System Design
=============

The System Design page shows inputs for design point parameters that determine the pumped thermal energy storage system's nameplate capacity. Use the System Design inputs to define the nominal ratings of the system, and then specify details for each part of the system on the appropriate input pages.

Some independent inputs are related, and SAM does not enforce valid relationships between variables. Be careful that the parameters you define represent a feasible design. For example, the heat pump coefficient of performance, cycle thermodynamic efficiency, and storage temperatures are all related.

There are two options for automatically populating the design point inputs with parameters from a calculator that determines parameter values from more detailed component inputs:

* Click **Design Point** to open the :doc:`Pumped Thermal Energy Storage <../window-reference/win_ptes_design_pt>` window.

* Run the PTES Import Design :doc:`macro <../reference/macros>` to generate inputs in NLR's detailed design-point PTES model in MATLAB and import them to SAM. To use the Macro, click **Macros** under the Simulate button and choose the macro from the list.

.. note:: All of the system design inputs are nominal values, or values at the system's design point. SAM calculates actual values during simulation and reports them in the :doc:`results <../getting-started/results_page>`.

Heat Pump
~~~~~~~~~

**Heater multiple**
  The heater multiple determines the nominal **Heat pump heat out** as a multiple of the **Cycle thermal input power**.

**Heat pump heat out, MWt**
  The heat pump thermal output to the Hot storage hot tank under design conditions. SAM displays the heat pump capacity power on the :doc:`System costs <../installation-costs/cc_ptes>`   page.

*Heater Thermal Power (MWt) = Heater Multiple × Cycle Thermal Input Power (MWt)*

**Heat pump heat in, MWt**
  The heat pump thermal input from the Cold storage cold tank under design conditions.

**Heat pump coefficient of performance**
  The thermodynamic coefficient of performance of heating at design conditions. This calculation only includes power imparted on the working fluid, not power consumption external to the fluid (e.g. HTF pumping power).

*Coefficient of Performance = Heat Pump Heat Out / Heat pump thermodynamic power*

**Heat pump thermodynamic power, MWe**
  Net power imparted on the heat pump working fluid. Additional power consumption like electric motor inefficiency, cooling parasitics, and HTF pumping power are captured in separate inputs on the :doc:`Heat Pump <ptes_heat_pump>`   page and reflected in **Total electricity consumption at design charge** and **Net round-trip efficiency**.

Thermal Energy Storage
~~~~~~~~~~~~~~~~~~~~~~

**Hours of storage, hrs**
  The nominal thermal storage capacity expressed in hours at full load: The number of hours that the storage system can supply heat at the cycle thermal power.

**Heater hours of storage, hrs**
  The nominal thermal storage capacity expressed in hours of heater thermal power.

*Heater Hours of Storage (h) = Full Load Hours of Storage (h) ÷ Heater Multiple*

**Hot storage hot temperature, °C**
  Temperature of the hot tank of the hot reservoir at design. This is also the temperature of the hot HTF exiting the heat pump hot heat exchanger at design and the temperature entering the cycle hot heat exchanger at design.

**Hot storage cold temperature, °C**
  Temperature of the cold tank of the hot reservoir at design. This is also the temperature of the hot HTF entering the heat pump hot heat exchanger at design and the temperature exiting the cycle hot heat exchanger at design.

**Cold storage hot temperature, °C**
  Temperature of the hot tank of the cold reservoir at design. This is also the temperature of the cold HTF entering the heat pump cold heat exchanger at design and the temperature exiting the cycle cold heat exchanger at design.

**Cold storage cold temperature, °C**
  Temperature of the cold tank of the cold reservoir at design. This is also the temperature of the cold HTF exiting the heat pump cold heat exchanger at design and the temperature entering the cycle cold heat exchanger at design.

Power Cycle
~~~~~~~~~~~

**Cycle thermodynamic power, MWe**
  Net power generated by the working fluid. Additional power consumption like electric motor inefficiency, cooling parasitics, and HTF pumping power are captured in separate inputs on the Power Cycle page and reflected in Net electricity output at design discharge and Net round-trip efficiency.

**Cycle thermodynamic efficiency**
  The thermodynamic efficiency at design conditions. This calculation only includes net power generated by the working fluid, and does not consider power consumption external to the fluid (e.g. HTF pumping power).

*Efficiency = Cycle Thermodynamic Power / Cycle Thermal Power Input*

**Cycle thermal input power, MWt**
  Heat input to cycle at design conditions.

**Cycle heat rejection to cold temperature TES, MWt**
  Portion of total cycle heat rejection that is transferred to the hot tank of the cold reservoir. 

**Cycle heat rejection to surroundings, MWt**
  Portion of total cycle heat rejection that is rejected to the surroundings

System Metrics
~~~~~~~~~~~~~~

**Thermodynamic round-trip efficiency**
  System round-trip efficiency calculated from only net heat pump power imparted on the working fluid and net cycle power generated by the working fluid.

**Net electricity output at design discharge, MWe**
  Net electricity output from the cycle subtracting parasitic electricity consumption from the cycle thermodynamic power.

**Total electricity consumption at design charge, MWe**
  Net electricity consumption by the heat pump adding parasitic electricity consumption to the heat pump thermodynamic power.

**Net round-trip efficiency**
  System round trip efficiency including all parasitics.

**Design Point**
  Click **Design Point** to open the :doc:`Pumped Thermal Energy Storage <../window-reference/win_ptes_design_pt>` window and calculate system design paramters from more detailed component inputs.