Journal of Power and Energy Engineering, 2013, 1, 73-76
http://dx.doi.org/10.4236/jpee.2013.15012 Published Online October 2013 (http://www.scirp.org/journal/jpee)
Copyright © 2013 SciRes. JPEE
The Characteristics of the Evaporator/Evaporator for
Direct Expansion Solar Assisted Heat Pump System
Mingyan Zhu, Huanrong Xie, Biao Zhang, Xin Guan
Institute of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai, China.
Email: zmy117060164@163.com
Received October 2013
ABSTRACT
Direct expansion solar assisted heat pump (DX-SAHP) technology is developed by combining solar energy heat utiliza-
tion with heat pump energy saving technology. The experimental researches of the DX-SAHP hot water system are
conducted in this paper, and overall performance of DX-SAHP is analyzed with three different structures of collec-
tors/evaporators, namely a bare-plate collector, a glass-plate collector and double collectors/evaporators (a bare-plate
collector and a glass-plate collector). The influence factors and overall performance are studied, which show that the
overall performance of the system is mainly influenced by solar irradiation intensity an d the collector area. Comparing
with glass-plate collector in similar conditions, bare-plate collector system COP is higher. While increasing collector
area is conducive to improve the system COP, but will reduce the collector efficiency and increase the workload of the
compres s o r by c omparing the ba re -plate collector with double-plate collecto rs.
Keywords: Direct Expansion Solar Assisted Heat Pump; Collector/Evaporator ; Experimental Research
1. Introduction
Energy sources are widely utilized in many aspects with
a high-speed human society development period. Solar
energy is known as the renewable and “free” energy
source, without doubt, it is the best choice to be a heat
source of heat pump like the air source. In order to im-
prove the heat pump COP, the idea of combining the heat
pump with solar energy application system has been
proposed and developed by many researchers around the
world, which is the direct expansion solar assisted heat
pump(DX-SAHP), the solar collector and the heat pump
evaporator are installed into a single unit (collector/eva-
porator), where the refrigerant is directly evaporated in
the solar collector-evaporator by absorbing the solar
energy (and/or ambient air energy) to undergo a phase
transition from liquid to vapor. The DX-SAHP concept
was first proposed by Sporm and Ambrose in 1955 [1].
Following their w ork, many theoretical and experimental
studies (thermodynamic analysis, numerical simulation
etc.) have been rep orted. Such as the United Sta tes Sporm
S.K, Chaturvedi, M.P.O ‘Dell, Australian G.L. Morrison,
Hawlader, Krakok and Lin in Japan, Huang BJ etc [1-8].
Chaturvedi conducted a theoretical analysis for several
types of collectors/evaporators in 1979 and found that
using the inexpensive bare-plate collector can have a
high COP and collector efficiency, whether the capacity
of the collector and the compressor capacity match or not,
which directly affect system performance, in order to
achieve higher COP and the collector efficiency, the col-
lector/evaporation temperature should keep greater than
ambient temperature at a range of 5˚C - 10˚C [3,4]. In
order to solve the reliability problems, Shanghai Jiaotong
University Guo Junjie studied two different evaporation
areas and found that system’s reliability has improv ed by
increasing the evaporation area in low-temperature con-
ditions [9].
2. Experimental System Device Introduction
In order to investigate inf luence of collectors/ev aporators
on thermal performance of DX-SAHP, we set up the
DX-SAHP experimental equipment, which is shown in
Figure 1. It mainly contains the solar energy collector/
evaporator, compressor, condenser, heat storage water
tank, gas-liquid separator, filter drier and thermal expan-
sion valve parts, and the structural parameters of the
main components are as follows: 1) Solar collector/eva-
porator: Sampux “PYT/L2.0-3” tablets of finned tube
type collector/evaporator, two pieces of collectors/eva-
porators (one is a bare-plate collector, the other is a
glass-plate collector), both the collectors area are 2 m2,
the valid heating area 1.87 m2; 2) Compressor: NJ6226Z
type Hermetic reciprocating compressor, the rated power
of 735 W; 3) condenser: “BL14-20D” type plate heat
exchanger with heat transfer area of 0 .35 m2; 4) h eat sto-