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Food Industry: Optimising your airflows for substantial energy savings

The food industry consumes a lot of energy to control the temperature and air quality in processing areas. A few simple actions can frequently deliver substantial energy savings. We present below some examples emblematic of food industry workshops: the cooking/baking workshop and its air extractor, and the processing/packaging workshop with its air handling unit (HVAC).

 

Controlling air extraction in cooking workshops

Many food industry operators face the same dilemma: reduce the heat exposure of their staff by ventilating the cooking/baking shops and avoid contaminating the food removed from the ovens with coarsely filtered cooling air. Yet it is possible to respond harmoniously to both challenges, and to do so virtually without any CAPEX!

Room cooling is generally the job of air extractors, placing the cooking shop in partial vacuum. Several tens of thousands of cubic meters per hour of hot air are thus extracted and replaced with “fresh” air at ambient temperature. “The quality of this fresh air may be questionable”, says Yves Bergeron, Industrial Energy expert at Blu.e. “The air intakes may for instance be positioned flush with the floor in the maintenance shop. Air velocity may be such that the ‘fly-off’ effect is significant. And generally this fresh air is simply prefiltered since a fine filtration of such airflows is impossible.” In an optimization process – and for once! – energy demand management and control of microbiological quality can both come together: the first improvement lever relates to adjusting the air extractor at the lowest level necessary to ensure acceptable temperatures on the shop floor.

  |  Example of a practical case in a sliced bread baking factory

“The air extraction level was set so high that it was extracting air from the other end of the factory, in the post-packaging storage area. By shutting down one of the three extractors, the impact on temperature in the baking room proved to be negligible, and the problem of dirty air aspiration was eliminated. In addition, the energy consumption was reduced by one third!”, notes Yves Bergeron.

 

Another very simple action is to ensure that the air extractor runs only when needed. Does the extractor start running too early, when the oven and the room are still cold? Does it shut down too late? “The number of extractors and/or their operating level need to be adjusted according to the weather conditions (outdoor temperature, sunshine), but also according to the activity of the workshop itself”, recommends Yves Bergeron.

 

Optimizing the operational setpoint of the air handling unit (HVAC)

As a general reminder, the air handling unit ensures that air quality in the workshop during production complies with applicable standards (room temperature, microbiological quality).

A first avenue for improvement consists in optimizing the energy consumed during off-production time. The issue is particularly important if the workshop runs during short periods. It should be remembered that a workshop operating 8 hours a day, 5 days a week, is three times more often in shutdown state than in actual production!

As a reminder, the air exchange rate required by standards during production was calculated by design to eliminate any contamination from air inflows into the workshop (from products, packaging, staff, etc.).

Apart from production and maintenance periods, whenever the doors of the workshop are closed and there are no inflows, this air exchange rate can be reduced significantly, while still ensuring the required microbiological air quality.

The temperature setpoint required during production in the workshop is most likely excessively high during off-production periods: “Yet the standard does not apply at that time since there is no production, even if you need of course to ensure (and prove) that the air quality is properly controlled and will comply with the standard as soon as production restarts”, reminds Yves Bergeron. “During production shutdowns, conventional support measures consist in locking doors, sealing any openings and covering the equipment. You might be surprised to find that the air quality at production start-up will frequently improve significantly as compared with the quality you get by leaving the AHU running full blast during production shutdowns.”

This initial success justifies challenging the preconceived idea that “We run the HVAC system full blast all the time, this way we won’t have any problem!”. However, a small effort is necessary as a prerequisite: gain perfect knowledge of the applicable standard. Proper understanding of the standard will enable you to challenge the quality managers constructively and define jointly with them the operating setpoint actually necessary for the most demanding activity level. It then becomes possible, by working in stages interspersed with long observation periods, to gradually reduce the operating level of the air handling unit down to this optimum operating setpoint. It might even be possible to take it a step further in some workshops: “The real air exchange needs may be sharply dependent on the production activity, the number of people on the floor, the flows of products or packaging materials… For instance, if the bread is sliced in situ and generates a lot of particles, or if it is cooled in the baking shop and generates moisture…”, explains Yves Bergeron. It is not rare for the most demanding activity to actually be the least frequent. Optimization can then be extended for the most common levels of activity.

 

Real supervision for all-time wins

Obviously, adjusting the operating level of air extractors and air-handling units to the activity level and to weather conditions will increase the complexity of the task. “This is where centralized supervision becomes truly meaningful. Firstly, to conveniently keep track of historical operating status records, compare them with production data, and analyse their energy impacts at the scale of each production shop. Secondly, to identify the most efficient parameters and duplicate them in other workshops. It is not necessary to go all the way up to the SCADA system, and disseminating simple setpoint instructions along with the production schedules is generally sufficient”, says Yves Bergeron. Plan for at least one year to compile an appropriate corpus of data, and then you can start reaping the fruit of your energy-efficiency efforts: It is perfectly conceivable that your energy consumption could be divided by half!