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Commercial kitchens are one of the most energy-intensive areas of buildings. In addition to cooking, dishes are washed and food is kept cool, all of which requires a lot of energy; in addition, each of these processes creates a lot of internal heat and moisture, which has to be drawn out of the kitchen with sufficiently dimensioned ventilation systems. Energy-efficient kitchen equipment therefore offers benefits in several ways – it saves energy, generally reduces internal loads, and thus allows smaller ventilation units to be used. The topic is especially timely as Germany switches to all-day schools with school cafeterias.
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A wide range of applications contribute to energy consumption in commercial kitchens – which means that there is also a wide range of possibilities for reducing that energy consumption, from thrifty hot water consumption to efficient cooking.
In addition, the type of kitchen ventilation greatly influences energy demand in commercial kitchens. Energy demand can drop considerably if kitchen equipment with reduced extract air demand is used, if kitchen appliances are of the right size, if heat is recovered from extract air, and if the ventilation system has a control system. For detailed approaches, see [Bräunlich 2013].
The technologies already available allow energy demand to be reduced by up to 70 % for all energy applications, including building services, for a typical final energy consumption per hot meal of around 2 kWh.
[Kah 2012] discusses the steps in detail. Optimization of each core process was found to be decisive. For instance, if dishwashing is energy-efficient, the dishwashing machine's energy demand is lower, and so is the need for secondary processes to draw off heat and improve indoor air quality.
There is considerable energy-saving potential in cooking. It was shown that proper selection of the cooking process and the thermal optimization of cooking utensils of the right size reduce energy demand to a third of what is common in conventional cooking. Furthermore, energy data for kitchen appliances and utensils should be stated in terms of specific meals. Otherwise, considerable influential effects are not taken into consideration.
Despite moderate indoor air temperatures, heat given off by hot surfaces reduced thermal comfort to unsatisfactory levels in one kitchen studied. To further improve comfort, steps need to be taken to reduce radiated heat in addition to ensuring moderate indoor air temperatures.
Dishwashers with effective technologies to improve efficiency are already for sale. Energy demand is reduced considerably when heat is recovered from wastewater and extract air (vapors). Vapor condensation turned out to be especially interesting because it simultaneously improves indoor air quality and reduces the need for extract air. “Integrated planning” also offers tremendous potential. It is crucial for a project's success that everyone involved (including kitchen planners and managers) start participating as early as possible and that actual requirements be specified.
Only part of the energy consumed in kitchens is devoted to the actual goals (such as cooking), with the rest being emitted within the room as heat. One interesting synergetic effect of energy-saving technologies is that reducing energy consumption simultaneously provides better air quality by reducing vapors and waste heat. Some kitchen appliances already have solutions integrated in them that simultaneously greatly reduce the need for extract air. The further development of such solutions in kitchen appliances seems crucial for efficient commercial kitchens of the future.
These findings were compiled by the working group on affordable passive houses (with funding from DBU, HMUELV, ProKlima, and FAAG GmbH) as part of its focus on "energy-efficient cafeterias and commercial kitchens" (only available in German).
[BGR 111] Berufsgenossenschaftliche Regeln für Sicherheit und Gesundheit bei der Arbeit, Arbeiten in Küchenbetrieben, Hauptverband der gewerblichen Berufsgenossenschaften, 2011.
[Bräunlich 2013] Bräunlich, K., Ventilation in commercial kitchens, 17th International Passive House Proceedings, Frankfurt, Passive House Institute 2013.
[Kah 2012] Kah, O., Optimierungspotentiale in gewerblichen Küchen, in Protokollband Nr. 47 „Energieeffiziente Kantinen und Gewerbeküchen“ des AkkP (only available in German), Passive House Institute, Darmstadt 2012.
[PHPP] Passive House Planning Package, Passive House Institute, Darmstadt 2012.
[Schjær-Jacobsen 2009] Jørgen Schjær-Jacobsen, Energy efficient cooking - The EffiCooker, Report (R-215), Department of Civil Engineering, DTU 2009.
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Overview of all articles on Passipedia about cafeterias and commercial kitchens
List of all released conference proceedings of the 17th International Passive House Conference 2013 in Frankfurt
Conference Proceedings of the 17th International Passive House Conference 2013 in Frankfurt