Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

10/13SEER blend

Not out of line at all :o).

In an automotive application every component in the system is of known size/fixed. (evap, condenser, compressor, dryer, lines) The charge is predetermined based on the size of these components all being the same. You would charge the system with the predetermined amount (usually printed on a label in the engine compartment). Assuming a PROPERLY operating system, yes its a done deal. I think Superheat and subcool are not methods used for charging in automotive applications because of this. This is why Ive never heard of them.

In residential systems, the mix of equipment size, brand, line set lengths, etc can almost never be predicted. So I guess the charge amount they quote on the condenser labels is for the condenser only? As a result of this, I assume superheat and subcool methods are recommended? Charge weight (for a total system) can not be quoted. You agree?

I agree though that superheat and subcool could be good diagnostic methods.

Either way, I've learned some new terms!


  • S Ebels
    S Ebels Member Posts: 2,322
    What should I recommend?

    Looked at a four year old, 4T, 10SEER condenser this past week that was absolutely smoked by lightning. Everything on it is burned up. Owner wants is replaced but so far I'm having trouble finding a 10SEER condenser to match the coil in the Unico system installed in the house.

    So here's the question.........What are the ramifications of installing a 13 SEER condenser on the 10SEER Unico evap? Are we asking for trouble or will the TXV on the Unico take care of any differences in condensing characteristics
  • Charles G.
    Charles G. Member Posts: 113
    10/13 S.E.E.R.

    > Looked at a four year old, 4T, 10SEER condenser

    > this past week that was absolutely smoked by

    > lightning. Everything on it is burned up. Owner

    > wants is replaced but so far I'm having trouble

    > finding a 10SEER condenser to match the coil in

    > the Unico system installed in the house.


    > So

    > here's the question.........What are the

    > ramifications of installing a 13 SEER condenser

    > on the 10SEER Unico evap? Are we asking for

    > trouble or will the TXV on the Unico take care of

    > any differences in condensing characteristics

    A 13 S.E.E.R. condenser requires a TXV control. sounds like you have that. The condensing unit is what's rated @ a given
  • Charles G.
    Charles G. Member Posts: 113

    A 13 S.E.E.R. condensing unit requires a TXV control. Sounds like you have that. It's the condensing unit that has the S.E.E.R. rating and the TXV helps the unit achieve that. There are no different evap. coils for 10/12/13/14/16 etc. S.E.E.R. rated units. There are TXV coils and piston or fixed orifice coils, period. And per a previous thread, yes you could use a fixed orifice coil on a higher S.E.E.R. rated condenser, but A) you don't get the rating from your equipment, and B) you won't be compliant w/manufacturer matchings and he probably won't stand behind any failure issues down the road, and C) why would you want to?
    Also, if you're dealing w/"an artificially generated power surge" (lawyer talk) consider this a burn-out and treat ALL components of this thing accordingly. The coil and lineset may be considered collateral damage. Do it right or do it over...
  • S Ebels
    S Ebels Member Posts: 2,322
    I was curious because

    The 13 SEER condenser/evap combos that we are getting for standard furnace driven systems are packaged with evap coils that are much larger than the old equivalent 10 SEER units. I was wondering if anyone knew if Unico had a 13SEER evap available for their unit.
  • jim lockard
    jim lockard Member Posts: 1,059
    did you

    ask Unico if the existing coil would work? or if they have a coil that will?
    Most of the high pressure systems use another manufactors condenser so there has to be some "play" in the system. My thought is if its cooling only you maybe able to dial the charge in rather tight and be ok. If its a heat pump thats a different animal. Best Wishes J.Lockard
  • Empire_2
    Empire_2 Member Posts: 2,343
    S Ebels

    Yes the larger A coils in standard units give More surface area for the increase of seer rating which all manufacturers want us to do. TXV is a must but with the Unico ( I have only heard) that they are OK to match with up to 12 Seer cond. Don't forget with the 13 seer and higher condensers there is an increase in net refrigeration effect which is basically the result of sub cooling due to the larger Condenser coils and as a result they like to see a larger "A" coil to take advantage of this. IO think Eugene can clarify more on this subject.

    Mike T. Good Luck....
  • Jim Bergmann_3
    Jim Bergmann_3 Member Posts: 5
    Evap Coil

    If you pair it up with a 13 seer you will get something less than 13 seer but higher than 10. Unico recommends a 12 seer or higher with their evaporators. Many of their systems use a multi-capacity evaporator. If the system was a 3036, and used at 2.5 ton, the system would already have an oversized evaporator and you would get the higher efficiency. The airflow is what determines the tonnage on these systems the more outlets you have the higher the airflow when you hit the max airflow the tonnage is limited by the condenser. I would not hesitate to install a 13-seer condenser on the system. There is a lot of crap going around about mismatched systems. It all comes down to this. If the system is not matched with an approved coil combination, the performance guarantee of 13 seer cannot be achieved. No manufacture will guarantee the efficiency of a mismatched system. But all manufactures will still guarantee the condensers and quality of the components and manufacturing. A mismatched 13 seer system with correct charge and airflow will cool and do it more efficiently than a 10 or 12 seer condenser. The way we have always increased efficiency is to increase the size of the coils. A larger condenser paired with 10 seer evaporator will provide good results but possibly not achieve 13 seer. The airflow and the refrigerant charge are the most critical things. If they are not right the efficiency will decrease dramatically. How do you get the charge correct? Charge to the manufactures recommended sub cooling listed on the data plate if it is a TXV, use a Trane or Carrier charging calculator if it is a fixed metering device. You charge a fixed metering device to the evaporator size and the airflow.
  • Empire_2
    Empire_2 Member Posts: 2,343

