Re: [EnergyPlus_Support] “Zone/Sys Sensible Load Predicted” and “Purchased Air Total Cooling Rate”

["Michael J. Witte" <mjwitte@xxxxxxxx>]

My apologies for the delayed reply.

I assume that your purchased air object is using no outside air.  As you 
suggest, the difference is from latent loads.  If you compare "Purchased Air 
Sensible Cooling Rate", you should find it agrees with the other values.

Purchased Air is a *very* simple system.  First, it determines the required 
flow rate to meet the zone sensible load.  Then it calculates the energy 
required to take that flow rate of zone air and supply it at the specified 
temperature and humidity.  So, decreasing the cooling supply humidity ratio 
will actually increase the latent load.

Mike


On 14 Jul 2004, at 14:00, g_kokogiannakis wrote:

> Hi all,
> 
> I am trying to simulate an office (with Lights and People at normal 
> working hours, e.t.c.) with EnergyPlus. I am using the Purchased Air 
> for Heating and Cooling (setpoints at 20 and 24 oC respectively) and 
> I am running an annual simulation to get the annual heating and 
> cooling loads and the peak heating and cooling loads. For the Report 
> Variables, I am taking results for "Zone/Sys Sensible Load Predicted" 
> (hourly and for the run period which is actually annual), "Zone/Sys 
> Sensible Heating Rate" (hourly), "Zone/Sys Sensible Cooling Rate" 
> (hourly), "Purchased Air Heating Rate" (hourly and for the run period 
> which is actually annual) and "Purchased Air Total Cooling Rate" 
> (hourly and for the run period which is actually annual). As far as I 
> can see from these results:
> 
> When heating is needed, the "Zone/Sys Sensible Load Predicted" is 
> most of the times (apart probably from the first timestep when the 
> heating is on) the same with the "Zone/Sys Sensible Heating Rate" and 
> the "Purchased Air Heating Rate".
> However, the same does not happen when cooling is needed: "Zone/Sys 
> Sensible Load Predicted" and "Zone/Sys Sensible Cooling Rate" are 
> again most of the times the same but "Purchased Air Total Cooling 
> Rate" is significantly higher. Thought this was because maybe the 
> latent loads were taken into account for the "Purchased Air Total 
> Cooling Rate" but I am not quite sure for the reason. Any idea? Which 
> of these results is actually the result that I want?
> I made smaller actually the values of the "Heating Supply Air 
> Humidity ratio" and "Cooling Supply Air Humidity ratio" fields of the 
> Purchased Air but still there are differences in all these results.
> 
> Thank you in advance,
> 
> Georgios
> 
> 
> 
> 
> 
> 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
> 
> 
> 
> 
> 
> 



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



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