Ad
CitCop - Värmepumpar med installation i hela Sverige
Svenska apotek med tillstånd
Annonsera i Värmepumpsforum, klicka här för att ställa e-postfråga och få mer info.
Kampanj från Polarpumpen!.
Varför betala dyrt för nåt enkelt?
 

Författare Ämne: Trimma din vp med superheat/supercool och tryckdata  (läst 16468 gånger)

0 medlemmar och 1 gäst tittar på detta ämne.

Utloggad ElVikingo

  • Expert på värmepump
  • ****
  • Stad/land: Landsbygd
  • Antal inlägg: 227
  • Kön: Man
  • Hellre en värmepump i handen än två på foten
Trimma din vp med superheat/supercool och tryckdata
« skrivet: 24 januari 2008, 18:17:25 »
Egentligen ett svar till Art Deco som jag lägger som eget ämne här.

Jag håller mig till heatläget i min skiss.

Vp som maskin är en metod att förvandla vätska till gas, sedan gas till vätska, där kompressorn + finurliga slingor och dimensionsförändringar tvingas påverka temeraturer i ett köldmedel.
Värme tas upp och avges på grund av förändringar i köldmedlets tillstånd, i relation till trycket.

Processen är både möjlig att köra baklänges och möjlig att reglera, men ex. rördimensioner är fasta, så det som kan ske är relativt enkelt att förutse.
Det är som att gå bakvägen och konstruera en pump med 410A som skall utföra ett visst arbete.
Då vet vi att vid ett visst tryck har 410A en viss temperatur. I vp-världen är alltså ofta tryck=temperatur. Omvänt så skall en viss temperatur ge ett visst tryck. I teorin.

Det tryck du enkelt kan läsa av är det du har i serviceventilens miljö.

På samma sätt så vet vi att vissa förändringar sker vid vissa temperaturer=tryck igen.

Alltså det som skall ske i kondensor och evapurator är förändringar från vätska till gas och omvänt.

Helst skall all vätska omvandlas till gas på rätt plats, liksom all gas skall bli vätska på rätt plats.

Om detta ej sker är processen ej optimal. Du får för mycket eller för lite is, för hög eller för låg värme.

Teoretiskt finns det alltså ett rätt läge för hela processen.

Om allt annat är rätt, inga fel i konstruktionen av hela vp, med pump, rör, ventiler, sensorer, inget är trasigt, så sker rätt process endast om du har rätt gasmängd/mängd kylmredel.
Därav. ett par temperaturer, värden från en tabell, ett tryck och du kan se om du ligger rätt i gasmängd.
Detta gäller i all kylverksamhet, vpverksamhet, utom i de fall där du får flytande variabler.

Teorin gäller fortfarande, dvs viss temp=visst tryck men det blir besvärligt att ta fram värden för en process som tex kompenserar gasbrist, med mer kompressorarbete.
Här blir det inte en enkel kalkyl utan ett nördarbete, som få utför i sin helhet.
På samma sätt skulle en kondensor som ändrar storlek lura dig att tro att hela kondensorn används. (har aldrig hör talas om en variabel kondensor, men i teorin kan du ju föreställa dig att datorn säger att kondensorn är för stor för denna köldmängd, och då minskar den, DÅ skulle den ju bli lagom fast gasmängden är fel, eller är den?)
Man kan säga att där superheat/cool inte är lätt att använda, där behövs den inte lika mycket.
Finessen är ju att en avancerad inverter faktiskt hela tiden optimerar processen bättre än en enkel pump gör.

Tebax till huvudfåran... Det går alltså att mäta om du har en optimal process i en enklare pump.
Pytsar du då in eller släpper ut en viss mängd, förändrar sig dina värden.

Att optimera innebär då att du har rätt gasmängd för just din pump, med just din rörlängd.

Hur intressant är detta? Tja jag vet att en viss Panasonic skall ha 980gr en viss midea 900 för 3-7 meter rör+ca 30gr per extrameter (eller -30gr för ner till 3 meter vilket är minsta rek längd)
Om gas räcker till 3-7,5meter med du skall lägga till 30gr om du har 8,5 meter, säger det sig själv att här finns en slarvmarginal.
Denna slarvmarginal är tyvärr verkligen en slarvmarginal. Det är som om man säger processen sker från temp x till x +- y. Detta är fel.
Ångbildning,vätskefas,isbildning sker vid ett värde och inget annat.
Vatten kokar vid 100+ inte 98-102.

Här finns lite att trimma in. I praktiken lyckades tex ett projekt trimma fram 101% i förhållande till uppgivna data, där verkligt värde låg på 98% av det uppgivna förut.
(I verkligheten så måste ju 101% vara rätt processvärden, dvs 100%)
De trimmade alltså fram 3% bättre värden.

Gör man det? No way. Man väger gasen och utgår från att man kan leva med att ligga på en toleransnivå, ovan  3% för lågt.

Jag är däremot övertygad om att vissa superexperter här har med finess och fingertoppskänsla anat underskott och då gasen finns hemma, pytsat in en skvätt på känn.
Jag har i alla fall läst flera göra det med goda resultat.

Tyvärr så vet vi vanliga dödliga inte vad som finns från början. Jag tror det var bosse vp-dr som märkt att överfyllnad var vanlig i vissa pumpar, och då skall man ju snarare pytsa ur.
Inga problem, exakt samma teori gäller där.

