The Many Uses of a Buffer Tank
The generic term “buffer tank” is used to describe a pressure vessel that will be installed in a closed-loop chilled and heating water circuit.
When ordering and installing a chilled water buffer tank, it’s important to be clear about its desired function. The addition of a chilled water buffer tank will not give the required results if it’s not designed and fitted with the correct internal equipment.
Having to retrofit internal pieces such as a baffle or sparge that should have been included in the original supply scope is costly and extremely inconvenient to all parties involved.
For this reason, an understanding of the different functions of a buffer tank will ensure you correctly specify the correct tank and thus receive the tank most suited to your application.
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Increasing the volume of your system
This is the most common function of a buffer tank. For a chiller to operate correctly, your system must have a certain volume. We refer to this as “loop volume”. You can size your chilled water buffer tank using this formula.
In the event of short pipe runs, the chiller could start and stop in a low-load situation. For this reason, a buffer tank is installed to add volume and prevent cycling, which can be extremely damaging to the chiller.
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Serving as a storage tank
A buffer tank can be applied as a storage tank where you require a large volume of chilled water to be stored for release into the system in the event of a power outage.
The short interval of time (usually around 5 minutes) it takes for the system to switch over to a temporary generator power supply can upset the regularity of the system.
This kind of application is used in data centres, where continuity of supply is critical to ensure no data is lost in the 5-minute downtime.
Storage tanks are installed after the chiller, so cold water will be coming in to charge the tanks.
Stratification (separation of water temperature in layers) must be maintained in the tank. There needs to be a thermocline (thin but distinct layer of temperature change).
Remember that warm water rises and cold water sinks. A storage tank equipped with a sparge pipe at the inlet uses these properties to work effectively.
To work out what sized storage tank you’ll need, use this formula.
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Serving as a decoupler
This buffer tank will have no baffle, but requires 4 connection points.
In a primary/secondary system, the buffer tank would be installed in a manner to ensure both circuits are connected.
Chilled or heated water would be produced in the primary circuit, whereas chilled or heated water would be distributed around the building for air conditioning and space heating/cooling in the secondary circuit.
The primary and secondary circuits would be connected by a 4-pipe buffer tank acting as a decoupler, with hot water on top and cold on the bottom.
The water within the tank can flow either way, depending on the demand of the building.
In the rare instance that the building’s system is at maximum load and requires 100% of the system’s designed capacity, all the primary water will flow to the secondary circuit, which then disconnects/decouples both circuits from one another.
For the other 99% of the time, the system will be operating at part load.
In this scenario, some of the primary water will flow to the secondary circuit and some will pass through and head back to the chiller/boiler.
By effectively separating both system and chiller/boiler flow with minimum flow disturbances, a more constant delivery temperature (as well as a longer chiller/boiler operational cycle) can be achieved.
This reduces cycling, increases efficiency, and reduces the maintenance costs of the chiller/boiler.
We hope we’ve made clear the differences between tanks being used to increase system volume (buffer tank), store liquid (storage tank) or serve as a decoupler.
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If you have any further questions, please reach out here or contact us at 02 9748 2022.