Optimization Strategies for the Chiller Plant

October 13, 2014 By Eric Erpenbeck

Eric Erpenbeck

Healthcare, commercial, and institutional facilities often use a chiller plant to provide chilled water for air conditioning. It should come as no surprise that chilled water generation is a major contributor to a facility’s utility costs. Organizations are well served to seek ways to optimize their facilities for the best possible performance and energy usage, yet many organizations simply aren’t aware of the full range of chiller plant optimization strategies available to them. This often leads to missed opportunities to save energy and money.

The fact is, there are a range of effective techniques that many organizations never think to leverage – and not all of them are centered on the chiller itself. Let’s take a look at some of the most notable ways facilities with chiller plants can improve their efficiency.

Solutions at the Chiller

One of the most common chiller plant optimization strategies is to retrofit the chiller with variable frequency drives – devices that modulate motors’ electrical frequencies to improve efficiency. This improves the efficiency on any given chiller at reduced loads, but does very little for peak conditions which can be frequent with large systems.

Another consideration that can make a large impact is the capacity at which you’re running your chiller. Ordinarily, the ideal load for maximum chiller efficiency is between 60 and 80 percent of capacity. In addition, loads lower than 50 percent can significantly drop efficiency.

One strategy for improving overall efficiency may seem counterintuitive at first, but it’s proven highly effective for many facilities. By operating multiple chillers near their maximum efficiency points a facility can often improve efficiency over both reduced and peak system demand.

Facility managers who wish to keep their operating strategies as straightforward as possible may not gravitate toward this solution, but for many facilities it can provide truly valuable savings.

Solutions at the Condenser

As we said at the start, though, not all chiller plant optimization strategies center on the chiller. Though small commercial chillers tend to use air cooled condensers to reject waste hear, larger more efficient systems utilize condenser water systems. These condenser systems use pumps and cooling towers to reject heat from the chiller.

A key strategy is to use automated monitoring and system adjustment to achieve the ideal condenser water temperature. The efficiency of the chiller is directly impacted by the condenser water temperature, which is often impacted by weather conditions. When condenser water is on the cooler side – around 60º F (15º C) – the chiller can perform up to 15% more efficiently than at 85º F (29º C).

In order to accomplish this reduced condenser water temperature, you will need to consume additional power at the cooling tower; however, the power at the chiller will often be reduced to provide a net power savings.

This means you need to balance your cooling tower usage carefully, accurately, and responsively based on the weather conditions of a given day. Automated systems can help you achieve this balance effectively, leveraging the cooling tower when it makes sense and helping you to continuously optimize your systems.

Free cooling

Yet another way to optimize your facilities is called free cooling. Facilities with winter cooling requirements (including data centers, college campuses, and hospitals) may find this an effective solution. This strategy has been utilized for many years in process facilities, however with more and more IT server rooms it is becoming more common to require winter cooling within commercial and institutional facilities.

With a free cooling system (also known as a water-side economizer), you can use a dedicated heat exchanger in lieu of an electric chiller, relying on outside air temperatures during winter to provide chilled water thus avoiding chiller operation.

There are numerous opportunities to fine-tune your chiller system for optimum performance in a wide range of circumstances. By considering how various elements of your system can impact others and making thoughtful adjustments, you can either build your system or expand it to achieve optimized results, saving both energy and money.

Eric Erpenbeck is a mechanical engineering manager and head of Central Utilities Group for Fosdick & Hilmer.

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