Energy Efficiency Improvement in Professional Ovens

Tackling the climate change by reducing energy consumption is among the biggest, most urgent challenges society is facing and requires a continuous efficiency improvement of thermal systems.With the aim of reducing energy consumption and improving energy efficiency of professional appliances, this thesis is the results of the investment Electrolux Professional Spa has made. The industrial research started with an analysis of the state of the art of the energy standards applied to a professional oven. It continues, identifying a new methodology for the energy efficiency evaluation of a combined oven structured on the experimental analysis of the balance of fluxes in coming and out coming from the oven in different cooking modalities. The new developed methodology is based on the first principle of thermodynamics and it helped in the identification and application of a series of technical options for improving the energy efficiency of an oven. From the analysis is emerged that the thermal insulation and the washing system were among the main potential energy savings improvements in the overall efficiency. Based on the constitutive energy conservation equations of a professional oven, a dynamic model has been developed. It was build up in order to get a general understanding of the best possible configurations and combinations of insulation materials for the cavity walls. The code was developed in Matlab© and it was validated by comparison with a set of experimental data obtained with a current production model. After the model development, the washing plant of a professional appliance was optimized in terms of energy efficiency, water consumption, detergent and rinsing agent consumption. During the experimental test on a prototype of the washing circuit, a possible cavitation problem has appeared. Generally, in the hydraulic circuit of a professional appliances, in particular in a oven, the working fluid is a solution of water and detergent at 70 °C. The actual trend in this kind of professional appliances is to reduce both energy consumption and time needed for cleaning process: this involves short washing cycles conducted at low temperatures with a solution of water and highly concentrated chemistry. High concentrated chemistry could impact on the working conditions of the pump and on cavitation. The wide range of variables affecting cavitation has led to the development of a laboratory rig for testing different sizes of centrifugal pumps with aqueous solutions representative of those used in the warewashing sector. This test rig permits measuring pump performances at various operating conditions, in order to obtain its characteristic curves, and also forcing cavitation to measure its Net Positive Suction Head required (NPSHr) at different flow rates. The pump test rig allows also testing various configurations of the pump at different cavitation conditions, obtained by changing not only the suction pressure and temperature of the fluid but also its properties, adding detergents and additives. Cavitation inception can be detected measuring both the corresponding prevalence decrease and the change of vibration and noise level. A representative chemical component present in detergents (Polyox WSR 301) has been selected and tested at different concentrations in the rheometer in order to identify the concentration values at which the solution switch from the diluted to the concentrated regime. It has been also measured the influence of the chemical components on the pump characteristic curves and the vibration level. The results are quite impressive, because with the increasing of the concentration there is a decreasing of the pump vibrations and also the characteristic curves at certain conditions are improved. In literature there are no studies analyzing the impact of detergent components on pump vibration induced by cavitation.