feb 26, 2019

The different types of sub-loop water systems for the design of cold use of WFI

This article belongs to Jose Gallardo, Process expert in Pharmabios. Also published in his Linkedin account.


“Cold points of use on WFI loops, design considerations


Water for injection is usually distributed in hot distribution rings (80°C is often used as the reference temperature) to reduce the probability of contamination and keep the water under bacteriostatic conditions. However, in many applications it is necessary to have water available for use at room temperature. One of these applications may be a sink for the use by operators to wash components, but it is not the only application in which cold use of WFI may be necessary.

This involves a sub-loop water system at room temperature, or ambient point of use, that cools the water to the temperature required for the application.

There are different ways of doing this, and each of them has advantages and disadvantages, I would like to discuss in this article all the types I know, with the intention of sharing this information, and to start a small debate to learn about other options that I may not have been taken into account.


Single point of use without sub-loopSingle point of use without sub-loop

At this point of use, the hot ring valve is opened, then the WFI is cooled to the desired temperature and the WFI is drained until the right it is obtained. Once the right temperature is reached, the drain valve closes and the point-of-use valve opens.

Advantages: Cost-effective and easy to install.

Disadvantages: Water is wasted during cooling and the piping will probably need to be sanitized or sterilized after each use.



Ambient sub-loop without flow control

Ambient sub-loop without flow controlWhen the ambient point of use is not in use, the inlet and outlet valves of the sub-loop are open and the rest closed. When water is needed at ambient temperature, the by-pass valve of the sub-ring and the drain valve is opened and the return valve of the sub-ring is closed. Once the right temperature is achieved in the two temperature probes, the drain valve closes and the point-of-use valve opens.

When the use is finished, the valves return to their original position.

Advantages: When there is no use, the sub-loop is kept hot under bacteriostatic conditions.

Disadvantages: WFI is wasted during cooling. The pressure drop of the heat exchanger must be properly sized, since all the water in the ring must circulate through the heat exchanger when the sub-ring is not in use. When in use, there is stagnant water in the return of the sub-loop.



Ambient sub-loop with flow controlAmbient sub-loop with flow control

A modulating valve located in the sub-ring bypass regulates the flow rate of the sub-loop by means of a flow set point in the sub-loop return. When the use starts, the water is cooled to the right temperature, and then the point of use is opened. It is possible to have different set points of flow rate for situations of use or not use of water at ambient temperature.

Advantages: No water is wasted. It can be adjusted so that there is always turbulence in the sub-loop.

Disadvantages: The modulating valve and flowmeter are expensive. The modulating valve and pipe diameter must be carefully selected so as not to disturb the rest of the loop.


Continuous ambient sub-loop

Continuous ambient sub-loopThe hot water is cooled continuously by cooling water, used at the different points of use and reheated to return it to the main loop.

Advantages: It is possible to reduce costs if there are several points of use.

Disadvantages: Steam and cooling water are used continuously. Pressure losses must be checked.

These are just a few examples of how to obtain ambient temperature WFI from a hot ring. Depending on the application, there can exist many variants and types of cooled points of use. Each WFI distribution loop is different, and it is important to know how to adapt to each particular problem with innovative solutions.”


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