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What does changing seed value in Algorithm Settings do?

asked 2019-12-05 20:34:59 -0500

y.tanaka gravatar image

updated 2020-01-07 17:33:36 -0500

Context:

  1. I am working with project_singlefamilydetached from the ResStock project
  2. I have location.tsv and location-region.tsv fixed to only simulate homes in Alpena, Michigan
  3. I have changed the vintage.tsv for Alpena, Michigan to my own probabilities of my choosing

I have been using PAT tool to simulate differences in energy use for homes with a Propane Furnace only vs. GSHP only. However, I noticed that for different seeds, the building characteristics remain identical after analysis has finished.

An example is shown below: image description

The average, annual total heating costs for 5 different analyses, with 5 unique seeds, produce almost identical values. To produce the results you see before you, I utilized the electricity_heating_kwh and propane_heating_mbtu outputs from the enduse_timeseries.csv for each of the buildings.

If changing the seeds does not change the outputs of enduse_timeseries.csv, then, what does it change? I wish to create a distribution of comparisons, but in order to do that, the results outputted by PAT needs to change as well.

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answered 2019-12-05 23:51:17 -0500

ResStock projects do not use this PAT interface input.

Note that ResStock's sampling algorithm is part deterministic and part random. The deterministic part occurs when ResStock determines how many of a given option to choose for a given building characteristic. For example, if a probability distribution for wall insulation is 30% uninsulated, 50% R-13, and 20% R-19, and you asked for 20 buildings, ResStock's sampling would always yield 6 buildings with uninsulated walls, 10 buildings with R-13 walls, and 4 buildings with R-19 walls.

Randomness thus only comes into play when these wall options are combined with other parameters (HVAC options, appliance options, etc). However, ResStock currently uses a hard-coded random seed to make the sampling algorithm repeatable. If you really want to generate different combinations of building characteristics, you can change this value between runs.

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It worked! Changing the seed value in the ruby script does in fact change my results. Thank you!

y.tanaka gravatar imagey.tanaka ( 2019-12-06 14:15:39 -0500 )edit

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Asked: 2019-12-05 20:34:59 -0500

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Last updated: Dec 05 '19