2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 299 -
Abstract
--Variable primary flow pumping in chilled
water system is used as a benchmark to calculate the
theoretical system pressure drop of the distribution
network. The system of nonlinear equations consists of
pump performance curve and system of characteristic
curves of distribution network with twelve (12) energy
transfer stations (ETS).
Multi-variable Newton-Raphson and Singular-Value
Decomposition methods are used in solving the nonlinear
equations. Method of Least Squares and Cholesky
Decomposition are adapted to derive new sets of pump
characteristic curves taken from Similarity Laws
considering that pumps are modulated at its best efficiency
point.
Index Terms
—
Cholesky Decomposition Method, Energy
Transfer Station, Multi-variable Newton-Raphson Method,
Variable primary flow pumping system, Singular-Value
Decomposition Method
I.
N
OMENCLATURE
ܿ
frictional coefficient
ܥ
ு
head coefficient
ܥ
ொ
flow coefficient
ܥ
power coefficient
ܦ
pump’
s impeller diameter
ߜ
pressure drop
ߟ
pump efficiency
ఌ
pump’s relative roughness
ఌ
pipe’s relative roughness
݃
gravity
݄ሗ
pump head
ࡶ
Jacobian matrix
ܮ
pipe length
ߣ
friction factor
ߤ
absolute viscosity
݊
pump rotative speed
߱
volume flow rate
pipe diameter
ܳ
pump volume flow rate
ߩ
mass density
ܶ
torque
II.
I
NTRODUCTION
District cooling system (DCS) uses thermal energy in
the form of chilled water from a central cooling source to
multiple building through a distribution network of
underground pipes for use in process cooling. The
cooling process takes place in the central plant which
eliminates the use for separate systems in each building.
The district cooling system primarily consists of three
(3) components namely; the central cooling plant, the
distribution system
and the customer’s energy transfer
station (ETS). The cooling equipment, cooling towers,
power generation and thermal storage if any, are the main
components of central cooling plant. The distribution
system is a piping network that transfers the cooling
medium or chilled water from the central cooling plant to
different energy transfer stations of individual building at
controlled rates
. The customer’s energy transfer s
tation
(ETS) consists of plate heat exchangers, secondary
pumping system and chilled water piping of the building.
A large-scale district cooling plant could save up to
25% - 40% of energy consumption costs as compared
with conventional centralized air-conditioning system of
each building. However, as the distribution network is
often the most expensive portion and requires large initial
investment cost of the district cooling system, careful
design is needed to optimize its use. Proper identification
of chilled water velocity and pressure drop limits to
minimize the initial investment cost and operational cost
are the design criteria for optimum piping network
selection. To meet this objective, the system pressure
drop and system flow rate must be properly calculated to
evaluate the performance of complex piping systems
before any hardware is procured. In this study, the
hydraulic calculation of a simple distribution network is
presented wherein the system pressure drop and flow rate
requirements in each ETS room are determined.
III.
DISTRIBUTION NETWORK MODEL
A model of distribution network is shown in Fig. 1.
Note: DCP means District Cooling Plant
Fig. 1. Schematic diagram of distribution network.
Hydraulic Calculation of District
Cooling Distribution Network
G. L. Augusto* and A. B. Culaba**
* Research and Development, AVANTIS Limited, (
Hong Kong S.A.R.
)
** Faculty of Mechanical Engineering, De La Salle University, (
Philippines
)
