Thermal Energy Storage For commercial Buildings

Why do we need TES? In many regions of the world, ventilation system account for up to 60% of buildings electricity demand during peak hours.  Electricity companies charge separate demand charge per kW of energy consumed per month.  More electricity consumption at peak, More electricity needs to be produces, More fossil fuels needs to be burned, More CO2

How much costly on peak charge can be?

Ways to store Energy in Thermal form Ice Storage Latent Heat Storage Low Specific Heat 57-142 $/kW Chilled Water Storage Sensible Heat Storage High Specific Heat 57-85 $/kW Phase Change Material Under Research

Ice Storage Heat exchanger to convert ice in chilled water Secondary chiller required to super cool the water to make Ice. Thermal Conductivity is lower than chilled water Melting of ice is not uniform and depend on internal/externa melt process Higher heat storing capacity for same volume Run Chiller on Full load capacity during off peak time and make Ice Heat exchanger to convert ice in chilled water Shut-off chiller during peak time and use stored energy

Ice Storage Techniques Secondary coolant freezes the external water into ice during charging period Same fluid flows in the pipes during discharge period but rejects heat into ice and cools down. Mostly used. Ice formation on evaporator surface and periodically dropped Tank is partially filled with ice & water

Chilled Water Storage Charging Discharging Super chilled water during night Partially or fully run on stored energy Use chilled water to serve heat load during peak load Charging Discharging

Chilled Water Storage Techniques Series Tank Gradually increasing water temperature Flow rate needs to be increased as temperature increase for constant load Stagnation More than one valve needs to be opened be opened as the supply temperature increase for constant load Complex controls strategy Good because keeps hot and cold water separate by thermocline layer Easy control strategy

Case Study Building Type: Education Area: 240,277 m2 out of that 37% conditioned Peak load 2276 TR Mechanical Chiller capacity 800TR Partially chilled water & chiller at the same time operation Results Annual benefit: $188143 Payback period: 1.8 year

Is this Practical? Energy Modelling Approach

Office Building Energy Model Area: 20,000 sq ft with 100 people Building Operation time : 9AM to 5 PM Location: Chicago(No demand charge) v/s Austin Heating & Cooling Energy source: Electricity Construction: ASHRAE 90.1 Equipment efficiency: ASHRAE 90.1

Throughout year Energy Consumption (kWh)

Summer Cooling Energy Demand (kW) Chicago Austin

Energy Rates   ComEd (Chicago) ($) Austin Energy (Austin) Off-peak energy charge 0.0619 /kWh Jan-June & Sept-Dec 0.07527 (0-10 kWh) 0.05083(10-300 kWh) 0.04627 (>300 kWh) June-Sept 0.028290 On-peak energy charge 0.0619/kWh Demand charge - 12.44 (10-300 kW) 14.65(>300kW) Austin: Chiller peak kW electricity consumption in range 5-32kW with 32 kW Peak demand in July & August Chicago: Chiller peak kW electricity consumption in range 0-27.4 kW with 27.4 kW Peak demand in July

Payback Analysis Storage capacity Number of Hours Chilled water Storage Cost ($) Utility peak energy rate ($/kWh) Utility peak demand rate ($/kW) Demand Charge ($) After Installing Storage Demand Charge ($) Demand Charge Saving different ($) Energy savings (30 days) ($) Total Savings (30 days) ($) Payback period Months Chicago 20 3 $900.00 0.0619 0.00 111.42 8 2 $600.00 74.28 Austin 0.04627 12.44 398.08 149.28 248.80 83.29 332.09 55.52 304.32 Installation Cost $15/kWh from Hasnain, S. M. Review on sustainable thermal energy storage technologies, Part II: cool thermal storage. Energy Conversion and Management 39, 1139-1153

Evaluate current TES cost in region Run Energy Model Know utility rates Evaluate current TES cost in region Find optimum point Conclusion Both locations, Chicago & Austin showed <10 months payback period (when system is at peak) Installation/Maintenance cost may vary based on location It is recommended to evaluate energy storage payback period for a project

Reference: Lizana, J., Chacartegui, R., Barrios-Padura, A. & Manuel Valverde, J. Advances in thermal energy storage materials and their applications towards zero energy buildings: A critical review. Appl. Energy 203, 219-239 (2017). http://www.energy.ca.gov/reports/500-95-005_TES-REPORT.PDF Yau, Y. H. & Rismanchi, B. A review on cool thermal storage technologies and operating strategies. Renewable and Sustainable Energy Reviews 16, 787-797 (2012). Hasnain, S. M. Review on sustainable thermal energy storage technologies, Part II: cool thermal storage. Energy Conversion and Management 39, 1139-1153 (1998). Thermal storage. In: ASHRAE handbook. American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc., Atlanta: HVAC Applications; 2007 [chapter 34]. Wu, C. & Tsai, Y. Design of an ice thermal energy storage system for a building of hospitality operation. International Journal of Hospitality Management46, 46-54 (2015). Sanaye, S. & Shirazi, A. Thermo-economic optimization of an ice thermal energy storage system for air- conditioning applications. Energy and Buildings60, 100-109 (2013). https://www.comed.com/Pages/default.aspx http://austinenergy.com/ https://www.dntanks.com/wp-content/uploads/2015/03/SanAntonioLackland_TX_ProjectProfile.pdf Ahrinet.org. (2017). HVACR Equipment/Components. Available at: http://www.ahrinet.org/contractors.aspx?S=141. Trane Trace 700 software

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