This is a forum for EPlus users.
I know how to use EPlus, but I am not active in modelling all the different models for LEED certification.
My interest on the forem is simply give those user who had problems in EPlus simulation some help in the IDF coding.
My comments are generally on real system related idea, and not on ASHRAE guide lines for modelling..
You mentioned that you are a control engineer playing with HVAC control. Control engineering covers a wide field. In my BSc days, control engineering was on controllers, sensors, actuators, and feed-back systems using analogue simulators. There were some mathematical analysis on system stabilioty.
EPlus is based on heat balance calculatin to reach a controlling objective of meeting a temperature set point. Usually do not have stability problem, except dealing with very thick construction material of large thermal mass.
When the room is cooled to a particular temperature, EPlus compute the heat trasfer into the building from outdoor air, solar radiation conditions, etc. A zone usually have four walls and a floor and a ceiling. Heat would conduct through these surfaces, The solar radiation will pass through the windows. The two conduction and radiation compnents are calculate separately. There are internally added loads, such as people, lights, equipment. If there are windows on the opposite side, some solar radiation may be radiate out there.
All these heat are added together. The floor usually has a lower ground temperature below, and leak away some of the total heat from the envirnment above ground. The different temperatures of the surfaces are mixed together by convection into a zone mean air temperature. This is the un-controlled or natural temperature of the building, at that time of the day. At night, whatever is collected during the day would be conducted out to the OD and ground.
When the room is to be cooled to say from 30°C to 25°C, a volume of air at 30°C is replaced with air of 20°C and mixed in the zone. The will balance the building heat input to provide a fixed set point temperature of 25°C When the environment condition changes, the natural temperature would change, and the inlet cool temperature will be changed to match. Because of this process, the zone thermostat does not behave like a real one which has a dead set back range.
If the 20°C cool air cannot be provided, the system will issue a set point not met warning at that time step. This is something you can play around and by re-designing, or something wrong with the code.
In the control engineering, some delay may be needed to make the system stable. Feed back loop is not used or simulated at present.
The ASHRAE objective is to make living comfortable using HVAC in buildings.
The strong part of EPlus is the calculation of the heat load on the building envelope.
If you are not interested in the building characteristics, you can fave the other part of EPlus which is simulate the HVAC system, DX coil, water coil, fan, pumps, chiller, boiler, colling tower, etc. Connected together to form a HVAC for a building.
A real system can usually be simulated by EPlus if the components are being characteristed into an object for simulation.
All those items mentioned in your mail are available.
The simulation program requires the input data to be in exact form. This is doen by generating a input data file (IDF). The complete structure of the IDF is in the IDD file.
Each component object is a fixed format text segment terminated with a semicolon. The whole IDF is a collection of these segment, some of which must be placed in a certain order.
User of EPlus usually down load the complete EPlus program from the EPlus website, listed at the end of this mail.
GettingSatarted Manual (PDF) provids with the definition of all the files used and generated in the simulation and a tutorial to use the IDFeditor and to add features to the IDF.
The download came with over 200 examples in the exampleFiles directory.
The complete description of all the IDF objects are in the Inut/Output Ref. Manual. (PDF)
The programming principles are in the Engineering Ref. Manual.
There are a few thousands of pages of manual with further references are included in the EPlus download.
The getting started manual will provide you a simple 5 zone building, which you can modify. There is a 3 zone building to show a recidential model. The reason for the 5 zone is to isolate the walls in the four directions, so that you can study the solar component in detail in a 24 hour period. You can rotate the building to change the anble of incident of the sun and windows, etc.
There are many other models of building available in the exampleFile directory for you to play with, without going to GoogleSketchUp or OpenStudio to generate your own. You can start building the IDF directly from OpenStudio. It is nice to play with at the beginning, but you find it harder and harder when you wanted to make changes.
I would suggest that you download the EPlus program, and read the Getting Started.PDF in the Documention folder.
After that, depends on whether you have programming or other skills, to optimize direction of using the EPlus program.
I myself do not know all the features available in Eplus. I can usually find what I need from the manuals.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: loveoflife219@xxxxxxxxx
Date: Tue, 3 Apr 2012 22:35:27 +0000
Subject: [EnergyPlus_Support] Re: Can we let supply air temperature float?
__._,_.___
Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
![]()
__,_._,___
I know how to use EPlus, but I am not active in modelling all the different models for LEED certification.
My interest on the forem is simply give those user who had problems in EPlus simulation some help in the IDF coding.