Det skulle vara intressant att veta om ni som verkligen kan det där med superh/c nyttjat detta för att trimma vp och vad detta då gett för resultat.
På Bosse förstår jag att det inte är möjligt att på kortare tid hamna rätt med en inverter, men det omöjliga är ju just vad nörden ger sig på. Har någon gjort detta på en inverter?

Superh/c är det som en kyltekniker kan, som gör att vissa svar signalerar kunskap, tex när man frågar om isbildning.

Jag känner mig fortfarande ringrostig även om jag läste på här om dagen. Men även om jag svamlar så är det mesta nära sanningen, eller??? Vad säger experterna?
Tänk att det kan vara så svårt, att vara efterklok i förväg....

Många fiskar små...får plats i en stor å

Utloggad luckyman

  • Känd från TV
  • Dignitär inom värmepump
  • ****
  • Stad/land: se
  • Antal inlägg: 2040
  • Kön: Man
  • We´re all from the ghetto, Halleluuujah
SV: Trimma din vp med superheat/supercool och tryckdata
« Svar #1 skrivet: 24 januari 2008, 18:28:54 »
 Sc:,h Sc:,h Vad är detta för nåt??
Fattar inte direkt ngting, tror Elvikingo sitter vid ett bord och arbetar om dagarna eller har jag fel??
Superheat/supercool är det ngn maskin eller driftläge Sc:,h vad har du fått de ifrån b00k
Ingen som kan översätta grekiskan till yrkesmässigt hanterbara meningar
« Senast ändrad: 24 januari 2008, 18:31:48 av luckyman »
Mest kyla men lite värme också

Utloggad ace

  • frostaknöl med 3.2-cert i kombination med livets hårda skola,samt en omättlig nyfikenhet på teknik. tråd-reträtt pga utmattning förekommer.
  • Guldmedlem
  • Dignitär inom värmepump
  • ******
  • Antal inlägg: 2703
  • ju fler strängar på lyran, ju bättre låter det !
SV: Trimma din vp med superheat/supercool och tryckdata
« Svar #2 skrivet: 24 januari 2008, 18:40:43 »
1. jag är helt ense om att de flesta VP är aningen överfyllda,troligen för att ge marginaler för 7m rör ,nåt spill  ::) mm

2. ett visst tryck är inte = en viss temperatur.....det är en viss kondenserings eller förångningstemperatur som måste uppnås vid ett specifikt tryck !

enkelt utryck: vi komprimerar hetgaser till 90 ºC...kondenserar dessa i kondensorn vid tex 50 ºC....underkyler till 47 ºC...allt med exakt samma tryck ! kondenseringstemperaturen var 50 ºC, ..men den riktiga temperaturen var sjunkande från 90 - 47 ºC !


3.superheat = överhettning, vilket indikerar köldmedieflödet kontra energiupptagningskapaciteten i förångaren !

4.supercool= underkylning, vilket indikerar köldmedieflödet kontra energiavgivningsförmåga i kondensorn....brukar användas som referens för "rätt" fyllnadsmängd !

mvh. ACE
drygt 800 kvm yta uppvärmd till skiftande temperaturer
husqvarna tekniktank, några solfångarsystem och en Daikin bergvärmepump med 280m borrhål.
Diverse l/l pumpar samt en modifierad nibe 1215 med 140m borra till bostadshuset.

Utloggad luckyman

  • Känd från TV
  • Dignitär inom värmepump
  • ****
  • Stad/land: se
  • Antal inlägg: 2040
  • Kön: Man
  • We´re all from the ghetto, Halleluuujah
SV: Trimma din vp med superheat/supercool och tryckdata
« Svar #3 skrivet: 24 januari 2008, 18:45:25 »
Ja ja
Fick du verkligen med allt där ace Sc:,h Sc:,h
Elvikingo hade ju skrivit 1 helt a4 block, så du måste fuska *roflmao*
Mest kyla men lite värme också

Utloggad ElVikingo

  • Expert på värmepump
  • ****
  • Stad/land: Landsbygd
  • Antal inlägg: 227
  • Kön: Man
  • Hellre en värmepump i handen än två på foten
SV: Trimma din vp med superheat/supercool och tryckdata
« Svar #4 skrivet: 24 januari 2008, 18:47:40 »
Luckyman;
Jag trodde du var en vpguru, men dignitär betyder tydligen inte dignitär inom vp.
Hoppas du kan engelska. Här har du ett exempel för ett fabrikat.

Superheat Adjustment Procedure
 
  
Superheat" is the term used to describe the difference between the vapor point (ie. temperature at which the refrigerant evaporates at a given pressure) and the actual temperature of the refrigerant exiting the evaporator coil. On your Glacier Bay system the superheat adjustment is located on the back (opposite the exit) of the expansion valve under a 19mm cap which protrudes at a 450 angle from the valve body.
To adjust the superheat you will need the following tools:
1. Refrigerant gauge set
2. 19mm socket or wrench
3. Flathead screw driver
4. Pressure-Temperature chart for HFC-134a
5. Accurate surface reading thermometer (remote probe type)

Warning - If you do not have these tools do not attempt to adjust the super heat setting. Do not attempt to adjust the superheat based on the "frost line" of the suction return.


Measuring Superheat
The adjustment process should be started when the holding plate is approximately 1/2 frozen. If the plate is fully thawed, allow the system to partially freeze down before taking your measurements.


