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Solar Thermal Energy

Other Components Solar Thermal Energy

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Thermal solar energy systems incorporate components that allow their correct operation and control. Some are mandatory (safety elements) and others are incorporated for better performance and maintenance of the system.

The expansion vessel is one of the essential safety elements for the system to work correctly, since its function is to absorb the expansion of the fluid at the moment it overheats.

Closed expansion vessels are the most widely used in solar thermal systems, since all of them are carried out in a closed circuit.

In this case, it is a hermetically sealed container divided into two chambers, one for fluid (1) and the other for gas (2), separated by a membrane (3) as can be seen in the diagram below.

The membrane (high quality synthetic rubber) is flexible and allows chambers volume to be variable depending on each moment needs.

What is intended is to provide an extra capacity to the circuit, which allows it to absorb fluid expansion, so it must be dimensioned to support said expansion in the most unfavorable conditions.

When membrane has expanded to the maximum and the vessel can no longer absorb any more expansion, the circuit pressure will increase as the temperature of the fluid increases, until causing the safety valve to actuate (limit situation).

In principle, the expansion vessel can be located both at the outlet and at the return of the system because, as it is a closed circuit, the fluid expansion will be the same on one side as on the other. Despite this, it is always better to locate all components, if possible, in the cold part of the system for greater durability.

The expansion vessels will preferably be connected to the suction of the pump.

Another important component is the manometer. This element is used to know the pressure value in kg/cm2 inside a pipe or tank.

MANOMETRO I.S.R. M1/4" 6 bar - Industrial llobera

The choice of valves will be made according to the function they will perform and the extreme operating conditions (pressure and temperature).

The nominal pressure PN, expressed in bar or kp/cm2, and the nominal diameter DN, expressed in mm or inches, shall be stamped on the valve body, at least when the diameter is equal to or greater than 25 mm.

The minimum nominal pressure of all types of valves and accessories must be equal to or greater than 4 kp/cm2. The free diameters in the valve seats must correspond to their nominal diameters, and in no case less than 12 mm.

The characteristic valves of a solar thermal energy system are:

1) Safety valve: due to their important function, they must be capable of deriving the maximum power from the collector or group of collectors, even in the form of steam. Its placement is recommended in all circuits subjected to pressure and temperature variations.
The pressure at which the valve acts (set) allowing the fluid to escape must be less than the pressure that the most delicate element of the system can withstand, which is usually the expansion vessel or the manifold.
It is convenient to place a drainage funnel in the discharge to know when a safety valve acts.

DUCO Válvula de seguridad Solar H-H

2) Non-return valves: they only allow fluid flow in one direction. Most used are:
– Those with a clapper: when the fluid circulates, it pushes a gate that closes immediately when circulation stops, preventing passage in the opposite direction. They produce little load loss, so they are recommended for primary circuits. It is not advisable to use them in diameters greater than 40 mm.
– The shell: when the fluid circulates, it pushes a spring, which moves the shutter shell, allowing its circulation. When circulation ceases, the howitzer returns to its initial position, preventing passage in the opposite direction.
They cause a greater pressure drop than those with clapet, so they are only recommended for secondary circuits subjected to mains pressure.

Válvula antirretorno: ¿Qué función tiene y dónde colocarla? – STHexpert

3) Stop valves: they are responsible for totally or partially interrupting the fluid flow through the pipes. Those of total closure separate a part of the installation or isolate it from the service. The partial closing ones produce an additional pressure drop in the circuit to regulate the flow or balance the system.

Instalación solar: Componentes y válvulas para placas solares

4) 3 and 4-way valves: they are used for fluid circulation through alternative routes. They are almost always placed with automatic devices so that an electrical signal, generally coming from a thermostat or probe, activates the mechanism by opening and closing corresponding pathways.

OVENTROP: Válvulas de 3-vías de mezcla y distribución "Tri-CTR" PN16

5) Drain valves: they are generally placed in the lower part of the circuits for maintenance operations or replacement of a damaged component of the system.

Válvulas de vaciado archivos - Potermic

For different reasons (filling, cooling after a large expansion of the heat transfer fluid, etc.) solar thermal systems are sometimes affected by a problem that can impair their operation or greatly reduce their performance: air bubbles in inside the pipes.

To eliminate bubbles from the heat transfer fluid, there are devices called purgers, which are designed to capture these bubbles and expel them to the outside.

Its operation is automatic, due to the fact that the bubbles tend to rise and settle above the fluid, the trap is placed at the highest point of the system.

Sometimes it is mounted on a deaerator, a device that has a great capacity to trap the bubbles in the fluid, the purger being in charge of evacuating the air.

Purgador Solar 3/4" FERCO PS3

The thermometer will allow us to measure the temperature of the fluid in different places of the system.

