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Old 09-25-12, 02:18 AM   #31
Vlad
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Originally Posted by opiesche View Post
Very interesting - I was thinking about using an Arduino, but the ease of setting up and programming the Pi (and the fact that it goes for $35) has completely sold me on it. I'm usually more of a C++ guy as far as programming goes (software engineer by trade), but being able to quickly whip something like this up in Python and take advantage of its facilities to easily wrangle data from text has some real perks.

For plotting, I use MatPlotLib (matplotlib: python plotting — Matplotlib 1.1.1 documentation), a really full featured Python library. With it and a couple other pieces of freely available code, I can read data from .csv files into arrays that can then be directly used to generate a plot and save it to an image file. The code for this is really simple, as you'll soon see. The images are saved directly to the web server directory, from where I can grab them from any web connected machine (the plot images in this thread are pulled live from the Pi's web server).

As for the data amount, it's really less than it seems. The .csv files for each day are only about 6kBytes in size, the .PNG images about 55k. With a cheap 4GByte SD card in the Pi, I could store 100 years of data and still have room to spare.

I'd like to put additional sensors on it as well (at least one upstairs, one downstairs, and one outside), and will have to experiment a little with the maximum wire length. I'm using the DS18B20 sensor (also Dallas 1-wire) - do you have any idea how long the wires can be before you start getting problems with signal degradation?
Web control of your heating or cooling system is super cool but most people have no idea how to set it up. Professional DDC systems are super expensive making them useless for DIYers. But we can share and benefit from each other knowledge. The problem with this thread is it is growing very fast and it is almost impossible to find what you found ones. I think it would be very useful to have separate thread about automation and web interface.

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Old 09-25-12, 02:41 AM   #32
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Originally Posted by AC_Hacker View Post
Vlad,

Thanks for posting your approach to heat sizing, your method is really appropriate and can only come from much experience... this is a very valuable insight.

But, at the same time, I think that opiesche is really on to something here... He is trying to determine the total thermal response characteristic of his house, which could be expressed in a simple mathematical expression... this could have utility far beyond just heating his house against the winter cold.

Best,

-AC
I do agree with you. This is probably the most sophisticated way to determine your heat demand. My heat loss calculations were done by "professionals" and they gave me 50000+ BTU number. My HWT which is the only heat source I used has 24000 BTU net output. We use it for heating hot water also. With 2 babies and 4 adults our hot water demand is very high. But we never ran out of hot water or heat even on coldest days. So just like always "thumb rules" rule the world. Heat demand has very wide range from 0 to maximum. For this reason I put "2 layers" of controlling (heat and flow).

This is a small story about professionals. Ones I was checking the boiler room in public library and noticed that boiler is short cycling. There were 2 boiler but only one was working. It was cycling at 30-40 SECONDS intervals. You only can imagine the efficiency of this boiler...... I brought this up but... But wait a sec this is a public place who cares about efficiency???? Tax payers don't get refund....
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Old 09-25-12, 10:36 AM   #33
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Originally Posted by opiesche View Post
I'd like to put additional sensors on it as well (at least one upstairs, one downstairs, and one outside), and will have to experiment a little with the maximum wire length. I'm using the DS18B20 sensor (also Dallas 1-wire) - do you have any idea how long the wires can be before you start getting problems with signal degradation?
I'm using 4-strand bell wire that I had laying around just because I had it. I'm using a three-wire system because for me it's much easier to use an extra wire strand than to take all the precautions that a 2-wire setup require. I'm hearing that the 2-wire setup can be finicky.

Pure hear-say on this one, but the guy I got my Arduino data logger from said that he was able to deploy at least 70 sensors, and that runs of almost 100 feet are possible.

From the experiences of other, it seems that if you put branches in your system, you can risk the reliability of your data.


1-wire boards, front & back. ("COW" should read "COM")

I am using some tiny printed circuit boards that were designed by a local guy to mount my sensors onto and to connect the leads to, also. There's nothing particularly worth noting about the boards, with the exception that there are pads for soldering a termination resistor onto for the last sensor (sensor most distant from the micro-processor board). The idea is that a signal pulse that travels down the wire, will 'echo back' if it hits a drastic change in impedance, like if it hits an open (zero impedance) at the end of the line. The board also has pads for tiny caps to go from V+ to ground, if required. No one around here has needed to use the caps.

My house is small, two-story with a basement, and I'm running my sensor string up along the chimney, which is pretty much in the center of the house.

So far on my system, I am doing everything wrong... I have two single-sensor branches (short ones) coming off the main line, and no termination resistors and no power line caps anywhere. I'm getting good, reliable data. My total length is about 30 feet, excluding the short branches. I figure I have another 25 feet, and three sensors to go.

I have read horror stories about people who have used CAT-6 cable, and have gotten horrible results, I have also read reports about the same setup and people who get great results.

I had one apparent problem with one mounted sensor, so I replaced it with another, problem solved. Closer inspection revealed that my bad mounted sensor had a bad solder joint. I re-soldered the joint and it is now reliably in use.

Aside from violating all the rules, I have been careful in the construction and deployment of my sensors... I check for good data, at each step. So far, I have not entered into the ZONE OF UNRELIABILITY. If things begin to get sporadic, I'll start with a termination resistor... If that doesn't do it, I'll go with the tiny caps... if that doesn't do it, I'll replace the branching topography with a linear one.

That's what I can tell you at this point, hope it is of some use to you.

