See My comments below.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: xing.shi.2006@xxxxxxxxx
Date: Wed, 17 Aug 2011 04:18:36 +0000
Subject: [EnergyPlus_Support] Re: How to define ventilation rate to get proper HVAC system energy consumption
Dr. Li:
The thing I am not quite clear about is that we have different ways to tell E+ that we want to have a certain amount of ventilation into the zone. We can use ZoneInfiltration or ZoneVentilation:DesignFlowRate or Sizing:Zone.
If our purpose is to find the actual HVAC energy consumption, which one of these three should we use?
My understanding is as follows:
(1)if we use ZoneInfiltration, the load brought in by outside air should be the same. But we lose the energy consumption by the fan because all ventilation is caused by infitration. No fan is needed. This is to simulate the real situation, because the building is not perfectly sealed. The leak quantity is not well defined, as it depends on the external wind velocity.
(2)we do not have to have Sizing:Zone/System/Plant if our goal is to get actual energy consumption of the HVAC system. You will need sizing objects, if any equipment size is autosized by EPlus. The sizing object input your design requirements for EPlus to calculate the equipment capacity required for the demand.
All we need to do is to use branchers/objects/nodes/...to correctly model the HVAC system.
These describe how the equipment are connected together, and do not have the capacity infomration in all of them. You will typically use autosize for most of these. The maximum values are for safety and to warn you that you have made some wrong gesses.
The thing I am not quite clear about is that we have different ways to tell E+ that we want to have a certain amount of ventilation into the zone. We can use ZoneInfiltration or ZoneVentilation:DesignFlowRate or Sizing:Zone.
If our purpose is to find the actual HVAC energy consumption, which one of these three should we use?
My understanding is as follows:
(1)if we use ZoneInfiltration, the load brought in by outside air should be the same. But we lose the energy consumption by the fan because all ventilation is caused by infitration. No fan is needed. This is to simulate the real situation, because the building is not perfectly sealed. The leak quantity is not well defined, as it depends on the external wind velocity.
(2)we do not have to have Sizing:Zone/System/Plant if our goal is to get actual energy consumption of the HVAC system. You will need sizing objects, if any equipment size is autosized by EPlus. The sizing object input your design requirements for EPlus to calculate the equipment capacity required for the demand.
All we need to do is to use branchers/objects/nodes/...to correctly model the HVAC system.
These describe how the equipment are connected together, and do not have the capacity infomration in all of them. You will typically use autosize for most of these. The maximum values are for safety and to warn you that you have made some wrong gesses.
You need the controllers and managers to link in the schedules.
You need to specify what type of equipment or components to be used., fans, coils, pumps, etc. Pipes are generally adiabatic, but are there if you need to add losses, etc. This is the difference between EPlus and the grading soltware. EPlus has more detailed calculation of the building envelope and the equpment used.
After one successful siminulation, you can then look at the values in the EIO, ESO
, csv to compare and enter fixed values of your own, replacing some of the autosize values in order to match your read equipment used..
Am I right? Thanks!
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@...> wrote:
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> Hi, Xing
> ZoneInfiltration:DesignFlowRate would add some air into the zone with a fan. The fan power is listed in the report as virtual fan.
> ZoneVentilation:DesignFlowRate does not use fan. The air flows through cracks.
> Sizing:Zone is required to provide design information to the program to size the zone equipment.. You will need system and plant sizing as well. If you use template as input, these will be provided by the template expansion program. Total HVAC energy consumption would be the sum of all the components, fans, pumps, compressors. GSHE has a circulating pump. Tower has both pump and fan. Chiller is the heat pump which has compressor and pump. The zone equipment has a fan per zone or a common fan in the AHU. When the heat pump cannot provide the heating, additional heating power is added.
>
> Dr. Li
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: xing.shi.2006@...
> Date: Mon, 15 Aug 2011 11:40:37 +0000
> Subject: [EnergyPlus_Support] How to define ventilation rate to get proper HVAC system energy consumption
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> In the following 3 objects, which one should we use to model HVAC system energy consumption:
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> ZoneInfiltration:DesignFlowRate
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> ZoneVentilation:DesignFlowRate
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> Sizing:Zone
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> Our HVAC system is chiller plus cooling tower. Air system is constant volume fan. Heating provided by ground source heat pump.
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> Thanks!
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