Waste heat / Process air

Do you operate industrial systems that release waste heat to the environment?
According to the applicable requirements of energy efficiency legislation, are you required to report this waste heat in a waste heat register? Or are you already facing the assessment or implementation of a waste heat recovery solution?

In these cases, the key question is how the waste heat potential can be quantified. In other words: what temperature level is available, and what is the level of thermal power over time?

Three levels of waste heat potential determination

Luftmeister supports this important task of waste heat potential determination with three different service levels, which are illustrated in the following figure and explained in more detail below.

Point-based waste heat potential assessment

There are cases in which it is sufficient to consider the waste heat flow at a single point in time. This applies when it can be reliably assumed that both the thermal power and the temperature of the waste heat flow remain constant over time. In addition, a point-based assessment can serve as an appropriate first step in the initial characterisation of waste heat.

In such cases, Luftmeister provides professional support with its expertise and measurement equipment. In addition to capturing the flow across the entire duct cross-section, temperature, humidity and absolute pressure are recorded in order to determine and document the mass flow rate, enthalpy and thermal power.

As illustrated in the following figure, non-constant processes must be expected to exhibit significant fluctuations in thermal power. This can result in considerably overestimated or underestimated potential values, which may lead to costly misdimensioning of heat exchangers and heat recovery systems (such as heat pumps or ORC systems).
In these cases, the measurement series or permanent measurement installations described below are recommended.

Measurement series for waste heat potential determination

Determining the waste heat potential of non-continuous processes requires measurements to be taken not only at a single point in time, but over an appropriate time period. Only in this way can reliable data be obtained that allows for sound heat exchanger design, heat planning and correct sizing of heat recovery systems. Depending on the characteristics of the upstream processes, this period may range from one day to one week or even longer.

For such cases, Luftmeister offers measurement series. A continuously recording measurement solution is installed and calibrated, transmitting all measured values to the data logger of the connected air energy meter. As these measurements are often carried out on rooftops or outdoors, Luftmeister provides weatherproof enclosures to protect the measurement equipment.

After completion of the measurement series, the measurement system is dismantled on site, sent to Luftmeister, and subsequently read out and documented.

Permanent measurement installation for waste heat potential and optimisation

In many cases, a permanent measurement installation is used instead of a measurement series (see above). In terms of waste heat potential assessment, this provides the same level of data quality as a measurement series, as the same probes are used in both cases and the data is evaluated over a defined period of time.

However, once a heat exchanger has been installed and the waste heat is continuously utilised, a permanent installation offers two additional, tangible advantages during operation. If not only the (secondary) recovered thermal power is measured, but also the (primary) emitted thermal power via the air energy meter, the following important optimisations can be derived from the measured data:

• optimisation of the utilisation rate of the waste heat recovery system
• determination of the optimal point in time for cleaning the heat exchanger

The latter is particularly relevant for the operating costs of waste heat recovery systems.

Waste heat utilisation options

Luftmeister has supported numerous waste heat projects and contributed its core expertise in the reliable determination of the time-dependent profile of waste heat power and other waste heat potential parameters. In addition, Luftmeister identifies and outlines suitable options for waste heat utilisation.

If a project is pursued in greater depth, Luftmeister can rely on experienced implementation partners who provide support in areas such as power generation or cooling from waste heat, as well as in the supply of heat exchangers and heat pumps, up to and including thermal energy storage solutions.

Heat flow in process air or flue gas

Many waste heat potentials use flue gas as the heat transfer medium. In practice, non-specialists often calculate flow rates and heat flows using air-based calculation factors, which can lead to significant measurement errors. The reason is that the enthalpy (heat content) and density of flue gas are governed by different equations than those of air.

Luftmeister’s pragmatic solution is to extract the relevant flue gas parameters from existing emissions measurement reports and store them in the air energy meter. In this way, the device effectively becomes a flue gas energy meter, enabling accurate determination of heat flow in flue gas applications.