single point measurements are worthless. pressure means nothing unless its seen in relation to lineset temperature. yep superheat.

im guessing your superheat was quite high indicating a starved evap, ie very little of it doing any work. after adding more refrigerant ( pressure/saturation temp went up) now more of the evap is doing more work resulting in colder supply temps.

never connect your gauges without measuring lineset pipe temps as well

 

Yea my superheat was I’m the 50s, (suncool around 12) and dropped to normal ranges after addding the refrigerant. Indoor temp was around 85.

 

Why would adding refrigerant make the evaporator do more work? I’m confused by this concept. My intuition is just making me think a blower working through a 28 degree evaporator should blow colder than a 40 degree coil. Obviously some of this is over my head at this point but that’s why I’m here.

 

Your evap was ohmost empty. There was no or very liquid refrigerant inside it to boil off. If it isint there to boil, your not going to lower lower your supply temperature. If your supplying the evap with a full column of liquid it has the ability to boil off at 100% in this case. Being you were 85f inside. If your giving it very little liquid because you have a low charge it can’t do any work. It’s like having a car battery with 12v but no amperage to turn the motor over.


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all the work in done when boiling off liquid freon to vapor.
high superheat= lots of vapor/ little saturated freon=little work
low superheat= lots of saturated (boiling freon)/little vapor= lots of work.

uber basic explaination....

 

dont confuse temperature with heat.

you need to remove heat ( btus)

 

Ok thanks guys this is starting to come together in thinking about it as removing heat into a saturated liquid as opposed to just cooling the area by blowing cold air.

 

Right.
A wise old journeyman told me when I started in the service field, "there is no such thing as cold air, it's air that lacks the presence of heat".
I was perplexed by his comment for about an hour, then he explained about superheat being the amount of heat being absorbed by the refrigerant as it passed through the evaporator coil, then as it makes its way back to the condenser it the amount of heat removed from the refrigerant as it passes through the condenser coil being pulled out and rejected to the outdoors by the condenser fan motor.
His explanation was far more simple than any superheat/subcooling education I had received prior to that.

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Why would than a very high super heat be bad? If I measure a 72 F suction line in this same case, why does it not mean that it’s just absorbing a lot of heat, doing it’s job.

This is prob a dumb question here

 

This is prob a dumb question here

and keep asking them " dumb " questions too and dont worry about what anybody else thinks when you do it is the only way you will UNDERSTAND ..... look out for yourself

been doing this for 20 years and I still ask them " dumb " questions

 

Yes the superheat is higher, but this does not mean better cooling.

If you take water as an example, most energy is stored in the molecular bonds. The phase change for liquid to vapor takes five times the amount of energy then it takes that amount of water to heat form 0 - 212 degrees. So, to heat up water form 0 degrees to 212 degrees takes energy, like form a stove burner. But it takes a lot of energy to "push it over the top" to change molecular structure, break bonds, and boil. Once the vapor is past the saturation "boiling" point again it dose not take a lot of energy to increase the temperature of the vapor "superheat".

So to reiterate it take a fair amount of energy to heat water to boiling "saturation" point, then a massive amount of energy to change phases, then less energy to heat the vapor. The concept you are missing is Heat Transfer. You are mistaking temperature for energy.

So if a refrigerant is like the water, and the air around the evaporator pushed by the blower is like the burner. Which part would you want more of? liquid "overcharged", Phase change "Perfect Charge", or vapor "undercharged". The answer is you would want the most possible phase change in your evaporator. You can think of the air around the evaporator as the burner to get the most heat out of it you want phase change resulting in more heat out of the air, cold air because it lost its energy to the phase change. Sure it will lose energy heating up the vapor past saturation into superheat, but not as much as the phase change.

Hope this helps

 

Yes the superheat is higher, but this does not mean better cooling.

If you take water as an example, most energy is stored in the molecular bonds. The phase change for liquid to vapor takes nine hundred, seventy times the amount of energy then it takes that amount of water to heat form 32 - 212 degrees. So, to heat up water form 32 degrees to 212 degrees takes energy, like form a stove burner. But it takes a lot of energy to "push it over the top" to change molecular structure, break bonds, and boil. Once the vapor is past the saturation "boiling" point again it dose not take a lot of energy to increase the temperature of the vapor "superheat".

So to reiterate it take a fair amount of energy to heat water to boiling "saturation" point, then a massive amount of energy to change phases, then less energy to heat the vapor. The concept you are missing is Heat Transfer. You are mistaking temperature for energy.

So if a refrigerant is like the water, and the air around the evaporator pushed by the blower is like the burner. Which part would you want more of? liquid "overcharged", Phase change "Perfect Charge", or vapor "undercharged". The answer is you would want the most possible phase change in your evaporator. You can think of the air around the evaporator as the burner to get the most heat out of it you want phase change resulting in more heat out of the air, cold air because it lost its energy to the phase change. Sure it will lose energy heating up the vapor past saturation into superheat, but not as much as the phase change.

Hope this helps

sorry i had to correct a few mistakes. its hard to watch a guy who wants to learn get poor incorrect info :angel:

 

correction thanks

Thanks for the correction I pulled the info directly from wiki and forgot to convert the 0 to 32. Do not understand why US is not using metric system yet.

