OpenStudio November 19, 2020
In these YouTube videos we discuss the some advanced steps that may be needed to create a building energy model using OpenStudio.
All software used for these calculations (SketchUp2017, OpenStudio, FloorSpaceJS, and EnergyPlus) are open-source and free to download.
Table of Contents:
1. OpenStudio - Create VAV System with BCL Measure
2. OpenStudio - Create Central Plant Systems
3. OpenStudio - Create Air Loops
1. OpenStudio - Create VAV System with BCL Measure
In this video, we will show how to quickly create and assign a Variable Air Volume (VAV) air handler system with chilled water and heating water loops to your building using a measure downloaded from the Building Component Library.
Transcript:
We have a fairly complex, and large, office building.
I am going to show you how to input the HVAC system for this building.
But first, I will show you a building component library (BCL) measure that works real well for inputting a common system.
It will not apply to this building. This building is older, with an older type of system.
But, I will show you the shortcut first. Just to show you some of the power of the building component library measures.
Go to your model and go to the measure tab.
Let us take a look at the building component library. We will check to see if this measure needs any updates.
This measure is under HVAC-Whole System.
It is part of the advanced energy design guide (AEDG) series of measures. We will use AEDG as a search term.
Let us look at this. The one we are going to use is this AEDG Office HVAC VAV with Chilled Water System (AedgOfficeHvacVavChw).
It looks like it is up-to-date. If it was not up-to-date, it would tell you this measure is not up-to-date.
You may download the latest version. Check it and click the download button.
But, it looks like it is up-to-date.
The other thing that I wanted to show you; On the building component library there are a whole new bunch of measures that you can download.
The measures will change your building systems and even install whole systems onto your building.
These were created by the national renewable energy laboratory (NREL).
They are based on the ASHRAE Advance Energy Design Guide recommendations.
You will see a whole bunch of different options that you can choose from.
But, we are going to choose the office building VAV system with a chilled water plant.
Go up to components and measures-apply now.
Go to HVAC and it is going to be a “whole system”. Let us select the VAV system with chilled water.
The first input is asking if we have any ceiling return air plenums.
We do have ceiling cavities, but all of our (air) returns are ducted.
So, we do not have any ceiling return plenums.
But, you can choose what space type to assign to a return air plenum.
We do have ceiling cavity plenums, but like I said, all of the returns are ducted inside that plenum.
So, we do not need to apply that now.
Here, it is asking for the cost of the system.
This check box, “apply recommended availability and ventilation schedules for air handlers”; we will leave this checked.
Click “apply measure”.
It looks like the measure was successful. we started with zero air loops or plant loops or conditioned zones.
We ended up with ten air loops, two plant loops, and sixty-nine zones that are conditioned.
I should say that this measure applies one of these vav air loops to each story.
You will have to assign stories on your building model.
You can see that I have got several stories assigned. I will set to "render by building story".
Each one of these stories was assigned an HVAC air handler system.
You can see that in this info right here, there are zero errors or warnings.
Sometimes you might get some errors or warnings that you will have to troubleshoot your model if the measure doesn't run. You might be missing key information.
It applied the measure to the model. Let us go ahead and save this as a newer version.
Okay. We can go to our air loops and you can select the air loops drop down here.
You will notice it has created all of these air loops based on the story and it has assigned those air loops to the spaces within that story.
It has created a VAV air handler with an air-to-air heat exchanger for heat recovery, a cooling water coil, a heating water coil, and a variable flow fan.
It has a set point manager based on an outdoor air reset. There are a bunch of VAV terminal boxes with no reheat and the zones of course.
You can go to the thermal zones tab and you will see that each one of these thermal zones was assigned a VAV terminal box.
The zone also has a convective hot water baseboard for for zone level heating.
We can go back to the HVAC systems tab and we should see a chilled water plant and a heating water plant that was created as well.
Yes, we have a chilled water loop here. Air cooled chiller. Variable flow pump. All the chilled water coils and the air handlers.
Likewise, the heating water loop, stame thing. Variable flow pump. Boiler. Set point controller and all of the air handler heating coils and baseboard coils.
Finally, we can go and run the simulation and see if it works.
First, we are going to go to the simulation settings tab. We will just shorten the simulation run to a single day. That way we are not sitting here forever.
If you want to speed it up even more, we can put the number of time steps per hour to just one.
Click save.
There are other advanced settings that you can do to speed up your simulation for shading and convergence and all that stuff.
But, we will just go ahead and run right now.
So...there is um...looks like there is output warnings...um...but all in all it actually completed successfully.
I did forget I had some output variables selected, so that probably increased the the post processing for the sql file.
