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[EnergyPlus_Support] Re: Zones without HVAC return nodes
Hello Dr. Li,
thanks again for your ideas.
I have some temperature measurements for a house with this heating system and I will compare the simulations with those data to check that as a beginner I am not going too far wrong.
What I was trying to do was to model the infiltration (important in this house) and air flow from one zone to the next through the internal doors using AirflowNetwork:Multizone:Surface objects. However I wanted to be able to run the AirflowNetwork:SimulationControl in "MultizoneWithDistribution" because the infiltration would provide an important load for the heating system.
That is where I run into the problem. The distribution network defined by AirflowNetwork:Distribution objects has to be a closed network using AirflowNetwork:Distribution:Linkage objects to connect the nodes. The doors cannot provide that linkage and so I have to define an additional "fake" duct linking each zone to the hall zone (plenum) in order to close the network.
Also because the Hall is a plenum it cannot have the controlling thermostat for the system (the configuration in one of the houses that I am modeling)
You have given me a lot of ideas on how to explore the model behaviour using other approaches and I will keep working with those.
Thanks, Andrew.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@...> wrote:
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> Hi, Andrew I do not know what you are trying to do. If you wanted to see the effect of opening and closing of the door, you can simply change the air flow fraction for the Air distribution terminal for that zone. The some of the fractions adds up to 1.0 for all the rooms. The simplest way is to add the reduction amount to the largest room. With the reduced air flow, the room temerature would change. The zone does not care how the air reduction is done. This is the advantage of having a common plenum (hall or coridor). The heat balance is done for each zone and then the return air is fed to the plenum zone and mixed. If all the zones have the same temperature, the plenum will also have the same temperature. Any internal load will be added to the return air and will make the plenum hotter. This is also the observed real life condition. You can make the plenum the master zone as well, but will less ducted air flow, under normal operation. When all the room air flow are reduced, more air should flow directly through the hall. Then closing the vents and doors in the rooms surround it will use less heat in Winter, because the hall temperatue will be heated faster and shut down the system. This will show in the simulation, because the temperture between inner and ouuter surface wall is reduced, the heat loss is reduced.
> Thee are many ways that the simulation may be run. You must have a real situation to test the result.. The zone air mixing object can be used to simulate an open door, with a specified temperature difference between the zone. Air leak through each room to the outdoor air can use zone infiltration object. AFN is common name for a simulation module. It has many special features. Dr. Li
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: drajperry@...
> Date: Tue, 4 Oct 2011 10:50:39 +0000
> Subject: [EnergyPlus_Support] Re: Zones without HVAC return nodes
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> Hello Dr Li,
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> thanks for your reply - I have been working on other things so this is a late response.
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> I guess my naive thinking was that since the door provides a linkage between the conditioned zone and the hall I could use it in the AFN or even the HVAC loop. As you point out, when the door is partially closed the flow will be reduced via that path.
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> However it doesn't seem possible to do this since the AFN has to have input and output linkages for each node and the MultiZone:Component objects like the doors cannot be used as linkages.
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> So I need to add "fake" ducts to complete the AFN from the conditioned zones to the hall which then returns the air to the furnace.
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> I will have to do a lot more study of your suggestions and EPlus to work whether there is a way to handle this or whether it is just something that will have to be left out of my model.
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> Thanks again, Andrew
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> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@> wrote:
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> > Hi, Andrew The name plenum is used by EPlus to model the two region above and below each floor for air inlet and oulet connection to the whole floor. False ceiling can also be part of the plenum. The plenum itself is usually not air-conditioned. It is not part of an AFN. It is a zone which receive air from all the other connected zones, well mixed and exhaust to the air loop. Heat from the lamp fixture, etc. may be added directly to a plenum. (addition heat in the hallway may be added as well.) In a house, if the hall way is not air conditioned, it is similar to the plenum condition. As far as air flow is concerned, when the door is open or closed, the air from the vent will be returned via the door bottom leak to the hall. If the gap is small, the flow will be reduced, but the total volume will be about the same, as more air will channelled to the other rooms. If you have the temperature change value, you can then vary the fractional ratio for that room. You can measure the temperature variation of the room, with the door open and closed. Zone mixing may provide you with some information on this change. AFN may not work, unless you have the full description of the other room flow conditions as well. The door would be a damper in the distribution duct. I have not tried this myself. The hallway is the mixing point of the distrubution ducts.
