Felipe,
If you are preparing a model for a “Baseline” system, then the pressure rise and fan efficiency must be selected to result in the proper power per ASHRAE 90.1.
You can calculate the desired pressure drop for an ASHRAE Baseline system 1-4 using the formula below:
Pressure rise (IP units) = (0.00094 + (Pressure Credit inches w.c.)/4131)*(Assumed Fan Efficiency as decimal)*6356)
e.g.,
ASHRAE Baseline #1
Fan Efficiency = .5
Pressure Credit = 0.0
Pressure Rise = (.00094 + 0/4131) * .5 * 6356
= 2.99 inches water column
The same approach can be used for ASHRAE #5 and higher using .0013 instead of .00094
As I mentioned earlier, the fan efficiency can be selected at any value. When used together with this calculated Pressure Rise, E+ will calculate the proper fan power.
You’ll have to determine the SI correction factors! I hope that this gives you an idea of the procedure.
James V Dirkes II, PE, BEMP, LEED AP
www.buildingperformanceteam.com
Energy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Felipe Durán
Sent: Monday, August 27, 2012 4:52 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Fan Pressure Rise for a PTAC
Jim,
Thanks again, I ve got one more question. According to the appendix G, I have a formula to obtain the fan power for each PTAC. Do I have to calculate each pressure rise to obtain the correct power or is it enough to have a reassonable fan pressure rise and efficiency combination for all PTAC?
Kind Regards,
Felipe Durán Palma
Arquitecto UC, MPhil. U. Cambridge, LEED AP BD+C
Gerente de Proyectos
B-green Chile S.A.
El 24-08-2012, a las 15:26, Jim Dirkes <jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx> escribió:
Felipe,
I do not know of such a table or reference.
A few thoughts related to this:
1. Every fan can be selected to perform in a fairly wide range of efficiency. The more inexpensive, or mass-produced, or competitively priced the equipment, the less likely it is to be a very high efficiency. i.e., cost and other competitive constraints tend to erode efficiency efforts.
2. In an energy model for which you have actual equipment data , such as your 110W / 0.16 m3/s PTAC fan, it does not matter so much what the actual efficiency is. This is because your primary goal is to attain correct power consumption, and efficiency is only one of the variables that produces it. For example, the same power can result from 5 completely different combinations of efficiency and pressure rise. If you know the power, feel free to use any combination that results in the correct power!
3. That said, I draw on my past experience for approximate values of fan efficiency and pressure rise as a check value for other information I may have, but normally I can obtain good values for flow and power, so the other values (efficiency and pressure rise) matter little. (If I must make an estimate for fan efficiency, I normally assume 20-30% for very small fans and no more than 60% for large fans which are part of an air handler. It is fairly difficult to obtain higher efficiencies outside of a laboratory!)
James V Dirkes II, PE, BEMP, LEED AP
www.buildingperformanceteam.com
Energy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Felipe Durán
Sent: Friday, August 24, 2012 3:02 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Cc: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Fan Pressure Rise for a PTAC
Jim,
Thank you very much for your quick and clear reply.
I ve got one more question. Do you know where I can find a table with fan efficiency values for typical applicarions such as PTAC, package rooftops, etc.
Kind Regards,
Felipe Durán PalmaArquitecto UC, MPhil. U. Cambridge, LEED AP BD+C
Gerente de Proyectos
B-green Chile S.A.
El 24-08-2012, a las 14:07, Jim Dirkes <jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx> escribió:
Felipe,
I am unfamiliar with the calculation in SI units, but recommend that you refer to a text such as the ASHRAE Handbook of Fundamentals.
For IP / US units, it looks like:
<image001.png>
You will need to determine the fan efficiency (“η” in the equation above). For the small fan you are using, it is probably in the range 20-40%.
For a PTAC, pressure rise is normally in the range 0.20 � 0.50 inches water column (50-125 Pascalls)
James V Dirkes II, PE, BEMP, LEED AP
www.buildingperformanceteam.comEnergy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Felipe Durán
Sent: Friday, August 24, 2012 1:11 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Fan Pressure Rise for a PTAC
Dear All,
I am wondering how to calculate the fan pressure rise for a PTAC. The max. flow rate is 0,16 m3/s = 339 CFM x 0,3 = 101 W.
Since I ve got the fan power (101 W) and the max flow rate (0,16 m3/m) ¿Does anybody knows how to calculate the fan pressure rise?
Kind Regards,
Felipe Durán Palma
Arquitecto UC, MPhil. U. Cambridge, LEED AP BD+C
Gerente de Proyectos
B-green Chile S.A.Recent Activity:
- New Members 17
__._,_.___
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.
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch to Fully Featured
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe
__,_._,___