Lecture Objectives: Summarize sorption chillers Learn about Chiller modeling Cooling towers and modeling

Example of H 2 O-NH 3 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

LiBr-H 2 O Systems

Twine vessel LiBr-H 2 O Systems

System with no pump (Platen-Munter system) H 2 O-NH 3 + hydrogen

Useful information about LiBr absorption chiller et%207%20-%20Absorption%20Cooling.pdfhttp:// et%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.

Central chiller plant

Modeling of Water Cooled Chiller (COP=Q cooling /P electric ) Chiller model: COP= f(T CWS, T CTS, Q cooling, chiller properties) Example of a vapor compression chiller

Modeling of Water Cooled Chiller Chiller model: Cooling water supply Cooling tower supply Available capacity as function of evaporator and condenser temperature Full load efficiency as function of condenser and evaporator temperature Efficiency as function of percentage of load Part load: The coefiecnt of performance under any condition Chiller data: Q NOMINAL nominal cooling power, P NOMINAL electric consumption for Q NOMINAL The consumed electric power [KW] under any condition of load Reading: page 597.

Example of a chiller model

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

Cooling Towers Power plant type Major difference: NO FAN

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

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

Function fitting for a chiller q = f (condensing and evaporating T) 18