I still do not know what you wanted to used in the final design.
You were asking about the ratio between the water system and the electrical system.
They cannot be compared this way uing simple ratio.
The electrical heater can be turned on and off any time. The DX coil can be turned on and off by turning on and off the compressor pump, just like a refrigerator.
If you have a water system, you can turn on and off the fire to the boiler, but temperature will not come up instantly. If you have long supply pipes, the pipes need to be warmed up as well. This is also the reason why the DX split unit cannot be too far apart.
I mentioned using a working example model and not a template model because the templates are still too flexible.
5ZoneVAV-Pri-SecLoop.idf is a water system, with reheat in the zone. The reheat heater will only come on when the flow rate is at the minimum damper position. Therefore, if you reduce the minimum damper postion to zero or very small, the reheat will not come one. There is no need to remove the coil.
If you want VAV, a reheat heater is usually required. If your real system do not have a variable speed fan, the VAV model is not the right one to use.
The boiler setpoint temperature at 50 - 80°C is the input to the heating coil. If the water flow rage is small or zero, the coil temperature would be the air temperature. In the air loop, you are setting the air temperature. The water flow rated is adjusted to give you that temperature. Therefore, it does not matter how hot you make the boilder temperature, so long it is hotter than the air temperature.
There are many set points in the IDF. I do not know which heating design temperature you are referring to; sizing for plant, system, zone or in the equipment. You should not change them without knowing what thay are for.
This is why I suggested that you write them down on the schematic diagram of the system node points. The number I have plotted is the output node of the fan, and is the setpoint you specify in the setpoint manager as the reference point after the expansion, I think. I have not actually looked at the expIDF again. If you use a scheduled setpoint values, the setpoint plot will not be a constant straight line.
If you change the values in the expIDF, and run the template IDF again, the values in the template IDF will be used.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: n_junk@xxxxxxxxxxxxxx
Date: Fri, 22 Jul 2011 22:43:05 +0000
Subject: [EnergyPlus_Support] Re: Problem with removing reheat coils in VAV
Hi,
In these days I have studied with careful the HVAC system I have to model in my thesis and for the problems I had with my file.
At this point I finally can mantain the zones' temperatures between 20-25ºC has I wanted. What I did was to remove some autosize fields and insert there the values I have in reality, and force the VAV damper to be always fully opened (which is the situation I have in reality). I also forced the system to insert in the zones the outdoor air I need.
The point that Dr. Li made about the internal loads made me understand better the problems I have. Both suggested programs were also useful, many thanks to you all!
I still have one big problem though. I'm currently using an Electric Heating Coil in each RTU, but I really need to use a Hot Water Coil and a Boiler. The problem is that when I switch from the electric to hot water coil the zones' temperatures drop below the setpoint and thermostat value (below 20ºC). More strange than that is that the setpoints are all the same, I only changed the coil type and add a hotwater loop and a boiler, but the outlet temperatures from the system drop a lot. If I rise the heating design temperature, the autosize feature increases the estimated heating coil capacity but the temperatures doesn't change at all... Do you know what's going on?
Note that this time I'm only using the HVACTemplates. To emulate the problem just open a example file with packagedVAV and just change the gas or electric heating coil for one with water.
If everything else fails (I'm running out of time), is there any known ratio between a electric coil's and a equivalent hot water coil's capacity? Like, for a same design heating temperature, a electric coil with x capacity is equivalent to a water coil with x/y capacity?
Once again many thanks to you all for all the precious help!
__._,_.___
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 were asking about the ratio between the water system and the electrical system.
They cannot be compared this way uing simple ratio.
The electrical heater can be turned on and off any time. The DX coil can be turned on and off by turning on and off the compressor pump, just like a refrigerator.
If you have a water system, you can turn on and off the fire to the boiler, but temperature will not come up instantly. If you have long supply pipes, the pipes need to be warmed up as well. This is also the reason why the DX split unit cannot be too far apart.
I mentioned using a working example model and not a template model because the templates are still too flexible.
5ZoneVAV-Pri-SecLoop.idf is a water system, with reheat in the zone. The reheat heater will only come on when the flow rate is at the minimum damper position. Therefore, if you reduce the minimum damper postion to zero or very small, the reheat will not come one. There is no need to remove the coil.
If you want VAV, a reheat heater is usually required. If your real system do not have a variable speed fan, the VAV model is not the right one to use.
The boiler setpoint temperature at 50 - 80°C is the input to the heating coil. If the water flow rage is small or zero, the coil temperature would be the air temperature. In the air loop, you are setting the air temperature. The water flow rated is adjusted to give you that temperature. Therefore, it does not matter how hot you make the boilder temperature, so long it is hotter than the air temperature.
There are many set points in the IDF. I do not know which heating design temperature you are referring to; sizing for plant, system, zone or in the equipment. You should not change them without knowing what thay are for.
This is why I suggested that you write them down on the schematic diagram of the system node points. The number I have plotted is the output node of the fan, and is the setpoint you specify in the setpoint manager as the reference point after the expansion, I think. I have not actually looked at the expIDF again. If you use a scheduled setpoint values, the setpoint plot will not be a constant straight line.
If you change the values in the expIDF, and run the template IDF again, the values in the template IDF will be used.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: n_junk@xxxxxxxxxxxxxx
Date: Fri, 22 Jul 2011 22:43:05 +0000
Subject: [EnergyPlus_Support] Re: Problem with removing reheat coils in VAV
Hi,
In these days I have studied with careful the HVAC system I have to model in my thesis and for the problems I had with my file.
At this point I finally can mantain the zones' temperatures between 20-25ºC has I wanted. What I did was to remove some autosize fields and insert there the values I have in reality, and force the VAV damper to be always fully opened (which is the situation I have in reality). I also forced the system to insert in the zones the outdoor air I need.
The point that Dr. Li made about the internal loads made me understand better the problems I have. Both suggested programs were also useful, many thanks to you all!
I still have one big problem though. I'm currently using an Electric Heating Coil in each RTU, but I really need to use a Hot Water Coil and a Boiler. The problem is that when I switch from the electric to hot water coil the zones' temperatures drop below the setpoint and thermostat value (below 20ºC). More strange than that is that the setpoints are all the same, I only changed the coil type and add a hotwater loop and a boiler, but the outlet temperatures from the system drop a lot. If I rise the heating design temperature, the autosize feature increases the estimated heating coil capacity but the temperatures doesn't change at all... Do you know what's going on?
Note that this time I'm only using the HVACTemplates. To emulate the problem just open a example file with packagedVAV and just change the gas or electric heating coil for one with water.
If everything else fails (I'm running out of time), is there any known ratio between a electric coil's and a equivalent hot water coil's capacity? Like, for a same design heating temperature, a electric coil with x capacity is equivalent to a water coil with x/y capacity?
Once again many thanks to you all for all the precious help!
__._,_.___
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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