My comments are generally on real system related idea, and not on ASHRAE guide lines for modelling..
You mentioned that you are a control engineer playing with HVAC control. Control engineering covers a wide field. In my BSc days, control engineering was on controllers, sensors, actuators, and feed-back systems using analogue simulators. There were some mathematical analysis on system stabilioty.
EPlus is based on heat balance calculatin to reach a controlling objective of meeting a temperature set point. Usually do not have stability problem, except dealing with very thick construction material of large thermal mass.
When the room is cooled to a particular temperature, EPlus compute the heat trasfer into the building from outdoor air, solar radiation conditions, etc. A zone usually have four walls and a floor and a ceiling. Heat would conduct through these surfaces, The solar radiation will pass through the windows. The two conduction and radiation compnents are calculate separately. There are internally added loads, such as people, lights, equipment. If there are windows on the opposite side, some solar radiation may be radiate out there.
All these heat are added together. The floor usually has a lower ground temperature below, and leak away some of the total heat from the envirnment above ground. The different temperatures of the surfaces are mixed together by convection into a zone mean air temperature. This is the un-controlled or natural temperature of the building, at that time of the day. At night, whatever is collected during the day would be conducted out to the OD and ground.
When the room is to be cooled to say from 30°C to 25°C, a volume of air at 30°C is replaced with air of 20°C and mixed in the zone. The will balance the building heat input to provide a fixed set point temperature of 25°C When the environment condition changes, the natural temperature would change, and the inlet cool temperature will be changed to match. Because of this process, the zone thermostat does not behave like a real one which has a dead set back range.
If the 20°C cool air cannot be provided, the system will issue a set point not met warning at that time step. This is something you can play around and by re-designing, or something wrong with the code.
In the control engineering, some delay may be needed to make the system stable. Feed back loop is not used or simulated at present.
The ASHRAE objective is to make living comfortable using HVAC in buildings.
The strong part of EPlus is the calculation of the heat load on the building envelope.
If you are not interested in the building characteristics, you can fave the other part of EPlus which is simulate the HVAC system, DX coil, water coil, fan, pumps, chiller, boiler, colling tower, etc. Connected together to form a HVAC for a building.
A real system can usually be simulated by EPlus if the components are being characteristed into an object for simulation.
All those items mentioned in your mail are available.
The simulation program requires the input data to be in exact form. This is doen by generating a input data file (IDF). The complete structure of the IDF is in the IDD file.
Each component object is a fixed format text segment terminated with a semicolon. The whole IDF is a collection of these segment, some of which must be placed in a certain order.
User of EPlus usually down load the complete EPlus program from the EPlus website, listed at the end of this mail.
GettingSatarted Manual (PDF) provids with the definition of all the files used and generated in the simulation and a tutorial to use the IDFeditor and to add features to the IDF.
The download came with over 200 examples in the exampleFiles directory.
The complete description of all the IDF objects are in the Inut/Output Ref. Manual. (PDF)
The programming principles are in the Engineering Ref. Manual.
There are a few thousands of pages of manual with further references are included in the EPlus download.
The getting started manual will provide you a simple 5 zone building, which you can modify. There is a 3 zone building to show a recidential model. The reason for the 5 zone is to isolate the walls in the four directions, so that you can study the solar component in detail in a 24 hour period. You can rotate the building to change the anble of incident of the sun and windows, etc.
There are many other models of building available in the exampleFile directory for you to play with, without going to GoogleSketchUp or OpenStudio to generate your own. You can start building the IDF directly from OpenStudio. It is nice to play with at the beginning, but you find it harder and harder when you wanted to make changes.
I would suggest that you download the EPlus program, and read the Getting Started.PDF in the Documention folder.
After that, depends on whether you have programming or other skills, to optimize direction of using the EPlus program.
I myself do not know all the features available in Eplus. I can usually find what I need from the manuals.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: loveoflife219@xxxxxxxxx
Date: Tue, 3 Apr 2012 22:35:27 +0000
Subject: [EnergyPlus_Support] Re: Can we let supply air temperature float?
Dear Dr. Li,
Thanks for your reply. I guess I need to play with schedules in E+. Anyway, you said that there are several possible system implementations available. Can you point me to some sources or links? Or some search terms to search for? I want to read up on this, but couldn't find anything useful (I'm a newbie so I may not know the right terms).
Thanks!
