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What does multiplier means for loads and sub surfaces in Openstudio

asked 2016-04-25 12:36:49 -0500

updated 2020-01-26 11:49:01 -0500

I am curious to know when I have just one zone and only one door what does multiplier of the door means?(This is by default 1 for example if I change it to 2 what will happen for my door?) image description image description

And what about loads! how multiplier works for them?(people, lights, electric equipment, infiltration). image description Thanks in advance for any answers!

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answered 2016-04-25 15:10:06 -0500

updated 2016-04-26 03:55:08 -0500

OpenStudio translates OS:SubSurface objects to the equivalent EnergyPlus FenestrationSurface:Detailed object type. Multipliers assigned to the subsurfaces are translated directly to that object, and represent the number of identical surfaces that exist on the base surface. In this way if you had multiple exact windows on that surface, but didn't want to explicitly draw them (or simplify them into one big window), you could use the multiplier field as an easy way to get the effect of additional windows.

Internal load objects (lights, equipment, etc) in EnergyPlus don't have native 'Multiplier' input fields. Looking at the code that translates the OpenStudio inputs to EnergyPlus inputs, it's pretty clear that the load definition multipliers are applied to whatever value is used to define the power for that load (either design level, power per unit area or power per person) and the 'multiplied' value used in the EnergyPlus object. Thus if you wanted to model a room with ten computers, instead of defining the total power for all ten, you could set up your load to reflect the power of a single computer, and assign a multiplier of ten.

I'm pretty sure there is no multiplier input for the infiltration load; the spacing of that column in the Spaces tab is just weird.

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Thanks @Eric Ringold, I missed the sub surface part of his question. You are correct that infiltration objects, along with design specification OA and water use equipment loads don't have a multiplier. It is also a bit odd that infiltration objects have dedicated columns under the "General" view and then also show up under the Load Name column in the "Loads" view.

David Goldwasser's avatar David Goldwasser  ( 2016-04-25 15:34:11 -0500 )edit

@Eric Ringold, and @David Goldwasser, THANK you very much for your helpful and informative answers.

4Designer's avatar 4Designer  ( 2016-04-26 03:57:15 -0500 )edit

answered 2016-04-25 15:00:14 -0500

The multiplier does just multiply the load to x times what it would be otherwise. When the load definition for an instance is described as per area (W/ft^2) the multiplier is typically set to 1. When the load defintion for an instance use a design level (W) you typically use a multiplier larger than one. For example if you know you are using a specific lighting fixture that uses 60 W each, the load definition is 60 W. The multiplier defines how many fixtures are in the space. So if you have 5 fixtures, the load (if the schedule value is 1 for a a specific timestep) is 60 W x 5 x 1 or 300 W.

If the load instance is directly assigned to a space, then that space would have 300 W of lighting from the load instance. If the load instance is assigned to a space type, then each space using that space type would have 300 W of lighting from the load instance. Generally you wouldn't use this approach for a space type, unless it was applied to many similar spaces like guest rooms, or apartments, where each room may have one microwave, 3 lamps, and 2 people; independent of the specific geometry of the space.

A last note on multipliers, they don't have to be integers, they just need to be a positive number. So you can have a multiplier of 2.5, or even 0.2. The use of non-integers was enabled for a few special use cases, so most users may not want to use a non-integer multiplier.

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Regarding subsurface multipliers: the EnergyPlus idd for FenestrationSurface:Detailed multiplier notes: "Non-integer values will be truncated to integer" (and additionally: "Used only for Surface Type = WINDOW, GLASSDOOR or DOOR").

ericringold's avatar ericringold  ( 2016-04-25 15:13:24 -0500 )edit

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Asked: 2016-04-25 12:36:49 -0500

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Last updated: Apr 26 '16