# Convert a solar DHW tank (or fuel oil) into a thermodynamic water heater with a small swimming pool heat pump

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izentrop
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## Re: Transform a solar DHW tank (or fuel oil) into a thermodynamic water heater with a small swimming pool heat pump

Hello,
Have you tried to reduce the speed of the circulator to the lowest, see if that changes the duration of the cycle which is about 6 hours, according to your curves?
You write here water-pumping-filtration / transforming-a-solar-DHW-tank-into-thermodynamic-water-heater-with-a-small-pool-t17035-160.html # p481584
b) Estimate of the real flow at 3kW of heat exchange: P = q * 1,16 * deltaT

Q (m3 / h) = 3 / (1,16 * deltaT)

2.5 ° C delta: 1,03 m3 / h

1.9 ° C delta: 1,36 m3 / h
My calculation may not correspond to anything, but by multiplying flow rate by deltaT, you transmit roughly the same temperature to the tank:

- 1.03 x 2.5 x 6 = 15.45° for 42 WH
- 1.36 x 1.9 x 6 = 15.5° for 132 Wh consumed by the circulator.

The 3 kW announced are theoretical, the power transmitted at 3 m3 can be calculated: Pt (kWh) = delta T tank * 1.162 x 3
To obtain it, it would be necessary to know exactly the temperature of the volume of water in the tank before and after, but with stratification, it would be necessary either to have several probes, or to mix the water before and after.
A probe placed under the insulation of the balloon could perhaps give a good idea of ​​this deltaT

-
Last edited by izentrop the 02 / 03 / 23, 10: 25, 1 edited once.
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Christophe
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## Re: Transform a solar DHW tank (or fuel oil) into a thermodynamic water heater with a small swimming pool heat pump

It's already at its lowest...it's at 6W-7W...

Now that I have a time analysis tool, ok I can change it to max it out to see if that changes anything to the cycles...but I don't really believe it...I think it will degrade operation.

The problem is that when it's too fast and the hot source is quite low in C°, exchanges do not have time to be done properly in the ball, so I think the lowest is the best configuration.

Don't forget the circuit is very short (compared to a circulator of a heating network) and with very few pressure drops because everything is in 1 inch or more...

ps: it works pretty well, so I'm not going to worry too much about optimization anyway... but I'm going to put the circulator on high speed, to see... 22W suddenly...
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izentrop
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## Re: Transform a solar DHW tank (or fuel oil) into a thermodynamic water heater with a small swimming pool heat pump

Ok, we agree and for the probe under the insulation of the balloon to calculate the power transferred to the water?
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Christophe
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## Re: Transform a solar DHW tank (or fuel oil) into a thermodynamic water heater with a small swimming pool heat pump

Mea Culpa, I just checked this season it was at half speed 16-17W...so the 6h / 30min cycles correspond to this setting.

I switched it to low speed at 6-7W...

If it changes anything to the cycles after X days, I would test in high speed 22W...

Well the problem is that I sample the temperatures at 30 min, so it's difficult to have a precision on the duration of the cycles better than 30 min... (no kidding)

I can go down to 1 min, but if I change it erases all history
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izentrop
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## Re: Transform a solar DHW tank (or fuel oil) into a thermodynamic water heater with a small swimming pool heat pump

Christophe wrote:I can go down to 1 min, but if I change it erases all history
No big deal since it's recorded in your curves...
Did you see my last question?
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Christophe
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## Re: Transform a solar DHW tank (or fuel oil) into a thermodynamic water heater with a small swimming pool heat pump

I don't really understand what you want to show with this montage: I only use the upper part (about 150L) of the balloon...so there is inevitably stratification...

With a mounting on the solar exchanger (bottom) it would have been better at the exchange level (but also it would increase the losses)... but it was already occupied then I don't need 300L of DHW...
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izentrop
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## Re: Transform a solar DHW tank (or fuel oil) into a thermodynamic water heater with a small swimming pool heat pump

In this case, you can still have an approximate vision of the power transmitted to the 150 l of water outside the solar cycle (deactivated) and not in use during a heat pump cycle, by measuring the deltaT with a temperature probe placed at the top of the balloon under the insulation, I think.
Pt (kWh) = tank delta T x 1.162 x 0.15 Ben already on the pump side: 15.5*1.162*0.15 = 2.7 kWh
https://www.ista.com/fr/ista/blog/combi ... 0Wattheure.
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Christophe
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## Re: Transform a solar DHW tank (or fuel oil) into a thermodynamic water heater with a small swimming pool heat pump

Except that making a precise assessment is complicated in my case because the heating delta varies: the water arrives preheated at the moment at 26°C... but 1 month ago it was at 18°C...

In terms of electricity consumption, I am at 1.1 to 1.2 kWh per day on average (there are other consumers on the wattmeter) for 150L, ​​i.e. around 8 kWh/m3 VS 32 kWh/m3 from your link: we find a COP of around 4...

The heat pump when running consumes 650W, so it sticks quite well with 4 cycles of about 30 min...

As a reminder, a (fast) shower is 2kWh on DHW...
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izentrop
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## Re: Transform a solar DHW tank (or fuel oil) into a thermodynamic water heater with a small swimming pool heat pump

Christophe wrote: the water arrives preheated at the moment at 26°C... but 1 month ago it was at 18°C...
Is it the water that comes in when you draw hot water? Doesn't matter if you don't draw water during a measured cycle.
Strangely, it does not change the duration of the cycle of 6 hours?
Christophe wrote:The heat pump when running consumes 650W
Wh no?
Christophe wrote: 4 cycles of about 30 min...
What is the 6 hours then?
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sicetaitsimple
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## Re: Transform a solar DHW tank (or fuel oil) into a thermodynamic water heater with a small swimming pool heat pump

izentrop wrote:
Christophe wrote: 4 cycles of about 30 min...
What is the 6 hours then?

If I understood everything, it's about 30mn walk from the CAP, then about 6h stop, then 30mn walk, ..etc...
As for the W and Wh, you're exaggerating a little... It "consumes" 650W, but over 1/2h it would be around 325Wh.
A bit like a car that consumes 6,5l/100km but only does 50km....
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