Performance analysis on a hybrid air-conditioning system
of a green building
Q. Ma, R.Z. Wang
, Y.J. Dai, X.Q. Zhai
School of Mechanical Engineering, Institute of Refrigeration and Cryogenics,
Shanghai Jiao Tong University, Shanghai 200030, China
Received 23 May 2005; received in revised form 25 July 2005; accepted 5 August 2005
This paper presents the performance analysis on a hybrid air-conditioning system according to the hybrid building energy system of the green
building demonstration project in Shanghai, in which a 150 m
solar collector is used to power two 10 kW adsorption chillers, a vapor compression
heat pump is used to cool air in the evaporating end while the condensing heating at about 80 8C is fully used to regenerate a liquid desiccant
dehumidiﬁcation system. In the hybrid system, the sensible cooling to the air is treated mainly by solar adsorption cooling and vapor compression
cooling, whereas the latent heat is treated by the liquid desiccant dehumidiﬁcation system with regeneration from the condensing heat of the heat
pump. The results show that the performance of this system is 44.5% higher than conventional vapor compression system at a latent load of 30%
and this improving can be achieved by 73.8% at a 42% latent load. The optimal ratio of adsorption refrigerating power to total cooling load for this
kind of hybrid systems is also studied in this paper.
# 2005 Elsevier B.V. All rights reserved.
Keywords: Liquid desiccant; Hybrid air-conditioning; Adsorption refrigeration; Solar energy; Performance analysis
Up to now, most of the air-conditioning systems all over the
world are based on conventional vapor compression cooling
devices. In order to overcome the latent load, the air
temperature must be decreased to be lower than its dew point
which requires the evaporating temperature of air conditioner
or chillers as low as about 5 8C. This temperature is much lower
than normally required for air-conditioning (room air
temperature about 26 8C, evaporating temperature about
15 8C), and consequently reduces the coefﬁcient of perfor-
mance and then leads to a large amount of energy consumption.
If the latent heat and sensible heat for cooling purposes can be
treated independently, for example, if air is dehumidiﬁed by a
desiccant system (latent heat), the evaporating temperature for
vapor compression system could then be raised up to 15 8C
(sensible cooling). If the sensible cooling is at 15 8C
evaporating temperature, and the latent heat could be treated
by waste heat or solar energy, the electrical COP of the air-
conditioning system could then be increased obviously.
Hybrid systems, which consist of desiccant cycle and vapor
compression cycle, are very attractive due to its energy-saving
and its function to kill virus to make air clean. Such combination
systems reduce the moisture content of air by liquid desiccant
directly. Liquid desiccant dehumidiﬁcation can be driven by low-
grade energy such as solar energy, waste heat of industrial
processes and terrestrial heat so that it consumes little primary
power. Hybrid systems are able to control humidity and
temperature independently, as a result, the evaporating
temperature can be increased up to 15 8C, and hence the COP
of a chiller will be signiﬁcantly improved. In addition, hybrid
systems avoid condensing water on coils and prevent devices
from corrupting, so the maintenance costs can be cut down.
Many investigations have been carried out on the feasibility
and energy-saving potential of hybrid air-conditioning systems.
In 1986 Howell et al.  drew a conclusion that hybrid systems
with a vapor compression cycle for sensible cooling and a liquid
desiccant cycle for latent heat removal could reduce energy
consumption by 35% if compared with single vapor compression
systems. A kind of solar powered hybrid vapor compression with
liquid desiccant has been studied by Yadav  who gave a
simulating result that the hybrid system could save energy about
53% at 40% latent load and this saving increased to 80% at 90%
latent heat load compared with typical vapor compression
Energy and Buildings 38 (2006) 447–453
* Corresponding author. Tel.: +86 21 629 33838; fax: +86 21 629 33250.
E-mail address: firstname.lastname@example.org (R.Z. Wang).
0378-7788/$ – see front matter # 2005 Elsevier B.V. All rights reserved.