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In this Discussion
- bbok March 2016
- CothermanDistilling May 2016
- gixxerpilot750 March 2016
- grim May 2016
- jacksonbrown May 2016
- Johnboy March 2016
- Mickiboi May 2016
- punkin March 2016
- Sandman March 2016
- TheMechWarrior March 2016
Comments
I need to do a lot more testing before I can recommend anyone spending money on this.
I also need to find better controllers than the REX which is why I am going to use a proper programmable controller to get it right.
The orange hose goes straight back into the cooling tower for cooling, it is not mixed back into the circuit.
The valve can have a CV between .6 snd 1.4. Its a full divert valve. Missed a decimal point and a digit on the pressure drop, should be 13.5kpa. This valve is CV 1.2 because the chinese factory only make 1.2 and 4. I would have preferred about .8. Raf said it will work just might have to lower the inlet pressure, but it works fine. The Belimo equivalent was $345 for the valve and $192 for the actuator. Not cheap.
How this thing going?
It's a nice tidy setup. Is the vapour temp still working out?
I see you are using the valve to restrict the inlet, and the RC is not under any pressure.. do you think it would work better if the valve was restricting the outlet?
No the valve is not restricting the inlet. The 2 pumps provide a full flow through the condenser. The valve is fully open to the full flow of the pumps. With no current (4mA) applied to the valve (4-20mA) there is 20 litres a minute flowing through the valve and the condenser. The setup is mixing. When coolant is needed the other port is under pressure and water is injected into to the loop as the valve opens. I havent done anything lately as I have had a few dramas in the family. Girlfriends father snapped his back cutting trees, now a paraplegic and my brother is undergoing bypass and mitral valve replacement surgery. I have heaps of strip to test run through this when I manage to find some time. If you need a drawing to understand better let me know and I draw one up and post it.
the valve restricts new water from entering... I was asking if it would work better stopping water from exiting the system... I have found that this way seems to purge air better...
Water cant exit the system unless water enters the system. Also the pumps suck from the bottom up and discharge into the top of the condenser so air is not a problem either. To purge the system of air, I set the valve to 10mA with no pumps running and allow the condenser to fill with water through the blue pipe. When its full, water exits via the orange pipe. I then turn the system to auto and the valve closes (fully open to pump flow and closed to cooling water) and then the pumps start. Its running from a plc. So it forms a closed loop. Water cannot exit as the pumps suck it back in from the bottom of the condenser.
I think i might post a couple of drawings when i manage to find time for myself.
I used to use full flow for both the PC and RC.
The major benefit of the full flow approach is throughput, it is significantly more effective than variable flow. I can manage ungodly distillate rates through my PC. This has to do directly with increasing velocity/turbulent flow, as well as essentially eliminating the temperature gradient in the heat exchanger (maximize delta t).
My problem with full flow on the RC was that the pump and valve were located a significant distance from the heat exchanger, this in conjunction with the system volume introduced a level of dead time that I simply couldn't tune out. Trying to increase the pump speed only introduced significantly more oscillation.
One major error I made - was the temp probe in the RC in this design. The temperature probe should have been immediately after the mixing valve. This would have eliminated the measurement lag almost entirely. With a fixed flow rate, the measurement point didn't need to be within the RC. But only realized this blunder after we'd re-plumbed to move the valve to the RC and move to variable flow/bypass.
I understand how it works... and if it works fine, great! just running things by you to get your thoughts...
I am thinking that if you have a small air leak and are limiting the input water, air replaces the loop water and you get a larger air pocket... with the valve limiting the water exiting the system, you would see the leak since it is under slight pressure, and fix it...
Also, in my experience if you are filling a condenser from the top, you never seem to get all the air out..
You are absolutely correct - purging this kind of system is a tricky matter.
When we drain our recirc tank, it allows air to enter the lines.
We need to force valves to 100% through, increase pump speed to max, slowly close the valve, re-open, etc etc etc.
This is filling bottom up too.
If the lines get really air-bound, we need to break a union to act as a vent.
We now go out of our way to not let air in the system.
The big issue is that with the pump in the loop - after the valve, you always have a certain amount of bypass - unlike in a variable flow - where 100% of the loop contents return to the tank, in the fixed flow model- you can have a situation where some portion is recirculated, and if that includes air - it tends to stay entrained in the loop. Top feeding - I would imagine purging this kind of system would be painful.
when you have a system that is under pressure, especially 'mains pressure', keeping air out is easy, the exit from the system has to be at the high point...
I had one of these desuperheaters on my house. The pump is tiny, but never had an air-bubble issue like I have had with other systems... any air went to the top of the water heater ... bonus, I never had to turn on the water heater as long as the A/C ran once or twice a day...
I had a glazed domestic hot water panel above above a hot tub for 10 years, since the collector was above the open area (the tub), I had to way oversize the pump to prime the system, and it was not under much pressure, I really wanted a way to have the panel below the tub, self clearing of air, and thermosiphon would have eliminated the need for a pump altogether... but it did a fine job of keeping the tub at 104F for many, many years...
my pool had solar water heating circulator too, but that was just brute force of a 1hp pump on 1.5" line to clear the air, and it had a vacuum breaker to drain the panels....
I don't have any air issues or purging issues. It fills in about 2 minutes. Even air in the system doesn't make any difference since I am drawing from the bottom exactly the same as a car does. I did test this half full of water (or half full of air however you want to see it). As you can see the pumps and valve are about 4 inches away from the entry point of the condenser so when the valve cracks the water is injected straight into the loop from the top, the hot reject water leaves the loop at the bottom. Nothing is working under any sort of pressure. The coolant feed to the valve comes from an aquarium pump, no pressure there either. I have even run it without a feed pump, the suction from the two pumps is more than enough to draw water into the system with out the need for a feed water pump but I am leaving it on for safety sake. There is also no problem with hunting (oscillating) within the loop. 4 reasons for this.
