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Re: [EnergyPlus_Support] Energy Balance

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Energy Balance
From: "Michael J. Witte" <mjwitte@xxxxxxxx>
Date: Fri, 9 Sep 2005 14:24:37 -0500
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What kind of HVAC system is being used?  Are the heating and cooling setpoints 
being met?  If the zone air temperature does not match the setpoint, then these 
values will not agree.  For example, if the zone heating setpoint is 20C and 
the system is only able to heat the zone to 18C, then the predicted load for 
the next time step will include the "current" load for that time step plus the 
heat required to raise the zone from 18C to 20C.  If this continues over time, 
the same "unmet" load repeats each time step.  So, accumulated values for the 
predicted load are only meaningful if the setpoint is met at all times.

Mike


On 8 Sep 2005, at 16:10, Ali_Ajmi wrote:

> Thanks very much Mike for your valuable comments. To make sure that the outputs
> are represent truly the zone load, I paste some of the outputs results below.
> First and second columns are representing the actual heating/cooling that
> transfer to the zone in a single day. Third column represent the total predicted
> heat of the zone. So, the question is why the predicted much higher than the
> actual heating/cooling rate? While the fourth and fifth columns are representing
> the load predicted to the heating/ cooling set point, why is the predicted
> heating to set point to heigher than the heating predicted to the zone/sys?
> Finally, Is this amount of heat enough for a zone (240 m2) at that date 01/01 at
> Chicago?
> 
> 
> ZONE NORTH:Zone/Sys Sensible Heating Rate[W](Daily)ZONE NORTH:Zone/Sys Sensible
> Cooling Rate[W](Daily)ZONE NORTH:Zone/Sys Sensible Load Predicted[W](Daily)ZONE
> NORTH:Zone/Sys Sensible Load to Heating Setpoint Predicted[W](Daily)ZONE
> NORTH:Zone/Sys Sensible Load to Cooling Setpoint Predicted[W](Daily)ZONE
> NORTH:Zone/Sys Thermostat Control Type(Daily)ZONE NORTH:Zone/Sys Thermostat
> Heating Setpoint [C](Daily)ZONE NORTH:Zone/Sys Thermostat Cooling Setpoint
> [C](Daily) 424.0039
> 
> 409.4996
> 
> 1519.962
> 
> -1421.69
> 
> 7520.035
> 
> 4
> 
> 20
> 
> 22
> 
> 
> Regards
> Ali
> 
> 
> "Michael J. Witte" <mjwitte@xxxxxxxx> wrote:
> See page 722 (pdf p. 755) for explanations of these variables. In a nutshell,
> these report the load request from the thermostat. Your example says that the
> zone requested heating (predicted load is positive), but the HVAC system
> delivered cooling. Check the HVAC system controls and availability schedules to
> determine why the system did no provide heat when requested.
> 
> Mike
> 
> 
> On 5 Sep 2005, at 11:59, Ali_Ajmi wrote:
> 
> > "These are all explained in the Input Output Reference "... I search it before
> > sending you email and I tried again now, unfortunately, I could not find
> > enough information on Page 1044, could advise any different documents. Mike,
> > thanks for the elaboration of the first question. However, still I could not
> > understand the the second and third variables: 2- Zone/Sys Sensible Load
> > Predicted [W] 3- Zone/Sys Sensible Load to Cooling Setpoint Predicted[W]
> > 
> > Also, the Zone/Sys Sensible Load Predicted int the my output for the North
> > Zone is 1.52 E+03 where the Zone/Sys Sensible Cooling Rate [W] is 4.09E+02.
> > Why they are so different? 
> > 
> > Thanks in advance
> > 
> > Ali
> > ZONE NORTH:Zone/Sys Sensible Cooling Rate[W](Daily)ZONE NORTH:Zone/Sys
> > Sensible Load Predicted[W](Daily)4.09E+021.52E+034.73E+027.00E+02
> > > Mike, if I am using DX:Cooling Coil System (unitary), is it possible 
> > to know how
> > > much each zone has used out of the total DX system consumption or 
> > load? Is any
> > > of the above variable represent the zone load that sum with other 
> > zones load
> > > which at the end represented by the DX:Cooling System.
> > > 
> > 
> > 
> > "Michael J. Witte" wrote:
> > These are all explained in the Input Output Reference (search the document for
> > the report variable names). If the system has no outside air, then number 1
> > (Zone/Sys Sensible Cooling Rate) will be equal to the DX coil sensible load
> > (DX Coil Sensible Cooling Rate[W]) minus any fan heat (Fan Electric Power[W]
