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How to use solar thermal energy to heat the water in the house?

In the following text we are going to talk about another of the uses of solar energy. Everyone knows that solar energy has multiple applications such as electricity generation, lighting, etc. 

How to use solar thermal energy to heat the water in the house?

But did you know that one of the most advantageous options is the use of solar thermal energy to heat water? Solar energy can be used to meet almost all of your home’s hot water needs. A solar thermal water system captures solar thermal energy (heat from the sun) and then channels that heat to produce hot water for different uses.

What are the main domestic uses of solar thermal energy?

Heat water for DHW generation

What is the ACS? ACS simply refers to the acronym for: Sanitary Hot Water. It is drinking water intended for human consumption that has been heated. It is used for sanitary uses: bathrooms, showers… and can also be used for other cleaning uses such as dishwashing, washing machines, dishwashers, floor scrubbing, etc.

It is estimated that, on average, hot water for sanitary use accounts for about 25% of the energy consumption of a home.

The domestic supply of hot water for the shower, in order to obtain greater comfort, requires an ideal hot water outlet temperature between 37ºC and 42ºC. The use of thermal energy from the sun is extremely effective for heating water for these uses.

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Solar panels or solar collectors are responsible for capturing solar radiation that heats the water or heat-carrying fluid that circulates inside. The fluid increases its internal energy and its temperature. This fluid circulates through a heat exchanger that allows thermal energy to be transmitted to the water that we want to heat.

Solar hot water installations require an accumulator or water tank that is well insulated thermally, to accumulate hot water and then have it available for the use we want.

The most commonly used system of solar thermal energy, if we only want to generate DHW, are compact thermosyphonic solar equipment. In this equipment, the solar panels or collectors are united in a single set with the tank, and the whole set is located outside the house in a place where it correctly receives the sun’s rays. This system works by simple thermodynamics, the hot water rises to the tank and the cold water descends to the heat collectors, so it does not need electricity for its operation.

Forced circulation solar systems are also used , which can be used in a home to generate DHW. But they are normally used when, apart from generating hot water for DHW, it is also intended to generate hot water for heating and/or generate hot water to heat the pool.

What is a forced circulation solar thermal system and what elements make it up?

It is based on a closed fluid circuit that transports solar heat from the solar panels or collectors to the storage tank. This type of closed circuit can be very wide and the heat transfer liquid does not circulate by thermodynamics, but circulates by means of the mechanical action of a recirculation pump.

A forced circulation solar thermal system is made up of different elements, among which we find:

-One or more Solar Thermal Collectors : They are responsible for collecting the energy received from the sun and raising the temperature of the heat-carrying liquid. They can be flat solar panels or vacuum tube collectors .

-One storage tank or several depending on whether the system is only for DHW or Heating or if it is for DHW + heating or…: The main function of a water storage tank is to keep the water inside the tank that we are heating with the sun and that later we will use. It is the way that when we need that hot water, we have the hot water available instantly.

– Expansion vessel: It serves to absorb the increase in water pressure that originates in the primary solar circuit. When heated, the water expands and presses on the elastic membrane, compressing the air or gas contained in the other part of the vessel, which means that the increase in pressure in the circuit is much lower than if there were no expansion vessel.

-Hydraulic group, whose main component is the delivery pump : It is responsible for circulating the water or heat transfer liquid through the primary circuit between the solar panels and the tank.

-Control accessories: The differential thermostat with its temperature probes is in charge of controlling the activation and stopping of the pump so that the liquid only recirculates through the circuit when the temperature is higher in the panels than in the tank, in order to heat the Deposit. This recirculation will be activated as long as the tank has not already reached the desired temperature also set in the differential thermostat.

Heat Water for Heating

To provide heating with thermal solar energy, a forced circulation system must always be used and we always recommend the use of evacuated tube collectors , since in adverse weather conditions (very cold and little sun, which is when there is more need for heating) can provide significantly more heat than flat solar panels .

As we have already seen in forced circulation systems, in order to support the generation of hot water for heating, the use of an accumulator or buffer tank is also required. This deposit is usually inserted in the heating circuit in the return of the radiator system or underfloor heating just before the entrance to the boiler.

 Therefore, with the solar system we can heat the water in the circuit or at least preheat it before reaching the boiler, which will either not be activated (when the water is hot enough) or will reduce its consumption due to that contribution made by the solar system.

Heat the pool water

Although there are hot moments when we feel like taking a good dip in the pool, sometimes we get to the pool with a lot of desire and when we get into the water we back down, because the pool water is too cold.

There are different ways to maintain a comfortable temperature and heat the pool water. From electric heaters, heat pumps, diesel boilers,… But we are going to focus on a much more economical and sustainable way: Solar thermal energy!

In the same way that it is used to produce DHW or heating, solar thermal energy can be used to heat the pool water. It is generally used in the following situations:

  • at the beginning of the bathing season when the ambient temperature already encourages bathing but the water is still too cold
  • at the end of the bathing season when it is still hot during some hours of the day but the drops in temperature at night mean that the water is already too cold
  • in areas where it is difficult for the water to reach the correct temperature for bathing even in the height of summer

For all these purposes , polypropylene solar collectors are normally used since they allow the pool water to pass directly through the interior of the panels themselves and this fact makes the necessary solar thermal system to be installed very simple.

In fact, the potential of solar thermal energy for this use is such that, depending on the size and type of installation, the bathing season can be extended in an outdoor pool or even water heated throughout the year in a swimming pool. heated interior. 

For use in indoor pools throughout the year, it is necessary to use a forced circulation system with a heat exchanger and normal solar panels or vacuum tubes, since polypropylene ones are not thermally insulated from the outside. , they cannot work by supplying heat when the ambient temperature is not sufficient.

One of the determining points to make good use of the sun’s energy to heat water is to install the appropriate number of panels. The more panels, the greater the investment, yes, but nevertheless falling short will mean not achieving the desired objective. 

We carry out thermal studies completely free of charge to calculate the optimal solar system in each case, whether for DHW and heating, only heating, DHW and swimming pool, only swimming pool, DHW, heating and swimming pool or for any other use that you want to give it. . You can contact us through any of the ways you can find in the footer.

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