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> > If you declare the hallway as a plenum, all the zone return air will be connected to the hallway and use it as a return mixer to the AHU return air node, which is usually on the OA mixer. This is the standard way to model an air loop. Dr. Li
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> > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
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> > From: drajperry@
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> > Date: Thu, 15 Sep 2011 12:47:46 +0000
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> > Subject: [EnergyPlus_Support] Re: Zones without HVAC return nodes
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> > Hello Dr. Li,
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> > Thanks for your detailed response to my question. I need to run some tests to check on how to apply what you suggest.
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> > Yes, the house is in a cold region (southern highlands of Australia) although I have also seen houses in Northen California with the same gas furnace/no AC arrangement.
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> > The system is as you described. There is an inlet and outlet on the furnace.
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> > The return air flows from the rooms into the hall then into a collection vent and through a duct to the inlet of the furnace.
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> > Modeling the hallway as a plenum in the HVAC system, as you suggested, does work.
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> > My problem with using that approach is that I can't find out how to represent, correctly, a plenum in an AirflowNetwork.
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> > The AFN node definitions only allow for a mixer to combine multiple air paths. If I use a mixer object in the AFN I get errors.
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> > So far the only thing that works is to connect the outlet nodes of the zones to the air node in the hallway using ducts. This seems to be a kludge so I don't know whether to trust the results.
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> > Thanks, Andrew.
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> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@> wrote:
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> > > Hi, Andrew I noticed that you are only using heating, I assume that you do have a cold Winter. In Canada, all the residential house has a basement for water main to enter the house, so that it will not be frozen in Winter. The gas furnace is mounted in the basement. The furnace is rectangular in shape and has two ducts. There will definitely a horizontal one to distribute the warm air, from the top of the furnace box. The return air may enter the box from the bottom where the fan is mounted. I have seen such a picture in the EPlus document. In my condo, there are two ducts at the ceiling level, one for warm air and one for return air.==================For a bungalow, the return duct may not be present. The air flowing down the starcase to the basement and the fan filter is sufficient for the convection flow. The hot air is forced upwards near the wall and windows. Kitchen and bathrooms will have small exhaust fans. You do have a return duct from the hall way. You may ignore this or model it as a zone with air mixing from the other zones, to keep the temperature the same as the other zones. To make it plenum, simply declare this as a zone (plenum) and use it as a mixer of the air loop. You need not have to declare how the room air get into the plenum zone. All the air flow through the ATU's will enter this plenum as return air in simulation. You may declare an additioanal infiltration for air leak to outside air, and add an OA intake with an OA mixer box.. The furnace will have a fresh air piple and a chinmey pipe. These are usually not simulated, although the chimney pipe is suitable to act as inlet air pre-heat.======================In a two or three storey house, part of the partition wall space is used as vertical is used a the return air duct with a grill opening at each upper floor. This is usually away from the stair case and thus have two return parths from the upper floors. The air outlet cover usually has a adjustable slider. This is the EPlus ATU:..:uncontrolled.=======================If you need to study the temperature in the house, then divide the floor area into more zones as the 5Zone exmple model, or in actual room divisions. Rooms without a hot air outlet would be a passive zone. Heating can be assumed to be by wall conduction or with some zone air mixing from the other rooms. How the air is returned from each zone to the furnace is not very emportant. With a constant volume fan, a fixed fraction of this volume enters a zone, and the same amount leave the zone at a different temperature. This heat balance or difference causes the zone temperature to be slightly above or below the controlled AHU supply air temperature.==================Full Airflow network is designed to work with external environment condition as well. The AFN distribution duct network takes into account of duct temperature and pressure changes and pobably the flow between the diffuser and the exhaust ports.======================In the above described case, the room temperature can be observed. The temperat>
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> > > Dr. Li
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> > > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
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> > > From: drajperry@
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> > > Date: Tue, 13 Sep 2011 12:08:31 +0000
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> > > Subject: [EnergyPlus_Support] Zones without HVAC return nodes
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> > > Hello All,
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> > > I have been trying for some time to model a type of residential house which uses a simple gas furnace for heating.
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> > > Heated air from the furnace passes through ducts to the simple delivery terminals (AirTerminal:SingleDuct:Uncontrolled) in each room.
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> > > There are no return air terminals in the rooms. In the real house, the air flows from the rooms through doorways and is collected at a single return vent (usually in a hall) and then through a duct back to the inlet of the furnace.
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> > > The house cannot be modelled as a single zone since important temperature differences between rooms do occur in practice.
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> > > Is there a "right" way to model this in EnergyPlus?
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> > > I have made the hall zone a return plenum for all the room zones but that is not really what plenums are for.
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> > > In addition if I use a plenum I cannot find documentation or examples on how to handle it in an airflow network so that I can correctly include the airflow through the doors.
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> > > Any guidance would be greatly appreciated.
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> > > Thanks, Andrew
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