Continuous Refrigerant Monitoring System at Denver’s Xcel Energy

Xcel Energy is headquartered in Minneapolis, Minn., and is the largest electrical energy provider in Colorado. The company also provides electricity and natural gas to eight states in the Upper Midwest and Southeast. Its thermal energy business began in 1998, but its history as an electrical power supplier began more than 100 years ago in many of the states it serves. Xcel Energy serves more than 3.6 million electricity customers and two million natural gas customers. It is a forward-thinking energy company when it comes to providing clean power. It has set a carbon reduction goal of 80% from 2005 levels by 2030 and has an aspirational goal of offering 100 percent carbon-free electricity to customers by 2050. Xcel Energy currently employs about 12,000 people.

Refrigerant monitoring updates were needed at Xcel Energy’s Chilled Water building in downtown Denver. The different types of refrigerant monitoring systems that were in use offered no communications ability among plant locations in the city. The Thermal Energy team was spending time conducting constant walkthroughs of five separate buildings to check the health and functionality of 16 chillers and related mechanical equipment, including the refrigerant.

There was also inconsistent monitoring and the absence of data that could identify leaking refrigerants. This, plus the lack of consistency and reliability in the refrigerant equipment used throughout the plants, made troubleshooting difficult and finding correct spare parts from manufacturers arduous.

The result was sub-optimal refrigerant use, monitoring and communications plus inefficiencies in maintenance and repairs and potential safety issues. Today, Xcel Energy uses refrigerant monitors in its five locations to monitor the chillers. Each plant has its own Multi-Zone (MZ), Halogen Gas Monitor and they all communicate with the building automation system, which records levels of refrigerant readings while each plant is continually monitoring for potential refrigerant leaks. The MZs use an NDIR (Non-Dispersive Infrared) sensor that enables early refrigerant leak detection to 1 ppm and a pump that allows for fast sequential sampling up to 16 points.

Michael O’Malley, Operations Manager at Xcel Energy’s Thermal Energy Department in Denver, Colorado, has been with the company for 10 years and has double that experience in operations management. He and his team are responsible for a system that includes five different locations, 16 chillers and four miles of underground pipes that distribute chilled water to some of the city’s most important downtown buildings, including the art museum, main branch of the city’s public library, convention center, hotels, data centers, courthouses and Denver city and county buildings. In each building heat exchangers have been installed, eliminating the need for owners to provide their own equipment.

Clear Requirements

After evaluating refrigerant monitoring products and understanding the operation of the legacy system, Mr. O’Malley thought it important to find active sampling refrigerant monitoring equipment. A system that used a pump for sequentially monitoring different locations would get air through to the sensor and the possibility of increasing sampling frequency could help to prevent any serious consequences. To be proactive and quickly counteract any refrigerant leaks, Mr. O’Malley wanted to set up alarm sensitivities at levels lower than what a passive refrigerant monitor is able to detect. “The cost of a large refrigerant leak to our organization could range from $10,000 to $100,000 or more, depending on the size of the leak,” said Mr. O’Malley.

Using different refrigerant gases such as R22, R123, and R134a at multiple locations, it was also important that the same monitoring system within the different buildings look for all these refrigerant types and that all monitors could communicate with the main plant.

Rocky Mountain High Implementation

The implementation and installation of the first new refrigerant monitor involved a collaborative effort between Xcel Energy, Bacharach and the local representative. A number of refrigerant monitors were installed at different Xcel Energy facilities, so there were some concerns about product reliability. Michael O’Malley wanted to make sure the products would last a long time, be reliable and not require a lot of maintenance. Once Xcel Energy selected the unit it wanted, the initial installation went great, recalled the local representative. Shortly after, however, they were experiencing issues with filters and false alarms. Due to Denver’s mile high altitude, the diaphragms in the pump were working much harder. The issue was quickly remedied by replacing the sealed unit with a more robust rubber diaphragm that would not crack or break. The MZ was installed at a remote plant and as budgets allowed a total of 5 MZs were installed.

Latest Technology

The role of technology is inseparably linked to the Xcel Energy Chilled Water Plant. It remains an important safety factor to the team to have highly sensitive leak detection technology incorporated into the refrigerant monitors. Using a technologically advanced sensor that recognizes a variety of refrigerants and a system that provides faster cycle times for all monitoring zones would provide continual sampling to detect any refrigerants that might leak into the mechanical room. Mr. O’Malley said, “It’s important that the operations team have confidence that it’s safe to go into the room–that no refrigerant leak happened in the mechanical space and that nothing is leaking into the environment. We need to keep refrigerant inside the chiller. That’s important, so I’m not constantly buying refrigerant.”

The local representative noted that Xcel Energy was not using the same gases in all the chillers and not all those gases were supported in the product they were using. This situation could be addressed by the HGM-MZ’s extensive library of gases built into the monitor plus the accuracy of the refrigerant readings provided.

The HGM-MZ has a library of over 60 refrigerant gases, solving the refrigerant variety issues within the plant for detecting R22, R123 and R134a. Product standardization keeps maintenance easy by using the same product for spare parts and for quick replacement. The Xcel Energy Operations Team has had a significant reduction in the frequency of the walkthroughs they need to conduct. The MultiZone system also keeps refrigerant emissions at bay by having 1ppm performance. It also solved the issue of needing to monitor for different refrigerants at different locations.

Clear Financial Advantage

Reducing lost refrigerant, cutting technician travel time for repair work and having the right system to do the job were important from a cost and environmental perspective. According to Mr. O’Malley, “It’s critical we find refrigerant leaks early. Most importantly, we are concerned with the negative effects on the environment. I don’t want refrigerants getting into the atmosphere. The second concern is the financial impact. The machines’ performance will suffer if they don’t have the refrigerant. It’s like gas leaking out of your car.”

Because of the time it took to check the legacy product, it was critical to have a product that would constantly be drawing sequential samples at the chillers and recording refrigerant levels to ensure the product was in operation, no matter the location. “Having reliable, continuous monitoring that we could see from a central location would allow us to dispatch a technician only when having to make an assessment or deal with a minor issue,” Mr. O’Malley said. The technician’s time alone would save costs. Additional benefits include system performance, lower energy costs and reduced refrigerant cost.

Reliability

Being able to rely on the equipment in continual operation was another important consideration. The manufacturer’s representative remembers visiting the Xcel Energy chiller plant in downtown Denver and noted that it was the largest underground chiller plant he had ever visited. He recalls that Xcel Energy wanted a “set-it and forget-it”’ type unit and that they had some concerns surrounding code compliance. Wanting to focus on refrigerant sensitivity, the representative demonstrated that the refrigerant monitor could detect leaks down to 1pm.

“The monitors have been reliable. I don’t recall having to change out the pumps in quite some time,” said Mr. O’Malley, “You basically hang them on the wall and will get years and years and years of service out of them.”

Building Automation System and Communications

The facilities supplied with water by Xcel Energy are either directly owned by the building’s owners or are leased. At any time customers can request records from Xcel Energy on the management of the system. “If a customer wanted to see records on how we’re managing the system, all we would have to do is pull the data to show them the preventive maintenance we are doing and the historical data,” said Mr. O’Malley. “The monitor can talk back to the building management system if the pump goes bad or if the unit sees refrigerant. It will tell you and you don’t have to walk by it to find out.

Functionally, it “talks” the building system language,” he said. Based on the equipment performance, impression and usability, Mr. O’Malley and his Operations team are making good use of the MZs reliability, ensuring the 16 chillers remain in good operating condition and helping keep Xcel Energy’s environmental commitment and reliable service to customers.