Tim
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@...> wrote:
>
>
> I am not a HVAC building appraisor. I am responding only on operatin of equipment.If we can do the followings:
> 1)Turn off heat supply to the heating coil in the AHU, and let the supply air temperature float (uncontrolled);If you have intellegent control, this is possible. EPlus has economy cycle mode which use Outside air for increased ventilation, when the OD air temperature is at a suitable range.
> 2) Still run the fan to circulate air in the system. Still mix some fresh air from outside if required for ventilation; This depends on the building plan. The ducted air can always be circulated. VAV diffuser can change the amount of air flow at each diffuser (a veriable damper). The operation of these type of system always require some common computer control. The VAV diffuser itself can be self adjusting, as it can have duct and room temperature senser and a controller board in the unit, with a remote control to set the desired room temperature and move the damper. The controller and remote control is not simulated in EPlus.
> then we can extract excess heat gain from the first zones and redistribute it to the entire system. Some call this heat recovery. I usually like to use active heat control. For example, the heat from the light can be resecced into the false ceiling and collect as return air and treated separately. Printing room and other equipment can have ducts, so that the heat is vented out in Summer, and kept in in Winter. So we save energy and reuse free heat gain. Of course, after some time, when the zone temperatures decay below a threshold, we need to return to normal operation (controlled SAT). For simulation purposes, these ideas are already in Energy Plus, but the comptrollers and sensors are only inprepended as schedules and register values with set-point values, and calculated heat balance in each zone.
>
> IMy two questions:
> 1) Is this strategy practical and realizable in real systems? If not, why? Are there anything technically wrong?There are several possible system implimentation available.
> 2) In EnergyPlus, if I want to play with this idea, how can I turn off the heat supply to AHU and let the SAT float (while still running the fan)? In EPlus there is a dual band theremostat with a dead band temperature zone. Within the dead band, neither the heating nor cooling equipment would be ON. The fan can remail ON. However, high internal load can push the system into the cooling mode in Winter. It is not necessary to over cool and reheat, if this is not your choice.
> In Winter, you can let in outdoor air for cooling. However, some designer insisting on using the cooling sysem. The EPlus economy cycle mode do use the cold air and limit tis use to 5°C minimum in order to prevent the un-expected freezing of equipment and at the air inlet point. In EPlus, the VAV system can be operated without the reheat coil in the zone. Dr. Li
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: loveoflife219@...
> Date: Tue, 3 Apr 2012 19:34:28 +0000
> Subject: [EnergyPlus_Support] Can we let supply air temperature float?
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> Hi all,
>
>
>
> I'm not an HVAC person, but a control engineer playing with HVAC control. So please excuse me if my questions are stupid :-)
>
>
>
> My main question is: is it possible to let the supply air temperature float (uncontrolled) some time during the day (not at night)? The details are as follows.
>
>
>
> Let's say we have a building in winter and the heating system is supplying hot air to the zones. The envelope is tight, so the heat loss to outside air is not very much. During the day, there is time when some zones have very high heat gain (from occupants, solar), even larger than their heat loss. Thus, even if the VAV boxes open at minimal level (for ventilation), or even closed, the net heat gain is still positive and the zone temperatures rise, which may cause discomfort. On the other hand, other zones have low heat gain, so they still require some heat load from the AHU.
>
>
>
> I understand that one solution to this issue is to always run the cooling system and supply chilled air to the VAV boxes, then reheat it at the terminal as required by each individual zone. However, I think this wastes energy, both because air is cooled then reheated, and because (free) excess heat gain in the first zones are not used.
>
>
>
> If we can do the followings:
>
> 1)Turn off heat supply to the heating coil in the AHU, and let the supply air temperature float (uncontrolled);
>
> 2) Still run the fan to circulate air in the system. Still mix some fresh air from outside if required for ventilation;
>
> then we can extract excess heat gain from the first zones and redistribute it to the entire system. So we save energy and reuse free heat gain. Of course, after some time, when the zone temperatures decay below a threshold, we need to return to normal operation (controlled SAT).
>
>
>
> My two questions:
>
> 1) Is this strategy practical and realizable in real systems? If not, why? Are there anything technically wrong?
>
> 2) In EnergyPlus, if I want to play with this idea, how can I turn off the heat supply to AHU and let the SAT float (while still running the fan)?
>
>
>
> Thank you very much!
>
> Tim.
>
Thanks for your reply. I guess I need to play with schedules in E+. Anyway, you said that there are several possible system implementations available. Can you point me to some sources or links? Or some search terms to search for? I want to read up on this, but couldn't find anything useful (I'm a newbie so I may not know the right terms).
