My comments below in red.
You may send me the building information directly to my hotmail ID.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: n_junk@xxxxxxxxxxxxxx
Date: Sun, 24 Jul 2011 10:57:37 +0000
Subject: [EnergyPlus_Support] Re: Problem with removing reheat coils in VAV
Hi Dr. Li,
I have to simulate a real system, installed in 1996, with five RTUs (rooftop air handling units),
The roof top air handling unit is usually the compressor part of a split unit. if the coils and fan are in the zone.
If it has two fans, one for the air into the building, and one to cool the condensor coil. it is not a split unit.
I am not sure that you describing them correctly. These fans are not thermostat controlled variable speed fans, I am quite sure. It may have two speed, star/delta connection or pole change motors for starting purposes..
each one with a air mixing box, two variable speed fans (one in the entrance of the RTU, right after the "Return Air Outlet" Node, and one at the exit, right before the "Supply Path Inlet" Node, but I only need to simulate the second fan at the exit) and one Heating Coil of Hot Water. There is then a Hot Water Loop, which connects the RTUs to the Boiler, and, of course, a Hot Water Boiler, with propane gas as fuel.
You should note the size or capacity of the units. Is the water coil on during Summer? If they are, these may be used as reheat coils. The outside container box is not the air mixer box. There is another enclosure inside. The fan which is normally visible is not in the air path. If the unit is larger than 15 HP, the compressor motors may need a starting control, that may be the variable speed you are talking about.
Since the cooling coil and reheat coils do not exist at all in the system, I don't simulate them: I deactivated the cooling coil in the schedule and I removed the reheat coils.
The correct description should be ' coils do not exist in the zone equipment'. Do you have a variable thermostat controlled damper in the zone? I do not think you have. Therefore you have chosen a wrong air terminal unit. Should use an uncontrolled one.
In the present moment I had to simulate with an electric heating coil to reduce and concentrate in only one problem. Now that I can finally heat correctly the zones, I have to remove the electric coil and insert the hot water coil, hot water loop and boiler. And when I do that, the zones are not heated at all.
Simply use the plant section of the example file I asked you to look at, or my macro file.
The supply pipes are not very long, the boiler is not very far from the RTUs. I'm using the 80º-70ºC temperatures for the hot water, because they are the temperatures used in reality in my system.
The water supply temperature is always that high. This is not the working temperature of the heating coil. The water enters the coil at 80°C and leave the coil at a low temperature. When you simulate the standard example file, you can very that. The mass flow rate controls the temerature. The termostat does not control the boiler. It turns the water supply on and off. The coil gets hot, cools down repeatedly to give the required air temperature.
I'm limiting the number of variables I change to limit the sources of error. I try to use only the templates and only change the variables I really need. I already made a drawing of the system nodes some time ago, to help me out at pinpointing the problems, but in this case it didn't helped me much. Strangely the hot water enters the heating coil at 80ºC and leaves it at 80ºC, not changing its temperature at all.
This is the strange characteristic of digital simulation. If the register says 80, it can remain at 80, with no water flowing.. If the input and output are the same, there is no heat transfer. It is up to the programmer to arrange this values. When there are water flowing, these numbers will change.
I can send you my file to your private e-mail, if you don't mind, but first I will try to analyse your file and comments to see what I can do first, so I don't waste too much of your time, because the building is quite big (4 stories and more than 2000 square meters and 5 VAV systems).
This is not a big size building, only 20 zones. However, you need to stop talking of using VAV unless you have 20 controlling thermostats to be used. In 1996, computer control is not yet popular, I doubted that you have VAV diffusers in your building.
If you have one thermostat per RTU, it is not a VAV system. The air from each RTY is ducted to the other zones and air volume balanced with fixed dampers, each passing a fixed fraction of the total air from one RTY. This the simple master / slave air loop system and is very easy to simulate.
Once again I really thank you very much for your help and patience!
