No presente trabalho é estudada a utilização da medição setorizada como instrumento de gestão da demanda de água em sistemas prediais. Para tanto, a caracterização dos medidores e a análise das interações dos elementos de medição com o sistema de suprimento de água fria e de equipamento sanitário são realizados a partir de um enfoque sistêmico e de desempenho. Considerando a coleta de melhores informações, qualitativamente e quantitativamente acerca do consumo, essencial para a gestão da demanda de água, e especialmente em um contexto de ações de conservação, neste trabalho levantou-se os sistemas de telemedição. Apresentou-se uma proposta de planejamento de implantação da medição setorizada e quais elementos que devem ser observados para a gestão da demanda. Para subsidiar as avaliações, realizou-se o estudo de caso da medição setorizada na Universidade de São Paulo, no qual foi possível verificar a importância da sua aplicação e os resultados extremamente positivos que justificaram sua implantação. / In this work it is studied the use of submetering as an instrument of water demand management in building systems. In such way, the characterization of the meters and the analysis of the interactions of its elements with the building hydraulical system are carried on a systemic approach and performance analysis of the proposal. Considering the collection of better information of water consumption essential for the water demand management, especially in a conservation context, it was searched out the systems and the technologies of remote metering. A proposal for the planning of the submetering implantation was showed, as well as the elements that should be considered for the demand management. To make the evaluations, the case study of the submetering program in the University of São Paulo was accomplished, in which it was possible to verify the importance of its application and the extremely positive results that had justified its implantation.

Esta tese teve por objetivo verificar como expansões de área irrigada no país aumentariam o uso de água regional. Para isso, os cenários descritos no Plano Nacional de Recursos Hídricos (PNRH) foram utilizados como política de expansão para a irrigação no país. Os cenários descritos são cenário 1 (água para todos), cenário 2 (água para alguns) e cenário 3 (água para poucos), e são situações hipotéticas reportadas pelo plano. Estes cenários foram adaptados com as informações de áreas potencialmente irrigáveis descritas no estudo do Ministério da Integração Nacional (MI) sobre a Análise Territorial para o Desenvolvimento da Agricultura Irrigada. Para tal, utilizou-se um modelo computável de equilíbrio geral denominado TERM-BR, um modelo dinâmico, bottom-up, inter-regional para as simulações dos cenários de demanda futura para o uso da água. O método de Thornthwaite e Mather foi utilizado para estimar o balanço hídrico climatológico (CWB) para os estados do Nordeste e com isso avaliar a situação da disponibilidade hídrica em condições determinadas nessa região. Diversos trabalhos foram utilizados na elaboração da base de dados com informações municipais (agricultura e consumo humano) e informações estaduais (pecuária e indústria), produtividade das culturas, áreas plantadas e colhidas também foram utilizadas. Os resultados simulados sugerem que as expansões de área irrigada proporcionariam mudanças positivas nas variáveis macroeconômicos como consumo das famílias, investimento, gastos do governo, exportações, PIB para o país. Em relação as variáveis macroeconômicas regionais, o estado do Mato Grosso se destacaria em todos os cenários e apresentaria uma mudança no PIB e investimento maior no cenário 1. Expansões de área irrigada na região Centro-Oeste e Norte são viáveis em todos os cenários, especialmente nos estados do Mato Grosso, Goiás, Tocantins, Pará e Minas Gerais na região Sudeste. A maior mudança percentual no uso da água ocorreria na soja e no algodão e o maior volume de uso de água (milhões de metros cúbicos) ocorreria na cultura da cana de açúcar e no arroz. Os resultados da interação entre o modelo TERM-BR e o método de CWB para os estados do Nordeste indicam que os estados de Alagoas e Pernambuco seriam os mais propensos a ter problemas com a disponibilidade hídrica. O aumento no uso de água por região hidrográfica é condizente com o proposto no PNRH e esse aumento deveria ser maior nas regiões hidrográficas do Tocantins-Araguaia (Tocantins, Pará, Mato Grosso e Goiás) e no Atlântico Nordeste Ocidental nos estados do Maranhão e Pará. / This dissertation aimed to verify how expansions of irrigated area in the country would increase the regional water use. For this, the scenarios described in the National Water Resources Plan (PNRH in Portuguese) were used as policy for expansion of irrigation in the country. The scenarios related are scenario 1 (water for all), scenario 2 (water for some) and scenario 3 (water for few), and are hypothetical situations reported by the plan. These scenarios were adapted with the information about irrigable areas described by Ministry of National Integration (MI) on the Territorial Analysis for the Development of Irrigated Agriculture. A computable general equilibrium model namely