Morphing Air Conditioner into Autocascade System

[[XC] gomeler]

The laws on using R290 in refrigeration systems make me question our governing bodies. I imagine if my AC system outside was charged with R290 instead of R22 it would run cooler while consuming much less power. We can argue all day long on the safety issues of using a hydrocarbon but at the end of the day it won't matter much. I don't see builders dropping R1150 as a refrigerant as R14 is expensive and so destructive. There are R22 substitutes that are primarily R290, and I wouldn't be surprised if we see R600 replace R134a in some applications.

[yngndrw]

Nol: Walt isn't "jabbing" at you, he's just stating a few facts about the use of R290, especially those who sell units charged with it. (And plenty do !)

While you state that it's not illegal to modify your own tools, I'm pretty sure that Walt is correct about it being illegal to modify a torch.

Regardless, this is overshadowing mytekcontrols's awesome work. (I should really find a new word instead of saying awesome all the time.)

[wdrzal]

Regardless, this is overshadowing mytekcontrols's awesome work. (I should really find a new word instead of saying awesome all the time.)

Your right,I didn't even relize what thead I posted in sorry mytek.
But even mytek agees safety is alwyas the #1 concern.

[n00b 0f l337]

R14 is expensive and so destructive.

Expensive yes, destructive no. It's a green gas as far as i've read and been told.
As for modify a torch, actually the thing I Have now is not a torch. I'd say modifying the torch end of a... torch. Would be dangerous, you could easily create a bomb, however, cutting off the fitting is not exactly dangerous to those around you.
I agree that its not a jab persay, however I don't like the way it was stated.

[[XC] gomeler]

Expensive yes, destructive no. It's a green gas as far as i've read and been told.

My last post on this subject before we derail this thread.

. Its atmospheric lifetime is 50,000 years and global warming factor is 6500 (carbon dioxide has a factor of 1). Although structurally similar to chlorofluorocarbons, tetrafluoromethane does not deplete the ozone layer.

That being said, it's a fantastic compound.

[mytekcontrols]

I leave for a minute (well... actually hours), and you guys take over

Just kidding

Actually some interesting points were made about using HC's.

• Yes it is dangerous in the wrong hands.
• Many of them are considered to be very Green.
• As we saw in another post earlier this week, even R22 can be explosive when using poor practices.
• As for legality; at least in Europe, R-600a has been approved for use in home refrigerators.

I truly think that HC's will be the next big change in refrigeration. Same as what we saw happen when CFC's were banned. It no longer is just about Zero ODP, but now also has to be low global warming potential as well. HC's are currently the only viable way to achieve both in a phase change system (at least that I know of). HFC's only address the ozone concerns. HFE's show promise, but for the most part have numerous problems to work out, such as oil solubility.

Thank you all for your input

[{.bLanK} GoD]

I prefer the later, since it will allow me to keep my package size small.

Really? I thought you'd be looking at increasing your package size.

Very very nice autocascade mytek, best I have ever seen. And you reckon you could get it going better? You're the man.

[tim-]

impressive work, especially due to the size..

one thought.. how would r23 be as a substitute to r170?

[n00b 0f l337]

R170 is the substitute for r23

[godmod]

R170 is the substitute for r23

In auto cascades?

[mytekcontrols]

Really? I thought you'd be looking at increasing your package size.

My wife would disagree

impressive work, especially due to the size..

Tim have you been talking to my wife?

Well in all seriousness let's get back to the subject at hand...

one thought.. how would r23 be as a substitute to r170?

As Adam pointed out, R-23 and R-170 are interchangeable with virtually the same boiling points, and very similar COP . Although R-170 seems to work just a little better, perhaps due to it's superior oil solubility.


Static BP Results:

My static BP turned out to be 202 psig (as checked against a Mirror Gauge), with the unit's internal temperature warmed up to 15.8C (I thought it would be as high as 215 psig). It would probably go up a few more psi in a normal room temperature ambient. Part of what I forgot to factor into my calculations when adding up all the refrigerant additions made during the tuning process, is that often times there will be a "soak-in" of the refrigerants with the oil which can lower the overall pressure by 6-12 psi.

Edit: Updated Test chart BP data as seen in this post. Also reviewed heat loss calculations for line and load insulation vs. temperature differential, and added this as well (estimated losses to be 20-25 watts). Total for maximum load = 150 watts + 25 watts heat losses (175 watts)

I did a compressor start-up and immediately came up to 295 psi on the discharge, with a peak current of 4.8 amps. Within 4 minutes of running, the current had backed down to 4.1 amps, and the discharge pressure was at 385 and rising. At this point I did a quick bypass of the discharge to the expansion tank using the manifold valves. This of course immediately dropped the discharge pressure down to about 300 psi. However it once again started rising as the pressure was sucked back out of the tank via the expansion tank captube (no surprise). It didn't take long before the discharge pressure was getting back into dangerous territory. So I manually bypassed it again to the expansion tank. Had to do this several more times within the first 15 minutes of run time, until the discharge pressure stayed in a more comfortable range.

My analysis of all this; seems to indicate that a more restrictive captube going from the expansion tank to the compressor suction would have allowed me to get away with bypassing the discharge only once (greater delay imposed on returning refrigerant back to the system). However with the present setup, and doing multiple bypasses whenever the discharge pressure approached 325-350 psi, I saw an incredibly fast pull-down in my evaporator temperatures. Within 15 minutes the mid-point of my evaporator coil was colder than -100C. This got me thinking.

