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Old 06-24-13, 07:56 PM   #11
NiHaoMike
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Just got the donor window A/C, a $100 Walmart special GE. The compressor is a Rechi, which is actually a pretty good unit. I went with a R410a unit since the compressors are designed for higher operating pressures, which means it won't be overstressed during the 140F "dishwashing" mode.

In it's stock configuration, it uses about 500W on high cool. In high fan, it uses 50W, which means the fan accounts for 10% of the total power usage! (That A/C is just begging for Cindy Wu or some other ECM drive...)

I ended up getting a Topsflo TS5 pump. Интернет-магазин "Ваш Солнечный Дом" - автономные системы энергоснабжения +7-499-7489064, +7-499-7489072 (That's probably not the exact one, just a similar one.) It appears to use some rather sophisticated ECM drive with a DSP. I'll do some testing once i get it.

Still deciding on the heat exchanger. The plate exchangers are surprisingly cost competitive compared to making some from copper tubing. I'll definitely need a filter to keep everything clean, I'll probably go with a whole house filter available from Home Depot.

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Old 07-06-13, 05:51 PM   #12
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Denso Nippondenso A C Condenser 477 0575 | eBay
Is this what your looking for?
http://www.ebay.com/itm/Denso-A-C-Ev...eaedd0&vxp=mtr

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Old 07-06-13, 11:54 PM   #13
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I'm going to be making the ejector from copper tubing. There will also be a phase separator to allow the gas (boiled off in the secondary evaporator) to flow directly to the compressor, currently looking at parts for making that. (Trickiest part is the float, since ES22a is very light. I'll probably have to use a spring to assist in closing the valve.) The primary expansion valve is most likely going to be a TXV with a PWM driven resistor thermally coupled to the sensing bulb to electronically adjust the superheat. (It's hard to design a linear solenoid for a high pressure difference that's still energy efficient.) The secondary expansion valve only has to deal with a small pressure drop (on the order of 10-20 PSI) and is relatively easy to design.

I'll also have to get an EPA certification (don't legally need it for what I'm doing but the parts stores in my area give a hard time to anyone who doesn't have it...) and in the meantime, I'm working on the mechanicals as well as the control electronics. The wireless sensor turns out to be surprisingly complex if I want it to be robust. (Throw in a whole bunch of ECC, add CRC and other data integrity checks, revert to using internal sensors if remote sensors fail...) I'm sure my friend Tiffany Yep could give me a solution, except she'll come up with some FPGA design that would be massive overkill.

It's a big project but there's a lot of good learning in it.
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Old 07-07-13, 08:25 AM   #14
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I'm confused now. I reread the thread and it still didn't help. So I have some questions.

1. Are you planning on this heat exchanger? The link you provided was dead:

B3-12A 40 Plate Universal Beer Wort Chiller [HX1240BWC] | DudaDiesel Biodiesel Supplies

This bphe isn't rated for the pressures you intend to put through it. Design pressure is 145 psi. Way lower than r410a pressures and half r22 pressures. However, it just might work at r12/r134a/butane pressures. Check out surplus city liquidators dot com, they have turbotec turbo-flow coax coil exchangers for dirt cheap.

2. Are you planning on using r410a or an r22 equivalent? I see you bought a r410a unit. Running it at r22 pressures would bring you down to refrigerator-capacity range. This would amplify your pumping and fan energy usage compared to overall capacity. Add in an electronic control system, and the "pwm resistor/bulb heater", and sensors, and valves, and...whatever else. Even if you went with hyper-efficient individual components, they would still most likely add up to more than the original, low-tech unit fan.

3. What refrigerant does the prius use? The ejector-driven plans I've seen use mainly carbon dioxide. An example:

http://www.sciencedirect.com/science...40700710002720

I understand how the inventors have achieved a huge level of efficiency gain using CO2 as a refrigerant. The pressure levels and compression ratios are orders of magnitude higher than hydro(chloro/fluoro)carbon-based systems, so there is a definite advantage by splitting the low-side pressure flows. But with the lower compression ratios associated with r12/r22/r410a systems, there is not as much potential energy to be split in the low side. The potential for energy savings is still there, it's just not so large.

