Solar project / heat exchanger control

[mfqd]

Hi,

I'm making a big solar project. This project involves the heating of water tanks with solar energy until a maximum of 80 ºC. This water heats the consumption water flow through a heat exchanger. The cosumption water can exit at max. of 55ºC.
In solar simulation software, if we make the simulation of the solar heat circuit considering a regime of 80ºC/60ºC (Temp. inlet HE / Temp. outlet HE), the total efficiency of the solar system is worst than if we use a 70ºc/50ºC regime. The explanation that some people give is that the solar pannels increase it's efficiency if they work in lower temperatures.

1) The last argument is correct.
2) My question is: if the solar system functions with a principle that if the water tank temperature exceeds the temperature of the solar pannels the solar circuit stops, this means that the circuit enters in stagnation and we must wait that the solar fluid increases it's temperatura uppon 8ºC in relation to the tank temperature. So, most of the time the 80ºC can be reached. The only difference is that the solar circuit will start/stop more times.

Is this correct?....Can anyone give me their opinion.

Thanks

 

[MikeHalloran]

Huh?
"..the solar circuit stops"????

How do you turn off the sun?



Mike Halloran
Pembroke Pines, FL, USA

 

[Zesti]

It is a case of temperature difference:

The sun is able to warm up the surface of the collector to a certain temperature. This gives a temperature difference with the water flowing through the collector and this is the driving force for the exchange of heat.

An equilibrium will arise with as a result a specific temperature of the collector and the amount of heat transfered to the water.

When the mean temperature of the water is lower, the equilibrium will be at a higher level.

The big question is: do you really need 80°C ?!?

 

[mfqd]

MikeHalloran,

"The solar circuit stops" means that the pump stops. This occurs becaus de DT between the pannels and the storage tank, decreases to, for example, 3ºc.

Zesti,

Sincerelly, i didn't understand perfectly what you said...Sorry.
Yes i need 80 or 70 ºC. This is because there is a tank of 50 m3 that needs to be heated to 55ºC. For this i need to transfer energy to that water with a heat exchanger and the temperatures regime must be higher, therefore the 80 or 70 ºC needed.

Thanks

 

[vazdecarvalho]

és uma tal besta!

Não percebes nada disto.

Abraço

 

[Haz9119]

I install solar heating systems all the time for a few years now.

Your logic is fine. That is how it will have to work: Start...stop. That is normal depending on how the water is consumed.

Haz

 

[mfqd]

Dear Haz9119,

The systems that you have installed have 200 flat solar pannels, or are little installations, because it's i bit different.
Don't take me wrong

I ask this, because it's important to me to obtain help with someone with some experience in this kind of projects and if you have it please i would like to know more.

Thanks