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HVAC Connections in Individual Rooms of a Single Thermal Zone

asked 2015-09-13 22:16:47 -0600

nadish21's avatar

updated 2015-09-14 09:11:07 -0600


I have a confusion regarding the modeling of HVAC system for a single thermal zone. My simulation is for a single small House (although its template is not available in EPlus, but I am using the Midrise Apartment's template) with a single HVAC unit. I am not sure if the Air Terminal:Single Duct: Uncontrolled Object is enough to ensure that the Conditioned air from the HVAC unit is reaching Equally to all the Rooms in my Thermal Zone. I have not set up any duct work or other objects for the HVAC system manually.

I am Attaching the IDF file for a sample simulation. I would appreciate any help in this matter.


Nadish Anand

IDF Link

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answered 2015-09-14 11:34:37 -0600

updated 2015-09-14 13:59:14 -0600

In EnergyPlus, there are no "rooms" within a thermal zone. The attached idf has one thermal zone, so anything connected to that zone such as HVAC or internal loads will impact the entire zone. If there are building surfaces that divide this zone into smaller rooms, the energy balance still lumps these all together. For a residential application, however, I would recommend breaking the model into more thermal zones. The unitary HVAC equipment allows a single system to serve multiple zones with one zone specified as the control zone where the thermostat is located.

The control zone is specified in the main HVAC unit (e.g. AirLoopHVAC:Unitary:Furnace:HeatCool). Each thermal zone will typically have an AirTerminal:SingleDuct:Uncontrolled to deliver air to that zone.

The terminal units can be given hard flow rates, or they may be autosized. If they are autosized, each zone requires a ZoneControl:Thermostat to specify the setpoints for calculating the design loads. (Note that these thermostats will not be active during the simulation, just used for sizing).

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Hello Mr. Witte,

Thank you for the reply. I was suspecting something similar. I have however more questions regarding the implementation of such a setup: 1) How will I designate the Control Thermal Zone? 2) How will I divide the flow rate of the Heated or cooled air between the different zones? 3) Is there a variable for the Average temperature of the whole house or Envelope in Energy+ or I would need to take average of all the Zones', Zone Air Temperatures? 4) Will this affect the Sizing calculations of the HVAC system?

I greatly appreciate your time and help.


Nadish Anand

nadish21's avatar nadish21  ( 2015-09-14 12:03:21 -0600 )edit

I added 1 and 2 to the main answer box. There is no variable for average temperature across multiple zones. And, yes, this will most likely affect the HVAC system sizing, but that's very dependent on the characteristics of the zones.

MJWitte's avatar MJWitte  ( 2015-09-14 14:00:49 -0600 )edit

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Asked: 2015-09-13 22:16:47 -0600

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Last updated: Sep 14 '15