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How does humidity effect the condenser

ChrisJ
ChrisJ Member Posts: 16,274
in A-C, Heat Pumps & Refrigeration
I'm curious what effect if any does RH have on the cooling of a condenser?  Does higher RH levels tend to provide better or worse cooling?
Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment

Comments

  • Empire_2
    Empire_2 Member Posts: 2,340
    No

    Good question.  90* @60R/H% or 90* @ 95R/H%,...  Your condenser is used to change hi pressure/temp. vapor plus heat of compression to a hi pressure/temp. saturated liquid.  Any additional drop in temp is sub cooled liquid refrigerant.  In this example: a head pressure of aprox. 240 to 260 psig/R-22,...say at 260psig your saturation temp of the ref. is aprox. 120*f.  We are changing state at this point and R/H%, and direct sunlight has no effect on condenser mainly because we are using air over coil to drop our temps.  Indoor R/H% a whole different story.  R/H% here affects out latent heat content which in turn shows on your gauges.  Wet bulb temp is key when determining where lo pressure should be at a given temp and pressure when using fixed restrictor or cap tube.  Anyone wish to add, be my guest.  Hope this helped a little.



    Peace;



    Mike T.
  • Techman
    Techman Member Posts: 2,144
    Heat is Heat or is it?

    If you know the answer ,then it's an easy guess. But ,are we talking sensible heat only? Or does "enthalpy" enter into this? Does  more moisture in the air transfer heat better than just air? What happens to the head press when you lovingly spray the cond coil w/ that fine mist/spray from the garden hose? More moisture?
  • meplumber
    meplumber Member Posts: 678
    The "E" word.

    Techman said the "E" word. Enthalpy.



    Mike's answer is correct. I disagree on a couple minor points but 4 knowledgeable techs could argue those points for hours and never know who was right.



    Enthalpy is the key here. Enthalpy is the amount of heat capacity in one pound of air. It is expressed in btu/lb. Warm, wet air has a higher heat capacity than dry, cold air. Hence the lower limit capacity of heat pump applications. As Mike stated, we are changing the state of the refrigerant in the condenser, (hence the name "condensing") from a vapor into a liquid. How do we do that? We absorb or extract heat from the refrigerant. In this case, we are extracting heat from the refrigerant to condense it back into a liquid.



    In extreme heat and humidity, think Houston, TX or Savannah, GA where enthalpy numbers are in excess of 50 btu/lb, the humidity does effect the capacity of the condenser to a degree. This goes to Tech's point about misting. By misting the condenser coil with cool water from a garden hose, we are cooling the air passing through the condenser coil and allowing it to absorb more heat from the refrigerant.



    In heat pump mode, where the condenser is trying to absorb heat from the outside air, we run into the opposite effect at lower enthalpy. At about 7 btu/lb enthalpy, the heat capacity of the air is not sufficient to change the state of the refrigerant in the condenser and we lose our heating output of the heat pump.



    So, yes and no. Humidity alone does not effect the condenser performance, but enthalpy does.



    Here is an interesting paper on the subject. I don't fully understand the math, but the concepts are pretty good.



    http://www-esl.tamu.edu/docs/terp/2008/ESL-HH-08-12-42.pdf



    Sorry for the long response. I hope it makes sense. Guys, Opinions?
  • Empire_2
    Empire_2 Member Posts: 2,340
    Ah Yes, great answers by all

    Points made across the board here.  I know what you mean spraying water on the condenser coil.  I can't help but do just that when I water the lawn......I know....It just seems like the fun thing to do...lol.  Let's not forget the water sprayed even lightly is still in liquid form and does it's magic when it evaporates.  Kinda like a cool breeze when you are sweating.  RH% is in percentage until totally saturated.  Warm air will hold more water content than cooler air.  At 70*, 100% RH will hold exactly 22 pints of air no more.



    I have to tell you guy's I love these conversations.  Almost like point and counter point.  I can always pick up others way of looking at things.  Always fun.



