ReplyHere's another consideration for you.
The higher the suction pressure, the greater the capacity of the compressor.
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Ok i am not shure where i would find the numbers for normal refrigerants so i will use r718 here goes.
So 1 btu raises 1lb of r718 1*
970.4btu will vaporize 1lb of r718
So a 3 ton system would have a mas flow rate of 37.09810387469lb/hour
And we would gain 2225.88623248btu/hour
So our 36000btu system would move 38225.88623248btu/hour
Thats not as bad as i thought but i don't know the numbers for r22 or r410a
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Here's another consideration for you.
The higher the suction pressure, the greater the capacity of the compressor.
I do a triple evac with nitro to remove non condensables.
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I could be wrong but i think the suction pressure would stay roughly the same.
I know i could increase capacity by running the coil at 50* instead of 40* but then i lose latent capacity. And i am investigating the affect of free subcooling at the moment.Sent from my rotary telephone using TapatalkOriginally Posted by BBeerme
"Is this before or after you fired the parts cannon at it?" - senior tech
I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
Unless we change direction we are likely to end up where we are going.
"It's not new, it's better than new!" Maru.
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How should i understand these numbers?
R22@ 40* 83.28 psia 21.688btu/lb liquid enthalpy 108.191btu/lb vapor enthalpy
Do those numbers tell me the latent heat of vaporization? If so which one?
Why do liquid and vapor have different numbers at the same temperature and pressure?
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"Is this before or after you fired the parts cannon at it?" - senior tech
I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
Unless we change direction we are likely to end up where we are going.
"It's not new, it's better than new!" Maru.
Professional Member
I think the term is net refrigeration effect and it would be the difference between the two enthaly #s you listed
Side note order up a copy of "pressure enthalpy without tears." recommended reading if you havent already
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I thought of another non conventional idea. What effect would it have if you put the txv outside?
Just weld it in after the liquid line service port, weld an equlizer port in the vapor line to leave your service port open, strap the bulb to the vapor line and insulate the liquid and vopor lines really well. Also remove the piston of course.
Do youall think it would work like normal or would it effect the efficiency?
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"Is this before or after you fired the parts cannon at it?" - senior tech
I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
Unless we change direction we are likely to end up where we are going.
"It's not new, it's better than new!" Maru.
Professional Member*/Membership Committee
It seems to me like if nothing else the compressor would run cooler due to lower superheat.
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"Is this before or after you fired the parts cannon at it?" - senior tech
I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
Unless we change direction we are likely to end up where we are going.
"It's not new, it's better than new!" Maru.
Professional Member*/Membership Committee
Also just to clarify. I dont plan on doing any of these things in the field. Its just food for thought.
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"Is this before or after you fired the parts cannon at it?" - senior tech
I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
Unless we change direction we are likely to end up where we are going.
"It's not new, it's better than new!" Maru.
Professional Member
Mini split units do this all the time to quiet down the noise at the indoor unit. Works well. Just insulate the lines properly and make sure it forms a good vapor barrierI thought of another non conventional idea. What effect would it have if you put the txv outside?
Just weld it in after the liquid line service port, weld an equlizer port in the vapor line to leave your service port open, strap the bulb to the vapor line and insulate the liquid and vopor lines really well. Also remove the piston of course.
Do youall think it would work like normal or would it effect the efficiency?
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Edit: should also note that you are then sizing the outlet of the TXV to maintain your low pressure liquid /vapor mix as such until it gets to the distributor at the evaporator. I don’t have a table for that but it would want to be within your considerations. You could probably get a line sizing chart from one of the install manuals out there. If you run a typical suction line size from the TXV to the evaporator then that suction line would become part of your evaporator and ice up pretty quickly. Keep the pipe small to reduce the room for expansion and preserve the liquid quality.
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That is where the thought came from. I just wondered what else it would effect.Sent from my rotary telephone using TapatalkMini split units do this all the time to quiet down the noise at the indoor unit. Works well. Just insulate the lines properly and make sure it forms a good vapor barrier
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"Is this before or after you fired the parts cannon at it?" - senior tech
I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
Unless we change direction we are likely to end up where we are going.
"It's not new, it's better than new!" Maru.
Professional Member
I’m guessing it reduces the efficiency slightly because it would pick up a small amount and f heat along its travels. But if the line size is short and the insulation is good it’s probably negligible.That is where the thought came from. I just wondered what else it would effect.
