Re: [EnergyPlus_Support] Zone Cooling Design Supply Air Temperature

Hi,

I have attached the idf file, the following errors are displayed:

** Severe ** Sizing: Coil:Cooling:DX:SingleSpeed "OS:COIL:COOLING:DX:SINGLESPEED 1": 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=[3.074E-005], 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 = "OS:COIL:COOLING:DX:SINGLESPEED 1"

** ~~~ ** 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 = 4.31 C

** ~~~ ** ...Inlet Air Humidity Ratio = 1.125000E-002 kgWater/kgDryAir

** ~~~ ** ...Outlet Air Humidity Ratio = 6.976137E-003 kgWater/kgDryAir

** ~~~ ** ...Total Cooling Capacity used in calculation = 24000.00 W

** ~~~ ** ...Air Mass Flow Rate used in calculation = 0.713176 kg/s

** ~~~ ** ...Air Volume Flow Rate used in calculation = 0.737977 m3/s

** ~~~ ** ...Air Volume Flow Rate per Watt of Rated Cooling Capacity is also out of bounds at = 3.0749021E-005 m3/s/W

** ~~~ ** During Warmup, Environment=MEDELLÃ?N, at Simulation time=03/21 00:00 - 00:15

** Fatal ** Check and revise the input data for this coil before rerunning the simulation.

...Summary of Errors that led to program termination:

How can I change the "Rated air volume flow rate per watt" without change the "Rated Total Cooling Capacity"?

Thanks

Jaime Zuluaga M

From: Jason Kirkpatrick <jason.alan.kirkpatrick@xxxxxxxxx>
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Sent: Thursday, 22 August 2013, 17:06
Subject: Re: [EnergyPlus_Support] Zone Cooling Design Supply Air Temperature

Jaime,

while the field that you were asking about (Cooling SAT) will not change with changes to the DDY file, the system size will, which is likely why you're seeing a change in the flow per power metric. You may have hard sized the power consumption of the unit, but now are changing the size of the unit by editing the outdoor air conditions used for sizing. (my best guess)

You might get a better answer by posting your file however.

Jason

On Thu, Aug 22, 2013 at 2:47 PM, Jaime Zuluaga Machado <jaimezuluagam@xxxxxxxxx> wrote:

Hi Jason, thanks for answering

I thought the same that you said (The Zone Cooling Design Supply Air Temperature has nothing to do with the DDY file) but I do not why when I change de dry bulb temperature of the DDY this change the Rated Vol Flow Per Watt of the HVAC unit. Do you know what would happened?

Jaime Zuluaga M

From: Jason Kirkpatrick <jason.alan.kirkpatrick@xxxxxxxxx>
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Sent: Thursday, 22 August 2013, 16:31
Subject: Re: [EnergyPlus_Support] Zone Cooling Design Supply Air Temperature

Jaime,

The Zone Cooling Design Supply Air Temperature is the temperature of the air that you are supplying to a zone in order to meet the cooling setpoint. It has nothing to do with the DDY file. The DDY file is the External Cooling and Heating Design Day conditions which define the external environmental conditions to be used when sizing the HVAC systems.

Suppose you are modeling a 90.1 baseline system 7, you should follow appendix g 3.1.2.8:

G3.1.2.8 Design Airflow Rates. System design supply

airflow rates for the baseline building design shall be based on
a supply-air-to-room-air temperature difference of 20Â°F or the
required ventilation air or makeup air, whichever is greater. If

return or relief fans are specified in the proposed design, the
baseline building design shall also be modeled with fans serving
the same functions and sized for the baseline system supply
fan air quantity less the minimum outdoor air, or 90% of
the supply fan air quantity, whichever is larger.

This is saying that if you are cooling to a zone air temperature setpoint of 75 deg F, then you should be supplying air at a 20 deg delta T, so in this case your 'Zone Cooling Design Supply Air Temperature' would be 55 deg F = 12.8 deg C

Generally engineers will select systems using this 55 deg F / 12.8 deg C supply air temperature for cooling

Now for the heating conditions, with a VAV with HW reheat system, the air temperature leaving the AHU in heating mode needs to be less than the cooling design setpoint, so the 'SYSTEM Heating Design Supply Air Temp' here would be 12 or so, and the 'ZONE Heating Design Supply Air Temp' would be 90 deg F or 32.2 deg C for a zone heated to 70 deg F

Hope this helps,

Jason

On Thu, Aug 22, 2013 at 2:10 PM, Jaime Zuluaga Machado <jaimezuluagam@xxxxxxxxx> wrote:

Hi,

How I must set the "Zone Cooling Design Supply Air Temperature"? how it works with de DDY file?

Thanks

Jaime Zuluaga M