Table of Contents

What are Modular Chillers?

Modular chillers are relatively small units (typically 15 to 80 tons) that are installed together and work as a single large chiller, controlled by a master controller that stages the modular units.

Modular chillers can be used in small plants with just 2 units, or in large plants (>1000 tons), where dozens of modular units are installed together. They are available in air cooled and water cooled versions.

The air cooled units are available as chillers, integrated free cooling chillers, reversible heat pumps and simultaneous cooling and heating units.

The water cooled units are also available in many different types, such as chillers, reversible heat pumps and simultaneous cooling and heating units.

The several different options available make this type of units an interesting option in a multitude of different applications, from process cooling to space cooling and heating and energy efficient plant solutions.

The modular units are installed next to each other, providing the necessary clearance spaces, and piped in parallel to a common header. The master controller stages the units to keep the set point satisfied.

This type of units provides a very high level of redundancy; a failure in one unit represents losing only a very small percentage of the overall plant capacity. They are also a perfect solution for jobs phased in time, where there are plans for chiller plants expansion.

Read about the world's first stackable modular chiller. The WWM. 

How Do They Work?

Modular chillers are normally installed next to each other, and only need access from 2 sides. It is externally important that the access spaces are satisfied to guarantee that the units can be serviced.

They are piped in parallel to a common header, and will be started/stopped responding to the master controller, that stages the units to keep a set point satisfied.

The units are connected in a daisy chain that goes to all the units and into the master controller. The master controller reads the inlet and outlet temperature from the common temperature sensors and starts / stops a number of units to guarantee the load of the building is satisfied.

In the case of integrated free cooling chillers, an ambient temperature sensor is also needed, so that the controller can compute when to start the free cooling operation. In order to maximize the free cooling savings, an ambient temperature can be set, at which all the units will start in free cooling mode only, starting compressors only if the free cooling is not enough to satisfy the building load.

Modular heat pumps have the ability to control either a cooling or heating set point.

Simultaneous cooling and heating modular units can control both set points at the same time.

These units can work with constant flow but are normally designed to work on variable flow plants. The typical design includes an electronic butterfly valve on each unit that opens / closes when the master controller starts / stops each unit. The VFD pump is controlled by a dP sensor across the chillers that will respond to the opening / closing of the unit’s valves. In this way, each modular unit works with constant flow through its heat exchanger, but the whole plant works on variable flow. The total GPM depends on how many units are working.

Why Modular Units?

Chiller plants usually have one large chiller to handle the required cooling load, and another chiller equally sized to provide redundancy.

Modular chiller plants are an alternative that allows using multiple smaller chillers, working together as a single chiller. This solution offers a higher degree of redundancy, avoiding the need to have a large chiller as a backup. Since several chillers are already present in the plant, the addition of only one small modular chiller will be enough to provide the required redundancy.

The use of several small refrigeration circuits means that in case of refrigerant leaks, only a very small amount of refrigerant will be released into the mechanical room as the amount of refrigerant in each circuit is very small.

Modular chillers are a perfect solution for plants that have expansion plans. In this way, the building owner can phase out the purchase of the chillers, adding chillers to the plant when they are needed. On a 150 ton modular plant, for example with (5) 30 ton chillers it will be extremely easy to add another 60 tons of modular chillers, simply by adding another (2) 30 ton chillers to the bank of units.

Finally, modular chillers are much smaller than a large packaged chiller, and that could be very important if the mechanical room has limited access. Modular chillers can normally fit through elevators and regular doors, simplifying the process of getting the units into the mechanical room.

Read about our modular chiller. The NYB. 

Other Systems

There are multiple advantages of using modular chillers comparing to large units. The level of redundancy is the highest one can get; a failure in one unit represents losing only a very small percentage of the overall plant capacity while on a plant with two large centrifugal chillers, a failure in one unit represents losing 50% of the plant capacity what can lead to long periods of operation below the building load, causing discomfort to the occupants (in case of air conditioning applications), or production losses in process applications.

These units are also the perfect solution for businesses that have expansion plans. They are commonly used in grow op plants for example, that typically have 2 or 3 development phases. The owner can buy only has many chillers has needed for the first stage, and easily purchase the additional units when they are needed, avoiding a hefty initial cost.

Another big advantage is the small size of these units that makes them possible to install in any mechanical room, even if elevators are the only way to reach it. It is common to see modular chillers being used to replace big old centrifugal chillers that are in mechanical rooms where a new chiller cannot fit, and the small modular units are the perfect solution for those retrofit jobs.


Modular units can be used in many different applications.

Air cooled free cooling units can be used in cold regions, in applications where cooling is needed year round (data centers, process applications, large buildings with permanent core cooling load, etc.). Free cooling chillers have the highest efficiency of any chiller working in cold ambient temperatures.

Air cooled modular chillers are used in many different applications, such as hotels, schools and commercial buildings.

Modular air to water heat pumps are a great solution for buildings with seasonal change over, or DHW applications. Modular heat pumps are mostly used in mild climates, where the COPs of these units are best. Cold climate zones will usually use water cooled heat pumps that can get heat from a geothermal loop, providing a better COP at those conditions compared to an air to water heat pump working with very low ambient temperatures.

Modular simultaneous cooling and heating units are a clever addition to plants that have needs for cooling and heating. Again, air to water units are mostly used in mild climate zones, and water to water in cold climate zones. These units are used in schools, hospitals, condo buildings, offices and many commercial applications. Any building with simultaneous needs for cooling and heating will save energy by using these units.

Water cooled modular chillers are typically used with cooling towers or dry coolers, and can be used in any building that needs cooling and has a condenser loop.

All in all, modular units can be used in any job that needs chillers, integrated free cooling chillers, heat pumps or simultaneous heating and cooling, with the added benefits of a modular plant.