>
__._,_.___
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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You may send me the building information directly to my hotmail ID.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: n_junk@xxxxxxxxxxxxxx
Date: Sun, 24 Jul 2011 10:57:37 +0000
Subject: [EnergyPlus_Support] Re: Problem with removing reheat coils in VAV
Hi Dr. Li,
I have to simulate a real system, installed in 1996, with five RTUs (rooftop air handling units),
The roof top air handling unit is usually the compressor part of a split unit. if the coils and fan are in the zone.
If it has two fans, one for the air into the building, and one to cool the condensor coil. it is not a split unit.
I am not sure that you describing them correctly. These fans are not thermostat controlled variable speed fans, I am quite sure. It may have two speed, star/delta connection or pole change motors for starting purposes..
each one with a air mixing box, two variable speed fans (one in the entrance of the RTU, right after the "Return Air Outlet" Node, and one at the exit, right before the "Supply Path Inlet" Node, but I only need to simulate the second fan at the exit) and one Heating Coil of Hot Water. There is then a Hot Water Loop, which connects the RTUs to the Boiler, and, of course, a Hot Water Boiler, with propane gas as fuel.
You should note the size or capacity of the units. Is the water coil on during Summer? If they are, these may be used as reheat coils. The outside container box is not the air mixer box. There is another enclosure inside. The fan which is normally visible is not in the air path. If the unit is larger than 15 HP, the compressor motors may need a starting control, that may be the variable speed you are talking about.
Since the cooling coil and reheat coils do not exist at all in the system, I don't simulate them: I deactivated the cooling coil in the schedule and I removed the reheat coils.
The correct description should be ' coils do not exist in the zone equipment'. Do you have a variable thermostat controlled damper in the zone? I do not think you have. Therefore you have chosen a wrong air terminal unit. Should use an uncontrolled one.
In the present moment I had to simulate with an electric heating coil to reduce and concentrate in only one problem. Now that I can finally heat correctly the zones, I have to remove the electric coil and insert the hot water coil, hot water loop and boiler. And when I do that, the zones are not heated at all.
Simply use the plant section of the example file I asked you to look at, or my macro file.
The supply pipes are not very long, the boiler is not very far from the RTUs. I'm using the 80º-70ºC temperatures for the hot water, because they are the temperatures used in reality in my system.
The water supply temperature is always that high. This is not the working temperature of the heating coil. The water enters the coil at 80°C and leave the coil at a low temperature. When you simulate the standard example file, you can very that. The mass flow rate controls the temerature. The termostat does not control the boiler. It turns the water supply on and off. The coil gets hot, cools down repeatedly to give the required air temperature.
I'm limiting the number of variables I change to limit the sources of error. I try to use only the templates and only change the variables I really need. I already made a drawing of the system nodes some time ago, to help me out at pinpointing the problems, but in this case it didn't helped me much. Strangely the hot water enters the heating coil at 80ºC and leaves it at 80ºC, not changing its temperature at all.
This is the strange characteristic of digital simulation. If the register says 80, it can remain at 80, with no water flowing.. If the input and output are the same, there is no heat transfer. It is up to the programmer to arrange this values. When there are water flowing, these numbers will change.
I can send you my file to your private e-mail, if you don't mind, but first I will try to analyse your file and comments to see what I can do first, so I don't waste too much of your time, because the building is quite big (4 stories and more than 2000 square meters and 5 VAV systems).
This is not a big size building, only 20 zones. However, you need to stop talking of using VAV unless you have 20 controlling thermostats to be used. In 1996, computer control is not yet popular, I doubted that you have VAV diffusers in your building.
If you have one thermostat per RTU, it is not a VAV system. The air from each RTY is ducted to the other zones and air volume balanced with fixed dampers, each passing a fixed fraction of the total air from one RTY. This the simple master / slave air loop system and is very easy to simulate.
Once again I really thank you very much for your help and patience!
>
__._,_.___
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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