Heater#
The heater parameters describe the characteristics of the electric heating equipment that supplies heat to the heat transfer fluid (HTF) to be delivered to the thermal energy storage (TES) system. The heater model currently uses a simple approach to calculate the required mass flow rate to achieve a target heat input given an inlet temperature and target outlet temperature. The model does not explicitly model the HTF pump and assumes that pumping inefficiencies are converted into heat. Future work may add heat losses to the environment and a pump model.
System Design Parameters#
The system design parameters are variables that you specify on the System Design page. They are shown here for reference.
- Heater multiple
The heater multiple determines the heater’s nominal thermal power as a multiple of the Cycle thermal power.
- Heater thermal power
The heater’s thermal output under design conditions. SAM displays the heater thermal power on Installation costs page.
Heater Thermal Power (MWt) = Heater Multiple × Cycle Thermal Power (MWt)
- HTF hot temperature
The HTF temperature at the heater outlet under design conditions.
- HTF cold temperature
The HTF temperature at the heater inlet under design conditions.
HTF Properties#
The properties of the HTF that transfers heat from the heater to the TES.
- HTF type
One of two types of solar salt used for the heat transfer fluid, also called the working fluid. You can also add a user defined HTF by choosing the user defined option and clicking the Edit button to open the HTF properties editor.
- Property table for user-defined HTF
When the HTF type is User-defined, click Edit to open the HTF properties editor. See Custom HTF for more about working with custom fluids.
Startup#
- Fraction of design power allowed during startup
Fraction of the design heater thermal power allowed to bring the system to operating temperature after a period of non-operation. Used by the dispatch module to calculate the required start-up energy.
- Duration of startup at max startup power, hr
The amount of time required to reach operating temperature during startup.
- Heater startup energy, MWt-hr
The energy required during the startup period.
Heater Startup energy (MWt-hr) = Heater Thermal Power (MWt) × Fraction of Design Power Allowed During Startup × Duration of Startup at Max Startup Power (h)
- Minimum heater operating fraction
The minimum heater power allowed as a fraction of the heater thermal power.
Custom HTF#
If the heat transfer fluid you want to use in the solar field is not included in the Field HTF Fluid list, you can define a custom heat transfer fluid using the User-defined option in the list. To define a custom fluid, you need to know the following properties for at least two temperatures:
Temperature, ºC
Specific heat, kJ/kg-K
Density, kg/m³
Viscosity, Pa-s
Kinematic viscosity, m²-s (not required, see note below)
Conductivity, W/m-K
Enthalpy, J/kg (not required, see note below)
Note
The kinematic viscosity and enthalpy data in the table are not used by the CSP models. These properties are redundant: Kinematic viscosity is the ratio of viscosity to density, and the heat balance equations use specific heat instead of enthalpy.
To define a custom heat transfer fluid:
In the Field HTF fluid list, click User-defined.
In the Edit Material Properties table, change Number of data points to 2 or higher. The number should equal the number of temperature values for which you have data.
Type values for each property in the table.
You can also import data from a text file of comma-separated values. Each row in the file should contain properties separated by commas, in the same the order that they appear in the Edit Material Properties window. Do not include a header row in the file.
Note
Each row in the materials property fluid table must be for a set of properties at a specific temperature. No two rows should have the same temperature value.
SAM calculates property values from the table using linear interpolation.
The rows in the table must sorted by the temperature value, in either ascending or descending order.
The physical trough model uses the temperature, specific heat, density, viscosity, and conductivity values. It ignores the enthalpy and kinematic viscosity values (the empirical trough model does use those values).
For the physical trough model, if you specify user-defined HTF fluids with the same properties for the solar field and thermal storage system, on the Thermal Storage page, SAM disables the Hot side HX approach temp and Cold side HX approach temp inputs, and sets them to zero internally to represent a system with no heat exchanger. (When the hot and cold side approach temperatures are zero, Thermal storage exergetic efficiency is one.)