Otherwise, it ran successfully and it actually took energy plus a minute and thirty seconds.
So, that is how you quickly assign an HVAC system to an energy model without having any systems input previously.
Next video we will describe how to manually intput a dual-duct vav system onto this building.
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2. OpenStudio - Create Central Plant Systems
In this video, we will show how to create steam and water loop systems using the district heating and cooling objects. We will also discuss fluid to fluid heat exchangers and how to connect equipment between loops.
The first task: We have to install some of the central plant loops.
This building is served by a central steam system.
We have to create a central steam system plant loop. Go to the plus button at the top.
Let us scroll down to empty plant loop. Add to model.
I should note: OpenStudio does not support steam, although EnergyPlus does.
We are going to get around that by just increasing the system operating temperature.
It will throw some errors when we run the simulation, but it should not cause a severe error.
It will just be a warning saying that we are using too hot of a temperature for the loop.
To start our loop we will install a pump. Go over to the library tab, let us input a variable speed pump.
Just drag and drop the variable speed pump over here. We can select this.
Once again, this is a steam system so we don't actually have a circulating pump.
In order to get around that we can just put the rated pump head at zero.
That way this pump will not use energy during the simulation. So, we will not have a pump energy penalty because of course the system is steam.
The rest of the stuff we can leave at auto-sized.
This this should not matter. We will do "intermittent" for this pump.
It does not matter since we are not going to have a penalty for this pump. Because this is a steam system.
Next, we want to install a district system.
You can use district heating or district cooling systems when you do not want to go through the trouble of sizing a boiler system and distribution piping and all that stuff.
The district systems mean that they have unlimited capacity. Although, you can hard size the capacity.
With auto-size it basically means they will have unlimited capacity for heating or cooling.
Now, we need to install an adiabatic pipe. Let us see. We need to go to pipe, adiabatic.
If you do have pipes that have interior or exterior heat losses, you can install those.
But, for the most part, I do not worry about those unless there are significant pipe heat losses on your system.
We will install an adiabatic bypass pipe on here.
Again, this is a steam system, so it it really should not matter.
Anytime you create a loop, and specifically if you have a constant volume system, you must have a bypass pipe or duct.
This is for when your boiler or chiller or VAV boxes are not operating.
If you have a constant volume pump or fan, it can bypass around.
If you have a variable speed pump or fan, generally, you do not need those bypasses. But, we will put that in here anyway.
Next, we want to create a setpoint manager. We will selecte a SetpointManager:Scheduled.
Scheduled hot water temperature. We should probably rename these. District steam heating.
Scheduled steam temperature. You can see that it dragged in a schedule for us called "hot water temperature".
We need to go up to the schedules tab and rename that and adjust to steam temperature.
I believe it is about 240 fahrenheit. I cannot remember what the steam pressure for that is.
We will go back to the HVAC systems tab.
Go to plant loop one. Look at the set point manager. Now the schedule's name is steam temperature.
We will call this steam loop. We will just leave this as water. We do not want to make things worse on the error outputs.
This maximum loop temperature: 240 fahrenheit.
We can leave the rest of this stuff as default. This building has a steam to hot water heat exchanger on it.
We will put the heat exchanger on the demand side of this loop.
Go down to heat exchanger. Were is that fluid-to-fluid...we can put that in here.
Same thing with the bypass pipe. Now we have our fluid to fluid heat exchanger.
We can call this "steam to water heat exchanger".
Most of the stuff we can leave as auto sized unless you know specifically what size it is.
For the model type, again, you can choose what type of heat exchanger you have. We will just leave it as ideal for now.
Like I said in previous videos, if you want to find out more about these components you can go into the EnergyPlus input output reference.
You can look up HeatExchanger:FluidToFluid and read all about it. Type in HeatExchanger:FluidToFluid and then search for the item in the EnergyPlus input output reference.
You can read about all of the inputs and outputs for this particular object.
We can leave these as auto sized for control type.
We will choose "heating set point modulated" because we are going to be modulating the steam to control our heating water temperature.
This is the temperature difference to activate the heat exchanger.
It is the temperature difference across the heat exchanger that allows the heat exchanger to operate.
Let us see...loop to loop. We will just leave this as "loop to loop".
All the rest of the stuff we can leave as default sizing factor of one. The maximum temperature we will input 250°F.
One more thing. Going back to our steam loop. I forgot to mention.
If you do have a...well this is a steam loop, so it is not really applicable.
But, if you do have a common pipe system, you can select common pipe down here.
In this case you have to place a pump right here and that is how you would create a primary-secondary pumping system with a common pipe.
