17 - Start Create and Define Multi-zone Airside Systems

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´╗┐Hi everyone. This is Harshul Singhal, again. For our last class we talked about the zone equipment. We talked about different kinds of systems, like package terminal heat pumps,PTACS, the zone part of fan coil unit systems, and a lot of other information, okay. For this class, for today,we'll talk about air loops. There's a lot of information on HVAC that we need to provide and that's one of the reasons why we decided to segregate this HVAC component into multiple classes. We don't want to give you more information on plant loops today, because, again, you will get confused. And, that's why we wanted to, we wanted you to understand the difference between air loops and plant loops, okay. Let's move forward. I'm going to create some air loops today, they're different ways to do that.

And, as I mentioned you earlier, in past, whenever you want to start working on any energy modeling, you have to bring all the information with you on your table. You can't start working on HVAC systems without having the MEP layouts with you. And, a lot of times you need to simplify those complex systems. For example,let's just assume that you are working on a high-rise office building and you have very complicated systems, but just for energy modeling, you want to simplify the complex system so that you can create it easily, here. And, for those kinds of things, or for those kinds of steps, you need to simplify everything in advance. You can't just like, sit with your MEP layouts and start working on energy modeling software. You have to do all that kind of work in advance, so that when you are on an energy modeling software, things are easier for you, okay. Again, very important. Try to simplify your complex systems, okay.

Next thing is the terminology in HVAC system components, or HVAC layout. There are different ways to start. The first way is to generate an HVAC system using the component, using the OpenStudio measures. We will talk more about those OpenStudio measures in our next class, when we are done with plant loops. But, for this class, we'll talk about two methods. First one is to create an HVAC system using the HVAC system template method, I'll explain to you later. But, the most, the default method is using the air loop method. You basically bring an empty air loop in your energy model. And then, I start putting all the components in it. For example, if you click on this plus sign here, on this HVAC system tab, go to this top left side of your screen,click on this plus sign. The initial systems are based on ASHRAE 90.1 appendix G. Something like, system 1, which is, packaged rooftop unit, or PTAC, rooftop heat pumps, then package DX rooftop VAV with reheat. If you keep scrolling, then you have VAV with parallel fan power box with reheat, then system 7 is VAV with reheat, again.

And then, you have these empty loops. Why they have provided you empty loops, here? Well, in case you want to start everything from scratch, you can easily do it, here. For now I'm going to click on this empty air loop. Click on this, add to model, and it will bring in a loop for you. You can see this is totally empty, there is no DX coil, or fan, or any diffusers, or anything. Your two sides of this loop. First one is supply keep inside. Where you provide something like, fans, or heating, or cooling coil, outdoor air terminal, and so on. And, in demand side, you can provide something like, diffusers, maybe VAV boxes, or different other kinds of things, okay. Again, like, you can see this empty loop, here. If you click on these dots here, the tiny circles, we call them nodes, you basically drop down all the components on these nodes. We'll talk more on these nodes later. Then you have these splitters. Basically, there is a pipe coming. Let's assume that there is a pipe coming here, or duct coming, and then it divides that supply into two ducts, or two diffusers.

When you see such kinds of things, it means that you have some kind of splitting happening, here. Then you have a mixer, again. Then these two ducts, or pipes, they got mixed into one pipe, or they got, yeah, so.And then, you have something like, bypass pipe. I will show you how you create bypass pipes later. For now let's move on to some complex system. Let's say, maybe a VAV with reheat pipe, a VAV with reheat boxer system. Again, as I mentioned, we are going to start with an empty loop. First thing that you want to do is click on this dotted line, here, in the center. And then, you can size your system. You can rename it. Let's assume the name as VAV with reheat, VAVR - 1, that's the name of my system. Then you can hard size it, or auto size it. It's totally up to you, you know the deal.

And, you have mixer name, splitter name. I won't suggest you to touch these things, for now, in case you are a new user. Then you can provide a return air bypass flow temperature set point schedule, again, for a system like VAV with reheat. Unless you are provided with this information, I won't suggest you to play around with these things. And, in case you need to learn more about them, you can just go to EnergyPlus documentation, and search for these terms. You know how that input and output section works in EnergyPlus documentation. Then, in case you need to size the system, you can do it, here. In case you want to size the system, just on sensible loads, you can select the sensible, which is the default option, here. In case it's the dedicated outdoor air system, then it's going to be a ventilation requirement. We'll talk about the OAS systems later. And, what else, in case you need to change the outdoor air flow rate, the default one is auto size, you can hard size it. Just click on this hard size option, and provide some CFM's. Then you can change the minimum system airflow ratio, which is default by 0.3 as for ASHRAE 90.1.

