Page 4 of 99 FirstFirst 12345678910111454 ... LastLast
Results 40 to 52 of 1276
  1. #40
    Join Date
    Mar 2004
    Location
    NJ
    Posts
    1,214

    Re: thehumid1

    Originally posted by twcpipes
    Question about the below statement in your last post:

    as the national Weather Service shows Jan-Mar ambients of 59-63 degrees and then again in Dec of 62. Depending on the ratio of NRE of the cooling coil to space tonnage requirements, are we sure there will always be an at, or near, 100psig drop across the TXV to accomplish required tonnage when needed? Especially if a higher efficient condenser is used.

    *1) A head pressure or weatherization control in Hollywood Florida is absolutely unnecessary but a TXV will give your system better efficiency.*
    Well first of all I never trust weathermen but those ambients seem extremely low for that area of South Florida what city where you looking at and the only times I used them there was on walk-in cooler/ refrigeration applications and most of them don't even have one. Sure there will be conditions like maybe 3-10 days out the year where it could actually be used. And I can never always be sure of anything in this business like a 100 psig drop across the txv......as there are many variables that can affect this one of which is low ambient temp causing too much subcooling of the LL.
    So you if you are designing a system to meet every posible extreme necessary regardless if the condition is only going to exist 1% of the time than I would agree it is necessary. In this case I would call it overkill.
    thehumid1-------I live in NJ, a state where it's free to come in but you have to pay to leave!

  2. #41
    Join Date
    Nov 2004
    Location
    Hollywood, FL
    Posts
    365
    Allen, I'm not quite sure I understand your post, could you restate your comment??

    Thanks

  3. #42
    Join Date
    Nov 2004
    Location
    Hollywood, FL
    Posts
    365
    The unit I am installing has a Thermal Expansion Valve, and not a metered connection.


  4. #43
    Join Date
    Sep 2002
    Posts
    1,389

    thehumid1

    first off, I was looking at Hollywood Florida:

    http://www.weather.com - type in Hollywood, select Florida, select yearly highs and lows.

    I offer this for your consideration:

    1. The internal load for this project is relatively constant and is subject to outdoor ambients to maintain indoor tonnage requirements.

    2. It is not like refrigeration where you would pull the load down and require less tonnage to maintain said load once it reaches its setpoint. Especially since the product helps to hold intself.

    3. Tonnage requirements are necessary to maintain the high loads of a server room and since Refrigerant-22 TXVs are designed for their rated tonnage at 100psig drop across the valve, it is usually good practice to try and maintain close to that pressure drop. If another refrigerant is to be used, that pressure drop will need to be addressed.

    4. In reviewing the average lows, it would appear that there are more than 1% of the year the lows require refrigerant cycle attention to guarantee sufficient tonnage for this room.

    5. Over the last 40 years I have found that the refrigerant cycle is still the refrigerant cycle and the load is still the load. Little of that has changed as it is still the basics. If the proper design is not paid proper attention to on the front end prior to installation, the price paid down the road after start up will average fourfold to correct the situation.

    And with that said I have completed my humble offerings to this thread.
    tom

  5. #44
    Join Date
    Mar 2004
    Location
    NJ
    Posts
    1,214
    I agree with you that the heat load from the equipment will remain constant yet the heat load of the room will be less due to the lack of a solar heat gain and less overall in the winter due to the reduced amount of sunlight in that season and less on colder days as the heat will transfer quicker from the room to the exposed exterior walls. Also in table A4-1 of Manual J 7th edition for Miami(Ft Lauderdale is not listed) you have a total of 21.8 days below 60 degrees(which is really when that valve would really be needed because of low ambient) which comes out to be 6% not 1 % so I was off slightly there. Besides all that engineering b.s. it is experience. I started my career in Hvac in South Florida and worked there a total of 12 years and never once came across this valve on a residential
    or commercial airconditioning split system 5 tons or under. As well if he is installing a Trane it has a low pressure cutoff switch if the unit starts to ice up. But for 6% of the time it would be nice to have,maybe throw in solenoid valves and a pressure cutoff, defrost timer, and electric defrost while we are at it and electric heat defrost as well.
    I guess I am just a little gun shy about over engineering especially when the bozos who come up with these theories(including parts of Manual J) are far removed from real world applications and what has to be done.

