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Old 05-21-2017, 08:03 PM
Goody Goody is offline
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Goodwrench, you are amazing!
Old 05-21-2017, 08:16 PM
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Goodwrench, you are amazing!
Fortune 500 companies contract me for big bucks for the past 18 years to be amazing
Old 05-21-2017, 08:29 PM
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Your cooling of the condenser with water will only help the condenser to condense the vapor into liquid... which is great.

BUT THAT WILL NOT KEEP YOUR COMPRESSOR FROM DRAGGING DOWN YOUR DC VOLTAGE SYSTEM

I believe I explained this a couple times. So please stop boring me with all that other nonsense ... it doesn't relate to this.
OK Goodwrench, I'll hear you out again.

So you claim the compressor in my system will "drag down" the "DC voltage system". I'll give you some parameters to consider. An 89 cc Sanden piston compressor driven at 450 rpm, R143a, automotive evaporator, and condenser saturation temperature of 85F (made possible by river water cooling). Estimate the DC amps assuming a 24v system. Now, tell me, would this load really drag down a 5 KWh rated battery connected to a 2500 watt solar array?
 
Old 05-21-2017, 08:33 PM
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Hey Goody....I m tired of slinging mud....how about you?

Just to get a few things straight...

I never doubted your artificial cooling of the condenser....like I said I have done that hundreds of times

I never doubted anything else about your ideal.....except for how you are gonna run that energy absorbing monster we call the compressor

Every time I ask that question..... the responses are all the same...
Physics ....Physics...Physics....

So....do you think you can explain your plan to do that?
without all the mumble jumble.....
Old 05-21-2017, 08:35 PM
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But nothing you stated changes the fact that your compressor will kill your D.C. Electrical system.
Automotive AC compressors can stall a 4 cylinder engine.... do you think you can come up with a brush type D.C. motor that can handle that? I kind of doubt it....because you still have your head stuck in the sand.
Just an FYI, a number of modern cars come with 72V electrically driven AC compressors. No belt or external drive. Solar panels will run them just fine.

OH, and FYI, 3 of our aircraft use 24V, DC motor, belt driven Sanden compressors. They cool incredibly well. The picture shows the motor and compressor as removed.



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Old 05-21-2017, 08:36 PM
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Please read this again OP.....
I did.

Please read this (I would write "again", but I doubt you read it the first time):

http://www.achrnews.com/articles/883...tem-efficiency

EXCERPT: "For example: Letís say an R-134a air-cooled condenser is running at a condensing pressure of 147 psig (110F) at an ambient of 90F. (See Table 1.) This is a Delta T of 20F. If this condenser becomes dirty or is blocked, the condensing pressure might rise to 215 psig (135F) at the same 90F ambient. The Delta T or temperature difference between the condensing temperature and the ambient is now 45F. The condenser can reject heat at this Delta T, but it makes the entire system very inefficient. Often, if a high-pressure control is not protecting the system, a compressor burnout can occur with time."
Old 05-21-2017, 08:38 PM
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Just an FYI, a number of modern cars come with 72V electrically driven AC compressors. No belt or external drive. Solar panels will run them just fine.

that's nice.....but that's not the design the OP is using......
Old 05-21-2017, 08:39 PM
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I will bow out here as I really can't add much more to the discussion without doing a lot of testing or internet researching. I still think cooling the condenser will drastically lower the condenser pressure (PV=nRT even if the coolant doesn't really behave like an ideal gas in that state).

I mean if you think about it at all, why would manufacturers put fans on the condenser coils if it did not improve system efficiency (lower power draw for equivalent cooling). They always try to cut pennies, and even a cheap fan costs a quarter or so.

I will submit that you may need more coolant (R134a?) in the system if you cool the condenser so much that it changes the flow a lot. This is where I would have to do research because I have no real clue how to do that in theory.

So good luck on the argument. Both of you being Navy and all, should be good fun.
Old 05-21-2017, 08:40 PM
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Hey Goody....I m tired of slinging mud....how about you?

Just to get a few things straight...

I never doubted your artificial cooling of the condenser....like I said I have done that hundreds of times

I never doubted anything else about your ideal.....except for how you are gonna run that energy absorbing monster we call the compressor

Every time I ask that question..... the responses are all the same...
Physics ....Physics...Physics....

So....do you think you can explain your plan to do that?
without all the mumble jumble.....
Well, Goodwrench, this is a physics problem. Actually, mechanical engineering is a better description.

Your concern is the DC amp load. I gave you the parameters. Determine the required mechanical power for the compressor, then consider a 70% efficient 24v DC motor. Once you determine the amps, then you will be in a position to assess whether or not the load is excessive. It's that simple.

BTW, there has been no mud slinging from this end - except whatever I returned to you. I assure you I returned only a fraction of what you sent my way.
Old 05-21-2017, 08:44 PM
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Goody, I do want to know more about your boat plans as we are wanting to modify a 38 to 44 foot sailboat to be all electric drive/solar with a small generator backup and a large lithium battery (like a 30kW out of a crashed electric car or something). Do you have a boat thread going that I have not found?
Old 05-21-2017, 08:44 PM
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I did.