I could go to a very long and small id captube to increase the delay time on sucking the refrigerant out of the expansion tank. Although I am already using 12 feet of 0.031id. Could go to 0.026id, but I'm not sure if even this would be enough without using an extremely long piece (I thought 12 feet was a lot). Another thought was; why not use a feed-thru PRV between the discharge line and the expansion tank? One that has a blow-off point of 350 psig. This would be simple, and not require any timers. I think this will be my next approach... now just got to locate a PRV.

BTW; for future reference, I'll be calling this a buffer PRV.

In combination with the feed-thru PRV, I'll also be adding a high pressure switch set to 375 psig, as a safety cut-off for my compressor (was always planning on doing this anyway... just haven't implemented it as of yet).


Photo of warmed-up static balance pressure, verified against mirror gauge:

[[XC] gomeler]

I had a similar issue on my last "autocascade" if you can call it that. Since it's the HXs that aren't cooling down fast enough, would it be wiser to place the buffer PRV past the 1st oil separator on the gaseous so that most of the butane and what little high-stage refrigerants that have entered into the oil/butane solution can begin chilling the 1st HX?

[Moc]

Expensive yes, destructive no. It's a green gas as far as i've read and been told.

lol? R14 has a GWP of 6500!

[godmod]

Since it's the HXs that aren't cooling down fast enough, would it be wiser to place the buffer PRV past the 1st oil separator on the gaseous so that most of the butane and what little high-stage refrigerants that have entered into the oil/butane solution can begin chilling the 1st HX?

That's a good point!

[mytekcontrols]

...would it be wiser to place the buffer PRV past the 1st oil separator on the gaseous so that most of the butane and what little high-stage refrigerants that have entered into the oil/butane solution can begin chilling the 1st HX?

Yes it would! I'm glad that you picked up on that. It'll be tricky to do on my foam insulated system, but I'll be wanting to tap into the top of my 1st phase separator for the discharge gas source leading into the Buffer PRV.

Edit: Of course I will need to monitor the valve's temperature to be sure it doesn't get too cold for proper operation and re-seating. I suspect it won't, since the valve's operation will be very intermittent and the mass should preclude any problems with freeze-up.

[n00b 0f l337]

A small wrap heater can solve that issue as well Mytek

[mytekcontrols]

A small wrap heater can solve that issue as well Mytek

Good idea, but I've been researching the idea of using a PRV repeatably as in the proposed Buffer PRV application I have been discussing. Apparently using a PRV this way is not recommended due to inconsistencies in operation after repeated opening and closing. Here is a good discussion on the topic: click here (might need to scroll up to the top of the page)

I think I'll have to go with a pressure switch and solenoid valve instead. This will also allow tweaking the setting and differential as well, to better match the use.

[godmod]

What about a Selenoid Valve in combination with a High Pressure Cut Off with a auto reset? HPCO triggers the Selenoid Valve and resets (closes the Valve) again.

[n00b 0f l337]

Yep thats easy enough. Or just a handvalve if your willing to deal with un-automated. But a solenoid "open" linked to a high pressure cutoff. You can wire it in a rather odd way that will allow you to cut off to open a shorted circuit if you'd like. Or just have a powered coil all the time holding it open, and should pressures get high cutoff, opens the coil and tada.

[godmod]

Why should he use a hand valve when he tried to fit everything into this nice case...

[n00b 0f l337]

Hahaha sorry just came to mind

[mytekcontrols]

What about a Selenoid Valve in combination with a High Pressure Cut Off with a auto reset? HPCO triggers the Selenoid Valve and resets (closes the Valve) again.

That is exactly what I intend to do I guess I didn't explain myself well enough, but it's good to see someone else thinking the same thoughts.

Does anyone have a good source (as in inexpensive) for an Auto Reset HPCO that can be set to cut-in (turn on solenoid) at 350 psig, and cut-out (turn solenoid valve off) at 300 psig? Most pressure switches that i've seen have an SPDT switch, so the logic should not be a problem.

For my other safety aspect, I just ordered a fixed high pressure switch today from under-the-ice.com (400 psig cut-out, 300 psig cut-in). This will be used to shut-down the compressor if the discharge pressure gets out of hand. Unfortunately the other PS that they stock (350 psig cut-out, 250 psig cut-in) has too much of a differential. Otherwise I would have liked to use it for the Buffer aspect.

And as for the hand valve suggestion adam... well although it would work, I really am trying to have this thing work all on its own (automatic).

[n00b 0f l337]

www.under-the-ice.com is run by Runmc here
You'll get your order quick, in the mean time *psst ron send me his home address and phone! jk*
Lemme find you a pressure valve.

http://cgi.ebay.com/RANCO-CONDENSER-...QQcmdZViewItem
$50

[mytekcontrols]

http://cgi.ebay.com/RANCO-CONDENSER-...QQcmdZViewItem
$50

Thanks for the link Adam. I bought it

It'll work perfect, just needs a relay to reverse the logic (which I have already).

Why the sad face? I think it was very reasonably priced.

[n00b 0f l337]

Heh I could get ones with opposite open and close for $25 ish.