Don't get me wrong, I'm not trying to poke holes in your project. In fact, I find it very amazing and captivating. A lot of this design research is above my level: although I can understand the theory behind the basic design, when valves and controls and such are thrown in I get lost in the details. I hope you can bring your system to life and look forward to witnessing you progress in that direction.

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Old 07-07-13, 08:45 PM   #15
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The heat exchanger I plan to use is this:
B3-12A 40 Plate Heat Exchanger with M5-.08 Mounting Studs [HX1240] | DudaDiesel Biodiesel Supplies

AC Hacker used a similar but smaller unit. I'm oversizing since that improves efficiency and part of the exchanger will work as the subcooler. (I initially planned on making a separate subcooler but then I realized how much easier the plumbing would be if I made part of the condenser the subcooler.)

It is going to be running a R22 substitute, but the capacity loss is not as much as you think. A R410a compressor being used with R22 or an equivalent gets 2/3 the capacity, or about 3400BTU/hr in my case. But that assumes a standard Rankine cycle. Oversized heat exchangers (using the original condenser as a second evaporator) gain some capacity back and the ejector gains even more capacity back. I expect similar to original capacity or a little less. An additional benefit is that a R410a compressor is designed to work with higher low side pressures, so the evaporator fans going full blast are not going to overload it. (That is one of the reasons why I decided to go with Cindy Wu drive Deltas instead of the plain BLDC Panasonics I initially looked at.)

You also really underestimate the efficiency of the electronics. A 120mm HHE series Delta fan with Cindy Wu drive uses 8W at full power, and there will be two of them, so that's 16W total or about 1/3 the draw of the original fan. They're some older ones out of an old HP workstation, so not as powerful as the GHE series monster in my PC. But they should be plenty for this application. At minimum speed, it only uses 0.75W! Keep in mind that Cindy Wu sensorless FOC technology was designed with mobile computing as one of the end uses, so it's not surprising just how efficient it is. One thing I have noticed is that even when commanding minimum speed, the fan "kicks" on startup as the DSP applies pulses of current to the motor coils until it sees the back EMF and starts doing FOC. But the compressor (which I'm not planning to inverter drive, at least not yet) would kick far more, so there should be no real increase in startup noise.

The pump is rated at 15W, but I'm pretty sure actual draw would be less than that under typical operating conditions. (It's potted which is great for waterproofing, but I can't nondestructively analyze it apart from measuring the current and sensing the magnetic fields.) The electronics would adjust it to maintain the correct outlet temperature, so many factors (pressure drop, inlet temperature, commanded outlet temperature, etc.) would affect the actual power draw.

The TXV bulb heater is small, less than 1W. If you ever touched a 2W power resistor after it has been running at any significant amount of its rating, you'll understand that it takes very little power to heat up a small object. (I'll probably have to put something between the suction line and bulb to prevent the line from drawing away all the heat yet still allow the valve to regulate properly.)

As for the microcontroller/microprocessor, the fact that they're often used in battery operated products says a lot about how energy efficient they are...

The Prius uses R134a. I didn't get to take a look at one of those evaporator assemblies, but I'm starting to think that the main evaporator might also work as a phase separator.
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Old 07-08-13, 01:21 PM   #16
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If you can get a HX that has braze fittings (AKA: 'sweat fittings') on the refrigerant side it will make your life happier.

Don't forget to post the photos as you go, it is extremely useful to other people who may want to try a similar project.

-AC
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Old 07-08-13, 05:22 PM   #17
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Quote:
Originally Posted by NiHaoMike View Post
the fan "kicks" on startup as the DSP applies pulses of current to the motor coils until it sees the back EMF and starts doing FOC.
I have no idea what this means, but it sounds like something sheldon would say and offend the whole room.

