Glycol Chiller

[NH3ISFORME]

I work alone in a refrigerated warehouse and still am new to the trade. We have 26 banana rooms supplied with chilled glycol from a ammonia chiller. the pump supplies glycol down to supply lines which feed each room down the two lines 13 on each supply line. i have two rooms that won't pull temp at the end of one run. my question is this how do i lower the temp of the glycol? pull a lower suction is what i think i need to do. or do i make a adjustment to the backpressure regulator. or do i adjust the hand expansion valve for the high pressure liquid that supplies the chiller.

[Andy]

Hello NH3ISFORME
you could lower the glycol leaving set point (temperature on the chiller) but I suspect the problem may be poor supply of the glycol to the end of runs. This would be down to pressure drop and the pumps not overcoming this. Either the pumps have been designed to the correct head, but not the correct flow or the wrong head (too low design pressure).

What about the strainers on the valve station are they clean

Has the system been balanced? If you are allowing the glycol to take the path of least resistance, you won't have any flow at the ends of you runs.

Kind Regards Andy D

[MJS]

Lots of variables, If youre ripening its a lot more critical than if just holding. Might be able to fudge the glycol temp on a holding only coolers.
If ripening, you either you need a little more impeller or a little more HP or both to use existing piping set up, and maintain glycol temp.

Id shut down the rooms next to the end first and see if the glycol flow is adequate at the end rooms first. That way you will know if it is a flow or a head problem.

Watch your step

[mbc]

1- might your pump head and flow is not right
2- might you have air in your system = remove it by opening vent valve

[NH3ISFORME]

Yeah, purged air off both supply lines and got a minute of air with the ball valve half open. That's definately not right. The expansion tank at the chiller has a sight glass that is completely full not sure about that consulting with some engineers. Checked pressure at various points of the system where glycol feed evaps are and pretty much got 10 pisg with the pump pressure at 39 psig and 35 foot of rise. We'll see.

[NH3ISFORME]

Oh yeah, plus BG balancing valves are at 100 percent and there are NO strainers in this system.

[nike123]

Oh yeah, plus BG balancing valves are at 100 percent and there are NO strainers in this system.

It looks like unbalanced system.
How is temperature of each room regulated. Is it by 3way diverting valve or some other method?

[NH3ISFORME]

three way valve modulated by johnson controls 4-20ma controler

[Magoo]

Can you describe the control on 3 way vavs, some have flow restrictors which act as a balancing device.
Another possible problem is that the supply is not up to the required duty ie glycol pump.
magoo

[NH3ISFORME]

three ways act as mixing valves as they are modulated for each coil 5%-100% open and BG balancing valves are used as restrictors to slow flow through coils for beter heat transfer or greater delta t. I dropped the chiller down 1 deg F and adjusted the BG down 30% seems better now. on the troubled room. Need to replace auto air valve cause they look like crap and don't work. Also someone had auto air valve on two of the highest points in the system, when they (the two points) are operated amnually they suck in air. I think I'm just going to plug them.

[mbc]

((they (the two points) are operated amnually they suck in air)) you put . So :
might it is in suction line . if I am right turn off pump then let air goes out . also check water level and valve of between them

[Magoo]

Sounds strange that you have a negitive pressure at highest points, does system have static header tank / make-up tank/expansion tank?. Should have one some where. Normal at the highest point.
If you have negitive pressures at highest point would generally indicate a lack of supply as negitive static return creates a negitive press result/ gravity effect on return.

magoo

[NH3ISFORME]

yes there is a expansion tank. However, the sight glass is full. I don't think this is correct.

[nike123]

Depending on pump location and restrictions in system it is possible to have negative pressure. If that is the case, you probably have low static pressure in glycol system. Static pressure in system should be high enough so that all points are above 1 bar absolute pressure when system works. That is achieved with correct dimensioning of expansion tank, its precharge pressure and safety valve opening pressure. Also, if fited, automatic make up should be adjusted for right pressures.

What is height difference between expansion tank and highest point in system?
What is height difference between place where glycol pressure is measured and highest point?
What is height difference from pump to highest point?
What is pressure of glycol at point of measurement when pump is stopped?
Is pump at lowest point of loop?
What is pump make and model #?
What is glycol percentage?

[mad fridgie]

Just to make things clear, one single pump head (supply line), return is it gravity, suction pump or pressure from pump head? (this is required for solution) Controls are diverting not mixing?
Simply your problem is insufficient pressure difference on the end runs. Maximum pressure drop on each leg = lowest pressure differential
Your pressure drop across the coil and control valving is to high,
Droping temp may seem to help, but this could effect humidity in rooms (lower)
A small dedicated pump on each of the last coils could be a simple solution,
Not sure what BG valves are (BG =?)