Did you know that a recirculation loop is usually poorly designed and presents numerous dangers? First and foremost, what is a recirculation loop? In the rhetorical sense, a recirculation loop ensures that the temperature in a water network is maintained by recirculating the water constantly. Sometimes it is necessary to keep a fluid at a certain temperature for operational or production reasons. However, a large majority of drinking water recirculation loops have become illegal under a law added to the National Plumbing Code in 2021.

Why can a recirculation loop be illegal?

Mixed water recirculation

Section 2.6.1.1 paragraph 3 of the National Plumbing Code requires that a hot water recirculation be at a temperature of at least 55^{°C 1}. For its part, the CMMTQ suggests that cold water recirculation be maintained below 20^{°C 2}. Within these values (see Figure 1), the water is considered mixed and favours bacteria growth. This poses a direct risk of contamination of a drinking water system. For this reason, it is extremely important to design a separate recirculation loop for cold water and one for hot water.

Pipe length

Also, Article 2.6.1.1 paragraph 2 of the National Plumbing Code (2021) requires that hot water pipes of more than 30 meters and/or higher than four floors⁴ must contain a recirculation loop. Indeed, long branches of non-recirculating pipes create another problem: stagnant water! Stagnant water promotes the growth of bacteria such as Legionella pneumophila. As a result, your drinking water system is at risk of being directly contaminated.

Let us see how a recirculation loop should be designed.

What equipment is required on a recirculation loop?

On a recirculation loop, it is important to have:

- One or more water heater(s)

The water heaters provide water at a desired temperature. According to section 2.6.1.12 of the National Plumbing Code, the temperature of the water leaving the water heater must be a minimum of 60°^{C 5}.

- One or more recirculation pump(s)

They provide the water with the energy needed to be recirculated throughout the entire loop.

- An expansion tank

It protects the equipment from thermal expansion.

- One or more balancing valves

They regulate the water flow to maintain a constant temperature through the various branches of the network.

- Thermal insulation

This reduces heat and economic losses in the long term.

- Supports

Maintain the structure in place.

- Shut-off valves

They are optional. However, placing shut-off valves on a water network is a good practice, as it isolates each piece of equipment to simplify maintenance.

But why is good design so important?

To reduce losses:

- Thermal

- Load

- Financial

Design may seem long and tedious, but in the long run, it proves very cost-effective, both for user safety and from an economic perspective.

In short

The following must be avoided at all costs:

- Mixed water loops,

- Non-recirculated pipes longer than 30 metres and/or higher than four storeys.

How to do this?

- Select the right equipment,

- Emphasize on good design to reduce the various losses.

The dangers of a poorly designed Recirculation Loop

Why can a recirculation loop be illegal?

Translation of the original “Figure 1 - Plage de températures à considérer dans un réseau de distribution d’eau” appearing in the National Plumbing Code (CMMTQ)³

Figure 1 - Plage de températures à considérer dans un réseau de distribution d’eau (CMMTQ)³

What equipment is required on a recirculation loop?

But why is good design so important?

References

The dangers of a poorly designed Recirculation Loop

Translation of the original “Figure 1 - Plage de températures à considérer dans un réseau de distribution d’eau” appearing in the National Plumbing Code (CMMTQ)3

Figure 1 - Plage de températures à considérer dans un réseau de distribution d’eau (CMMTQ)3

Translation of the original “Figure 1 - Plage de températures à considérer dans un réseau de distribution d’eau” appearing in the National Plumbing Code (CMMTQ)³

Figure 1 - Plage de températures à considérer dans un réseau de distribution d’eau (CMMTQ)³