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Re: [EnergyPlus_Support] some questions about E+

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] some questions about E+
From: "Michael J. Witte" <mjwitte@xxxxxxxx>
Date: Tue, 22 Jun 2004 15:31:44 -0500
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1.  The only way to approximate this is to set your supply air temperature to 
equal the "preset minimum" value and run the air system as priority 1 for 
cooling.  If this is not sufficient to meet the cooling load in the space, then 
the radiant panels will activate to meet the remaining load.  However, the 
current controls in EnergyPlus have difficulty with such combined radiant/air 
systems, so you may have to adjust things to get a reasonable simulation.

2.  As far as EnergyPlus is concerned, the delta pressure and pump head can be 
as small as you like.  They are used only to calculate the fan and pump power 
consumption.  In the example files, the window AC unit uses a fan pressure of 
75 Pa and the VAV system uses 600 Pa.  For the pump head, if this office is 
part of a large building, then using a pump head appropriate for the whole 
building would give a reasonable approximation of the additional pump power 
required to serve this load.

3.  In the current version, the zone list multiplier does multiply the heat 
gain impact of lights and equipment, but it does not multiply the power 
consumption on the electric meters.  If you use the zone multiplier in the ZONE 
object instead of the zone list multiplier, everything is multiplied as you 
would expect.

Mike


On 22 Jun 2004, at 11:39, Xu H.T wrote:

>   I have some questions about E+.
> 
>   1. For the combined conditioned system, such as cooled-ceiling system combined
>   with displacement ventilation system, the simulation sequence (I want it) is
>   that, at a given air supply flow rate, the required air supply temperature is
>   calculated. If the supply temperature is below the preset minimum, the ceiling
>   panels will be 'activated', and the activated panel surface temperature will
>   be calculated, and consequently, the required chilled-water temperature are
>   calculated using a heat-exchanger model. 
> 
>   So, can E+ carry out this simulation strategy?
> 
>   2. Now, I am simulate a very small office space (5.1m*3.6m*2.64m), served by a
>   plant. For practice, it's not true that a plant only serves a single small
>   space. From simulation point, I only need to investigate the energy
>   consumption of this office and assume a plant serves it. I think it is
>   reasonable, right? During the simulation, the AUTOSIZE can be used for sizing
>   of plant, condenser, etc. However, for the pump and fan, the Rated Pump Head
>   (Pa) and Delta Pressure (Pa) are needed to specify. The question is, at such
>   little flow rate, how to choose these two pressures? Any references for it?
> 
>   3. If it's not reasonable for the pressure specifications at such little flow
>   rate, I think I can multiple a single office heat load to a larger one and use
>   the larger flow rate to choose the Rated Pump Head and Delta Pressure from
>   industrial pump or fan parameters. However, the zone list mutliplier is not
>   being applied to internal gains such as LIGHTS and ELECTRIC EQUIPMENT. So, how
>   to consider the light and electric equipment heat load for the total multiple
>   space conditioned load?
> 
>   Xu
>     ----- Original Message ----- 
>     From: zhaicq98 
>     To: EnergyPlus_Support@xxxxxxxxxxxxxxx 
>     Sent: Tuesday, June 22, 2004 8:30 AM
>     Subject: [EnergyPlus_Support] please help with modeling of roof top unit
> 
> 
>     Hi,
> 
>     I am trying to simulate a roof top unit, which includes a DX cooling 
>     coil, heating coil and variable speed fan. I am always getting a lots 
>     of warning messages, which 
>     said "COIL:DX:COOLINGBYPASSFACTOREMPIRICAL "MAIN COOLING COIL 1" - 
>     Air volume flow rate per watt of rated total cooling capacity is out 
>     of range." I checked the input output reference, and understood that 
>     there is a range for this factor. The range is from 0.00004699 to 
>     0.00006041 (m3/s)/W. The rated capacity of my DX coil is 20000 W, and 
>     the rated air flow rate is 1.1 m3/s, resulting in a factor inside the 
>     required range. 
> 
>     I am modeling a VAV system, and the design flow rate of the system is 
>     1.1 m3/s. I set the minimum flow fraction of the system to be 0.3. 
>     Thus the actual flow rate of the system could go beyond the range 
>     required by the DX coil, when the system is operating. If I have to 
>     stick to the range, then the actual flow rate of my system can only 
>     vary between 0.00004699*1.1 = 0.94 and 0.00006041*1.1 = 1.21 m3/s. I 
>     think this is not a real VAV system performs. 
> 
>     Can anyone tell me whether these warning messages matter or not? In 
>     addition, what is the proper way to deal with the system I am 
>     modeling?
> 
>     Thanks a lot for your help.
> 
>     -Chaoqin
> 
> 
> 
>     The primary EnergyPlus web site is found at:
>     http://www.energyplus.gov
> 
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>     http://groups.yahoo.com/group/EnergyPlus_Support/
> 
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> 
> 
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> 
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========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx



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References:
- [EnergyPlus_Support] some questions about E+
  - From: Xu H.T

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