The most used are:
– Contact: they are placed by holding them on the pipes by means of a clamp.
– Immersion: they are inserted inside the pipe, accumulator or exchanger inside a sheath and are provided with a bulb of different lengths. Their reliability is greater because they are in direct contact with fluid.

Termómetro y Termostato - Eficiencia Energética

Thermostats are responsible for transforming a predetermined temperature reading on their scale into an electrical signal that activates a certain mechanism (starts or stops it) depending on the function entrusted to it.

The differential thermostat and the temperature probes that it has must ensure that the circulation pump only works when the collectors can provide a useful gain and stops when there is no capture or it is not sufficient.

One of the probes is placed at the outlet of the collectors and the other at the bottom of the storage tank. The differential thermostat will be connected to the circulation pump. Connections must be made with solder and wires must not have splices.

The mission of the differential thermostat is to compare the temperatures recorded by the probes, so that when there is a predetermined temperature difference between them favorable to the collectors, the circulation pump starts up.

Termostato Varilla Termo Electrico Ø6 x 270 mm. | eBay

The immersion electrical resistance is an element widely used as an auxiliary system in solar energy systems for the production of DHW. As it is a submerged hot spot in the circuit, it tends to accumulate calcareous deposits. To avoid this, some manufacturers incorporate it in the primary circuit. This is a serious mistake because this energy source can be given priority to the detriment of the energy coming from the collectors.

Resistencia eléctrica 3000w OW-R3

Medium and large systems have an electrical and control device.

The analog variables that must be measured by the monitoring system will be at least 6, and among which the following 4 must be included:

Cold water inlet temperature.
Solar hot water supply temperature.
Temperature of hot water supply to consumption.
Consumption water flow.

With the recorded data, the results will be analyzed and the daily performance of the system will be evaluated. These data will be filed in a historical record of benefits.

Energía Solar Térmica para ACS en un Colegio de Barcelona - ATEGA Instal·lacions S.L.L. Expertos en Energía Solar

This content was extracted from the Solar Thermal Energy Technical-Commercial Manual and is part of Solar e-learning.

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Solar Thermal Energy

Solar Thermal Insulation

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Thermal insulators are essentially characterized by their thermal resistance and thermal inertia.

Thermal resistance is defined as difficulty that a product of a given thickness presents in allowing heat to pass under unit surface conditions, temperature difference and time. By definition, it is ratio of thickness to thermal conductivity.

Thermal inertia is physical ability of a material to maintain its temperature.

The best insulators are air, polyurethane foam, fiberglass, cork (expanded), glass foam, wood fiber sheeting, sponge rubber, PVC, expanded vermiculite, sawdust, loose vermiculite, and linoleum.

Thermal insulation primarily represents economy, because by preventing heta transmission, passage of energy from one body to another is avoided. In addition, thermal insulation represents an investment that will be recovered in a relatively short time, with energy savings that will be obtained, and with best efficiency and operation of equipment and machinery.

If solar thermal system is not thermally insulated there will be a loss of heat and to counteract this phenomenon system will have to resort to auxiliary energy to be able to maintain the required temperature. Therefore, if the system is thermally isolated, heat loss will be avoided and solar energy will be used, preventing auxiliary energy equipment from being activated.

Thermal insulation will also represent protection for personnel who may be in accidental contact with hot surfaces.

Resultado de imagen de aislamiento solar térmico

Characteristics of a good insulator:

1. Low heat conductivity.
2. Lightweight (do not burden system weight)
3. Fireproof and rot resistant
4. That it is not attacked by rodents or insects and that it does not breed insects
5. Inert
6. Easy to place.

Places where insulation is most relevant are: collectors back, pipes and accumulator.

As a reference, minimum insulation thickness of interior pipes is set in Spain by the RITE (Regulation of Thermal Installations of Buildings), as indicated in the following table:

Resultado de imagen de grosor mínimo del aislamiento de las tuberías interiores está fijado en España por el RITE

For materials with a thermal conductivity other than 0.04 W / m ºC, thickness will be determined by multiplying table value by λ and dividing by 0.04.

For pipes sections installed outside, minimum thickness indicated in the previous table must be increased by 10 mm.

The insulating material shall be secured with suitable means, so that it cannot detach from the pipes or fittings.

Insulation will not leave visible areas of pipes or accessories, leaving only the elements that are necessary for proper functioning and operation of components to the outside.

For protection of outdoor insulating material, a plaster cover or coating protected with asphalt paints, fiberglass reinforced polyesters or aluminum sheet may be used. In case of tanks or heat exchangers located outdoors, plastic fabric linings may be used.

Special care must be taken to guarantee pipes insulation durability, especially in outdoor sections exposed to sun, which must have the following insulation characteristics:

• Inalterability due to atmospheric agents and resistance to fungi formation.
• Resistance to solar radiation; otherwise, it must be adequately covered with protective covers or paints.
• Sealing of passages to outside and elimination of thermal bridges.