TERM-BR was used in the simulation, this is dynamic, bottom-up, interregional model for simulations of scenarios for water. The Thornthwaite and Mather method was employed to estimate the Climatic Water Balance (CWB) for Northeastern states and to assess the water availability situation under specific conditions in that region. Several studies were compiled to elaborate the database; some with municipal information (agriculture and human consumption) and others with state information (livestock and industry). Crop productivity, and planted and harvested areas were also used. The results suggest that the expansions in the national irrigated areas would provide positive changes in macroeconomic variables such as household consumption, investment, government spending, exports, and national GDP. Mato Grosso state would stand out in all the scenarios regarding regional macroeconomic variables, and change in regional GDP and investment would be greater in scenario 1. Expansions in the Center-West and North regions are feasible in all scenarios, especially in Mato Grosso, Goiás, Tocantins, Pará and Minas Gerais state. The highest percentage change in water use would occur in soybeans and cotton crops and the largest volume of water use (millions of cubic meters) would occur in sugar cane and rice crop. The results for the interaction between the TERM-BR model and CWB method for the Northeastern states indicate that, Alagoas and Pernambuco state would be the most likely to have problems with water availability. The increase in water use by hydrographic region is consistent with that proposed in the PNRH, and this increase should be higher in the Tocantins-Araguaia hydrographic regions (Tocantins, Pará, Mato Grosso and Goiás) and in the Western Northeast Atlantic in Maranhão and Pará state.

Submitted by (lucia.rodrigues@ufrpe.br) on 2016-09-20T11:29:50Z No. of bitstreams: 1 Bianca Silva Tavares.pdf: 1057667 bytes, checksum: a43ae04d9ffa33d26ecca81010cdcde7 (MD5) / Made available in DSpace on 2016-09-20T11:29:50Z (GMT). No. of bitstreams: 1 Bianca Silva Tavares.pdf: 1057667 bytes, checksum: a43ae04d9ffa33d26ecca81010cdcde7 (MD5) Previous issue date: 2010-09-20 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / In the basin where the city of Garanhuns-PE is inserted, there are quantitative conflicts related to water resources, with potential claims over the availability. This fact makes relevant the need for proper planning of water use, especially with respect to irrigated agriculture. In recent years has increased the development and use of simulation models of water balance turned to agriculture to assist in the agricultural planning. The objective of this study was to determine the relative productivity and water balance of irrigated and rainfed conditions in micro-region of Garanhuhs, using modeling, for later use this information in agricultural planning. The study was conducted in the municipality of Garanhuns - PE, considering data from a rural property. The Computational Model for Decision Support and on Irrigation and Drainage (MCID) was used to determine the irrigation requirement (RIT) and relative productivity (YRT) in response to different management strategies for irrigation, taking into account technical and economic information of two perennial and six annual crops, time series of climate data, soil data, technical coefficients of production costs, different management of irrigation and of some rainfe crops. From the simulations it was found that the methods and irrigation management strategies used were effective in preventing drought in irrigated crops, which maximized the expression of crop yields and made null the risk related to this aspect. In terms ofrelative yield, irrigated crops banana, beans, passion fruit, corn, peppers, cabbage and tomato were optimized. The dryland crops had severe yield reduction due to water deficit. Higher values of standard deviation were observed in these crops, highlighting the uncertainties inherent in rainfed crops. Regarding the relative productivity of rainfed crops only the beans was financially viable. / Na bacia hidrográfica do Rio Mundaú onde o município de Garanhuns-PE está inserido, verificam-se conflitos de ordem quantitativa relacionados aos recursos hídricos, com demandas potenciais acima das disponibilidades. Este fato torna relevante a necessidade de planejamento adequado da utilização dos recursos hídricos, principalmente com relação à agricultura irrigada. Nos últimos anos tem aumentado o desenvolvimento e a utilização de modelos de simulação do balanço hídrico voltados às atividades agrícolas visando auxiliar no planejamento agrícola. O objetivo deste trabalho foi determinar a produtividade relativa e o balanço hídrico de cultivos irrigados e de sequeiro na microrregião de Garanhuns, utilizando modelagem, para posterior emprego destas informações no planejamento agrícola. O estudo foi realizado no município de Garanhuns - PE, considerando-se dados de uma propriedade rural. O Modelo Computacional para Suporte e Decisão em Irrigação e Drenagem (MCID) foi utilizado para determinar o requerimento de irrigação (RIT) e a produtividade relativa (YRT) em resposta a diferentes estratégias de manejo de