American Wheatley HVAC’s Chilled Water Buffer Tank (CBT) is designed to be used with chillers that do not have significant water volumes of sufficient size about the chiller. An insufficiently sized system does not have enough of a buffer capacity for the chilled water causing poor temperature control, erratic system operation, and extensive excessive compressor cycling.
With HVAC Chilled Water Buffer Tank, these problems can easily be avoided. American Wheatley’s CBT adds water to the buffer system and reduces the rate of change of the returned water. With a properly sized CBT tank, the system will run smoothly without a hitch.
What does a Chilled Water Buffer Tank do?
The Chilled Water Buffer Tank adds the necessary volume to "buffer" a system with low water volume.
A properly sized and installed chiller system will prevent the chiller compressor from short cycling
A unit's water volume is based upon certain requirements; for example, a typical air conditioning unit requires 3 to 6 gallons per ton of water. A properly sized and installed chiller system will prevent the chiller compressor from short cycling.
Without proper system water volume, the source temperature will be reached quickly and the compressor will shut off. Many chiller compressors can only start 3 times per hour; if the compressor is off when there is a demand for chilled water, the demand cannot be met because the compressor cannot turn back on. One can imagine this would cause very unsatisfied people within the building who cannot have the required cooling.
ASME Certified Chilled Water Buffer Tank
American Wheatley ASME Chilled Water Buffer Tanks are designed for water systems with insufficient water volume capacity, about the chiller capacity. Relatively low water volume systems require additional “buffer” capacity.
Features
- Constructed by ASME Section VIII, Division I, Latest Edition
- Carbon Steel Construction
- Maximum Temperature 450°F Intermittent
- Design Pressure 125PSI
- Primed Exterior
Optional Features:
- Manway Handhole
- Higher pressures
- Stainless Steel Construction
- Upper Mounted System Connections
- External Coatings
- Insulation / Jacketing*
Typical Specifications
The tank must be constructed by the most recent addition of Section VIII of the ASME Boiler and Pressure Vessel Code
Furnish and install as shown on plans and ASME Chilled Water Buffer Tank as manufactured by American Wheatley HVAC Products. The tank shall incorporate a baffle to promote tank water storage temperature stratification. The system water connections must be in inches (NPT/flanged/grooved).
The tank must be constructed by the most recent addition of Section VIII of the ASME Boiler and Pressure Vessel Code. Each Chilled Water Buffer Tank shall be American Wheatley Model AWCBT.
How to size a water buffer tank?
Chiller manufacturers recommend that somewhere between two to six gallons per ton for nominal cooling in a typical system. Even higher, six to ten gallons when temperature accuracy is critical.
To calculate what size Chilled Water Buffer Tank that you need, use the following formula.
CBTR = SVR - ASV
For clarification, refer to the instructions below.
SVR
Determine the system volume required by the manufacturer. Remember to check with the manufacturer for their recommendations as to how many gallons they suggest per ton.
SVR = System Volume Required = Total chiller tons X manufacturer-recommended system volume required per ton
ASV
Calculate the actual existing volume of piping and equipment Table A, below indicate gallons per linear foot of schedule 40 pipes.
ASV = Piping Volume (PV) + equipment volume (EV) gallons
CBTR
Calculate actual Buffer Tank size required (CBTR)
Deduct the actual system volume (ASV) from the System Volume Required (SVR).
CBTR = SVR - ASV
Refer to American Wheatley AWCBT Charts for standard sizes. Larger sizes are available POA.
How are Chilled Tanks Installed?
American Wheatley Chilled Water Buffer Tanks are typically installed to ensure adequate water volume
American Wheatley Chilled Water Buffer Tanks are typically installed to ensure adequate water volume along with decoupling and mixing action necessary with today's primary-secondary systems. All steel tanks manufactured by the American Wheatley HVAC Products are constructed by the best commercial practices.
The ASME Boiler and Pressure Vessel Code, Section VIII, Division 1 (an American National Standard published by the American Society of Mechanical Engineers) provide rules for the construction of pressure vessels.
This includes requirements for materials, design, fabrication, examination, inspection, and marking. All steel tanks constructed by all of the applicable rules of the Code are identified with the official Code Symbol Stamp on the vessel nameplate. All steel tanks that include the Code U stamp will also include a National Board Number and registration with the National Board of Boiler and Pressure Vessel Inspectors.
