This article was originally published in the Northeast Ohio Properties magazine June 2024 issue beginning on page 53. Written by Alexis Omilion, Director, Business Development at Corix.
The Environmental Impact of Heating and Cooling a Building
Conventional heating and cooling systems in commercial buildings include equipment like boilers, chillers, cooling towers, heat pumps, and air conditioners, which are powered by either natural gas or electricity. The emissions produced from burning fossil fuels to generate heat or electricity include carbon dioxide (CO2), which accounts for nearly 80 percent of greenhouse gases emitted by human activities in the United States. Additionally, heat and electricity generation for commercial and residential properties account for 31 percent of all U.S. greenhouse gas emissions [1]. With increasing pressure to reduce greenhouse gas emissions, organizations, institutions, and municipalities are setting aggressive decarbonization goals. These goals typically aim to reduce scope 1, 2, and 3 greenhouse gas emissions in the short term and achieve carbon neutrality by 2050.
Understanding the Building’s Emissions Factor
The environmental impact of heating and cooling buildings, in terms of CO2 emissions, depends on two variables – the efficiency of the system and the source of energy. As equipment ages and degrades, system efficiency decreases significantly, which proportionately increases energy consumption and CO2 emissions. Sourcing an alternative form of energy can be an effective method of decreasing carbon dioxide emissions. However, care must be taken to understand the emissions factor associated with the energy generation. For example, while using electric equipment like heat pumps or electric boilers to heat a building can potentially reduce greenhouse gas emissions, the electricity being used to power the equipment must be generated from lower-carbon sources.
Reducing Emissions Factors through Efficiency Gains
The simplest method of reducing a building’s emissions factor is to maximize the efficiency of the heating and cooling systems. By connecting to a district energy system, a building can achieve higher efficiency than what is possible on an individual building basis. District energy systems supply steam, hot water, and chilled water from a central plant to multiple buildings in a district through a network of underground piping. The energy generation equipment inside each building is replaced with a simple heat exchanger that transfers the thermal energy to the building’s HVAC system.
Figure 1. District heating and cooling system illustration.
By aggregating the load of multiple buildings in a district, the equipment at the central plant operates at higher load factors and, therefore, higher efficiencies than equipment at individual buildings. The distribution piping acts as a form of thermal storage, which further smooths the load for the central plant and provides built-in system redundancy. Furthermore, economies of scale allow for industrial-grade, high-efficiency equipment that is not feasible on an individual building basis. District energy plants also can cogenerate heat and electricity, resulting in a combined efficiency of up to 75%, compared to a national average of 50% when the services are provided separately [2].
The impact of these efficiency improvements on building CO2 emissions can be seen in Figure 2, which compares the CO2 emissions factors for in-building chillers and Cleveland’s downtown district cooling system [3]. While both scenarios use chilled water for building cooling, the district energy system takes advantage of load aggregation, high-efficiency equipment, diligent maintenance, and 1 MW of cogeneration at the central plant to reduce electrical consumption from the grid. Compared to in-building chillers, the amount of CO2 emitted per square foot of building floor space is reduced by approximately 22 percent with a district-chilled water system.
Figure 2. Comparison of carbon dioxide emissions factors per square foot for in-building chillers and district cooling.
Providing Flexibility for Future Needs of the District
Buildings can connect to an existing district energy system, like the one in Downtown Cleveland, or new district energy systems can be built alongside and integrated within new developments. A district approach to energy provides the scale and diversity needed to implement low-carbon technologies such as geothermal, biomass, waste heat recovery, and cogeneration. Figure 3 compares the CO2 emissions for some typical heating technologies [4]. A district energy system often combines conventional and low-carbon technologies, significantly reducing the CO2 emissions of buildings on the system.
Figure 3. Comparison of building carbon dioxide emissions factors per unit energy for different heating technologies.
District energy also provides the flexibility to adapt to clean technologies such as onsite renewable electricity or green hydrogen over time. With the distribution system already in place, the equipment at the central plant can be upgraded to cleaner technologies without any need to replace, modify, or upgrade the equipment at individual buildings. Achieving decarbonization goals will require a combination of efficiency improvements and the implementation of low-carbon technologies. District energy maximizes the efficiency of thermal energy generation while providing the flexibility to easily adapt to low-carbon technologies as the district’s needs evolve.
[1] Emissions estimates are sourced from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2022.
[2] Data from the U.S. Department of Energy, Office Energy Efficiency & Renewable Energy.
[3] The emissions factor for in-building cooling was calculated using the U.S. Energy Information Administration’s 2018 Commercial Building’s Energy Consumption Survey data for buildings in Northeast Ohio’s climate zone. The emissions factor for Cleveland’s downtown district cooling system was calculated using Corix Cleveland Thermal’s natural gas and electricity consumption for its chilled water system.
[4] Emissions factors for grid electricity are calculated from the Environmental Protection Agency’s eGRID database. Grid electricity in Ohio currently has an average GHG footprint of 1,000 lbs/MWh.
