Chilled water and Supply air temperatures parametric study

asked 2015-03-23 05:25:54 -0600

Waseem

flag of United Kingdom of Great Britain and Northern Ireland

2532 ●4 ●19

updated 2015-07-11 13:13:37 -0600

__AmirRoth__

4446 ●5 ●17 http://bleedinggreenna...

I would like to perform a parametric study of chilled water and supply air temperatures but unable to find them in my IDF. The idea is to put EMS sensors and actuators to change these two temperatures to find their relationship with energy consumption. I have used Chiller:Electric:EIR as my chiller model, do I have to consider Condenser outlet temperature as the chilled water supply temperature? Also, How can I set supply air temperature to my own values? I believe I can study the change of supply air temperature by changing the room set-point temperature, Agree? Not sure about Chilled water temperature. I have considered placing actuator and sensors as below;

EnergyManagementSystem:Sensor,
Occu_Schedule, !- Name
2864,           !- Output:Variable or Output:Meter Index Key Name   Occupancy Schedule
Schedule Value;  !- Output:Variable or Output:Meter Name

EnergyManagementSystem:Actuator,
Chiller_set_point, ! Name
CHILLER CONDENSER OUTLET NODE, ! Component Name
System Node Setpoint, ! Component Type
Temperature Setpoint; ! Control Variable

EnergyManagementSystem:ProgramCallingManager,
Temp_69,  !- Name
EndOfZoneTimestepBeforeZoneReporting,  !- EnergyPlus Model Calling Point
Temp_Control69;     !- Program Name 8

EnergyManagementSystem:Program,
Temp_Control69,     !- Name
IF Occu_Schedule > 0, 
SET Chiller_set_point = 6,               
ELSE,
SET Chiller_set_point = 3,
ENDIF;

But when I plot Condenser outlet by using Output:Variable,*,Chiller Condenser Outlet Temperature,hourly; !- HVAC Average [C], it always give me different results then I assign. Any ideas?

Results are:

Flow rate vs temp plots are:

image description

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My IDF file is available at Chiller parametric IDF

Waseem ( 2015-03-23 05:41:15 -0600 )edit

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2 Answers

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answered 2015-03-23 06:09:00 -0600

Ivan Korolija

911 ●3 ●7

Hi Waseem,

Your question is a bit unclear. Having look into your EMS code (based on temperatures 6C and 3C) it seems you would like to control a chiller leaving temperature (chilled water stream which goes to a building) rather than a condenser loop (connecting a chiller's condenser and a cooling tower) which temperature is higher.

The best way to control a chilled water temperature is to modify the SetpointManager:Scheduled, CHW Loop Setpoint Manager. The schedule 40 (6C all the time) is assigned to this object and it can be modulated by EMS.

Supply air temperature is also controlled by a SetpointManager, in your case "warmest" for controlling cooling and "coldest" for controlling heating. You can try to overwrite them by EMS as well, or to change them to a constant temperature (SetpointManager:Scheduled) and assign desired values by EMS.

Cheers, IK

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Hi @Ivan Korolija, You are right, I want it for the chilled water supply temperature. I have tried to change the schedule 40 and make it to 8C (all time) but it does not stay at 8 degrees all around the year. Also, what will be the exact output variable for this? I have tried plotting CHILLER CHW OUTLET NODE:System Node Temperature, AIR LOOP COOLING COIL WATER INLET NODE:System Node Temperature [C](Hourly), Chiller Evaporator Outlet Temperature,hourly; for chilled water supplied temperature and they all change and does not stay at 8C (according to the new schedule). Any ideas? Thanks

Waseem ( 2015-03-23 07:56:23 -0600 )edit

I also tried to set up an actuator in Chiller CHW outlet node but this did not worked at all.

Waseem ( 2015-03-23 07:57:25 -0600 )edit

Chilled water loop temperature setpoint is assigned to the "CHW Loop Supply Side Outlet" node.

Ivan Korolija ( 2015-03-23 08:03:43 -0600 )edit

@Ivan Korolija: Its not working. It does stay at 8C during first 3 months (I think when it is not needed) but then changes in Summer. Even setting an actuator on CHW Loop Supply Side Outlet does not work and the temperature does change between 8C and 16C, ideally actuator should restrict it to 8C regardless of months.

Waseem ( 2015-03-23 08:19:47 -0600 )edit

My actuator set up:

EnergyManagementSystem:Actuator,

Chillersetpoint, ! Name

CHW LOOP SUPPLY SIDE OUTLET, ! Component Name

System Node Setpoint, ! Component Type

Temperature Setpoint; ! Control Variable

EnergyManagementSystem:ProgramCallingManager,

Temp_69, !- Name

EndOfZoneTimestepBeforeZoneReporting, !- EnergyPlus Model Calling Point

Temp_Control69; !- Program Name 8

EnergyManagementSystem:Program,

Temp_Control69, !- Name

SET Chillersetpoint = 10;

Waseem ( 2015-03-23 08:20:23 -0600 )edit

@Waseem: You should check flow rates as well. I believe that when the temp is above 8C the flow rate is 0. Check also "CHW Loop Demand Side Inlet" and "Air Loop Cooling Coil Water Inlet Node". Try first without EMS just to check if temperatures are OK. I also think the EMS calling point is not appropriate for such applications. Schedule changes should use"BeginTimestepBeforePredictor" instead of "EndOfZoneTimestepBeforeZoneReporting".

Ivan Korolija ( 2015-03-23 08:55:18 -0600 )edit

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answered 2019-09-04 01:46:14 -0600

Scott-Zhenxi
1 ●1

Hi Waseem, I have the same question as yours. The chilled water supply water temperature can't be controlled at a stable value all year round. Have you figured out this?

MA zhenxi