Solar project / heat exchanger regime

[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

 

[srivatsanvr]

Hi,

I see that 80C from the solar side is pretty high and you can extract so much from this. I am a heat exchanger person and I am interested in knowing little about this project.

What is the inlet temperature of consumption side? and what are the flow rates on both sides?

Probably I can give you the performance from my side, that might be of helpful to you.

 

[mfqd]

Dear srivatsanvr,

Thank you very much for your reply.
In fact i'm studying this because is not a straight question as we have for example in a heat exchanger with a boiler in the primary circuit.

I can say to you that in normal operation during daytime, we may assume that the consumption side works on a regime of 50/55 ºC, but in the morning, the temperature is a bit lower, when the system starts.

My problem now for the dimensioning is that the solar circuit as a very dynamic behaviour. But, if we want to heat the consumption side, i think that we can't lower too much the solar circuit temperature's regime.

In relation to the flowrates, i have in the consumption side a flowrate of 100m3/h at 4bar. Now the consumption is heated onlçy by rthe boiler through a plate HX. The boiler circuit flowrate i don't know, but the temperatures regime is 110/100 ºC. This HX as a capacity of 4500000 kcal/h.

I hope that this can say something too you, because i really need some help.

THANK!!

 

[srivatsanvr]

Hi,

I think I understand your case. Is that your consumption side inlet is 50 C and oulet is 55 C? With the given heat load and solar side temperature, we can balance the load and then go ahead with sizing.

 

[mfqd]

Dear srivatsanvr,

Thanks once more.
The problem is to obtain the solar side temperature. As you understand, this value varies throughout the year and throughout each hour in a day. I'm making a dynamic simulation of the solar system to determine some of the temperatures obtained. But i don't have them yet.
This was the real reason why i posted this question. In a dynamic systema as this one, it's quite complicated to do the sizing. Maybe we must start with some assumptions, but i don't know wich.

Thanks