THERMAL ENERGY STORAGE TANK DOWN UNDER

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1 THERMAL ENERGY STORAGE TANK DOWN UNDER OWNER ENGINEER TANK BUILDER

2 Thermal Energy Storage Tank Walnut, CA Los Angeles area Community College serving over 50,000 students Host to the 2020 U.S. Olympic Track & Field Competition

3 Why Mt. SAC Considered TES Campus expansion plan through 2025 Increased district cooling requirement Limited space for central plant Reliability Redundancy of the chilled water system Reduce daytime noise Economic benefits

4 Economic Benefits of TES Lowest first cost and operation & maintenance costs when compared to adding more central chiller plant equipment Energy cost savings by shifting the electric load to off-peak periods Permanent Load Shift incentives and State energy efficiency funds

5 What led to a Fully Buried TES Tank? Limited space in central plant area Eliminates aesthetic concerns Less maintenance with a concrete tank

6 Engineering Perspective

7 Engineering Perspective Underground TES tanks have challenges that are not faced by above ground applications. A few significant ones are: The water elevation of the tank may be lower than some or all of the buildings and plant. The tank s venting and access location will be at grade. Draining the tank may require pumping.

8 Tank Water Level in Relation to Building Equipment TES tanks operate as open systems the top of the tank is at atmospheric pressure. If the tank water is at a lower elevation than other parts of the system there is a possibility of chilled water lines going in to a vacuum and/or the tank may overflow.

9 Controlling Pressure in Buildings A pump and control valve arrangement works well for maintaining positive system pressure during tank discharge. Pump the water from the bottom of the tank when discharging TES tank. Maintain positive pressure at all air handlers and fan coils. Pump the water from the top of the tank when charging and control the chilled water return line pressure.

10 Controlling Pressure During Regeneration A pump and control valve arrangement works well for maintaining positive system pressure during tank regeneration. Pump the water from the top of the tank when charging and control the chilled water return line pressure. Maintain positive pressure in the central plant.

11 Alternative Pressure Control & Isolation Methods Pressure sustaining valves are often used, but represent a fixed pressure drop in the system and result in higher pumping energy. For very large elevation differences a pressure isolating heat exchanger may be required, but this poses other concerns: o Second pump system will be added. o Thermal losses in the heat exchanger.

12 Tank Venting and Access The tank needs to have a point of entry and be vented to the atmosphere. With a buried tank, this may be at grade. Securing the access from the public is needed.

13 Draining and Overflow The tank requires an overflow pipe: o Route to sanitary drain? Check with local authorities. o May require a long underground pipe route to get to a suitable drain. o May require a separate sump with a pump. Overflowing the tank is abnormal and designer should provide a means to detect and isolate. Tank may need to be pumped out if it is to be emptied if gravity flow is not feasible.

14 TES Tank Level Control The system chilled water make-up must be controlled by the tank water level. o The tank is the expansion control. o Other make-up water sources must be isolated. Example of level sensor types: o Ultrasonic sensors. o Pressure sensor at the bottom of the tank Ultrasonic Level Sensor LD31 Pressure Sensor

15 Engineering Summary Look at the issues associate with hydraulic elevations. Coordinate the location of the access hatch and vent. Coordinate the tank drain and overflow locations. Control tank water level and isolation any other sources of make-up water.

16 Tank Builder Perspective

17 Example TES Tank Applications College Campuses Los Angeles, CA - USC Riverside, CA - UC Orlando, FL - UCF Government and Municipalities Lackland AFB, TX San Antonio, TX - Airport Raleigh, NC Brooks, CA CCC Resort Santa Clara, CA DFP Front Royal, VA Dominion Private Industry, Power Plants, and Data Centers

18 2.0 MG TES Tank - Considerations for Fully Buried Under a Parking Lot Groundwater level Roof loading HS20 (think firetrucks) Internal distribution piping and diffuser piping among columns Access into the excavation during construction Access through the roof after backfill

19 Floor Construction and Seismic Considerations Column locations 8 thick reinforced concrete floor Seismic restraints

20 Temporary Shoring and Wall Form Placement Form for cast-in-place reinforced concrete wall Temporary Shoring

21 Horizontal Prestressing and Cast-In-Place Roof 12.7 miles of steel cable under 140 ksi of tension placing the wall sections into compression 18 thick reinforced concrete roof

22 Upper Diffuser Piping Stainless steel hangers and supports Sch. 40 PVC distribution and diffuser piping Reinforced concrete columns