irrigação, levando-se em consideração informações técnicas e econômicas de duas culturas perenes e seis anuais, séries históricas de dados declima, dados de solo, coeficientes técnicos dos custos de produção, diferentes manejos de irrigação e alguns cultivos de sequeiro. A partir das simulações, verificou-se que os métodos e manejos de irrigação empregados foram eficazes em evitar o déficit hídrico, nas culturas irrigadas, o que favoreceu a expressão máxima de produtividade das culturas e tornou nulo o risco com relação a este aspecto. Em termos de produtividade relativa, os cultivos irrigados de banana, feijão, maracujá, milho, pimentão, repolho e tomate foram otimizados. Os cultivos de sequeiro tiveram severa redução da produtividade devido ao déficit hídrico. Maiores valores de desvio padrão foram observados nestes cultivos, evidenciando as incertezas inerentes aos cultivos de sequeiro. Com relação à produtividade relativa dos cultivos de sequeiro apenas o feijão foi viável financeiramente.

Water shortages in certain periods have led to serious social conflicts, as well as economic and environmental impacts resulting from irrigated agriculture, especially of rice growing, which represents a high demand of water. The present study proposes a methodology for analyzing the water sustainability of rice growing through the implementation the temporary dams at the river-bed of water courses, with the study area the watershed of Arroio Grande, which has a growing need to match the conditions of supply and demand. The analysis of water supply and demand conditions was made in the context of the watershed and by control point, three scenarios are composed: scenarios 1 - the existing situation; scenario 2: considers compliance to environmental legislation, with elimination of rice growing areas in areas of permanent preservation and destination of the portion of environmental flow (30%Q90) an; scenario 3: considers compliance to environmental legislation and implementation the temporary dam at the river-beds of water courses upstream of where the shortage was indicated, as a way to expand and ensure water supply for rice growing. The results show that the in the scenario 1 the demand is met, although for control points 5 and 6 it is equivalent to 89% to 97% of its availability, besides not meet environmental legislation. For the scenario 2, control points 5 and 6 indicate water scarcity for the months analyzed (November February), indicating the places where water supply should be expanded. In scenario 3, it is concluded that the temporary dams proposed have the may partially meet the water requirements and PC 5, PC 6, the results indicate no compliance between supply and demand. Therefore, concluded that the conflicts over water use in the watershed of the Arroio Grande resulting from irrigated agriculture can be minimized with the installation of temporary dams. However, the results indicate that the water sustainability of rice growing can only be achieved by reducing the irrigated area, specifically between the PC 3-5 and 4-6. / A escassez de água em determinados períodos vem provocando sérios conflitos sociais, econômicos e ambientais, decorrentes da agricultura irrigada, especialmente da cultura orizícola, que apresenta alta demanda hídrica. Desta forma, o presente estudo propõe uma metodologia para analisar a sustentabilidade hídrica da cultura orizícola através da implantação de barragens temporárias no álveo de cursos d água, tendo como área de estudo a sub-bacia hidrográfica do Arroio Grande, que apresenta uma crescente necessidade de compatibilizar as condições de oferta e demanda. A análise das condições de oferta e demanda hídrica foi realizada no contexto da sub-bacia e por ponto de controle (PC), sendo compostos três cenários: cenário 1 - situação existente; cenário 2: considera o atendimento a legislação ambiental, com a eliminação de áreas de cultivo orizícola em Áreas de Preservação Permanente (APP) e destinação da parcela de vazão ambiental (30%Q90) e; cenário 3: considera o atendimento a legislação ambiental e propõe a implantação de barragens temporárias no álveo de cursos d água, a montante dos locais que indica escassez, como forma de ampliar o suprimento hídrico da cultura orizícola. Os resultados mostraram que no cenário 1 a demanda é atendida, embora para os pontos de controle 5 e 6, equivale de 89% a 97% da disponibilidade hídrica, além de não atender a legislação ambiental. Para o cenário 2, os pontos de controle 5 e 6 apontam escassez hídrica para os meses analisados (novembro a fevereiro), indicando assim os locais em que a oferta hídrica deverá ser ampliada. No cenário 3, conclui-se que as barragens temporárias propostas poderão atender parcialmente a demanda hídrica do PC 5 e, no PC 6, os resultados indicam não haver conformidade entre oferta e demanda. Desta forma, conclui-se que os conflitos pelo uso da água na sub-bacia hidrográfica do Arroio Grande decorrentes da agricultura irrigada poderão ser minimizados com a implantação das barragens temporárias. Entretanto, os resultados indicam que a sustentabilidade hídrica da cultura orizícola somente poderá ser alcançada com a redução da área irrigada, especificamente, entre os PC 3 - 5 e, 4 - 6.

