Topical Article: The State of Art of Heat-Pump integrated Thermal Energy Storage for Demand Response


In the US, as much as 75% of the electricity is used in buildings. And of this, almost half is used for heating, ventilation and air conditioning. Even worse, buildings contribute heavily to the electricity grid stress by using as much as 78% of the morning peak hours electricity.

One way to diminish this problem and reduce peak-hour electricity demand is to introduce thermal energy storage (TES) connected to the heat pump system. The storage is charged with thermal energy when the grid demand is low and discharged by releasing thermal energy into the building’s system when the demand is high. Used properly, this shifts the electricity demand from peak to off-peak hours. In this way, the stress on the electricity grid during peak hours is reduced.

For thermal storage, phase-changing materials (PCM) have proved to be an interesting choice. They can either be embedded in the heat pump equipment or the building envelope. A number of ways to set up such a system have been researched, looking at both passive and active storage. Incorporating the storage into the building has also varied, which could have high potential in energy demand reduction without occupying the space required.

Passive storage is most common. The PCM can then be installed in the building envelope or even embedded into the building material itself. In active storage, the PCM is actively charged and discharged. Charging and discharging is related to ambient temperature. The storage could be a stand-alone tank with a heat exchanger, a configuration relatively easily connected to existing buildings. The potential for load shifting to release grid stress is higher with active storage. Both material and packaging development is required to attain maximum potential.

Research literature shows advantages from using PCM in thermal energy storages connected to heat pumps. Energy use is shifted to off-peak hours, and there is a general reduction in energy use. But the benefits vary depending on how the system is configurated, where the storage is located, and whether it is passive or active. In general, active TES systems outperform passive systems. The reduction in building energy consumption ranges from 9% to 62%, while the reduction in peak load varies from 12% to 57%.

Sara Sultan, Kyle R. Gluesenkamp, United State

 

This text has been shortened by the HPC team.

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