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  1. #651
    Join Date
    May 2004
    Location
    Los Angeles, CA
    Posts
    1,560

    Your move my friend.

    Dear Thehumid1,

    Regarding your previous post, sorry for chopping your post up into small bits, but I find it the best way to comment, and/or answer your many questions:

    “But it seems pretty cut and dry how it works or correct if i am wrong similiar in nature to a TXV”

    In terms of being a dynamic valve (one that reacts to the refrigeration systems changing conditions) you are correct, in terms of being an operational valve that is always in the refrigeration system, it is not. Even when this valve is installed in a refrigeration system, it is only used when it’s needed. Under most operating times this valve will not open, and therefore will not affect the operating characteristics of the refrigeration system at all.

    “it senses the suction pressure from the suction line leaving the evap”

    Although it can do that, depending upon the actual valve model used, it senses either the outlet pressure of the valve itself, or the pressure at the end of the equalization line that it may have. This equalization line, if used, senses suction pressure after the evaporative coil assembly as you’ve pointed out.

    “if it is below a minimum setpoint the valve opens allowing hot gas from the discharge line to enter between the TXV and distributor on the evap”

    Here again, depending upon the refrigeration system itself, the introduction of the discharge hot gas can either be at the junction you’re referenced, after the evaporative coil assembly altogether, upstream of the suction line accumulator, or after the suction line accumulator.

    “and then as the coil temp rises back above the setpoint it closes again.”

    Remember, not by temperature, but by pressure. As the pressure of the evaporative coil and/or suction line drops below the preset value, then the valve starts to open, as the valve starts to open, it throttles itself to maintain the evaporative coil/suction line pressure precisely, then as the pressure rises to the point of the preset value again, it closes altogether.

    In conclusion, it’s only used when it’s needed, and it’s setting is preset, so automatic operation is possible.


    And now to my question from you:

    ”What I would see as a big advantag in using this kind of HGB valve would be in conjunction with a EPR valve. The EPR to mainain an constant evap temp of lets say 30 degrees and the evap HBG to prevent the coil from icing which is kind of the idea I was getting at in my post to the original question. So the coil would always be as cold as possible and this kind of HBG would prevent it from icing. I would think using the two together would then easily maintain serverrooms 65 degree desired temp easily.”

    You have to remember that the main function of this valve and process, is not to maintain the coldest evaporative coil temperature possible, but rather to “prevent” the evaporative coil surface from freezing. In that function, this would be the only valve required to complete the task.

    In fact, if this valve process were installed, then Serverroomcooling could set his thermostat down as far as he’d like, and never have to worry about icing up the evaporative coil surface again.

    Not that we would recommend this practice to him, but he could technically set the thermostat to 40 degrees F, and the system would continue to operate without cycling the compressor off, and the server room temperature would settle at the point of system capacity equalization, somewhere between 70 and 40 degrees, and would vary in temperature only as the outside ambient and building’s central HVAC system affected the server room’s HVAC system. But of course, we would never recommend this to him for the obvious reasons (ie. humidity condensation, energy conservation, compressor life expectancy reduction, room overcooling, and the like).

    This elimination of evaporative coil surface freezing is exactly why this valve and process was originally designed, and therefore is exactly why I first recommended it after finding out that Serverroomcooling wanted to operate his system below the traditional operating standard of 72 degrees F.

    Any more questions or comments my friend?

    Respectfully Submitted,
    John J. Dalton

  2. #652
    One think I still can't understand, if freezing up is your big issue, why didn't anyone put a freeze stat on that unit. They are very reliable, easy to install and cheap.
    Hey cockroach, don't bug me! ©

    www.AskTheDiceman.com

    www.TheColdConspiracy.com

    www.Pennwood-HVAC.Com

    Bring Em Home....

  3. #653
    Join Date
    May 2004
    Location
    Los Angeles, CA
    Posts
    1,560

    Whats left.......

    Dear Serverroomcooling,

    Regarding your posted questions;

    “What needs to be done to finish the commisioning??”

    1. Obtain all the readings we were asking for to verify that the system is first of all, fully charged.

    2. After analyzing the above readings, correct any problem that may surface. If no problem(s) are detected, then the commissioning process is complete.

    At that time, we should be able to inform you what this system of yours is capable of, and what it is not capable of.

    Respectfully Submitted,
    John J. Dalton

  4. #654
    Join Date
    Nov 2004
    Location
    Hollywood, FL
    Posts
    365
    I think I might be able to answer this one...I hope if I'm wrong no one shoots me...

