Acta Polytechnica CTU Proceedings https://doi.org/10.14311/APP.2022.38.0389 Acta Polytechnica CTU Proceedings 38:389–395, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague ECOPOOL+++: DEVELOPING A SUSTAINABLE OUTDOOR HEATED SWIMMING POOL Miguel José Oliveiraa,∗, Armando Invernoa, Fátima Farinhaa, Jânio Monteiroa, Cristiano Cabritaa, Maria Seguraa, Francisco do Carmob, Adelino Venturinhac, Gina Matiasd a University of Algarve, Campus da Penha, 8005-139 Faro, Portugal b Cristal Construções – Materiais e Obras de Construção Civil, Sítio da Mesquita, Mexilhoeira Grande, 8500-132 Portimão, Portugal c Itelmatis Control Systems, R. da Fonte Velha, 8700-178 Olhão, Portugal d Itecons, Rua Pedro Hispano, s/n, 3030-289 Coimbra, Portugal ∗ corresponding author: mjolivei@ualg.pt Abstract. The University of Algarve, in consortium with “Cristal Construções – Materiais e Obras de Construção Civil”, “Itelmatis Control Systems” and “Itecons – Instituto de Investigação e De- senvolvimento Tecnológico para a Construção, Energia, Ambiente e Sustentabilidade”, is developing a new concept of outdoor heated sustainable swimming pool, having a higher energy efficiency and lower environmental footprint. The main objective is to minimise energy and water consumptions, while assuring a comfortable temperature for the user, extending the utilization of the pool in the Algarve region, from the summer months, to at least 8 months of the year. In order to do it, different systems will be tested, including solar thermal and photovoltaic panels, inverted underfloor heating, heat accumulator exchanger with phase change materials and energy dissipating pipes. An innovative thermal insulation system will be included in the interior of the pool tank, together with a new system for the covering of the water plane. All these systems will be monitored and controlled by an industrial automation system that will communicate, via a programmable logic controller, using industry standard communication protocols, with a SMART platform, that will be in charge of the global operation’s optimisation. This platform will support an intelligent and predictive control and monitoring module, that controls the automation system to maximize the energy usage of the renewable sources, while assuring the user preferences. One of the main outputs of this project is the construction of a smaller scale prototype of a swimming pool, with the characteristics mentioned above, in order to test and validate the proposed developments. Keywords: Outdoor heated swimming pool, solar energy, PCM heat accumulator, smart energy and water management system. 1. Introduction Most existing swimming are largely inefficient due to heat and water losses, having a substantial impact in the associated environmental footprint. Tyler et al. [1] calculated the environmental impact of residential swimming pools in Arizona (USA) and other warmer regions, pointing out, as the main impacts per pool the following numbers: a water footprint from 45 to 185 m3/year; an energy footprint between 2 400 and 2 800 kWh/year; a carbon footprint of 1 400 ± 50 kg CO2e/year. In terms of heat losses, outdoor heated pools require very high energy consumptions, due to: (1.) evaporation of water into the surrounding air, (2.) radiation to the sky; (3.) convection near the surface of the water and (4.) conduction through the walls and floor to the ground. The water in swimming pools is an excellent medium for heat accumulation, which is the reason why, when there is greater availability of solar radiation, particu- larly in the summer period, the conditions for its use improve. Outside this period, the environmental con- ditions tend to no longer be favourable, causing lower free heat gains and simultaneously, greater thermal losses. The large energy losses in outdoor swimming pools, as previously mentioned, are due to evaporation, radi- ation and convection, in descending order of impor- tance. As the water surface is the pool area where the greatest heat exchanges take place, it is essential that it is efficiently and safely protected. A conventional roof with thermal insulation can reduce energy losses by between 50 % and 70 % [2]. Muleta [3] considers that it is possible to reduce evaporation by about 95 % using composite material coverings. By reducing, for example, the effect of evaporation, using an adequate coverage, benefits are not only associated with the 389 https://doi.org/10.14311/APP.2022.38.0389 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en M. J. Oliveira, A. Inverno, F. Farinha et al. Acta Polytechnica CTU Proceedings reduction of water replacement needs, but also in the subsequent reduction in the consumption of chemicals for water treatment. Thermal losses due to conduction through the walls and floor are usually neglected. There are some ther- mal