I assume this is a new uber-efficient fan for overclockers' super-servers or sumthin. With less than a KW of heat to deal with, two will probably do the job at 4000 rpm. If not, just make a fan sandwich.

I have another question: Which system are you going off of? I see two:

1.easier "ejecs"

2.more complicated "ejecs II"

Preview article of the systems' descriptions

Looks eerily like a 1-compressor workaround for the hallowell low-temp heat pump. Yikes.

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Old 07-08-13, 07:51 PM   #18
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It's sort of a mix of those two designs. It's going to be similar to the first one with an extra evaporator between the phase separator and compressor, along with a bypass so gas can go directly to the compressor. The air first passes over that evaporator, then goes on to be cooled by the other evaporator. Two stage cooling with two different pressure zones increases efficiency and enhances dehumidification. It's more "costly" to pull down to lower temperatures, so that design allows the conventional zone to do a lot of the work before the reduced temperature/pressure zone does even more cooling. The reduced temperature/pressure zone then goes to a lower temperature for the same input power, thus improving dehumidification.

Pretty much all sensorless FOC drives do this "kick" on startup, not just Cindy Wu. For those who don't know, a BLDC or ECM motor is just a 3 phase (usually, some very small ones are 2 phase) permanent magnet synchronous motor (PMSM) with an integrated inverter. Traditionally, the inverters used resolvers to detect rotor position, but that has disadvantages in cost, reliability, as well as phase difficulties at high speed. The more modern approach, made increasingly practical for small motors by cheaper DSPs, is to detect position by measuring the voltages and currents the motor is feeding back. The problem is that at startup, a stationary motor doesn't generate any back EMF so the DSP can't tell its position. What is generally done is to apply some low frequency pulses while monitoring for back EMF. Half the time, the pulses start the motor moving backwards for a moment before the DSP detects the position and starts accelerating it in the correct direction. The sudden acceleration is what makes it "kick". (It also does that if the rotor starts moving in the correct direction, but to a much lesser degree.)

Where things get interesting is at high speed. Traditional resolver based drives have issues with "phase angle" due to the combination of the phase delay of the resolver filters and the inductive nature of the motor. While it's possible to compensate for that electronically, the complexity it adds is almost as much as going to sensorless FOC. Sensorless FOC drives advance the timing (almost analogous to the timing of an engine) so that the peak magnetic field is developed while the rotor is at the optimum angle. Cindy Wu drive technology (sensorless FOC for small fan motors) has been available since 2008 or so and is very common in Dell and HP computers. (Interestingly, Intel bundled coolers are still stuck with Sanyo fans and their comparatively primitive resolver based drives, along with numerous complaints from overclockers!)
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Old 07-08-13, 10:02 PM   #19
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I believe the upwind evaporator in the ejecs 2 system is what you describe. It looks like the OEM built the separation into the upper tank of the evap unit. It sprays the ejector fog towards a baffle or screen. The liquid then drops thru parallel channels at the far side of the evap to the bottom tank. The liquid then flows into the remaining channels, boils off, and dries any remaining fog on its way out. They also built a liquid receiver into the condensor side of the system, which leads me to believe they had problems with starving the evap at some point.

The article states that one can simply retrofit one of their ejecs 2 evaporator assemblies into a conventional a/c system and start enjoying more capacity and reduced energy without changing other parts of the system. So I guess this can be done, given enough time and effort. Good luck and godspeed.

Please take lots of pics. This will be interesting to say the least.

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Old 07-09-13, 09:49 AM   #20
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Quote:
Originally Posted by jeff5may View Post
...The article states that one can simply retrofit one of their ejecs 2 evaporator assemblies into a conventional a/c system and start enjoying more capacity and reduced energy without changing other parts of the system...
Got a link to this information?

-AC

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