Water temperature in pipe sensor

Hi,
I wish to make some automation at home for my central water heating system.
I was looking a lot on the internet but did not found an in pipe temp sensor (3/4" DN20)

I have a central system that uses the sun to heat water. This water then run all over the building and pass through each home water boiler (inside special pipes). The problem is in the winter, if I heat up my electric boiler and the water in the central system is running this will draw heat out from the water in the boiler.

So I wish to measure the temperature of the central heating system on the input and output from my boiler. I also wish to measure the water flow and have an option to open and close the central heating input pipe.

I found these:
Flow sensor- http://www.aliexpress.com/item/3-4-DN20-Brass-Hall-flow-sensor-meter/32578331910.html
Motorized valve - http://www.aliexpress.com/item/DC3-6V-2-3-5-Wires-Brass-3-4-full-port-electric-valve-for-HVAC-heating/965182598.html

But I could not find any temp sensor to measure the water inside the pipe.
Does anyone know of a sensor for this?

Zohar

I'm not familiar with "DN20", is that metal pipe? Try googling "thermometer well".

The DS18b20 will do fine on the outside. ebay 301402205489

I have made thermowells for them but they work just as well tucked under some insulation sleeve.

"DN20" is a standards reference for copper pipe - a futile attempt to metricate the unmetricatable. Plumbers still refer to it as "3/4", which is what it is.

I did use a DS18B20 and taped it to a heating pipe and put insulation around it in the past.

Worked very well. With 2 sensors about a meter apart I could estimate the speed of the flow.

@Nick:
Thats what I was going to suggest, I didn't know what "DN20" was.

Lots of options here for temp sensing:

Thanks all!
So I will just measure the temperature from outside the pipe.

robtillaart, how can you calculate flow from temperature difference?

And now for the next step:
Being to totally newbie to arduino which board should I buy for my project?
I wish it to just measure these 3 sensors and open / close the valve accordingly and also keep a running log of the measurements.

Zohar

ZoharML:
robtillaart, how can you calculate flow from temperature difference?

Zohar

assume a pipe with 2 sensors S1 and S2 with M (typically 1) meter distance in between

Cental Heater =======> S1 ====================> S2 ========>

Suppose the system heats up then the hot water will replace the cold in the pipe.
The water will pass first along sensor S1 and then along sensor S2.

S1 will go through a heating curve and S2 will go through the same heating curve
(in fact this is not exactly true as between S1 and S2 some energy is lost, with good isolation you can minimize the loss so it becomes true enough)

Assume a cold pipe is 20C. When heating to e.g. 80C you can check every N degree the speed

wait for S1 to reach 21C ==> time t1
wait for S2 to also reach 21C ==> t2
the heatwave has now travelled M meters in (t2-t1) seconds,
so the speed is M/(t2-t1) mtr/sec == 3.6 * M /(t2-t1) KM/Hr

and you can do that for 22C 23 C ... 80C and you will get a quite good indication of the speed of the flow. Yes the method stops working when the temperature stabilizes or when the water pump is switched off.

Nick_Pyner:
"DN20" is a standards reference for copper pipe - a futile attempt to metricate the unmetricatable. Plumbers still refer to it as "3/4", which is what it is.

With solar systems that normally refers to 20 mm metric stainless steel corrugated flexible pipe.

OP description sounds strange.

Properly designed systems do not have a problem as separate heat exchangers are used and stratification within the tank takes care of it.

A diagram would be handy.

ZoharML:
Hi,

have an option to open and close the central heating input pipe.

Zohar

That would require valves.
If as it sound this is a community heating system you will need the apartments plumber for that, or you risk shutting down the entire system.

ZoharML:
Being to totally newbie to arduino which board should I buy for my project?
I wish it to just measure these 3 sensors and open / close the valve accordingly and also keep a running log of the meas

Get a Mega. You might not need it immediately, but you probably will before long

Did some more thinking and decided to go the easy way.
My problem (the situation in which the central sun heating system can make my boiler water cooler) can happen only in the winter after I turn my boiler electric heater.

So all I need is whenever I turn on the boiler (only in the winter) is to close my input pipe from the central heating for about 6HR. (each apartment have a mechanic valve on the in/out pipe, so it's no problem to put an electric valve after it)

This means a simple setup:
The power to my electric boiler will go to some AC-DC board with big capacitor. This will give power to the controller and the valve.
When the controller wakes up it will close the valve on the in pipe.
Wait for 6 hours.
Open the valve.
Cut the power to itself (not sure if I need this).

So now I need a super simple controller board with:
Two outputs for the valve.
Two inputs for the valve position sensors.
Some kind of timer that can count up to 12HR.
Maybe 4 more outputs for the power cut, leds, buzzer.

So what board should I use in this case?

Zohar