Enthalpy of vaporization

On the other hand, the molecules in liquid water are held together by relatively strong hydrogen bonds, and its enthalpy of vaporization, 40.65 kJ/mol, is more than five times the energy required to heat the same quantity of water from 0 °C to 100 °C.

not sure about where the 970 times the amount.

 

Thanks for the correction I pulled the info directly from wiki and forgot to convert the 0 to 32. Do not understand why US is not using metric system yet.

Enthalpy of vaporization

On the other hand, the molecules in liquid water are held together by relatively strong hydrogen bonds, and its enthalpy of vaporization, 40.65 kJ/mol, is more than five times the energy required to heat the same quantity of water from 0 °C to 100 °C.

not sure about where the 970 times the amount.

1) your welcome

2) forget wiki, we here are a lot smarter

3) its all about BTU's your british thermal units... hey dont the British use the metric system???

4) ok here it goes...

it takes 0.5 btus to raise one pound of cold ice 1 degree F to warmer ice, say 20 degrees F to 21 degrees F.

to change the state of 32 degree ice to 32 degree water that one pound needs to absorb 144 btus, the latent heat of fusion.

now to raise that one pound of 32 degree water to 212 degree f water requires another 180 btus ( one btu per degree per pound, you do the math)

now latent heat of vaporization, to change state of that one pound of 212 degree water to one pound of 212 degree steam takes 970 btus. you did ask where 970 came from?

there ya go. want more? to raise the temperature of 0 psig steam its 0.44 btus per pound per degree

oh yeah forget wiki. we're smarter :cheers:

 

Picture, 1000 words, Yadda Yadda.

The temp transition from the blues to the reds should be in the last row or two at the top, not 40% of the way down the coil leaving about half of the coil unused and doing no cooling.

Somebody with a thermal camera please do several more such images at various superheat levels.

 

put some gas in it and see what happens! go back when it aint 110 degrees and fix/find/replace/ problem

 

Responses here really exceeded my excpectations. This has really helped.

Only real question I have would be, what is the point of superheat than? Wouldn’t it be better for refrigerant to have low superheat as possible, so that more of the line would have the best ability to absorb heat with the saturated refrigerant?

However I guess with low superheat that would mean the coil isn’t doing it’s job in absorbing heat.

 

Superheat is there to protect the compressor...period. Refrigeration compressors do not like to compress liquid refrigerant. Superheat is the safety net to prevent this from happening.

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Superheat, the amount it is being heated above it's saturated temperature.
Picture a dumptruck, it has a fill capacity, too little it's not carrying enough of a load away, too much and it's over loaded and loses load.
Superheat and subcool are telling two sides of the story of refrigeration, superheat is telling you how much your dump truck is hauling out of the house, subcool is telling you how much it is dumping outside so you are able to see your dump truck is moving the right capacity from both inside and out.

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Sorry if it's a stupid analogy, makes sense to me, and people I talk to face to face when they ask about SH&SC

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Running with 0 superheat is referred to as a flooded evaporator and requires a suction accumulator to store the excess liquid so that it doesn't reach the compressor. Ensuring that the evaporator is always flooded requires that the metering orifice be oversized to prevent the condenser from building up subcooling, of course this allows uncondensed flash gas to reach the evaporator which wastes energy since boiling liquid does the cooling. Think of flash gas as a warm gas bypass putting artificial load on the system. Orifice tube car A/C systems operate like this.

In theory if you added a liquid receiver to try to always have solid liquid AKA no flash gas at the metering device with minimal or no subcooling and made the metering device be controlled by a float in the accumulator to maintain a set liquid level you could maximize the efficiency by minimizing the unused coil area. It isn't done because the extra hardware costs money. Per a google image search it also isn't exactly a new idea.
https://musingsonentropy.com/2013/04/04/1930s-household-refrigerators/

If it were done today I could see them trying to integrate the receiver, accumulator, and float expansion device all in one proprietary non-serviceable monoblock unit.

 

I'm confused just a little here.

If you had 1 lb of 211*F water,then you add just 1 BTU to make that 1 lb of 211*F water into 1 lb of 212*F water. Then you need 970 more BTU to change that 1 lb of 212*F water into 212*F steam.

If starting at 32*F water w/ 1 lb of water,there is needed 180 BTU to raise that 1 lb of 32*F water into 1 lb of 212*F water.Then the same 970 btu is needed for the change of state into 212*F steam.

 

no confusion at all Terry. this is the laws of physics and the basis of many HVAC heating and cooling mediums. steam heat and refrigeration. its written in many many textbooks. you do read all these textbooks you speak of?

No, but the OP is a younger tech, and hitting him with the exact BTU properties to change ice to steam is way above his questions regarding superheat. While I understand it's relativity, and many others do it is just way over what he's asking and could just flat out confuse him.

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maybe i did go in a bit deep for a newer tech ( the op) but someone else responded with incorrect information. nothing can be worse to a new guy trying to learn. he did ask about 970.

 

Putting way too much lipstick on this pig

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There were a few diff versions of the amount of BTU required and how many "times" the amount of BTU needed for the change of state. They are all correct?

 

No, but the OP is a younger tech, and hitting him with the exact BTU properties to change ice to steam is way above his questions regarding superheat. While I understand it's relativity, and many others do it is just way over what he's asking and could just flat out confuse him.

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Low juice in the evap means no heat is being absorbed or very very little and air is just being sent out just as it came in.