Achieving the ideal efficiency is key in air conditioning systems, and in this specific case, in solutions for a sweet industry that presents constant design challenges.
by Camilo Botero*
In documents issued by CABA (Continental Automated Building Association) on controls in buildings, it can be seen that it is very important for all those involved in air conditioning projects, to understand what the trends are and where the efficient use of energy is focusing and its relationship with the control of the systems, for the changes are truly significant, dizzying and effective.
In several countries of the world, mainly in Europe and the United States, governments are leading very significant movements towards the Rational Use of Energy (URE) and the care of the environment. There are organizations such as, ISO; ASHRAE (American Society of Heating, Refrigerating and Air Conditioning Engineers), the Green Building Council of the USA, the Institute of Illumination and the American Institute of Architects, which are writing and promoting standards that will ultimately result in mandatory codes.
If this orientation in Latin America is well understood, and the direction in which our industry must be mobilized, we can be accompanying the changes and providing guidelines for all actors involved in the design, construction, operation and maintenance, to minimize the energy costs of their facilities and their impact on the environment, especially in relation to Air Conditioning systems (Air Conditioning, Refrigeration, Heating, Ventilation and Humidity Control) and to be able to use these standards, or to elaborate their own, that adapt to the climatic conditions, types of construction and regional technologies.
ASHRAE's approach is to move towards a zero energy balance by 2030, an overly ambitious but absolutely necessary goal. This is to encourage a building to collect all the energy of which it is capable, which comes from renewable sources of energy, but always maintaining an acceptable functionality. Buildings will be able to access energy from the public grid, but on the condition that the energy balance on an annual basis is "almost" zero. This is the great challenge that all the engineers and technicians of the world are facing and even more so those who are involved with the issue of air conditioning.
This implies substantial changes in technology, bold proposals in standardization and legislation and use of very effective methodologies for the design, construction, operation and maintenance of buildings such as commissioning and energy audits; but above all a deep awareness of the need and goodness to incorporate this concept into our daily lives.
The goal is to definitively change the way we use energy and how we transform it, so that without deteriorating the quality of life that has been achieved, we do not deteriorate the environment and leave planet for future generations.
This will force us to minimize the use of energy from hydrocarbon-based sources and move towards unconventional energies. CABA reports trumpet: Controls, Controls, Controls!!!! ... to achieve maximum system efficiency; with which I fully agree and we must ensure that all new air conditioning systems, and especially the old ones, are properly controlled and that this control remains with its design conditions over time. That is, it must have reliability.
I have been immersed in mechanical engineering for half a century and more specifically in thermal engineering, from various perspectives (maintenance, assembly, operation, design, auditing, training, standardization, certification, trade union activity and recently "commissioning") and it is increasingly appreciated with greater evidence that the science and technology associated with these disciplines is already very decanted because it is secular and the changes that are presented are relatively scarce in the field of air conditioning. Unlike the above, electronics, software, ICT (Computer and Communication Technologies) have impacted in a very significant way the performance of these systems, in terms of air conditioning, which must operate with maximum efficiency, comply with indoor air quality and minimize the impact on the environment, which is achieved by controlling and monitoring them accurately.
But what have I been able to observe? There is a dichotomy and distance between thermal engineering designs and control system designs that must optimize them. Thermal systems react in minutes and even hours, while electronics do so in milliseconds and even if this happens, if the following disciplines are not thoroughly known: thermodynamics, heat transfer, fluid mechanics, mass and energy balance and the psychrometry associated with the process; most of the time, control systems do not work properly. This aspect must be corrected to achieve the maximum benefit of the new control technologies, so that the energy consumption is exactly what the system requires, under given operating conditions.
CABA argues that there are three key objectives in the issue of control:
1. Design and selection of the system: What is chosen and why?, what should be the criteria for a building with Zero Energy Balance?
2. The Energy Impact: What energy use performance do these buildings actually have?
3. The user experience: How are the controls being operated, what is effective and what is needed?
Efficiency vs Effectiveness in HVAC Systems in the Candy Industry: When the candy industry requires cooling, dehydrating or drying processes for its products, it has three options available in the market:
1. Buy imported line systems from large manufacturers that produce this type of equipment,
2. Develop and adapt imported systems in operation in candy factories, to later manufacture them locally and,
3. Hire in Colombia consulting and specific designs, for the type of product that must be dried, cooled or dehydrated, to later develop and install it locally.