    Peace



    \Mike T.
  • ChrisJ
    ChrisJ Member Posts: 16,274
    Interesting

    Thank you for all of the responses!



    I have to admit, unfortunately I am an electronic tech so I'm classed as a "homeowner" here rather than someone in the field.  I do consider refrigeration a hobby of mine and I enjoy it though I am by no means an expert for sure.  I am currently restoring a 1933 and a 1934 GE monitor top refrigerators and have done some other things in the past.



    In regards to direct sun not effecting a condenser, how is this possible?  I would have to think direct sun would heat the condenser regardless of how it is being cooled.  I have also sprayed a mist of water over a condenser and have considered putting a sprinkler to spray across several units at work when its 100F out and the units cannot keep up.  I have heard some say doing this could cause slugging, though I don't see how.  If your system is at a point its not keeping up I would think the chances of getting liquid back to the compressor are slim.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Empire_2
    Empire_2 Member Posts: 2,340
    Sun/Rain, hi Hum...

    Since none of these factor are or have no effect on the sizing of the equipment, we have to ask ourselves a question;  Why not?  Since the coil has air passing over it, it's purpose is to take heat during the A/C season off the coil.  In my opinion, the coil will see only a split second of outside affects per inch of coil.  Yes the sun beating down on it is hot, but is a non factor since we are dropping mainly sensible heat.  I'm sure if you hit the books in affects of radiation (which the sun is) it will give a measurable reading, but that not how the ref. cycle is sized.  I will agree if you had 200 sq/ft on a flat exposure side, it MAY and I mean may be considered, but in the final scheme of things, is a non factor.  I'm sure all of us could go into this topic for hours and have valid points, but let's keep it on the simple side.    



    Mike T.
  • meplumber
    meplumber Member Posts: 678
    edited July 2012
    Agreed

    I expended my ammo on Enthalpy.
  • Empire_2
    Empire_2 Member Posts: 2,340
    Funny...

    I bought Ammo because of enthalpy...?   lol   Smile guy's, it's FRIDAY.



    Mike T.
  • Techman
    Techman Member Posts: 2,144
    The Sun,The Son

    The direct sunlight does affect/effect the overall capacity of the AC system. One cond unit w/o air baffels and the sun directly shining on the cond coil has a higher head press than a cond unit around the corner in the shade.Put your butt on a car fender in the sun and I'll bet you say something  like "Son -of -a gun thats hot " Then gently back your girlfriend/wife into that fender in the shade and what does she say?
  • Empire_2
    Empire_2 Member Posts: 2,340
    OK

    Can you tell me what the increase is in terms of head pressure, temperature in and out, sub cooling, and the capacity change in terms of numbers.  It must have a factor that causes the increase in some of these numbers.  Does a unit in Seattle where it is usually cloudy vs a unit in California at 85* have different tonnage for the same square footage of building?  Does the unit in CA need to be larger due to the suns affect on capacity?  Does the system charge need to be adjusted due to this?  I'm curious.  How much higher is the head pressure? aprox.  When checking for non condensables, how can we do it on a sunny day?  With the unit off and in pump down I could see the sun having an affect, but what about in motion during a normal cycle. 



    Mike T.
  • TonyS
    TonyS Member Posts: 849
    I would guess

    that high humidity does affect cooling. Helicopter pilots know that the more humid the air, the more collective or pitch change and power will be needed to hover because humid air is less dense than dry air, therefore in order to keep the same amount of air flowing through the blades the pitch of the blades must be changed.

    Our condenser does not have that ability, so less air is flowing over the condenser.

    Spraying water on the condenser will cool the condenser because a change of state has not taken place, humidity on the other hand has already changed state and can no longer help with the cooling. Using that premise, and having a few hours on very humid days where I had no collective left and engine temps were getting high, I would say it has the same affect on a/c systems
  • Techman
    Techman Member Posts: 2,144
    edited July 2012
    The sun shine.

