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RE: [EnergyPlus_Support] Dometsic Hot Water System modeling



 
Hi Merid,
 
I will try to answer your questions.  In addition to the documentation on p. 493, you might want to look at the water heater object as used in a solar water heating application on pp. 871-875.  Also I recommend looking at the example files called SolarCollectorFlatPlateWater.idf, which illustrates two water heaters in a plant loop, and WaterHeaterStandAlone.idf, which shows some water heaters without a plant loop, i.e., in "stand-alone" mode.  
 
If it is a really simplified domestic hot water system that you want to simulate, then the stand-alone example might do everything that you need:  Instead of using the WATER USE CONNECTIONS object with a plant loop, you would just aggregate all of your hot water loads into one schedule that would be referenced by the Use Flow Rate Fraction Schedule field.
 
And to your specific questions:
 
1)  The Use Side Inlet Node and Use Side Outlet Node fields define the node names that are connected to the plant loop.  You only need them if the object will be connected to a plant loop.  If you do put node names, these are the names that are referenced by the BRANCH object so that the rest of the plant network knows what components are connected to what other components.
 
The red node for Figure 68 on the "Use Side" is the Use Side Outlet Node.  
 
2)  Yes, the source side fields can be left blank.  The source side connections represent a fluid inlet and outlet pipes for some external heat source.  Some real life examples of a heat source could be solar hot water collectors, heat recovery from a generator (see the HeatRecoverywithStorageTank.idf example file), or any component that can provide heat via a plant loop.  The source side nodes are also used when the water heater is used with the heat pump water heater compound object.
 
3)  The Outlet Node of a WATER USE CONNECTIONS object represents return water to the plant loop.  That return water usually does return back to the water heater, but it might have to pass through some other nodes in the plant loop first.  Keep in mind that the plant loop is a network of many nodes.  There will never be a direct connection between the WATER USE CONNECTIONS Outlet Node and the WATER HEATER Use Side Inlet Node--they won't have the same node name.  The flow does return to the water heater but will probably pass through several other nodes along the way.  
 
4)  Yes, it is possible to simulate hot water recirculation using the current version.  There are two possible approaches that I can think of:
 
a)  Use the water heater in stand-alone mode with a schedule for your hot water loads.  Simulate the recirculation pump using an ExteriorFuelEquipment object to set a constant rate of energy consumption.  
 
b)  Use a plant loop with the WATER HEATER on the supply side of the loop and the WATER USE CONNECTIONS on the demand side.  Using a plant loop requires you to put in a pump anyway, so just put in the correct values to get the energy consumption you want.  Finally, make sure the pump runs all the time by putting in a bypass branch in parallel with the CONNECTIONS object.  You will also probably have to set the pump to be PUMP:CONSTANT SPEED and Pump Control Type set to "Continuous".  This is obviously the more complicated option, but does capture the effect of any pump heat added to the water flow.  
 
 
Hope this helps,
P
 
 
-----Original Message-----
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]On Behalf Of aboyemeplus
Sent: Tuesday, March 20, 2007 1:05 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Dometsic Hot Water System modeling



Hi,

I am trying to model a simplified domestic hot water system which 
consists of a "Water Heater" and a "Water Use Connections" object 
connected to the "Use Side" of the Water Heater. Please help me 
understand the definition of some of the fields used in these 
objects.

1) On page 500 of the I/O reference, what is the object of reference 
used to describe "Use Side Inlet Node" and "Use Side Outlet Node"? 
Or, referring to Figure 68 (pg 493), is the Red Node on the "Use 
Side" "Use Side Inlet Node" or "Use Side Outlet Node"? 

2) Can the "Source Side" fields be left blank if the energy source 
is specified as an electric heating element within the Water Heater? 
What exactly does the "Source Side" represent in a "Water Heater" 
object? Can you please provide a real life example?

3) Does the "Outlet Node" of a "Water Use Connections" object 
represent return water to the water heater? In other words, is 
the "Use Side Inlet Node" of a water heater the same as the "Outlet 
Node" of a "Water Use Connections" object? 

4) Is it possible to simulate DHW systems with hot water 
recirculation using the current version of E+? If so, can you 
provide me with generalized guidance and/or point to a sample file 
of relevance?

Thank you for your support.

Merid



 


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