Lecture Objectives: Analysis of Absorption Cooling Cycles

Carnot Cycles COPvapor_compression=Qcooling/Pelectric COPmax=Tcooling/(Tenviromnet-Tcooling) COPabsorption=Qcooling/Qheating COPmax= Tcooling/(Tenviromnet-Tcooling) ∙ (Theat_source-T environment)/ Theat_source COPmax_absorption= COP vapor compression x Correction for VC cycle

Absorption cooling with preheater (system improvement #1) Rich ammonia vapor 4 5 Refrigeration and air conditioning (Ramesh et al)

Absorption cooling with preheater Saturated vapor at p1’ 1’’’V=3 Major heat source 6 1’’’ mixing isotherm 6h 1’’ Useful cooling energy 1’’’L =2 4 5 1’ 2’ , 2’’ Saturated liquid at p1’ 1 Saturated liquid at p1 Cooling tower Pumping energy COP= Q cooling / Q heating (Pump ???)

For Real energy analysis you need real h-x diagram! hfg for H2O hfg for NH3 For Real energy analysis you need real h-x diagram!

Use of precooling (system improvement #2)

Absorption cooling with precooling Saturated vapor at p1’ 1’’’V=3 Major heat source 6’ 6 6h 1’’’ mixing Saturated liquid at p1’ isotherm 1’’ Useful cooling energy (larger!) 1’’’L =2 4 1’ Saturated liquid at p1 2’ , 2’’ 4’ 5 1 Cooling tower (needs to cool more!) Pumping energy

System improvement #3 Generator with of Enrichment NH3 8V 9 8L 10 8LLP Different 8V 9 8L 10 8LLP 11

Heat rejection with separation into liquid and vapor (Enrichment NH3 in the vapor mixture) This is our point cooling 1 4=2V Separator 6=5V Q12 /m1 cooling Q45 /m4 x8 m8 8 7 m1 =m2 5 2 sub cooled liquid mixture isotherm m3 2L Q12 x1 x8

Ammonia Enrichment Process (rectification)

Absorption system with Enrichment (no preheater nor precooler) Saturated vapor at p2 3V 8V 3 mixing 11 8L 1’ Useful cooling energy 8LLP 10 3L 2 9 Saturated liquid at p2 1 Saturated liquid at p1

Example of H2O-NH3 System Text Book (Thermal Environmental Engineering) Example 5.5 HW 1: Solve the problem 5.6 from the textbook (LiBr-H2O) Beside example 5.6, you will need to study example 5.6 and 5.7 Due date February 25th.

LiBr-H2O Systems

LiBr-H2O Systems

Twine vessel LiBr-H2O Systems

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

System with no pump (Platen-Munter system) H2O-NH3 + hydrogen http://www.youtube.com/watch?v=34K61ECbGD4