So, that is how you create the steam loop.
Next, we need to create the water loop. We will go up to the plus button at the top.
Scroll down to empty plant loop. Add to model.
Next, go to the library. We will just drag in this adiabatic pipe here.
We want to put in a variable speed pump...variable speed.
I will call this heating water pump. I can leave these as auto-sized.
I can not remember. I think for this particular project...I do not think I had the information for this pump.
We will just leave this as default.
If you have the specifics on the pump performance, you can enter those here.
Pump control type: we are going to set this as intermittent. It will only run as needed.
If you have it set as continuous, it will run all the time. So, it is important to set that as intermittent.
If you have the pump located in some zone where it is losing heat to the zone you can select here.
We will put this in the basement thermal zone.
Finally, the design minimum flow rate fraction.
This is also applicable if you do not select the minimum flow rate for the pump. The minimum stable flow rate for the pump.
You can also just put in a fraction here and I think typically we do not let the pumps run below 30 percent.
We will just put in 30% here.
Next, we need to drop in our heat exchanger. Go to my model tab. Heat exchanger fluid to fluid.
Drag this from there. You can see that this is connected and it is automatically connected to the previous loop.
You can see it has these connectors right here. If you click the connector, it will take us to our district steam loop right here.
Likewise, the heat exchanger is down on the demand side of the steam loop.
If we click this connector, it will take us to the supply side of our heating water loop. We will select the plant loop.
We are going to call this "heating water loop". Fluid type is
water. Maximum loop temperature here is 180°F.
I beleive I had that information...oh...let us see...maybe it was 120°F.
Anyway we will just leave that as 180°F for now.
Minimum loop temperature...and the rest of this stuff we can leave as a default.
Load distribution scheme. If you do have multiple sources on your loop, you might look at the load distribution scheme and how those sources are being staged on and off.
We will just leave this as "optimal" for now. Optimal just stages it based on the most efficient part load ratio for each piece of equipment.
If you do have a primary-secondary system, you would select this. You would either have a common pipe or a two-way common pipe.
You would have to install the the secondary loop pump on the demand side down here. Loop type is heating. 180°F.
We will just leave the rest as it is. Then we need to go back to library and install a setpoint manager.
We will use a scheduled set point manager again. Scheduled hot water temperature.
In this case it is automatically called hot water temperature. I don't really like that name.
We should call it "heating water temperature" not "hot water temperature".
Heating water temperature. I believe we had that set for 180°F for the loop temperature.
You can just hover over it type in the temperature that you want.
Let us go back to the HVAC tab.
The heating water loop. We have our setpoint manager installed. Now, the loop is ready to take on any demand side equipment.
And, that is how you input both a district steam system and a heat exchanger and a heating water loop.
Next, we can go up to the plus sign again.
We will install our district cooling system. Go to empty plant loop, add to model. Scroll down.
Let us just do a variable speed pump, adiabatic pipe, district cooling.
Do auto sized on this. We will leave the pump head as normal. We will name this cooling water plant loop.
I can leave the rest of this as default. Let us see. Design loop exit temperature was 45°F.
We can just set this to maybe 80°F. It does not really matter. The rest of this stuff, we can leave as normal.
Go to the library tab. We need to put a set point manager. Select scheduled setpoint manager: scheduled chilled water temperature.
Go back to the schedules. Chilled water temperature. Make sure that this is set for 45°F.
Go back to the loop.
That is how you install a district chilled water system. It is now ready to take on any demand side equipment.
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3. OpenStudio - Create Air Loops
In this video, we discuss how to create custom air loops for heating, ventilation, and air conditioning systems. We will create a simple heat-vent system and a dual-duct system and connect them to our central plant systems.
The next task is to install a heat and vent system for the basement area.
This basement area also has baseboard hot water heaters in the zones.
Go to the thermal zones tab.
Fortunately for us, the basement is considered a whole single thermal zone.
We only have to worry about this one thermal zone. The basement.
Go to the library tab. We will search for baseboard convective water.
Drag that into our zone equipment. Now the basement has baseboard hot water heaters as its primary heating source.
Now, go up to this chain link icon up here on the edit tab. Click it.
Select heating water loop as the heating water source for these baseboard convectors.
The rest of this stuff is customizable.
Rated average water temperature maybe 160°F (71.1°C).
We will just leave the rest of this stuff as default and auto sized.
If you do know the specifics, you can change those items there.
Let us go to the HVAC systems tab. Go to the plus at the top.
We will add a new...well we can do this warm air gas-fired furnace.
We will add this to the model. It comes in as all prepared for us.
However, we are not going to use a gas furnace for heating.
