HVAC Autosizing Limits

docs/read_the_docs/source/advanced_tutorial/heat_pump_upgrades.rst

@@ -10,8 +10,8 @@ The ResStock workflow allows modeling heat pumps with either "integrated" or "se
 Definitions for each are given below.
 See `HPXML Heat Pumps <https://openstudio-hpxml.readthedocs.io/en/latest/workflow_inputs.html#hpxml-heat-pumps>`_ for more information.
 
-- *integrated*: the heat pump’s distribution system and blower fan power applies to the backup heating (e.g., built-in electric strip heat or an integrated backup furnace, i.e., a dual-fuel heat pump).
-- *separate*: the backup system has its own distribution system (e.g., electric baseboard or a boiler).
+- **integrated**: the heat pump’s distribution system and blower fan power applies to the backup heating (e.g., built-in electric strip heat or an integrated backup furnace, i.e., a dual-fuel heat pump).
+- **separate**: the backup system has its own distribution system (e.g., electric baseboard or a boiler).
 
 Lockout Temperatures
 --------------------
@@ -20,8 +20,8 @@ The ResStock workflow allows for controlling the compressor and/or backup heatin
 Definitions for each are given below.
 See the `Backup <https://openstudio-hpxml.readthedocs.io/en/latest/workflow_inputs.html#backup>`_ section of the OpenStudio-HPXML documentation for more information.
 
-- *compressor*: minimum outdoor temperature for compressor operation.
-- *backup heating*: maximum outdoor temperature for backup operation.
+- **compressor**: minimum outdoor temperature for compressor operation.
+- **backup heating**: maximum outdoor temperature for backup operation.
 
 For example, a heat pump upgrade option could be defined with a compressor lockout temperature of 5F and a backup heating lockout temperature of 40F.
 See below the argument assignments that would need to be added to the ``options_lookup.tsv`` file.
@@ -35,11 +35,16 @@ These values would override the OpenStudio-HPXML defaults.
 Replacement Scenarios
 ---------------------
 
-When defining a heat pump upgrade, the new heat pump can either (a) replace the primary (existing) system, or (b) retain the primary (existing) system as its backup heating system.
-In the latter case, all properties (e.g., capacity) of the primary (existing) system are retained as properties of the heat pump backup heating system.
+When defining a heat pump upgrade, the new heat pump can:
 
-Replace Primary System with New Heat Pump
-*****************************************
+- :ref:`replace_the_existing_primary_system`, or
+- :ref:`retain_the_existing_primary_heating_system_as_backup`, or
+- :ref:`use_autosizing_limits_for_ductwork_restriction`
+
+.. _replace_the_existing_primary_system:
+
+Replace the Existing Primary System
+***********************************
 
 For example:
 
@@ -56,10 +61,13 @@ For example:
  lifetime: 30
  - option: HVAC Cooling Efficiency|Ducted Heat Pump
 
-Primary System becomes Backup to New Heat Pump
-**********************************************
+.. _retain_the_existing_primary_heating_system_as_backup:
+
+Retain the Existing Primary Heating System as Backup
+****************************************************
 
 Use the ``Heat Pump Backup|Use Existing System`` option from the lookup.
+In this case, all properties of the existing primary system are retained as properties of the heat pump backup heating system.
 The following properties are retained:
 
 - fuel type
@@ -83,7 +91,7 @@ For example:
  - option: HVAC Cooling Efficiency|Ducted Heat Pump
  - option: Heat Pump Backup|Use Existing System
 
-For this scenario, the type of the backup is (automatically) determined based on information in the table below:
+For this scenario, the type of the backup is automatically determined based on information in the table below:
 
  ============= ============= =========== =============================
  New Heat Pump Backup System Backup Type Example
@@ -99,12 +107,37 @@ For this scenario, the type of the backup is (automatically) determined based on
 
 Other situations and considerations:
 
-- The primary (existing) system does not become backup to the heat pump when:
+- The existing primary system does not become backup to the heat pump when:
 
  - the primary system is a heat pump
  - the primary system is a shared system
 
-- When a secondary (existing) system exists:
+- When an existing secondary system exists:
 
  - it remains secondary if the heat pump upgrade is integrated backup
  - it is removed if the heat pump upgrade is separate backup
+
+.. _use_autosizing_limits_for_ductwork_restriction:
+
+Use Autosizing Limits for Ductwork Restriction
+**********************************************
+
+Use the ``HVAC Distribution|Ductwork Restriction`` option from the lookup.
+The heat pump's heating/cooling autosized capacity is limited to the maximum of the existing duct system's heating/cooling airflow rate (cfm) divided by 400 cfm/ton.
+Additionally, the blower fan efficiency (W/cfm) is adjusted to account for the duct system becoming more restrictive.
+
+For example:
+
+.. code-block:: yaml
+
+ - upgrade_name: ASHP
+ options:
+ - option: HVAC Heating Efficiency|ASHP, SEER 22, 10 HSPF
+ apply_logic:
+ - HVAC Has Ducts|Yes
+ costs:
+ - value: 50.0
+ multiplier: Size, Heating System Primary (kBtu/h)
+ lifetime: 30
+ - option: HVAC Cooling Efficiency|Ducted Heat Pump
+ - option: HVAC Distribution|Ductwork Restriction

docs/read_the_docs/source/workflow_outputs/csv_tables/cost_multipliers.csv

@@ -1,4 +1,8 @@
 Annual Name,Annual Units,Notes
+upgrade_costs.air_flow_rate_cooling_system_primary_cfm,cfm,"Air Flow Rate, Cooling System Primary"
+upgrade_costs.air_flow_rate_heat_pump_backup_primary_cfm,cfm,"Air Flow Rate, Heat Pump Backup Primary"
+upgrade_costs.air_flow_rate_heating_system_primary_cfm,cfm,"Air Flow Rate, Heating System Primary"
+upgrade_costs.air_flow_rate_heating_system_secondary_cfm,cfm,"Air Flow Rate, Heating System Secondary"
 upgrade_costs.door_area_ft_2,ft^2,Door Area
 upgrade_costs.duct_unconditioned_surface_area_ft_2,ft^2,Duct Unconditioned Surface Area
 upgrade_costs.floor_area_attic_ft_2,ft^2,"Floor Area, Attic"