Improve cooling tower pump regulation for up to 70% energy savings

Grundfos boosts system efficiency with intelligent temperature controlPHOTO: In typical cooling towers with oversized pumps and widely varying system loads, the Grundfos iSOLUTIONS approach to control can save up to 70% of energy expenses, according to application manager Michael Laustsen.
Intelligent temperature control

Industrial cooling systems use some of the biggest pumps in constant operation, but lack of responsibility around their set-up often leads to reduced efficiency and expensive energy bills, according to Michael Laustsen, Grundfos Application Manager.

“Often a consultancy company will buy a cooling compressor from one supplier, the cooling tower from another, then the pumps from us and get a local contractor to put it together,” explains Michael Laustsen. “If the contractor is unaware of what to do about the connections and programs them incorrectly, the energy waste and cost implications are huge,” he says.

“The focus is usually on optimising the process of whatever the factory is producing. Nobody really takes responsibility for ensuring that the cooling system operates efficiently.”

Grundfos can help companies to avoid such expensive inefficiency – with savings of up to 70% or more in common scenarios with changing system loads.

“We have been in this business for decades,” says Michael Laustsen. “We have the depth of knowledge of cooling systems and electronics to solve the issue. We know the suppliers of cooling towers and cooling compressors, and we know how the components operate together. We also have the control systems, so we can actually do something about it.”

“Industrial cooling applications rarely have a constant load. As soon as you cut the load, the direct temperature control solution is by far the most beneficial.”

Michael Laustsen, Grundfos Applications Manager

FIGURE 1: Regulating valve with pump running constantly at full speed

Choosing a control strategy

If we take a standard heat exchanger as an example, there are three main ways to control the temperature out (Figures 1-3, in ascending order of total efficiencies achieved).

Each solution has the same purpose: to maintain constant temperature out of the heat exchanger. Which one is chosen can have a significant impact on overall system efficiency and, therefore, running costs.

The second option (Figure 2) also regulates temperature with a valve, but incorporates a frequency converter in order to maintain constant differential pressure.

FIGURE 2: Constant differential pressure with a speed-regulated pump

“This solution has the benefit of avoiding excessive pressure in the system and saving some energy compared to the first set-up,” says Michael Laustsen. “However, the issue of pressure loss over the valve still remains, and set-up costs increase, since it requires both a regulating valve and a frequency converter. Also, the system becomes complicated as you have two regulations to get to one duty point.”

No valve needed
The third set-up takes a more direct approach. No regulating valve is required, since a sensor measures temperature where it is most important – in the heat exchanger pipe – and sends the signal directly to the pump, which has a frequency converter. The pumping speed changes depending on how much flow is needed to get the right temperature.

FIGURE 3: Temperature-controlled. Temperature signal feeds back directly to the speed-regulated pump.

“There are no extra control cabinets, electronic converters or regulating valves between the critical point where you monitor the temperature and the component giving you what you want,” explains Michael Laustsen. “So, for instance, there is no problem of pressure loss via the valve. The pump maintains high efficiency no matter what the variation in load, and it uses less energy.

“It is also possible to monitor and store temperature data, which is particularly useful for food, beverage and pharmaceutical companies who have to document everything,” he adds.

“The only drawback of this approach is that it cannot be used in all applications – for instance, if you have more than one cooling loop after the pump. Then the system cannot work out which pump to regulate, so you will have to choose setup No. 2 with constant differential pressure.”

“Nobody really takes responsibility for ensuring a factory’s cooling system operates efficiently.”

Michael Laustsen, Grundfos Applications Manager

FIGURE 4: In systems where the duty point is constant, each of the three strategies perform equally well, but when the load is reduced, direct temperature control offers optimum efficiency and energy savings.

Increase efficiency and save energy
For pumps that are small and/or seldom used, system efficiency is not a major concern, but cooling pumps tend to be among the largest running in a factory and run 24/7. That means cooling applications are highly influenced by the control strategy, system efficiency and the load profile.

“If you have a system that requires the same duty point all the time and the pump is sized properly, there is no difference in results between the three regulating strategies,” explains Michael Laustsen. “But industrial cooling applications rarely have a constant load. As soon as you cut the load, the direct temperature control solution is by far the most beneficial” (see Figure 4).

Source: Grundfos


The influence of load profiles on energy use
Clearly, therefore, it is vital to consider the load profile when choosing a set-up. The three sample load profiles in Figure 5 show significant savings with the constant differential set-up compared to the regulated valve system. However, direct temperature control is by far the most energy-efficient option.

FIGURE 5: Three sample load profiles – A, B and C – and the percentage energy savings using alternative constant differential pressure and temperature control options. Load profile A has a random flow request from the system, so the pump supplies flows from all over the pump curve. Load B is a stable process with the same flow requirement most of the time; the pump can be sized so it operates in its best efficiency point most of the time. Load C is “maybe the most common situation we see in many applications,” says Michael Laustsen. “The pump is simply oversized and it is operating at a much lower flow than it is actually designed to do. This results in a low efficiency on the motor and pump most of the operation time.” Source: Grundfos

“Most cooling pumps are oversized, and load profile C is the most common we come across,” says Michael Laustsen, “and for this load profile, the temperature control solution has a massive advantage.” Indeed, as Figure 5 shows, the temperature control set-up brings a 72% energy savings in this scenario.

The intelligent solution
The five factors affecting the operating cost of an industrial cooling application can be summarised as follows:

• Pump and motor efficiency
• Regulating mode
• Sizing of system
• Load profile
• Losses in the system

This is where Grundfos iSOLUTIONS (intelligent solutions) comes into play. The approach goes beyond the pump to optimise the entire pumping system. Grundfos works to identify customers’ needs and help them avoid situations that will cost them in the long term – for example, by setting up the most intelligent and efficient pump regulation in an industrial cooling application.

“We train our sales people to explain the pros and cons of different solutions for their specific application,” says Michael Laustsen. “Some customers may say, ‘I don’t care – I’m not paying extra for a frequency converter,’ but we always try to clearly explain the costs and benefits of each option. If you are building a new system, the earlier you talk to us, the better.”

IMAGE: Factories tend to focus on optimising the process of whatever they are producing, says Michael Laustsen. “Nobody really takes responsibility for ensuring the cooling system operates efficiently.”

About Grundfos Temperature Control

Click here for more information on how Grundfos helps companies to optimise temperature control systems for maximum efficiency and minimum energy usage.

Story by Justyn Barnes

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