We are going to use a hot water heating coil. So, we will delete that.
Go to the library tab. We need to search for coil heating water.
Hot water heating coil. We will drop this in here.
We can select the heating water coil. We will just call this HV for heat and vent.
Again, for the heating water coil, you go up to the the chain link button on the edit tab. Click it.
We need to link this heating water coil to our heating water loop.
Go back to the edit properties tab. We can leave all the rest of this stuff at its default values.
I recall this system was a constant volume system.
We will just leave this as a constant volume fan.
We will just rename all these things.
This is going to be a HV. I will just call it HV-1.
The airflow rate for this was 3,000 cfm (5,100 m3/h).
Design outdoor air flow rate. I do not think I have that information.
We will just leave all the rest of this as a default for now.
Design supply air temperature was 105°F (40.6°C).
Well let us see. This is for sizing. We probably want to size the coil for 100% outdoor air in heating and cooling.
That would be the sizing of the system. We can just leave all the rest of this stuff as default for now.
You will note that it already has a air terminal (constant volume diffuser) on the demand side.
If you know what size any of this stuff is, you can always go to the edit tab and edit those.
We are just going to assign the zones. We will click the splitter right here.
We only have one zone, so we are going to click the basement (zone). Add that basement zone to the HV system.
Then, as discussed before, this is a constant volume system, so it is good to have a bypass duct...
oh...let us see...
I am not sure if a bypass duct is necessary...but...nope
It will not let us do that. Yeah...that would be only for...
I believe that would be only for VAV systems.
There might be some additional settings under your air loop system for bypass on constant volume systems.
That is it for our heat vent system.
Now, we need to add the dual duct air handlers.
Go up to the plus button. This time we will scroll down to a dual duct air loop. Click "add to model".
We will call this AHU1.
We can leave this auto sized for now. The central heating maximum system airflow ratio.
Let us see...I think for this system it was 50%.
What else.
Design supply air temperature. This was 105°F (40.6°C). Yep.
The rest of this stuff we can leave as default.
Click save.
Next we need to install an outdoor air system. Air loop hvac outdoor air system.
Let us see, I have a bunch of stuff in here from a library connection.
Let us go back to default libraries and we will just remove this. Click OK.
That way we do not have that cluttering up our list.
Let us go back to the air loop.
We need to add an air loop hvac outdoor air system.
Drop that there...call it AHU1 Outdoor Air System.
We also need to add in a an air-to-air heat exchanger.
Air-to-air. Here we go. You can choose what type of heat exchanger.
I believe we have an energy recovery wheel on this system.
We will just drop this in between here. One energy recovery heat exchanger.
We also have a fan. An exhaust fan. Powered exhaust fan; variable speed.
Drop this in here.
Let us see. I am trying to remember if this fan had inlet guide vanes.
We will get into those details later.
Let us go to outdoor air. This was 17,500 cfm (29,730 m3/h).
Maximum flow rate was 150,000 (254,850 m3/h).
Ok,so minimum was 17,500 maximum was 150,000.
Economizer control type: fixed dry bulb.
That should be it for the outside air system.
Next we need to go to our heat exchanger.
I think I just left the performance criteria on the default values for this.
Except for the flow rate.
Those default values were pretty close to what the performance was on the heat exchanger.
Let us see, we had a rotary heat exchanger.
The frost control strategy was exhaust only.
And, lockout for economizer: yes. This basically locks out the heat wheel if the system is calling for economizer (free cooling).
Let us go to our powered exhaust.
Fan total efficiency was 80%. Pressure rise: 7"W.C. (1,740 Pa).
Maximum flow rate was 60,000 cfm (101,940 m3/h)...that does not seem right...
Our maximum flow rate was...oh...this was 60,000 cfm.
Yeah. My mistake. Maximum flow rate for the outdoor air system should be also be 60,000.
It is a hundred percent outdoor air system.
Fan power minimum flow rate input method: we will select fraction for this.
If we select fraction, we have to put in a minimum flow fraction on here.
Minimum flow for the system I believe is 33%.
If you select fixed flow rate instead, you would have to put in a minimum air flow rate value in this category.
Fan power coefficients: I believe these were left as a default.
They fit pretty well because this was a single fan.
If you have dual fans or parallel fans these fan power coefficients will change.
I will have to go into more detailed analysis of those in a different video.
Next, we need to install our heating coil.
Let us look for coil, heating, water. We will drop our heating water coil in here.
This is AHU1 Pre-Heat Hot Water Heating Coil.
Again, we have to go to the chain link button to connect it to our heating water loop.
I think I just left all this stuff as auto sized for now.
We can just leave all of this stuff as auto sized.