    But it would certainly be a nice extra or tech commission for someone like Service Experts to tack on an extra $500 for installing.
    thehumid1-------I live in NJ, a state where it's free to come in but you have to pay to leave!

  6. #45
    Join Date
    Nov 2004
    Location
    Hollywood, FL
    Posts
    365
    for an extra $500 I would defenitly ask for it. I will speak to the instalation guys and see what he says about adding a head pressure control. As I said before, this unit does come with a thermal expansion valve already, and adding a head pressure control would be nice and $500 is reasonable to me especially if I tell my boss it will prevent the system from freezing up

  7. #46
    Join Date
    Mar 2004
    Location
    NJ
    Posts
    1,214
    I was being sarcastic about the price to make a point. It should be much less than that to have it installed only crooks in tech uniforms would charge that kind of price for it and I will leave it at that as pricing is not allowed to be discussed here.
    thehumid1-------I live in NJ, a state where it's free to come in but you have to pay to leave!

  8. #47
    Join Date
    Sep 2002
    Posts
    1,389

    serverroomcooling

    An acceptible retrofit for head pressure control would be:

    Johnson #P66 with a new condenser fan motor to replace the new existing one.
    Motor: ball bearing, totally enclosed, 60C, same horsepower, direct replacement.
    This replacement motor should be a shelf stock item at most wholesale supply houses your contractor would be frequenting and will last for quite some time.
    Good luck,
    tom

  9. #48
    Join Date
    Mar 2004
    Location
    NJ
    Posts
    1,214

    Re: serverroomcooling

    Originally posted by twcpipes
    An acceptible retrofit for head pressure control would be:

    Johnson #P66 with a new condenser fan motor to replace the new existing one.
    Motor: ball bearing, totally enclosed, 60C, same horsepower, direct replacement.
    This replacement motor should be a shelf stock item at most wholesale supply houses your contractor would be frequenting and will last for quite some time.
    Good luck,
    tom
    Just wondering why do all that when a hot gas bypass valve and reciever would be much more effective and probably as cost effective as swapping out a fan motor:
    Turning off a condenser fan stops airflow through the condenser, but the condenser is still left as a fully effective heat exchanger. If a wind blows through the condenser, it can be as effective a condenser as if the fan was running. Fan cycling also causes sudden large changes in head pressure that has an adverse effect on the TXV. Fan cycling is the most common method of head pressure control because it is the cheapest method. The best low ambient head pressure control method is to flood the condenser with liquid refrigerant. This is the only method that effectively makes the condenser inactive.

    Also why reccommend that one there are other fan control kits that can be used that do not require changing the fan motor as well. Do you work for Johnson controls?

    [Edited by thehumid1 on 12-07-2004 at 12:11 PM]
    thehumid1-------I live in NJ, a state where it's free to come in but you have to pay to leave!

  10. #49
    Join Date
    Sep 2002
    Posts
    1,389

    thehumid1

    I guess you'll just have to stay with me on this:

    First of all, no I don't work for Johnson Controls. I am a commercial/industrial mechanical contractor specializing in cleanrooms, data centers, laboratories, and surgical facilities in the Los Angeles/Orange County area.

    The P66 does not turn the condenser fan on and off but creates a variable speed motor/control operated at head pressure setpoint. (And believe it or not, the wind does not blow all the time.)
    Hot gas bypass only works when the head pressure is up. See Sporlan data for tonnage vs. PD vs. line size vs. evaporator conditions for that.
    A receiver is not cost effective as I see no reason for one on this application as long as the condenser is large enough to hold a subcooled charge throughout the whole season. A hi-efficiency condenser will acommodate that.

    Since this is a fairly basic 105/40F application, I don't see why you wish to continually, post after post, keep bringing up remedial actions that fit more an 85/5F application.

    The above owner can do what he wants, I only suggest things I have successfully used for 40 years. But then again there are other ways and maybe you can explore them with him.

  11. #50
    Join Date
    Mar 2004
    Location
    NJ
    Posts
    1,214
    I can't help but respond to a few of your comments:

    1) I am a commercial/industrial mechanical contractor specializing in cleanrooms, data centers, laboratories, and surgical facilities in the Los Angeles/Orange County area.
    I only suggest things I have successfully used for 40 years.

    So you are suggesting what works in Los Angeles not Florida.

