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  1. #1
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    Question Sizing Condenser to Evaporators for different Applications


    Hello there,
    How does one go about deciding on the best size Condensing Unit to match an Evaporator for a specific purpose?
    for eg. I have a 15 ton Larkin Evap. (three Fans four bladed 27 degree pitch, 26inch diameter) that I intend to use in a 24x12x8ft insulated Box, I would like to ceate a "Blast Freezer" running R404A to operate at -30 F or lower, so what size Condenser do I use???

    If I wanted on the other hand to create a maintaining Freezer whereby Frozen product is inserted and is maintained frozen, how can I go about deciding what size compressor/condenser to use?

    Peter



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    Re: Sizing Condenser to Evaporators for different Applications

    Because you're a energy consultant, you perhaps have to take another approach then a customer or a tech.
    You specific needs to select a condenser which will make that the whole set-up will run with the less energy as possible.

    What will you use? Open or hermetic compressors.
    In theory you need a condenser equal to the evaporating capacity + absorbed capacity by the compressor and selected with a DT of 10K compared to the hottest expected outside temperature. If outside temperatures can swing between large margins, you also need some sort of HP control on the fans (HP pressostat, VFD...) to maintain HP for your TEV.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Question Re: Sizing Condenser to Evaporators for different Applications

    Proper operation of the Blast Freezer is ALL that is needed to Save Energy in the Application for which it is to be utilised. I simply need to have as much BTU's above 95,000 as posible at a Temperature at or lower than -30 F with more than 1800 CFM of air circulation. I intend to use Semi Hermetic Compressor, and the hotest days in our area can reach 35 C while nights are lowest at 21 C. From my limited understanding of what you have outlined, I can see that a 15 Ton Condensing Unit cannot deliver, therefore should I go with a 20 Ton???

    Incidentally what is the defination for the abbreviation "DT"??

    Peter
    Last edited by PHENERGY; 28-03-2005 at 02:18 PM.

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    Re: Sizing Condenser to Evaporators for different Applications

    Quote Originally Posted by PHENERGY
    Proper operation of the Blast Freezer is ALL that is needed to Save Energy in the Application for which it is to be utilised. Peter
    This is not ALL what is needed to save energy. It's a wrong statement. It starts and depends almost solely with a proper design.

    You can have more BTU's if you lower the HP (and even rise the LP), so a lower DT over the condenser and also designed that way. Because once designed and installed, you can't change it afterwards.

    The air circulation doesn't say anything: the design of the whole concept, especially the room itselves is much more important.

    You need a condensing unit who can give at 95,000 BTU at the desired evaporating and condensing pressures. That's all.
    If the 95,00 is correct of course.
    I'm not familiar wit IP units but did a conversion from your 95.000 BTU to tons which gave me completely different figures.
    You need something around a 30 Hp unit, given that 95,000 is correct.

    Do you need capacity control, partial load, is room stacked always full, is it a FIFO freezer, ....

    DT: if outside conditions are 35C then you're compressor must be able to condense at max 45C or ....psi (you didn't gave the gas you will use)

    Without having the intention to be rude....designing a blast-freezer is not that easy as it looks on the first sight.
    I strongly recommend that you try to find someone experienced to figure out, eventually together with you what your client needs.
    Last edited by Peter_1; 28-03-2005 at 04:39 PM.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Thumbs up Re: Sizing Condenser to Evaporators for different Applications

    Well, you did initially state that my outlook is gonna differ because I an an energy consultant, the fact of the matter is that the system that the blast Freezer is to REPLACE uses quite alot more energy. The Gas Iwill Use is R-404A. I do not use a blast Freezer simply to blast freeze but as part of a totally different concept, so from my perspective ALL I have to do is to get a proper operation at
    -30 F and the minimum air circulation and presto I will have saved lots of energy ( will post results after completion of this design) the fact of the matter too is that I am in consultation with a Very experienced Contractor but I like to cross reference and have an idea of things before he makes his recomendations he is to give me his design tomorrow. For a previous blast freezer he designed and used two 15 HP condensing Units, but I did not know the evap size, this time arround I know the Evap size, so I guess he may design at or arround 30 HP as you have suggested.

