Performance assessment of integrated energy systems for HVAC applications

ABSTRACT

In this article, energy and exergy analyses are conducted for two integrated systems which can be used in HVAC applications. These two systems are analyzed for the cases of single generation, cogeneration and trigeneration, and their performances are evaluated through energy and exergy efficiencies. The parametric studies are performed to investigate the effects of using cogeneration and extended to trigeneration on the system performance. To perform the comparisons between the systems for multiple options, the same amounts of outputs (in terms of electricity, heating, cooling) are produced for all systems. The energy analyses of systems 1 and 2 show a great benefit for moving from single generation to trigeneration, with the trigeneration efficiencies of 83.5% and 87.2%, respectively, and single generation efficiencies of 47% for both systems. However, the exergy analyses show that trigeneration may not always become more efficient than single generation, particularly for system 1, due to the fact that the trigeneration exergy efficiency is 38.7% and the corresponding single generation efficiency is 44.3%. For system 2, the trigeneration exergy efficiency is 52.7% while the single generation efficiency becomes 44.3%. Depending on the type of cogeneration or cogeneration design, the system can be more efficient.

KEYWORDS:

• Energy
• exergy
• efficiency
• cogeneration
• trigeneration

Nomenclature

	=	Specific exergy (kJ/kg)
	=	Specific enthalpy (kJ/kg)
	=	Mass flow rate (kg/s)
P	=	Pressure (kPa)
	=	Heat rate (kW)
	=	Specific entropy (kJ/kgK)
T	=	Temperature (°C)
	=	Work rate (kW)

Greek symbols

α,β,δ,γ	=	Number of atoms of the fuel chemical composition
	=	Energy Efficiency
	=	Exergy Efficiency

Subscripts

abs	=	Absorber
c	=	Condenser
CG	=	Cogeneration system
Cool	=	Cooling effect
	=	Destruction
e	=	Evaporator
gen	=	generator
H	=	High
	=	Heat pump
Hx	=	Heat exchanger
L	=	low
NG	=	Natural gas
s	=	source
S	=	system
SG	=	Single generation
T	=	Turbine
TG	=	Trigeneration
0	=	Reference environment
1…32	=	State numbers

Acknowledgment

The first author would like to acknowledge the scholarships received from the Ministry of Higher Education in the Kingdom of Saudi Arabia through the Saudi Culture Bureau in Canada.