    I have heard that it was 12 and lower without problems?...humm I will get to the bottom of this.:-)

    Mike T.
  • S Ebels
    S Ebels Member Posts: 2,322
    Should be OK

    From what I'm reading here I should be OK. The Evap coil currently in the system is the 48/60 model so it's likely going to be oversized a tad for the 4T condenser attached to it. The Evap has a TXV on it as do all Unico systems.

    It just made me wonder due to the foggy response I got from the resident "expert" at the distributor that handles Unico.
  • clammy
    clammy Member Posts: 2,831
    13 seer

    Steve i just compleated a unico 5 ton a/h with a 13 seer areco air condensing unit i have never had any promblems with installing 12 or 14 seer condenseing units with unico systems but you will not get that seer when with use unico equiptment but usually a 12 or higher seer units come with a 10 year compressor warranty and are way quiter then 10 or builders model units .I have also done some unico with 410 a and they also worked great just had to change the expansion valve .The expansion valves if i remenber right are equilized but a time delay is a smart extra for the condensing unit and of course a hard start kit always goes a long way .I have used carrier ,byrant and rheem 13 and 14 seer equiptment with unicos and have not had a promblem .Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • jim lockard
    jim lockard Member Posts: 1,059
    Hey S.

    I ran across a guy today that does a lot of unico systems, He said that coil should work on 13 seer no problem --hope he is right good luck. J.Lockard
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380

    We have been mismatching condensing units and evaporator coils for years and nobody flinched. Now, with the 13 SEER issue everybody is running scared. Here are a few tidbits to help ease the pain.

    Mismatching condensing units and evaporator coils will work, but the resulting effiicency is not certain, nor can it be guaranteed.

    Use evaporator (not system) supeheat when charging systems with fixed bore metering devices.

    Use condenser subcooling when charging systems with TXV's. 15 to 20 degrees of condenser subcooling is good number to start with.

    System capacity (nameplate) is to be delivered under ARI design conditions, which is a 95-degree outside ambient temperature and a 75-degree return air temperature at 50% RH.

    As the outside ambient temperature and/or the inside air temperature rises, the delivered capacity decreases and the system efficiency decreases as well. In addition, as the length of the refrigerant lines increase, the efficiency of the system will also drop.

    As the outside ambient temperature and/or the inside air temperature dropss, the delivered capacity increases. Also, shorter line sets increase system efficiency.

    In order to determine the system efficiency, the Coefficient of Performance (COP) for the system needs to be determined first.

  • Mark_46
    Mark_46 Member Posts: 312

    Off the subject, but I've seen the superheat and subcool methods mentioned here on the wall many times. Can you explain the differences?
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Sure Thing, Mark

    Gauge readings provide what is referred to as latent heat information. This indicates the temperatures and pressures at which the refrigerant changes state. In the evaporator, refrigerant changes from a liquid to a vapor and, in the condenser, refrigerant changes from a vapor to a liquid. The information obtained from the gauges does not indicate how much liquid or vapor is present in either the evaporator or the condenser. It is imperative, however, that we know the approximate amount of liquid/vapor in a coil to determine system charge and the overall operating efficiency of the system.

    So, in order to do so, we need a means by which we can determine the quality of the refrigerant in the coils.

    If your still here, please read on.

    If we had a block of ice at a temperature of 32 degrees that we wanted to melt, we would have to add heat to it. Now, as we add heat to the ice, it will slowly turn from ice at 32 degrees to a mixture of ice/water at 32 degrees and finally to 100% water at 32 degrees. The temperature of the ice has not changed, but there was a heat transfer that resulted in the changing of the state of the substance. This is referred to as a latent (or hidden) heat transfer as the temperature of the substance remained constant.

    Now, let's continue to add heat to the 32 degree water. What will happen? The temperature of the water will increase. Now let's say that the final temperature of the water is 40 degrees. Since we can measure the change between the 32 degree water and the 40 degree water, this type of heat transfer is referred to as a sensible heat transfer.

    Now, back to the superheat stuff.

    In the evaporator, refrigerant enters the coil as a saturated mixture of liquid and vapor. Let's say that the temperature of this liquid is 40 degrees. As the refrigerant in the evaporator coil absorbs heat from the air passing over the coil, more and more of the liquid boils off into a vapor, but the temperature of the refrigerant remains constant at 40 degrees (latent heat). Now, at some point in the coil, all of the liquid will have vaporized, leaving us with 100% vapor at 40 degrees. As the air from the conditioned space continues to pass over the coil, the vapor continues to absorb heat. Since the refrigerant is 100% vapor, the temperature of the refrigerant will rise (sensible heat).

