Lecture Objectives:

1. Lecture Objectives: • Discuss Project 1 • Learn about thermal storage systems

2. For Project 1 you will needWet bulb temperature Empirical equation based on T DB [°C] and RH [0-100] Exact calculation require solving 3 equations For this modeling the empirical equation is fine.

3. Merging Two Models Temperature difference: R= TCTR -TCTS Model: Link between the chiller and tower models is the Q released on the condenser: Q condenser = Qcooling + Pcompressor - First law of Thermodynamics Q condenser = (mcp)water form tower (TCTR-TCTS) m cooling tower - property of a tower TCTR= TCTS - Q condenser / (mcp)water Finally: Find P() or The only fixed variable is TCWS = 5C (38F) and Pnominal and Qnominal and m cooling tower (Rnominal) for a chiller (defined in nominal operation condition): Based on Q() and WBT you can find P() and COP().

4. Example of CHP + Cooling We need a thermal storage somewhere in this system !

5. Thermal storage • Store heat • Many issues to consider (∆T, pressure, losses,…. ) • Store cooling energy • Chilled water • For cooling condenser • For use in AHU (cooling coils) • Ice storage • Compact but… • Other materials (PCMs) that change phase the temperature we need in cooling coils • Many advantages, but disadvantages too!

6. On-Peak and Off-Peak Periods This profile depends on the type of building(s) !

7. Chilled water tank Use of stored cooling energy Store Use

8. Which one is better ? • Depends on what you • want to achieve: • Peak electric power reduction • Capacity reduction • …..

9. Downsizing the Chiller • Lower utility costs • Lower on-peak electrical consumption(kWh) • Lower on-peak electrical demand (kW) • Smaller equipment size • Smaller chiller • Smaller electrical service (A) • Reduced installed cost • May qualify for utility rebates or other incentives

10. Sizing storage system (use Annual Cooling-Load Profile) How often you need to use it? What are the cost-benefit curves ? What is the optimum size ?

11. Stratified chilled water tanks

12. Temperature and dynamics Temperature at outlet during the changing cycle of the tanks

13. Stratified chilled water tanksdiffuser geometry Challenge: “Pull” large amount of energy without disturbing stratification

14. Ice Storage Tank Many issues ! …. As freezing progresses progress the ice becomes thicker and significantly impedes heat transfer

15. Open Ice Storage Tank Also issues ! …..

16. Fluid Flow Rate and Freeze ΔT

17. Impact on Chiller Efficiency

18. PCMs A. Sharma et al. / Renewable and Sustainable Energy Reviews 13 (2009) http://www.docunator.com/bigdata/1/1367142535_c566e7d75e/reviewexample2.pdf

19. Other latent heat thermal storage systems (research is ongoing)

20. Construction and benefits Active Passive (wall)

21. Modeling(stratified tank) Write energy and mass balancer equation for each section

22. Installation of thermal storage system Upstream Downstream • Increases chiller efficiency • Increases chiller capacity • Overall system efficiency ??? • Decreases storage capacity • Simplifies system layout • ….. • Decreases chiller efficiency • Decreases chiller capacity Overall system efficiency ??? • Increases storage capacity •…… • Does not allow chiller shut down!