Adverse impact of poor IAQ only came to surface after number of cases of health complaints escalated. Sick Building Syndrome (SBS), Tight Building Syndrome, Building Related Illnesses were the terms coined to describe effect of poor IAQ on health.

The last twenty years have witnessed the development of a number of IAQ guidelines by governmental and professionals institutions.

ASHRAE standard 62, - Ventilation for Acceptable Indoor Air Quality, specifies ventilation standards which are four times more than prevailing standards. Energy management in maintaining IAQ standards, therefore, becomes the challenge.

With technological advances, higher degrees of monitoring and control race to keep pace with codes and standards to enhance indoor air quality.

For example, as electronic control technologies continue to expand their reach into building design and operation, electronic monitors are replacing many of the daily inspection rounds typical of building engineering and maintenance.

For the indoor environment, this translates into more consistent control but greater risk that something like accumulation of water in a drain pan may promote growth of micro organisms which might produce contamination of ventilation systems.

Beginning with multidimensional use plan tor a building, a designer is confronted with selection of the appropriate technologies for structural, mechanical, electrical and related systems that can produce a high quality indoor environment within the project budget.

To meet all these needs of humidity control energy and IAQ; only one equipment will meet the challenge; that is the heat recovery device using the enthalpy wheel.

What is an Enthalpy Wheel?

The enthalpy wheel is a cylinder, usually 4 to 10 inches deep, packed with a heat transter medium that has numerous small air passages, or flutes, parallel to the direction of airflow. The flutes are triangular or semi-circular in cross-section. The honeycomb matrix, is produced by interleaving flat and corrugated layers of a high conductivity material, usually alliminiun, surfaced with desiccant. Stainless steel, ceramic, and synthetic materials may be used instead of aluminiuim, in specific applications. The flutes in most wheels measure between 1.5 mm to 2.0 mm in height. The surface area exposed to airflow in a wheel lies between 300 to 3300 m2/m3 depending upon the configuration.

Universal Rules of total Energy Wheels

In a typical installation, the wheel is positioned in a duct system such that it is divided into two half moon sections. Stale air from the conditioned space is exhausted through one half while outdoor air is drawn through the other half in a counter flow pattern. At the same time, the wheel is rotated slowly (2 to 20 RPM). Sensible neat is transferred as the metallic substrate picks up and stores heat from the hot air stream and gives it up to the cold one. Latent heat is transferred as the medium to condenses moisture from the air stream that has the higher humidity ratio through adsorption by the desiccant (with a simultaneous release of heat) and releases the moisture through evaporation (and heat pickup ) into the air stream that has the lower humidity ratio.

Integrating the Enthalpy Wheel in HVAC Systems

The most widespread application enthalpy (heat) wheels is preconditioning fresh outside air before it is introduced to a building. The system can easily be tapped in an existing ventilation system. A portion of the air that would normally be recirculated through the system is exhausted through the wheel and fresh air is introduced into the building in its place. Operating in virtually any climate zone, a single desiccant wheel operated with just small motor to rotate the wheel can deliver fresh air on a year round basis that is generally withing 3-7 degrees and 10% RH of inside conditions, regardless of what outside conditions are. The cost to provide high levels of fresh air ventilation becomes minimal compared to the normal heating cooling requirements of the building. The potential benefits are numerous.