    I think a freeze stat will shut the system down when it detects ice, allowing the coil to defrost....this will make my room thermal in a few minutes....plus, won't it shut the system down every time it begins to ice up??

    I can't have the system cool the room to 66, and then have a freeze up....freeze stat shuts the system down temporarily, ice defrosts, the system turns on...cools down to 66 again and then ice forms again....this wouldn't be a good situation.

    I'm not sure if a HGB would be much better....the system would always be running, so that gives it one leg up.

    Guys, am I learning anything here??

    Diceman, do you think installing a tstat that forces the system to be cycled off for a minimum of 5 minutes would allow me to drop the tstat to 65 and not worry about freezeups? Will 5 minutes off be enough time to melt the ice if it start accumulating on the coil?


  5. #655
    Join Date
    May 2004
    Location
    Los Angeles, CA
    Posts
    1,560

    Hold up on that statement......

    Dear Serverroomcooling,

    Regarding your posted questions;

    “and I will be armed with enough information to prove my point and argue with any HVAC guy who says a residential people cooler will work...”

    I hate to burst your bubble but, I could take a residential people cooler, and with a few inexpensive modifications, make an HVAC system that would be able to keep your server room at 65 degrees F, or even 60 degrees F while the outside weather was either 40 degrees F or 115 degrees F for a lot less money than the Liebert guy would charge you. But that is me, and I’m not unfortunately in Florida with you. Just wanted to clarify your statement my friend.

    Respectfully Submitted,
    John J. Dalton

  6. #656
    Join Date
    May 2004
    Location
    Los Angeles, CA
    Posts
    1,560
    Dear Serverroomcooling,

    Regarding your post;

    “I think you are right...70 is a safe temp for me in the room and at the system level....I think I can cruise from here unitl March and April”

    I 100% agree with you, leave the thermostat at 70 degrees F for now…….

    ”The bad news is that I haveequipment I need to buy....I've been holding off the order....I just hope things stay staable. I'll add slowly, and if things get crazy, it's time to upgrade”

    What about another cycle rate with the outside temperature posted. This should be done anywhere between 1:00 PM and 5:00 PM, in the warmer part of the day. This will give us an estimated field heat load of the server room under the outside conditions you’ll post.

    Respectfully Submitted,
    John J. Dalton

  7. #657
    Originally posted by serverroomcooling
    Diceman, do you think installing a tstat that forces the system to be cycled off for a minimum of 5 minutes would allow me to drop the tstat to 65 and not worry about freezeups? Will 5 minutes off be enough time to melt the ice if it start accumulating on the coil?

    Since you have a rigged up system as it is, a freeze stat will not hurt. You can run the unit at colder temps. If it freezes, it kills power to the condenser, evap keeps running and still blows icy cold air into the room, when the stat warms up, condenser comes back on. It is a good backup no matter what and will not adversely affect the operation.
    Hey cockroach, don't bug me! ©

    www.AskTheDiceman.com

    www.TheColdConspiracy.com

    www.Pennwood-HVAC.Com

    Bring Em Home....

  8. #658
    Join Date
    Mar 2004
    Location
    NJ
    Posts
    1,214
    Ok I understand to prevent icing this would be the only valve needed for that...Yet the EPR itself could be used for that as matter of fact one of the reasons it is used on multi evap systems the epr's are put on the evaps that have higher operating temps then the evap with the lowest operating temp so that these ones do not ice up.

    BAJA BUGGY: My thought was to use both one the EPR to maintain a set evap pressure so the coil regardless of load fluctations and set the EPR at 43 psig(R-22) which would be the equivalent of 20 degrees fahrenheit then the evaporator HGB valve would kick in when the coil was close to icing ... it would be a constant battle between the two valves but it should ensure the lowest possible evap temp without icing...
    And in this case the valve would be used many times a day ensuring the customer got his monies worth out of the valve.


    Of course the right evap fan/coil setup with elec defrost would be have been better from the get go but had nothing better to think about today.


    And of course since you did not answer my questions...

    I will make posibly my last attempt to convert you from fan cycling control

    Here is someone else opinion (climaticcontrol.com) which states:

    The flood valve system is the best head pressure control system for smooth, accurate, and trouble-free low ambient control.

    Fan cycling can control head pressure but has drawbacks. Systems that use dampers to control airflow through the condenser are very expensive and leak refrigerant. There are few condenser damper control systems in use. The flood valve system is the best head pressure control system for smooth, accurate, and trouble-free low ambient control.



    Head pressure control is needed on air-conditioning at 60°F ambient and on commercial refrigeration at 50°F ambient and lower.