This content was extracted from the Solar Thermal Energy Technical-Commercial Manual and is part of Solar e-learning.

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Solar Thermal Energy

Solar Thermal Pumping Systems

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There are three main types of pumping systems or electrocirculators:

1. Alternatives
2. Rotary
3. Centrifuges

Usually used in solar thermal energy systems are centrifuges.

The electrocirculator or pump is the element of solar thermal system in charge of moving the fluid from primary circuit, or other closed circuits of the system (circuit between accumulator and external exchanger, recirculation rings for domestic hot water, heating circuits, etc.).

In the particular case of primary solar circuit, the objective of forcing this circulation is to transport the heat from solar collectors to exchanger, compensating for pressure losses (resistance to fluid movement) of different accessories that make up the circuit: pipes, valves, branches, manifolds and exchanger.

In most solar hot water production systems, circulating flows are not very important. The most widely used pumps are in-line, single-phase and small-power type.

Ver las imágenes de origen

Different materials are used to manufacture pump body depending on the circuit in which it is integrated:

– Closed circuits: cast iron is the most used material in manufacture of the hydraulic body of pumps intended for these circuits, since it is cheaper than other materials. Circulating liquid is always the same, generally water with anti-calcareous and antifreeze additives. In addition, this fluid is not for consumption, so it does not have to keep the characteristics of water unchanged.

– Open circuits: bronze and stainless steel are the most widely used materials in open circuits. The liquid that circulates is drinking water and, therefore, salts that it contains dissolved cause calcification and corrosion problems in certain materials, such as cast iron. Furthermore, having to be in contact with drinking water, the construction material of roller must keep the characteristics of water unchanged.

The behavior of the electrocirculator is represented:

P = C. p

Where:

P is the required power

C is the flow (l / sec) between two points of a pipe with pressure difference p

This means that pump power is a function of head loss and flow rate.

With these two axes manufacturer will represent it in its characteristic curve, each pump having its own characteristic curve.

Ver las imágenes de origen

With time passage, pipes acquire corrosion, so pressure drop increases. Generally the calculations are made as if there were only water in the system, while antifreeze is often added, for this reason in practice the chosen pump must be a little oversized.

The pumps usually have several speeds and manufacturer indicates this in their graphics. It is advisable to work at an intermediate speed in order to increase or decrease speed if we have fallen short or have oversized the pump respectively.

By associating two electric pumps in series, manometric height is greatly increased and flow rate is low, while if they are connected in parallel, flow rate increases greatly and pressure does little.

Pump has to counteract pressure drop only on the worst track. If circuit is balanced, one will be chosen at random.

Circuit is preceded by a filter to prevent impurities from entering the welds and rest of system into the pump. It also has a non-return valve to prevent backflow of heat transfer fluid from collector to the pump. The cutoff wrenches are used in case of pump failure to be replaced or repaired.

By operating stopcocks, we obtain delivery pressure and suction pressure on the manometer. If we subtract the results, pressure drop is obtained, which must coincide with that of the system.

At the rear electrocirculator must have a small pressure to be able to start, regulations indicate that it must be at least 2 bar or 5 bar for high temperatures.

Funcionamiento de la energía solar térmica | Ekidom S.L. Energías ...

Experience indicates that for a flat collectors system minimum necessary flow is 50 liters per hour per m2 of collecting surface if heat transfer fluid is water. If it is an antifreeze mixture, flow rate will be higher to compensate for lower capacity to transport heat. For this we must take into account relationship between antifreeze mixture Ce and water Ce.

In general, thermal flow should be at least equal to 50 kilocalories for each collector´s square meter, for each hour and for each thermal jump degree centigrade. For example: if fluid experiences a thermal jump of 5º C in collectors, minimum thermal flow will be = 50 x 5 = 250 kcal / h / m2.

When we speak of a certain flow we are referring to volume that each collector’s square meter actually passes through in time unit considered.

Once the flow has been found, head losses that this flow causes in system must be calculated, which will be the sum of head losses of each components (pipes, accessories, exchanger, etc.).

The best way to carry out calculation will always be to go to the flow-pressure characteristic curves in pump´s technical data sheet.

This content was extracted from the Solar Thermal Energy Technical-Commercial Manual and is part of Solar e-learning.

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Panama

Panama Solar Thermal

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Despite solar radiation high levels and its strong dependence on fossil fuels, only in 2018 did Panama begin to promote solar thermal technology incorporation.

The starting point was “Termosolar Panamá”.

This is a project executed through an inter-institutional alliance between the UN Environment Regional Office for Latin America and the Caribbean and the National Energy Secretariat (SNE), with the financial support of the Global Environment Facility (GEF) and the support of various allies from public and private sectors.

The objective is to install 1 million square meters of solar thermal technology applications for water heating throughout the country by 2050. With this, country will reduce 6.4 million tons of CO2 and Panamanians will save more than US $ 3 million annually in fossil fuels.