    So, by taking a temperature reading at the outlet of the evaporator and comparing this temperature to the temperature at which the refrigerant boils off in the evaporator, we get our evaporator superheat.

    Superheat example:

    R-22 system

    Low side gauge reading = 68.5 psig

    Evaporator outlet temp = 55 degrees

    From the P/T relationship for R-22, 68.5 psig corresponds to a temperature of 40 degrees.

    Evaporator supeheat = Evaporator outlt temp - evaporator saturation temp = 55 degrees - 40 degrees = 15 degrees.

    In English, evaporator superheat is the amount of sensible heat picked up in the evaporator after all of the liquid has vaporized.

    In a similar fashion, the condenser subcooling if the amount of sensible heat given up in the condenser after all of the liquid has changed from a vapor to a liquid.

    Hope this helps.
  • ddlong1286@yahoo.com
    [email protected] Member Posts: 139
    Which Superheat?

    Hey there professer

    Are you saying the charging charts are wrong about the superheat method? Most say to take your readings at the suction service valve at the condenser.

    I know that to set txv sh reading you should take readings at evap outlet.

    I had a boss once that said the charts where wrong and that you should set fixed orfice sh at outlet of evap instead of the condenser suction service valve. Just wondering?

    Thanks Don in Mo
  • mtfallsmikey
    mtfallsmikey Member Posts: 765
    Great Info Dr. Silberstien!

    I personally appreciate you helping me to refresh my feeble memory on system charging methods. We had to start doing the system mismatch dance years ago with the first generation heat pumps, and was blessed with having an AC Dead Man who worked for a local wholesaler guide me thru some tough situations (Remember the Westinghouse HiReLi?). Is there a point length-wise and height of rise where the refrigerant lines will be a detriment to system efficiency? Anyway, if it were me, I'd rip it all out and start from scratch. It's much easier that way, and keeps a system repair from becoming a science project.
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    The Reason for That is...

    The answer is... it depends...

    Typically, there are no service ports at the outlet of the evaporator, so we use our low side pressure reading at the condensing unit, which, for the most part, is pretty accurate. This is assuming that the line set is relatively short.

    Ideally, to measure evaporator superheat, you need to take the pressure (latent heat portion of the superheat calculation) and the suction line temperature (sensible heat portion of the superheat calculation) at the outlet of the evaporator.

    If we are taking both readings at the suction service port at the condensing unit, we are NOT calculating evaporator superheat. You are calculating what is often referred to as system superheat, which includes the suction line.

    Thermostatic expansion valves do not maintain constant SYSTEM SUPEHEAT, they maintain constant EVAPORATOR SUPERHEAT.

    If the suction line is well insulated and short, the system superheat and the evaporator superheat will be relatively close together.

    To get an idea of how much evaporator superheat you are working with you can determine the temperature rise in the suction line and then subtract that number from the system superheat result.

    Have fun guys!
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    refrigerant lines

    The shorter the lines, the more efficient the system will be. As soon as you start adding any length to the line set, you are sacrificing efficiency.

    So, keep in mind these two little tidbits: Keep the lineset as short as possible and insulate the suction line well.

    Keep smiling.
  • Mark_46
    Mark_46 Member Posts: 312
    Ah ha

    Eugene, thanks for the very thorough explanation.

    Actually, it wasnt too hard to follow as I do have extensive experiance with automotive heat and AC systems. As you may know, automotive systems are typically charged by pounds and ounces (and later checked by pressure) probably becasue the system size and capacities are fixed and known. In residential systems- lines sets, equipment, etc all vary.

    But as I indicated, I never heard the terms superheat and subcool. In a very Cliff Note type description, both of these methods are the temperature differences between the inlets and outlets of either coil. Yes?
  • Empire_2
    Empire_2 Member Posts: 2,343
    Hello Mark;-)

    Can I ask you 1 question? OK, I know you will bite...;-) If you were to weigh in a charge on an automobile and say the suction is real lo. Lower than normal,....you know you put in the right weight as far as refrigerant goes where do you go from there? What tells you that the blower is not running as opposed to the evap is partially plugged? Super heat can be real handy here instead of just replacing parts until you fix it. (Ouch)!!!! I didn't mean that in a Diss way, but how can you never have heard of S/H or Sub/Cool? Do you just weigh in the charge, bless it and send it on its way?

    I am sure I am going to get pounded here, but if I am out of line or I misunderstood you..... I am sorry.

    Eugene, I am probably out of line and I apologise to the 2 of you, BUT it's FRIDAY!!!!!;-))))))))

    Mike T.
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Thanks Mikey..

    Always a pleasure to help...
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Time for a Re-Post

    There have been some off-the-Wall requests for superheat and subcooling information, so I am bumping a post from last month that addressed these issues as well as the SEER mismatching issue that so many of you are concerned about.

This discussion has been closed.