Two heating systems for solar energy in swimming pool water

Two heating systems for solar energy in swimming pool water

The heating of the pool water by the solar energy can be divided into a direct heating system and an indirect heating system according to the heat transfer type, the direct system is also called a primary circulation system, and the indirect system is called a secondary circulation system.

1 Direct heating system

This heating method is that after the swimming pool water is purified, the water is directly heated by the solar collector and then sent to the swimming pool. Swimming pool water direct solar heating system generally consists of collector, circulating water pump, auxiliary heating equipment, vacuum suction valve, pipeline and accessories and automatic control system. The system composition is as follows.

The vacuum suction valve is used when the circulating water pump stops running, and the air enters the pipeline through the valve, so that the water in the pipe returns to the swimming pool under the action of gravity, ensuring the water in the emptying pipe to prevent the cold winter pipe from being frozen. 

The working principle of the system is that the pool water is pressurized by the circulating water pump and sent to the collecting plate on the roof surface, and the water generated by the heat collecting plate is taken away by the flow of water to heat the water, and then the water after the heating is sent. Go back to the pool and reciprocate to warm the pool to the temperature required by the design. The temperature difference between the inlet and outlet water of this form of heat exchange is only 1 ° C ~ 3 ° C.

2 Indirect heating system

The heat exchange method uses the water heated by the solar collector as the heat source high-temperature water, and then uses the high-temperature water to exchange and heat the swimming pool water through the heat exchanger to prevent the chlorine-containing disinfectant residue from corroding the metal. The solar pool indirect heating method is generally composed of a collector, a hot water storage tank, an auxiliary heating device, a control system, a circulating water pump and a heat collecting pipe. The system composition is as shown in the following figure.

Because it is a secondary heat exchange, not only the thermal efficiency is lower than that of the direct heat exchange, but also the resistance of the heat exchanger is large, and the energy consumption is also large. This method is generally suitable for solar collectors of glass materials with high temperature and low flow rate.

From the above analysis, the indirect heating is better than the direct heating system in terms of the heating effect of the domestic hot water, but for the swimming pool water heating, the direct heating system has its special advantages:

1) Direct solar heating is to directly heat the swimming pool water in the solar collector, which belongs to the primary heat exchange and has high heat collecting efficiency; the indirect solar heating uses the heat transfer medium and then heats the circulating pool water by the heat exchanger. The method belongs to secondary heat exchange, and the heat collecting efficiency is lower than that of the direct heat exchange method.

2) The direct solar heating system has a large flow rate per cycle, and thus the temperature rise is also low. Generally, the primary circulating water temperature is only increased by 1 ° C to 3 ° C; while the indirect solar energy generates less flow per heating and the temperature rises. Higher, generally up to 50 ° C ~ 60 ° C.

3) The direct solar heating system has low heat loss, generally 0.24~0.26m3/h.m2 (selected by module area), and the head loss is only 0.5m. It is especially suitable for swimming pool water constant temperature direct heating, and indirect heat loss is large.

4) The direct solar heating system does not need to set the secondary heat exchange water tank to save the building space; while the indirect solar energy needs to set the secondary heat exchange hot water storage tank to increase the investment.

Therefore, because the swimming pool water heating feature is to supplement the swimming pool heat dissipation, the swimming pool water temperature is basically unchanged, and the swimming pool circulating water heating flow is required to be large and the heating temperature is not large, which is suitable for the heat exchange mode in which the water temperature rises slightly and the flow rate is large, thus For the heating of the pool water, it is more suitable to use the direct heat exchange method.

However, when the swimming pool water is heated directly, there are some issues to be aware of:

1) Direct solar heating Because the swimming pool water is directly heated in the solar collector, in cold regions, especially in winter, it is necessary to ensure that the residual water in the collector pipe is removed in time to prevent freezing of the cold winter pipeline, usually The practice is to install a vacuum suction valve.

2) Since the tap water is directly heated in the solar collector, it is necessary to ensure the water quality of the solar collector. If the water quality does not meet the requirements, the blockage of the collector and the service life are reduced.

3) One cycle generally only increases by 1 °C ~ 3 °C, so generally should set up solar radiation induction probe and water temperature induction probe in the system to achieve automatic control of the system to ensure economic and reasonable operation of the system.

4) Due to the low temperature rise and high flow rate of direct solar heating, it is more suitable to use collectors of rubber or plastic materials, and the heat collecting efficiency is up to 60%, which not only absorbs the heat of the sun but also absorbs the radiant heat of the roof panel (see the following figure). ).

3. in conclusion

In summary, we can draw the following conclusions:

(1) China's solar energy resources are relatively abundant, and solar energy can be used to heat the swimming pool water in most areas to realize the utilization of renewable energy.

(2) For indirect solar heating, because it belongs to high temperature secondary heat transfer, high temperature rise and small flow, it is generally suitable for heating domestic hot water or swimming pool water;

(3) Direct solar heating system, one heat exchange, small heat loss, high heat collecting efficiency, large flow, small temperature rise, suitable for swimming pool water heating, and generally suitable for plastic and rubber solar collectors .

The application of solar energy to the heating of swimming pool water and bathing water has realized the utilization of renewable energy. It has responded to the national “four sections and one environmental protection” policy and is one of the development directions of swimming pool heating technology in the future. For the heating of swimming pool circulating pool water, direct solar heating system has strong development potential.