Completed Research
Understanding Fan Coil Components and Their Relationship to Energy Consumption and Modeling

From ASHRAE Journal Newsletter, May 25, 2021

ASHRAE RP-1741, Understanding Fan Coil Components and How They Relate to Energy Consumption and Energy Modeling, benchmarks the energy savings of modulation control relative to the conventional on-off control of hydronic fan coil units. Understanding the energy savings of modulation control could promote wider adoption of electronically commutated motors and modulating valves. Principal investigator Peng “Solomon” Yin, Ph.D., Associate Member ASHRAE, discussed this research with ASHRAE Journal. To access the full research report on RP 1741, click here (ASHRAE login required).

1. What is the significance of this research?

The increasing use of electronically commutated (EC) motors and modulating valves in hydronic fan coil units (FCUs) enables load tracking operation that can potentially provide superior thermal comfort and energy efficiency. The goal of ASHRAE RP-1741, Understanding Fan Coil Components and How They Relate to Energy Consumption and Energy Modeling, is to benchmark the energy savings from air and water modulation control relative to conventional on-off control of hydronic FCUs. Understanding the energy savings of modulation control could promote wider adoption of EC motors and modulating valves. Developing an algorithm for modeling modulation operation could enable model-based energy analysis and system design.

2. Why is it important to explore this topic now?

Similar to other HVAC equipment, hydronic FCUs are generally oversized to be able to provide the peak cooling and heating loads. Consequently, FCUs rarely operate at their full load for an extended time. Running fans and pumps at part-load conditions could enable energy savings. Based on varying airflow and water flow with thermal loads, the modulation control can take advantage of oversized equipment and operate them at part-load conditions for saving energy.

3. What lessons, facts and/or guidance can an engineer working in the field take away from this research?

Building energy simulation conducted in this study showed that modulation control could save over 50% FCU fan energy compared with cycling on and off. The modulation control can also maintain a higher chilled water  at part-load conditions, leading to over 50% savings in pump energy and more efficient chiller staging. The total HVAC system savings ranges from 5% to 15%, compared with the conventional on-off control.

4. How can this research further the industry's knowledge on this topic?

Modulating oversized fans and pumps responding to thermal load variation has potential for significant energy savings. The developed performance models and operating sequence of hydronic FCUs in ASHRAE RP-1741 could be used in building energy simulations to estimate the energy savings from modulation control compared with cycling on and off.