A general introduction to mixing loops

Get an overview of the theory behind mixing loops and learn about the various designs and what differentiates them.

When it comes to controlling flow temperature, mixing loops are crucial. In this course, we will give you a general introduction to mixing loops, why they are used and how they can be designed.

We will also touch upon the various components that make up a mixing loop. Let’s get started.

First of all, mixing loop systems are intended to adjust the flow temperature of the water.

They consist of a primary side and a secondary side. The flow on the primary side is controlled by the valve, and the flow on the secondary side is controlled by the pump. Simply put, the basic principle of a mixing loop is to mix the primary water with the return water in a suitable proportion to obtain the required flow temperature.

But why should you use a mixing loop? Well, one of the main reasons is that a mixing loop has the ability to zone the temperature in buildings. Typically, larger buildings are divided into zones. All of which have different needs. So, if one part of the building is exposed to less sun than another side, that section of the building may need more heating.

Likewise, it may depend on the average usage – a work office is mainly used from Monday to Friday, whereas a shopping area is also active during the weekends. In order to control the flow temperature of a zone, you need a mixing loop.

As a heating installation in each zone consists of either radiators, an underfloor heating system or air-handling units, they all require a different flow temperature. Additionally, by using the outdoor temperature compensation, in which the flow temperature is regulated according to the temperature outside, your transmission heat losses will typically decrease, thus increasing the energy savings up to 5-10%.

So, with the outdoor temperature compensation, you can obtain the best possible comfort with the lowest possible energy consumption. There are a number of different mixing loops. The two most common are a pressurised injection circuit with a two-way valve, and a non-pressurised mixing circuit with a three-way valve. Let’s take a closer look.

In a pressurised injection circuit with a two-way valve, the primary pump will typically force water into the mixing loop through the valve from the primary side. In a non-pressurised mixing circuit with a three-way valve, the pump is on the secondary side, and from here, it will typically suck the water into the mixing loop through the valve when it’s open. Now that we’ve touched upon the different circuits, let’s take you through the components of a mixing loop system.

First of all, you have the control valve. This is the valve that regulates the circulating medium and thus controls the flow temperature. Next, there is the balancing valve. Balancing on the primary side helps to circumvent starvation between zones, contributing to an optimal delta-T between supply and return. Then, there’s differential pressure controller. In systems with varying flow, there will be a varying pressure on the primary side. So, if the pressure increases to a higher level than the desired pressure, the differential pressure controller will ensure that you still receive the volume of water that you’ve sized your mixing loop for. Next up are the non-return valves. Simply put, their job is to prevent unwanted backflow. Finally, there is a controller and the temperature sensors. By receiving input from both the application and the outdoor temperature sensors, the controller can control flow temperature by means of, for instance, a heating curve. Connecting the mixing loop to a Building Management System allows you to control and monitor your system remotely. So, that sums up our introduction to mixing loop systems.

Let’s recap:

• Mixing loops are crucial to the adjustment of liquid flow temperature.

• By controlling individual zones in a building with a mixing loop, you can ensure a high level of comfort, while the outdoor temperature compensation results in energy savings.

• There are multiple application types and hydraulic circuits for different circumstances.

• And finally, you can control your mixing loop system locally or remotely via your preferred BMS solution.

Course overview

Modules: 3
Completion time
Completion time: 20 minutes
Difficulty level
Difficulty level: Intermediate