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Old 03-27-13, 08:00 AM   #1441
AC_Hacker
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Quote:
Originally Posted by cbearden View Post
...it might be advantageous to include a couple of well-placed sensors hooked to my microcontroller as a type of an alarm.
You mean something like this?


-AC

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Old 03-27-13, 11:05 AM   #1442
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interesting. looking over the specs on this sensor online, it looks like it detects not only different gases but also smoke.
it interfaces via a analog signal.
So, that looks like it would hook to something like an Arduino?
I have a spare Arduino laying around that I use to play with something like this.
Since it would be costly (analog pin-wise) to use the existing analog pins on my Raspberry Pi (main controller), and this doesn't seem to support digital I2C networking and the Arduino does...
I could possibly use the Arduino as a sacrifical lamb for it's analog pins, hook its I2C connection into with my Raspberry Pi and then have them both talking together while not using any additional analog pins on my main controller.

If it works, that has the potential to allow someone to setup a small network of arduino's with sensors placed wherever they want as long as they can get a digital I2C connection back to a main control board.
I've never tried this before, but I've read about similar things being done.
Programming is not my strength, so it would take me some time to try to figure this one out. But it would be a good challenge!
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Old 03-27-13, 12:00 PM   #1443
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...costly (analog pin-wise) to use the existing analog pins on my Raspberry Pi (main controller), and this doesn't seem to support digital I2C networking and the Arduino does...
I haven't worked with the Pi, but on the Arduino, various pins come up by default as PWM or digital or analog, etc. But in the header of your sketch or program, you can initialize the pins as you wish, thus changing the default condition.

Also, if you had the heat pump in some room, it would of course be best if the sensor was able to trigger an exhaust fan which draws air from the floor and sends it out side (and an alarm, too). But it is important that neither electro-mecnanical relays, which can spark, nor brush-type fans, which can spark, be involved as they could be an ignition trigger.

Solid state all the way and ECM fans, too!

My personal favorite approach is a small masonry shed that is separated from the main structure, which has the refrigerant-to-water HX sending only warm water into your dwelling. That would be where you would locate the sensor and extractor fan and alarm. That's how they seem to be dealing with flammability issue in the UK.

But I like your I2C network idea, keep going with that.

* * *

BTW, only yesterday I had a talk with one of my friends who, through neglect, set his living room ablaze and nearly burned his whole house down. It had absolutely nothing to do with heat pumps or hacking or flammable gases, but it did have everything to do with irresponsible, mindless neglect.

Take heed,

-AC
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Old 03-27-13, 12:17 PM   #1444
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awesome ideas AC!
I could do something similar with my house to help with any insurance issues later down the road. Just picked up my braze-on valves and silver braze material. Now it's onto the pawn-shops this weekend to look for a cheap recovery unit or a small AC unit/fridge that I could possibly use for this purpose.
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Old 03-27-13, 03:22 PM   #1445
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Anyone know of a source for brazed plate heat exchangers that are rated at high pressures?

The air conditioner i've started dismantling uses R410A and looking at the rating plate i need a heat exchanger rated at 36 Bar working pressure. after searching ebay etc. the best i can find are from Germany rated at 30 Bar.

Thanks steve
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Old 03-27-13, 05:24 PM   #1446
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awesome ideas AC!
I could do something similar with my house to help with any insurance issues later down the road. Just picked up my braze-on valves and silver braze material. Now it's onto the pawn-shops this weekend to look for a cheap recovery unit or a small AC unit/fridge that I could possibly use for this purpose.
Yeah well, as long as it is for a good purpose...

HERE IS A POEM about a guy who burned his house down so that he could buy a telescope.

-AC
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Old 03-27-13, 05:38 PM   #1447
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Default Hack Your Own High Pressure Brazed Plate HX

Quote:
Originally Posted by Ormston View Post
Anyone know of a source for brazed plate heat exchangers that are rated at high pressures? The air conditioner i've started dismantling uses R410A and looking at the rating plate i need a heat exchanger rated at 36 Bar working pressure. after searching ebay etc. the best i can find are from Germany rated at 30 Bar.
That is one of the big advantages of lower-pressure refrigerants.

You could build a tube-in-tube, similar to what randen did.

Otherwise, I took a look at some high-pressure brazed plate HXs... can't remember the company at the moment, but it appeared to be not very different from a regular BPHX, with the exception that thick metal plates, top & bottom, were bolted around the edges of the HX to contain plate bulging. The top & bottom plates looked to be maybe 3/16" thick.

How easy could that be?

-AC
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Old 03-28-13, 01:09 AM   #1448
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Quote:
Originally Posted by Ormston View Post
Anyone know of a source for brazed plate heat exchangers that are rated at high pressures?

The air conditioner i've started dismantling uses R410A and looking at the rating plate i need a heat exchanger rated at 36 Bar working pressure. after searching ebay etc. the best i can find are from Germany rated at 30 Bar.
My condenser HX is rated at 25 bar. Not knowing any better I originally asked for a 30 bar unit, but the supplier pointed out (A) I didn't need one, and (B) if I still wanted one it'd be nearly twice the price.

410a is more efficient because there are less frictional losses with the lower mass flow. In a self contained unit (not split with relatively long pipes) there is little efficiency to be gained, and considerable difficulties to be faced (for the typical diy'er) using a high pressure refrigerant like 410a.

The only thing you will see is you won't see the rated output from your compressor. You get proportionally less mass flow as it'll have a much smaller displacement than an R22 unit. Having said that, it'll not work as hard, so your power input will be proportionally less also, although your power factor will probably go to poo too.
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Old 03-28-13, 09:00 PM   #1449
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Quote:
Originally Posted by Ormston View Post
Anyone know of a source for brazed plate heat exchangers that are rated at high pressures?

The air conditioner i've started dismantling uses R410A and looking at the rating plate i need a heat exchanger rated at 36 Bar working pressure. after searching ebay etc. the best i can find are from Germany rated at 30 Bar.

Thanks steve
36 bar is a ridiculous pressure. 30 is just fine. R410 at 50C is just under 30Bar. What temps do you want to heat to? Above this temp, the HPs are usually CO2 or 2 stage units.

There are lots of SWEP or Alfa Laval HX rated and available.

Don't forget, if the HX is rated at 30bar, it has been tested to maybe 45bar
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Old 03-29-13, 04:04 PM   #1450
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Originally Posted by Mikesolar View Post
36 bar is a ridiculous pressure. 30 is just fine. R410 at 50C is just under 30Bar. What temps do you want to heat to? Above this temp, the HPs are usually CO2 or 2 stage units.
The 36 bar is what is on the ratings plate of the air conditioner, probably as the evaporator will see 25-30C so the condenser could well be 60+ C.

I,m only looking for 45-50C so i guess i don't need such a high rating.
Looks like i may not have chosen the best AC as a first heat pump.

Thanks for the replys Mikesolar,BradC,AC

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