International Journal of Air-Conditioning and Refrigeration
World Scientific Publishing Company
1
Theoretical parametric study of Wrap-Around Heat Pipe (WAHP) in air
conditioning systems
Mridul Sarkar
Integrated Environmental Solutions India Pvt. Ltd.
Pune-411021, India.
Warp around heat pipes (WAHP) belong to a special class of recuperative heat exchangers that transfer
heat from inlet to outlet locations via thermal gradient, without using any energy. In the present work,
effects of various mechanical parameters on the performance of a WAHP dehumidifier system that are
based on the underlying principles of heat and mass conservation are presented primarily from a
theoretical point of view. A simplified methodology pertaining to wet cooling coils is applied here for
defining the case of moisture condensation during precooling process at WAHP evaporator. Inlet air
temperature, inlet humidity ratio, air mass flow rate, dehumidifier outlet temperature and effectiveness
are the main operational parameters considered in this study. On the other hand, comparative
performance study of the WAHP system is done through other set of thermodynamic parameters like
the supply air temperature, supply humidity ratio, specific coil load and recovered enthalpy. The subtle
variations in these factors against the operational parameters not only help in stipulating functional
characteristics of the WAHP, but also allow HVAC designers to make informed decisions for system
design and performance without relying entirely on manufacturer’s equipment data.
Keywords: Wrap-around heat pipe (WAHP), dehumidification, humidity, coil load, recovered
enthalpy, effectiveness
1. Introduction
Due to global rise in energy prices and demand, it
becomes very important that the energy sources be used
and managed in an efficient and prudent way. Almost,
10-30% of annual energy consumption in building
sector is due to air conditioning equipment1. In recent
years, serious strides are taken in the field of energy
recovery for cooling and dehumidification applications,
which is a major requirement from HVAC systems
particularly for hot, humid and temperate climates. The
usage of heat pipes in air conditioning equipment for
air-to-air heat recovery and efficient dehumidification
is becoming more popular in recent time due to its ease
of integration, less maintenance and no supplementary
energy requirement for operation2-3. In fact, thermal
conductivity of heat pipes is reported to be several times
higher than many conductors of comparable
dimensions4-5.
Performance investigations of heat pipe heat
exchangers (HPHX) and WAHP applied in HVAC
systems for heat recovery are important topics of
research. El-Baky et al. performed experimental
investigation6 on the effect of return to fresh air mass
flow ratios and fresh air temperatures on the
effectiveness of HPHX system. Experimental study on
a 2-Row copper HPHX7 charged with R-134a
refrigerant by Yau et al. is aimed towards the
investigation of the influence of evaporator inlet
temperatures and face velocity on heat pipe
performance. From the results, they concluded that the
sensible effectiveness of HPHX actually decreased as
the evaporator face velocity is increased. However, in
the temperature range considered for the study, the
sensible effectiveness stayed almost constant. Noie-