> > less any motor heat fraction which is not in the airstream).
> > 
> > Mike
> > 
> > 
> > 
> > On 2 Sep 2005, at 18:13, Ali_Ajmi wrote:
> > 
> > > Mike I am still have confusing of interpretation some of the report
> > > variables. Could you kindly elaborate the meaning of the following
> > > variables: 1- Zone/Sys Sensible Cooling Rate [W] 2- Zone/Sys Sensible Load
> > > Predicted [W] 3- Zone/Sys Sensible Load to Cooling Setpoint Predicted[W]
> > > 
> > > Mike, if I am using DX:Cooling Coil System (unitary), is it possible to know
> > > how much each zone has used out of the total DX system consumption or load?
> > > Is any of the above variable represent the zone load that sum with other
> > > zones load which at the end represented by the DX:Cooling System.
> > > 
> > > Regards
> > > Ali
> > > 
> > > "Michael J. Witte" wrote:
> > > No attachment received (not allowed on this group). In the yahoo group files
> > > area, in the Examples folder there are two zip files with example UAdeltaT
> > > calculations. Is your example steady-state? Are you adding the inside and
> > > outside film coefficients to the construction conductivities (these are
> > > report variables)? I am very confident it will balance. I suggest you create
> > > a very simple model (no windows, no internal gains, constant temperature,
> > > single material layer) and prove the balance first. Then add other
> > > components one-by- one. Also, for windows, the "heat gain" and "heat loss"
> > > report variables are net, including solar gains as well as conduction, so
> > > these should not be added again in the UADeltaT summation.
> > > 
> > > Mike
> > > 
> > > 
> > > 
> > > On 31 Aug 2005, at 17:06, Ali_Ajmi wrote:
> > > 
> > > > Thanks Mike. I calculated the heat gain/loss through the opaque using
> > > > UADelataT, even thought the U was quite high 28.7 W/m2.K. Then added the
> > > > results to heat gain/loss from the windows and constant load (lighting,
> > > > peoples) that done by E+. This summation has been compared to the load
> > > > calculated from multiplying the mass flow rate by the enthalpy difference
> > > > of the in/out North Zone as an example. The result, shown in the attached
> > > > excel sheet, shows the zone load much higher than the system load. Could
> > > > you please advise of error(s) in this approach.
> > > > 
> > > > Regards
> > > > Ali
> > > > 
> > > > "Michael J. Witte" wrote: 
> > > > Are you interpreting "energy transfer" as the envelope heat transfer
> > > > to/from the zone? This is not what it represents. The Energy Transfer
> > > > meters are used for various HVAC system energy flows. See the meter
> > > > details (mtd) output file for a list of specific report variables that are
> > > > accumulated on a given meter.
> > > > 
> > > > 
> > > > There are no report variables available for the envelope contribution to
> > > > the zone load. The list of variables here are heat *gains*, presumably all
> > > > components except the heat transfer through opaque surfaces. The HVAC
> > > > system meets heating/cooling *loads*, and portions of the gains become
> > > > loads significantly later due to thermal mass. Comparing over a daily
> > > > basis helps, but not all gains become a load. 
> > > > 
> > > > If you want to confirm the physics and calculate the opaque surface heat
> > > > transfer, then the only accurate way is to set up a steady-state design
> > > > day and use UAdeltaT to calculate the surface heat transfer.
> > > > 
> > > > Mike
> > > > 
> > > > 
> > > > On 25 Aug 2005, at 19:11, Ali_Ajmi wrote:
> > > > 
> > > > > Hi All,
> > > > > I tried to balance the energy that losses in the North zone, in my five
> > > > > zone building, and energy needed by the system and gain by the solar to
> > > > > cover that losses. The report and meter variables that shown below shows
> > > > > that the energy transfer out of the zone in the first day of January too
> > > > > high comparable to the energy should be compensated the loss by the
> > > > > heating coil, people, lighting. A short list for the variables that I
> > > > > used to do this analysis is below. could any one figure out which
> > > > > variable I may missed or error of value conversion from W to J.
> > > > > 
> > > > > ZONE NORTH:Zone Window Heat Gain[W](Daily)
> > > > > 
> > > > > ZONE NORTH:Zone Window Heat Gain[J](Daily)