Best,

-AC
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Old 09-25-12, 10:48 AM   #34
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Tiny little circuit boards, definitely very small cows :P
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Old 09-29-12, 06:34 AM   #35
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I didn't see this info anywhere but are you using O2 barriered tubing. If not, you will need a bronze pump, strainer, no steel fittings and the water heater should not be used for domestic water. I would look at the Vertex water heater as a heat source. It is condensing, reasonably priced and won't short cycle.

Oh, and we always use Beldon twisted pair wiring for sensors. It is the industrial standard.

Cheers
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Old 09-29-12, 02:13 PM   #36
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Originally Posted by Mikesolar View Post
I didn't see this info anywhere but are you using O2 barriered tubing. If not, you will need a bronze pump, strainer, no steel fittings and the water heater should not be used for domestic water. I would look at the Vertex water heater as a heat source. It is condensing, reasonably priced and won't short cycle.

Oh, and we always use Beldon twisted pair wiring for sensors. It is the industrial standard.

Cheers
No, I'm not using O2 barrier tubing. It's a closed loop system and the water heater will be dedicated, and the manifold has an air eliminator at the end of the return side, so air that the tubing accumulates through expansion and subsequent contraction of the water should be removed by that to avoid corrosion. Do you figure I still need a non-ferrous pump and fittings?

I'll check out the Vertex water heater - the significantly higher efficiency would definitely make a condensing one more attractive, but they are usually so %$#^ expensive compared to regular ones :P

Thanks for the info!
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Old 09-29-12, 02:29 PM   #37
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Originally Posted by AC_Hacker View Post
So far on my system, I am doing everything wrong... I have two single-sensor branches (short ones) coming off the main line, and no termination resistors and no power line caps anywhere. I'm getting good, reliable data. My total length is about 30 feet, excluding the short branches. I figure I have another 25 feet, and three sensors to go.

Aside from violating all the rules, I have been careful in the construction and deployment of my sensors... I check for good data, at each step. So far, I have not entered into the ZONE OF UNRELIABILITY. If things begin to get sporadic, I'll start with a termination resistor... If that doesn't do it, I'll go with the tiny caps... if that doesn't do it, I'll replace the branching topography with a linear one.
-AC
Cool, that's great info to have! I'm getting some wire this week to rewire the controller and put the sensors and controller into a semi-final position. I'll post some more pictures of the setup when it's done.

BTW, I've also, as Vlad suggested, posted the controller piece into a separate thread:

Custom hydronic heating controller

As for the branching setup, electrically it should make no difference to a linear setup - the only difference is that you're attaching a bit of wire to the pins of each sensor - if you think of the sensor's legs themselves as short runs of wire, there's no practical difference between putting all the sensors onto one long wire run, or giving each sensor its own - you're only moving the place where all the signals start running in the same wire, but since two sensors aren't sampled at the exact same time, that shouldn't matter.

In a linear setup, you'll have more wire for each sensor, and hence more resistance and capacitance. Since it's DC, capacitance of the wires is irrelevant, and the resistance should only lead to a negligible voltage drop - at 50 feet with halfway decent wire, I would expect 1% at the very most (or 0.03 of 3.3V, which should be well within the tolerance of the sensors).
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Old 09-29-12, 03:37 PM   #38
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Originally Posted by opiesche View Post
No, I'm not using O2 barrier tubing. It's a closed loop system and the water heater will be dedicated, and the manifold has an air eliminator at the end of the return side, so air that the tubing accumulates through expansion and subsequent contraction of the water should be removed by that to avoid corrosion. Do you figure I still need a non-ferrous pump and fittings?

I'll check out the Vertex water heater - the significantly higher efficiency would definitely make a condensing one more attractive, but they are usually so %$#^ expensive compared to regular ones :P

Thanks for the info!
Absolutely, the pump and fittings need to be non-ferrous. While you may get the air out of the system, the O2 in the water will still attack ferrous components. I have removed many iron body pumps from jobs where the (usually plumber) has installed non barrier tubing and the rust has eaten out the non ferrous components. Another thing to remember is that some zone valves are designed for closed loop systems only because they do not have stainless steel components. I cannot tell you off hand which ones apply but typically ball valve type are fine.

Also, try to have the pump on a vertical pipe so that any sediment doesn't sit in the pump volute.
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Old 09-29-12, 03:58 PM   #39
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Absolutely, the pump and fittings need to be non-ferrous. While you may get the air out of the system, the O2 in the water will still attack ferrous components. I have removed many iron body pumps from jobs where the (usually plumber) has installed non barrier tubing and the rust has eaten out the non ferrous components. Another thing to remember is that some zone valves are designed for closed loop systems only because they do not have stainless steel components. I cannot tell you off hand which ones apply but typically ball valve type are fine.

Also, try to have the pump on a vertical pipe so that any sediment doesn't sit in the pump volute.
OK, thanks! Going for a different pump than I originally intended, then. The zone valves are built into the manifold, so I don't know what type they are - but it is a closed loop system. I'm still debating whether I want a mixing valve that I can control electronically so I can adjust the water temperature if necessary. I'd need something that I can switch via a relay - I've got a little research to do yet
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Old 09-29-12, 04:03 PM   #40
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Like this?

Danfoss Heating - North America

These 24vac motors will drive with any signal. I would think one of the guys could come up with an outdoor reset control that uses the PID control I saw on here. tekmar has one but it is more fun to make it.

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