Magister Administrationis - MAdmin / This study examined the impact of the City’s water management strategies, specifically the water management devices, on selected households in Saxonsea. The impact of cost recovery policies on poor households was interrogated in the light of government’s distributional and procedural equity in service delivery. The main issues arising from the study were lack of consultation, inadequate information, and perception of powerlessness. The study concludes that although water management devices have contributed to significant improvements in water saving, poor households are burdened with the responsibility of saving water. If the idea is to save water across the board, this regimen should be extended to all water users and not targeted at poor households only

Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Globally, irrigation constitutes the human activity with increased freshwater demand. In this sense, it is necessary strategies that reduce the most of this consumption. Irrigation of sugarcane, an alternative is to synchronize the phenological stage of the plant that requires more water, the season of greater water availability in the region, reducing spending on irrigation and reducing costs in production. Thus, the aim of this study is to establish time of sugarcane plantations, second sheet, which results in greater efficiency of water use, when considering the summer planting of Northeastern Brazil. For this, two experiments were conducted, evaluating two varieties RB92579 and RB962962 cane. The experiments were conducted in the commercial area of plant Cururipe SA using subsurface drip irrigation system. The experimental design was a randomized block design with four replicates per variety, with the treatment the planting dates: E1-October, E2-November, E3-December 2013, E4-January and E5-February. At the end of the crop cycle were evaluated physical and technological yields of the crop. Efficiency in water use (USA) for each treatment was defined as the ratio between the physical performance (TCH) or technological (TAH) culture and the volume of water that entered the system, either through irrigation, the total rainfall or effective rainfall. In both varieties of sugarcane, the E1 and E4 treatments had the highest values of TCH and TAH. The variety RB92579 both planting October as the January showed greater US. The variety RB962962 the largest US using as a basis the TCH was in the months of October and January, already in base TAH were the months of November and January. The months of planting that maximized the net of the production system of sugarcane revenues were October and January for the variety RB92579 and the variety RB962962 plantations November and January. / Em termos globais, a irrigação se constitui na atividade humana com maior demanda de água doce. Neste sentido, é preciso estratégias que diminuam ao máximo este consumo. Na irrigação da cana-de-açúcar, uma alternativa é a sincronização da fase fenológica da planta que mais necessita de água, com a estação do ano de maior disponibilidade hídrica da região, reduzindo gastos na irrigação e diminuindo custos na produção. Com isso, o objetivo do presente estudo é estabelecer a época de plantio de cana-de-açúcar, primeira folha, que redunda em maior eficiência de uso da água, quando considerando o plantio de verão da região Nordeste do Brasil. Para isso, foram conduzidos dois experimentos, avaliando duas variedades de cana RB92579 e RB962962. Os experimentos foram conduzidos em área comercial da Usina Cururipe SA utilizando sistema de irrigação por gotejamento subsuperficial. O delineamento experimental utilizado em cada variedade foi em blocos ao acaso, com quatro repetições, tendo como tratamento as épocas de plantio: E1-Outubro, E2- Novembro, E3-Dezembro de 2013, E4-Janeiro e E5-Fevereiro. Ao final do ciclo de cultivo foram avaliados os rendimentos físicos e tecnológicos da cultura. A Eficiência de Uso da Água (EUA) para cada tratamento, foi definida através da razão entre o rendimento físico (TCH) ou tecnológico (TAH) da cultura e o volume de água que entrou no sistema, seja através de irrigação, da precipitação total ou da precipitação efetiva. Em ambas as variedades de cana, os tratamentos E1 e E4 obtiveram os maiores valores de TCH e TAH. Na variedade RB92579 tanto o plantio de Outubro quanto o de Janeiro apresentaram maior EUA. Na variedade RB962962 a maior EUA usando como base o TCH foi nos meses de Outubro e Janeiro, já em base de TAH foram os meses de novembro e janeiro. Os meses de plantio que maximizaram a receita líquida do sistema de produção da cana-de-açúcar foram Outubro e Janeiro para a variedade RB92579 e para a variedade RB962962 os plantios de Novembro e Janeiro.

