Hi, Jean
I am not a HVAC expert. I have not read ASHRAE guidelines, except looking at those when my students asked me to clarify. They provide the documents.
My replies are mainly based on EPlus implementation and practical systems.
It is not true that the radiant system has its own thermostat. It uses the same zone thermostat values. If the zone temperature is changed, there is only one thermostat object to pass the value.
The radiant system appears to have its onw temperature, because it works on the difference temperature of many other objects selectively. MRT, Operative, Zone mean are all based on the zone thermostat with an add-on value.
The DOAS system normally feeds the zone with low temperature air regardless of the zone temperature or load except CO2 values. The capacity is always set below the zone demand, because it is only feeding the fresh air. Although the DOAS temperature is low, it will never cool the zone to the thermostat value. If it does, a reheat coil should kick in.
The other system cools the zone to the thermostat value. This is the reason for the priority setting, so that the reheat coil and system cooling should not be on together.
Without the radiant cooling panel, the DAOS air need not be controlled to 18°C to prevent condensation. Hence, the more economical air loop system with the condensation taking place at the cooling coil of the air loop.
VAV is mainly to prevent the maximum demand penalty, and extra comfort of individual zone temperature control which the user does not really need.
Heat recovery, economizer, etc. requires extra control and sensors. They cannot be implemented in the past, because the intelligent controller cost is high. Now, these controller chips with colid state device controller are must lower in cost and size. They are design in America and made in China.
When you set the cooling coil to provide a 18°C air at the fan outlet, the dehumidification is automatically provided. This is the convensional way of controlling zone humidity. The duct would heat it up slightly and acting as the reheat so that air coming out at the diffuser would be at 20°C and above.
The last problem is due to the control or sensor placed at the wrong point. The OA inlet should not be controlled. The air volume is controlled by the fan and zone damper. The zone damper is controlled by the CO2 sensor. Increased number of people present needs more air. The fresh air system should not care what the zone temperature is. When the zone damper ask for more air, the fan should respond. (pressure sensor for VAV.)
This is not the most economical system, but will follow what you wanted. I still maintain that the zone loads cannot be split as some one suggested to reduce energy usage. Radiant panel is a luxury item and is good as a reheat heater. A modular four pipe system with individual OA is what I would use. A central computor control can look at the load situation to reduce the maximum demand of power usage.
At the University 40 years ago, we had a program to time the water pumps and air-conditioning pump motors so that they would run together and the maximum demand meter value is reduced (registered at a lower value).
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: jeannieboef@xxxxxxxxx
Date: Fri, 30 Sep 2011 06:51:33 +0000
Subject: [EnergyPlus_Support] Re: fan problem
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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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I am not a HVAC expert. I have not read ASHRAE guidelines, except looking at those when my students asked me to clarify. They provide the documents.
My replies are mainly based on EPlus implementation and practical systems.
It is not true that the radiant system has its own thermostat. It uses the same zone thermostat values. If the zone temperature is changed, there is only one thermostat object to pass the value.
The radiant system appears to have its onw temperature, because it works on the difference temperature of many other objects selectively. MRT, Operative, Zone mean are all based on the zone thermostat with an add-on value.
The DOAS system normally feeds the zone with low temperature air regardless of the zone temperature or load except CO2 values. The capacity is always set below the zone demand, because it is only feeding the fresh air. Although the DOAS temperature is low, it will never cool the zone to the thermostat value. If it does, a reheat coil should kick in.
The other system cools the zone to the thermostat value. This is the reason for the priority setting, so that the reheat coil and system cooling should not be on together.
Without the radiant cooling panel, the DAOS air need not be controlled to 18°C to prevent condensation. Hence, the more economical air loop system with the condensation taking place at the cooling coil of the air loop.
VAV is mainly to prevent the maximum demand penalty, and extra comfort of individual zone temperature control which the user does not really need.
Heat recovery, economizer, etc. requires extra control and sensors. They cannot be implemented in the past, because the intelligent controller cost is high. Now, these controller chips with colid state device controller are must lower in cost and size. They are design in America and made in China.
When you set the cooling coil to provide a 18°C air at the fan outlet, the dehumidification is automatically provided. This is the convensional way of controlling zone humidity. The duct would heat it up slightly and acting as the reheat so that air coming out at the diffuser would be at 20°C and above.
The last problem is due to the control or sensor placed at the wrong point. The OA inlet should not be controlled. The air volume is controlled by the fan and zone damper. The zone damper is controlled by the CO2 sensor. Increased number of people present needs more air. The fresh air system should not care what the zone temperature is. When the zone damper ask for more air, the fan should respond. (pressure sensor for VAV.)
This is not the most economical system, but will follow what you wanted. I still maintain that the zone loads cannot be split as some one suggested to reduce energy usage. Radiant panel is a luxury item and is good as a reheat heater. A modular four pipe system with individual OA is what I would use. A central computor control can look at the load situation to reduce the maximum demand of power usage.
At the University 40 years ago, we had a program to time the water pumps and air-conditioning pump motors so that they would run together and the maximum demand meter value is reduced (registered at a lower value).
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: jeannieboef@xxxxxxxxx
Date: Fri, 30 Sep 2011 06:51:33 +0000
Subject: [EnergyPlus_Support] Re: fan problem
Thanks for the warning of the allotherdays and that designday is included here. I use alldays for everything as I'm only running the designday simulation, this runs the schedules for all day types.
What I find most interesting is how different the "American" approach to HVAC is in it's mind set. I can see by your replies that modeling a VAV system and a low temperature radiant system which acts as the priority cooling system is not something that is often modeled. Econimiser as such has little meaning in the German world of DOASs where this basically means that the cooling coil simply doesn't turn on.
Low temp radiant system objects in e+ opperate almost completely alone. They have their own room thermostat and they get sized independantly to the Air Systems. This means I can set a seperate "normal" dual setpoint zone thermostat for the Air Systems of 50 degC so that the Air Systems are only occupied with meeting outdoor air requirements and not cooling the zone. I set a setpoint manager at the coil outlet to maintain the supply air at a constant 18 degC (no dehumidification).
This system would work fine except that the fan object (variablevolume) will not turn on if it sees no zone cooling loads. This is a incredible restriction. I must also be able to model a dumb system.
What I find most interesting is how different the "American" approach to HVAC is in it's mind set. I can see by your replies that modeling a VAV system and a low temperature radiant system which acts as the priority cooling system is not something that is often modeled. Econimiser as such has little meaning in the German world of DOASs where this basically means that the cooling coil simply doesn't turn on.
Low temp radiant system objects in e+ opperate almost completely alone. They have their own room thermostat and they get sized independantly to the Air Systems. This means I can set a seperate "normal" dual setpoint zone thermostat for the Air Systems of 50 degC so that the Air Systems are only occupied with meeting outdoor air requirements and not cooling the zone. I set a setpoint manager at the coil outlet to maintain the supply air at a constant 18 degC (no dehumidification).
This system would work fine except that the fan object (variablevolume) will not turn on if it sees no zone cooling loads. This is a incredible restriction. I must also be able to model a dumb system.
__._,_.___
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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