How does an enthalpy wheel work?Enthalpy wheels — or energy recovery wheels (ERWs), as they are sometimes known — are established as one of the leading energy recovery devices on the market. In a world increasingly concerned with climate change and sustainability, enthalpy wheels are among the most effective technologies available for transferring sensible and latent energy from exhaust (or outgoing) air to incoming outdoor air. There are three different types of enthalpy wheel. Some transfer only sensible energy (heat). Others transfer only latent energy (moisture). The third type transfers both sensible and latent energy from exhaust air to incoming outdoor air. Installed and used correctly, enthalpy wheels offer several significant ‘green’ benefits. By recycling energy from the exhaust air, enthalpy wheels reduce the burden on air-conditioning systems to provide all the energy needed to get incoming outdoor air to the desired temperature. This saves valuable fuel resources and, in turn, lowers the energy costs faced by building owners and operators.

Typically, today’s leading energy recovery wheels save enough money in their first three years of operation to cover the cost of their purchase and installation. Given that most enthalpy wheels enjoy expected lifespans of more than 20 years, the potential for long-term savings is clear

By contributing to lower energy costs, enthalpy wheels also make it easier for buildings to maintain a suitably high turnover of fresh air. Good ventilation is seen as vital in the wake of the Covid-19 pandemic. Enthalpy wheels make it possible to ventilate at higher levels without being restricted by prohibitive energy costs

Overall, enthalpy wheels have been — and remain — a substantial advance in air-conditioning technology. They are a key part in complying with many of the new building regulations active around the world. And they will play a significant role in the HVAC industry for decades to come.

Enthalpy wheel working principles

Enthalpy is the measurement of energy change between the exhaust and incoming air streams. By capitalizing on the first law of thermodynamics — that “energy can neither be created nor destroyed” — enthalpy wheels are designed specifically to capture and transfer as much energy as possible from one airflow to the other.

Enthalpy wheels are constructed so that incoming air and exhaust air pass through the wheel in two separate but adjacent airflows. As the enthalpy wheel turns, it captures sensible and latent energy from the outgoing air flowing through the system. As the wheel continues to turn, the energy captured from the exhaust air is subsequently transferred into the incoming airflow.

The design of an enthalpy wheel is considered to the smallest of details. Usually, ERWs are made with porous materials, which increases the wheel’s surface area and maximises its potential energy transfer. Desiccant coatings are also used in the matrix core. In Swiss Rotors’ energy recovery wheels, for example, a 3A molecular sieve is applied. The coating ensures high latent recovery efficiency and guarantees the hygienic quality of the device because only molecules measuring 3 angstroms or less (water molecules measure 2.7A) can pass through. Contaminants usually have much more complex — and larger — molecular structures, meaning the 3A molecular sieve blocks them.

Finally, it is important to understand that enthalpy wheels can either heat or cool incoming air. There is no restriction on which way warmth flows. Energy from exhaust air can be used to heat and humidify colder incoming air. Or, in warmer climates such as the Middle East, energy from exhaust air can be used to cool and dehumidify incoming air. This versatility is a crucial advantage in modern enthalpy wheels.

What influences the performance of an enthalpy wheel?

Several factors have to be considered when assessing or trying to improve the effectiveness of an enthalpy wheel. ERWs are complex pieces of engineering, with more than one variable that can significantly affect overall performance. Typical examples include:

  • How sensible and latent energy is captured. What type of porous surface has been installed on the enthalpy wheel? Desiccant coatings such as 3A molecular sieves are ideally suited to this function.
  • The percentage of the effective area of the wheel. The smaller the casing and mounting as a proportion of the overall unit, the more effective the wheel. Wheels that are made with a single structure, rather than segments, can secure even higher levels of effective energy recovery.
  • How much air leaks from the enthalpy wheel. Excellent sealing systems are key  to manufacturing a wheel that delivers the highest possible sensible energy transfer.
  • The efficiency and reliability of the drive system. Each component needs to be made to the highest possible standards, and with the most enduring materials available. Should any of the motor, belt, gearing or bearings fail or degrade, the performance of a wheel will be negatively affected. Having confidence in these parts is essential.

Why the Swiss Rotors enthalpy wheel is a true market leader

Engineers at Swiss Rotors have pored over every detail of the company’s ERW. Painstaking research has been completed to determine the best possible combination of materials, components and design principles. The result is a heat recovery wheel that offers better performance (energy recovery efficiency of up to 87%) and larger energy cost reductions than any other on the mainstream market.

The fast-acting 3A molecular sieve coating found on all Swiss Rotors’ enthalpy wheels is excellent at capturing and releasing both sensible and latent energy. The inherent antimicrobial properties also help to ensure the wheel’s longevity and create hygienic indoor conditions wherever it is installed.

Each Swiss Rotors enthalpy wheel is also manufactured in a patent-pending continuous process. By eliminating segments from the traditional wheel construction, our engineers have also been able to remove the additional structures needed to support the segments. As a result, the weight of our wheels is reduced while the overall effective area of the wheel is increased. This means the Swiss Rotors model enjoys an effective energy recovery area up to 8% larger than competitive segmented wheels.

Minimal air leakage

However, the effective energy recovery area is not the only aspect of the Swiss Rotors wheel that outperforms its rivals. A clever double-sealing system has been proven to minimize air leakage from the exhaust to intake airflows, while an optional purge device eliminates cross-contamination between the air streams. The double-sealing system increases the wheel’s overall effectiveness by up to 2% compared to its competitors. These gains — in both effective energy recovery area and minimized air leakage — are considerable when viewed as a whole.

Away from the actual wheel, our engineers have also taken precise care in the choice of each specific component. A Fenner PowerTwist belt is installed in each of our enthalpy wheels. Designed specifically to maintain optimal belt tension, the result is lower maintenance costs (no more labor costs for re-tension procedures) and ongoing unit efficiency.

Certified and recognized for excellence

An EC motor with an integrated variable frequency drive (VFD) adds to our wheels’ efficiency. Energy recovery is also aided through the double-wall casing, extruded aluminum wheel hubs, and the permanently lubricated 200,000 hours (L50) bearings.

All of these factors combine to produce a wheel widely recognized for its excellence, effectiveness and durability. Made in the USA and AHRI 1060 certified, the Swiss Rotors enthalpy wheel is available in 4” and 8” widths. This makes it ideally suited for retrofit applications. The SF Series (4” wheel) offers nine wheel diameters ranging from 32” to 76”. The RT Series (8” wheel) is available in 17 different sizes from 28” to 95”.

Find out more about the Swiss Rotors enthalpy wheel today and take the first step to make your building more hygienic, efficient and environmentally friendly.