insulation solutions on the market for the swim- ming pool tank, which are based on the application of extruded polystyrene sheets on the outside of the tank, in contact with the ground [4], or on modular systems that integrate the structural and insulating function in the panel [5] or in the block [6]. This type of solution is, however, aimed at new pools, being difficult to implement or even impractical to apply in existing pools. Rose [7] proposes that the thermal insulation of the walls and floor in existing swimming pools is done from the inside of the tank, based on rigid phenolic panels (high pressure laminates) or cel- lular glass, together with a rigid waterproof mortar and PVC coating. In addition to the innovative construction system for reducing thermal losses, highly efficient solutions from an energy point of view are required, such as heat storage systems. Systems integrating Phase Change Materials (PCM) were studied by Silva et al. [8] in building structures of brick masonry walls. The PCMs that have greater interest in buildings and civil con- struction in general, are well characterised in [9], where 150 of these materials are carefully described. Zsem- binszki et al. [10] simulated the thermal behaviour of an outdoor swimming pool with 50 m2 and 1.65 m depth, in three locations in Spain using local climatic data such as temperature and relative humidity of the outdoor air, solar radiation and wind speed. The bottom and walls of the pool were composed of a heat exchanger, coated with 3 cm of PCM for heat accu- mulation, allowing the control of the water temper- ature in advance (about 20 hours) in relation to the foreseeable period of use of the pool. Salgueiro [11] presents a good characterisation of mortars based on light materials with PCM mixtures. It describes the methods used to determine the mechanical and ther- mal properties of different specimens, having different compositions of mortars. The energy consumed in pumping water, for circu- lation through the filtering systems, is not negligible, even though it depends on the size of the pool. As suggested by Hunt and Easley [12] and Zhao et al. [13], the replacement, in swimming pools, of simple pumps that work only at nominal speed by pumps equipped with variable speed drives, which enable the motor to run at different speeds of rotation, can allow a 75–80 % energy reduction. In terms of water losses, Severine [14] refers the im- portance of optimising the regeneration operations of swimming pool filtering systems to reduce water con- sumption. This author also highlights the possibility of reusing the water from washing filters for watering green spaces. Water losses also result from leaks in the hydraulic circuits. At this level, the most used detection method is the evaluation of pressure varia- tion. Thus, the existence of an intelligent automatic control system for the detection of leaks in swimming pools is relevant, allowing the minimisation of human intervention, in similar way to what is already done in free surface drainage channels [15] or in fuel tanks [16]. Active measures can be used to reduce the impact of water losses and to increase the utilization of lo- cally installed renewable energy sources, reducing the energy requirements of swimming pools. At this level, the best market practices point to the implementation of industrial automation systems, made-to-measure using programmable logic controllers for the supervi- sion and control of equipment in an integrated manner for the interconnection of hydraulic systems, water treatment, and water heating systems. These sys- tems already exist in some hotels pools and spas, normally integrated in building management systems, called BMS (Building Management System) through industrial communication buses. Complemented with alarmist software modules, they promote the optimi- sation of energy and water consumption as well as the reduction of response times in the detection and resolution of occurrences, with their advantages be- ing widely recognised [17]. These intelligent control systems that allow the monitoring of parameters, im- posing user-defined limits and generating alarms when they occur, are already used today in a wide variety of situations. For instance, in the context of swimming pools, the low-cost solution proposed in [18], aims to reduce the requirements of human intervention in the maintenance of the pool. In terms of intelligent control algorithms, to im- prove the energy efficiency of indoor swimming pools, Marín in [19] proposes the use of predictive control in a hybrid control system that involves solar collec- tors and a boiler (possibly powered by biomass) for the thermal regulation of temperature. Using this methodology, it is possible to reduce the pool’s energy demand significantly (in the order of 18.76 %) and consuming 42.64 % less fuel compared to a conven- tional Proportional Integral Derivative (PID) control. Still in the context of optimising energy efficiency and specifically with the aim of reducing response time, Machine Learning techniques such as Random For- est [20] or predictive control based on models [21, 22] can be considered. 