Step 1
Ensure that the sensing bulb for the thermostat is firmly clamped to the suction line on a horizontal tubing run at the 10:00 or 2:00 o'clock position.

Step 2
Remove the protective cap covering the superheat adjustment screw.

Step 3
Connect the refrigerant gauge set and purge. Only the suction side need be connected. It is good to re-calibrate your gauge to "0" before connection.

Step 4
Securely attach the thermometer probe to the suction line immediately after the manifold elbow and fitting.

Step 5
Start compressor and allow the system to run at least 10 minutes to stabilize.

Step 6
Determine Suction line pressure drop. The suction side pressure you are reading at the compressor includes line losses as the refrigerant gas makes it's way back to the compressor. To accurately determine the superheat we need to know the suction pressure at the evaporator. Therefore, we need to determine, and then add back in, any additional pressure drop which occurs between the evaporator and the compressor. Fortunately, this loss can be easily seen on the pressure gauge as an immediate "jump" at the moment the compressor is turned off. Typically, line pressure drop will only amount to 1 or 2 psi. However, with long tubing runs it may be higher. Manually, turn the compressor off and on a couple of times to determine the pressure drop in your system. Once determined, leave the compressor running.

Step 7
Determine the evaporator temperature. Do this by reading your suction pressure displayed on the gauge and adding back in the line pressure drop. Use your temperature/pressure chart to determine the actual evaporator temperature. For example: gauge reading (10 psig) + line loss (2 psi)=12 psig. The temperature/pressure chart tells us that HFC-134a has a vapor point (evaporator temperature) of 100 F at 12 psig. Therefore, the system evaporator temperature is 100 F.

Step 8
Measure evaporator exit temperature. Use your surface reading thermometer to read the temperature of the suction line at the holding plate exit point. For example: 180 F.

Step 9
Calculate superheat. Evaporator exit temperature (180 F) - Evaporator temperature (100 F)=80 F superheat.


Adjusting Superheat
The correct superheat setting for a Glacier Bay system is between 60 F and 80 F. To change the superheat setting, turn the flathead adjustment screw clockwise to increase the superheat, counter-clockwise to decrease.   Adjust the screw no more than 1/4 turn at a time and allow the at least 5 minutes running before re-measuring. Large adjustments and fine-tuning must sometimes be done over several "pull-down" cycles because of the amount of compressor run time required to stabilize the system after each adjustment.
 
 

Questions & Answers
Q - New laws in force world-wide mandate that only properly licensed service technicians (complete with recovery equipment "on-site" at all times) perform certain operations. Does the adjustment of superheat fall into this category?
A - In most cases. These laws apply anytime it is necessary to "break into the refrigerant stream". Unless you have permanently mounted gauges, you will need to connect them into place. By doing so, you then fall under the regulations. Fines up to $50,000 are now being regularly issued. Violations do not need to be documented in the usual fashion, as "reasonable likelihood" has been found sufficient cause for the issuance of fines.

Q - Why does my refrigeration serviceman always talk about the "frost-line" when referring to superheat settings.
A - Unfortunately, in spite of the fact that proper superheat adjustment in vital to the efficient operation of any refrigeration system, most marine servicemen have only a vague understanding of it. Many do know, however, that severely low superheat can (in some cases) cause physical damage to the compressor. An easy "rule-of-thumb" which ensures that the superheat is not set so low as to cause such damage is to adjust it until the "frost-line" is some distance from the compressor. While this practice does safeguard the compressor from damage it often, particularly in the case of freezer plates, gives in a superheat setting which is much too high. The result is inefficient operation and excessive compressor run time.

Q - Does under and/or overcharging effect superheat?
A - Yes and No. In the case of capillary tube systems, superheat adjustment in the field is accomplished entirely by the amount of the charge. In expansion valve systems (including all Glacier Bay equipment), the superheat would only change (increase) in the case of very severe under-charging. While cover-charging does cause other problems, it does not change superheat in an expansion valve system.

Q - Since the correct superheat setting have very little latitude for error, how do I know that the gauge and thermometer are accurate enough?
A - Most analog (dial type) refrigeration gauges are surprisingly accurate if they have not been abused and have been re-calibrated to "0" before pressure is applied. Thermometers, even very expensive ones, can be problematic. If possible, try to cross-check with another thermometer or two at the temperatures you expect to be reading.

Q - Where do I get a temperature/pressure chart?
A - From your Glacier Bay dealer or your local commercial refrigeration supply house.

Q - If I don't have a temperature/pressure chart but have a gauge set with a temperature scale for HFC-134a, can I use that instead?
A - No. It isn't going to be accurate enough.

 
Tänk att det kan vara så svårt, att vara efterklok i förväg....

