ReplyWhy control it with a pressure switch? Most of the time its used to control evaporated temp based on load. A hot gas bypass open all the time would severely lower capacity.
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i service a SS water chiller and all summer long they have be saying that the water temps have been a bit higher than normal. i figured it was due to the extreme heat in the midwest
today i looked things over and noticed that there is no control for the hot gas solinoid it just on all the time. there is a bypass regulator on this machine. so its not so bad but i thought thats kind of a waste of btu's
getting to my question, can i control this solinoid with a pressure switch? or was it designed to bleed HG into the evap for a reason...
when bypass is not needed the hot gas in the line may condense and then i have a water hammer effect on the line...?
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Why control it with a pressure switch? Most of the time its used to control evaporated temp based on load. A hot gas bypass open all the time would severely lower capacity.
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the hot gas bypass valve should only be opened when the evaporator/suction pressure drop below the acceptable limit (application dependant but usually used to keep the pressure above freezing but not always)). the solenoid valve is used to isolate the hot gas line during pump down. hot gas line sizing and regulator/valve sizing and placement are very important things to consider if you want it to work properly.
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Don't step on my favorite part of the Constitution just to point out your favorite part.
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There has to be something to energize the solenoid ... Look at the electrical schematic .
If it's energized all the time then I would expect to see some type of adjustable regulator.
In other words the controller may energize as needed for capacity control or may energize in a run condition and a regulator takes over .
Hot gas is NOT normally used for suction pressure control ...it is generally for unloading IE capacity control ....yes there are other uses but I am responding based on my interpretation of your post
Regular Guest
what he said +1Originally Posted by jdblack
Professional Member*
Typical HGBP operation has the solenoid on at all times. From a Liebert Crac unit to a Carrier Chiller.
Thst solenoid needs to be closed only on pump down.
It should have a hot gas pressure regulator down stream of the solenoid valve.
For typical comfort cooling applications its set to start openining and put a false load on the evaporater. Its just a capacity control.
For R22 you would want to set it for 58 psi and 410A set for 102 psi.
If its adding Hot gas to your evaporater check the setting on the valve or confirm your'e not low on gas or have a restriction on that circuit.....or both..
Professional Member*
Trane runs the HGBP thru a control solinoid and a pressure regualator allen keyed,or hat adjusting nut.then at 55PSI for 22 is should start to bleed discharge into the evap to keep the machine on..basically your nearing setpoint shut dow.the hgbp keeps the machine on till the actual load increases is the regulator mounted with the solinoid.basicly HGBP should be active only on staging down cause setpoint is being reached
"when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY
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You May As Well Check The Solenoid Valve Mechanical Mechanism, Because Sometimes The Electric Coil May Be Good, But The Valve Won''t Work.
Regular Guest
Normally a hot gas bypass is used for compressor capacity control when unloading is not available, or hot gas bypass is used with a compressor which has capacity control and its last step of unloading does not accurately control evaporator pressure.
A hot gas bypass such as a Sporlan ADRHE-6 is factory set to begin to open @ 60 PSIG. As the the saturation temperature drops below this setting the valve will modulate to open, and would be at its rated capacity @28 degrees saturation temperature or 52 PSIG. This equates to approximately 8 PSI from the point of fully closed to its rated capacity or fully open.
It will normally be up to the person who sets up the control to establish a good set point but in any case should not be set below 32 degrees saturation temperature...
In any case it is normally required that some sort of control such as a solenoid valve be in line before the hot gas bypass. Depending on the unit requirements and control strategy that is necessary to obtain a pump down effect at start up or pump out at end of cycle.
As for trouble shooting the system this can be done very easily by closing the hot gas valve 100% so that actual operating conditions can be established. By doing this you will see how the unit is really performing. Actual operating pressures will be visible and you can identify problems such as low charge, superheat settings, obstructions in liquid filter/driers and so forth.
After this the valve is reset to what ever position you feel is correct. 59 PSI as an example.
This is just the minimum to consider. The application and design of piping is also very important, in addition to oil return, and overheating.
Hope this helps
_______________
Understand the symptoms and you will find a solution.
Regular Guest
That's the right concept.