23 TES Tank Ready to be Backfilled

24 Backfill and Parking Lot Restored

25 Performance of the TES Tank

26 Performance Requirements and Details of Mt. SAC s TES Tank 20,000 ton-hrs useable TES capacity 16 F chilled water ΔT 5,000 gpm maximum chilled water flow rate 2,000,000 gallons total volume inside diameter x 29-9 water depth

27 9/12/ :00:00 AM PDT 9/12/ :27:00 AM PDT 9/12/ :54:00 AM PDT 9/12/ :21:00 AM PDT 9/12/ :48:00 AM PDT 9/12/ :15:00 AM PDT 9/12/ :42:00 AM PDT 9/12/ :09:00 AM PDT 9/12/ :36:00 AM PDT 9/12/ :03:00 AM PDT 9/12/ :30:00 AM PDT 9/12/ :57:00 AM PDT 9/12/ :24:00 AM PDT 9/12/ :51:00 AM PDT 9/12/ :18:00 AM PDT 9/12/ :45:00 AM PDT 9/12/ :12:00 AM PDT 9/12/ :39:00 AM PDT 9/12/ :06:00 AM PDT 9/12/ :33:00 AM PDT 9/12/ :00:00 AM PDT 9/12/ :27:00 AM PDT 9/12/ :54:00 AM PDT 9/12/ :21:00 AM PDT 9/12/ :48:00 AM PDT 9/12/ :15:00 AM PDT 9/12/ :42:00 AM PDT 9/12/ :09:00 PM PDT 9/12/ :16:00 PM PDT 9/12/ :43:00 PM PDT 9/12/ :10:00 PM PDT 9/12/ :37:00 PM PDT 9/12/ :04:00 PM PDT 9/12/ :31:00 PM PDT 9/12/ :58:00 PM PDT 9/12/ :25:00 PM PDT 9/12/ :52:00 PM PDT 9/12/ :19:00 PM PDT 9/12/ :46:00 PM PDT 9/12/ :13:00 PM PDT 9/12/ :40:00 PM PDT 9/12/ :07:00 PM PDT 9/12/ :34:00 PM PDT 9/12/ :01:00 PM PDT 9/12/ :28:00 PM PDT 9/12/ :55:00 PM PDT 9/12/ :22:00 PM PDT 9/12/ :49:00 PM PDT 9/12/ :16:00 PM PDT 9/12/ :43:00 PM PDT Performance Test Chilled Water Flow Rate Thru Tank Chilled Water Flow Rate (gpm) - TES Tank - Sept 12, Discharge Period Discharge Period Coincides with On-Peak Electric Demand Charge

28 Instrumentation Inside of a TES Tank Level Sensor Thermocline Temperature Sensors

29 9/12/ :00:00 AM PDT 9/12/ :20:00 AM PDT 9/12/ :40:00 AM PDT 9/12/ :00:00 AM PDT 9/12/ :20:00 AM PDT 9/12/ :40:00 AM PDT 9/12/ :00:00 AM PDT 9/12/ :20:00 AM PDT 9/12/ :40:00 AM PDT 9/12/ :00:00 AM PDT 9/12/ :20:00 AM PDT 9/12/ :40:00 AM PDT 9/12/ :00:00 AM PDT 9/12/ :20:00 AM PDT 9/12/ :40:00 AM PDT 9/12/ :00:00 AM PDT 9/12/ :20:00 AM PDT 9/12/ :40:00 AM PDT 9/12/ :00:00 AM PDT 9/12/ :20:00 AM PDT 9/12/ :40:00 AM PDT 9/12/ :00:00 AM PDT 9/12/ :20:00 AM PDT 9/12/ :40:00 AM PDT 9/12/ :00:00 AM PDT 9/12/ :20:00 AM PDT 9/12/ :40:00 AM PDT 9/12/ :00:00 AM PDT 9/12/ :20:00 AM PDT 9/12/ :40:00 AM PDT 9/12/ :00:00 AM PDT 9/12/ :20:00 AM PDT 9/12/ :40:00 AM PDT 9/12/ :00:00 AM PDT 9/12/ :20:00 AM PDT 9/12/ :40:00 AM PDT 9/12/ :00:00 PM PDT 9/12/ :20:00 PM PDT 9/12/ :40:00 PM PDT 9/12/ :00:00 PM PDT 9/12/ :20:00 PM PDT 9/12/ :40:00 PM PDT 9/12/ :00:00 PM PDT Performance Test Water Level in the Tank Water Level (feet) TES Tank September 12, 2017 Water Level Varies Very Little Throughout the Day

30 Performance Test Temperature Readings in the Tank

31 Thermocline Performance Test Temperature Readings in the Tank

32 Q&A James Valiensi P2S Engineering Guy Frankenfield DN Tanks