[00:00:00] In the last video, we added packaged terminal heat pumps to the energy model.  In this video, we placed that system with a variable air volume system.  This is quite an interesting part of the workflow in EnergyPlus and it’ll take us into more detail on the HVAC Systems page.  So the first thing we’ll need to do here on the HVAC Systems page is to remove all of the PTHPs we added.  So I’m just going to select one of those from the drop down menu, probably from the top of the list is the best place to start and I’m just going to use the Delete button.  I’m just going to keep clicking on that until I get back to a clean slate.  So here we have the service, hot water, refrigeration, and VRF loops and that’s what a clean slate looks like.

[00:00:55] So what we’ll do in this video is add three air handling units, and those three air handling units are going to serve three different sort of areas of the building.  We’ll have a south side, an internal, and a north side air handler.  Now what we’ll make use of is the OpenStudio template system.  So click on the green button and add an HVAC system.  We’re going to add a packaged rooftop VAV with reheat.  Clicking on that adds a number of plant groups.  We have a condenser water loop, a hot water loop.  This is the air loop, which is named VAV with Reheat, and there’s also a chilled water loop.  So clicking on that template sets up all of the plant loops and each of the components that you need on each of those loops.  But what it doesn’t do is allow us to set up more than one air load.  If that’s the intention, the way to do that is to add your own air loop and extend the HVAC system in that way, so that’s what we’ll do in a moment’s time, but before we get to that point, let’s just have a quick look at the equipment on each of these loops.

[00:02:16] So on the condenser water loop, we see a cooling tower.  There’s some pipes, pumps, set point manager, and we see a chiller on the demand side.  On the hot water loop, we see a boiler here on the supply side.  There’s pump, set point manager’s pumps, and we see the hot water coils on the demand side of the loop.  Very similar set up on the chilled water loop.  Here we see the chiller on the supply side and we see the cooling coils on the demand side.  So let’s go back to the air loop.  Now this at the moment has the name VAV for variable air volume with reheat.  Now to me, that’s not a particularly helpful name.  That’s fair enough because that’s sort of straight out of the box.  So let’s rename this.  Now to get to the edit fields, hover your mouse over the Supply Equipment/Demand Equipment area of the loop.  Clicking on that will open the air loop HVAC object details and in the Name field, I’m going to name this to AHU Internal.

[00:03:33] Now my intention is to add all of the internal spaces or areas within the sort of center of the building on both level one and level two onto this air handler.  So I’m going to rename it so I can keep track of that.  Now to get the drop down menu to refresh, just give it a bit of a chance and click onto one of the other loops, and coming back to that air loop, you see it’s now renamed.  So let’s just identify the components on this loop.  We have an outdoor air system.  This is obviously where the air exits and this is where the air enters the system.  We’ve got a cooling coil, a heating coil, a fan, variable volume, a set point manager, and an air terminal single-duct VAV reheat.  And note that that has a hot water coil included in that component.  And I’ll just briefly show you, under the chain icon, the link or connection to the hot water loop for that air terminal unit.

[00:04:43] So that’s the air handling unit sort of diagram, plant loop.  And what we can do now is add the thermal zones to that AHU.  So from the My Model.  So I’m just going to do a File, Save As at this point and I’m going to say this is Video Learning.  Now My Model doesn’t seem to be showing me any zones, which is interesting.  There are zones in the model.  So going back to the HVAC Systems page and back to the air handling unit loop and to My Model.  So it just looks like it needed a bit of a refresh.  Navigating away from that page and coming back seems to have refreshed that list and the thing we’ll do now is add all of the internal zones to this air handler.

[00:05:53] In the summary report that comes along with the course, there is a list of all of the zones that we will put onto each air handling unit.  So let’s go through that list now and just add all of those zones.  First of all, the vestibule 114.  Next we have the corridor lobby printing.  When you drop these zones, it’s worth double checking that the hot water coils on the air terminals have been properly connected, and again, you just need to click on to the chain icon and check that the tick in the box there for the hot water loop is ticked.  Let’s go back to My Model, expand the thermal zones section and continue with adding internal zones.  I’m looking for the cafeteria.  Now you’ll need to zoom out so that you have enough space on the screen to drop these onto the track from Library here.  So I’ve added the cafeteria.  Next is the corridor 122.  Next is the vestibule 105.  On level two, we need to add the corridor lobby space.  And finally, Files 217.  There’s just enough room for me to drop it there.  If there wasn’t, I would’ve had to abandon that drop, zoom out a little bit, and then try again.

[00:07:46] So that takes care of all the zones on the internal AHU.  I’m going to do a File, Save at this point.  And so we’re not ready to add an empty air loop and to add all of the components that we need onto that air loop to make it a fully defined air handling unit.  So what we do is, from the green + button, select a empty air loop and Add to Model.  And now what we do is add all of the components onto the supply side of that loop.  Just to give you a refresher of what components we need to add, the strategy here is quite straightforward: we’re just going to mimic what we see on the system that we got out of the template.  So we’ve got an outdoor air system, a cooling coil, a heating coil, variable volume fan, and a set point manager.  So it’s relatively straightforward to do this.  Just have to copy what we see on that existing AHU.  Before I do that, I’m just going to rename this.  Let’s call this the AHU South Side.

