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Height vs SubCooling vs Freon Charge

KindaSorta ,On a 90* day , how much SC do I need for each 10' (per floor) of rise? . Is there a chart for knowing how much liquid Freon "backs up "in the cond coil, as the vertical rise goes beyond the Factory lineset length of 15' by todays standard,and 25' by yesteryears standard. At the moment I don't know how much extra Freon to put into a system to compensate for the increase of SC along w/ an increase in the # of passes of tubing in the cond coil that fill up w/ liquid Freon.. So, this is why I charge a system to a full LL at the TXV , and then I get to see what SC comes w/ a full charge.I think. Name plate SC is not for every job ,I think.


  • meplumber
    meplumber Member Posts: 678
    Nameplate SC

    Great point.

    Nameplate SC is a range that applies under a certain "normal" set of installation conditions.  It won't work in every situation.  Most of the US manufacturers factor a maximum of 15'-20' lift in the SC range.  If you exceed the factored lift, then you have to make a field correction to the SC target.  By applying the 1/2 PSI rule, you can trim your charge accordingly.
  • Paul S_3
    Paul S_3 Member Posts: 1,257
    how does

    The 1/2 psi rule work? Thanks Paul s
    ASM Mechanical Company
    Located in Staten Island NY
    Servicing all 5 boroughs of NYC.
    [email protected]
  • Techman
    Techman Member Posts: 2,144
    edited July 2014
    H vs SC vs FC

    What is SC? What is it used for? Why do we care about SC ? When should we be concerned about SC? Why are SC #'s  being stamped on unit nametag's more and more these days? Who cares about SC in the first place? Who has ever played with SC?

    Electricity - do you use a voltmeter to verify to see WHAT the voltage is ( 208-230- 212- 240-246- - - - - ) ?

    TXV  -  do you check to VERIFY that the TXV  is indeed getting a full boat of refrigerant ? And it ain't being done out there by the cond unit. Other than units inside of the Mfrg's lineset rules.!
  • icesailor
    icesailor Member Posts: 7,265
    Two Hundred and eight points:

    The isolated place I worked only had 208 volt 3-phase, 220/240 volt single phase. I can't remember how much equipment I say that was ordered as single phase, because no sales person asked or checked if the building had a 208 3-phase service in the building and sent 240 volt single phase equipment. Then, when you had high power use and voltage drops, you could have appliances (dishwashers, electric water heaters) running in 185 volts.

    Kept that water heater recovery on the low side and electric motors running REALLY hot.

    They don't call the electrician when they are running out of hot water. Usually.

    Its not all that difficult to go outside and count the wires on the service drop. 3 wires and it's probably single phase. 4 and it is probably 3 phase. But you still need to check. Ask me how I know.
  • Spence
    Spence Member Posts: 316
    Sub Cooling

    SC has to be measured at the outdoor unit, since it is part of the condensing process. SC ensures the condenser outlet is full of liquid refrigerant. Proper sizing and installation of the liquid line ensures that only liquid is available at the TXV inlet.
  • Techman
    Techman Member Posts: 2,144

    Being a stickler here. SC is a process AFTER the condensing process has STOPPED condensing. SC is to insure a full LL at the TXV ,not at the CondUnit. A full LL @ the cond unit DOES NOT insure/guarrante the the LL is still full at the TXV . So another system is undercharged if you are relying on the SGMI at the cond unit, this is on systems with more than 15' of vertical rise of LL.
  • icesailor
    icesailor Member Posts: 7,265
    A question:

    You all use the term "Lift". That usually means in the world of pumps. that you are "lifting" the liquid UP by suction. If the compressor is at ground level, the compressor is a pump. Therefore, the liquid being raised to a level or "head" is actually being pushed UP to that point.

    So, the question I ask is, don't the same rules for pumping hot water in a heating system apply in pumping refrigerant? That if you pump UP to a head level that is too high, won't you get gas expansion from a liquid if you go high enough that the available pressure can't keep the liquid from boiling? Wouldn't that phase change cause a loss in available heating/cooling BTU's? If the only thing you want to go into the expansion valve is liquid, isn't it a bad idea to have gas bubbles mixed in the liquid too?

    Just asking. I don't know.
  • Techman
    Techman Member Posts: 2,144

    you are correct.You sound like a ReferHead!!!! As the height rises, the 1/2psi press drop rule causes a press drop. So, on a vertical LL that goes up 30' there will be a 15 psi press drop at the top of the riser . Now ,heres the tricky part , that 15psi press drop causes a drop in TEMPERATURE at the sametime.
  • icesailor
    icesailor Member Posts: 7,265
    High Altitude Cooling:

    Because of the loss of the heat from compression?