    Sorry Mike, I don't have any of those #'s. Now,again, I'm talking about a cond coil that is exposed to direct sunshine with a good Southern Western exposure.Not the typical residential cond unit that has a "sunshine blocking" air baffel protective metal louvered outer jacket.Some  commercial packaged RTU's cond coils are exposed to sunlight. Lot's of refrigeration cond units are also exposed to direct sunshine.Give this a try.On a hot sunny day ,measure the head press of a given unit.Then block the sunlight (not air flow) w/ a junky piece of cardboard or something ,even your own body will work , and the head will drop.So ,I'm guessing most of all of those readings will be affected.The head press will drop a little when the sun is blocked by clouds and then climb back up when the sun comes back out.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,858
    What do you refer heads think of pre cooling?

    http://www.piec.com/precooler.htm



    It obviously would be limited in when and where it can be deployed and used, but looks interesting for dry climates like Denver has.



    Thoughts and or comments?



    ME

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  • Techman
    Techman Member Posts: 2,144
    edited August 2012
    What a nice man you are ME

    Years ago I asked our very own  Refer Head leader(Professer Silberstein) if we could be called that! But it was "thumb's down". Why not? The other guy's have "Wet Head"! LET's Start A Chant!!!!!!!!!!!!!!! Refer Heads we are,Refer Heads we want to be,Refer Heads go far,Even on planes & ships out at sea.! Or something like that! But not ATTICA! ATTICA! (Dog Day Afternoon)

    Hi ME! The Pre-Cooler sounds like a good thing. Anything to lower that head press.  There has to be maintenance and such stuff to offset the bennies a little. What about the cond fan motor? There has to be a penalty for the increased restriction of air flow ?Is there any info for energy savings in HI-ER humidity areas? How many gallons of water would evaporate in their given example ? Is there a Pre-Cooler Pre-Filter to eliminate dust and pollen and stuff?
  • don_9
    don_9 Member Posts: 395
    No effect

    Great topic guys.The fact of the matter is that humidity has no effect at all on the condenser as for rejecting the heat.Remember the effects of sensible heat of air as it is heated.Think of the condenser as a furnace that heating the air.

    The dry bulb temp increases,wet bulb temp increases,enthalpy increases and the specific volume increases.The dew point is unchange and the specific or absolute humidity (grains) remained unchange.

    Its the mass flow rate of the refrigerant that changes the capacity of the condenser and that leads us back to the evaporator as being the boss bc it the one that dictate the load on the compressor.



     
  • Techman
    Techman Member Posts: 2,144
    edited July 2012
    Humidity & condensors

    I totally agree that the freon in the cond coil is subjected to sensible heat for its heat of rejection.Once that BTU leaves the freon ,goes thru the cond coil material and enter's the outdoor air ,then I believe that Enthalpy does effect the overall BTU's of the system. A BTU is a BTU, and on a hi humid day those BTU's are trying to hitch a ride on a cubic ft. of air that has more BTU's in it. So today's higher Enthalpy will not allow ,or pick up, as many BTU's per cu.ft. as a cu.ft. of drier air would.So I'm saying (right or wrong) the heat rejection of the cond coil will "back-up" a little in the cond coil on a higher Enthalpy day.Thus raising the head press a little.Thus affecting the total system
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,858
    Nothing derogatory intended...

    I considered vapor heads, but the steam folks have that tied up. Compressor head, evaporator head and condenser head just didn't fit, hence Refer head.. Maybe I should have used Refrer head as opposed to Refer head...



    What ever, I still hold you all in high regards because you think in terms that most well educated people don't even know exists. Even I have trouble grasping some of the complex theories.



    Regards pre coolers, I am sure that it is an air washer, which should alleviate some dirt loading on equipment. And as I said, the theory won't work well in all climates at all times, but it seems that anything that can be done to increase cooling efficiency is probably a worthwhile proposition.



    Thanks for the input.



    ME

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  • meplumber
    meplumber Member Posts: 678
    Bingo Techman

    We don't see the effects of Enthalpy as much in the sensible heat stage, it really shows up in the latent heat portion of the cycle, when we change state.



