The answer to fighting energy wastage is not to reduce ventilation, argues Keith Sprague of Reznor UK, who outlines the benefits of a new breed of recuperative plate heat exchanger.
The combination of a worsening recession and the need for energy efficiency sets an onerous challenge for UK businesses.

Green targets can be tough to hit when your focus is on keeping costs down. Thankfully, many buildings already have improved insulation. But, although thermal properties are improved, and heat loss through the structure is reduced, ventilation still account for immense energy wastage.

But the solution is not to reduce ventilation. As building regulations decree, maintaining air quality in a work environment is essential.

There are a number of firms with systems that combat energy wastage and elevating costs. One of those is Reznor UK, with a new generation of recuperative plate heat exchangers which is changing the way we look at heating needs for commercial buildings.

'Designed for incorporation into air handling units or as part of an air distribution system, it is playing a critical role in the drive to achieve effective and economic ventilation, heating, cooling and air distribution for buildings,' Andrew Patch, OEM sales manager, explains.

With a high thermal conductivity, the exchanger optimises heat transfer from warm exhaust air to incoming fresh air. In other words, it sustains an optimum environment within a building by efficient re-use of heat that has already been generated.

This has a dramatic effect on the building's running costs. Rather than continually using new energy to heat air, the energy from previously heated air is recovered and reused to heat the incoming fresh air.

In the latest regulations, minimum ventilation rates have been increased from eight to ten litres per second per person. In school classrooms, an increase in ventilation of up to threefold is now recommended to reduce CO2 and improve concentration. In industrial environments, contaminant levels need to be kept to safe limits. The trick is to ensure that heat is used effectively and air quality is optimised.

Two streams

The recuperative heat exchanger does both. It works on the principle of transferring energy from either heated or cooled exhaust air to the incoming fresh air ventilation. The two air streams are separated by thin heat transfer plates.

The exhaust air and the incoming fresh air streams never come into contact with one another and cannot mix. Consequently, the transfer of humidity, pollution, bacteria or odours from the exhaust air to the incoming fresh air is eliminated.

Cross plate heat exchangers have been used for several years in air distribution systems supplying ventilation, typically achieving efficiencies of 50-60%. This efficiency has now been increased by the new generation of counter-flow plate heat exchangers by up to 85%. In turn, this allows designers the freedom to incorporate adequate ventilation while reducing energy consumption and carbon emissions.

Aluminium is used instead of cheaper plastic plates, taking advantage of the high thermal conductivity of the lightweight metal, which is 237W/m-K compared with plastic at 0.08W/m-K.

This means heat transfer is optimised and the system's operational life expectancy is extended. The material can also be recycled at the end of its life, minimising its environmental impact.

High-efficiency energy recovery can play an important role in reducing carbon emissions. For each 1m3/s of fresh-air input, up to 17,000kg a year of CO2 can be cut (based on 24-hour, seven-day operation).

Cutting carbon

The Carbon Trust already recognises the important contribution that recuperative plate heat exchangers can make in reducing carbon emissions. And units are listed on the Energy Technology list to allow qualifying end users to offset costs against tax.

As well as making a significant environmental contribution, high-efficiency heat recovery also makes financial sense. The additional cost can be recovered in less than a year and the size of heating plant can be reduced.

Additionally, with efficiencies of 85%, it is possible to eliminate low-pressure hot water or electric re-heat coils from air input units, with the benefit of saving on both equipment and installation costs.

The increased efficiency of the new-generation recuperative heat exchanger technology offers designers, consultants and contractors new options in air distribution systems, whether for heating or cooling, or both.

The system has strong green credentials, and is capable of handling large volumes of air and distributing it efficiently and economically in buildings of all types and sizes. Following its simple installation, it can provide cost and energy savings that, in the current environmental and economical climate, just cannot be ignored.