Solar thermal heating

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Solar thermal heating




by Which » 29/10/23, 10:13

Hello everybody

I am considering solar thermal collectors on the roof with a storage tank and a heated floor.

What device allows you to send water at 27°C into the floor, assuming that the water in the tank is at 90°C?

Thank you for your advice.
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Re: Solar thermal heating




by Remundo » 29/10/23, 10:23

difficult to answer your question.

Coil heaters do not have a uniform temperature, between the inlet of the coil and its outlet, you will have an approximately linear decrease in temperature.

If the flow is low, the other end will be at room temperature, if it is very high, the water will not have time to cool and will return to almost 90° in the tank.

The flow rate of the circulator as well asa thermostat on the return water to activate it or not should solve your problem.

There must be a sufficiently large temperature difference between the circulating water and the floor, otherwise the heat exchanges are too slow.

For maintenance heating, 35°C is recommended, and for faster heating, 45°C.
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Re: Solar thermal heating




by Which » 29/10/23, 10:52

Thank you, Do you need a variable speed circulator or does it work all or nothing?

Stupidly I thought of a mixer which provides a little very hot water from the tank and a lot of cold water from the coil.
I don't know if it exists? I don't know much about heating.
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Re: Solar thermal heating




by Ahmed » 29/10/23, 11:01

It's called a 3 or 4-way valve and actually allows less hot water from the return to be mixed with the water coming directly from the hot source; a simple graduated lever allows you to adjust the desired temperature by varying the respective flows...
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Re: Solar thermal heating




by Remundo » 29/10/23, 11:02

I think your water at 90°C is too hot from the start. Normally heated floors have a standard of 50°C maximum so as not to exceed 28°C on the surface.

You risk having a very, very hot ground at the entrance to the coil, which can burn your feet, or cause the materials to expand with problems of cracks/wear due to thermal cycles.

The heated floor is precisely designed not to work with very hot water. Your hot water tank should not exceed 50°C. It would be necessary to restrict it from the start rather than having complicated systems. Making it too hot and adding cold water doesn't seem logical at all.
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Re: Solar thermal heating




by sicetaitsimple » 29/10/23, 11:15

Remundo wrote:I think your water at 90°C is too hot from the start.

I have no experience with solar thermal heating, but reaching 90°C in the buffer tank during the heating period seems unrealistic to me in any case.
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Re: Solar thermal heating




by Which » 29/10/23, 11:15

Remundo wrote:I think your water at 90°C is too hot from the start. Normally heated floors have a standard of 50°C maximum so as not to exceed 28°C on the surface.

You risk having a very, very hot ground at the entrance to the coil, which can burn your feet, or cause the materials to expand with problems of cracks/wear due to thermal cycles.

The heated floor is precisely designed not to work with very hot water. Your hot water tank should not exceed 50°C. It would be necessary to restrict it from the start rather than having complicated systems. Making it too hot and adding cold water doesn't seem logical at all.

Yes I agree, a heated floor should not exceed 27°C for health reasons for the blood circulation of the legs.
I imagine that the water can go a little beyond 27°C but not to 90°C, that's for sure.

My problem is how to store as much solar thermal energy as possible when the weather is very good.
Storing water at 40 or 50°C would force me to either increase the storage volume or waste energy.
Already in the summer I would waste a lot of it because of the reduced storage volume.

This type of heating works well directly with the sensors, we vary the speed of circulation to adjust the temperature.
The idea is to do a little better than direct solar.

It's the ball that complicates everything.
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Re: Solar thermal heating




by Which » 29/10/23, 11:21

sicetaitsimple wrote:
Remundo wrote:I think your water at 90°C is too hot from the start.

I have no experience with solar thermal heating, but reaching 90°C in the buffer tank during the heating period seems unrealistic to me in any case.

This can happen at the end of summer before the heating season.

I'm considering the worst case.
Last edited by Which the 29 / 10 / 23, 11: 23, 1 edited once.
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Re: Solar thermal heating




by Remundo » 29/10/23, 11:22

sicetaitsimple wrote:
Remundo wrote:I think your water at 90°C is too hot from the start.

I have no experience with solar thermal heating, but reaching 90°C in the buffer tank during the heating period seems unrealistic to me in any case.

It depends on the thermal sensors.

IF they are vacuum tubes, it can go much higher.

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Re: Solar thermal heating




by Which » 29/10/23, 11:29

For cost reasons I would use a flat sensor.
Although the sensor's performance drops as the water temperature rises, it is possible to boil water.
I already did it in the summer with a small homemade flat sensor, to see.
That's why I'm considering 90°C.
Any degree gained is stored energy, even if there is a lot lost.
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