Controlling thermal energy storage
A method of flattening electric energy demand from an electric grid including during less-than-peak electricity demand periods, freezing Phase Change Material (PCM) in a Thermal Energy Storage (TES) system, and during peak electricity demand periods, using the TES to cool air conditioning refrigerant fluid. A system of flattening electric energy demand of an air-conditioner from an electric grid including an air conditioner, a Thermal Energy Storage system, and a controller, wherein the controller is programmed to implement the above method. A method of freezing Phase Change Material (PCM) in a Thermal Energy Storage (TES) system including setting a temperature of heat exchange fluid at a temperature higher than −10 degrees Celsius when directed to ice bricks containing water and an ice nucleation agent. A Thermal Energy Storage (TES) system controller programmed to discharge more than 50% of a heat capacity of the TES. Related apparatus and methods are also described.
1 . A method for controlling a thermal energy storage (TES) system installed at a facility, wherein the TES system comprises a TES unit comprising a heat transfer fluid (HTF) to transfer thermal energy to the facility, the method comprising:
a. predicting a profile of total electricity demand over time, including cooling energy demand of the facility, based on monitoring of a main electric meter of the facility;
b. calculating available energy of the TES unit;
c. monitoring temperatures of the HTF; and
d. controlling flow rate of the HTF during discharging of the TES unit based on the temperatures of the HTF, the available energy and the profile.
2 . The method of claim 1 , comprising monitoring a rate of change in electric demand in the facility to determine the predicted profile of total electricity demand over time.
3 . The method of claim 1 , comprising using the TES system to cool a refrigerant of an air conditioner in the facility.
4 . The method of claim 1 , comprising:
determining a desired discharge schedule; and
causing discharge of the TES at different discharge rates in accordance with the schedule.
5 . The method of claim 1 , comprising predicting the profile of total electricity demand over time based a weather forecast.
6 . The method of claim 1 comprising predicting the profile of total electricity demand over time based on a time of day.
7 . The method of claim 1 wherein the TES unit encloses a plurality of capsules containing a phase change material (PCM) and having the HTF flow therethrough.
8 . The method of claim 1 comprising monitoring an operating point of a chiller at the facility and controlling flow rate of the HTF during discharging of the TES unit based on the operating point of the chiller.
9 . A thermal energy storage (TES) system installed at a facility, the system comprising:
a TES unit comprising a heat transfer fluid (HTF) to transfer thermal energy to the facility; and
a controller comprising instructions for:
a. predicting a profile of total electricity demand over time, including cooling energy demand of the facility, based on monitoring of a main electric meter of said facility;
b. calculating available energy of the TES unit;
c. monitoring temperatures of the HTF; and
d. controlling flow rate of the HTF during discharging of the TES unit based on the temperatures of the HTF, the available energy and the profile.
10 . The system of claim 9 comprising an array of fluidly connected thermal energy storage units, each thermal energy storage unit enclosing a plurality of capsules containing a phase change material (PCM) and having a heat transfer fluid (HTF) flow therethrough.
11 . The method of claim 1 comprising identifying an anticipated peak in the profile and mitigating the anticipated peak based on the temperatures of the HTF, the available energy and the profile.
12 . The system of claim 9 wherein the controller monitors an operating point of a chiller at the facility and controls flow rate of the HTF during discharging of the TES unit based on the operating point of the chiller.