What are OpenStudio Measures?

In its most basic form, an OpenStudio Measure is a program (or 'script', or 'macro', if you like) that can access and leverage the OpenStudio Model and API to create or make changes to a building energy model, as defined by an OpenStudio Model (.osm).

Typically, a measure modifies an existing .osm in order to implement a given energy conservation measure (ECM). For example, a measure might change the insulation rating of the exterior walls, change the window-to-wall ratio of a specific facade, or modify operational or occupancy schedules. Measures may also generate reports on the input and output of a given energy model; as such, these are referred to as reporting measures.

Measures may be linked together in a workflow in order to implement complex ECMs, or to repeatably implement ECMs across building types or climate zones; measures can even generate entire -- code-compliant and climate-zone specific -- building models solely from user inputs. Through this workflow, cove.tool automatically translates the model inputs to OpenStudio file where users can perform compliance level modeling.

ENVELOPE

Wall - The default R values for the walls (assembly) are populated for each cove.tool project based on the energy code and building type. cove.tool directly translates this value into OpenStudio as shown in the figures below.

Roof - The R-values are automatically populated based on the location of the project assuming the Insulation Entirely above Deck roof type for all commercial building types except small office (Attic and Other). This is then directly translated into the OS model as shown in the report.

Window - The glazing U-value and SHGC are automated based on the energy code and location of the project. These values are used to set the OpenStudio window parameters.

Skylight - The skylight U-value and SHGC are automated based on the energy code and location of the project. These values are used to set the OpenStudio skylight parameters.

Envelope Heat Capacity - Heat Capacity is the ratio of the heat added to an object to impact the resulting interior temperature. To accurately translate the impact of different options of 'Envelope Heat Capacity', the following multipliers have been used in OpenStudio measure.

Blinds/Curtains/Shades - The type for blinds/curtains/shades can be set from OpenStudio application. (Spaces>Subsurfaces>ShadingControl>ShadingType)

Wall Emissivity – The emissivity is defined as the fraction of energy being emitted relative to that emitted by a thermally black surface (a black body). cove.tool refers to ASHRAE Handbook – Fundamentals version 2009 for wall emissivity values. The values are assigned to the Roof surface as a thermal multiplier as shown in the report.

USAGE AND SCHEDULES

Occupancy Schedules- Within OpenStudio, the occupancy schedules are automated based on the respective PNNL prototype building. Cove.tool picks the appropriate PNNL prototype based on information provided on the projects page and the geometry page

Daylight Sensors - A daylight sensor is a photo-cell detecting device that reads available light in a space and sends a signal to the control system. 'Partial' option for 'Daylight Sensors' controls the 50% space where 'Sensors' option controls 100% of the space. Daylight sensors have also been shown to provide between 20%-60% in Light Savings.

Occupancy Sensors - The LPD (W/ft2) value will be modified based on the option (partial, sensors, No sensors) selected for the occupancy sensors input.

Lighting (W/ft2) - Set the lighting power density in the building to a specified value for all spaces that have lights. This is applied to the entire building during the occupied hours.

Lighting (Unocc. Hrs) - The lighting power density unoccupied is translated to OpenStudio as a fraction of the lighting power density occupied.

Exterior Lighting Power – Exterior lights are typically used for safety, guidance, and recreation. The power (Watts) entered in cove.tool gets translated directly to OS as shown in the image.

Appliance Use (W/ft2) – Set the equipment power density in the building to a specified value for all spaces that have lights. This is applied to the entire building during the occupied hours.

Appliance Use (Unocc. Hrs) - The equipment power density unoccupied is translated to OpenStudio as a fraction of the equipment power density occupied.

Metabolic Rate – The activity inside an area affects its internal heat gain. The OpenStudio model selects the activity schedule based on the building type.

Heating Set-Point, Heating Set back, Cooling Set-Point, Cooling Set back - Within OpenStudio, these parameters are automated based on the respective PNNL prototype building.

Total Occupants(Occupied Hours) - Number of occupants are transferred from cove.tool to OpenStudio with the measure.

BUILDING SYSTEMS

System Type - The system types from the dropdown menu have been mapped to the closest matching system in OpenStudio. More system-specific details can now be modeled within the OpenStudio app.

Based on system type selection, OpenStudio populates the standard values for the following parameters:

  1. Integrated Part Load Value
  2. Heating System COP
  3. Cooling System COP
  4. Fan Flow Control Factor
  5. Specific Fan Power
  6. People Outdoor Air Rate
  7. Area Outdoor Air Rate

Heat Recovery System - The desired heat recovery system can be assigned from the OpenStudio application (HVAC Systems > Library > Heat exchanger Air to Air Sensible & Latent)

Infiltration – The infiltration values (as shown in the table below) in cove.tool are calculated with a pressure difference of 4 Pa. This leakage rate is then converted to 50 Pa and further to an ACH value as required by the OpenStudio measure.

Pump Control for heating/ Pump control for cooling – The pump control setting in cove.tool takes into consideration the transmission losses. OpenStudio takes into consideration the pump motor efficiency.

Ventilation Control - Ventilation can be reduced during the hours of operation when spaces are vacant or at lower than peak occupancy. In cove.tool, the user can choose from ‘Demand control’, ‘Always on’ and ‘Off during unoccupied hours’ which translates into the OpenStudio model.

DHW Gen. and Hot Water Distribution System - The demand hot water and generation system can be assigned within the OpenStudio application

Domestic Hot Water Demand - The domestic hot water demand per year is Autosized in OpenStudio based on the number of people and building area

ENERGY GENERATION

PV Generation (Solar Panel Surface Area, Solar Panel Module Location, Solar Panel Module Type) – For calculating the energy generated by having PV onsite, the values entered by the user would be translated into annual energy generated (kWh) in OpenStudio.

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