Många fiskar små...får plats i en stor å

Utloggad luckyman

  • Känd från TV
  • Dignitär inom värmepump
  • ****
  • Stad/land: se
  • Antal inlägg: 2040
  • Kön: Man
  • We´re all from the ghetto, Halleluuujah
SV: Trimma din vp med superheat/supercool och tryckdata
« Svar #5 skrivet: 24 januari 2008, 18:51:00 »
Ta de på svenska, kan bara lite engelska.  cat  window å snake
Eller var det de du försökte översätta innan
« Senast ändrad: 24 januari 2008, 18:56:54 av luckyman »
Mest kyla men lite värme också

Utloggad ElVikingo

  • Expert på värmepump
  • ****
  • Stad/land: Landsbygd
  • Antal inlägg: 227
  • Kön: Man
  • Hellre en värmepump i handen än två på foten
SV: Trimma din vp med superheat/supercool och tryckdata
« Svar #6 skrivet: 24 januari 2008, 18:51:21 »
Superheat: The Best Way to Tune an Air Conditioning System

Unfortunately, many technicians take shortcuts when it comes to performing their superheat calculations. Some technicians, under pressure to hurry to the next job, speed the process by making assumptions without taking measurements, or take quick measurements with inadequate instrumentation.

Bill Brown, HVAC instructor at Brownson Technical School, Anaheim, CA, gives this example: "Instead of measuring suction line temperature, some technicians will wrap their bare hand around the pipe and judge by feel. The theory is that if the line is as cold as good cold beer, the system is charged. Unfortunately, that's just not accurate, and we do everything we can to dis-courage this kind of sloppiness."

The results of these "guesstimates" are overcharged or undercharged systems that burn power and operate below optimum levels. In some cases, poor superheat calculations can lead to compressor burnout.

To determine the best way to measure super-heat, we asked some HVAC instructors how they taught superheat, and what instruments they recommend to make taking superheat measurements faster and easier.

Defining Superheat
Superheat is defined as the difference between the temperature at which the refrigerant boils at the given pressure in the evaporator, and the temperature of the refrigerant gas as it leaves the evaporator. In essence, it's how much extra temperature the refrigerant picks up after it has boiled. In a worst-case scenario with an over-charged system and a low indoor heat load, the refrigerant in the evaporator remains in liquid form in the coil and moves into the compressor as a liquid, quickly destroying it.

A distinction must be made between systems that employ a thermostatic expansion valve (TXV) and those that have a fixed restrictor/flow-rater. In a properly adjusted system, the TXV controls the flow of refrigerant to ensure superheat is always within a certain range regardless of the condition.

On a TXV system that is starved (undercharged), the superheat will go up above the range. But on an overcharged TXV system, the superheat will not go below the range. The TXV will pinch off the flow of refrigerant to keep the superheat within specified conditions, resulting in significantly decreased efficiency. For this reason, to properly charge these systems the technician simply charges to the subcooling.

Most problems with superheat occur on fixed restrictor systems. In a well-tuned system, the actual (or measured) superheat varies with the load. The higher the load, the sooner the refrigerant turns into a gas, the more heat it picks up after it evaporates, and the higher the superheat. The lower the load, the later the refrigerant evaporates in the evaporator coil, the less heat is picked up after evaporation, and the lower the superheat.

Target Superheat vs. Actual Superheat
Using superheat measurements to determine the correct refrigerant charge is not that difficult, and the savings in energy and potential repairs are significant.

There are only four measurements to take: two to determine the target super-heat and two to determine the actual superheat.

For target superheat, the two measurements are outdoor dry bulb temperature and indoor wet bulb temperature.

For actual superheat the measurements are boiling/saturation point and suction line temperature.

First, determine the target superheat. To do this, take the outdoor air temperature from the air that is going into the condenser coil. Then, determine the wet bulb temperature from in front of the indoor return grille, or better yet, just in front of the evaporator coil.

"The dry bulb temperature is obvious," says Les Haddix, an HVAC instructor at Sequoia Institute, Fremont, CA. "However, many technicians think that wet bulb refers only to indoor comfort. In reality, it's very important in determining the right superheat.

"One of the shortcuts a lot of technicians use is to assume a relative humidity of 50% when determining super-heat. But that's just the system's design parameter. If the relative humidity is higher than that and the technician assumes 50%, the tech will overcharge the system. If the humidity is lower, he'll undercharge."

Armed with these two measurements, refer to the manufacturer's display chart supplied with the unit, usually with wet bulb temperature across the top and dry bulb along the side. The target superheat is displayed where the two intersect.

After you've determined the target superheat, you need to determine what the superheat actually is. To determine the actual superheat, you need only two more numbers: The boiling point (saturation point) of the refrigerant in the evaporator (at that pressure), and the suction line temperature.

The boiling point is easy. "The technician can measure the pressure at the condensing unit suction port with a pressure gauge, and in most cases read the boiling point right on the gauge," notes Rob Featherstone, HVAC instructor at Oakland Community College in Auburn Hills, MI. "If the boiling point for the refrigerant you're working with isn't on the gauge, you can look it up on a pressure temperature chart."

To determine the temperature of the refrigerant in the suction line pipe, all you need to do is measure the temperature of the pipe itself within 6-in. of the suction valve.

When you know the boiling point and the suction line temperature, subtract the boiling point located on the gauge or chart from the suction line temperature to get the actual superheat. This is the increase in temperature of the refrigerant gas after it has evaporated.

Once you know the actual superheat and the target superheat, compare them to determine if the system is properly charged. If the actual superheat is lower than the target superheat, recover refrigerant; if it's higher, add refrigerant. Just be sure to always let the system stabilize, and check again after adding or subtracting refrigerant.

Testing Challenges
Unfortunately, as many technicians can attest, it sounds a lot easier than it is. The problem is the three temperature measurements. They're not as easy to take as it would seem.