> > > > > 
> > > > > ZONE NORTH:Zone Window Heat Loss[W](Daily)
> > > > > 
> > > > > ZONE NORTH:Zone Window Heat Loss[J](Daily)
> > > > > 
> > > > > ZONE NORTH:People-Total Heat Gain[J](Daily)
> > > > > 
> > > > > ZONE NORTH:Electric Eq-Total Heat Gain[J](Daily)
> > > > > 
> > > > > ZONE NORTH:Cat00 Electric Eq-Total Heat Gain[J](Daily)
> > > > > 
> > > > > ZONE NORTH:Infiltration-Sensible Heat Loss[J](Daily)
> > > > > 
> > > > > ZONE NORTH:Infiltration-Sensible Heat Gain[J](Daily)
> > > > > 
> > > > > EnergyTransfer:Zone:ZONE NORTH [J](Daily)
> > > > > 
> > > > > 6.67E-01
> > > > > 
> > > > > 2.40E+06
> > > > > 
> > > > > 1.57E+03
> > > > > 
> > > > > 8.64E+12
> > > > > 
> > > > > 1.09E+08
> > > > > 
> > > > > 8.48E+07
> > > > > 
> > > > > 8.48E+07
> > > > > 
> > > > > 1.62E+08
> > > > > 
> > > > > 0.00E+00
> > > > > 
> > > > > 1.15E+08
> > > > > 
> > > > > Thanks in advanced 
> > > > > 
> > > > > Ali
> > > > > 
> > > > > 
> > > > > 
> > > > > ---------------------------------
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> > > > > [Non-text portions of this message have been removed]
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > The primary EnergyPlus web site is found at:
> > > > > http://www.energyplus.gov
> > > > > 
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> > > > > Yahoo! Groups Links
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> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > 
> > > > 
> > > > 
> > > > ========================================================
> > > > Michael J. Witte, GARD Analytics, Inc.
> > > > EnergyPlus Testing and Support 
> > > > EnergyPlus-Support@xxxxxxxx
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > The primary EnergyPlus web site is found at:
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> > > > 
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> > > > The primary EnergyPlus web site is found at:
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> > > 
> > > 
> > > 
> > > ========================================================
> > > Michael J. Witte, GARD Analytics, Inc.
> > > EnergyPlus Testing and Support 
> > > EnergyPlus-Support@xxxxxxxx
> > > 
> > > 
> > > 
> > > 
> > > 
> > > The primary EnergyPlus web site is found at:
> > > http://www.energyplus.gov
> > > 
> > > The group web site is:
> > > http://groups.yahoo.com/group/EnergyPlus_Support/
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> > > The primary EnergyPlus web site is found at:
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> > 
> > ========================================================
> > Michael J. Witte, GARD Analytics, Inc.
> > EnergyPlus Testing and Support 
> > EnergyPlus-Support@xxxxxxxx
> > 
> > 
> > 
> > 
> > 
> > The primary EnergyPlus web site is found at:
> > http://www.energyplus.gov
> > 
> > The group web site is:
> > http://groups.yahoo.com/group/EnergyPlus_Support/
> > 
> > Attachments are not allowed -- please post any files to the appropriate folder
> > in the Files area of the Support Web Site.
> > 
> > Yahoo! Groups Links
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> > The primary EnergyPlus web site is found at:
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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
> 
> 
> 
> 
> 
> The primary EnergyPlus web site is found at:
> http://www.energyplus.gov
> 
> The group web site is:
> http://groups.yahoo.com/group/EnergyPlus_Support/
> 
> Attachments are not allowed -- please post any files to the appropriate folder
> in the Files area of the Support Web Site.
> 
> Yahoo! Groups Links
> 
> 
> 
> 
> 
> 
> 
> 
> 
> ---------------------------------
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> Yahoo! Photos. Get Yahoo! Photos
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> 
> 
> 
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> 
> Attachments are not allowed -- please post any files to the appropriate folder
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> 
> 
> 
> 
> 
> 
> 



========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx




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- Re: [EnergyPlus_Support] Energy Balance
  - From: Michael J. Witte
- Re: [EnergyPlus_Support] Energy Balance
  - From: Ali_Ajmi
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