    As to pre-coolers, ME what you are describing is a smaller version of an industrial or institutional air washer.  It would be similar to combining a Swamp cooler as the pre-cooler on the makeup air side of a traditional refer system.  I have actually seen this on old Quonset huts that were converted to office spaces out in the desert of California, many, many moons ago when I was a lowly jarhead.  The swamp cooler dropped the temperature of the air coming into the makeup side about 10-15 degrees on those 120 deg + days.  This would drop the head pressure on the condenser coil enough so that it could function.
  • Empire_2
    Empire_2 Member Posts: 2,340
    edited July 2012
    BTU is a BTU?

    Techman, you said it yourself a btu is a btu.  Where do you see the btu increasing?  90* @40RH or 90 @ 96RH,........Still 90 * period.  No increase in temp.  Plot it on a PE chart.  There is no back up, storage, effect, or increase.  Condenser operation is base on temperature alone...  You cannot raise temp or btu value by adding water vapor.  100RH is rain or the point where no more water vapor can be added.  The temp is said to be 100% saturated.  The temp remains at 90* in this case.  The  change from 40% to 96%rh does not raise BTU content.  No rise in temp/btu, no change in head pressure.  Heat index does not apply here ( just like wind chill does not change the outside temp because the wind is blowing).  The refrigerant does not care how humid it is outside.  Just because it feels hotter does not mean it is.  This is physics, not opinion.  Add all the humidity you want, it will not change temp or the BTU value!  I know what you are thinking, but it does not work that way.  You have not added or picked up any additional btu's.  Notta 1.



    Mike T.
  • Techman
    Techman Member Posts: 2,144
    edited July 2012
    Enthalpy

    There are more BTU's in a cu.ft. of higher humidity air than drier air.Those economizers with an Enthalpy control will be open on a 55* day w/40% RH and closed on a 55* day w/85% RH due to the higher BTU #'s in the 85% RH air.
  • Empire_2
    Empire_2 Member Posts: 2,340
    Apples and Oranges.

    What does that have to do with raising head pressure?  Your latent heat example of air in relationship to an economizer will not add it's latent value to refrigerant thus raising it's pressure.  Sensible and latent.  they are both real and measurable.  Rise in head pressure at a given temp requires sensible change.  Temperature and pressure are relevant.  Adding more humid air will not change the air temp across the coil to raise it's sensible reading to the refrigerant.  Since air temp stays the same, head pressure will not change.  Latent heat value of air does not add itself to refrigerant to change its sensible value thus raising it's pressure.  Latent heat is or can be expressed in terms of RH%, but other than our change of state, it holds no relevant value in term of affecting sensible readings.  I guess we'll wait until Eugene can chime in and solve this problem.



    Mike T.
  • Techman
    Techman Member Posts: 2,144
    edited August 2012
    apple vs. oranges or oranges vs.apples

    Just the fact that there is a higher ammount of BTU's in a cu.ft. makes it harder to add more BTU to that cu.ft. as compared to a cu.ft. of a lesser ammount of BTU.My AC rejects 3452 BTU into 80*20%RH and another AC rejects only 3450 BTU into 80*80% air.KindaSorta.Everybody, put out a mental call to the Professor,he'll respond!
  • paul_79
    paul_79 Member Posts: 91
    humidity and condenser

    heat flows to cold or so i am told. The humidity is a red herring. so as long as the temp of the refrigerant in the condenser ( a sealed system) is higher and the temp. of the air is cooler the refrigerant will condense. the principal works with the water cooled condenser as well. cooler temp is the key.
  • Empire_2
    Empire_2 Member Posts: 2,340
    Ahh the elusive Eugene

    Since we have different opinions, I believe the good professor can shed some light on the subject.  We have pretty much beat this thing from all angles.  We are all friends here and what ever the out come you have to admit we all have valid and well thought out points.  As you and I throw latent and sensible statements at each other,....lol I coulld only wish all techs give at least half the thought as was displayed here.  That's what separates the pros from the non pros...