    As I already stated: I started my career in Hvac in South Florida and worked there a total of 12 years and never once came across this valve on a residential
    or commercial airconditioning split system 5 tons or under. Why is that? Could all these contractors in South Florida be making a such a big mistake?

    2)(And believe it or not, the wind does not blow all the time.)
    Quite scientific (especially in South Florida Hurricane central but at least that control will work those times the wind is not blowing).

    3)"Hot gas bypass only works when the head pressure is up. See Sporlan data for tonnage vs. PD vs. line size vs. evaporator conditions for that.
    Since this is a fairly basic 105/40F application, I don't see why you wish to continually, post after post, keep bringing up remedial actions that fit more an 85/5F application. "
    First of all the valve should always selected for tonnage. I am not thinking of a Sporlan Valve either but a Climatic Control Inc valve that they sell not sure who the mfr is or if they are but the valves are made specifically for a 105/45 degree application where it the valve begins to open at 63 psig and is fully open at 55 psig.


    But again in South Florida I would not waste my time putting either a fan control or a bypass valve because it is overkill and not needed that is why I have never seen it used there.

    I think this customer should ask his contractor who seems very knowledgeable and see what he thinks he will probably say the same as me. He has gotten other bids too and no one mentioned this to him as well. Guess us rednecks just don't crap and should stick to gator hunting. Thanks for teaching us "How ya all do things in L.A.!"

    This is what I found direct from Sporlan where if you read it you will see they recommend the valve as an economical means to achieve system capacity control in an airconditioning systems.

    Also Danfoss offers the RGE condensor control which can be used with any fan motor which would be a even cheaper way to do it than the Johnson control but again pointless for the geographical location of this customer.



    SYSTEM CAPACITY CONTROL

    On many air conditioning and refrigeration systems it
    is desirable to limit the minimum evaporating pressure
    during periods of low load either to prevent coil
    icing or to avoid operating the compressor at a lower
    suction pressure than it was designed to operate.
    Various methods have been used to achieve this result
    — integral cylinder unloading, gas engines with variable
    speed control, or multiple smaller systems.
    Compressor cylinder unloading is used extensively on
    larger systems but is too costly on small equipment,
    usually 10 hp and below. Cycling the compressor with
    a low pressure cutout control is a method often used
    but is being re-evaluated for three reasons.
    1. On-off control on air conditioning systems is
    uncomfortable and does a poor job of humidity
    and mold control.
    2. Compressor cycling reduces equipment life.
    3. In most cases, compressor cycling is not economical
    because of peak load demand charges.
    One method that offers a practical and economical solution
    to the problem, is to bypass a portion of the hot discharge
    gas directly into the low side. This is done by a
    modulating control valve — commonly called a
    Discharge Bypass Valve (DBV). This valve, which opens
    on a decrease in suction pressure, can be set to automatically
    maintain a desired minimum evaporating
    pressure regardless of the decrease in evaporator load.
    Sporlan manufactures a complete line of Discharge
    Bypass Valves including non-adjustable models, for specific
    customer requirements. Contact your Sporlan representative
    for assistance with special needs.
    APPLICATION
    Sporlan Discharge Bypass Valves provide an economical
    method of compressor capacity control in place of
    cylinder unloaders or the handling of unloading
    requirements below the last step of cylinder unloading.
    On air conditioning systems, the minimum allowable
    evaporating temperature that will avoid coil icing
    depends on evaporator design and the amount of air
    passing over the coil. The refrigerant temperature
    may be below 32°F, but coil icing will not usually occur
    with high air velocities since the external surface temperature
    of the tube will be above 32°F. For most air
    conditioning systems the minimum evaporating temperature
    is 20°F to 25°F. However, when air velocities
    are reduced considerably, the minimum evaporating
    temperature should be 26°F to 28°F.
    Sporlan Discharge Bypass Valves can be set so they
    start to open at an evaporating pressure equivalent to
    32°F saturation temperature. Therefore, they would be
    at their rated capacity at 26°F evaporating temperature.
    On refrigeration systems, discharge bypass valves are
    used to prevent the suction pressure from going below
    the minimum value recommended by the compressor
    manufacturer.

    [Edited by thehumid1 on 12-07-2004 at 03:03 PM]
    thehumid1-------I live in NJ, a state where it's free to come in but you have to pay to leave!

