Use the outddor air directly. (Lower limit of the Economizer cycle is setable. But you dare not set it too low.)
In Canada the outdoor unit is covered up during the Winter months.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: brent.griffith@xxxxxxxx
Date: Mon, 31 Oct 2011 13:41:21 -0600
Subject: RE: [EnergyPlus_Support] Disable a DX coil below "xx" temp
Jim, I totally agree with you. Outdoor drybulb minimum limit control is on the list of high-priority development items.
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Jim Dirkes
Sent: Monday, October 31, 2011 1:29 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RE: [EnergyPlus_Support] Disable a DX coil below "xx" temp
Dear Chandan, Brent, Jean,
Thanks for the feedback! I must say, though, that I was hoping to avoid learning EMS for maybe 30 years or so?
Perhaps this is actually a development issue, but I thought about this a bit more and would like to know your thoughts in response:
The normal warning I receive is shown below and is quite understandable.
Occasionally a DX coil ?wants? to start to satisfy a cooling load in cool weather due to high internal loads, or (as is my case) it may be a DOAS with hot gas reheat and is trying to dehumidify a humid zone. Both uses are legitimate. Both will result in a lot of warnings.
In the first case, I can live with a slight increase in the zone temperature during those hours. In the second case, the zone humidity will probably drop once the air system operates for a while (my DOAS was trying to dehumidify in the first few hours after startup)
Most commercial HVAC equipment, however, is equipped with a low temperature limit control for the DX cooling that prevents its operation below a fixed temperature. It sure would make an energy modeler?s life more simple if I could just turn the coil OFF with a standard object field instead of EMS! (something like the feature that already exists for the Heat Pump DX heating coil)
** Warning ** Coil:Cooling:DX:SingleSpeed "CLGCOIL1_PROPDOASWVRF0" - Full load outlet air dry-bulb temperature < 2C. This indicates the possibility of coil frost/freeze. Outlet temperature = 1.77 C.
** ~~~ ** ...Occurrence info = FOURPOINTSSHERATON, 01/01 06:18 - 06:20
** ~~~ ** ... Possible reasons for low outlet air dry-bulb temperatures are: This DX coil
** ~~~ ** 1) may have a low inlet air dry-bulb temperature. Inlet air temperature = 12.200 C.
** ~~~ ** 2) may have a low air flow rate per watt of cooling capacity. Check inputs.
** ~~~ ** 3) is used as part of a HX assisted cooling coil which uses a high sensible effectiveness. Check inputs.
The Building Performance Team
James V. Dirkes II, P.E., BEMP , LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Chandan Sharma
Sent: Monday, October 31, 2011 1:57 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Disable a DX coil below "xx" temp
Prior to V7, Availability managers can only be used to set turn on/off flags for the fan (pump) of entire air (plant) loop. They can not be applied to individual components.
In V7, this feature has been added to several zone components like PTAC, PTHP, Window AC, Unit heater etc.
The availability managers always act on the fan/pump availability schedule. (not the availability schedule of component which has fan).
In V7, when applying availability manager to zone component object (e.g. PTAC), the component object must be available.
Then if its fan schedule is set to off during the night and night cycle availability manager is used to turn the fan on in certain conditions, the night cycle availability manager will make the fan available even if the fan's availability schedule is set to off. But if the DX heating and cooling coils are unavailable they won't be turned on by the availability manager.
In your current configuration, LowTempTurnOff should turn off the heat pump fan whenever the temperature at "NodeIn_OA_BaseSys2-11" is below 12.8 C.
Not aware of any other way to achieve your goal. Sorry for the inconvenience.
Chandan
On 10/31/2011 1:18 PM, Jim Dirkes wrote:
Dear Dr. Li,
I understand that part. I?m trying to turn off the COOLING coil below ~13C.
The Building Performance Team
James V. Dirkes II, P.E., BEMP , LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
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