Exergy-analysis Based Comparative Study Of Electric Compression Heat Pump And Absorption Heat Pump In District Energy Systems

With widely use of district energy system(DES),how to recove and utilize waste heat in low temperature recycle water through heat pump has attracted more and more attention.There are principally two types of heat pump: absorption heat pump(ABHP)and electric compressor heat pump(ECHP).These two kinds of heat pump have respective advantages in aspect of energy or exergy,therefore which heat pump is more efficiency becomes a hot topic in DES engineering field.This paper performs comparative study of those two kind of heat pump supplying heating or cooling in DES,in order to provide reference for the choice of heat pump in the design of DES.This paper established thermodynamics model of ABHP and ECHP.In the design conditions,it reveals that COP of ECHP is 2.25 times as high as ACHP,but its exergy efficiency is just 71% of that of ABHP when heat supplied to users.COP of ECHP is 3.26 times as high as that of ABHP,but exergy efficiency of those two kind of heat pump are almost equal,when cold is supplied to users.Those two kind of heat pump have respective advantages in energy or exergy when heat or cold energy is supplied.Based on the thermodynamics model,this paper established exergy analysis model of energy supply system under difference distance between power station and energy supply systems,under the consideration of steam exergy destruction and water pump power when transported.Equation of exergy efficiency about two kind of energy supply system are derived based on the model.Result shows exergy efficiency of both energy supply system decreases with the increase of distance.The cooling capacity/heating capacity when exergy efficiency of energy supply systems are equal decreases with the increase of distance,when heat or cold energy is supplied.Based on the exergy analysis of energy supply system,the equation of exergoeconomics about energy supply systems is derived,under different distance,steam exergy price/electric price and cooling capacity/heating capacity.It is clear that the cooling capacity/heating capacity when exergoeconomics of energy supply systems are equal decreases with the increase of distance and steam exergy price/electric price,when heat or cold energy is supplied.In the design conditions,when steam exergy price/electric price is equal or more than 1.14,the exergoeconomics of absorption energy supply system is better than electric energy supply system constantly,therefore DES should choose electric energy supply system.When steam exergy price/electric price is less than 1.14,if the cooling capacity/heating capacity of this energy supply system is more than the cooling capacity/heating capacity that make exergoeconomics of two energy supply systems equal,the exergoeconomics of electric energy supply system is better than absorption energy supply system,therefore DES should choose electric energy supply system,otherwise absorption energy supply system should be selected.The research method and result are helpful for the selection of energy supply system from the aspects of energy and exergy in the design of DES.