2. ECOPOOL+++ project The ECOPOOL+++ project aims to develop a new heated pool solution, more efficient, in terms of en- ergy and water requirements, integrating an intelligent management of the various systems. The main system to be developed will consist of a thermal insulation solution inside the tank’s envelope, which will reduce energy losses and, consequently, the heating needs. An attempt will also be made to develop a new system for covering the water surface, made up of multilayer panels of glass and air, which will reduce evaporation 390 vol. 38/2022 ECOPOOL+++: Developing a sustainable outdoor heated . . . losses, which are both heat and mass, as well as heat losses by convection and radiation. Regarding water heating needs, efforts will be made to ensure that these are fully met using solar energy, maximizing solar gains through the water plan and integrating solar energy capturing systems through the use of solar panels and a heat collector floor. The possibility of heat storage through the use of reserve tanks con- taining PCMs will also be analyzed. The possibility of “diverting” the excess heat from the water body of the tank for other purposes will also be analyzed, either directly for the production of domestic hot water or for the heating of the ventilation air of changing rooms, in periods when the water temperature exceeds com- fort needs. Regarding water efficiency, systems will be studied and designed to contribute to the reduc- tion of water consumption, either through the early detection of leaks, or through the minimization of water consumption in the regeneration operations of the filtration and eventual reuse of the resulting efflu- ents. Finally, a control and monitoring system will be designed, with intelligent and predictive functions, capable of interconnecting the various technologies described above. Through the comprehensive monitoring of all sys- tems in operation in a real context, it will be possible to evaluate their respective performances (individual and in collective operation). This information will make it possible to decide which is the best opera- tional set of recommended systems for each situation in view of its geographic location. The main market objectives of this project, are: (1.) to ensure the existence of an aggregated final solution, enhancing water and thermal savings, sup- porting with greater thermal comfort (water tem- perature with an adequate level of comfort for most of the year using only solar energy) and (2.) provide the leading company’s product portfolio with a disruptive pool solution. Within the scope of this project, a small-scale proto- type will be built, incorporating all the recommended solutions, in order to test and validate the intended developments, in the technical, environmental and economic aspects, allowing the final solution to be commercially valuable and with a potential to be ex- portable. The solutions developed, in part or in a whole, will be able to be applied in existing swim- ming pools, in order to improve their energy and water efficiency. 3. ECOPOOL+++ systems In the following a description is made of the develop- ments occurring in the aim of ECOPOOL+++ project to implement the prototype of a sustainable swimming pool. 3.1. Thermal insulation system The functions, requirements and properties of the new thermal insulation systems inside the pool were stud- ied, and the main requirements that the layers of the system must meet have already been established. The system must ensure not only the limitation of heat losses by the interior lining, but also a good mechani- cal performance. The thermal insulation layer must not only have high thermal resistance but also have re- sistance to deformation. The base layer must present protection characteristics of the insulating material (impact resistance and deformation), waterproofing and support capacity of the coating, deformation ca- pacity balanced with rigidity and resistance to blis- tering under negative pressure. The bonding mortar, which will support the final coating, must comply with good adhesion to the final coating (generally ceramic), high deformability (low susceptibility to cracking and chemical resistance (joint mortar). 