[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[EnergyPlus_Support] Re: Unitary DX for cooling - not sizing well
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Richard Raustad <RRaustad@...> wrote:
>
> Inserted answers......
>
> On 6/13/2012 9:13 AM, Jean marais wrote:
> >
> >
> > 1 minute pulldown time is unrealistic, i aggree. As I understand it, this influences only the Air Volume Flow Calculation, right. Meaning the air volume flow rate capacities of the equipment will be too large.
> Correct. For DX, air volume is used to set capacity based on delta
> enthalpy across the coil at peak load time.
> > What is a realistic pull down rate? 10 min? 1hr? As stated before, ASHRAE requires less than 300 hrs per year, for hours SP not met. I could run a parametric simulation testing different averaging intervals to get best results and set the Averaging Window this way. But no one else is doing this, so how do they size?
> In my home, I am lucky to get 1F / hr, but my AC is undersized. I think
> 2 or 3 F per hour is realistic.
> Is it 300 hrs occupied or any time? If you start the AC early enough,
> the SP is met before occupants arrive. If it's anytime, then pull down
> is an issue.
> > Also, I would have to decide on a fixed tolerance for the SP not met reporting, before the parametric study. James uses 0.5ºC from what I remember. The default is 0.2ºC (0.5ºF from DOE). Allowed by ASHRAE 55 is 1.1ºC (2ºF) peak to peak variation over a 0.25hr period. Minimum throttling range for low-temperature radiant systems is 0.5ºC.
> I'm not sure I understand "peak to peak variation over 0.25 hrs up to
> 1.1C". What's wrong with using Std 55 max tol for SP not met?
> >
> > ASHRAE 90.1 2010 defines
> > temperature control throttling range:
> > as the number of degrees that the room temperature must change to go from no-heating to full heating or from no-cooling to full cooling.
> > unmet load hour:
> > an hour in which one or more zones is outside of the thermostat setpoint plus or minus one half of the temperature control throttling range. Any hour with one or more zones with an unmet cooling load or unmet heating load is defined as an unmet load hour.
> Now here they talk about any "hour". Since E+ has sub-hourly time steps,
> and counts during the fractional hours, I guess it's fair to include
> sub-hourly "not met" hours in the total. If hrs are counted when
> unoccupied, then the pull down is important. For hourly simulations
> (DOE-2), maybe that first hour's "avg" zone temp gets closer to the SP
> and hrs not met are smaller? Should the "hrs not met" be increased for
> sub-hourly simulations for this very reason (not likely to happen)?
>
> What would happen if the AC is scheduled on all year (wkend and wkday)?
> With a constant set point (no SB)? Both the baseline and proposed would
> see the same schedules, and then energy savings could still be compared
> (energy magnitude would increase, % savings would decrease).
>
> I don't do 90.1 simulations, so I am sure someone will tell me if I am
> way off the mark with those last comments.
>
> >
> >
> >
> >
> > ------------------------------------
> >
> > Primary EnergyPlus support is found at:
> > http://energyplus.helpserve.com or send a message to energyplus-support@...
> >
> > 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 currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
> >
> > EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
> > Yahoo! Groups Links
> >
> >
> >
> >
>
> --
> Richard A. Raustad
> Senior Research Engineer
> Florida Solar Energy Center
> University of Central Florida
> 1679 Clearlake Road
> Cocoa, FL 32922-5703
> Phone: (321) 638-1454
> Fax: (321) 638-1439 or 1010
> Visit our web site at: http://www.fsec.ucf.edu
>
> UCF - From Promise to Prominence: Celebrating 40 Years
>
------------------------------------
Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to 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 currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/EnergyPlus_Support/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/EnergyPlus_Support/join
(Yahoo! ID required)
<*> To change settings via email:
EnergyPlus_Support-digest@xxxxxxxxxxxxxxx
EnergyPlus_Support-fullfeatured@xxxxxxxxxxxxxxx
<*> To unsubscribe from this group, send an email to:
EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/