Honeybee Energy and Natural Ventilation appearing as a substantial cooling component in the Energy Balance

Hi All

I feel again I will be pointed towards a solution that already exists somewhere on this discussion board, but my search cannot find it. I am running a simple energy balance with Ideal Loads on a five zone commercial building floor. I cannot get the openable windows to contribute more than a tiny fraction to the cooling.

I have chosen to define ventilation capability in the program (in terms of ACH - setting the other ventilation inputs such as flow per person etc to zero)- and even at Air Changes per Hour of 20 the cooling effect is minimal.

Trigger points for ventilation are
Heating below 18C
Open Windows above 23C
Close windows, turn on AC above 26C
Temp difference between inside and out has to be > 2C for windows to open
Windows do not open if outdoor temp too cold (tried 10C and 15C here)

Racking my brains to solve this one. Unsuccessfully


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@MichaelDonn ,

A couple of points:

  1. The _ventilation_ that is assigned to room or the program objects is mechanical ventilation (or minimum outdoor air requirement through the HVAC). So it is not related at all to the outdoor air flow through operable windows.
  2. 3C (or 26 - 23) is a really small range in which to naturally ventilate. The adaptive comfort model indicates that occupants are usually fine with temperatures up to 28C (or even 30C if you are in the tropics). I wouldn’t expect to see a significant cooling term for natural ventilation unless you have a range of at least 5C.
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You can find these couple of discussions useful, this and this.

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Also, once you have some initial setpoints, I found I can usually boost performance significantly by plugging the setpoints into an optimization algorithm and letting it search 0.1 C increments around each setpoint. The native GH Simulated Annealing component works pretty well for this. If we had a decent surrogate model for natural ventilation then we could really start taking advantage of optimization.


Thanks. I have (Elzine suggested the same thing) created two parallel models:

  • one with ideal loads to get a picture of the room/Building Loads
  • one with the HVAC defined (essentially I have created two programs; all inputs are the same except for one program the (Mechanical) Ventilation is not connected)


Hi All again.

Thanks so much for the previous responses. And indeed for the cross reference here: Confused about Cooling Energy when Using Operable Windows? - #14 by SaeranVasanthakumar

However, I have some remaining questions about the Energy Balance reporting.

I have tried to set up a model to produce an energy balance, and it does this well if I ignore Natural Ventilation.

It’s a well insulated high mass building placed in Europe. The windows are labelled as operable for the model producing this energy balance graphic. Some minor disparities between heat gain and loss reflected in the "Storage"term.

However, if I introduce a ventilation control object after the ideal loads into the room, then the error term represented by "Storage"become huge.

The difference in the modelling between these two situations is THIS:

versus THIS:

I have tried altering the settings on the Vent control element with no significant change.

While my past practice with EnergyPlus has been to set
Outdoor Temperature above which the windows are opened for cooling is 15C
Indoor Temperature above which windows are opened for cooling is 22C (Heating below Indoor 18C)
Indoor temperature above which windows close and air conditioning turns on is 26C.

I have tried making the Cooling on Temperature 28C, while windows close at 26C.
Outdoor Temperature below which windows close 10C.

Nothing changes.

Varied inputs to the Vent Control also do not make a significant difference (including turning off “Cross Ventilation”

Any and all comments welcomed


If I introduce Ventilation control


It looks to me like you have no cooling (or heating) loads in the second graph, which is creating unbalanced room loads and thus the high thermal storage load. Can you check if the cooling loads are non-zero (i.e with the Ladybug Deconstruct Data component)?

My intuition tells me that the cooling system is in the simulation but you just didn’t request the right type of output to get the cooling results. What _load_type_ is being used in the requested outputs? Also, maybe you should just use the “HB Annual Loads” component since this will almost always create the correct energy balance without you having to worry about whether you requested the right load type.

Hi folks

Thanks for this rapid response.

The requested outputs for this simulation are as follows:

The Cooling load looks like this:

This is a 5 zone building.

I am now deeply suspicious of the schedules… why would the cooling disappear in May?

Schedules fed into the Settings for the Programs added to each model look OK (though standard naming approach where the widget adds Sunday to the label names is counter-intuitive

More investigation to follow.


Hi @MichaelDonn Maybe you should upload your grasshopper definition file for further discussion.

Hi @MichaelDonn
Probably it has something to do with the combination of temperature setpoints for natural ventilation and for cooling. You can find out quickly if you look at the year overview of indoor air temperature.

Hi folks.

Sorry for the delays. I have been trying to put together a submission on the proposed changes to the New Zealand Building Code daylight and energy / insulation requirements, so took my eye off this particular ball.

@minggangyin - thanks for the suggestion about the definition file, but as a generic script to encourage student exploration it has a ludicrously complex input session, that I am sure would not help, hence the isolation of the issue with, I hoped, sufficient detail to allow diagnosis. I appreciate the offer.

@Erikbeeren - thanks for the suggestion. I have tried various combinations of heating, ventilation and cooling setpoints. There are some interesting features of EnergyPlus revealed here. Conventionally in New Zealand modelling we might sett the Heating set point at 18/20C; the windows open at 23C; the windows closed and cooling on at 26C; and the outdoor temperature below which the heat removal windows also do not operate as 15C, because below this outdoor temperature, we increase the heating energy use. This last point is interesting because this outdoor temperature can be set lower if the number of times E+ does its energy balance per hour is increased to 20 from 6…

Exploring these combinations does not seem to have addressed the issue.

Hello, I am a student who wants to learn about energy consumption.
I would like to ask some basic questions about the above picture.
Why is the energy of cooling negative, while other lamps and equipment are positive?

Hope someone can answer for me, thanks !

Hi @Tai,

The energy visualised in the energy balance is thermal energy and not electrical energy. All energy which increases the temperature is called positive, all energy which reduces the temperature is called negative.