  12. #51
    Join Date
    May 2004
    Location
    Los Angeles, CA
    Posts
    1,560

    STOP!!!!!!!!!!!!!!

    Serveroomcooling,

    I just took the last 30 minutes to read the original question you posted, and all the subsequent posts from my colleagues that followed. First of all……stop!

    After 30 years in the trade as a field technician, certified mechanical engineer, and contractor I can say without fail a project always starts with a heat load calculation to determine the heat being generated in the given zone. The BTU’s, watts, and tonnages being thrown around on this thread remind me of a man that wants to know just enough to get himself into real trouble.

    Several of my colleagues have already stated you should not design this project from this forum. We all can sympathize with your plight of trying to find a knowledgeable, reputable, and honest contractor to perform the specialized work obviously required for this project. I know my counterparts are just trying to help you decide which contractor you should choose to complete this project, but…………we can’t! Your asking a group of surgeons how you should perform a lung transplant over the internet. The answer is….you can’t. An example of this problem rests in the very beginning of this thread, the unit required to perform the task. A simple question that has had several incorrect answers given based upon incomplete information provided. You originally stated your load was 12,000 watts plus 2,800 BTU. The heat load for this equipment is 43,744 BTU/Hr. sensible. All standard HVAC units with anywhere between 400 and 500 CFM/per ton will only put out approximately 69 to 73% sensible heat from their total BTU capacity, therefore, your equipment load alone is approximately 61,242 BTU/Hr or 5.10 tons. Now wait……..before you start looking at a five ton system to fulfill your cooling needs we have yet to add the lighting and structural load to your overall cooling requirements. Just now we can see you need a system larger than five tons, but wait again……there are more factors such as what about a package unit located on the roof of your seven story building so that an economizer might be utilized during cooler weather or when the cooling cycle goes out, what are you going to do about filtration or unit short cycling when you have over 150 air changes per hour based upon only a five ton system, standard office air changes are 6 – 8 per hour.

    Lastly, the three contractors you have already had out have not shown to me, and I’m sure many of my colleagues their ability to design, install, or maintain a system that you need for this project. I would suggest you first ask the next contractor thru your front door for his written heat load calculations outlining all cooling requirements, equipment, lighting, and structural loads, sensible and latent loads for your project and if they say they do it in their head or they just figure based upon square foot, or by rule of thumb, you give them the thumbs down instead.

    Hope this is received in the spirit that it was written.

    John J. Dalton

    PS: For my colleague that said he had never seen a condensing speed control in any five ton residential or commercial unit in the eleven years he was in Florida I ask this question. How many of these residential or commercial units ran 24 hours a day, 7 days a week, 365/6 days a year even when it was cold and raining outside????Some sort of condensing speed or flooding will be require on this project, remember the client can’t afford to be down even on the occasional cold day. Thank you!

  13. #52
    Join Date
    Nov 2004
    Location
    Hollywood, FL
    Posts
    365
    I learned a tremendous amount from this thread. I did not make any decisions based on this thread....I got things clear in my head enough that my building agreed to pay for a 3 ton unit. I decided to go with the contactor who did provide a heat load test that he placed in an hvac application. I have the fild and opened it in the hvac application that created it (it is available on the Internet) It was chinese to me but I did see all the numbers and calcs there.

    Do I know what to do? No, but I feel I can trust him to get the unit in and stand by it. He instsits that the unit he is installing can handle 24 hour operation in all weather with no problems, and if he is wrong, I trust that he will stand by his work and fit us with a better (more expensive) system. If it were up to me I would have put in the 5 ton system by APC as those contractors dead with server rooms. Sometimes in my position I only get what I need when things go wrong. I wanted a very large room, but lost that argument so I got stuck with this tiny room that heats up way too fast.

    I will keep my portable spot coolers for the first 2 weeks of operation, and if things go sour I can turn them on and be ok. Worse case, I can always rent them with 24 hour notice, sometimes faster.

    I thank everyone for the help. I gained a lot, but I do agree that things may have gotten a bit out of control. I'm just a computer guy who needed enough information so my building, who agreed to provide an air conditioning system without even specing it out first, did not get away with stiffing us on an appropriate size unit.

    I'll let you guys know how it goes, and thanks again to everyone. I know that I'm not installing the best system for my room. I just hope it is adequate enough for a couple years.

Page 4 of 99 FirstFirst 12345678910111454 ... LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event