Some 10 million dollars will be invested to achieve this objective.

Termosolar - Calentamiento de agua con energía solar en Panamá ...

The project began in June 2018 and has been supported by a broad portfolio of partners from public and private sectors, such as the Banco General, the Panama Green Building Council, the Technological University of Panama, the Municipality of Panama, the National Institute of Vocational Training and Training for Human Development (Inadeh), among others.

One of the 4 direct objectives of the project is the implementation of demonstration pilot projects with solar water heating systems nationwide. This involved carrying out energy audits in residences, shops and hospitals that were selected to participate; which led to the identification of savings opportunities and market potential that exists in the country.

The project has so far installed a total of 100 pilot heaters in health and social care buildings, hotels, private companies and private residences.

Some of the centers where the use of technology was contemplated are the San Miguel Arcángel Hospital in Panama, the Luis “Chicho” Fábrega Hospital in the province of Veraguas, the José Domingo de Obaldía Maternal and Child Hospital in the Chiriquí province, and children dining rooms in Panama City.

The Veterinary Wildlife Clinic of Panama Summit Municipal Park became first beneficiary of public sector.

Of 100 pilots established, 30 were assigned to residential sector.

Panamá instalará 100 calentadores solares en edificios públicos y ...

The project envisages the development of a package of political and fiscal measures that allow the growth of solar thermal technology in country, as well as the adoption of quality assurance and control standards, both for equipment to be imported or manufactured, and for techniques of equipment installation.

Termosolar Panamá also contemplates the creation of capacities and professionals training for solar water heating systems management.

The General Bank designed a financial mechanism to grant credit lines to residential and commercial sector that it wishes to implement this system. Feasibility analyzes and design of solar water heater system will be financed by the project.

This government initiative has managed to stimulate the reactions of Panamanian private company. Scopes with an interesting and very marked potential are hotel, food and health sectors.

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Solar Thermal Energy

Solar Exchanger

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In solar thermal energy systems, heat exchanger is in charge of transmitting the heat energy collected by solar collectors to medium that needs to be heated.

Depending on type of heat transfer system used, they can be classified into:

• Direct: Domestic hot water for consumption circulates through primary circuit and, therefore, will circulate through collectors. This system is suitable for small systems located in areas where there is no freezing danger. The trend is towards the restriction of its use, not being admitted in several countries.

• Indirect: Domestic hot water for final consumption circulates only through secondary circuit, which means that heat transfer liquid only flows through the primary circuit and is never in contact with domestic hot water. In this case, an exchanger is needed to pass the heat collected in first to second circuit.

The selected exchanger will withstand the maximum working pressure of the system.

According to section HE-4 of Spanish CTE:

– In case of an independent heat exchanger, the minimum power of heat exchanger P will be determined for working conditions in day central hours, assuming a solar radiation of 1,000 W / m2 and a performance of solar energy conversion to heat of 50 %, fulfilling the condition:

P = 500. A

Being:
P = minimum power of the exchanger [W]
A = the collector area [m2].

– In case of an exchanger incorporated into the accumulator, the ratio between useful exchange surface and total collection surface shall not be less than 0.15.

In each of water inlet and outlet pipes of the heat exchanger, a shut-off valve will be installed next to the corresponding sleeve.

The heat exchangers used in sanitary water circuits will be made of stainless steel or copper.

The design head loss in the heat exchanger shall not exceed 3 m / ac, both in primary and in secondary circuit.

Solar exchangers type:

Plate heat exchanger: This type of heat exchanger is made up of a series of corrugated metal plates, joined together in a frame by pressure and sealed by a gasket. Plates form a series of interconnected corridors through which working fluids circulate. These fluids are powered by pumps.

In order to choose correct plate heat exchanger for the system, it is necessary to consult the manufacturer’s guidelines. However, it is recommended that the thermal power to be transferred (in Kw) is equal to 2/3 of the collecting surface (in m2).

Ver las imágenes de origen

Double wrap exchanger: this system consists of a tank in which the secondary fluid (hot water) is accumulated and which has a double wall through which heat transfer fluid circulates, giving heat to domestic hot water.

Exchanger’s operating conditions dictate the choice of its material, which is usually carbon steel or alloy steels. Minimum exchange surface must be between 1/4 and 1/3 of useful collectors surface. However, there is a geometric limit to its use, which is given by housing dimensions. For a certain range of measurements, exchange surface can become less than a quarter collector surface. For volumes greater than 750 liters, the necessary exchange surface (which is the accumulator wall) is increasing and could result in very high accumulators for which it would be necessary to have a suitable machine room.

Ver las imágenes de origen

Coil exchanger: is made up of a tube that is submerged in a tank where the secondary fluid accumulates. The primary or heat transfer fluid circulates inside the tube, giving heat to the secondary fluid.