For example, while outdoor dry bulb is the most obvious and easiest super-heat measurement to take, temperatures can vary considerably in the area around the condenser.

"We used to use an analog thermometer in class," says Featherstone. "But it took too long to get the right reading and it was a chore to hold it in position. We started using a stick meter with a K-type thermocouple and got the job done faster and more accurately."

With some K-type thermocouple thermometers, there is a temperature reference junction inside the meter (the "cold junction") that is monitored by a thermometer inside the meter.

Both the reference junction and the thermometer need to be at the same temperature to ensure an accurate reading. Some meters employ an adapter, with the reference junction in the adapter, not in the meter, and not thermally close to the thermometer inside the meter. Any difference in temperature between the external reference junction in the adapter and the internal thermometer inside the meter will show up as an error.

By simply holding this adapter in your hand, you can alter the reading that the multimeter displays. And be aware that if you take a warm adapter from your pocket and put it in a cold meter from the truck, it will be several minutes before you can get an accurate reading.

Indoor wet bulb temperature measurement also presents a problem. Technical articles, manuals, and educational texts suggest technicians use such things as moistened toilet tissue and paper napkins wrapped around the bead. This nuisance factor is one of the reasons some techs take a short cut here, and simply assume a relative humidity of 50%.

To make it easier to take wet bulb temperatures, there are K-type thermocouples available with a "sock" attached and alligator clip for attaching to grids and coils. These function with any K-type thermometer. Some manufacturers also offer test heads that fit onto stick meters and dataloggers, that display both temperature and wet bulb temperature. These self-contained units measure relative humidity, temperature, and dew point with no moistening, no sock, and no external sensor.

The last measurement presents an even bigger source for potential errors. The suction line temperature often can't be measured with a simple pocket thermometer because the thermal contact with the pipe is not good enough and the thermal contact with the ambient environment is too good.

The resulting temperature would be somewhere between the pipe temperature and the air surrounding it. The trick is to find a way to measure only the pipe temperature.

One way involves using a standard beaded thermocouple, and pushing it under the pipe insulation. Unfortunately, this only works if the insulation is dry and fits tightly.

Some thermocouples feature about an inch of insulation cut back from the bead. This allows you to wrap the whole inch of bare wire around the pipe and isolate it from the environment with a Velcro strip. Other thermocouples clamp directly to the pipe and seal out ambient air.

The newest solution to this challenge is an accessory head for thermocouples that measures both suction line pressure and suction line temperature simultaneously. It converts the pressure measurement to boiling point, subtracts it from the suction line temperature, and displays the actual superheat. This eliminates the need for reference charts and math.

By keeping in mind the pitfalls involved in dry bulb, wet bulb, and suction line measurements and by having the best tools available to get accurate results, you can easily determine the appropriate refrigerant charge for an air conditioning system, thereby assuring optimal operation and preventing serious damage to compressors.

Adolfo Wirtz is a senior research specialist for Fieldpiece Instruments, Brea, CA, a manufacturer of measuring instruments for the HVACR industry. Wirtz can be reached at 714/257-9060.

Tänk att det kan vara så svårt, att vara efterklok i förväg....

Många fiskar små...får plats i en stor å

Utloggad luckyman

  • Känd från TV
  • Dignitär inom värmepump
  • ****
  • Stad/land: se
  • Antal inlägg: 2040
  • Kön: Man
  • We´re all from the ghetto, Halleluuujah
SV: Trimma din vp med superheat/supercool och tryckdata
« Svar #7 skrivet: 24 januari 2008, 18:56:06 »
Ja, men de visste jag redan
Synd bara att luft-luft inte har ngn exp.ventil så man kunde justera bulbplacerinen och överhettningen.
Ps  på svenska  Ds
« Senast ändrad: 24 januari 2008, 18:59:36 av luckyman »
Mest kyla men lite värme också

Utloggad ElVikingo

  • Expert på värmepump
  • ****
  • Stad/land: Landsbygd
  • Antal inlägg: 227
  • Kön: Man
  • Hellre en värmepump i handen än två på foten
SV: Trimma din vp med superheat/supercool och tryckdata
« Svar #8 skrivet: 24 januari 2008, 18:56:55 »
Superheat & Subcooling
Sensible & Latent Heats

