Water fixture flow rate per person

asked 2016-02-06 02:15:12 -0600

PBrain
123 ●5

updated 2016-02-06 02:15:37 -0600

I would like to model a hot water system in OpenStudio.

The Water Fixture (Load) Definition seems to be the place for me to enter the peak demand and set fractional schedules. The definition requires Peak Flow Rate in cubic metres per second. I would like to set the flow rate proportional to occupant density.

Any guidance on this would be appreciated. Is there a measure for it ? Are there any fundamental issues with that approach ?

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This is a good feature request, so if you want do add water per person and or per area, you an addd a request on user voice. This could be a feature only to OpenStudio (and it would hard-size it on forward translation) or it could be implemented in EnergyPlus as well. For stop gap could write measures applied at run time to mimic this behavior.

David Goldwasser ( 2016-02-06 14:33:11 -0600 )edit

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answered 2016-02-06 05:14:56 -0600

Julien Marrec

29706 ●94 ●76 http://www.effibem.com/

updated 2016-02-06 05:16:39 -0600

What I've typically done for New Construction of residential buildings (mostly mid/high rise) is to follow the guidelines and calculator given by the ENERGY STAR Multifamily High Rise (MFHR) program. Basically, based on population classification it gives you how many gallons of hot water per day and per occupant. Multiply that by the number of occupants and you'll get your baseline usage.

The tool spits out a peak flow rate and a fractional schedule to use with it, so you just have to create these in OpenStudio.

Note that for the water fixture definition object, as far as I know these values are for a target water temperature of 120F.

You can download the Performance Path Calculator on this page.

You should also take a look at the ASHRAE Handbook of Fundamentals - HVAC Applications (2015, 2011, 2007...), chapter called "Service Water Heating". It has load profiles for different building types and a couple of different ways to size your heater.

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answered 2016-02-06 09:24:41 -0600

MatthewSteen

10147 ●19 ●26 https://www.nrel.gov/b...

updated 2016-02-06 11:55:52 -0600

It's important to note that the WaterUse:Equipment definition includes both hot and cold water use, which I typically assume is equal.

For a baseline model I typically use values from the DOE Commercial Prototype Building Models for building type and vintage. These values can represent only hot water, so I recommend inspecting the models and documentation to where they come from. After that I would compare the SHW end use percentage of the PBM to your model as a rough calibration.