Introduction
The United Nations Environmental Program, in its publication titled “District Energy in Cities: Unlocking the Full Potential of Energy Efficiency and Renewable Energy“, stated that:
• Cities account for over 70 percent of global energy use and 40 to 50 percent of greenhouse gas emissions worldwide.
• Half of the cities’ energy consumption is for heating and cooling.
• Building up modern district energy in cities is one of the least expensive and most effective ways to cut down on emissions and primary energy use.
Based on the above numbers, there is no doubt that urban comfort cooling in cities has an effect on greenhouse gas emissions around the world. The United Nations Environmental Program (UNEP) is advocating district cooling in cities as a viable solution for decarbonizing urban comfort cooling. The district cooling plant offers many benefits over the conventional in-building chiller plant. In this article, we will explore the key differences between the district cooling plant and the in-building chiller plant.
Definition of a District Cooling Plant
A district cooling plant is a centralized cooling system that provides cooling energy to multiple end-user buildings in a district through a network of chilled water distribution piping. The central chiller plant produces chilled water, which is then circulated through the distribution piping to the buildings that require cooling. The chilled water is then used in the buildings’ HVAC systems for comfort cooling or process cooling.
Definition of an In-Building Chiller Plant
An in-building chiller plant is part of a building’s HVAC system that provides comfort cooling to the building’s occupants. It consists of one or more chillers, pumps, cooling towers, and other components necessary to produce and distribute chilled water throughout the building.
District Cooling is a Utility Infrastructure
The district cooling plant is part of a utility infrastructure that supplies chilled water to multiple end-user buildings for the purpose of comfort cooling or process cooling. This makes it different from the in-building chiller plant, which is part of the building’s HVAC system. The district cooling plant is operated and maintained by a third-party provider, whereas the in-building chiller plant is typically managed by the building owner or operator.
Profit Center vs Cost Center
To a district cooling operator, the district cooling plant is a profit center that generates revenue and net income through the sale of cooling energy. The operator is responsible for the operation, maintenance, and repair of the district cooling plant. On the other hand, the in-building chiller plant is part of a building’s HVAC system, and the cost of air conditioning is usually built into the gross rental, calculated on a per-square-foot basis. Therefore, to a building owner, the in-building chiller plant is a cost center that incurs operation and maintenance costs in addition to capital depreciation charges.
Industrial Grade vs Commercial Grade Equipment
A district cooling plant is built to the standards of an industrial plant and utilizes high-efficiency industrial-grade equipment for its process. This robust equipment is designed to operate continuously and reliably with high availability. In contrast, an in-building chiller plant is part of a commercial building and is made up of commercial-grade equipment, which may not be as robust as the equipment used in a district cooling plant.
District Cooling operates 24×7
A district cooling plant is required to operate 24×7 without interruption or disruption. This is because the end-user buildings rely on the district cooling plant for their cooling needs. Any downtime at the district cooling plant can have a significant impact on the end-user buildings. Due to stringent availability and reliability requirements, the district cooling plant is equipped with robust, industrial-grade equipment and provided with adequate equipment redundancy to prevent unscheduled outages. In contrast, an in-building chiller plant usually operates according to the normal office hours or the operating hours of commercial retail tenants. It is not uncommon to see the building chillers switched off during the night.
Cooling as a service vs on-premise chilled water generation
The district cooling plant is part of an energy utility business that offers cooling as a service, while the in-building chiller plant is essentially an on-premise chilled water generation asset. From a building owner’s perspective, opting for cooling energy as a service from a district cooling plant is an asset-light strategy. The building owner does not have to commit to a substantial initial capital investment in an in-building chiller plant to get access to cooling energy. Instead, they pay for the cooling energy on a “pay as you go” basis, usually billed on a monthly basis. Furthermore, the operation and maintenance of the cooling energy plant are outsourced to the district cooling operator, allowing the building owner to focus and concentrate on their core business.
Economy of Scale Translates into Cost and Energy Efficiency
The district cooling plant serves a much larger cooling demand compared to the in-building chiller plant. Hence, the economy of scale enables the district cooling plant to utilize technology options such as thermal energy storage and high-efficiency series-counterflow chillers, which lower operation costs and increase energy efficiency. This translates into a lower cost of cooling energy for the end-users and a more sustainable energy solution for urban comfort cooling.
Conclusion
The key differences between the district cooling plant and the in-building chiller plant have been explored. Understanding these key differences is essential for engineers who are involved in the planning, design, development, operation and maintenanace of district cooling systems. The district cooling plant offers many advantages, including being part of a utility infrastructure, utilizing industrial-grade equipment, operating 24×7, and offering cooling as a service. The economy of scale enables the district cooling plant to be a more cost-effective and sustainable energy solution for urban comfort cooling.