Then preheat design temperature, preheat design humidity ratio, pre-cool design temperature. There's some default values already. Most of the time, you'll find yourself fine using these values, but in case your mechanical layouts tell you some other values, don't hesitate to change them,okay.But, again, don't make any changes without knowing about them,okay. In case you don't know what's going to be pre-cool design temperature for your project, look more into it.

Either talk to your mechanical engineers, read more about it, and then make changes,okay.Then, in case you have dedicated outdoor air system, then,that's when you need 100% outdoor air in cooling and heating. But, in case you are sizing the system, let's say, VAV reheat air loop for sensible load, then most probably you won't need 100% outdoor air in cooling as well as heating, all right. You can change it to no. Make sure that you change it for each and everyair loop of yours. At least check them once. And, there's some other properties, like, central cooling design, supply humidity ratio, and heating humid air, humidity ratio. A lot of other properties for sizing the system, okay. Again, most of the time, as I mentioned, you will find these values proper for your project. But, in case you have any changes, please do so, okay. Please make some changes as for your mechanical layouts, all right.

Once you are done with this dotted line, you want to start something with supply equipment. You need to go to your library, and look for something like,let's say, first thing, let's say, fans. Again,it's a long list of all the equipment, but we just need to understand how this layout works. You need to, I mean,you'll get used to it after a certain amount of time. For example, I know everything is alphabetical. In case I need to look for fans, I need to scroll down to F. And then, I can, I have like, a lot of options for constant volume fan as well as variable volume fan.I'm going to drag a variable speed fan, and drop it at this node here, okay. You can see that my fan is here, now. I can click on it now, or I can bring some other components. I like to bring all the components first and then I read them.

Next thing that I need to bring, something like,air loops HVAC outdoor air system. You definitely want to bring in outdoor air system, here. Drag and drop here, again. Again, you can click on it. You can make different changes.I'm going to wait for now. The next thing that I need to bring is,let's say, DX coil, DX cooling coil, as well as heating coil. That's the easiest heating and cooling component that you can bring in air loop. Scroll down to C, that's where you find these cooling and heating coils, here. I want a single speed DX cooling, for now. Let's just assume that's the simplest system that we have for our project. Drag and drop, again. And then, look for heating coil. I can bring heating coil here,heating DX single speed, that can work. And then, the most important thing for any air loop is the set point managers. You have to bring a set point manager. If you scroll down, you will see those set point managers. I would bring a set point manager schedule, here.I'm going to drag and drop this scheduled deck temperature.

Very important. What does set point manager do to yourair loop? Well, if I click on this set point manager, the control variable is temperature, the schedule for that temperature is deck temperature. If I go back to my schedules, and go to schedule tab, and look for the deck temperature. It is a temperature schedule that is automatically created by OpenStudio for you. If you click on before, the value is 55 degree Fahrenheit, okay. Same for design day profiles. If you go back to HVAC system, and, yeah, it takes some time when you jump from one tab to another tab. And, from this scroll down menu, if you look for this VAV R-1 system that we created just now. What it tells you here, like, this schedule instructs yourair loop that, hey, whatever you do, like, you have to provide the supply air ata temperature of 55 degree Fahrenheit. Whether it's heating or cooling, this set point manager will always control the temperature of supplier from this supply side of your air loops, okay. During summers, if you supply an air volume of 55 degree Fahrenheit temperature, that's good enough to cool down your space.

But, what happens in winters, you're supplying an air volume of 55 degree Fahrenheit. How can you heat up your spaces to,let's say,70 degree Fahrenheit. Well, I mentioned to you earlier, this is a VAV with reheat system. You will have reheat coils at your zone diffusers, okay. And,we create those diffusers later. Again, the temperature, the supply air temperature is 55 during winters, as well. And, those diffusers, the reheat diffusers, will heat up the that supply air to, let's say, 90 or 100 degree Fahrenheit, okay. Again,that's stored here to your design. I mean,don't quote me on those, these, what do you say, inputs that I'm trying to provide you here, okay. The next thing that I need to do is, I need to provide the diffusers, or,let's say reheat boxes.Again, in this library option, if I scroll down to,let's say, these a terminal duct section. You can see, I have some air terminal single duct series VAV reheat boxes, and I want an electric reheat box for now. If I scroll down here, and drop it in this this demand side, you can see I can, I have a diffuser here now, okay. I can click on this, and it has a lot of properties to edit. We will talk about these properties later.