    Peter
    Last edited by PHENERGY; 28-03-2005 at 09:02 PM.

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    Re: Sizing Condenser to Evaporators for different Applications

    Peter_1 is right. It is not hard to balance a unit cooler with a condensing unit. You simply plot the unit cooler at a couple of capacities and TD's (temperature diferences) and then cross plot the condensing unit against the unit cooler. Where ther cross is the balance point with no line losses. You need to offset the unit cooler by 2 dF to allow for suciton losses and that is you actual real world balance.

    Also, designing a blast freezer is not all that hard, but does require some knowledge of air flow and product spacing/packing. Does your Larkin unit cooler have cast air foril fans or are they the stamped flat sheet metal baldes? You generally want to rate a unit cooler fan for 1/2" W.C. (water column) static pressure (SP) because you will have some static loss in a blast cell getting the air through and around. A flat sheet metal blade can not produce the static pressure and will not produce sufficient CFM (air flow).

    If you want to balance a separate condenser with a compressor and them a unit cooler, you have a whole new ball game. It ican be balanced by hand, but takes a bit more work. Both of these are something that I do on a daily basis, bit not something to expalin over the net. If you post some model numbers, I can see if I have the literature on the equipment and could do a balance. If it is used equipment andyou are changing refrigerants, you need to watch out on the unit cooler. The distributor and nozzle may not work for te new application.

    Sounds as though you need to hire a refrigeration engineer to keep you out of trouble.

    Ken

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    Thumbs up Re: Sizing Condenser to Evaporators for different Applications

    Hey Thanks a lot Txiceman for offering to help, Peter_1 too.

    The Larkin Evaporator model # is ELT611704, the name plate says it is designed for use with R-12 or R-22 or R-502. but I will be using R-404A gas.
    The fan blades are riveted to a central metal plate with a detachable 5/8 hub with Allen nuts to tighten onto the motor shaft, 27 degree pitch. the blades are curved inward.

    There is a lesson for me to learn in all this. In the past I have used an experienced Refrigeration Contractor who has always delivered, he does not supply equipment but designs and installs and commissions. But this time around the refrigeration equipment supplier is new to me and he insisted that to maintain his warranties he would have to install and commission his systems, thereby forcing out my regular guy, and therein was the start of all these problems, basic errors has been made, the Texaco Capella oil instead of the POE with the R-404A a few weeks ago for example. Now he is offering a condenser driven by a coplamatic Compressor Model # 3DF3-090E-TFC-800 to work with the Larkin evap and I just do not believe it is properly matched to deliver a blast freezer, at the conditions previously stated in this thread
    I have since contacted my regular contractor and he will pay a site Visit today and see what can be done but I am always grateful for other opinions. I anxiously await your replies.

    It will be very difficult for any one to separate me from my regular guy in the future.

    Peter
    Last edited by PHENERGY; 29-03-2005 at 03:26 PM.

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    Re: Sizing Condenser to Evaporators for different Applications

    Hello PHENERGY,
    The best source for you to size that equipment, is typically the supplier of the evaporator and condenser. Larkin, is now owned by Heatcraft, and they have engineering that will help you size that specific evap coil to the needed condensing unit, with the energy efficienct condenser.
    Just a thought.

    Capt Steve

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    Re: Sizing Condenser to Evaporators for different Applications

    I'll look in my library tomorrow and see if I can identify the models. Are ou running 50 or 60 HZ power?

    ANd Capt'n, if he can get a factory Lain engineer,he can get some help. A lot of the local reps would be stretched to make a proper equipment balance.