Please read this (I would write "again", but I doubt you read it the first time):

http://www.achrnews.com/articles/883...tem-efficiency

EXCERPT: "For example: Letís say an R-134a air-cooled condenser is running at a condensing pressure of 147 psig (110F) at an ambient of 90F. (See Table 1.) This is a Delta T of 20F. If this condenser becomes dirty or is blocked, the condensing pressure might rise to 215 psig (135F) at the same 90F ambient. The Delta T or temperature difference between the condensing temperature and the ambient is now 45F. The condenser can reject heat at this Delta T, but it makes the entire system very inefficient. Often, if a high-pressure control is not protecting the system, a compressor burnout can occur with time."
you are right....I didn't read it......cause it doesn't have anything to do with what I m saying.....I m not concerned about the efficiency of the condenser....
Old 05-21-2017, 08:51 PM
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I will bow out here as I really can't add much more to the discussion without doing a lot of testing or internet researching. I still think cooling the condenser will drastically lower the condenser pressure (PV=nRT even if the coolant doesn't really behave like an ideal gas in that state).
The process is similar to water cooling a steam condenser of a steam engine. Automotive steam engine systems with air cooled condensers generally operate at around atmospheric pressure. Water cooled steam plants operate below 1 psia. With respect to an a/c system, one need only consider an extreme example. What would happen if the condenser were submerged in ice water during operation? Answer: The pressure in the condenser would fall to roughly equal the pressure in the evaporator. The pistons in the compressor would then force open the reed valves as soon as they start the compression stroke. The torque on the compressor would plummet. If driven by a constant speed electric motor, then the load on the motor would plummet as well. NOTE: Of course, this little test would not be good for the compressor.
Old 05-21-2017, 08:52 PM
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you are right....I didn't read it......cause it doesn't have anything to do with what I m saying.....I m not concerned about the efficiency of the condenser....
What about the discharge pressure on the compressor? It decreased from 215 psig to 147 psig in the example. You see, this allows a constant speed compressor to deliver the same mass flow rate of refrigerant with less work (i.e. efficiency increases), and vice versa.

Do you see now?
Old 05-21-2017, 09:10 PM
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Goody, I do want to know more about your boat plans as we are wanting to modify a 38 to 44 foot sailboat to be all electric drive/solar with a small generator backup and a large lithium battery (like a 30kW out of a crashed electric car or something). Do you have a boat thread going that I have not found?
I do not. I'm not the guy to ask for advice on such a big job. In fact, I know very little about boats. The boat design I have considered is exceedingly simple and limited to the slow waters on the Mississippi river. My only suggestion is to not neglect propeller efficiency. A slow moving propeller can increase efficiency a lot. It's all about selecting the right pitch and diameter for your desired speed and matching the torque using the motor and gearing. You don't need more than hull speed and boat. A lot of sailors worry about a large prop inducing drag, but from what I have seen (which is limited) it's not a serious problem.
Old 05-22-2017, 09:13 AM
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Back in the 60s-early 70s there was a tract of nice homes built across town and it was to be all electric. Electricty was so cheap then that SCE was just about giving it away because they had overbuilt.
The general contractor got a great deal on some local gas air conditioners, so the next phase had gas piped in for otherwise all electric homes. Most of these homes went gas, sooner or later, but the original air conditioning still works in most of those homes and it is the best around.
If built for the long haul of quality parts, I think gas would be my choice for HVAC, for cooking and for refrigeration. Now that we can have solar power with battery backup, it should be good for LED lighting and the fans needed to push the HVAC. Hook up to the grid, but have a great backup.
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Old 05-22-2017, 10:19 AM
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If built for the long haul of quality parts, I think gas would be my choice for HVAC, for cooking and for refrigeration. Now that we can have solar power with battery backup, it should be good for LED lighting and the fans needed to push the HVAC. Hook up to the grid, but have a great backup.
I had a similar mind set before I saw the cost for PV plummet. I got interested in various absorption and adsorption cooling systems, and I actually built a small test unit using lithium bromide as the absorbent. Since I do not have a lot of money, I had to get creative. It worked - very poorly. It was getting too expensive quickly, so I scrapped it. I learned a few things along the way. The problem was a very low cooling rate because of a poor absorber design. However, it would chill water to low temperatures. I could have made a reasonably good small refrigerator, ;-). Now, this was while solar PV was still more than $2 per rated watt. Shortly afterward, the price shot down below this point and it's now well below $1 per watt. I think today the best off grid configuration is to power electrical a/c systems at a high rate as opportunity loads on PV, then operate at a reduced cooling rate at night. A large home might use a split ductless system and operate only select zones at night and at low rate to minimize battery discharge. That said, absorption/adsorption cooling is fascinating and really simple once you sit down and examine it closely. The system I devised was very simple requiring minimum electricity and was designed to be used with a small furnace. It could show good results with a proper absorber design. I still haven't seen a simpler absorption cooling configuration. (However, I think vapor compression is simpler still)
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