According tube shape they are distinguished:

• Helical coil exchanger. The spiral wound tube that carries heat transfer fluid is submerged inside accumulator at the bottom.

Ver las imágenes de origen

• Tube bundle coil exchanger. They are commonly used to obtain ACS. Primary fluid circulates through several tubes, not one as in the helical. Liquid flows inside coil by forced circulation, while outside the fluid in contact with coil is renewed by natural circulation.

Ver las imágenes de origen

To know if a coil heat exchanger is suitable for use in solar applications, its minimum exchange surface must be between 1/4 and 1/3 of collectors useful surface.

The exchange surface of a helical coil or tube bundle will be the lateral surface of a cylinder based on outer section of the tube used and by height total length of the same. With this criterion it will be easy to size a tubular exchanger.

Some recommendations:
– The coil must be placed in the lowest part of accumulator.
– If it is helical, distance between turns should be equal to 2 times outer diameter of the tube.
– If we use antifreeze in a proportion of up to 30%, exchange surface must be increased by 10%.

This content was extracted from the Solar Thermal Energy Technical-Commercial Manual and is part of Solar e-learning.

All you need is Sun. All you need is Sopelia.

Solar Thermal Energy

Solar Accumulator Tanks

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Accumulator is responsible for storing the thermal energy generated by the solar collectors.

It is essential in solar systems since periods of solar radiation and energy transfer do not usually correspond to periods in which hot water consumption takes place.

Storing energy using hot water is cheap, easy to handle, has a high heat capacity and is at the same time the consumption element in case of DHW (domestic hot water).

Accumulator type depends on the application: domestic hot water, air conditioning, heating or industrial use.

Ver las imágenes de origen

Most common are:

– Domestic hot water accumulators: they must be able to withstand high levels of pressure and expected working temperatures, not suffer deterioration due to corrosion phenomena and compulsorily comply with requirements for storing drinking water.
They are generally offered with capacities of 100 to 5,000 liters of accumulation.

– Inertia accumulators: they are used as a heat accumulator for heating systems or for large DHW installations. They fulfill the function of buffer for heat or cold storage. They act as hydraulic memory between heat production and release.
They are generally offered with capacities of 500 to 5,000 liters of accumulation.

– Combined accumulators: they combine accumulation of DHW and accumulation of heating.
In the same accumulator, for example, 175 liters of DHW accumulation and 600 liters of heating accumulation are combined.
They are generally offered with capacities from 175 to 250 liters for DHW accumulation and 500 to 2,000 liters for heating accumulation.

The most used materials accumulators’ construction are:

– Steel: it needs internal treatments based on epoxy or vitrified to avoid corrosion.

– Stainless steel: it is without a doubt the best material.

– Galvanized steel: accumulation temperature must not exceed 65º C.

– Reinforced fiberglass: resists corrosion, weighs little and is easy to maintain, but withstands low temperatures (60º C maximum).

– Plastics: it has similar qualities to fiberglass.

– Aluminum: it is not advisable due to corrosion problems.

In addition to interior treatments, accumulators incorporate corrosion protection devices.

One of the problems caused by corrosion is that rust and sediments favor the legionella development.
It is essential to avoid it by building accumulators with noble materials such as some type of stainless steel and / or combination of some inner lining and a cathodic protection system.

Accumulators are usually cylindrical in shape and have a vertical dimension greater than horizontal one to favor thermal stratification of the inside water.
Hottest water from top will be located in the extraction zone towards consumption or towards conventional support system. Coldest water is in the lower part of the tank, which will be from where it will be pushed towards solar collectors.
In this way, we operate the collectors at the minimum possible temperature, increasing their performance.

Ver las imágenes de origen

Accumulation volume size depends mainly on three factors:

1 • Installed collectors surface

As a general criterion for DHW, an accumulation volume between 50-100 liters per m2 of solar collector is recommended.
Higher values do not lead to a significant increase in solar energy use, and accumulator cost increases.
In contrast, smaller sizes increase the temperature, thus decreasing collectors’ efficiency.
For small DHW systems production, solar tank capacity should be equal to daily hot water consumption.

2 • Operating temperature

This will determine type of stratification device, as well as insulator thickness to be used, depending on maximum losses that are admissible considered.

3 • Offset between collection – storage and consumption

Accumulation volume will be a function of lag between collection – storage and consumption period, which can be:

* Coincidence between collection period and consumption period (case of preheating a boiler in a continuous process).
In this case, accumulator specific volume will be 35-40 liters / m2.

* Offsets between collection and consumption not exceeding 24 hours (heating of sanitary water in multi-family homes, hotels, etc.).
In this case, volume will be 60-90 liters / m2.

* Offset between usual and periodic collection and consumption for more than 24 hours and less than 72 hours (heating of domestic hot water in industrial processes, etc.).
In this case, volume will be 75-100 liters / m2.