Thanks!
Tim
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@...> wrote:
>
>
> I am not a HVAC building appraisor. I am responding only on operatin of equipment.If we can do the followings:
> 1)Turn off heat supply to the heating coil in the AHU, and let the supply air temperature float (uncontrolled);If you have intellegent control, this is possible. EPlus has economy cycle mode which use Outside air for increased ventilation, when the OD air temperature is at a suitable range.
> 2) Still run the fan to circulate air in the system. Still mix some fresh air from outside if required for ventilation; This depends on the building plan. The ducted air can always be circulated. VAV diffuser can change the amount of air flow at each diffuser (a veriable damper). The operation of these type of system always require some common computer control. The VAV diffuser itself can be self adjusting, as it can have duct and room temperature senser and a controller board in the unit, with a remote control to set the desired room temperature and move the damper. The controller and remote control is not simulated in EPlus.
> then we can extract excess heat gain from the first zones and redistribute it to the entire system. Some call this heat recovery. I usually like to use active heat control. For example, the heat from the light can be resecced into the false ceiling and collect as return air and treated separately. Printing room and other equipment can have ducts, so that the heat is vented out in Summer, and kept in in Winter. So we save energy and reuse free heat gain. Of course, after some time, when the zone temperatures decay below a threshold, we need to return to normal operation (controlled SAT). For simulation purposes, these ideas are already in Energy Plus, but the comptrollers and sensors are only inprepended as schedules and register values with set-point values, and calculated heat balance in each zone.
>
> IMy two questions:
> 1) Is this strategy practical and realizable in real systems? If not, why? Are there anything technically wrong?There are several possible system implimentation available.
> 2) In EnergyPlus, if I want to play with this idea, how can I turn off the heat supply to AHU and let the SAT float (while still running the fan)? In EPlus there is a dual band theremostat with a dead band temperature zone. Within the dead band, neither the heating nor cooling equipment would be ON. The fan can remail ON. However, high internal load can push the system into the cooling mode in Winter. It is not necessary to over cool and reheat, if this is not your choice.
> In Winter, you can let in outdoor air for cooling. However, some designer insisting on using the cooling sysem. The EPlus economy cycle mode do use the cold air and limit tis use to 5°C minimum in order to prevent the un-expected freezing of equipment and at the air inlet point. In EPlus, the VAV system can be operated without the reheat coil in the zone. Dr. Li
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: loveoflife219@...
> Date: Tue, 3 Apr 2012 19:34:28 +0000
> Subject: [EnergyPlus_Support] Can we let supply air temperature float?
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> Hi all,
>
>
>
> I'm not an HVAC person, but a control engineer playing with HVAC control. So please excuse me if my questions are stupid :-)
>
>
>
> My main question is: is it possible to let the supply air temperature float (uncontrolled) some time during the day (not at night)? The details are as follows.
>
>
>
> Let's say we have a building in winter and the heating system is supplying hot air to the zones. The envelope is tight, so the heat loss to outside air is not very much. During the day, there is time when some zones have very high heat gain (from occupants, solar), even larger than their heat loss. Thus, even if the VAV boxes open at minimal level (for ventilation), or even closed, the net heat gain is still positive and the zone temperatures rise, which may cause discomfort. On the other hand, other zones have low heat gain, so they still require some heat load from the AHU.
>
>
>
> I understand that one solution to this issue is to always run the cooling system and supply chilled air to the VAV boxes, then reheat it at the terminal as required by each individual zone. However, I think this wastes energy, both because air is cooled then reheated, and because (free) excess heat gain in the first zones are not used.
>
>
>
> If we can do the followings:
>
> 1)Turn off heat supply to the heating coil in the AHU, and let the supply air temperature float (uncontrolled);
>
> 2) Still run the fan to circulate air in the system. Still mix some fresh air from outside if required for ventilation;
>
> then we can extract excess heat gain from the first zones and redistribute it to the entire system. So we save energy and reuse free heat gain. Of course, after some time, when the zone temperatures decay below a threshold, we need to return to normal operation (controlled SAT).
>
>
>
> My two questions:
>
> 1) Is this strategy practical and realizable in real systems? If not, why? Are there anything technically wrong?
>
> 2) In EnergyPlus, if I want to play with this idea, how can I turn off the heat supply to AHU and let the SAT float (while still running the fan)?
>
>
>
> Thank you very much!
>
> Tim.
>
__._,_.___
Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
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