Professional Member
those are all great responses,
first of all this is a retrofit newer condenser on an old evap and old controls
the hg solinoid is energized at the same time as the LL solinoid so it is hot gas all the time but i uses the regulator as a load control.
they make bread so on some days they use more ice water than other days (more or less mixers) so when all the mixers are on the load is high and the relulator is only alowing a small amout of HG to pass. on other days there are less mixers so more HG is needed.
there is an estimated 200 feet from condenser to evap. the HG solinoid is @ the evap. my question is : if i control that solinoid with a pressure switch. on days that the HG is not really needed will there be 200 feet of condesed HG liquid that will slug and hammer the pipe as the solinoid opens and closes?
im sure i am over thinking this but i want to be sure.
thanx for all the replys
Professional Member*
Your hot gas is probably not so hot after 200ft of pipe
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Professional Member*
With most of the mixers running there should be no bypass taking place, I would think. If you have most or all the mixers up and running and are still bypassing red flags should be going up. If this is the case disconnect the HGB solenoid with all or most mixers running, heavy load, and check you pressures. If below 58 on R22 start looking for that problem, fouled tubes, low charge, bad HGB regulator, etc. I would not change control of solenoid leave it energized with the LLS. IMHO.
Professional Member*
Correction if suction pressure is above 58 with solenoid disconnected then check your HGB regulator. Should only bypass when suction drops below pilot setting, usually around 58 on R22. With heavy or full load suction should be well above that and no bypass should take place.
Professional Member*
That solenoid and HGBP pass should be on the Condensor side not at the evaporator.
All you're going to get is hot gas up to the solenoid valve and then suction at the leaving side of the HGBP regulator.
Professional Member
like i said, HGBV sizing and placement are very important...how is the insulation (not that it really matters now)?
is the evap below or above the condenser? i don't remember reading that.
"Right" is not the same as "Wise".
Don't step on my favorite part of the Constitution just to point out your favorite part.
Just because you can measure it, doesn't mean it is important. Just because you can't measure it, doesn't mean it isn't important.
Regular Guest
Are you saying that you have an an air cooled condenser with a remote DX evaporator/ water cooler with a line set of 200 ft. If this is the case than there are many other thing to consider.
But first the load criteria needs to be established so that a properly designed system can be designed. This is more involved, than just simply replacing a condensing unit with the same Horse power or tonnage. The biggest issue which you will have is that there will be a pressure drop in your liquid line per every 100 feet of total developed length which must be calculated so as to properly maintain your sub-cooling in the liquid line and up to the TXV or metering device. You will need to consider raising your sub-cooling to at least 15 degrees to overcome the pressure loss in the system. This will be a major concern and if not address will lead to issues with improperly feeding the metering device. Remember that a TXV needs Liquid to meter refrigerant correctly, and with a loss in sub-cooling you are sure to have flash gas in the line and at the TXV. This is a topic which needs to be addressed all by it self.
The liquid line will need to be sized correctly but not over sized to the point where you will loose the velocity of refrigerant. Remember that oil must be returned to the compressor at an equal rate which will require a velocity of no less than 240 FPM and not more than 400 FPM. You will need to verify velocity for your application.
As for the hot gas by-pass which is installed with a Tee connection at the discharge line close to the compressor. It is also important that this line be sized correctly so as to maintain velocity. As for the connection to the evaporator it is usually connected with a distributor with a side inlet after the TXV. This is the most practical as the higher temperature in the evaporator will cause the TXV to open and de-superheat. It will be important to install the Hot gas solenoid at the evaporator so as to prevent a lower pressure in the developed length of pipe which will have a saturation temperature of usually around 34 degrees or less when at low capacity. Insulation is recommended for this reason.
There are also times where you can install at outlet of evaporator and is some times used for certain applications.
Sizing of the suction line is also very important and will need to be considered again to maintain minimum and maximum velocity of refrigerant for proper oil return.
Location of evaporator also needs to be considered depending if it is located above or below condenser. Trapping of oil needs to be considered for vertical lift and sometimes requires the installation of a double suction riser. Which leads to the question of circuits in the system.
This is a topic where there is not enough room to talk about here. But just some elementary things to consider.
I will try to upload a piping sizing chart soon for your use.
________________________________________
Understand the symptoms and you will find a solution
Professional Member
this is not a good idea...the HGBP valve and solenoid should be mounted at the condensing unit. this minimizes the charge at all load levels. at 200 feet, other piping precautions need to be considered as well.
"Right" is not the same as "Wise".
Don't step on my favorite part of the Constitution just to point out your favorite part.
Just because you can measure it, doesn't mean it is important. Just because you can't measure it, doesn't mean it isn't important.
Regular Guest
You are absolutely right Jayguy
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