3.2. Performance requirements of other technological solutions The technical specifications of the equipment to be installed will be defined, in order to obtain the per- formance output of the ECOPOOL+++ system and respective subsystems. A holistic analysis of the in- teraction between the different project specialties was already carried out. For this purpose, the study was segmented into 4 different areas of expertise, namely: (a) constructive solutions; (b) hydraulic and thermal systems; (c) electrical installation and industrial automation system; and (d) the SMART platform. In the following we describe each of these areas in more detail. (a) Constructive solutions The constructive so- lutions encompass all the studies carried out in the definition of functional and performance requirements of construction materials and thus proceeded to val- idate the possibility of implementing the test bed. After validation by the University of Algarve of the test bed installation site, a summary specification of the constructive solutions was created, namely, with the definition of materials, dimensions of the pool and of the engine room. The first studies were also carried out to verify the hydraulic and thermal performance of the system, using the SOLIDWORKS software, based on the first draft of the architectural project. (b) Hydraulic and thermal systems There are two different hydraulic systems, one dedicated to wa- ter filtration, common in every swimming pool, and another for the water heating purpose. The latter is schematically represented in Figure 1. 391 M. J. Oliveira, A. Inverno, F. Farinha et al. Acta Polytechnica CTU Proceedings Figure 1. Solar heating based systems. Although a common design option is to have only one circuit to perform both functions (filtration and heating), this solution is sometimes found in swim- ming pools. The choice for this singularity in the ECOPOOL+++ project comes mainly from the flexi- bility it allows in terms of individual control of each one of the heat recovering systems. This could be also done with one hydraulic circuit, but at expenses of more valves and controls. Furthermore, the other reason for the choice is that the water flows are significantly different; those used in recirculation and filtration are much higher than those used in heating systems. Finally, the measurement of both flow rates and temperatures, in this way, makes monitoring of each heating sub-system easier. The pool’s heating systems focus on the use of solar energy as an energy source through solar collec- tors, collecting floors and heat accumulation in PCMs, whenever generation exceeds the needs, to keep the water temperature in comfortable values, i.e. between 24–26 °C. The storage in PCM materials allows shift- ing its use in periods when the water temperature drops, by known atmospheric reasons, as for exam- ple one or more days with a sky cloud’s coverage or extreme heat losses at night. These solutions will be evaluated individually and their value verified in terms of contribution to the heating of the swimming pool, which will later be done in an integrated manner. Fig- ure 1 presents the operating diagram. Currently, the simulation has started and there is not yet any results of it that could be exhibited to show in a satisfactory way the performance of the outlined systems. (c) Electrical installation and industrial au- tomation system Several sensors will be integrated in the swimming pool, allowing the measurement of local variables such as the temperature at different points, the pH of the water and the chlorine level. It will also contain a set of devices, such as: (1.) water pumps that will be automatically con- trolled, (2.) electric valves in order to select if the water flows in the thermal production and retainment systems, (3.) automatic compensation of water tank refilling according to hydrostatic level proves, (4.) pressure sensors in different parts of the hydraulic circuit to check for pressure alarms and (5.) automatic backwash systems according to differ- ential pressure on the filters, among others to be determined during the project execution. All the systems’ controls will be made recurring to industrial PLC project, and all the digital/analogue system input/output will recur to low voltage and dry contact actuation on equipment and sensors, and all the analogue probes will communicate via generic 4–20 mA and 0–10 VDC, in order to simplify equip- ment’s maintenance and replacement routines, accord- ing to the best practices of automation systems. A local controller, called Swimming Pool Control and Monitoring System (SPMS) will be responsible for the communication with the set of sensors and actuators, including interfaces that will allow the inte- gration with Internet Protocol (IP) sensors, but also Modbus or KNX automation devices. The controller will also be able to connect directly with the IP net- work of a local area network, in the house using Wi-Fi or Ethernet interfaces, or connect directly to the Inter- net using a separate access router. The architecture also considers the communication between the local