Chicago, being the “windy” city that it is, is no stranger to temperature extremes. The weather can get quite harsh – winter seasons can get quite cold, while summers can definitely become scorching hot.
However, that doesn't mean it's a terrible place to live. Thanks to several cooling systems and a few cooling centers, Chicagoans can seek relief during the hot summer months. One of the most notable initiatives to combat heat is the use of refrigeration units.
Get an energy efficiency design for your cooling plant and save on electricity bills.
An Introduction to Chicago Cooling Plants
While HVAC systems are responsible for regulating the comfort levels of most indoor environments, a cooling plant acts as a centralized cooling system that provides cooling for a building or multiple buildings. Additionally, it provides a portion of the air conditioning by HVAC systems. According to the Energy Star website, about 39% of buildings larger than 100,000 square feet have a chilled water system.
Although cooling plants seem like an innovation, the concept is not actually new. Records show that the ancient Romans already used refrigeration in their indoor environments. However, they did not use a centralized plant, but rather used water to run down the walls of their buildings in order to cool the internal temperature.
In the 19th century, people began experimenting in an attempt to create a modern air conditioning system using electric fans to blow air onto cold surfaces. Unfortunately, these systems have not made it into the spotlight due to their enormous costs and inefficiency.
It wasn't until 1922 that a centrifugal chiller was invented by Willis Carrier, allowing the public to have easy access to air conditioning.
Components
Although chillers, also known as condensing units, are mainly used for air conditioning purposes, cooling plants, on the other hand, are made up of various mechanical equipment. The cold air is distributed throughout the building through a distribution system made up of metal ducts to transport the air and a fan to expel it.
Nowadays, most cooling plants also come with a variable speed drive capable of running multiple condensing units at the same time, which is more efficient than just turning them all on or off. In some cases, cooling towers are used to cool the air before it even enters the chiller.
How efficient are they?
According to the Department of Energy, 10-15% of the energy consumed by buildings goes to air conditioning. Although condensing units are becoming increasingly efficient with the introduction of new technologies, it is still possible to save more energy by reducing plant size and improving distribution systems.
Considering that chillers are among the biggest energy consumers in a building, this can have a huge impact on operating costs. Therefore, monitoring a plant's chillers is important to know how efficient the system is.
Calculating the efficiency of a chiller is really simple by measuring its CoP or Coefficient of Performance.
Basically, it is the relationship between the chiller's refrigeration effect and the amount of electrical energy required to produce it. These two units are measured in kilowatts (kW). Let's look at an example:
A chiller produces 3,000 kW of cooling, which is equivalent to 10,236,423 BTUs/h, while requiring an electrical energy of 500 kW to produce this effect. CoP can be calculated using this formula:
Cooling effect/requirement of electrical energy
So, using the given formula:
3,000 kW / 500 kW = 6. The Coefficient of Performance, in this case, is 6, which just means that for every 1 kW of electrical energy used, 6 kW of refrigeration is produced.
Keep in mind, however, that a chiller's CoP will depend on its cooling load, not to mention that each chiller has its own different efficiency. Chiller manufacturers typically provide CoP design data to make a performance comparison between chillers quicker and easier.
Cooling Plant Optimization and Its Impact on Buildings in Chicago
As central cooling units are often referred to as the “heart” of a building’s HVAC system, it is important to optimize them for better performance. Not only is a cooling plant the main source of cooling, it uses a large portion of a building's energy needs, resulting in huge energy costs.
For example, in a typical Chicago hotel, the HVAC system may use up to 50% of the total electrical load, and a refrigeration plant takes up a large portion of that load.
One of the real challenges with cooling plants is that many of them do not operate at the designed temperature differential. This is the temperature difference between the chilled water return (delta T) and the chilled water supply. In fact, cooling plants operating at suboptimal levels are common and, in most cases, have a much lower delta T than necessary. This is caused by several factors, such as the method used to control the equipment and the way airside systems operate.
Optimizing a cooling plant is possible starting with the chilled water pumps and chillers. The most efficient cooling plant arrangement used is the variable primary chilled water system, as it uses only a single set of pumps to distribute water throughout the building. Another efficient arrangement is primary-secondary, which uses two sets of pumps for the chillers and building systems.
It is extremely important to properly control equipment such as pumps, chillers and cooling towers, especially when combined with a quality control system. A quality system allows the coordination of all aspects of the system and grants access to the chiller's internal data.
This allows data to be used as input for creating an effective control program. By having an in-depth understanding of how the chiller works, it is possible to control the chiller plant in the most effective way possible. If there is not enough expertise available to efficiently control the plant, hiring a reliable control partner is the ideal option to achieve optimization.
This is how cooling plants work not just in Chicago, but in every state in general. The optimization process allows buildings to provide efficient cooling amid the state's hot climate without consuming too much electrical load. But of course this can only be achieved by hiring the right people for the job.