    Peace



    Mike T.
  • ChrisJ
    ChrisJ Member Posts: 16,274
    edited July 2012
    efficiency

    Though this question strays from the original topic slightly, what are the differences between a high efficiency system and an older system?  You know, the older 6 to 8 SEER systems vs the latest ones. 





    My guess is the condenser and condenser fan size as its the only thing I could see really making a difference? 
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • paul_79
    paul_79 Member Posts: 91
    efficiency

    the higher seer ratings of the present vs. the old  cond. units. well one is the size of the cond. coil itself and also the air movement (fan) being better. also the newer compressor designs, scroll vs. recip. add to that putting a txv. vs. a orifice (piston) and now you have a higher seer value. then you add r- 410a and now you are talking more efficient refrigerants. next step up vfd drive compressors.. ect.  in the old days you could add better performance in the refrigeration piping by adding a liquid line suction line heat exchanger thing which would help in sub cooling the liquid even more.
  • SWEI
    SWEI Member Posts: 7,356
    Precooling

    Fantastic as long as it's used in the right climate (Denver of course) for the right application.  Precooling of turbine inlet air is a huge win for power plants.  Integrating direct evaporative precooling with refrigerated air does add some work for the coil (removing the moisture that was introduced by the precooler.)  An indirect evaporative precooler gets around this at the expense of some efficiency and cost when compared with direct evap.



    BTW, both Premier and Spec-Air both make excellent products and have plenty of in-house expertise.
  • Eugene_Silberstein
    Eugene_Silberstein Member Posts: 349
    Very Nice Thread

    Very cool thread!!!!

    Yes... Vacation was awesome and it's great to be back...

    Here are a few words about the relative humidity of the outside air and its effects (or lack thereof) on condenser performance.

    As was mentioned throughout the thread, relative humidity DOES affect the heat content, or enthalpy, of the outside air. However, it is important to remember that heat content and temperature are very different! Let me give you an example: Consider a one-pound container of water that is at a temperature of 75 degrees. If we add 1 btu of heat energy to that water sample, the temperature of the water will risw to 76 degrees. Now consider a swimming pool that holds 40,000 gallons of water. In order to raise the temperature of the water in the pool from 75 degrees to 76 degrees, we would have to add over 333,000 btu of heat energy. It can be seen from this that the temperature, or level of heat intensity, of both water samples is the same but the amount of heat, or enthalpy, contained in the pool water is much greater.



    Now....Although there is moisure in the outside air, the moisture is at the same temperature of the dry air. Since the refrigerant in the condenser is not in direct contact with the outside air, the refrigerant only knows the temperature of its surroundings, not the makeup of the air. So, in the proverbial nutshell, the humidity of the ouside air has an effect on the enthalpy of the air, but no effect on the temperature of the medium to which the refrigerant is transferring its heat.



    Have fun!

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  • Techman
    Techman Member Posts: 2,144
    edited August 2012
    Humidity

    On a 85* day 80% RH  what is the RH  % of each  cu.ft. of discharge air coming out of the cond coil w/ say 115* cond  temp? Then the same for an 85* day w/ only 40% RH? Good to hear your voice again Professor!
  • Empire_2
    Empire_2 Member Posts: 2,340
    Welcom back Eugene

    I think we all need a vacation, but hard to take time off when business is good.  It's either feast or famine.



    Mike T.
  • Eugene_Silberstein
    Eugene_Silberstein Member Posts: 349
    Relative Humidity

    Greetings Terry!

    The relative humidity coming off the condending unit will be about 25% in the first case and about 10% in the second.

    Keep in mind that, in both cases, the amount of moisture in the air is not changing, just the ability of the air to hold moisture.

    All the refrigerant in the condenser knows is that the temperature of the "stuff" on the other side of the coil tubing is at a temperature of 85 degrees. It does not know how much of this "stuff" is water and how much is air. Both the water and the air that are passing through the condenser coil are at the same temperature.  



    Enjoy what's left of your summer!

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