Home Solar Heater Water Circulator Installation

Water circulation between tank and solar collector

If your home solar heater design is going to work by thermosyphon, you will not need to know anything about forced circulation with a water pump.

Forced circulation with a water pump is obviously done with a water pump, did you doubt it? :-D

I briefly explain what would be understood very easily with the graphic illustration of the following photo:

Use of solenoid valve or return valve

As marked in the previous photo, with the letter "E", here we can install a solenoid valve or return valve.

The intention of both devices is the same.
This is to prevent the water from circulating when the pumping process is stopped.

When the device that manages the pumping, normally a differential thermostat, is not operating the pump, it is because the temperatures of the collector and reservoir do not meet the necessary or ideal requirements for them to exchange the water.
But it can happen and does happen, that in cold conditions (as is usually the night) there will be a situation in which the tank will be hot and the collector cold. (The opposite of what the day usually is)
Then a natural thermosyphon circulation suddenly arises, due to temperature differences, in which the movement of water will go from the hottest place (reservoir) to the coldest place (collector).
Which is the opposite of what we want.

This circumstance is easily avoided by stopping the passage of this circulation.
And to be able to carry out this solution, we need an appropriate device for it.

Backflow valve

This is a check valve:

The non-return valve offers us this "stop" in a simple way without the need for any electronic device.

This allows the water to pass in one direction, and stops it in the opposite direction.

Advantages of the check valve

• You don't need any electronic device.
• Therefore it will work even if we do not have electricity supply.
• It is inexpensive and easy to find at plumbing supply stores.

Disadvantages of the check valve

• It reduces the flow and pressure of the water pump, in which the pump needs a certain initial pressure to be able to move the valve plunger.
• The valve plunger cannot be easily relieved.
• If the spring of the valve plunger rusts, it will give us problems.
• If the plunger spring stops exerting its pressure, reverse circulation can happen without realizing it

Solenoid valve

This is a solenoid valve:

 

The solenoid valve is a more modern device. It consists of a membrane that allows or stops the passage of water depending on whether we activate it or not by applying an electrical voltage.
There are solenoid valves of various types, alternating current or direct current.
This solenoid valve must be connected to a device that activates it when it is convenient for the water to circulate or stop.

The function and intention is exact to the non-return valve, but its mechanism is totally different.

Advantages of the solenoid valve

• It is inexpensive and easy to find at electrical or electronic supply stores.
• It is usually durable, and does not depend on physical elements such as the return valve.
• There is nothing that can rust over time, since the membrane is made of plastic.
• In theory there should be no pressure reduction since the open valve allows the water to flow freely from the automatic opening.

Disadvantages of the solenoid valve

• You need electricity. Therefore it will not work when we have no electricity supply. (at night we do not need electricity in the equipment, but in this case we would need it to avoid the reverse flow of water)
• You need an electronic device that tells you when to close or open your valve.

Water pumping in circulation or recirculation mode

Water pumping in circulation mode

Circulation will be when the sump of the tube that brings the water from the collector, is not submerged.
Then the water is poured into the tank, gushing out, like a tap.

 

The "S" represent the probes (although it does not come to the subject, it is something that will be present)
The water between the tank and the collector will be moved by the pump, which will suck the lower part of the tank, and will push it to the lower part of the collector.
This flow and pressure of water will push the water in the collector upwards, forcing it to leave the same.
Finally, the water that comes out of the collector inevitably ends up in the tank.
And so on repeatedly until the water pump stops.
At this point, it is assumed that it is understood that the pump will work only when the water in the collector is hot enough to bring its temperature to the tank.

Advantages of water circulation:

• We will not need the use of a non-return valve or solenoid valve.
• It is the most simplified and easy way to bring the water to the tank, even if the tank has a variable water level.

Disadvantages of water circulation:

• In the event that the collector and reservoir are at different heights, the water pump will need a minimal pressure force to push the water upwards.
• The more vertical distance there is between the two, the more pumping force we will need.

Water pumping in recirculation mode

Recirculation will be when the sump of the tube that brings the water from the collector is completely submerged in the water in the tank.

Advantages of water recirculation:

• In the vertical distance between collector and reservoir, the water pump will not need a noticeable extra pressure force, because it is not really pushing the water, but rather it is moving it in a closed circuit.

Disadvantages of water recirculation:

• In the need to keep the tube submerged, we cannot use variable level in the water tank, or we would need a floating tube strategy or maintain a minimum level relationship that does not leave this tube in the air.
• Yes, we will conveniently need the use of a non-return valve or solenoid valve, if we do not want the water in the tank to lose temperature.
• Being a closed circuit, the air that sometimes occurs naturally in the collector will not leave it if we do not apply some type of strategy, such as a vertical aerator.

The water pump that I have used in this project

The installation that I did on the roof floor had the tank and collector at the same level.
But as this roof did not have access and you had to climb 6 meters high with a ladder, I lowered the water pump to a window with the idea of being able to act if it gave me problems.
The water pump would be about 2.5 meters down, and although the water flow was level, it did need pressure to move the water.

The pump used by this project was this:

It is a centrifugal pump with a brushless motor, specially designed for very hot water (up to 100ºC).
It is an extremely silent pump whose electrical consumption does not exceed 10W.
At the time I started this project, it was very difficult to find this type of pump, and I did not want to use large complex pumps with high electrical consumption.