Featured Story – Efficient use of waste heat in air conditioning and process air

In this situation, it is proving very helpful that the media climate air (air conditioning systems) and process air (e.g. exhaust air from industrial processes) can now finally be recorded energetically. The air energy meter from Luftmeister GmbH is certainly trying to open the door to numerous worthwhile savings projects in air processes. It combines a precise flow measurement with an exact determination of enthalpy. If one considers that air ducts running straight ahead are absolute rarities in air technology, it becomes clear that flow measurement must prove its precision, especially with asymmetrical flow profiles. The air energy meter shows a special strength here due to its patented probe technology.

Very helpful for analyses and the assessment of heat potentials: not only the thermal energy (e.g. in kWh or BTU) is recorded, but also the thermal capacity (e.g. in kW or BTU/s) is made available as a control and monitoring variable. Thus, before implementing recovery of waste heat (from air processes), the question arises as to which thermal capacities are available at all and if waste heat recovery is worthwhile at all. Luftmeister GmbH offers on-site measurement series for this purpose. Two examples: In a large laundry in Düsseldorf, it was questionable whether a 90°C exhaust air pipe could serve as a heat source for waste heat recovery. A three-week series of on-site measurement with the air energy meter showed that only strongly fluctuating thermal capacity values were available. Thus it could be determined early on that the use of waste heat was not worthwhile. On the other hand, the determination of potential in a Northern German construction material plant showed that the warm exhaust air of thermal processes had an easily tappable, continuous thermal performance. This, however, at an 80% level of thermal capacity compared to the assumed 100% level – thanks to the measurement series, the heat recovery could then be appropriately dimensioned.

After implementation of the heat recovery system, the air energy meter continously helps to achieve energy efficient control. An air-conditioning technology example shows this. A large administration building has large geothermal air ducts, which are intended to precool the outside air in summer and preheat it in winter. With the help of the air energy meters (air mass flow measurement in the geothermal duct as well as enthalpy measuring points before and after the geothermal duct) it can be seen at any time which energetic benefit (measurable in kW net capacity) the flow through the geothermal duct brings about. If this benefit is higher than the cost of the additional fans required, the geothermal duct is used – in the opposite case, the bypass is opened. In this way, the system is optimally controlled in terms of energy and costs instead of a widely used temperature-based control system.

Whether in paint shops, the aluminium industry or numerous other applications: the air energy meter provides a decisive benefit by recording the thermal energy in the time before and after the savings measure. DIN EN 50003 stipulates that the energetic measures must be metrologically proven. Pure estimates are therefore not accepted in energy audits any more, as well as by subsidy providers.

This is very easy to understand, as both the audit and the subsidy project depend on the acceptance of the submitted savings measures. The air energy meter supplies the consumption data for the periods ‘before‘ and ‘after‘ for freely selectable periods and has already optimally supported numerous projects in this function, from the foundry exhaust air to the paint process heat recovery to the geothermal heat channel.