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Document autosizing methodology for e.g. dual-fuel HPs #1486

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Sep 25, 2023
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Document autosizing methodology for e.g. dual-fuel HPs #1486

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78e37b5
Document autosizing methodology for e.g. dual-fuel HPs.
shorowit Sep 19, 2023
6b099ba
A little cleanup.
shorowit Sep 19, 2023
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6 changes: 3 additions & 3 deletions HPXMLtoOpenStudio/measure.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -3,8 +3,8 @@
<schema_version>3.1</schema_version>
<name>hpxm_lto_openstudio</name>
<uid>b1543b30-9465-45ff-ba04-1d1f85e763bc</uid>
<version_id>5db80f7a-58be-4b4a-9942-487602e5a6e4</version_id>
<version_modified>2023-09-13T20:50:01Z</version_modified>
<version_id>5b3130f2-b6cd-4fd4-ba8d-1cb3be263f93</version_id>
<version_modified>2023-09-19T21:08:31Z</version_modified>
<xml_checksum>D8922A73</xml_checksum>
<class_name>HPXMLtoOpenStudio</class_name>
<display_name>HPXML to OpenStudio Translator</display_name>
Expand Down Expand Up @@ -280,7 +280,7 @@
<filename>hvac_sizing.rb</filename>
<filetype>rb</filetype>
<usage_type>resource</usage_type>
<checksum>44977F7D</checksum>
<checksum>6BA780E1</checksum>
</file>
<file>
<filename>lighting.rb</filename>
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2 changes: 1 addition & 1 deletion HPXMLtoOpenStudio/resources/hvac_sizing.rb
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Expand Up @@ -2010,7 +2010,7 @@ def self.process_heat_pump_adjustment(hvac_sizing_values, weather, hvac_heating,
end
end
if (not min_compressor_temp.nil?) && (min_compressor_temp > @hpxml.header.manualj_heating_design_temp)
# Calculate the heating load at the switchover temperature to limit uninitialized capacity
# Calculate the heating load at the switchover temperature to limit unutilized capacity
temp_heat_design_temp = @hpxml.header.manualj_heating_design_temp
@hpxml.header.manualj_heating_design_temp = min_compressor_temp
_alternate_bldg_design_loads, alternate_all_hvac_sizing_values = calculate(weather, @hpxml, @cfa, [hvac_system])
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21 changes: 16 additions & 5 deletions docs/source/workflow_outputs.rst
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Expand Up @@ -423,8 +423,7 @@ HVAC Capacities
~~~~~~~~~~~~~~~

System outputs are listed below.
Autosized HVAC systems are based on HVAC design temperatures/loads described below.
Capacities for individual HVAC systems can be found in the `in.xml` file.
Capacities for individual HVAC systems can be found in the ``in.xml`` file.

==================================================== ====================
Type Notes
Expand All @@ -434,11 +433,21 @@ Capacities for individual HVAC systems can be found in the `in.xml` file.
HVAC Capacity: Heat Pump Backup (Btu/h) Total HVAC heat pump backup capacity
==================================================== ====================

.. note::

Autosized HVAC systems are based on :ref:`hvac_design_temps` and :ref:`hvac_design_loads`.

For heat pumps with a minimum compressor lockout temperature greater than the heating design temperature (e.g., a dual-fuel heat pump in a cold climate), the compressor will be sized based on heating design loads calculated at the compressor lockout temperature.
This is done to prevent unutilized capacity at temperatures below the compressor lockout temperature.
Any heat pump backup will still be based on heating design loads calculated using the heating design temperature.

.. _hvac_design_temps:

HVAC Design Temperatures
~~~~~~~~~~~~~~~~~~~~~~~~

Design temperatures are used in the design load calculations for autosizing of HVAC equipment; see :ref:`hvac_sizing_control` for how they are derived.
Design temperatures can also be found in the `in.xml` file.
Design temperatures can also be found in the ``in.xml`` file.

===================================================================== ====================
Type Notes
Expand All @@ -447,12 +456,14 @@ Design temperatures can also be found in the `in.xml` file.
HVAC Design Temperature: Cooling (F) 1% cooling drybulb temperature
===================================================================== ====================

.. _hvac_design_loads:

HVAC Design Loads
~~~~~~~~~~~~~~~~~

Design load outputs, used for autosizing of HVAC equipment, are listed below.
Design loads are based on block load ACCA Manual J calculations using 1%/99% design temperatures.
Design loads can also be found in the `in.xml` file.
Design loads are based on block load ACCA Manual J calculations using :ref:`hvac_design_temps`.
Design loads can also be found in the ``in.xml`` file.

===================================================================== ====================
Type Notes
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