* Offsets between collection and consumption greater than 72 hours (heating of sanitary water in second home, on weekends.).
In this case, volume will be determined by balancing energy losses and gains and insulation optimizing.

This content was extracted from the Solar Thermal Energy Technical-Commercial Manual and is part of Solar e-learning.

All you need is Sun. All you need is Sopelia.

Nicaragua

Nicaragua Solar Thermal

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Undoubtedly, the emblematic project, in terms of thermal solar energy, is the system inaugurated on October 9, 2018 at the Doctor Alejandro Dávila Bolaños Military Hospital in Managua.

With an investment of US $ 4.3 million financed through a soft loan from Oesterreichische Kontrollbank and Raiffeisen Bank International and with the United Nations Agency for Industrial Development (UNIDO), and the National Production Center more Clean from Nicaragua support; This system provides 30% of the demand required for air conditioning and 100% of the demand for hot water (used in various hospital operational functions, such as: personal, patients and doctors hygiene, food cleaning and preparation in the kitchen, for laundry area, among others).

The solar system was installed in a 4,450 square meters area, is composed of 338 thermal solar panels and will have an environment positive impact eliminating more than 1,100 tons of dioxide carbon emission each year.

It is the second largest system in the world, the largest in hospitals and unique in Latin America.

Resultado de imagen de energía solar hospital militar nicaragua

Despite the increase in systems number, solar energy only represents 1% of Nicaragua’s energy matrix.

There is a feeling that decision making is more market focused and not as a development issue.

The key is to associate the solar technology development with economic activities, establish a relationship between water resources, renewable energy and food security and base on renewable energy the climate change adaptation.

Currently solar energy provides energy security in contrast, for example, to energy supply via hydroelectric dams that depends on rains that are varying more and more throughout the region due to climate change.

Resultado de imagen de energía solar térmica nicaragua

Energy sources diversification becomes indispensable and has led to a solar energy investments growth.

This has been possible due to public resources contribution to support this technology development, the political commitment and the role carried out by the private initiative.

In this sense, it is worth highlighting the work that the BID is doing in the region.

In spite of advances, the pending subject continues being the regional energetic integration.

An energy networks extension at regional level would help lower costs and a energy supply diversification would guarantee greater energy security.

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Solar Thermal Energy

Solar Thermal Pipes

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Connection of different components of the solar system is carried out with pipes, until the necessary hydraulic circuits are formed.

Normally, materials used for primary circuit pipes are copper, black steel and plastic materials

The cross-linked polyethylene pipes can be used without problems, provided that manufacturer guarantees their use above 120º C.

Galvanized steel should not be used in primary circuits (from collectors to storage) due to the strong deterioration that zinc protection undergoes with temperatures above 65º C.

In general, the fluid velocity must not exceed 1.5 or 2 m / s in the primary circuit.

Pipes diameter can be selected so that fluid flow velocity is less than 2 m / s when pipe runs through inhabited places and at 3 m / s when the route is outside or by uninhabited places.

When steel is used in pipes or fittings, working fluid pH should be between 5 and 9.

Pipes dimensioning will be carried out in such a way that the load unit loss in pipes never exceeds 40 mm of water column per linear meter.

The circuit load total loss must not exceed 7 m of water column.

The maximum load loss is applicable to primary circuit and secondary circuit. If it were larger, we would be obliged to choose the immediately superior pipe diameter.

For pools heating, PVC pipes are used, which can have large diameters without a significant additional cost.

All piping networks must be designed in such a way that they can be emptied partially and totally, through an element that has a minimum nominal diameter of 20 mm.

Ver las imágenes de origen

For pipeline selection, following aspects must be taken into account:

1º Fluid compatibility:

Materials to be used for ACS circuits may be:

• Metallic:

– Galvanized steel, UNE-EN 10.255 M series (only in cold water).
– Stainless steel, UNE-EN 10.312, series 1 and 2.
– Copper, UNE-EN 1.057.

• Thermoplastics:

– Non-plasticized polyvinyl chloride (PVC), UNE-EN 1.452.
– Chlorinated polyvinyl chloride (PVC-C), UNEEN ISO 15,877.
– Polyethylene (PE), UNE-EN 12.201.
– Crosslinked polyethylene (PE-X), UNE-EN ISO 15.875.
– Polybutylene (PB), UNE-EN ISO 15.876.
– Polypropylene (PP) UNE-EN ISO 15.874.
– Multilayer polymer / aluminum / polyethylene (PE-RT), UNE 53.960 EX.
– Multilayer polymer / aluminum / polyethylene (PE-X), UNE 53.961 EX.

Aluminum tubes and those whose composition contains lead are expressly prohibited.

2º Work pressure:

A minimum pressure of 1 bar and a maximum of 5 bar must be guaranteed at all points of consumption; so you can take 5 bars as pressure for series selection.

Although tanks safety valves are usually set at 8 bar this is a more appropriate design pressure.