[00:09:03] Now from the Library, I need a outdoor air system.  So air loop, HVAC, outdoor air system.  Drag the outside air system and I’m going to drop that onto this node on the right hand side of the supply equipment side of the loop.  And that will automatically move to the left of where I dropped it.  So there is our outdoor air system and that’s been added to the loop.  Next we’ll add a coil cooling water.  Next we add a heating coil.  Next we add a fan variable volume.  And next we add a set point manager scheduled.  This is one of the most simple set point managers that’s available and it just controls to a depth temperature.

[00:10:06] Now you’ll notice these coils are not connected to the relevant coil, so this cooling coil, we need to tick the chilled water loop and that adds these tabs bottom and top, and clicking on that tab goes to the attached loop.  So that confirms that it’s now connected to the relevant water loop.  It’s going to be the south side and I need to connect the hot water coil as well.  So let’s move to the demand side of the loop and we need to add an air terminal single-duct VAV reheat.  Air terminal single-duct VAV reheat.  And we want to add the hot water reheat.  Now once you drop that icon, we need to double check that the hot water loop is connected.  So we’re now ready to add the internal zones to this air handling unit.  So that’s how you add your own plant loop.  Relatively straightforward.  Getting a sense of which pieces of equipment you need and where they are in the list will, you know, take you a moment or two but it’s a pretty shallow learning curve and that’s something that OpenStudio does quite well I think.

[00:11:26] So what we do now is add all of the south side zones to this loop.  So from the My Model thermal zone drop down, I’m looking for the admin office.  I drop that adjacent to that air terminal unit.  Next is the reception zone.  And note when I drop that on the drag from Library area of that loop, it adds that air terminal for free.  It’s worth double checking that that is properly connected to the hot water loop, which it is.  So I’m going to go back to My Model, expand the thermal zone drop down, and I’m going to continue.  I need the vestibule 101.  I think what’s happened is I’ve misnamed vestibule 101 as 103 so I’ll add the 103 here.  Next we need conference 104.  Open office 201.  That’s actually broken into two parts.  There’s 201 and there’s 201A.  And finally, the conference room 204.  There’s just enough room for me to drop that.  So there we have all of the south side zones added to the south side air handling unit.  I’m going to save that at this point and we need to now add one more air handling unit for the north side spaces.

[00:13:34] So I add HVAC system from the green + button on the top left and I’m going to select a empty air loop.  Now I’m going to go through the steps that we just went through one more time.  Unfortunately, there’s no copy/paste.  It would be nice if I could just, say, copy the air handling unit south side and then rename it.  Unfortunately that’s not something that’s available in the software.  So I need to add a new air loop and then go through those steps again, the first one being rename it to AHU North Side.  Now I need to add all of the supply side equipment.  First of all is the outside air system.  Next is a cooling coil.  Coil cooling water.  Coil heating water.  Next is a fan variable volume.  Set point manager scheduled with the depth temp.  Right.  So pretty quick once you get the hang of it.  Let’s connect up these coils to the relevant water loops.  And now we can move to the demand side, and on the demand side, we need a single-duct VAV reheat and we’ll look for the hot water reheat icon.  Connect that to the loop and we’re ready to add the thermal zones on the north side of the building to this air handling unit.

[00:15:27] First of all, I’m looking for office 109 through 112.  Next is Files 107.  At this point, we just zoom out a little bit so you can still drop on the drag from Library area.  Meeting 106.  There’s meeting 105.  Possible that I misnamed it.  Let’s just go with meeting 105.  Office 209.  And finally the executive office.  All right, so that’s all of the zones we need to add to the AHU north side.  I’m going to do a save at this point and just refresh this drop down list so we see AHU Internal, AHU South Side, and AHU North Side.  Now straight out of the box, EnergyPlus and OpenStudio do a pretty good job of setting up these HVAC systems in a way that will work.  When I say “work,” what I mean is it’ll hold temperature in those spaces in a reasonably efficient way.  Of course, it’s not going to be perfect for every climate and every building and it’s not going to be perfect for every heating/cooling schedule that you give it.  However, it should work at this point.

[00:17:45] So what we’ll do is we’ll skip to the simulation stage and have a look at the results.  So before we run the simulation, let’s have a look at the simulation control and make sure that we’re doing all of the sizing.  So we want to do zone sizing, the system sizing, the appliance sizing.  We don’t want to run it for simulation sizing periods.  It will size it, but we don’t want to run it over those sizing periods and then extract the time series data, which is just on this here.  So that’s set up and ready to go.  We don’t need to add any additional measures at this point.  At this point, you might, for example, want to add a reporting measure on the – you could add the zone report that we’ve showed you previously.  We’ll skip that step for now and we’ll go straight to the simulation.

