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Glycol - Adding to chiller loop

SUMMARY
This article describes the steps that should be taken to add glycol to a chiller system. The article addresses some important things that must be considered in this process.

SYMPTOMS
There are many applications where a chillers process loop has the possibility of freezing by way of (direct or indirect) contact with cold ambient air temperatures or the process requirement of a chiller requires colder temperatures. This article addresses items that must be considered when adding glycol to a process chiller.

All chillers shipped by Legacy Chiller Systems are set up from the factory to run water only. This is done by design even if the customer supplied specifications call for process temperatures that WILL require glycol freeze protection to be added. The reason for setting chiller up this way is to prevent potential freeze damage to the equipment prior to glycol installation in the field.

Should a chiller require glycol freeze protection, adjustments may need to be made to several key components of the chiller to for trouble free operation.

CAUSE
Failure to make adjustments to a chillers refrigeration and control system for glycol operation can cause the following operational issues:

1. Poor cooling output
2. Low pressure (Lo1) safety trips
3. Process high temperature (HTA)alarms
4. Low flow safety trips

RESOLUTION
The following steps should be followed when adding glycol to a Legacy chiller:

1.Determine total system volume: For tank model chillers, (PACT,PWCT and EST models) volume is stated in the appropriate catalog sections. In addition to volume in the chiller, field calculations should be made to determine volumes in all external piping, fittings and the process equipment being cooled by the chiller.

2.Determine glycol concentration: Once total system volume is estimated, a target fluid loop freeze point must be determined. This is done by using a glycol freeze table, provided by the glycol manufacture. Attached, to this article generic tables have been provided. NOTE: NOT ALL GLYCOL MANUFACTURES HAVE THE SAME FREEZE POINTS. Once the desired freeze point is determined, use this simple formula to determine the amount of glycol needed: Glycol gallons = (total system volume) x (glycol concentration % needed to achieve desired freeze point). Example: Total system volume 200 of gallons. You need a 50% concentration of food grade propylene glycol to achieve 30F a freeze point. Result: 200 x .50 = 100 gallons of glycol. Note: When determining your desired freeze point, it is important to remember that the refrigerant temperature in the chillers evaporator can be as much as 20F colder than your SP1 set point. Because of this, it is recommended that enough glycol be added to prevent freezing or restricted flow as fluid reaches the outlet of the evaporator. For example: If your SP1 set point is 20F, your glycol concentration should be high enough to achieve a 0F freeze point.

3.Confirming freeze point: After adding the estimated amount of glycol to the system, the actual freeze point MUST be confirmed using an optical refractometer. ONLY when the freeze point is confirmed should the technician proceed with the following steps. NOTE(1): NEVER ADD GLYCOL UNTIL ALL AIR IS REMOVED FROM THE SYSTEM. ALWAYS ALLOW GLCOL TO MIX IN SYSTEM FOR 15-30 MINUTES BEFORE TAKING LOOP FREEZE POINT READINGS. Note(2): Hoffman #79 automatic air vents are recommend on the supply and return main heaters at the highest points in the system to remove air from the process loop.

4.With the all air out of your system, glycol mixed and freeze point confirmed the following adjustments can be made:

A.Set microprocessor LP trip: The factory pre-set for the LP trip is 54PSI (R22). Now that your freeze point is lower after adding glycol you should adjust this set point using the following formula: LP set = (confirmed freeze point) + (10F safety factor) converted to PSIG. Example: Freeze point is 30F on an R-22 system. Result: (-30F)+(10F) = -20F. 20F R22 = 10PSIG. In this case the LP trip point on the microprocessor should not be set lower than 10 PSIG. Attached to this article temperature / pressure relationship charts have been provided.

B.Adjust hotgas bypass (HGBP) system: All Legacy Chiller Systems are equipped with (HGBP). Under low-load, low ambient, low SP temperature setting conditions this valve may need to be adjusted to begin opening at a lower pressure other then the factory pre-set of 54 PSI.. Legacy recommends setting the initiation of HGBP no less than 10 PSIG higher than your adjusted LP trip point. For example, in using the 10 PSIG LP setting (Section 4a above) you would set your HGBP valve to start opening no lower than 20 PSIG suction. Attached to this article is additional information on the HGBP valve.

C.Adjust: TXV (also referred to as a TEV valve) superheat setting: In most cases making adjustments to the TXV is not needed however depending on operating conditions this may be needed. Legacy recommends a superheat setting in the range of 8-12 degree F. Attached to this article is detailed information on TXV operation, adjustment and advanced troubleshooting.

D.Flow switch re-calibration for glycol: Before leaving the factory, the chillers differential flow control safety is calibrate using water only. Since adding glycol to the process loop changes the viscosity of your process loop fluid, low flow errors can happen intermittently after adding glycol. See knowledgebase article concerning low flow errors for detailed instructions on how to re-calibrate the flow switch.
IMPORTANT: AT ANY TIME IF FRESH WATER IS ADDED TO A GLYCOL SYSTEM, THE FREEZE POINT MUST BE RE-CONFIRMED AND MORE GLYCOL MUST BE ADDED. FAILURE OF THE FREEZE POINT TO BE AT OR BELOW THE SETTING MADE IN STEPS ABOVE CAN RESULT IN SEVERE DAMAGE TO CHILLER EQUIPMENT. SUCH DAMAGE IS NOT COVERED UNDER THE MANUFACTURES LIMITED WARRANTY.

APPLIES TO
All models

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  • Posted 12/14/2005 :: 34561 views