Made Simple
By Norm Christopherson
The purpose of this article is to provide a simple explanation of these terms for those who desire a concise understanding as well as a review for those who understand the terms but want to review them. An understanding of these terms and the concepts related to them is essential to understanding the air conditioning and refrigeration mechanical – refrigerant cycle as well as being necessary to troubleshooting cycle problems.
Superheat:
Most materials can exist in three forms, solids, liquids and gases. Water is a common example. Water can exist as a solid (ice), a liquid, or a gas or vapor (steam). Only a gas or vapor (these are interchangeable terms), can be superheated. Let’s use water as an example as we explain these terms.
Water at sea level boils at 212 degrees F. When heated to 212 degrees F the molecules which make up water are moving at a high enough speed that they overcome the air pressure above the water. As additional heat is added to liquid water at 212 degrees, the water begins to boil. As the water boils it is changing state from a liquid to a gas. In addition, during the boiling process the temperature remains the same (212 degrees F). There is no change in temperature during a change of state. This phenomenon is true for all substances as they change state no matter how much heat is added. As long as the water is still boiling and not all the water has completely changed to a gas (steam) the temperature remains at 212 degrees F. This means that a thermometer placed in boiling water will remain at 212 degrees throughout the boiling process even though heat is added to cause the water to boil. This heat of boiling is called latent heat. The word “latent” is a Latin word for “hidden”. The heat added to the water is hidden from the thermometer since the temperature remains unchanged during the boiling process.
After all the water has changed to a gas or vapor (steam), then the addition of still more heat to the vaporized water or steam will cause the temperature of the steam to increase above it’s boiling temperature of 212 degrees. Any increase in temperature of the steam above it’s boiling point (212 degrees) is called “superheat”. Steam at 213 degrees F is superheated by one degree F.
Superheat is then any temperature of a gas above the boiling point for that liquid. When a refrigerant liquid boils at a low temperature of 40 degrees in a cooling coil and then the refrigerant gas increases in temperature superheat has been added. If this refrigerant changed from a liquid to a gas or vapor at 40 degrees and then the refrigerant vapor increased in temperature to 50 degrees F, then it has been superheated by 10 degrees.
We commonly think of boiling as always being accomplished by a liquid when it is hot. This is because we are familiar with boiling water. However, air conditioning and refrigeration systems use liquids (refrigerants) with much lower boiling points. If a liquid refrigerant boils at -10 degrees and is then warmed up to zero degrees, it is then a superheated gas containing 10 degrees of superheat. Heating that same refrigerant gas to +10 degrees means that it now has been superheated by 20 degrees.
Lowering the pressure over a liquid lowers the boiling point. There is less pressure above the liquid to overcome. That is why water at the top of a mountain may boil at 190 degrees (depending upon the altitude) rather than at 212 degrees F. By controlling the pressure over a liquid, we can control the boiling temperature. That is why a service technician monitors the pressures in an air conditioning system. The technician is actually monitoring the pressures and temperatures where the refrigerant is changing state.
Saturation:
Saturation is simply the term used to describe the point where a change of state in a substance is taking place. For water at sea level, the boiling temperature is 212 degrees F. Therefore, we say the saturation (boiling temperature) is 212 degrees. As soon as the temperature of the steam is heated above it’s “saturation” temperature, it has been superheated. Refrigerant that has boiled (turned into a vapor) at 40 degrees has a saturation temperature of 40 degrees. If the refrigerant vapor is heated to 41 degrees it is no longer saturated, it is then superheated by 1 degree. Remember, only a gas or vapor can be superheated. Superheat is any temperature of a gas or vapor above it’s saturation temperature.
Subcooling:
Subcooling is now easy to understand. Only liquids and solids can be subcooled. Subcooling is any temperature of a liquid or solid below it’s saturation temperature. Let’s use water as an example again. Liquid water at sea level has a saturation (boiling) temperature of 212 degrees F. If we were to add heat to the saturated water it would first boil away with no change in temperature (remember latent heat?) and then become superheated if still more heat were added to the vapor (steam) after it had all turned to a vapor.
Instead of boiling our 212 degree water by adding heat, we shall remove heat from the 212 degree water. As heat is removed from the liquid water it’s temperature will drop below it’s boiling (saturation) temperature. Water at 211 degrees has been subcooled by one degree F. If the temperature of the water is decreased to 180 degrees the water has been subcooled from 212 degrees to 180 degrees. That is, it has been subcooled by 32 degrees. When you drink 180 degree coffee, you are drinking a subcooled liquid!
Sensible Heat & Latent Heat:
Sensible heat is heat that can be measured by a thermometer. Anytime heat is added or removed from a substance and a temperature change occurs, a sensible heat change has taken place. Since both superheat and Subcooling are changes in temperature, they are both sensible heat processes.
When an air conditioning system cools air sensible heat has been removed. In fact, since the air is a gas or vapor and is heated far above it’s boiling (saturation) point, it is superheated air. Yes, you are breathing superheated air as the air is hundreds of degrees above the temperature at which the gases which make up air would condense back into liquid form.
Superheated does not necessarily mean hot. And, subcooled does not necessarily mean cold. Superheat and Subcooling are determined by the boiling temperature of the substance and unlike water many substances have low boiling temperatures.
Recalling that latent heat is the heat which is added to a liquid to cause it to change from a liquid to a gas (boiling) without a change in temperature, let’s go to the next step. When a gas or vapor is above it’s boiling point it is said to be superheated. Cooling the gas removes it’s superheat. When all the superheat is removed from a gas, the gas will condense back into a liquid. The heat removed from a saturated gas to allow it to condense back into a liquid is once again latent or hidden heat and is not a sensible heat process. That is, during the process of changing from a gas to a liquid it occurs at a constant temperature therefore a thermometer will not detect any temperature change. That is latent heat.
Air contains water vapor or moisture. Humid air is not comfortable. Too much humidity (moisture) in air is uncomfortable. As air containing too much moisture passes over a properly designed, installed and operating air conditioning system, the air is cooled by the air conditioning coil (evaporator) located at the indoor blower section. If the air containing the moisture is cooled to the condensing temperature (dew point) of the moisture in the air, some of the moisture will condense and deposit on the coil and fins of the cooling coil. Since the water vapor is changing from a gas or vapor to a liquid, this is a latent heat process. The condensed water should run off the coil and be drained away.
A properly operating air conditioning system both cools (a sensible heat process) and dehumidifies (a latent heat process) the air. For example, given a 3-ton residential air conditioning system, a percentage of the total capacity of the system is utilized to cool the air while the remaining percentage of the total capacity is used to dehumidify the air. Properly controlling both the temperature (sensible heat) and the humidity (latent heat) will provide the optimum comfort for the occupants.
Measuring Heat:
Latent heat cannot be directly measured as we can sensible heat. In order to properly adjust, troubleshoot and repair air conditioning equipment it is necessary that we understand heat and how to measure heat.
Superheat and Subcooling are both sensible heats and therefore can be measured with a thermometer. Superheat and Subcooling are also temperature differentials. That is, each is a number of degrees a gas or liquid are above or below their saturation temperatures. It is essential that a service technician be able to accurately measure these differentials and diagnose system operation from them.
A high quality, accurate electronic thermometer capable of measuring temperature differentials is almost an essential tool for the technician and highly useful to the interested homeowner. An example of such an instrument is Bacharach’s “Dual Channel. Model TH3000, digital thermometer” with data hold and max hold functions.
Another very useful digital thermometer capable of performing additional air quality test functions is Bacharach’s “Comfort Check” 100 & 200 model Indoor Air Quality Analyzers. Essential for anyone interested in investigating or monitoring indoor air quality.
Tänk att det kan vara så svårt, att vara efterklok i förväg....