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I figured the same. Also the evaporator would be very efficient becsuse it would be plenty well fed. And the compressor would have less superheated suction vapor so it would run nice and cool.Sent from my rotary telephone using Tapatalk
"Is this before or after you fired the parts cannon at it?" - senior tech
I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
Unless we change direction we are likely to end up where we are going.
"It's not new, it's better than new!" Maru.
Professional Member*/Membership Committee
And i expect the txv would not hunt much at all.
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"Is this before or after you fired the parts cannon at it?" - senior tech
I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
Unless we change direction we are likely to end up where we are going.
"It's not new, it's better than new!" Maru.
Professional Member
The problem I see with trying to run too low of a superheat is that you run the risk of turning part of your suction line into your evaporator. This could lead to icing up of your suction line, or at the least, preforming work where work didn’t need to be done which would reduce your efficiency. Then there is also the manufactures specs for their compressors, I hear from other techs on here that Copland wants something like 20 degrees superheat to their compressors. I haven’t seen the literature to support that but I also haven’t looked for it either. If you happen to see those documented I would be curious to see them also. I’m not sure if their required superheat is a blanketed number for all models or if scroll, for instance, would be different from their reciprocating units.I figured the same. Also the evaporator would be very efficient becsuse it would be plenty well fed. And the compressor would have less superheated suction vapor so it would run nice and cool.
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As for the stable hunting thing. You may see a reduction on that since the suction has a long time to mix all of the different distributors back into one slurry.
Edit, corrected my autocorrects.
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I dont remember them mentioning a required superheat number when i went to Copeland compressor school. But they do mention that the suction line temp shouldn't be above 65* in normal operation or the compressor will run hot and its life will be shortened. It seems that 10* is good safety. But i have seen units that call for 0* at the service valves. Also minisplits run much lower than 10*.Sent from my rotary telephone using Tapatalk
"Is this before or after you fired the parts cannon at it?" - senior tech
I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
Unless we change direction we are likely to end up where we are going.
"It's not new, it's better than new!" Maru.
Professional Member*
Yeah, that's always bugged me about mini splits. Just seems like it would not be efficient to have the metering device in the outdoor unit.
I do a triple evac with nitro to remove non condensables.
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I have always wondered how it works so well. The dramatically lower power consumption compared to conventional systems seem to indicate that is must not be too bad.Sent from my rotary telephone using Tapatalk
"Is this before or after you fired the parts cannon at it?" - senior tech
I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
Unless we change direction we are likely to end up where we are going.
"It's not new, it's better than new!" Maru.
Professional Member
I’ve seen those low requested superheats also, typically on mini splits. Those units that request that typically have EEVs with pressure transducers and thermistors all over the thing so they know exactly what the quality of refrigerant is exiting the evaporator, but I believe that number is to specify the superheat leaving the evaporator and not to specify the superheat entering the compressor. Those systems have always had an accumulator on them to protect against floodback if it were to occurring, from what I’ve seen.I dont remember them mentioning a required superheat number when i went to Copeland compressor school. But they do mention that the suction line temp shouldn't be above 65* in normal operation or the compressor will run hot and its life will be shortened. It seems that 10* is good safety. But i have seen units that call for 0* at the service valves. Also minisplits run much lower than 10*.
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8-12 is typically what I see manufactures request in their literature for a typical system when equipped with a TXV but haven’t had a need to look for anything mentioned by the compressor manufacture because the units installation instructions would supersede anything from the compressor manufacture.
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The 0* superheat i referred to was a piston metered ac. It was quite a curiosity to me. It was only at 105* outdoor with a fairly low indoor wet bulb.
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"Is this before or after you fired the parts cannon at it?" - senior tech
I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
Unless we change direction we are likely to end up where we are going.
"It's not new, it's better than new!" Maru.
Professional Member*
I believe, but am not 100% sure that mini-split EEV’s are in the outdoor unit. Though I think they still measure superheat st the coil.
If you do this with a TXV, unless you have perfect insulation the vapor would gain heat while returning, giving a falsely high superheat reading. TXV will then close farther than it should. Evan temp snd efficiency go down. You would have some loss in the liquid line from heat gain to the flashed refrigerant.
With perfect insulation, probably little difference.
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