Observing the HVAC market, in our case – in the field of air-to-air heat recovery, we encounter a number of solutions, each of which is promoted as the “most effective” or “most efficient” or even simply “the best…”. Browsing hundreds of products, we ask ourselves whether there is a common system for assessing the performance of various heat recovery systems? In other words – is there a common denominator, a reference point to make them comparable.

EN 308 – The Air-To-Air Heat Recovery Handbook

Designing our heat recovery components we need to keep in mind, that our products will be compared with solutions offered by our competitors by means of standardized evaluation methods. Such test methods used to evaluate the recovery systems is clearly listed on the pages of EN 308 – a standard, titled: ” Test Procedures For Establishing Performance Of Air To Air And Flue Gases Heat Recovery Devices”. It’s a standard issued by the European Committee for Standardization and is recognized in 34 countries – of course including all countries of the European Community.

For a better understanding of the complexity of designing a good recuperator or regenerator, as well as the way it is going to be assessed, let’s have a look at the scope of EN 308 – especially at the meaning of their Key Performance Indicators and the way we hire the advanced technology to achieve the best rating within each of these properties.

External leakage

Energy Recovery Wheel 4"The heat recovery device (a rotary heat wheel or counter-flow recuperator) installed in the Air Handling Unit has to be designed to minimize the transfer of the air participating in the recovery process to or from the direct ambient of the Air Handling Unit. Why the tightness between the supply or return air and the ambient is so critical?

Let’s imagine that for the supply fan installed downstream of the heat recovery block a certain amount of ambient air is transferred to the supply ducts – by the leak on the heat recovery block. Or – in case of the fan’s installation upstream of the recovery section – even a small amount of return air vented to the mechanical room where the Air Handling Unit is installed.

It’s easy to guess how much these leaks would adversely contribute to the quality of supply air or, conditions for personnel working in the mechanical room. Another question is how we deal with the external leakage problem, which results not only from applied manufacturing technology of heat exchange core. We must remember, that to avoid external leakages, the design and make of the heat wheel or counter flow block is one – but the precision of its installation in the Air Handling Unit is the latter. So, we also need to put strong attention to keeping the external dimensions of our products in tight tolerances accordingly to what we declare to our business partners.

Internal leakage

Counterflow Heat Exchanger Production

Another type of leak assessed by the EN 308 concerns air transfer from supply to the return side of the ventilation system or vice versa. In this case, all the handled air remains in the heat recovery process. However, this type of leak, commonly known as Cross-contamination is severely disadvantageous when directed from a return to supply air. In this case, some amount of the return air may carry contaminations to the supply air followed by spreading them across the building.

To avoid this effect, we engage the most advanced technology of ultrasonic welding when manufacturing our counterflow exchangers made of polymer. They must be perfectly airtight, when applied to healthcare facilities, especially, the infectious diseases hospitals fighting COVID-19

Temperature And Humidity Ratios

And finally, we got the heart of the matter in the field of heat recovery – its performance of it. It is a percentage value telling us, how much the heat energy (both sensible and latent) can be transferred from one airstream to the latter. In the wintertime – we care to catch as much as possible of the heat and humidity from the return air and move it to the supply.

For summer, the goal is to move the maximum amount of heat and humidity from the supply air and remove it together with the exhaust air stream. Knowing that heat transfer strongly depends on the exchange surface, we developed a highly corrugated structure for our plates and foil. Our heat wheels are equipped with a unique sealing system developed by us and dense brushes on the separating bars, to secure from adverse efficiency drop – all to reach the heat recovery LEVEL of our SYSTEMS even at 90%.

Air pressure drops

But how far we can expand the heat recovery surface? Can we boost the efficiency indefinitely or is there a limit we should not go beyond? Of course, there is one. We must keep in mind, that more and more heat recovery surfaces compacted in units of the same size will result in airflow resistance increase, followed by an increase in fan power demand.

So it may turn out, that additional heat recovery will skyrocket the electric power consumed by fans. So, each time we design our heat recovery systems, we keep in mind the necessity of finding the best compromise between the performance and air pressure drops, thus ensuring to meet ECODESIGN requirements.

How Can You Select Our Products On Your Own?

Besides defining the key performance indicators of heat recovery systems, the EN 308 standard tells us what and how we need to measure and how to turn these measurement results into a final performance report. Based on these recommendations, we have built our internal testing boot, where we can repeat tests as many times as needed till we get the results we expect. When satisfied of our research results, we turn our know-how into a ready product. Never before.

Having done hundreds of tests on our air-to-air heat recovery prototypes, we have collected thousands of records of their performance at various operating points. This huge database processed by our highly skilled engineers has resulted in the development of fully reliable selection software. Depending on your needs, it can be shared with you as an online tool, or as a .dll file – ready to run in your own AHU selection software.

Certainty Based On External Certification

Of course, some of you might be not fully convinced towards us as partners, hearing that all our product’s performance assessment, relies only on tests done internally in our own labs. Being aware of this, we have joined to the most reliable third-party certification programme – the EUROVENT. The base of this certification program is of course the EN 308 standard, which clearly dictates, how all technical information about our recuperators and regenerators should be rated and listed on our technical specification printouts.

What is more, the EUROVENT keeps our production under constant surveillance in terms of quality, technology and coherency between products and published technical specifications. In other words, the EUROVENT CERTIFICATION mark applied on our products as well as the technical specification sheets is proof, that our heat recovery systems are fully aligned with EN 308 and will perform exactly as specified. Check us on the EUROVENT CERTIFICATION website.