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Rainwater and graywater in EnergyPlus

asked 2014-11-17 13:21:21 -0500

updated 2015-11-12 14:23:17 -0500

I am trying to model a rainwater collector on the roof of a building that will be sent to a rainwater tank as a WaterUse:Storage component in EnergyPlus. That tank is then connected to my DHW WaterUse:Connections component as the "Supply Water Storage Tank Name" to supply cold water when the tank has ample volume, otherwise mains water will be used. Here are my issues:

  1. When it is raining, my output .csv file doesn't show a change in rainwater tank volume from the initial value.
  2. My annual simulations show no change in mains water used for DHW loads whether rainwater is collected or not.
  3. The volume for the graywater tank also doesn't change from the initial value.

Here is an excerpt from the .idf file:

    Restroom DHW Connections,!- Name
    Restroom DHW Inlet Node,  !- Inlet Node Name
    Restroom DHW Outlet Node,  !- Outlet Node Name
    Rainwater Tank,                        !- Supply Water Storage Tank Name
    Graywater Tank,    !- Reclamation Water Storage Tank Name
    ,                        !- Hot Water Supply Temperature Schedule Name
    ,                        !- Cold Water Supply Temperature Schedule Name
    ,                        !- Drain Water Heat Exchanger Type
    ,                        !- Drain Water Heat Exchanger Destination
    ,                        !- Drain Water Heat Exchanger U-Factor Times Area {W/K}
    Restroom DHW Equipment;  !- Water Use Equipment 1 Name

    Rainwater Collector ,!- Name
    Rainwater Tank , !- Storage Tank Name
    CONSTANT, !- Loss Factor Mode
    0.2 , !- Collection Loss Factor
    , !- Collection Loss Factor Schedule Name
    100000, !- Maximum Collection Rate
    Rainwater Collector Surface ; !- Collection Surface Name

    Rainwater Tank, !- Name
    Rainwater Harvesting, !- Water Quality Subcategory
    , !- Maximum Capacity {m3}
    5, !- Initial Volume {m3}
    , !- Design In Flow Rate {m3}
    , !- Design Out Flow Rate {m3}
    , !- Overflow Destination
    None, !- Type of Supply Controlled by Float Valve
    , !- Float Valve On Capacity {m3}
    , !- Float Valve Off Capacity {m3}
    , !- Backup Mains Capacity {m3}
    , !- Other Tank Name
    ScheduledTemperature , !- Water Thermal Mode
    Rainwater Temp Schedule , !- Water Temperature Schedule Name
    , !- Ambient Temperature Indicator
    , !- Ambient Temperature Schedule Name
    , !- Zone Name
    , !- Tank Surface Area {m2}
    , !- Tank U Value {W/m2-K}
    ; !- Tank Outside Surface Material Name

    Rainwater Temp Schedule,  !- Name
    Any Number,              !- Schedule Type Limits Name
    16;                     !- Hourly Value

I have created a Site:Precipitation object with an annual schedule from the PrecipitationSchedulesUSA.idf dataset, and that works fine. Any help would be greatly appreciated. I've thought about if there should be a pump connected to the rainwater loop, but there aren't input or output nodes for the WaterUse:RainCollector or WaterUse:Storage components.

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Could you attach the entire idf as a link in your question? At minima, are you sure you have actually defined a demand for cold and hot water? Is the level in your tank always "high"? (meaning the initial value = tank is filled).

Julien Marrec's avatar Julien Marrec  ( 2014-11-18 01:55:06 -0500 )edit

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answered 2014-11-25 11:25:35 -0500

Sorry for the late reply. There is also an example file titled "5zoneWaterSystems" that comes with EnergyPlus that uses rainwater harvesting capabilities. I have run this example file and been unable to find a rhyme or reason to when water flows into the tank (not all times that rain is falling) and out of the tank (not all times that makeup water is being used in the cooling tower). I initially did this using v8.0, then ran the same example file in v8.1 and VOILA, water flow times all correlate to rain fall and makeup water use. I guess chalk this up to a bug that was fixed between versions, and make a note that rainwater harvesting capabilities should only be modeled with v8.1 and above for EnergyPlus.

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Asked: 2014-11-17 13:21:21 -0500

Seen: 437 times

Last updated: Nov 25 '14