Los Angeles has historically been subjected to droughts and water shortages. This has led the city to acquire distant water resources, allowing the city to grow extensively. Today, the city is dependent on large water infrastructure to supply water over distances of hundreds of kilometres. This thesis explores how water demand in Los Angeles has been impacted by drought, focusing on drought years 2007-2010 and 2012-2019. The study compares hydrological, conservation and water demand data and places it into context by connecting it to policy changes. By looking at streamflow and precipitation data it is visible that the latter drought was drier than the former. Water demand has decreased in all consumer categories. Meanwhile, conservation has increased. Drought events have led the city to apply policy changes and conservation measures which in turn, has resulted in a reduction in water demand during both droughts. / I Los Angeles har det historiskt sett förekommit både torka och vattenbrist. Detta har lett till att vattenresurser anskaffats från avlägsna platser, som i sin tur har möjliggjort stadens tillväxt. I dagsläget är staden beroende av storskalig vatteninfrastruktur som försörjer invånarna med vatten från hundratals kilometer bort. I kandidatarbetet utforskas torkans inverka på vattenefterfrågan i Los Angeles. Torkan som rådde mellan åren 2007–2010 och 2012–2019 undersöks genom att studera data om hydrologi, vattenefterfråga och vattenbevaring, samt genom att koppla dessa till den politiska diskursen. Det framkommer att den senare torkan var torrare än den andra. Efterfrågan har minskat i alla konsument- klasser, medan bevarandet av vatten har ökat. Torka har lett till att staden implementerat politiska förändringar och bevarandeåtgärder som i sin tur lett till en minskad vattenefterfrågan.

This thesis is focused on the optimization of pressure conditions in the water supply network. There is a deep theoretical and critical search of the state of the art and there are fields where there is an insufficient field of knowledge, the so-called "knowledge gap". Experiments are proposed here to determine the dependence of water consumption on pressure conditions. There is a description of experiments and way how it was carried out, which were carried out on the water connection, in the pressure zone and in the laboratory on the hydraulic loop. There is proposed a methodology of experimental determination of the mathematical dependence of water consumption on pressure so that it can be used for optimization problems, where consumption is considered as an optimization criterion. The results of individual experiments are evaluated and a critical discussion of the achieved results is carried out. Finally, the achieved results are compared with the values found in a deep literature search.