3º Working temperature:

Hot water and heating pipes should remain stable with system working temperatures, sporadically be able to reach temperatures close to 95 ° C and continue to resist with a life expectancy of at least 50 years.

4º Charge loss:

When a liquid circulates inside a straight tube, its pressure decreases linearly along its length, even though it is horizontal.

That pressure drop is called charge loss.

Valves, constrictions, elbows, direction changes, derivations, etc. they cause load local or singular losses that must also be taken into account.

Total load loss, which is the sum of linear load loss and singular load losses, must be determined.

Ver las imágenes de origen

5º Pipe size:

To calculate pipe size we start from the flow data.

We must determine pipeline minimum diameter (ie the most economical) without load loss exceeding a reasonable limit, so as not to be forced to use a higher power pumping group with the consequent energy waste.

We know from experience that fluid circulation speed maximum recommended is approximately 1.5 m / s if it does so continuously (primary circuits) and 2.5 m / s if it does so at intervals (secondary consumption circuits).

It is also recommended (or required) that pressure drop for each tube linear meter does not exceed 40 mm ca.

These 2 conditions impose a lower limit on pipe diameter.

It is usual to start from an estimated diameter based on experience in similar systems and verify that choice implies values of load loss and speed lower than recommended maximums.

If this is not the case, verification should be repeated for an immediately larger diameter.

If on contrary, we can select a smaller diameter than initial one, we will save on material; especially if circuit has a considerable length.

As a first approximation, we can resort to following formula:

D = j C 0.35

Being:
D diameter in cm
C flow in m3 / h
j 2,2 for metal pipes and 2,4 for plastic pipes.

Initial estimation, whatever method used, must be verified by using load loss tables or abacuses.

There are tables and specific abacuses for each type of material (copper, steel, plastics) that allow to determine load loss due to friction and fluid speed in the tubes.

This content was extracted from the Solar Thermal Energy Technical-Commercial Manual and is part of Solar e-learning.

All you need is Sun. All you need is Sopelia.

Solar Thermal Energy

Solar Thermal System Protection

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The correct design of a solar thermal system involves foreseeing all the circumstances that may damage it and applying strategies that can prevent breakdowns that shorten its useful life.

There are basically 5 aspects to keep in mind:

I-Frost protection:

Protection method will depend on the heat transfer fluid used and specific weather conditions of system site.

It is not enough to protect only the collectors. Outer pipes must also be protected.

As anti-frost protection systems, following could be used:

1. Antifreeze mixtures: it is the most used solution to system protection from freezing danger.

2. Water circuits recirculation: this system is suitable for climatic zones in which periods of low temperature are of short duration.

3. Automatic drainage with fluid recovery: this system requires the use of a heat exchanger between collectors and accumulator to maintain hot water supply pressure in it. This solution is not recommended in case collector absorber is made of aluminum.

4. Outdoor drainage (only for prefabricated solar systems): this system is not allowed in custom solar systems.

5. Total system shutdown during winter: this solution is advisable for systems that are only used in summer and it should be taken into account that empty circuits are subject to greater corrosion risks.

6. Collectors heating by an electrical resistance.

7. Collectors capable of withstanding freezing: there are collectors on the market that have sufficient elasticity to withstand volume increase due to freezing.

8. Introduction in absorber circuit of elastic and watertight capsules containing air or nitrogen. By increasing pressure due to freezing, they are compressed avoiding failure due to breakage.

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II-Overheating protection:

An excess of heat in solar thermal systems occurs when there is too much solar uptake in relation to energy obtained consumption. When this happens, collectors retain the heat that has not been evacuated and raise its temperature to levels that can be dangerous for system.

It is estimated that a heat transfer fluid e temperature xceeding 90 ºC becomes dangerous for the system.

Problem arises when, for reasons already mentioned, temperature rises too high in collectors and the heat transfer fluid circulating inside primary circuit begins to boil, expand and emit steam.

Both dilation and vaporization raise the pressure inside the primary circuit.

On the other hand, when heat transfer fluid begins to boil in the primary circuit, scale builds up on surfaces of the various components that deteriorate equipment.

In collectors overheating, 3 cases can occur:

1. Closed circuit with outdoor expansion vessel: steam produced goes outside. This can cause scale and risk of emptying part of circuit, forcing it to be filled before it is put into service.

2. Open circuit (consumption water passes through collectors): if boiling pressure exceeds network pressure, the produced steam will discharge into network contaminating the water.

3. Closed circuit and closed expansion vessel: when temperature rises, pressure rises and safety valve will open when it reaches a certain predetermined value.

Overheating risk in storage is lower and it can be said that it could only occur if system has high performance collectors (eg, vacuum tube collectors) and lacks a dissipation mechanism.

When water is hard (content of calcium salts between 100 and 200 mg / l), necessary precautions shall be taken so that working temperature of any point of consumption circuit does not exceed 60 ° C, without prejudice to necessary requirements against legionella application.