    Control of head pressure is needed in order to maintain:



    1. Adequate pressure drop over a TXV for the refrigerant effect

    2. To prevent flash gas in the liquid line

    3. To provide pressure for hot gas by-pass, or hot gas defrost, if present



    Flooded condenser systems are able to maintain pressure within 5 to 10 psig. They can operate efficiently to very low ambients encountered in our cold winters. By flooding a condenser with refrigerant, we truly reduce the condenser’s capacity.



    Up to about 15 tons capacity, the HP Alco Headmaster can be used.



    See Figure 3. B is the connection for the discharge line from the compressor. R is the connection to the receiver, and C is from the condenser.




    thehumid1-------I live in NJ, a state where it's free to come in but you have to pay to leave!

  9. #659
    Join Date
    May 2004
    Location
    Los Angeles, CA
    Posts
    1,560

    What do you think?

    Dear Diceman,

    Regarding your post;

    “One think I still can't understand, if freezing up is your big issue, why didn't anyone put a freeze stat on that unit. They are very reliable, easy to install and cheap.”

    Although this would stop the HVAC system from freezing up, it would also stop the compressor as well, and therefore the cooling. We are looking for a way to not control the freezing of the evaporative coil assembly, but a way to actual prevent it from freezing altogether, even when the server room is at 65 degrees F or below, well below the standard operating temperatures for normal air conditioning systems.

    We have suggested the use of hot gas bypass in the form of a DBV valve system. Do you have another form to use, if not, do you think this system and valve would be appropriate?

    Respectfully Submitted,
    John J. Dalton

  10. #660
    Join Date
    Nov 2004
    Location
    Hollywood, FL
    Posts
    365
    John, if you were in South Florida, you would be here handling this project and we would both be very happy. I do not think I would be able to decide who is a qualified hvac guy to make these midifications, and even if he does make them, how will I know he will stand by his work, and what will I do when he disappears?? I'll have to pay for my piece of mind. On Wed I will see how inpressed I am with the tech that comes from the Liebert resleller.

    I will get the cycle times tomorrow between 3 and 4 PM. I'll post as soon as I gather the numbers.

    Diceman....my system is not supped up, it's a standard 3 ton residential Trane. I still have the cheap tstat on it...I haven't done a thing to it....two changes were made that may have prevented freeze ups, I turned the fan to "on" and rotated the gril closest to the return so it no longer faced the return.


  11. #661
    Join Date
    May 2004
    Location
    Los Angeles, CA
    Posts
    1,560

    Real close, but no cigar......not yet at least.

    Dear Serverroomcooling,

    Regarding your post:

    “I think I might be able to answer this one...I hope if I'm wrong no one shoots me...

    I think a freeze stat will shut the system down when it detects ice, allowing the coil to defrost....this will make my room thermal in a few minutes....plus, won't it shut the system down every time it begins to ice up??

    I can't have the system cool the room to 66, and then have a freeze up....freeze stat shuts the system down temporarily, ice defrosts, the system turns on...cools down to 66 again and then ice forms again....this wouldn't be a good situation.”

    Well said, your 100% correct in your statements to this point. The freeze thermostat would only try to control the freezing by cycling the compressor off, thereby shutting off the cooling in the process, and as you’ve said…… “this wouldn't be a good situation.”


    ”I'm not sure if a HGB would be much better....the system would always be running, so that gives it one leg up.”

    You’re still not quiet understanding the operating conditions and characteristics of a hot gas bypass system utilizing a DBV valve. This system operates just like a typical HVAC system, but can go much lower than the standard 72 degree F room temperature. This system still cycles off and on like a typical HVAC system.


    “Guys, am I learning anything here??”

    Your not quiet to the station, but you’re definitely on the right tracks!

    Respectfully Submitted,
    John J. Dalton

  12. #662
    Join Date
    Mar 2004
    Location
    NJ
    Posts
    1,214
    But.....it does not seem your system has a problem with icing from low ambient conditions as if it was 45 degrees out...In South Florida you are looking at 21.8 days under 60 degrees a condition that will occur 6% percent of the systems operating time in a year.

    Maintaining your 70 degree setpoint at a 97 ambient needs to be seen as much more of your problem will be your desire for this lower setpoint which will be harder to achieve in higher ambient temps but I still think you will squeek by.
    thehumid1-------I live in NJ, a state where it's free to come in but you have to pay to leave!

  13. #663
    Join Date
    Nov 2004
    Location
    Hollywood, FL
    Posts
    365
    does this mean that a HGB is sending hot gas to the coil on a regular basis....if so, I missed that point pages and pages ago...I was under the impression that there was some trigger that opened the valve to let the hot gas flow

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