Thermal Zones in OpenStudio

[00:00:00] In the last video, we looked at spaces.  In this video, we’re going to walk through the Zones page.  So what do we do here on the Zones page?  There are two important things I want to show you.  First of all is the cooling thermostat schedule and heating thermostat schedule.  And secondly, there is the turning on ideal air loads.  Those are the two things we’re going to do on this page, but before we get to that, I just want to briefly touch on the important distinction between spaces and zones.  So up until this point in the course, the concept that we’ve been talking about is most spaces and you may even have caught my using the word “space” and “zone” interchangeably.  If that has happened, it’s forgivable because spaces and zones are often talked about in the same way, especially in the context of OpenStudio.

[00:01:02] So what is a space?  Now a space is an OpenStudio concept and it’s introduced as a convenience to help us to apply schedules, constructions, internal loads, ventilation conditions.  A space is a container that describes the way a region in the building is used.  Now a zone is quite different.  A zone is a much more fundamental concept.  It’s fundamental to a mechanical engineer.  A mechanical engineer will think of a zone as a region in the building that is controlled to a certain temperature.  That region of the building is assumed to be relatively homogenous and that anything inside that area can be treated as basically at the same temperature, at the same condition.  Now thermal zone is also very fundamental to the EnergyPlus calculations.  The thermal zone is the basis for the heat transfer calculations.

[00:02:07] So where in our energy model we might have a number of spaces inside one zone, for example, you might have a closed office and an open office space, so you’ve got two spaces next to each other and those two spaces might be inside one zone and that one zone might have a number of air diffusers and all of those air diffusers are delivering air at the same temperature.  So that kind of wraps up nicely the whole concept of what the similarity and different between spaces and zones it.

[00:02:41] So as I said, there are two important things for us to do here on the Thermal Zones page.  First of all, we need to apply a cooling thermostat schedule.  So what is this thing that we’re talking about?  It’s basically a target temperature for when the HVAC system determines that the zone needs to be cooled.  So what we’re dropping into this column of the grid view is a target temperature.  Now it’s given a name called Thermostat Schedule and it takes the form of a schedule.  So to me, it’s a little bit of a confusing sort of container for what is quite a straightforward idea and that is we need to go through either the Library or My Model – probably My Model is best – and under the Schedule Rule Sets, we’re looking for the medium office cooling set point.  I’m going to drop that into the drop zone on that column and now I’m going to make use of the Apply to Selected sort of helpers here in the grid view.  So selecting all, I’m going to tick in all of those rows and I’m going to do that again where I drop the medium on this cooling set point in row number two and now I can apply to selected and that applies that cooling thermostat schedule to all of the zones.  I’m going to do likewise with the heating set point.

[00:04:17] So we’ve now got a cooling set point target temperature and a heating set point, which is again a target temperature.  But the most astute observers will realize that what I’ve done here is applied a cooling thermostat schedule to all the zones.  So that will include zones that I don’t really want to be conditioned, for example, the stairs.  So here we’ve got a stair.  Now we don’t really want to be controlling the temperature in those stair rooms.  In the vestibules, I do.  The other ones are restrooms.  I don’t really want to sort of control the restrooms to a certain temperature.  So to deal with that, once we get onto the ideal air loads, we’re going to untick ideal air loads for those spaces.  And that’ll be sufficient because if we don’t have ideal air loads on in the stairwell, then it’s not going to try to hold the temperature in that room, and that’s true even though it’s got a cooling and heating set point.

[00:05:22] So what we do next is to apply ideal air loads to all of the spaces and zones in the building that we want to maintain temperature.  Now unfortunately, the way that the grid view works in this current version of OpenStudio, you can’t apply to selected.  So there’s no Apply to Selected button up here.  So unfortunately, I would go through and tick each of these boxes.  It’s not too bad for 30 models but if I have 100 or 200 zones, personally I would look for a measure that could do this and I’m confident that there is a measure that could do exactly that in the Building Component Library.

[00:06:05] So without looking, I’m just going to tick all these boxes and then I’m going to come back and untick the stairs and restroom.  I should mention that you can also do this at the SketchUp stage.  When you’re in SketchUp, you can select all of the zones or spaces in the model and apply ideal air loads to all of them and that’s a bit more of an interactive and quick way you could do it in the SketchUp plugin.  So I’m going to untick these stairs.  Vestibules I do want conditioned and the restrooms I don’t want to be conditioned.

[00:06:53] So I like to add the idea air loads, run the model, check the envelope, schedules, constructions, all of that sort of basic level of detail and critically, we’re checking that the building can hold temperature.  Because if it doesn’t hold temperature with an ideal air system, then it’s certainly not going to hold it with a detailed air track system and it’s much quicker to debug the energy model when you’ve got that quick ideal air load system applied than it is to debug it when you’ve got a very complicated air track system.  So that’s the reason we add ideal air loads.  In the next video, we’re going to go on to run our first simulation.