    Ken
    Last edited by TXiceman; 30-03-2005 at 04:18 AM. Reason: Added

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    Re: Sizing Condenser to Evaporators for different Applications

    Isthis the one you're looking for?
    Attached Images Attached Images
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: Sizing Condenser to Evaporators for different Applications

    Peter, the Copeland compressor 3DF3A090E-TFC rated at -40dF SST, 20 dF superheat, 10 dF subcoling, and 120 dF CT on 60 HZ is 17,700 BTUH and it is a 9 HP compressor.

    I can not find a LarkinELT6-11704 unit cooler in my book, but if it is rated like they normally rate then, this is rated for 117,000 BTUH at -10 dF ET and a 0 dF room.

    It appears that it will take several 9 UP compressors.

    One word of caution. The ELT unit cooler is not suitable for a blast freezer application. It has the stamped sheetmetal fan blades and can not develope any real static pressure as it will see in a blast application.

    I have run up against contractors/reps trying to sell this model unit cooler for a blast cell before. From past experience, it will not work. Based on this fact, I will not attept to balance the equipment as it is a total misapplication of the unit cooler.

    You need to find a reputable refrigeration engineer in the area to work with and get this equipment done right.

    Ken
    Last edited by TXiceman; 30-03-2005 at 03:07 PM.

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    Re: Sizing Condenser to Evaporators for different Applications

    Hi Peter,

    I'm sure you can get here the information you require,

    http://www.heatcraftrpd.com/Larkin/aboutlarkin.htm

    Chemi

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    Re: Sizing Condenser to Evaporators for different Applications

    Hello Guys
    We are running on 60Hz down here the Condensing unit is to work at 208/220VAc 3 ph so too the Evap fans.

    Peter

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    Re: Sizing Condenser to Evaporators for different Applications

    I can not find that model on their website or in our old catalogs. Besides, the ETL is not suitable for a blast cell. It is a warehouse cooler.

    Ken
    Last edited by TXiceman; 30-03-2005 at 10:48 PM.

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    Re: Sizing Condenser to Evaporators for different Applications

    Well Thanks a lot guys for your responses to my call for help.
    Tomorrow myself and my regular contractor advisor will visit the supplier with a view to changing the equipment. To be fair, we did change the original fan blades the the Evap came with to obtain more air circulation, and got better results but not up to my satisfaction

    The main reason that I followed through on the Evap is that we might have to remove the box Iso-wall(TM) insulated wall panels to get it out of the box since a very expensive manifold was built infront of it after it was installed. so if there was any way to use it I would have done so.

    Finally, I wish to extend my heartfelt gratitude to all the wonderfull persons who participated, and to inform that that I believe this site to be a great idea, I will certainly be reccommending this forum to my friends in the industry and will help where I can specifically I specialise in digital control systems

    will follow through and let youall know how this all turned out.

    Peter
    Last edited by PHENERGY; 31-03-2005 at 12:08 AM.

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    Re: Sizing Condenser to Evaporators for different Applications

    Peter, since you change the fan out, do you have any idea of the air flow? If you do, and can give me some info on the Larkin cooler, such as tube OD, # of tubes high, rows deep, finned height, finned length, fins per inch and total air flow, I can make an estimate of the unit cooler capacity. Need to know what room temperature you are shooting for.

    In a blast freezer you normally want a rather high air flow and typically run the coil face velocity well over 500 fpm, closer to 700 fpm and higher.

    The problem with the sheet metal fans is when they are subjected to a static pressure they tend to flex and flatten out and not deliver as much air. You can go to a company such as Multi-wing and get a replacement blade (cast blade with an air foil cross section) designed for a static pressure. Next problem is do you have emough motor to drive the fan.

    Ken

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    Re: Sizing Condenser to Evaporators for different Applications

    PHENERGY,
    Just incase you want more information on that evaporator you currenlty have, here is a web site your can go to and possibly contact someone form the factory regarding that exact evaporator.
    www.heatcraftrpd.com/default.htm

    They are the company that builds Heatcraft, Bohn, and Larkin.
    It is worth a look!

    Good Luck!


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