Linda,
I got this idea about autosizing straight from the *.err file. When I ran the file with an input Rated Total Cooling Capacity, I got this result.
I've highlighted the sentence recommending that all three of these values be autosized.
** Severe ** Sizing: Coil:Cooling:DX:SingleSpeed "EL1-SYS1-PSZ-M.S DX COOLING COIL": Rated air volume flow rate per watt of rated total cooling capacity is out of range.
** ~~~ ** Min Rated Vol Flow Per Watt=[4.027E-005], Rated Vol Flow Per Watt=[6.660E-006], Max Rated Vol Flow Per Watt=[6.041E-005]. See Input-Output Reference Manual for valid range.
** Severe ** For object = Coil:Cooling:DX:SingleSpeed, name = "EL1-SYS1-PSZ-M.S DX COOLING COIL"
** ~~~ ** Calculated outlet air relative humidity greater than 1. The combination of
** ~~~ ** rated air volume flow rate, total cooling capacity and sensible heat ratio yields coil exiting
** ~~~ ** air conditions above the saturation curve. Possible fixes are to reduce the rated total cooling
** ~~~ ** capacity, increase the rated air volume flow rate, or reduce the rated sensible heat ratio for this coil.
** ~~~ ** If autosizing, it is recommended that all three of these values be autosized.
** ~~~ ** ...Inputs used for calculating cooling coil bypass factor.
** ~~~ ** ...Inlet Air Temperature = 26.67 C
** ~~~ ** ...Outlet Air Temperature = -73.85 C
** ~~~ ** ...Inlet Air Humidity Ratio = 1.125000E-002 kg/kg
** ~~~ ** ...Outlet Air Humidity Ratio = 1.000000E-005 kg/kg
** ~~~ ** ...Total Cooling Capacity used in calculation = 357175.80 W
** ~~~ ** ...Air Mass Flow Rate used in calculation = 2.754475 kg/s
** ~~~ ** ...Air Volume Flow Rate used in calculation = 2.378930 m3/s
** ~~~ ** ...Air Volume Flow Rate per Watt of Rated Cooling Capacity is also out of bounds at = 6.6603896E-006 m3/s/W
** ~~~ ** During Warmup, Environment=CZ15RV2 COLDEST DAY FROM WEATHER FILE, at Simulation time=12/29 00:00 - 00:15
** Fatal ** Check and revise the input data for this coil before rerunning the simulation.
The corresponding input as originally translated total cooling capacity is shown below.
Coil:Cooling:DX:SingleSpeed,
EL1-Sys1-PSZ-G.S DX Cooling Coil, !- Name
S1-Sys1-PSZ-FaQ3, !- Availability Schedule Name
35790.83, !- Rated Total Cooling Capacity {W}
autosize, !- Rated Sensible Heat Ratio
4.340692, !- Rated COP {W/W}
autosize, !- Rated Air Flow Rate {m3/s}
, !- Rated Evaporator Fan Power Per Volume Flow Rate {W/(m3/s)}
EL1-Sys1-PSZ-G.S Mixed Air Outlet, !- Air Inlet Node Name
EL1-Sys1-PSZ-G.S Cooling Coil Outlet, !- Air Outlet Node Name
Car_48PG0810A-Co, !- Total Cooling Capacity Function of Temperature Curve Name
SDL-C78, !- Total Cooling Capacity Function of Flow Fraction Curve Name
Car_48PG0810A-EI, !- Energy Input Ratio Function of Temperature Curve Name
SDL-C93, !- Energy Input Ratio Function of Flow Fraction Curve Name
VarSpeedCyclingPLFFPLR; !- Part Load Fraction Correlation Curve Name
In respect to the design day issue, I was using the coldest day and the hottest day from the CZ15RV02 weather file as the design days. For those who are familiar with these
CZXXRV weather files, they are semi-synthetic files not tied to any particular location, so I would challenge anyone to show that they can derive better Design Day criteria simply because long-term weather data do not exist!
The Winter Design Day that received so much suspicion is shown below:
SizingPeriod:DesignDay,
CZ15RV2 Coldest Day from Weather File, !- Name
17.800000, !- Maximum Dry-Bulb Temperature {C}
17.800000, !- Daily Dry-Bulb Temperature Range {deltaC}
6.700000, !- Humidity Indicating Conditions at Maximum Dry-Bulb
100533.4, !- Barometric Pressure {Pa}
2.9610000, !- Wind Speed {m/s}
153.00000, !- Wind Direction {deg}
0.0000000, !- Sky Clearness
0, !- Rain Indicator
0, !- Snow Indicator
29, !- Day of Month
12, !- Month
WinterDesignDay, !- Day Type
0, !- Daylight Saving Time Indicator
WetBulb; !- Humidity Indicating Type
That seems pretty normal to me for the warm desert climate of CZ15: max 64F , min 32F, low 6.7 RH, so why is the autosizing routine failing? If you don't
like the values, i.e., you think it's too high, the daily swing too large, there shouldn't be any solar (NOT what I did), etc., shouldn't the autosizing just return what you would consider an incorrect cooling capacity? Instead ,it's giving an exiting air temperature of -74 F and no solution at all, Shouldn't the EnergyPlus Team be
a little concerned why this can happen ?
Back on the topic of design days versus typical year weather data, I've done comparisons of the peak temperatures between the two and found them to be very
close at the lower criteria (2.5%, 1%, etc.), and diverging by a few degrees even at the top criteria (0.4%, 99.6%). This might raise some hackles, but I think the
fundamental reason why we distinguish between the two approaches is simply tradition. The reason I also say that design days have been somewhat mystified
is that the only number with solid statistical backing is the peak (or valley) dry bulb temperature. All the other stuff (diurnal temp swing, wind speed, wet-bulb
profile, solar conditions, etc.) are largely judgement calls.
Joe
Joe Huang White Box Technologies, Inc. 346 Rheem Blvd., Suite 108D Moraga CA 94556 yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx www.whiteboxtechnologies.com (o) (925)388-0265 (c) (510)928-2683 "building energy simulations at your fingertips"degree
On 3/17/2012 4:19 PM, Linda Lawrie wrote:
As Joe well knows, the weather files we make available, in general, are "typical" weather years -- not representative of the ASHRAE design conditions for the sites at all.
We do generate the full set of yearly ASHRAE design conditions from the tables of the HOF -- and again, everyone who is using conditions for sizing should be aware of the different flavors ASHRAE suggests for use -- different systems imply different design conditions for use. (Of course, one could just use all though the appropriate one might not be selected for the peak loads).
And we will be generating the "monthly conditions" shown in the HOF in the near future.
To select a random or even peak day from the weather file and use it for sizing is just not appropriate.
Joe, where did you get the idea that you should autosize when you got errors from the translated files? And definitely it is not suggested to mix autosize with hard sizes. (Better to autosize everything). If you're using multipliers, then you have to multiply the hard sizes by the appropriate multiplier even if you autosize others.
Linda
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