Rated inlet...make sure to change this...this was 180.
I believe that is what our hot water system was.
Rated outlet air temperature. This is just a preheat coil, so we will just set it for 55°F (12.8°C).
I do have a rated capacity. In the interest of time we will just skip over some of these. Just auto size most of the stuff.
If you do have these values, it is good to put them in there.
Next, we want to install a setpoint manager.
This is a mixed air or a preheat deck. A mixed air deck set point temperature.
We will go to setpoint manager scheduled.
We can just do scheduled deck temperature. It doesn't really matter. We are going to rename this anyway.
Scheduled mixed air deck temperature.
Now, go to schedules again. Edit this to call it mixed air deck temperature.
We will set this for 55°F (12.8°C). Go back to the air loop air handler.
Next, we need to install a fan. I do not know why this is always collapsing. It is always too small.
Fan, variable volume. We will just stick that here and call this AHU1 supply fan variable speed.
Again, you can you can edit all of these values.
Like I said, if you have parallel fans, your fan power coefficients might be slightly different.
Now, we need to install a hot deck heating water coil.
We will just leave all of these things as default values for now.
Rated outlet air; I think this was 105°F (40.6°C) for outlet air temperature.
We need to to do a set point manager. I believe this one had an outdoor air reset setpoint manager.
We will go down to setpoint manager: outdoor air reset.
Drag this in here. This was temperature. Outdoor low temperature.
The set point at the low temperature was 105°F(40.6°C). The maximum. The low temperature of outdoor air was 50°F(10°C).
So, when it gets down to 50°F it is supplying air at a maximum of 105 degrees fahrenheit.
If the outdoor air temperature gets up to...
Let us see...if the outdoor air temperature gets up to 65°F(18.3°C) it is going to be supplying a minimum of 70°F(21.1°C) air.
This one is very simple. If you do have a more complex system, where you are changing these values based on a schedule, you can add in that information there.
We do not have that.
Let us go to a coil: cooling coil, cooling water.
Again, drop this in here to the cold deck.
Click on the link. This time we are going to select the chilled water loop as the connection.
AHU1 chilled water coil. These can all be customized based on what you have for a chilled water coil performance.
We need to go to setpoint manager; outdoor air reset.
For this one, the set point for a low temperature resets up to 65°F(18.3°C) at a low oustide air temperature of 50°F(10°C).
The lowest cold deck temperature will be 55°F(12.8°C) supply air when the outdoor air temperature gets up to 65°F(18.3°C) or greater.
That is it for the supply side of the system.
Now, we need to go to our library and drop in a dual duct terminal box.
What are these called...yeah...vav dual duct...where were those...air terminal.
Here we go. Air terminal, dual duct, vav. We will drop this in here.
You can see that it automatically connects the cold deck duct and the hot deck duct to that dual duct terminal unit.
If you have a zone minimum airflow fraction of something other than 30% you can adjust those here.
This ensures a zone minimum ventilation air flow to the zone regardless of whether there is a demand for heating or cooling.
If you put this to zero, if there is no heating or cooling demand at the zone, it will shut that vav box down entirely.
Normally, you do not want to do that. You want to maintain some minimum level of ventilation airflow to the space.
The next task is to assign our zones.
It is plenum 2-3, 3-4, 4-5, 5-6,...oops...yeah that is not working is it.
We should be able to drag these plenum zones into...it should automatically populate with terminal boxes.
But, we can go to our library and go to thermal zones and drag those in here.
2-3NTZ...so we can drag that in here.
Then, if we select the splitter, it should populate with terminal boxes. There it goes.
Now we have terminal boxes on there. 4-5, 5-6, 6-7, 7-8, 8-9 and a whole bunch of zones...
Okay. Now you can see that we have our all of our zones assigned.
If you want to zoom out with these you can use these magnifying glasses up here.
We will just click on the magnifying glass to zoom out.
You can see that our system has a whole lot of zones.
We can zoom in if you want to see better.
That is how you install a dual duct vav air handler.
And it looks like we forgot to link this to our heating water system.
You can tell because it doesn't have the connectors on the coil.
So, let us go up to the chain link and connect it to our heating water loop.
Again, if you can click these connectors it will take you to that loop.
You can see that the heating water loop all of a sudden has a lot of coils attached to it.
You can see that this is AHU1 coil, baseboard heater, and the heat vent unit.
You can click these to take you back to the air handling equipment.
If you look, we can go to the thermal zones tab.
You can see that now we have that equipment assigned to our thermal zones.
So, that is how you install HVAC systems with heating and cooling coils.
Coils with heating water or chilled water systems.
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