Issue:
What is the minimum loop time?
Resolution:
As a guideline, ensure the water volume in the chilled water loop equals or exceeds these loop times. The loop time can be multiplied by the chiller design GPM for total gallons.
Current rotary screw units have a minimum loop time of 2 minutes
- RTAC
- RTAE
- RTAF
- ACRA
- RTHD
- RTWD/RTUD
- CGAM
- ACSA
Legacy products
- CGA is 5 minutes
- CGAF and CGWF is 3 minutes
If there is insufficient water volume in the system to provide an adequate buffer, temperature control can be lost, resulting in erratic system operation and excessive compressor cycling. To ensure consistent operation and tight leaving water temperature control, the chilled water loop should be at least two minutes. If this recommendation cannot be followed, a storage tank or larger header pipe should be installed to increase the volume of water in the system.
In a water-cooled unit, the only time that the condenser water loop will need to have a minimum loop time is when there is a need for controlling to the leaving condenser water temperature (such as the RTWD heat pump application), otherwise, the condenser water loop volume could be less than 2 minutes.
With modular scroll chillers:
To calculate the minimum water volume in the chilled water loop, multiply the minimum circuit (or step) in the chiller modules, times 25.
TechTV Video: Loop Time
Other Question/Problem/Cause Statements:
- Minimum Loop Time
- What is the water volume needed?
- What is the minimum loop time for my chiller?
- What are the evaporator loop times for various chillers?
- What is the smallest water loop I can have?
- What is the minimum loop time?
- Do I need a buffer tank?
- How large should the storage tank be?
- How many gallons per ton are needed?
- What if I have a short loop?
- Minimum Loop Time for chillers in Series
- What is the minimum loop time for chillers in series?
Facts:
- Air-Cooled Chiller (Pueblo) (RTAA 70-125T)
- Air-Cooled Chiller (Pueblo) (RTAC 140-500T)
- Compressor Chiller (Pueblo) (RTUA)
- Air-Cooled Chiller (CGA, 10-15 Ton)
- Water-Cooled Chiller (Pueblo) (RTHD 125-430T)
- Water-Cooled Chiller (Pueblo) (RTWA)
- Air-Cooled Chiller (CGA, 10-15 Ton)
- Water-Cooled Chiller (Pueblo) (RTWD 80-200T)
- Air-Cooled Chiller (Pueblo) (CGAM 20-130T)
- Air-Cooled Chiller (Pueblo) (RTAE 150-300T)
- Compressor Chiller (Pueblo) (RTUD 70-200T)
- Air-Cooled Chiller (Pueblo) (RTAF 115-520T)
- Air-Cooled Chiller (Pueblo) (ACRA 150-300T)
- Air-Cooled Chiller (Pueblo) (ACSA 140-230T)
Document Identifier: DOC-81051
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.