Control, regulation and command system of hydronic radiant floors heating by wireless and energy harvesting sensors and actuators

This paper presents the development of an innovative control, regulation and command system for hydronic radiant floors, more flexible and efficient that guarantees a better thermal comfort to the user and simultaneously improves the energy efficiency of this type of heating system. The majority of the actual control of hydronic radiant floors is done by thermostats that measure the air temperature and control the actuators (pumps and valves) in order to maintain the room at the specified temperature. These systems requires the frequent adjustment of thermostats set-point in order to obtain thermal comfort as it depends on other factors than just the air temperature, such as, the air humidity, external environmental conditions, radiant temperature, among others. This paper presents a control, regulation and command solution that requires minimum user intervention, as the user only has to choose the desirable thermal comfort level. The control algorithm is based on the calculation of PMV (Predicted Mean Vote) index as defined on Thermal Comfort Standard ISO 7730. Another advantage of the proposed system is related to the wireless and energy harvesting sensors and actuators that provide much more flexibility to the system.info:eu-repo/semantics/publishedVersio

Image recognition method for frost sensing applications

Frost formation in the heat exchangers of refrigeration systems is a well-documented phenomenon. This frost accumulation creates a thermally insulating barrier that can restrict, or even block, the airflow between fins, resulting in decreased efficiency and degradation of the food products. Several methods of frost detection and defrosting have been developed, although there is not an efficient mainstream method to measure and control frost formation. In previous works, the results of a small low-cost resistive sensor for frost detection were shown to be promising. This paper extends that research using computer vision to compare the results of this sensor with the frost formed on the heat exchanger, allowing for a better study of the sensor. This method allowed to trace and plot a frost formation curve of the sensor detected values.This work has been supported by the project Centro-01-0145-FEDER000017 -EMaDeS -Energy, Materials and Sustainable Development, co-funded by the Portugal 2020 Program (PT 2020), within the Regional Operational Program of the Center (CENTRO 2020) and the EU through the European Regional Development Fund (ERDF). The authors thank the opportunity and financial support to carry on this project to Fundac¸ao para a Ci ˜ encia e ˆ Tecnologia (FCT) and R&D Unit “Centre for Mechanical and Aerospace Science and Technologies” (C-MAST), under project UIDB/00151/2020. This study is within the activities of project “PrunusPos - Optimization of processes for the storage, cold ´ conservation, active and/or intelligent packaging and food quality traceability in post-harvested fruit products”, project n. ◦ PDR2020-101-031695, Partnership n◦ 87, initiative n.◦ 175, promoted by PDR 2020 and co-funded by EAFRD within Portugal 2020.info:eu-repo/semantics/publishedVersio

Case study

This paper describes the numerical results of a CFD parametric studies of the influence on the thermal performance of a cold room by (1) the number and arrangement (n = 6, 9, 18, 30 and 40) of meat carcasses hanging in an airway; (2) the air temperature in the antechamber (T = 5ºC; 14ºC and 22ºC); and of (3) opening the door of the cold room. The case studies were tested in a real facility. A steady state 3D CFD model of the cold room is developed, allowing the detailed evaluation of the airflow and heat transfer for each case study. The thermal conduction within the meat carcasses is also predicted. The numerical predictions show that the average air temperature inside the cold room as well as the average carcass temperatures increase with the number of products and depend on the arrangement of the carcasses in the airway. A minimum space between carcasses is required to improve the refrigeration process. Similarly, the heat load of the cold room increases with the air temperature of the antechamber and when the door of the cold room is opened. The carcasses temperature profile becomes less uniform when the door is opened, being the temperature of carcasses located near the door strongly affected. These parametric studies allow to evaluate details of the air flow and heat transfer by convection and conduction inside goods that can contribute to the design of cold rooms in order to focus on the improvement of thermal performance and consequently of food safety and energy efficiency.info:eu-repo/semantics/publishedVersio

Experimental testing of a resistive sensor for monitoring frost formation in refrigeration systems

An experimental study of a resistive sensor is developed. Its performance is evaluated in function of the temperature and relative humidity of air, the temperature of the refrigerant and the relative position of the sensor on the evaporator’s surface. A resistive sensor that include two electrodes measures the electrical resistance of the medium. The experimental study was developed in an experimental facility where different air and refrigerant conditions were set up. The results of the experimental study allowed analyzing the propagation of the frost layer and determining the existence of ice on the evaporator’s surface. The results agreement is satisfactory for water detection and high for the detection of the frost layer. The ice behavioral characteristics plays a key role in frost detection using resistive sensors.info:eu-repo/semantics/publishedVersio

Energy analysis and heat loads calculation approach: application to agrifood industrial premises

Nowadays, the agrifood industry is increasingly concerned about energy bills. Thus, there is an increasing trend on the implementation of measures and procedures that ensure and promote energy efficiency. Computational modelling is a powerful tool for project and design of engineering systems, allowing to anticipate and/or correct problems that may lead to inefficiencies. The purpose of this paper is to assess the energy performance of refrigerated premises of a real company modelled in EnergyPlus. The data that characterize the company and the production process were collected previously through an energy audit. Results of the comparison between real case and simulation show that the cooling system represents 56.4% and 47.8% of the total electrical energy consumption, respectively. Also, it is found that heat transmission loads trough cold rooms envelope and air infiltration are those that most affect the energy performance, accounting for almost 80% of the refrigeration needs of the company.info:eu-repo/semantics/publishedVersio