    As in, if I take my air tank and blow it up to 100# and let the tank cool to room temperature, and release the air and measure the temperature and measure the coldest temperature, then refill the tank to 50# and repeat the exercise, is the air colder leaving at 100# than it is at 50#? Yes. It is colder. More heat from compression at 100#. Like that?
  • icesailor
    icesailor Member Posts: 7,265
    Here's one for you:

    Here's one for you that occurred to me yesterday. Along similar lines.

    It has to do with Submarines. Which are just great big floating air pumps with an engine to push it along. Submarines store thousands of cubic feet of highly compressed air. Under enough pressure to blow water under pressure out of the ballast tanks at the deepest depth they can go to. As they dive deeper, the water in the ballast tanks is compressed by the outside water, causing the ballast water to take up a smaller space. Loosing buoyancy.  So they need to move high pressure air to maintain trim and buoyancy. If they start to rise to the surface, the compressed air in the buoyancy tanks starts to expand and the buoyancy increases. So, what do they do? Quietly suck the compressed air out of the tanks and save the compressed air? Floating bubbles on the surface could be hazardous to the health of the boat and crew.
  • meplumber
    meplumber Member Posts: 678
    edited July 2014

    The compressor is a pump.  My dad and grandad called it the pump.

    For example.  We installed and I still service a Liebert XD system with RPU's.  This is a pumped refrigerant system.  There are no compressors in the system so to speak.  Refrigerant moves around the system via (2) special Grundfos pumps.  The refer is kept just above the dew point because moisture in Data Centers is the Cardinal Sin and this is a major data center.

    Aside from the lack of a compressor, it is the same basic principle.  Refrigerant is cycled through the system where it hits an expansion device where the rapid pressure drop causes the refrigerant to rapidly cool and begin to change state.  As it moves through the coil, it absorbs heat from the server racks and becomes a gas.  A great example of how a compressor is just a pump.

    In this system, we use chilled water as a condenser, but there are other options.
  • Techman
    Techman Member Posts: 2,144
    edited August 2014
    Refrig stuff

    ice, the PD comes from flow resistances ,just like hydronics, . The heat of compression is just one of the SuperHeats that the freon picks up on its way thru the comp, and out thru the discharge line, then desuperheating then condensing then SC ,then too muck PD in the LL and there will be "flashgas" and less cooling.

    Ice, funny you should mention a Submarines hi press air tanks. On my sub we had 3000 psi air , it was one of my duty functions to open certain valves ,to let in a certain ammount of hi press air, for a certain time peroid ,to raise the sub on a certain angle or on an even keel. Or not, depending on how much trouble I wanted to get into . LOL
  • icesailor
    icesailor Member Posts: 7,265
    edited July 2014

    I should have known that someone here was a sub person. You guys are the smartest guys in the Navy. Especially the fully qualified sub guys.

    Back many moons ago, I picked up a tidbit from The Wall where someone had done a radiant floor job in a new factory building for a wood working shop. People were getting shocks from the wire mesh and the HW conduit A few Sub Guys chimed in with the unbalanced 3 phase service being only a single phase temporary service and the other phases were trying to balance out. That on subs, everything is 3 phase and if you don't keep all the phases in balance, you can burn a hole through the boat. I used to re-tell that pearl of wisdom to the Power Company when I got complaints from customers getting shocked on their outside showers. And that a piece of rubber hose on the handles wasn't a suitable solution. They needed to balance their 3 phase loads. You never know who says what and who will remember something on The Wall.

    Did you ever read "Blind Man's Bluff: about Subs in the cold war by Sherry Sontag & Christopher Drew? That's the book that let everyone know about that you could never tell your wife and family about. There's a story about the book. A retired Chief from subs read it and handed it to his wife to read. She read it. She looked at him with tears in her eyes and asked "Is this what you did"? He just looked at her and never said a word.

    Where I lived and worked, there was one of those SOSUS stations. The part with the two 50 ton AC units and the fence with barbed wire always had a lot of submariners stationed there. It was considered "Shore Duty". People don't think The Bay of Pigs wasn't a big deal? Why did they have armed guards with rifles and dogs walking the perimeter? When the Thresher and the Scorpion went down, there was a lot of anguish. The Thresher went down offshore and they probably heard the whole thing. They might have heard the Scorpion but that is still denied.


    If you like to read, check this one out. That boat was a swimming garbage truck. It had refrigeration leaks that were so bad, they had to carry extra Freon tanks just to keep up with it. There are other books out there that are all for the conspiracy buffs. IMO, they are BS. Once you read what a POS the boat was, you KNOW why it went down. This guy doesn't buy any of it and is a reporter who spent a lot of his life just researching it.