Chilled water buffer tanks (CWB) are used to address issues that arise when a chiller system does not have sufficient water volume. CWB tanks reduce temperature fluctuations, prevent excessive compressor cycling, and provide stable system operation. To size a CWB tank, the required and actual system water volumes are calculated based on chiller capacity and piping/equipment volumes. The difference between the required and actual volumes determines the needed CWB tank size. Insulation is also selected based on tank temperature and ambient conditions. CWB tanks solve problems from insufficient water volumes and allow chillers to function properly.

1. DESIGN & SELECTION OF
CHILLED WATER BUFFER TANKS
Rami Reddy., M. E. (R & A/C)
Engineer-Building Services
Bangalore

2. • Chiller basic requirements
• Insufficient water chiller system
• Chilled Water Buffer (CWB) tanks
• CWB piping Diagram
• CWB Sizing procedure
• Example
• Selection of equipment
• Schematic - Previous project
CONTENTS :

3. CHILLER BASIC REQUIREMENTS
 Chillers are designed to be used in systems with a
minimum water volume.
 3 to 6 gallons per ton for typical air conditioning or
6 to 10 gallons per ton when temperature accuracy
is critical.
 Chiller compressors can only start 3 times per hour.
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4. INSUFFICIENT WATER SYSTEMS
 Source temperature will be reached quickly and
the compressor will shut off.
 Compressor can not turn back on if the demand
for chilled water rises.
 Insufficient cooling for buildings.
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5. CHILLED WATER BUFFER (CWB) TANKS
Features
 Reduces the rate of change of
return water temperature
 Solves the cause of poor
temperature control
 Solves the cause of excessive
compressor cycling
 Solves the cause of erratic
system operations
CWB’s are designed to be used with chillers
which do not have water volumes of sufficient
size in relation to the chiller.

6. CWB Piping diagram

7. Sizing of CWB tank
 Step 1) Check Chiller manufacturers recommendation of system
volume (Say the system 3 to 6 gallons per ton for typical air
conditioning or 6 to 10 gallons per ton when temperature accuracy is
critical).
 Step 2) Required system volume (RSV)
= Chiller tons X Recommended system volume/ton
 Step 3) Actual system volume (ASV)
= Piping volume (PV) + Terminal equipment volume (TEV)
• Step 4) Required CWB tank size = RSV – ASV
 Step 5) Selection of Insulation thickness : Based upon tank
temperature and maximum ambient temperature + humidity

8. Example:
• Data:
• Building capacity: 100TR
• Flow Rate: 240 gpm
• Pipe dimensions: 300 feet of 4” pipe
Solution:
• Required system volume (RSV) = 100 tons X 5gallons/ton
= 500 gallons
• Actual system volume (ASV)
Piping volume = 300 feet X 0.66 gallons/ft =198 gallon
Terminal equipment = 35 gallon
Actual system volume = 198 + 35 = 233 gallons
• Tank size required = RSV – ASV
= 500 – 233 gallons
= 277 gallons
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9. Selection of equipment

10. Schematic – Previous project

11. Thank You