Många fiskar små...får plats i en stor å

Utloggad ElVikingo

  • Expert på värmepump
  • ****
  • Stad/land: Landsbygd
  • Antal inlägg: 227
  • Kön: Man
  • Hellre en värmepump i handen än två på foten
SV: Trimma din vp med superheat/supercool och tryckdata
« Svar #9 skrivet: 24 januari 2008, 19:06:17 »
Så blir det inte mer.  b00k
Luckyman; om din engelska är rostig så är mitt tips att likväl spara dessa texter. De innehåller hela vpläran i teoretisk form. Kan väl vara nåt att sätta i handen på en praktikant om inget annat.
jag tror att alla kyltekniker kan detta. I alla fall framgick detta i gamla inlägg från ?2005 där ngn hade uppe ett liknande ämne. Bosse vp-dr var då inne och jämförde med inverterns funktion.
Då verkade alla veta vad sh och sc var.

Som du förstår så är det lättare för mig att läsa engelskan och begripa denna än att översätta något i ett område där jag inte kan språket.
Jag har ingen aning om vad saturation/superheat/supercool heter på svenska.
Tänk att det kan vara så svårt, att vara efterklok i förväg....

Många fiskar små...får plats i en stor å

Utloggad ElVikingo

  • Expert på värmepump
  • ****
  • Stad/land: Landsbygd
  • Antal inlägg: 227
  • Kön: Man
  • Hellre en värmepump i handen än två på foten
SV: Trimma din vp med superheat/supercool och tryckdata
« Svar #10 skrivet: 24 januari 2008, 20:25:26 »
Subcooling and Superheat: Superheroes of System Charging
Skip Egner
01/23/2007
Here's a common scenario. You go on a service call, put your gauges on a condensing unit, and find that the suction pressure is low. What do you do?

In too many cases, the answer is "add refrigerant." But doesn't it seem like a good idea to confirm that low refrigerant is the problem before you start adding refrigerant? That's why checking superheat and subcooling is so important.

Let's go back to the beginning. You go on a service call and find low suction pressure. However, this time you consider the three main causes of low suction pressure, and check superheat and subcooling to make the correct diagnosis.

CAUSE #1: Insufficient heat getting to evaporator.
This can be caused by low air flow (dirty filter, slipping belt, undersized or restricted ductwork, dust and dirt buildup on blower wheel) or a dirty or plugged evaporator coil.

Checking superheat will indicate if the low suction is caused by insufficient heat getting to the evaporator. To check superheat, attach a thermometer designed to take pipe temperature to the suction line. Don't use an infrared thermometer for this task. Then take the suction pressure and convert it to temperature on a temperature/pressure chart. Subtract the two numbers to get superheat.
For example, 68 psi suction pressure on a R-22 system converts to 40F. Let's say the suction line temperature is 50F. Subtracting the two numbers gives us 10F of superheat. Superheat for most systems should be approximately 10F measured at the evaporator; 20F to 25F near the compressor.

If the suction pressure is 45 psi, (which converts to 22F) and the suction temp is 32F, the system still has 10F of superheat. The fact that these readings are normal indicates the low suction pressure is not caused by low refrigerant, but insufficient heat getting to the evaporator.

CAUSE #2: Defective, plugged, or undersized metering device.

Let's say a system has 45 psi suction pressure (converts to 22F) and 68F suction line temperature, the superheat is 46F (68 minus 22). This indicates low refrigerant in the evaporator. However, before adding refrigerant, check the subcooling to be sure the problem isn't caused by a defective, plugged, or undersized metering device.

While superheat indicates how much refrigerant is in the evaporator (high superheat indicates not enough, low superheat indicates too much), subcooling gives an indication of how much refrigerant is in the condenser.

Subcooling on systems that use a thermostatic expansion valve (TXV) should be approximately 10F to 18F. Higher subcooling indicates excess refrigerant backing up in the condenser. On TXV systems with high superheat, be sure to check the subcooling as refrigerant is added. If the superheat doesn't change, and the subcooling increases, the problem is with the metering device. In the case of a TXV, it's likely that the powerhead needs to be replaced.

