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Lecture Objectives:

Discussing HW4 using psychrometric chart, desiccant systems, and cooling tower performance in HVAC systems. Learn about heat recovery and enthalpy in NSM building at UT.

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Lecture Objectives:

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  1. Lecture Objectives: • Discuss HW4, answer your questions • Finish with desiccant systems • Learn about cooling towers

  2. Heat recovery system in NSM building at UT Enthalpy W Sensible W

  3. HW4 (Due March 23rd) 1) Using NMS’ AHU, show the process in the Psychrometric chart for Austin’s a) Fall humid day (Outdoor: T=24C & RH=90%) b) Fall dry day (Outdoor: T=24C & RH=50%) c) Winter (T=3C RH=70%) For fall: T hot deck is minimum 24C, T cold deck is 13C For winter: T hot deck is 35C, T cold deck is 13C For each case: (a,b, and c) calculate RH of supply air in hot and cold deck.

  4. Desiccant wheel

  5. Figure 3 – A desiccant-based cooling system combined with regenerative heat exchanger, vapor compression cooling, and evaporative humidifier (hybrid system). Desiccant wheel

  6. Variation in Cycles Much more in the paper I gave you (Technical development of rotary desiccant dehumidification and air conditioning)

  7. Cooling Tower • Similar to an evaporative cooler, but the purpose is often to cool water • Widely used for heat rejection in HVAC systems • Also used to reject industrial process heat

  8. Cooling Tower

  9. Various Use For small buildings For power plant (all kinds) One of the cooling tower at UT For industrial application

  10. Cooling Tower Performance Curve R TCTR Outdoor WBT from chiller TCTS to chiller Temperature difference: R= TCTR -TCTS TCTS Most important variable is wet bulb temperature TCTS = f( WBToutdoor air , TCTR , cooling tower properties) or for a specific cooling tower type TCTS = f( WBToutdoor air , R) WBT

  11. Coupling of cooling tower with the water cooled condenser

  12. System Modeling

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

  14. Function fitting for a chillerq = f (condensing and evaporating T)

  15. Cooling Tower Performance Curve R TCTR Outdoor WBT from chiller TCTS to chiller Temperature difference: R= TCTR -TCTS TCTS Most important variable is wet bulb temperature TCTS = f( WBToutdoor air , TCTR , cooling tower properties) or for a specific cooling tower type TCTS = f( WBToutdoor air , R) WBT

  16. Cooling Tower Model Model which predict tower-leaving water temperature (TCTS) for arbitrary entering water temperature (TCTR) and outdoor air wet bulb temperature (WBT) Temperature difference: R= TCTR -TCTS Model: For HW 3b: You will need to find coefficient a4, b4, c4, d4, e4, f4, g4, h4, and i4 based on the graph from the previous slide and two variable function fitting procedure

  17. Modeling of Water Cooled Chiller (COP=Qcooling/Pelectric) Chiller model: COP= f(TCWS , TCTS , Qcooling , chiller properties)

  18. Modeling of Water Cooled Chiller Chiller model: Chiller data: QNOMINAL nominal cooling power, PNOMINAL electric consumption forQNOMINAL Available capacity as function of evaporator and condenser temperature Cooling tower supply Cooling water supply Full load efficiency as function of condenser and evaporator temperature Efficiency as function of percentage of load Part load: The consumed electric power [KW] under any condition of load The coefiecnt of performance under any condition Reading: http://apps1.eere.energy.gov/buildings/energyplus/pdfs/engineeringreference.pdf page 597.

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

  20. 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 is given - 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 for a chiller (defined in nominal operation condition: TCST and TCSW); Based on Q() and WBT you can find P() and COP().

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