Experimental evaluation of an innovative command for hydronic radiant heating floors

This paper presents the results of an innovative control, regulation and command system for hydronic radiant floors, more flexible and efficient that guarantees a better thermal comfort to the user and simultaneously improves the energy efficiency of this type of heating system. The control algorithm is based on the calculation of PMV (Predicted Mean Vote) index as defined on Thermal Comfort Standard ISO 7730. To improve energy efficiency, the control algorithm was implemented on a microcontroller system that fea-tures wireless communication with sensors modules powered by energy harvesting systems. The experimental tests were performed in a hydraulic underfloor built into a laboratorial climatic chamber. The results show that for a water inlet of 35 ºC, the controller turn the valve on/off less than other control systems in order to adjust the PMV while maintaining the floor surface temperature less than 29 ºC as recommended by international standards.info:eu-repo/semantics/publishedVersio

A review

It is widely known that defrosting operation on commercial refrigerators is one of the main causes of inefficiency on these systems. Several defrosting methods are used nowadays, but the most commonly used are still time-controlled defrosting, usually by either electric resistive heating or reverse cycle, as most demand defrost methods are usually complex, expensive or unreliable. Demand defrost can work by either predicting frost formation by processing measured conditions (fin surface temperature, air humidity and air velocity) and/or frost accumulation symptoms such as pressure drop and refrigerant properties. Other way of knowing when to defrost is to directly measure the frost formation using sensors such as photoelectric, capacitive or resistive. This review gathers some of the methods that can be used for directly measuring frost accumulation on the evaporator fin surface.info:eu-repo/semantics/publishedVersio

Thermal performance, usage behaviour and food waste of domestic refrigerators in a university student community

Food safety and quality as well as storage conditions leading to food waste are related to the reduced thermal performance of domestic refrigerators, the mismanagement of food stored in it or the misuse of the equipment. This paper analyses the operative conditions of refrigerators in the student community of the University of Beira Interior (Covilhã, Portugal). A test sample of 51 appliances in the student households was instrumented with temperature dataloggers. Simultaneously, surveys on the use of refrigerator and food waste were applied to the students, ultimate users of the appliances. The students, with an average of 23 years old, mostly female (65.9%), live alone (6%), with their parents (24%), or with other students (71%). The test sample of appliances had, on average, a nominal electrical power of 126 W and an inner volume of 205 liters. It was found that the average storage temperature was 5.5ºC. The storage temperature in the appliances increased with the number of people who used it. This figure was largely due to improper use behaviour, in particular the number of times that the refrigerator door was open unnecessarily. The joint analysis of these data allows relating the use behaviour of with food waste. The comparison with similar studies conducted in the past shows that the average storage temperature in the current study is lower, mainly due to the technological evolution of appliances as well as the global awareness concerning food safety and food waste. The results of this work, apart from offering results about the performance of the operative conditions of refrigerators in a community not studied so far, highlights the need for further awareness of good practices to reduce food waste and simultaneously ensure food safety of the perishable food products stored in domestic refrigerators. These results could be extrapolated to the remaining people in order to develop strategies to improve cities sustainability.info:eu-repo/semantics/publishedVersio

Numerical modeling of cold room’s hinged door opening and closing processes

The need of rationalize energy consumption in agrifood industry has fasten the development of methodologies to improve the thermal and energy performances of cold rooms. This paper presents a three-dimensional (3D) transient Computational Fluid Dynamics (CFD) modelling of a cold room to evaluate the air infiltration rate through hinged doors. A species transport model is used for modelling the tracer gas concentration decay technique. Numerical predictions indicate that air temperature difference between spaces affects the air infiltration. For this case study, the infiltration rate increases 0.016 m3 s-1 per K of air temperature difference. The knowledge about the evolution of air infiltration during door opening/closing times allows to draw some conclusions about its influence on the air conditions inside the cold room, as well as to suggest best practices and simple technical improvements that can minimize air infiltration, and consequently improve thermal performance and energy consumption rationalization.info:eu-repo/semantics/publishedVersio

Experimental study and numerical modeling of the thermal performance of cold rooms for storage of meat products

This paper contributes to the energy efficiency and thermal performance improvement in cold rooms used for conservation and storage of meat products, commonly used in the agro industrial sector. An experimental analysis of the thermal performance of a cold room in the Covilhã region (Portugal) is developed, verifying its external conditions and construction parameters. A steady state 3D CFD model of the cold room is developed, allowing the detailed evaluation of the airflow and heat transfer. The CFD model setup required the definition of a physical-mathematical model based on the equations of continuity, momentum and energy. The comparison of numerical and experimental results allowed the validation of the CFD model. Thus, a parametric study is developed, which consists in changing the boundary condition values at the discharge grilles of evaporators. The parametric predictions show that the cold system, for product loading defined on the experimental analysis, is oversized, thus enabling the modification of the discharge air temperature and velocity. In this modification, the energy consumption is reduced maintaining similar thermal performance and ensuring the food safety. Thus, it is predicted an improvement of the energy efficiency and a consequent savings of environmental resources, energy and financial resources.info:eu-repo/semantics/publishedVersio