[00:18:35] So let’s press the Run.  At this point, you should expect to have some feedback from EnergyPlus.  The error file might contain some warnings, it might also contain some errors, and at this point, some debugging is often necessary.  Hopefully it’s not too time-consuming or too confusing what sort of debugging is necessary.  Usually the error file is pretty good at telling you what’s going on and it gives you a pretty strong hint on what to do to make it work.  But I can see now from the output that the simulation is warming up and it’s continuing the simulation.  So that indicates to me that the way that we’ve set up our HVAC system has been successful and in a couple of minutes, we’ll have some results to look at.

[00:19:29] So we see the EnergyPlus simulation has completed.  We’ve got 100% complete and it looks all green and we see there are 49 warning and zero errors.  Let’s have a quick look at the error file.  So we’ve got some warnings about schedules which don’t concern me.  We’ve got some warnings about the simple model air inputs.  Here we see a cooling coil leaving humidity greater than the entering humidity, so it just gets reset which is fine.  So nothing major in there and quite a low number of warnings.  So that’s good to go.  Let’s have a look at the results.  First of all, we’ll look at the OpenStudio results and let’s go to the Zone Conditions table.

[00:20:25] So straight away, we see a very large number of unmet heating hours through the building.  Here in the admin office, there’s 53 unmet heating hours.  In the central corridor zone, we see 235.  So that’s an excessive number of unmet heating hours and that’s something that would require further investigation.  We also see quite a high number of unmet cooling hours: cafeteria and in that lobby space.  Now to me, the first thing I would look at to troubleshoot that would be the way it would zone the building.  Now I know that the corridor 122 sits right next to the cafeteria and we also see quite a high number of unmet cooling hours for the cafeteria.  So that to me indicates that putting those two spaces on the same air handling unit may not be appropriate, or if it is, we need to allow that air handling unit to operate with a little bit more diversity.

[00:21:29] So that’s the first thing I would look at.  And that’s, to me, why it’s so important to look at the zone conditions report because if you have unmet heating hours and unmet cooling hours, it’s not really – your job’s not quite finished with the initial modeling.  You need to look in more detail at the way you’ve set things up.  So that’s the zone conditions report.  Let’s jump across to the EnergyPlus results and have a look at the HVAC sizing summary.

[00:22:01] So here we see our zone cooling table and our zone heating table.  I notice numbers haven’t changed, which is what we want from our previous runs.  We also now see the equipment sizing.  So now that we’ve got some HVAC plants and equipment in the model, EnergyPlus is giving us information about the sizes of the various pumps.  So here we see 180 kilopascal head on that variable speed pump.  Now if you were going to go into more detail, you’d want to rename that pump so that you know what pump you’re looking at there.  So you’d want to rename that, for example, to your Condensed Water Pump.  We also see information on our fans, we see the total pressure rise and rated power, air flow rates.  We see the sizes of the heating coils and we also should see sizes of cooling coils.  We see the sizes of our chiller.  So we’ve got a 70 kilowatt chiller.  We’ve got a 65 kilowatt cooling tower and a very large boiler – almost 200 kilowatts of boiler.

[00:23:20] Now what we’ll do is look at the energy end use component summary and we’re going to copy this table into our spreadsheet.  So I’m just going to Control C.  And now I’m looking for my Excel sheet and I’m just going to put that onto the VAV page here.  And that should bring across the numbers to my comparison table.  So we can see our heating number is quite a lot lower for our VAV system than it was for the packaged terminal heat pump.  And that’s partly to do with the fact that we’re using gas as opposed to electricity and so I think there’s better COP in the VAV case.  Cooling has gone down quite significantly.  Now interestingly, the interior lighting has gone up and the interior equipment has also gone up.

[00:24:18] Now EnergyPlus aggregates quite a number of different variables onto those component summaries, so you really need to dig into more detail there to understand what components have been added so that we can compare apples to apples.  We also see numbers for fans, pumps, and heat rejection.  Overall, however, the energy that’s consumed in the variable air volume HVAC option is actually lower than it is in the packaged terminal heat pump.  And that’s lower by, you know, a good 100 out of 1200, which is, you know, sort of 8%-9% improvement on the energy efficiency for that VAV setup as opposed to the packaged terminal heat pump.  And our chart here then compares those and we see the VAV wins on heating.  It also wins on cooling.  Slightly more electricity being consumed for lighting and interior equipment.  And as I said, the actual number for interior lighting should be the same between all three runs and that’s because EnergyPlus is aggregating other components onto that summary.  We see the fans is actually lower on the VAV as opposed to the PATHP and then it’s got much higher pumps and heat rejection requirements.

[00:25:42] So that completes the exercise of comparing the two HVAC options for our energy model and we have some initial information that the variable air volume system is more efficient than the packaged terminal heat pump system.  In this video, we have demonstrated how to add a variable air volume system using the detailed HVAC setup.  We did that with a template and then extended it by adding our own air loop and all of the individual pieces of equipment that we need to make that air loop run.  That brings us towards the end of the course.  In the next video, we’ll do a quick overview of all of the information that we’ve covered and wrap things up.