Knowledgebase: Central Plant > Chillers
How to calculate Generator HIR for Chiller:Absorption:Indirect
Posted by Michael J. Witte, Last modified by Michael J. Witte on 28 November 2017 07:15 PM


Question: Please explain how to calculate the Generator Heat Input Function of Part Load Ratio Curve (GenHir curve) for Chiller:Absorption:Indirect. Answer: Referring to the equations in the Engineering Reference section "Indirect Absorption Chiller" starting on pdf p. 487 (v5.0), with some additional notes: PLR: The partload ratio of the indirect absoprtion chillerâ€™s evaporator is simply the actual cooling effect required (load) divided by the maximum cooling effect available. PLR = Qevap/Qevapmax where PLR = partload ratio of chiller evaporator Qevap = chiller evaporator operating capacity [W] (current load on the chiller) Qevapmax = chiller evaporator available capacity [W] (Nominal capacity times temperature correction curves) Qgenerator = GeneratorHIR * Qevapmax * GenfCondT * GenfEvapT * CyclingFrac So, GeneratorHIR = Qgenerator / (Qevapmax * GenfCondT * GenfEvapT * CyclingFrac) If operating at nominal condenser and evaporator temepratures such that GenfCondT = 1 and GenfEvapT = 1, and if operating above PLRmin such that CyclingFrac = 1, then: GeneratorHIR = Qgenerator / Qevapmax Since PLR = Qevap/Qevapmax, then Qevapmax = Qevap/PLR GeneratorHIR = Qgenerator*PLR/Qevap or, stated another way GeneratorHIR = PLR/COP So, GeneratorHIR(fPLR) is *not* normalized by a nominal COP or HIR. When PLR = 1.0, GeneratorHIR = 1/COP. Also, because the denominator is Qevapmax, GeneratorHIR approaches zero as PLR approaches zero. For example, for a perfect chiller which has constant efficiency at all PLRs, with a nominal COP of 0.5 at full load at rated temperatures, the GeneratorHIR(fPLR) values would be: PLR = 0.0, GeneratorHIR = 0.0 (PLR/COP = 0.0/0.5 = 0.0) PLR = 0.2, GeneratorHIR = 0.4 (PLR/COP = 0.2/0.5 = 0.4) PLR = 0.5, GeneratorHIR = 1.0 (PLR/COP = 0.5/0.5 = 1.0) PLR = 1.0, GeneratorHIR = 2.0 (PLR/COP = 1.0/0.5 = 2.0)  
