Lecture Objectives: Cooling towers and modeling Project 1 Thermal storage systems

Cooling Tower Performance Curve Most important variable is wet bulb temperature T CTS = f( WBT outdoor air, T CTR, cooling tower properties) or for a specific cooling tower type T CTS = f( WBT outdoor air, R) from chiller Outdoor WBT T CTS R Temperature difference: R= T CTR -T CTS T CTR to chiller WBT T CTS

Cooling Tower Model Model which predict tower-leaving water temperature (T CTS ) for arbitrary entering water temperature (T CTR ) and outdoor air wet bulb temperature (WBT) Temperature difference: R= T CTR -T CTS Model: For HW 3b: You will need to find coefficient a 4, b 4, c 4, d 4, e 4, f 4, g 4, h 4, and i 4 based on the graph from the previous slide and two variable function fitting procedure

Combining Chiller and Cooling Tower Models 3 equations from previous slide Function of T CTS Add your equation for T CTS → 4 equation with 4 unknowns (you will need to calculate R based on water flow in the cooling tower loop)

Merging Two Models Finally: Find P(  ) or The only fixed variable is T CWS = 5C (38F) and P nominal and Q nominal for a chiller (defined in nominal operation condition: T CST and T CSW ); Based on Q(  ) and WBT you can find P(  ) and COP(  ). Temperature difference: R= T CTR -T CTS Model: Link between the chiller and tower models is the Q released on the condenser: Q condenser = Q cooling + P compressor - First law of Thermodynamics Q condenser = (mc p ) water form tower (T CTR -T CTS ) m cooling tower is given - property of a tower T CTR = T CTS - Q condenser / (mc p ) water

Two variable function fitting (example for a variable sped pump)

Function fitting for a chiller q = f (condensing and evaporating T) 7

Merging Two Models Finally: Find P(  ) or The only fixed variable is T CWS = 5C (38F) and P nominal and Q nominal for a chiller (defined in nominal operation condition: T CST and T CSW ); Based on Q(  ) and WBT you can find P(  ) and COP(  ). Temperature difference: R= T CTR -T CTS Model: Link between the chiller and tower models is the Q released on the condenser: Q condenser = Q cooling + P compressor ) - First law of Thermodynamics Q condenser = (mc p ) water form tower (T CTR -T CTS ) m cooling tower is given - property of a tower T CTR = T CTS - Q condenser / (mc p ) water

Low Order Building Modeling Measured data or Detailed modeling Find Q(  ) = f (DBT)

For Austin’s Office Building Number of hours Hours in a year kW Model: (Area = 125,000sf) Model =0 when building is off Used for component capacity analysis

For project 1 you will need Q(  ) for each hour Yearly based analysis: You will need Q(  ) for one week in July Use simple molded below and the Syracuse TMY2 weather file posted in the course handout section

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

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!

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

Chilled water tank Use of stored cooling energy StoreUse

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

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