Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question

How E+ calculate the ventilation loads ? And What is the output ?

asked 2018-10-22 03:01:11 -0500

Alexis's avatar

updated 2018-10-24 00:56:02 -0500

I am working with the hvac templates : dedicated outdoor air. I am using this templates like an AHU with heat recovery. Supply air : 20m3/h/pers. Efficiency of my heat exchanger : 0.75
I would like to know what is my ventilation heat gain, in watt. I would like to see the effect of the heat recovery on the cooling capacity of my room compared to outdoor air.

What output do I need to ask in E+ ? Zone mechanical and air system, its only energy so in J, not really what I want.
I tried "Zone Air Heat Balance System Air Transfer Rate", I dont know what is included inside but I dont think its the good output.
I also tried "Zone Air Heat Balance Outdoor Air Transfer Rate" but it is for infiltration.

Outside of E+, I am used to calculate the ventilation heat gain with this formula : - Sensible : airflow * difference of T * 0.34 * efficiency of my exchanger
- Latent : airflow * difference of humidity * 0.84 * efficiency of my exchanger
Does Energy+ calculate the ventilation heat gain in the same way ?

Link of my inputs, perhaps it could help to understand :
image description

image description

edit retag flag offensive close merge delete

1 Answer

Sort by » oldest newest most voted

answered 2018-10-23 08:24:10 -0500

updated 2018-10-23 08:24:54 -0500

When using HVACTemplate, the DOAS supply air is delivered to the zone using an AirTerminal:SingleDuct:VAV:NoReheat object which is contained within aZoneHVAC:AirDistributionUnit which produces the following outputs:

Output:Variable,*,Zone Air Terminal Sensible Heating Energy,hourly; !- HVAC Sum [J]
Output:Variable,*,Zone Air Terminal Sensible Cooling Energy,hourly; !- HVAC Sum [J]
Output:Variable,*,Zone Air Terminal Sensible Heating Rate,hourly; !- HVAC Sum [W]
Output:Variable,*,Zone Air Terminal Sensible Cooling Rate,hourly; !- HVAC Sum [W]

These outputs report the sensible heating or cooling energy delivered to the zone by an air terminal unit.

To clarify what Zone Air Heat Balance System Air Transfer Rate means, from the Input Output Reference definition:

The Zone Air Heat Balance System Air Transfer Rate is the sum, in watts, of heat transferred to the zone air by HVAC forced-air systems and air terminal units. Such HVAC systems are connected to the zone by an inlet node (see ZoneHVAC:EquipmentConnections input field called Zone Air Inlet Node or Node List Name) . . .

For this model, this would include the net sensible heating/cooling of both the DOAS terminal unit and the VRF system.

edit flag offensive delete link more


Thank you for your answer. When I try to plot this variable, I am surprised because my DOAS brings sensible cooling only when my equipment turns on, during 1 or 2 hours the morning.
What I have noticed is when my setpoint is reached, no more sensible cooling brings by my DOAS. Some days, I dont have any sensible cooling coming from my DOAS. I thought that a AHU brings cooling during all the day. I checked, my DOAS is working for all the day.
I have updated my posts with a picture. More over, the outside temperature is always superior to my inside temperature, I am in south Asia

Alexis's avatar Alexis  ( 2018-10-24 00:55:12 -0500 )edit

I was running out of characters, I have an other question : why only the sensible is reported ? No latent ?

Alexis's avatar Alexis  ( 2018-10-24 00:57:33 -0500 )edit

@Mantra please post a link to the full idf file here or send as an attachment to

MJWitte's avatar MJWitte  ( 2018-10-29 15:50:41 -0500 )edit

@MJWitte,here is the link :
So I have this issue with the DOAS and the sensible cooling. I thought that DOAS brings cooling during all the hours of operation. Its not what the curve is showing.
And, I have an other issue with the DOAS cooling coil rate. Outside of E+, I am using the psychometric diagram to determine the cooling capacity. But In E+, I am confused because when I change the efficiency of my heat recovery, my DOAS cooling coil rate is not changing. I would like to cool and deshumidy the OA

Alexis's avatar Alexis  ( 2018-10-31 00:41:44 -0500 )edit

@MJWittle, did you have Time to look at my file ? Any clue, why my DOAS doesnt bring cooling load for all the hours of opération ? Thank for your help

Alexis's avatar Alexis  ( 2018-11-05 05:39:25 -0500 )edit

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Training Workshops


Question Tools

1 follower


Asked: 2018-10-22 03:01:11 -0500

Seen: 1,573 times

Last updated: Oct 24 '18