than three decades in the industry, working in R&D, procurement, production and programming,

Lech Lakomy now heads business development in the EMEA region.

Sebastian Wejchert is a technical expert in charge of product engineering, whose main focus is on making sure all product parameters are of the highest quality.

Paul Rigby has more than 20 years of experience in B2B sales and now heads Swiss Rotors’ business development in the USA and Western Europe.

One of the most basic questions we are asked is: How do air-to-air heat exchangers work?

Air-to-air heat exchangers work by drawing cool, fresh air from outside across a device, known as a heat exchanger. It allows outgoing air to pass almost all of its heat to the incoming air without mixing the two airstreams. The incoming air, warmed by the outflowing air, then passes through the building, heating it and at the same time gathering odours and water vapour. This out-going airstream is then passed through the heat exchanger to warm more fresh incoming air before being expelled, along with the odours and water vapour. This type of system is referred to as heat recovery ventilation (HRV)

The second type of system, energy recovery ventilation (ERV), goes one step further than HRVs by capturing heat AND water vapour. As a result, ERVs can also control humidity levels in your building. This is important in more extreme climates. In hot, humid summers energy recovery ventilation pre-cools and dehumidifies incoming air. In dry, winter conditions ERV systems humidify and pre-heat incoming air.

What’s the difference between crossflow and counterflow heat exchangers?

In a crossflow heat exchanger, warm and cool airflows mix together, while in a counterflow heat exchanger the ingoing and the outgoing air streams remain at all times separate. Counterflow systems have a number of significant benefits. The new, next generation of plate heat exchangers operate with much higher efficiency compared to traditional crossflow units – and the best heat recovery ventilators, such as Swiss Rotors’ counterflow heat exchangers, operate with up to 90% recovery.

This new generation of counterflow heat exchangers extends the energy exchange path while maintaining a minimum possible pressure drop. They fully separate the supply and exhaust airstreams, maintaining air quality and dramatically reducing the risk of any cross-contamination. Swiss Rotors’ special manufacturing and sealing processes also make it ideal for particularly sensitive hygiene applications, such as hospitals or laboratories, where any air contamination is unacceptable.

Where are air-to-air heat exchangers used?

Air-to-air heat exchangers are used in new and re-purposed buildings, where high technical standards require them to be significantly more airtight than a few decades ago in order to improve energy efficiency. These include small and large commercial buildings, such as schools, hospitals, health centers and offices – and residential buildings – both homes and apartments. Air-to-air heat exchangers are a good solution for technical applications that need closed-loop cooling but do not require the cooling capacity of an air conditioner. They are used to cool sealed enclosures, and can withstand hazardous environments, such as harsh outdoor locations when equipped with proper National Electrical Manufacturers Association-approved types of enclosure. Examples of these applications include cooling for telecoms electronics, electrical equipment, production line control cabinets, and in food manufacturing plants.

What size are air-to-air heat exchangers?

They are very compact, making them easy to install in small, sealed enclosures. Swiss Rotors’ counterflow heat exchangers are manufactured in a range of sizes, from 496 mm x 271 mm to 1182 mm x 959 mm. 

What materials are used in their production?

Heat exchangers are generally produced from aluminum that may be epoxy coated to reduce corrosion and stainless steel. The cores of Swiss Rotors’ counterflow heat exchangers are made of two types of materials. The plates are made from either aluminum or a polymer, enclosed in an Aluzinc casing. The choice between a polymer or aluminum plate depends mainly on price and operating environment. The price for polymer core heat exchangers is generally lower because the raw polymer material is usually less expensive than aluminum and it is easier to handle in most manufacturing processes. However, aluminum cores have a wider range of operating temperatures. Swiss Rotors’ hexagonal heat exchangers with aluminum cores can operate from -40ºC to +70ºC. Those with polymer cores have tighter limits, from -20ºC to +50ºC.

Do air-to-air heat exchangers consume much energy?

Air-to-air heat exchangers are energy efficient because they provide heat from exhaust air by drawing the incoming and outgoing airstream across the heat exchanger using only a fan. In addition to this, technological advances mean that the efficiency of heat exchanger units is improving. This new generation of counterflow units, such as Swiss Rotors’ counterflow heat exchangers, have the potential to reach up to 90% efficiency in recovering sensible energy.

Do air-to-air exchangers remove humidity?

Of the two types of air-to-air exchangers – heat recovery ventilation and energy recovery ventilation – only the latter, ERV is suited to transfer both heat and moisture. They remove moisture from buildings in humid climates and add moisture in dry conditions, such as harsh winter environments.

Are air-to-air heat exchangers good for the environment?

Yes, air-to-air heat exchangers can help reduce your building’s carbon footprint. They capture heat, reducing energy use and energy waste. 

Does an air-to-air heat exchanger require a sealed enclosure?

Yes. The exchanger construction is sealed to ensure separation of the two air streams. The sealed nature of their construction makes them ideal for use in harsh conditions, where dust, dirt, water and corrosive chemicals could otherwise damage components.

How does ambient air temperature impact their work?

Yes, the temperature of the outside air can affect how well air-to-air heat exchangers perform. These systems depend on a temperature difference to drive the heat exchange process. So in order for the heat exchanger to work properly, the outside air temperature must always be lower than the internal temperature.

Air-to-air heat exchangers reduce your energy bills by cutting heating and cooling costs, and lower your building’s carbon footprint. Some exchangers, such as Swiss Rotors’ counterflow heat exchanger, operate with up to 90% recovery. 

If you are looking to design an HRV or ERV system, our counterflow heat exchangers may be what you need. Get in touch to learn more.