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Old 11-25-13, 04:31 PM   #31
NiHaoMike
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I'm working on the control software. At this point, I can "run" it by manually adjusting the water pump and fan speeds, good enough to prove that it works but not very practical. Can't get any real performance data (apart from that it draws only 300W or so with the fans maxed out and the suction pressure very high for a ES22a/R433b system) without the tank sensors and in any case, I would have to wait until next year to get meaningful results.

There's a dsPIC for the low level control and an OpenWRT (embedded Linux) platform doing the web UI stuff. There's a whole lot to learn. I'm much more familiar with hardware than software.

The interlink between the processors is a high speed UART link. I originally planned to use SPI, then realized it was already used by the SD card... The in-band framing is a little more difficult to program for, but I have learned a little about how to do it. (Reserve two values - a frame delimiter and an escape code, then XOR conflicting data bytes and denote that with the escape code.) The link can run up to 460kbaud (with a very clean signal according to my scope) so even realtime streaming of the voltage and current measurements (i.e. to detect compressor speed with FFT or to implement a "soft scope" in the web UI) should be easy to handle.

BTW, if you think all that is overkill for HVAC control, it is. I'm using it as a learning experience to get more familiar with software development.

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Old 11-25-13, 08:57 PM   #32
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Quote:
Originally Posted by NiHaoMike View Post
...BTW, if you think all that is overkill for HVAC control, it is. I'm using it as a learning experience to get more familiar with software development...
Overkill? Yes, of course it is.

Seems that if you put it together with duct tape and chewing gum and one syllable words, it would already be doing useful work for you... and would only get better, as your refinements were being applied.

At least, that would be my approach.

I learned a tremendous amount when I let my prototype heat pump run off of water from the backyard loop for a couple of months. I learned things that totally came in from left field, things that I didn't know were there to be learned, things like, "rain is a heat event". I never would have guessed that such was the case.


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Old 11-25-13, 10:04 PM   #33
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It's pretty cold (by Texas standards anyways) at the moment so I have a lot of time to work on the software. Once warmer weather is back, I'll be able to do a proper test and tune all the control parameters.
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Old 11-26-13, 12:15 AM   #34
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I'm nerding out over everything Linux_HPWH. You are logged in as root, lots of control there. That's a cool interface, you are winning the golden cocoon award for sure.
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Old 11-26-13, 03:57 PM   #35
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I rooted every Android device I have owned within a day of receiving them, often running a custom ROM if there's a good one out there. (The Jessica Simpson board runs OpenWRT instead of Android, but both are Linux...) That's what real engineers do...
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Old 03-22-14, 09:50 PM   #36
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Ok, I believe this is the machine you spoke of in the other thread. Am I correct?

If so, I still can't see how you rigged the unit to do its job. Did you finish, or is this still a work in progress?
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Old 03-22-14, 10:17 PM   #37
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I'm working on the firmware. The dsPIC is running FreeRTOS and does all the low level control. At this point, it is able to run, but the PID loops need tuning. Also, some features still have to be implemented.

BTW, I'm new to programming with RTOS so that's why it's taking a while. Plenty of learning, though!
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Old 03-23-14, 09:40 AM   #38
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OK, so is it in place or still on a bench?

I'm curious as to the plumbing, flow, and control scheme you have come up with and how it is working.

I remember discussing the design phase with you last year, but I never got the goods on how you did an ejector without a manufactured ejector. It looks from the pic u posted the unit has more txv in it than usual. Did u end up using a txv or 2 for the ejector nozzle(s)?

You never completely explained your refrigerant circuit, either. A sketch would be nice and would explain almost better than words. The last thing I heard was that it's a prius/acadia hybrid. A pricada, if you will, rhymes with cicada.

Hopefully it lives longer than a cicada.

Did you get inspiration from Rube, or are you working on a dissertation in modern refrigeration architecture? This rig looks very complex and confusing. And that only covers the mechanical side. The fact that you are still (1 YR LATER) tweaking and twiddling the control logic makes me not even want to ask about it. A simple diagram or 2 (like the mini-manuals hidden inside clothes dryers) along with some general installation specs and operation impressions would go a long way.
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Old 03-23-14, 11:06 AM   #39
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Here's the refrigerant flow diagram:

The ejector is a MIG welding tip brazed into a tee. The extra TXVs are for the reduced pressure zone and vapor return. The ejector creates the reduced pressure zone, making good use of energy that is otherwise wasted. The two stage cooling enhances dehumidification. Since the refrigerant exiting the ejector has a lot of vapor, a phase separator and third TXV are used to allow some vapor to bypass the first stage evaporator, reducing the pressure drop across it.
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Old 03-23-14, 04:15 PM   #40
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Ok, so I drew some arrows to try to make sense of this drawing.



Did I get the flows right? This looks like an ejecs II system, with a TXV instead of a cap tube driving the downwind evaporator, and TXV 3 added in.

original ejecs 2:


Mike's rig:


If so, I have a question: Why does TXV 3 have its sensing bulb tied to the inlet of EVAP 1? I get that it is meant to digest extra gas and send it to the suction line, but what if? Such as what if EVAP 1 frosted up, causing the phase separator to suddenly burp? This would vent fog/burp juice straight into the compressor. Only after it burped sufficiently would the temperature drop enough to close the valve. Then it's too late, the compressor has to deal with the vomit from TXV 3.

The other looming question is: How does this piggyback to the faucet supply? Draw from cold, pump into hot, or vice versa, or with a third "suction" line? And what controls the water pump?


Last edited by jeff5may; 03-23-14 at 05:25 PM.. Reason: clarity/pics
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