controller and Internet based cloud services, through a WebSocket protocol or a Web Application Program Interfaces (Web API). The user will be able to se- lect and configure its preferences using a web Human Machine Interface (Web HMI), made available at the local controller. The draft of the “point map” of the automation sys- tem, will result from the P&ID draft and the generic specifications of the hydraulic, heat production and storage equipment. A study and definition of the ar- chitecture of communication protocols between the industrial automation system will be required, includ- ing the subsystems to be supervised and controlled, and the interconnection between the control devices and the SMART platform. As a final product the idea is that all the monitoring and controlling systems will be integrated in the local automation system, so 392 vol. 38/2022 ECOPOOL+++: Developing a sustainable outdoor heated . . . Figure 2. Intelligent monitoring and control system. (a). ECOPOOL+++ prototype (option A). (b). ECOPOOL+++ prototype (option B). Figure 3. ECOPOOL+++ prototypes. that all relevant data can be provided to the SMART Platform in order for it to run algorithms that allow the optimisation of water and energy consumption, while detecting malfunctions and water breaches. (d) SMART platform The integration of sensors, HMI and controllers enabling an intelligent control system is shown in Figure 2. It illustrates the opti- mised monitoring, activation and control architecture responsible for managing all pool equipment in order to reduce consumption and maximise the use of renew- able energy sources. The system should place the user as a central element, preventing him from having to perform individual/detailed control functions. Thus, in addition to responding to the on/off request, the system should only require the specification of the value that the user wants for the water temperature. The control of all other parameters will be done au- tomatically. The system must also learn from the users’ actions, enabling an intelligent mode, adapting to the user’s habits, minimising the need for enter- ing parameters. The control and monitoring system will work autonomously using an external SMART server, placed on the Internet/Cloud, only when it is necessary to change usage patterns. All measured variables will be sent to a cloud server, as represented in Figure 2. The local controller, rep- resented in Figure 2 as SPMS, must collect the mea- surements from the sensors and Modbus devices, send- ing them later to the cloud server. The user will always have the possibility to access the local con- troller through a web interface, which allows him to control or monitor system data. 4. ECOPOOL+++ design The prototype of the ECOPOOL+++ project will be located in the University of Algarve, at Campus da Penha, Faro, Portugal. It was established that the pool will be 10 m long by 5 m wide. The average depth should be 1.20 m with a maximum depth that can reach 1.40 m. The engine’s room will be located on a wall adjoining the pool and must allow simultaneous access to several people, with a minimum area of approximately 10 m2 and a minimum height of 2 m. The heat storage tank must have a minimum volume of 2.5 to 3.0 m3, with easy access, and must allow the replacement of all materials, if necessary. Figures 3a and 3b illustrate 2 drafts of the proto- type’s architecture (still under discussion). 393 M. J. Oliveira, A. Inverno, F. Farinha et al. Acta Polytechnica CTU Proceedings 5. Conclusions In the ECOPOOL+++ project, an innovative solu- tion for heated outdoor pools is being developed with the aims of reducing thermal losses and integrating SMART water and energy management systems. The project started in 2021 and ends in June 2023. In this article, a bibliographical review was made about the various solutions that are being considered. A sum- mary of the work already carried out was presented as well as some basic layouts already established, which will be developed in the next months. Specifically, the ongoing ECOPOOL+++ SYSTEMS as presented, includes a thermal insulation system, an hydraulic and thermal systems, electrical installation and in- dustrial automation systems, together with a smart platform. Two solutions were also presented for the proposed prototype, which will be implemented at the University of Algarve and which will allow testing and validation of all the solutions developed. It will also constitute an excellent teaching model that can be used by students of this institution. Acknowledgements The project ECOPOOL+++ is funded by FEDER, PRO- JETOS DE I&DT EMPRESAS EM COPROMOÇÃO, Programa Operacional: Programa Operacional Regional do Centro, Programa Operacional Regional do Algarve, contact n. ALG-01-0247-FEDER-047231. 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