207 ICE STORAGE TANK
This component models an ice storage tank filled by an ice harvester or
similar refrigeration equipment. Water is sprayed over the top of the ice
and exits from the bottom of the tank. If the instantaneous ice inventory
exceeds 20% of the total storage capacity, the temperature of the water
leaving the tank is 32 F. As the ice inventory drops below 20% of total
storage capacity, the leaving water temperature approaches the entering water
temperature (Stewart 1994).
A simple effectiveness model is used to describe the performance of the ice
storage tank. The effectiveness depends on the "discharge fraction", or
fraction of the tank's storage capacity that has been melted or "burned".
For discharge fractions of less than 0.80, the effectiveness is unity. For
discharge fractions between 0.80 and 1.00, the effectiveness is assumed to
drop linearly from one to zero. The heat transfer rate in BTU's per hour to
the circulating stream of water is given by:
qwater = eff*WMFR*Cpw*(EWT - 32) (3.3.1)
where "eff" the instantaneous tank effectiveness, "WMFR" is the water mass
flow rate in lb/hr, "Cpw" is the heat capacity of water at constant pressure
in BTU/lb-F, and "EWT" is the entering water temperature in degrees
Fahrenheit.
The ice storage tank model uses an overall heat transfer loss coefficient to
calculate environmental losses in addition to calculating losses to the
circulating water stream. The remaining ice inventory is determined at the
end of each time step. This value is then used as the mass of ice present
at the beginning of the following time step.
Type 71 inputs, "derivative", parameters, and outputs include:
xin(1) entering water temperature [C]
xin(2) water mass flow rate [kg/hr]
xin(3) ice generation rate [kg/hr]
xin(4) temperature of environment [C]
t(1) ice inventory at beginning of time step [kg]
par(1) tank capacity [kg]
par(2) tank volume [m3]
par(3) tank height [m]
par(4) tank U-value [kJ/hr-m2-C]
out(1) leaving water temperature [C]
out(2) water mass flow rate [kg/hr]
out(3) ice inventory at end of time step [kg]
out(4) ice "burn" rate [kg/hr]
out(5) heat transfer rate to tank from environment [kJ/hr]
out(6) opposite of heat transfer rate from ice harv. to tank
out(7) heat transfer rate from circulating water to tank
References:
Cross, Kevin, An Evaluation of Ice and Chilled Water As Thermal
Storage Media for Combustion Turbine Inlet Air Cooling Systems, M.S. Thesis,
p 23, University of Wisconsin, Madison, 1994.
Stewart, William, Modeling of Ice Filling Process of Rectangular
Thermal Energy Storage Tanks with Multiple Ice Maker Openings, American
Society of Heating, Refrigerating, and Air-Conditioning Engineers
Transactions, Volume 100, Part II, Atlanta, 1994.