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How to Reduce and Decarbonize Steam

Steam and high-temperature hot water (HTHW) heating systems have been in use for more than a century and are inefficient, expensive, hard to maintain, and unsafe. These systems also frequently suffer from leaks and heat losses, leading to higher operating costs and greenhouse gas emissions. Transitioning to a lower-temperature hot water (LTHW) system addresses many of these challenges. LTHW systems are compatible with electric heat pumps, operate more efficiently and require less energy.

Making the transition to LTHW requires careful planning and a phased approach. If your system will serve multiple buildings, be sure to consult with your capital planning department and campus master plan to understand how a new district energy system will accommodate future plans.

The Decision Framework

Step 1

Identify existing system (steam, HTHW, MTHW)

Step 2

Assess load and supply temp needs

Step 3

Map plant options for creating LTHW

Step 4

Layer in phasing, incentives, and cost analysis

Step 1: Identify Existing System (Steam, HTHW, MTHW)

For a LTHW system to function, your building HVAC system) may require some equipment upgrades or adjustments to be compatible. This is because distributing hot water or steam for heat relies on the use of steam coils or radiators, whereas LTHW systems may use radiant panels, underfloor heating, or fan-assisted units. These heat distribution methods may require retrofits to function using LTHW.

Step 2: Assess Load and Supply Temp Needs

Decarbonization through electrification will increase electrical demand, potentially exceeding the capacity of existing circuits and electrical panels.

Assess the capacity of existing electrical infrastructure serving the campus and individual buildings slated for electrification to confirm that new all-electric equipment options are within the campus’s current electrical capacity. If not, you may need an electrical upgrade.

At the campus level, include the servicing electrical utility early in these conversations. If campus-level electrical service needs upgrading, consider other electrification projects that should be included in an electrical infrastructure upgrade to reduce the overall costs of the transition.

You will

Options for localized technologies, such as electric steam boilers or steam heat pumps, can address point-of-use steam needs and still meet your decarbonization objectives. Steam serves valuable purposes that are separate from space heating, such as providing humidification, lab sterilization, and food preparation

To make a determination of your campus steam needs, do the following:

Identify point-of-use steam needs and special use cases where steam is needed on site and consider safety procedures resulting from such
Determine loads and steam quality needs (temperature, pressure, water quality) and usage patterns
Replace district steam supply with alternative technologies such as electric steam boilers or steam heat pumps

Step 3: Map Plant Options for Creating LTHW

Low-temperature hot water for decarbonized space heating and cooling relies on natural sources from the air, ground, or water. This playbook offers guidance on several LTHW sources and heat pump technologies to distribute or remove heat from indoor spaces, like air-source heat pumps, ground-source heat pumps, and thermal storage.

When it comes to designing your system, and choosing your equipment and sizing, you’ll want to use this chart to guide your choices:

If you have…	You might want to…
Heating for ventilation systems provided via steam or HTHW	Replace existing steam coils with LTHW coils or add coils with additional rows if converting from HTHW to LTHW system Add energy or heat recovery devices to reduce the ventilation heating load
Zonal heating or perimeter heating provided by steam or HTHW radiators	Conduct thermal stress testing during peak winter months to understand actual heating load, reduce perimeter heating equipment needs and sizing Consider envelope or insulation upgrades to reduce perimeter heating loads Replace with LTHW radiators and supplement with terminal units as feasible
A current hot water system that supplies HTHW in the range of 160–180°F	Conduct thermal stress testing during peak winter months to understand actual heating load and if LTHW can satisfy the zone requirement without triggering occupant discomfort
A system experiencing energy losses and is highly inefficient	Adequately maintain and optimize existing steam or HTHW distribution systems to improve system efficiency, reduce energy losses, and lower utility costs
An existing cooling system consisting of absorption chillers that utilize steam	Replace with electric chillers, consider heat recovery chillers with three to six times higher efficiencies A single chiller serving both heating and cooling optimizes space use and is cost effective
Natural gas steam boilers used for specialized process uses (e.g., laboratory uses)	Replace space heating systems with a LTHW system and provide a separate localized heat pump or electric boiler to provide point-of-use steam
Natural gas steam boilers or steam generators (at cogeneration plants)	Replace with heat pump chillers (air source, water source, or ground source) with thermal energy storage
Steam piping and condensate piping	Replace both steam and condensate lines with LTHW supply and return or ambient loop piping Pipes will be larger than existing steam and condensate lines and must be carefully coordinated, especially in utility tunnels Reuse piping where feasible Carefully consider phasing
Steam traps and other accessory equipment (valves, etc.)	Replace with hydronic accessories for LTHW piping or ambient loop piping as needed

Step 4: Layer in Phasing, Incentives, and Cost analysis

Many campus steam systems are intricately intertwined throughout the campus infrastructure, and modifications will affect multiple buildings and multiple, sometimes specialized, systems.

Perform a thorough feasibility study to identify the most effective path for decarbonizing and modernizing campus heating infrastructure. This should include a clear phasing plan for each scenario, which should identify:

New equipment installation dates
Dates for demolition of existing systems
Connections between new and existing systems
Operational considerations in each phase
The level of disruption during each phase for each scenario

Of course, before implementing long-term solutions, you may want to run potential scenarios through some financial modeling and compare costs against a business-as-usual scenario (e.g., maintaining your current steam or HTHW system). To do so, you’ll want to consider financial impacts such as first costs, annual operating costs, incentives and grants, tax credits, rebates, and future carbon penalties.

Resources

Develop Your Decarbonization Plan
District Energy Strategies
Case Study: Pace University’s transition away from steam
NREL’s Decarbonizing Building Thermal Systems: A How-to Guide for Heat Pump Systems and Beyond [PDF] (see pages 69–74 for thermal stress testing and electrical load studies)
U.S. Department of Energy’s GHG Emissions Reduction Audit: A Checklist for Owners [PDF]
Steris Healthcare’s Guide to Optimal Steam Generation

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