An accurate model for RO process has significant importance in the simulation and optimization proposes. A steady state model of RO process is developed based on solution diffusion theory to describe the permeation through membrane and thin film approach is used to describe the concentration polarization. The model is validated against the operation data reported in the literature. For the sake of clear understanding of the interaction of feed temperature and salinity on the design and operation of RO based desalination systems, simultaneous optimization of design and operation of RO network is investigated based on two-stage RO superstructure via MINLP approach. Different cases with several feed concentrations and seasonal variation of seawater temperature are presented. Also, the possibility of flexible scheduling in terms of the number of membrane modules required in operation in high and low temperature seasons is investigated A simultaneous modelling and optimization method for RO system including boron removal is then presented. A superstructure of the RO network is developed based on double pass RO network (two-stage seawater pass and one-stage brackish water pass). The MINLP problem based on the superstructure is used to find out an optimal RO network which will minimize the total annualized cost while fulfilling a given boron content limit. The effect of pH on boron rejection is investigated at deferent seawater temperatures. The optimal operation policy of RO system is then studied in this work considering variations in freshwater demand and with changing seawater temperature throughout the day. A storage tank is added to the RO layout to provide additional operational flexibility and to ensure the availability of freshwater at all times. Two optimization problems are solved incorporating two seawater temperature profiles, representing summer and winter seasons. The possibility of flexible scheduling of cleaning and maintenance of membrane modules is investigated. Then, the optimal design and operation of RO process is studied in the presence of membrane fouling and including several operational variations such as variable seawater temperature. The cleaning schedule of single stage RO process is formulated as MINLP problem using spiral wound modules. NNs based correlation has been developed based on the actual fouling data which can be used for estimating the permeability decline factors. The correlation based on actual data to predict the annual seawater temperature profile is also incorporated in the model. The proposed optimization procedure identified simultaneously the optimal maintenance schedule of RO network including its design parameters and operating policy. The steady state model of RO process is used to study the sensitivity of different operating and design parameters on the plant performance. A non-linear optimization problem is formulated to minimize specific energy consumption at fixed product flow rate and quality while optimizing the design and operating parameters. Then the MINLP formulation is used to find the optimal designs of RO layout for brackish water desalination. A variable fouling profile along the membrane stages is introduced to see how the network design and operation of the RO system are to be adjusted Finally, a preliminary control strategy for RO process is developed based on PID control algorithm and a first order transfer function (presented in the Appendix). / Government grant

Desalination technology provides fresh water to the arid regions around the world. Multi-Stage Flash (MSF) distillation process has been used for many years and is now the largest sector in the desalination industry. Top Brine Temperature (TBT) (boiling point temperature of the feed seawater in the first stage of the process) is one of the many important parameters that affect optimal design and operation of MSF processes. For a given pressure, TBT is a function of Boiling Point Temperature (BPT) at zero salinity and Temperature Elevation (TE) due to salinity. Modelling plays an important role in simulation, optimisation and control of MSF processes and within the model, calculation of TE is therefore important for each stages (including the first stage, which determines the TBT). Firstly, in this work, several Neural Network (NN) based correlations for predicting TE are developed. It is found that the NN based correlations can predict the experimental TE very closely. Also predictions of TE by the NN based correlations were found to be good when compared to those obtained using the existing correlations from the literature. Secondly, a hybrid steady state MSF process model is developed using gPROMS modelling tool embedding the NN based correlation. gPROMS provides an easy and flexible platform to build a process flowsheet graphically. Here a Master Model connecting (automatically) the individual unit model (brine heater, stages, etc.) equations is developed which is used repeatedly during simulation and optimisation. The model is validated against published results. Seawater is the main source raw material for MSF processes and is subject to seasonal temperature variation. With fixed design the model is then used to study the effect of a number of parameters (e.g. seawater and steam temperature) on the freshwater production rate. It is observed that, the variation in the parameters affect the rate of production of fresh water. How the design and operation are to be adjusted to maintain a fixed demand of fresh water through out the year (with changing seawater temperature) is also investigated via repetitive simulation. Thirdly, with clear understanding of the interaction of design and operating parameters, simultaneous optimisation of design and operating parameters of MSF process is considered via the application MINLP technique within gPROMS. Two types of optimisation problems are considered: (a) For a fixed fresh water demand throughout the year, the external heat input (a measure of operating cost) to the process is minimised; (b) For different fresh water demand throughout the year and with seasonal variation of seawater temperature, the total annualised cost of desalination is minimised. It is found that seasonal variation in seawater temperature results in significant variation in design and some of the operating parameters but with minimum variation in process temperatures. The results also reveal the possibility of designing stand-alone flash stages which would offer flexible scheduling in terms of the connection of various units (to build up the process) and efficient maintenance of the units throughout the year as the weather condition changes. In addition, operation at low temperatures throughout the year will reduce design and operating costs in terms of low temperature materials of construction and reduced amount of anti-scaling and anti-corrosion agents. Finally, an attempt was made to develop a hybrid dynamic MSF process model incorporating NN based correlation for TE. The model was validated at steady state condition using the data from the literature. Dynamic simulation with step changes in seawater and steam temperature was carried out to match the predictions by the steady state model. Dynamic optimisation problem is then formulated for the MSF process, subjected to seawater temperature change (up and down) over a period of six hours, to maximise a performance ratio by optimising the brine heater steam temperature while maintaining a fixed water demand.