In any case, necessary means will be available to facilitate circuits cleaning.

In addition to safety elements there are other mechanisms to avoid overheating dangers:

• Use an organic fluid with a high boiling point.

• Angle of inclination of collectors higher than optimal to capture solar radiation preferably in winter. This ensures that the most perpendicular rays of summer fall with greater inclination on collector and take less advantage.

• Excess heat poured into the pool.

• Eaves. Through arrangement of strategically placed eaves it is possible to reduce the solar radiation that solar collectors support in summer.

• Cover collectors with covers.

• Heat sinks. These devices circulate superheated liquid through ducts to dissipate its heat in the air.
Some direct all the superheated flow of primary circuit to a unit where heat is dissipated with the help of fans (air heaters).
Others, however, are structures that are placed in each collector or battery of collectors and that dissipate only heat generated by the unit they are on. This type of heatsink works by gravity, without electronic components and is activated by means of thermostatic valves. It has the advantage that it continues to work in the event of a power cut.

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III-Pressure resistance:

In case of closed systems, maximum working pressure of all components shall be taken into account. The component that has the lowest maximum working pressure is the one that will set the pattern for entire system.

In case of open consumption systems with network connection, maximum pressure of the same shall be taken into account to verify that all components of the consumption circuit support said pressure.

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IV-Reverse flow prevention:

System installation must ensure that no relevant energy losses due to unintentional inverse flows occur in any hydraulic circuit of the system.

The natural circulation that produces the reverse flow can be favored when the accumulator is below the collector, so it will be necessary to take, in those cases, the appropriate precautions to avoid it.

In systems with forced circulation, it is advisable to use a non-return valve to avoid reverse flows.

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V-Legionellosis prevention:

It must be ensured that water temperature in hot water distribution circuit is not lower than 50 ° C at the furthest point and before the necessary mixture for protection against burns or in the return pipe to accumulator. System will allow water to reach a temperature of 70 ° C. Consequently, the presence of galvanized steel components is not admitted.

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This content was extracted from the Solar Thermal Energy Technical-Commercial Manual and is part of Solar e-learning.

All you need is Sun. All you need is Sopelia.

Solar Thermal Energy

Heat Transfer Fluid

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Heat transfer fluid passes through absorber and transfers energy to thermal utilization system (accumulator or exchanger).

Most used types are:

* Natural water: can be used in open circuit, when sanitary water passes directly through collectors, or in closed circuit (independent consumption circuit).

In first case, circuit can only be constituted by materials allowed for drinking water supply. In some countries this system is not allowed.

It will be necessary to consider water characteristics, especially its hardness (calcium and magnesium amount), which when heated produces a hard crust or tartar.

This crust accelerates corrosion, restricts flow and reduces heat transfer. The values start to be problematic from 60 mg / l. Very soft waters can also cause problems due to their corrosivity.

* Water with antifreeze: to avoid drawbacks of freezing and boiling of heat transfer fluid, use of antifreezes called “glycols” is the most widespread.

Mixed with water in certain proportions prevent freezing to a limit of temperatures below 0 ° C depending on their concentration.

On the other hand the boiling point rises making heat transfer is protected against too high temperatures.

Choice of concentration will depend on historical temperatures of the area where installation is located and on characteristics provided by manufacturer.

Most commonly used glycols are ethylene glycol and propylene glicol.

Resultado de imagen de tabla anticongelante solar

Fundamental characteristics of antifreeze:

• They are toxic: their mixing with drinking water must be prevented by making secondary circuit pressure greater than that of primary, for prevention exchanger possible breakage.

• They are very viscous: factor to take into account when choosing electric pump that is usually more powerful.

• Dilates more than water when heated: as a safety standard, when we use antifreeze in proportions of up to 30%, when sizing the expansion vessel, we will apply a coefficient of 1.1 and 1.2 if proportion is greater.

• It is unstable at more than 120ºC: it loses its properties so it stops avoiding freezing. There are some that withstand higher temperatures, but they are expensive.

• The boiling temperature is higher than that of water alone, but not too much.

• Specific heat is lower than that of water alone, so it must be taken into account in the flow calculation, conditioning pipe and pump dimensioning.

To calculate antifreeze amount that must be added to an installation, you must first consult the table of historical temperatures which is the minimum temperature recorded in that city or location.

Once it is known, goes to glycols graph supplied by manufacturer and value is transferred to indicate what percentage is.

* Organics fluids: there are two types, synthetic and petroleum derivatives.
Precautions mentioned in case of antifreeze regarding toxicity, viscosity and dilation are applicable to organic fluids. Additional risk of fire should be mentioned, but also that they are chemically stable at elevated temperatures.

* Silicone oils: they are stable and of good quality products. They have the advantages that they are not toxic and that they are not flammable, but current high prices mean they are not widely used.

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