To check subcooling, attach a thermometer to the liquid line near the condenser. Take the head pressure and convert it to temperature on a temperature/pressure chart. Subtract the two numbers to get the subcooling.

For example, 275 psi head pressure on an R-22 system converts to 124F. The liquid line temperature is 88F. Subtracting the two numbers gives 36F. High superheat and high subcooling indicates a problem with the metering device.

Keep in mind that subcooling won't increase on systems with a liquid line receiver, as extra liquid will fill the receiver instead of backing up in the condenser. Receivers are rare on air conditioning systems, but very common on small refrigeration systems such as walk-in coolers and freezers. If a system with a receiver has high superheat and the liquid line sight glass is full of liquid (no bubbles), check the metering device. If the sight glass has bubbles, the system could be low on refrigerant, or the liquid line filter/dryer could be plugged. Your clue here is that a noticeable temperature drop across a liquid line filter/dryer indicates it's plugged.

CAUSE #3: Low refrigerant.
Yes, it's true! There are indeed some cases where low suction pressure is going to be caused by low refrigerant. If the superheat is high and the subcooling is low, the refrigerant charge is probably low. Just keep in mind two things here: first, find and fix the leak. Second, monitor both superheat and subcooling as you add the refrigerant, to prevent overcharging.
Tänk att det kan vara så svårt, att vara efterklok i förväg....

Många fiskar små...får plats i en stor å

Utloggad ElVikingo

  • Expert på värmepump
  • ****
  • Stad/land: Landsbygd
  • Antal inlägg: 227
  • Kön: Man
  • Hellre en värmepump i handen än två på foten
SV: Trimma din vp med superheat/supercool och tryckdata
« Svar #11 skrivet: 24 januari 2008, 20:37:16 »
Länkar till R410A information som behövs för att beräkna sh/sc med tryck/temptabell.
Observera att tryck/temptabellen innehåller flera gaser så du inte läser i fel tabell.

http://refrigerants.dupont.com/Suva/en_US/products/suva410a.html
http://refrigerants.dupont.com/Suva/en_US/pdf/k10912.pdf
http://refrigerants.dupont.com/Suva/en_US/pdf/k05719.pdf
Tänk att det kan vara så svårt, att vara efterklok i förväg....

Många fiskar små...får plats i en stor å

Utloggad luckyman

  • Känd från TV
  • Dignitär inom värmepump
  • ****
  • Stad/land: se
  • Antal inlägg: 2040
  • Kön: Man
  • We´re all from the ghetto, Halleluuujah
SV: Trimma din vp med superheat/supercool och tryckdata
« Svar #12 skrivet: 24 januari 2008, 20:56:59 »
Ja precis länka en massa R22 det kan inte vara en kylkille av 2008 som gör det, men dessa värden har man ju på manometerstället så varför sitta å länka en massa skit??
Du får nog hålla detta till dig själv om du vill utvecklas, teoretiskt
En annan jobbar mer praktiskt å då hinner man inte med en massa utrikeska
Mest kyla men lite värme också

Utloggad ace

  • frostaknöl med 3.2-cert i kombination med livets hårda skola,samt en omättlig nyfikenhet på teknik. tråd-reträtt pga utmattning förekommer.
  • Guldmedlem
  • Dignitär inom värmepump
  • ******
  • Antal inlägg: 2703
  • ju fler strängar på lyran, ju bättre låter det !
SV: Trimma din vp med superheat/supercool och tryckdata
« Svar #13 skrivet: 24 januari 2008, 21:15:00 »
kort sammanställning:

det krävs bara ett manometerställ och en termometer för att kolla överhettning och underkylning !
vid ett fast köldmedieflöde (on/off):
högre överhettning= större energiutbyte förångare
högre underkylning= större energiutbyte kondensor

ganska basic kylteknik .......... ;) 

mvh. ACE
drygt 800 kvm yta uppvärmd till skiftande temperaturer
husqvarna tekniktank, några solfångarsystem och en Daikin bergvärmepump med 280m borrhål.
Diverse l/l pumpar samt en modifierad nibe 1215 med 140m borra till bostadshuset.

Utloggad Gäst 999

  • Dignitär inom värmepump
  • *****
  • Antal inlägg: 2321
SV: Trimma din vp med superheat/supercool och tryckdata
« Svar #14 skrivet: 24 januari 2008, 22:17:47 »
Vikingens ideer är inte fel när det gäller on/off men hur gör man med en inverter med kapilär kontra en inverter med elektronisk expventil?....Ace kanske har ett svar....hur får man ur mer ur en sådan pump med elektronisk expventil?

nibe, ctc, baxi, golvvärme, solenergi Mer n 20 rs erfarenhet av vrmepumpar
 


Annonser

Right Block

Vibrationsdämpare
Besök vår webshop, klicka här!
Energioffert.se
Energibutiken.se smarta varor på nätet, leverans till dörren
luftvärmepumpar, tillbehör, installationsmaterial, vi har allt!
Annonspriser

Online just nu!

Ad
CitCop - Värmepumpar med installation i hela Sverige
Svenska apotek med tillstånd
Annonsera i Värmepumpsforum, klicka här för att ställa e-postfråga och få mer info.
Kampanj från Polarpumpen!.
Varför betala dyrt för nåt enkelt?