I have no idea what you mean about a certain amount of bypass. Bypass to/from where to where? You have lost me. There is no bypass in this system.
Here is what I will try next...
You're going to burn that feed pump out. It need's a small line back to the inlet.
Put the red one on the other green one too.
not centrifugal... they are designed to run totally blocked... not for extended periods of time, as the water may get hot, but that will not happen in our situation...
and putting the red return on the other one, the feed pump will be in a loop... I want only very hot water returning to the container, I do not want the whole tote circulating, just the RC If I have too much bypass (I have a bypass on my PC), I lose more than half the cooling ability that way Currently, I get a thermocline that works its way down the tote, when inlet water starts to rise, I switch to another tote or shut it off..
March Pumps - General Installation Instructions (PDF)
Fury muff, so you're running a magdrive. I would still put a bypass on it regardless, with a small ball valve to tune the pressure. That way those oversized control valves you like using will be more comfortable.
So your flowing down through the RC?? then your recirc pump is drawn wrong. I would still just do what I originally said. It would give you the hottest water with minimal reflux sub-cooling and no dissolved gas would build up. You need to get that counter flow thing out of your head when dealing with a phase change. There's no deltaT in the vapour.
Correction. My valve starts to let water flow through at 5.12mA not 4.12mA. I have a Belimo CCV here as well and it cracks at believe it or not 5.3mA. Remember all these valves we are using are designed for HVAC so they really aren't that good.
Flow in the system is probably 70-80% A-Port on the valve (record), with about 20-30% B-Port (new water)? (at least it runs somewhere around there on my system) Given that the majority of the flow rate is recirculating - small entrained bubbles will stay entrained as they recirculate - that's all I meant. Should have said recirc, not bypass. What I meant by bypass was not returning to the tank/drain.
Program a 1ma offset in your PID to compensate. However, in the real world I can't imagine this matters as you would rarely be in a situation where that valve is operating in the full close position during a run.
In terms of good/bad/indifferent HVAC valves, I picked up a new Belimo to try. Q-Series fast running actuator - LRQB-24MFT.
It's got a 5 second full swing time - very very fast, hooked up to my bench power supply, it rockets back and forth tracking the voltage. My Johnson is considered relatively fast at 35 seconds full swing.
I have the current system dialed in well, but there are certain operating conditions that still cause an oscillation that I just can't tune out.
5 seconds is considered fast?
I have done that, I'm using a PLC.
When you change setpoints ftom full reflux to taking off product. The valve fully shuts then.
5 seconds is very fast for a motor-driven mechanical actuator - usually to get those kinds of speeds (or faster yet) you require a pneumatic or magnetic drive actuator.
However, it's largely moot - during a typical run the valve is barely moving, and the valve position changes are absolutely minimal. It's only when you make set point changes that the speed comes into play - or if somehow you have a big upset to the system - crank the power up or down, etc. Even then, the thermal mass and speed of change is low - at least on my system with the large dephlegmator.
If you are building a race car - here you go:
Siemens Modulating control valves with magnetic actuators, PN 16 (PDF)
Less than two seconds full swing with 1:1000 resolution.
Gotcha - on my system I manage full reflux by dialing in a lower setpoint - valve doesn't go full swing to get there.
Same here. Valve usually sits at about 9% open to hold 30 degc. But when i change it to 65 degc, it fully shuts, remember i still have 20 litres a minute flowing through the condenser. As it approaches the higher setpoint thats when all these dead times and delayed responses start to come back and haunt you. Tuning out the valve slack and getting it to open under the smallest signal change made a mountain of difference to my system.
Yeah, but your setup is about as good as you can possibly get, the time lags are almost completely minimized. The valve response time is going to be good, there is nearly zero measurement lag, there is minimal thermal mass, short piping lengths.
It's going to be hard to design a system better than what you have there. Maybe a faster valve. Possibly solenoid - but with that very high flow rate - the solenoids are going to absolutely slug the condenser, you would need something with a very high pwm duty cycle (talking double or triple digit hz). The solenoids and drivers are going to be expensive, and you'll be beating the hell out of them.
Agree about the slack - my Johnson valve has mechanical slack in the actuator linkage/assembly - even running stable, it causes a little bit of hunting back and forth (small changes are absorbed by the slack, so the controller tends to overcompensate seeing no change to the PV).
You are close to the holy grail as far as dephlegmator automation goes, that's just my 2 cents. I would do exactly the same except I can't mount a pump on my dephlegmator - as it would need to be explosion proof - and that's going to be very cost prohibitive.
Thank you @grim . Im pretty happy with it. I have ironed out every delay i can see and it is very quick.
I used to work for Johnson controls in Adelaide and i know those valves very well. They do have some slack in them all right.
I feel for you mate. Bound by regulations preventing you from doing what you want. Looking at my setup for a moment and think about this. If you used a pneumatic valve and an E to P transducer, you could mount the pump under the valve out of the classified area.The valve would be mounted the same as mine is. You could still use a pressure pump to push the water into the circuit. I dont think the size of the water loop matters that much as compared to how close you are to the injection point into the loop. Does that make sense?
I was running a nearly identical setup as you, but with the valve and pump some distance away, the dead time was horrendous, because we used low-power pumps and large diameter plumbing (4-5 gpm). The major flaw was having the thermometer in the dephlemator - no chance - it would have worked better if I had the probe immediately after the valve. This way the PID would have had immediate feedback of loop temp change, instead of what was about 1-2 minutes of complete dead time on a step change. It was only after we said "to hell with it" and moved the valve to the dephlegmator - and replumbed as a bypass system (variable flow) - that I thought of moving the probe.