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How are unmet hours calculated in Sefaira and are they related to dry buld temperature?

asked 2019-12-04 13:04:56 -0600

archy1 gravatar image

How does Sefaira calculate 'unmet hours'? I understand that this is the percentage of the number of hours in a year in which more than one room in the building is not "comfortable". I assume that "comfortable" is defined by the temperature range (rather than the setback range) of the HVAC system. What measure of thermal comfort is calculated for each room for comparison to the temperature range?

Furthermore, is there a relationship between unmet hours and dry bulb temperature?

I have been unable to find information about this in the offical Sefaira doccumentation and any help would be greatly appreciated! There are lots of tutorials that talk about thermal comfort but they all focus on dry bulb, operative temperature or ASHRAE.

Angus

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answered 2019-12-05 04:22:55 -0600

Andrew_Corney gravatar image

Hi Angus,

Thanks for your question (and thanks to the kind people who forwarded this to me as I am not often here).

The unmet hours in Sefaira are based on the ASHRAE 90.1 definition - ie if at least one occupied zone is outside its dry bulb setpoint range in any given hourly timestep, that timestep will be reported as an unmet hour in Sefaira.

If you export the idf file and run the same model in E+ you may not always get the same result. This is because with some HVAC systems temperatures often ride around or fractionally above the setpoint (we are talking less than 0.1°C). Sefaira has an adjustable tolerance surfaced in the application which gives you a way to ignore these marginal infractions in our reporting.

I am not a frequent enough unmet hours user to attach an image but if you click the "test tolerance" settings cog under the comfort output tab (with dry bulb the output selected) you will see it is set by default to 0.2C and there is a link to help. If you set this to zero you will get the same value as an unmet hours report generated from the same model.

This is explained in this support article which is linked to in the product: https://support.sefaira.com/hc/en-us/... - you need to be signed in to view this support article.

best,

Andrew Corney

Product Manager - Sefaira

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Asked: 2019-12-04 13:04:56 -0600

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Last updated: Dec 04