Dear Dr. Li,
I agree that you should not need the DX coil in cold weather months!
The situation seems to be that:
a) A startup condition (when the zone is too warm) causes E+ to use the DX cooling coil for a little while, or
b) In the dehumidification scenario I described earlier (when the zone is too humid), it also starts the DX coil
I have made my first attempt at using EMS Application guide (below), using example #10 in the EMS as my starting point. It looks like I should be able to override the coil’s availability schedule, but I must be missing something, because it has no effect. Will one of you EMS users please take a look?
p.s., I tried both “BeginNewEnvironment” and “InsideHVACSystemIterationLoop” as calling points; same result
!- =========== ALL OBJECTS IN CLASS: ENERGYMANAGEMENTSYSTEM:SENSOR ===========
EnergyManagementSystem:Sensor,
OutdoorTemp, !- Name
Environment, !- Output:Variable or Output:Meter Index Key Name
Outdoor Dry Bulb; !- Output:Variable or Output:Meter Name
!- =========== ALL OBJECTS IN CLASS: ENERGYMANAGEMENTSYSTEM:ACTUATOR ===========
EnergyManagementSystem:Actuator,
DXLowLimit1, !- Name
SchCpct_LowTempClgOFF, !- Actuated Component Unique Name
Schedule:Compact, !- Actuated Component Type
Schedule Value; !- Actuated Component Control Type
!- =========== ALL OBJECTS IN CLASS: ENERGYMANAGEMENTSYSTEM:PROGRAMCALLINGMANAGER ===========
EnergyManagementSystem:ProgramCallingManager,
DXLowLimit Management1, !- Name
BeginNewEnvironment, !- EnergyPlus Model Calling Point
DXCoilControl; !- Program Name 1
!- =========== ALL OBJECTS IN CLASS: ENERGYMANAGEMENTSYSTEM:PROGRAM ===========
EnergyManagementSystem:Program,
DXCoilControl, !- Name
IF (OutdoorTemp < 15.0), !- Program Line 1
SET DXLowLimit1 = 0.0, !- Program Line 2
ELSE, !- A4
SET DXLowLimit1 = Null, !- A5
ENDIF; !- A6
!- =========== ALL OBJECTS IN CLASS: SCHEDULE:COMPACT ===========
Schedule:Compact,
SchCpct_LowTempClgOFF, !- Name
On/Off, !- Schedule Type Limits Name
Through: 12/31, !- Field 1
For: AllDays, !- Field 2
Until: 24:00, !- Field 3
1; !- Field 4
Coil:Cooling:DX:SingleSpeed,
ClgCoil1_MainFlrDOAS, !- Name
SchCpct_LowTempClgOFF, !- Availability Schedule Name
91377, !- Rated Total Cooling Capacity {W}
0.7, !- Rated Sensible Heat Ratio
3.46, !- Rated COP {W/W}
3.9172, !- Rated Air Flow Rate {m3/s}
, !- Rated Evaporator Fan Power Per Volume Flow Rate {W/(m3/s)}
NodeOut_MA_MainFlrDOAS, !- Air Inlet Node Name
NodeOut_ClgCoil1Air_MainFlrDOAS, !- Air Outlet Node Name
DXCoil_Cap-FT_MainFlrDOAS, !- Total Cooling Capacity Function of Temperature Curve Name
DXCoil_Cap-FF_MainFlrDOAS, !- Total Cooling Capacity Function of Flow Fraction Curve Name
DXCoil_EIR-FT_MainFlrDOAS, !- Energy Input Ratio Function of Temperature Curve Name
DXCoil_EIR-FF_MainFlrDOAS, !- Energy Input Ratio Function of Flow Fraction Curve Name
DXCoil PLF_MainFlrDOAS; !- Part Load Fraction Correlation Curve Name
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 YuanLu Li
Sent: Monday, October 31, 2011 4:40 PM
To: EnergyPlus_Support
Subject: RE: [EnergyPlus_Support] Disable a DX coil below "xx" temp
If you have high internal load and the out door air is at -12°C, why do you need the Dx coil?
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
Dear Mr. Dirkes,
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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