It is possible to expand widely on each of the points described above highlighting their pros and cons, since these generate great discussions and opinions in the projects. The customer must have certainty in the solution to start production as soon as possible; another vision is the particular economic interest of the manufacturer or contractor and another the perspective of the designer or consultant who must weigh the previous two looking for a favorable cost-benefit for his client without limiting the effectiveness of the design.
Therefore, as a starting point, and in accordance with ASHRAE Standard 202, for project quality assurance, RDPs (Project Owner Requirements) should be defined very clearly with the help of consultancy. Normally, in the characteristics of our market, option number two is decided and implemented, in which the client provides guidelines and based on these the contractor or manufacturer builds and installs the client's requirement.
Likewise, it could be the case that the similar product manufactured in another latitude could have a greater or lesser percentage of humidity, to list only one of the variables. To this lack of deep knowledge on the part of the client about his product, is added the participation of the manufacturer or contractor who settles on what is raised by the client corroborating it with conventional relationships of air conditioning systems, such as: a ton of refrigeration, has an approximate flow of 400 CFM, erroneously concludes that the flow of its tunnel, Drying or dehydrating room must be proportional to that value, which leads to serious operating problems.
With the experiences learned in different types of processes in our region of Valle del Cauca, mainly where the sweet industry is traditional, in other parts of Colombia and abroad, it has been concluded that the speed of the air "bathing" the product is fundamental to meet the objective, since the number of Reynolds increases and higher Nusselt numbers are achieved that lead to higher transfer coefficients of heat and mass.
The previous sentence explains in colloquial terms the following: "The more flow can be injected, the easier the objective is met." This is where a fundamental tool called psychrometry comes in, because it is indispensable to describe all the thermodynamic processes involved in this type of production. In conventional air conditioning, the calculation of thermal load is made first and as a product of this, a flow rate is calculated; in the processes of the sweet industry, a flow rate is defined, based on mathematical models and the residence time of the product inside the equipment. Here the control of the processes is fundamental.
The following statement could also be made: "The more flow can be injected, the more cooling and post-heating capacity will be required." This is where the subtitle "Efficiency vs Effectiveness in cooling and drying system in the food industry" makes sense, since by seeking effectiveness in the processes you can not sacrifice the efficiency of the systems, which are already intensive in energy consumption.
Therefore, it is imperative that as participants in this type of development, all the tools that technology currently provides are used to achieve great efficiency in the process and as far as possible, simultaneously a great energy efficiency, which requires precise control of the processes.
With novel designs of face and by pass damper handling units (that is, those where part of the air can be distributed through the coils and part through a diversion), for example, consumption could be reduced by half or less, increasing the efficiency of the system without decreasing the effectiveness.
Likewise, Heat Pipe systems, combined recirculation and air treatment systems could also be used: systems with chemical dehumidification, chiller with heat recovery, etc. In general, all the efforts of our guild in energy savings are focused more on the optimization of energy use in buildings: Zero Energy Balance, Energy Quotient in Buildings, LEED certification, RITE, Energy Certification of Buildings etc, but not in the industry, where some efforts have been made with ISO 50.001, but still very incipient.
Unlike the above, we emphasize that the focus of our consulting company is focused on optimizing energy savings in production factories which, in the case of this article, is specifically the candy industry.
Some sweet industries can have installed up to 3,000 T.R in very small spaces, which generates a great possibility of improvement and savings for this type of customers. The important thing here is to approach this type of project from another perspective different from that of air conditioning, using mathematical models of cooling, reheating and drying, also resorting to valuable tools that psychometrics and control give us; if psychrometric processes are not perfectly understood, it is most likely that quality production will not be achieved, with the minimum of energy consumption and impact on the environment and in the shortest possible time.
Note: In the second part of this article we will know some specific examples of implementation of central cold water systems for the areas of confectionery and chocolate in a Colombian candy plant.
* Camilo Botero is the current Secretary of the Federation of Ibero-American Associations of Air Conditioning and Refrigeration - FAIAR; he was president of ACAIRE and is president of Camilo Botero Ingenieros Consultores Ltda. He has worked as a teacher in several Colombian universities, guilds and currently in ACAIRE in diploma courses of air conditioning projects, energy efficiency in air conditioning and refrigeration, cogeneration and trigeneration, applied psychometrics, thermodynamics, fluid mechanics, heat transfer and turbomachinery. ([email protected]).
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