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Hydronic Heating Systems

Wall-mounted hydronic heating system with copper pipes and components in a utility room.

What are hydronic heating systems?

This measure applies to hydronic heating systems that supply heat energy to the building’s hot water loop for various applications. The refrigeration cycle heats the liquid refrigerant, which absorbs heat from the outdoor environment (air or water, depending on the system) and evaporates into a gas. The compressor then transforms the refrigerant into a high-pressure, high-temperature vapor, which circulates to the inside coil. Heat exchangers absorb heat from the refrigerant and transfer it to the hot water loop for distribution throughout the building. After absorbing heat, the refrigerant becomes a slightly cooler, high-pressure liquid and cycles back to the exterior coil.

Before reaching the exterior coil, the system passes the refrigerant through an expansion valve, converting it into a low-pressure, low-temperature liquid. This enables higher heating capacity, and the refrigerant cycles back to the exterior coil.

Heat pumps can traditionally operate in reverse using a reversing valve to provide cooling to the building, essentially acting as a traditional air conditioning unit, but the focus of this measure is for heating mode to evaluate the potential gas offset from using the heat pump in comparison to traditional gas system such as a boiler or furnace. In addition, for cooler climates the heat pump may have the ability to operate in defrost mode resulting in periodic heating interruptions. Equipment sizing, a buffer tank and/or a supplemental boiler can all be used as strategies to mitigate heating interruptions.

Air-to-water heat pump

The air-to-water heat pump uses outdoor air to heat, following the refrigeration cycle described above. The system operates at design conditions until outside temperatures approach freezing, lowering efficiency, especially in cold climates. To prevent heating disruptions, buildings typically use a backup system, increasing operational costs in freezing conditions.

Water-to-water heat pump

A water-to-water heat pump system uses water as the heat source (or heat rejection in cooling mode). The water loop consists of a glycol solution, which has higher density and heat transfer properties than pure water, leading the “water source” pumps to consume more energy in comparison to the fan of an air-source system. This is in addition to traditionally higher installation costs. In cooler conditions the efficiency of the system will diminish as the water source temperatures decrease but carry an inherent advantage as water temperature typically stabilizes at or above freezing in cold climates. This is in comparison to air temperatures in cold climates that could experience air temperatures below freezing and may not require a backup system depending on conditions and demand.

What are the benefits?

This measure focuses on decarbonizing buildings by using an efficient, electric solution to heat the hot water loop.
Equipment can be used for space heating, heat recovery, simultaneous heating and cooling and process loads.
Energy efficiency with higher performance and lower energy use.
Expandable designs available for incremental size capacity, redundancy, and future load requirements.
Flexibility in capacity for small and large commercial applications.
Full commissioning and FDD ensure the system are operating to optimize maximum efficiency and to ensure consistent performance during equipment lifecycle.
May reduce installation and maintenance cost compared to a conventional chiller plant.
May reduce mechanical room requirements and installation area required for mechanical equipment.

What are the challenges/constraints?

Equipment efficiency may be derated for projects with required high hot water temperatures (typically greater than 120˚F).
Equipment performance optimization may require additional design, commissioning, and controls.
Initial cost impact, especially for a water-to-water system
Limited operating conditions at lower ambient or water temperatures.

Qualifications for inducements?

Air-to-water or water-to-water heat pump systems for heating, heat recovery or simultaneous heating and cooling applications.
The design team must define optimum operating conditions based on project-specific criteria and document them.
The system must be fully commissioned and operating at optimized design conditions.
Fault Detection Diagnostics (FDD) to ensure ongoing optimized performance are strongly recommended but not required.

Hydronic heating systems lead in decarbonizing buildings, offering reliability and advantages over traditional gas heating systems. They operate in versatile configurations. These systems integrate with others, require less installation space, suit diverse buildings, and reduce energy use and maintenance costs long-term.

Contact us for information on available inducement in the CEDA program.

Download the Hydronic Heating Systems Technical Guide (pdf)

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