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Timer circuit

Delta Prime

Jul 29, 2020
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I want to install a sprinkler valve controlled by a timer circuit that will open at 3, 4 or 5 minute intervals and remaining open for approx 1 minute on time before shutting off
Give the man what he wants!
So I did. As a potential option.
 

danadak

Feb 19, 2021
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That would work too. Once e temperature is reached the valve opens, allowing the hot water into the pool. THanks! How do I build it?

Here is an example that is quite flexible, based on an arduino type part :



Use an Arduino Nano type board :

1684969471955.png

Its like a [imath]2 -[/imath]3 board.


Here is code project to program it with. Attached. Download mBlock and open file
to config.

Then use a SSR(s) to control loads.


Regards, Dana.
 

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  • PulseGen and Timer.zip
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AnalogKid

Jun 10, 2015
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Wrong. The longer the water stays in the heater grid hoses the hotter it becomes.
Actually, Alec is correct. It gets hotter because its average flow rate is lower, and that matters.

As a physical quantity of heat, the calorie has been around since the 1820's, and for much of that time it was defined in terms of a quantity of water. If you have a large amount of water, such as a swimming pool in a closed-loop system, the amount of thermal energy needed to raise it one degree is independent of time. You can heat the pool over a long time with a lot of barely warmer water, or with less super-heated steam in a lot less time. Either way, the total energy needed is the same.

If you have a fixed energy input rate, such as sunlight, then the pool will take the same amount of time to heat up regardless of the speed and exhaust temperature of the heating system. This is because the flow rate and exhaust temperature are inversely proportional, but their product or sum or whatever is a constant (barring thermal losses to the air and through the pool walls).

ak
 

Delta Prime

Jul 29, 2020
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Calories huh? Thermodynamics!
I want to play...How many gallons of water does your pool hold? How many gallons of water does your pool heater hold? I'm on a diet so I'm not going to use Calories. If memory serves, heaters are sized according to their British Thermal Units (BTU) per hour. One BTU raises one pound of water by 1°F (0.6°C). One gallon of water is equal to 8.34 pounds of water, so 8.34 BTUs raises one gallon of water by 1°F (0.6°C).Way too many variables here!
As was already mentioned the walls of your pool is one big heat sink! We could actually minimize your trial and error approach if we crunch the numbers! And put a lid on your pool. And by the way Elvis had a pool in his Cadillac so there!
 
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kellys_eye

Jun 25, 2010
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You can heat the pool over a long time with a lot of barely warmer water, or with less super-heated steam in a lot less time. Either way, the total energy needed is the same.
Assuming zero losses - radiative etc
 

AnalogKid

Jun 10, 2015
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Assuming zero losses - radiative etc
I mentioned that.

Another real-world factor that is the flow rate through the heat exchanger, whatever it is that imparts heat to the water. The slower the flow, the more the water heats up; the more the water heats up. As the water heats, the delta-T between it and the heat source decreases, so the rate at which the water is heating decreases. This causes a "back-up", where the water is not removing heat as fast as it is coming in. The temperature of the heat exchanger assembly increases, increasing heat loss to the ambient environment. This means that for any particular exchanger design there is an optimum flow rate that is a trade-off between ambient losses and energy needed to move the water faster.

As above, in a completely lossless system none of this matters. No matter the flow rate (above zero), the average temperature of the pool will increase at the same rate, one that is determined only by the mass of the pool water and the solar constant.

ak
 

crutschow

May 7, 2021
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Wrong. The longer the water stays in the heater grid hoses the hotter it becomes.
True, but sorry, you are wrong about this helping heat the pool.
What you are wanting to do is adding unnecessary complexity and will actually reduce the amount of heat to the pool.
It's simple physics.
The amount of energy the panels absorb is determined solely by the sun and is maximum when the panels are cool.
Letting the panel heat up will actually reduce the amount of net energy absorbed, since now more will be radiated back to the surrounding cooler air.
So you want to keep the panels as cool as possible to minimize that loss, which means keeping the maximum continuous flow through the panels when the sun is shinning.

Two ways to get the pool warmer is to cover the pool completely when not using it, and/or add more panels.

I'm rather surprised at how many (besides Alec_t and AK) went along with variations of your scheme, without apparently realizing this. :oops:
 

Bluejets

Oct 5, 2014
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Letting the panel heat up will actually reduce the amount of net energy absorbed, since now more will be radiated back to the surrounding cooler air.
Panel cannot be hotter than the sun which produces the heat, sorry..........
 

crutschow

May 7, 2021
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Is it the nonlinearity of physics which is confusing you?
What makes you think I'm confused?
It's you that seems to be confused.
Nonlinearity has nothing to do with it.
How can slowing or stopping the flow put more energy into the water, then leaving it flow at full speed, which it where it will absorb the maximum energy from the sun?
 

Bluejets

Oct 5, 2014
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How can slowing or stopping the flow put more energy into the water,
Because it's the same in reverse as in a car radiator, allowing the water to flow more slowly in the coils allows more cooling/transfer of heat.
A well known f/up most people make when they have auto heat problems and first thing they do is pull the thermostat and throw it away, then wonder why the heat transfer is worse.
 

Delta Prime

Jul 29, 2020
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How can slowing or stopping the flow put more energy into the water
It is your interpretation put more energy into the water by slowing or stopping. We both know this cannot be done.conservation of energy. But to elaborate further would require an entirely different thread. Start a new thread and I will help you. :)
 

crutschow

May 7, 2021
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It is your interpretation put more energy into the water by slowing or stopping.
No, that's the opposite of my interpretation, if you carefully read my previous posts.
You put more energy in the water by keeping the water moving at maximum speed.
Slowing it down or stopping reduces the transfer.
Start a new thread and I will help you.
I need no help, and it's condescending to state that I do.
Since you and Bluejets both appear not to agree with what I have stated (or have misinterpreted it), further discussion on the matter would be superfluous.
 

AnalogKid

Jun 10, 2015
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The good news is that absolute maximum efficiency in a system such as this is not a critical requirement.

Thus, a superfluid is superfluous.

ak
 

danadak

Feb 19, 2021
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Heat transfer directly proportional to flow rate if the flow rate creates eddies.

But if its laminar flow all bets off. Where Laminar and Turbulent flow merge, ~ 2000.
Here we see convective / conductive ratio essentially insensitive to flow rate :

1685104884934.png


Regards, Dana.
 

Alec_t

Jul 7, 2015
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@HomerDodd
Perhaps this analogy will help, where heat energy is analogous to money :-
Consider you're a worker being paid£50 per hour to work an 8-hour day on a project.
Which gives you more, (a) being handed £50 every hour or (b) £100 every 2 hours or (c) £200 every 4 hours or (d) £400 each day?
 
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