180 likes | 211 Views
Learn about sorption chillers, chiller modeling, and absorption chiller practical tips for implementation. Explore LiBr-H2O and H2O-NH3 systems with advanced techniques. Consider cooling towers, central chiller plant modeling, and power plant type differences for optimized performance.
E N D
Lecture Objectives: • Summarize sorption chillers • Learn about • Chiller modeling • Cooling towers and modeling
Example of H2O-NH3 System • Text Book (Thermal Environmental Engineering) Example 5.5 • HW 4: • Solve the problem 5.6 (water – ammonia) • from the textbook • Based on example 5.5. • You may need to study example 5.6 and 5.7 • Due date is next Tuesday
System with no pump(Platen-Munter system) • H2O-NH3 + hydrogen http://www.youtube.com/watch?v=34K61ECbGD4
Useful information about LiBr absorption chiller • http://www.cibse.org/content/documents/Groups/CHP/Datasheet%207%20-%20Absorption%20Cooling.pdf Practical Tips for Implementation of absorption chillers • Identify and resolve any pre-existing problems with a cooling system, heat rejection system, water treatment etc, before installing an absorption chiller, or it may be unfairly blamed. • Select an absorption chiller for full load operation (by the incorporation of thermal stores if necessary) as COP will drop by up to 33% at part-load. • Consider VSD control of absorbent pump to improve the COP at low load. • Consider access and floor-loading (typical 2 MW Double-effect steam chiller 12.5 tons empty, 16.7 tones operating). • Ensure ambient of temperature of at least 5°C in chiller room to prevent crystallization. • http://www.climatewell.com/index.html#/applications/solar-cooling
Modeling of Water Cooled Chiller (COP=Qcooling/Pelectric) Chiller model: COP= f(TCWS , TCTS , Qcooling , chiller properties) Example of a vapor compression chiller
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.
Example of a chiller model http://www.comnet.org/mgp/content/chillers?purpose=0
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)
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().
Cooling Towers Power plant type Major difference: NO FAN
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
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
Two variable function fitting(example for a variable sped pump)
Function fitting for a chillerq = f (condensing and evaporating T)