And now, you need to create, or you need to assign these diffusers to your thermal zones. Before that,let's just edit the properties of all these components, here. First one is fan. Click on the fan. And, now you can see on the right hand side, you can edit the properties of this fan. You can rename it if you want. You can control the air supply from your air loops by providing a schedule, here. You can provide a schedule, let's say, from 9:00 a.m. to 5:00 p.m., you have a supply of air from this loop. But, from 5 p.m. to, let's say, early morning 9:00 a.m., there is no supply. You can either create on/off schedule. You provide, I mean, we have created an on-off schedule in last class. You know how it works. I can show you again. It should be some, one scheduledhere, somewhere, let me just see if I have an on/off schedule. If not, we can just create something real quick. Click on plus sign, go to schedule type on/off,hit apply. Rename it to,let's say, VAV R-1 fan schedule. I always like to really rename these schedule components properly, so that I know what am I doing.

And, from, let's say, from 8 a.m. to 4 p.m., you have supply. And, for the rest of the time, there is no air supply from you. Design air, I'm sorry, I'm sorry, we don't have it. Let's say, any supply air from 5 p.m. to early morning, 8 a.m., okay. Let's assume this. If you go to these, if you click on this HVAC system tab and go to your air loops, click on this fan. You can always change the schedule, here.I'm going to provide the new schedule to this fan. What I have created just now. That's my schedule here. Now, what is happening here, I have the supply air coming out of my supply side of air loops only from 8 a.m. to 4 p.m. Rest of the time, my system doesn't work at all,okay.Now, you can change the fan efficiency. Let's say if you have ECM fans you can change to 85%. You can change the pressurize. Again, you need to do those calculations for pressurized as per ASHRAE 90.1 compliance. You can find those calculations in appendix G.

Get familiar with that, with those calculations, if you are not. You can provide a maximum flow rate. Again, like this, the auto size, for now. Like most of the properties that you see in these components are auto sized, you need to hard size them, as per your mechanical layouts.
And, the next thing is, what kind of input method that you need. Do you want a fraction like, hey,let's just assume that you have a fractional flow rate of 30%, or you can change it, here. But, you can see the input method is fixed flow rate. If you make any changes in this fraction section, it won't work. You need to make any changes in this fan power minimum air flow rate. If I give it a property of,let's say, 200 CFM, the minimum CFM that you will get from this loop is going to be 200 CFM always, okay. It won't go to 0. Then you can change the motor efficiency. And then, you can change the efficiency curve for your fan. These are the default curves. But, in case you want to look more about the other kind of curves, or other kind of fans, you can go to PNNL 25130 document, that I mentioned to you in my previous class, click on it. And, you can read more about different kinds of curves for fans, chillers, and boilers, and other components, okay. I'm going to save this for now, and move to the next tab, or next component, which is this outdoor air system.

Again, this is, as you can seehere, this is the, these are the arrows that may, that explain to you, hey, this is this supply for outdoor air, and this is the exit of those,of that air, or return air, okay. You can, again, change the properties of this controller, here. You can hard size your outdoor air flow rate. You can hard size the maximum outdoor air flow rate. In case your economizer, you need to make all those changes in this outdoor air system component. Let's say you have an economizer, let's say, maybe fixed dry bulb.Your other options, you can see here. And then, you can change the economizer control action time. That default one is modulate flow, which is all right.You have another option, which is minimum flow with bypass. Then you can change the economizer maximum limit dry-bulb temperature.Let's say, as per ASHRAE, my value is 70 degree for this, change it. And then, other values like economizer maximum limited enthalpy if you check for this option like differential enthalpy. Then that's when you need to provide that property.

If you want to lock out your economizer, you can do it. If you, like,let's say, if you want to lock out with heating or with compressor, you can check these options, here. What else do you have?Then you have the minimum outdoor air schedule name, here. When you want to supply the outdoor air with a schedule, if yes, provide a new schedule, here. Then minimum fraction of outdoor air schedule, and so on, okay. A lot of times I don't even use these schedules. I mean, but for specific projects, we have to, okay. Make sure that you check all those properties,there.
Next one is, DX single speed coil. Again, you need to make a lot of changes, here. Is your coil auto sized, or do you have some kind of sizing, or BTU per hour values for this cooling coil? If yes,provide some properties. Otherwise, auto size is fine for now. Do you have any sensible heat ratio? I have this auto size option for now. COP, which is coefficient of performance. Again, as you know, this is the input that you need to provide in case you have some efficient systems.Let's say my COP is 4.4 for my DX single speed cooling coil, then you can hard size the air flow rate.

Then, here are some curves. Something like, cooling, total cooling capacity function of temperature curve, function of flow fraction curve, energy input ratio function of temperature curve. Again, these are some default values that are provided here, with OpenStudio. They are reasonable enough. But, in case you need to change these properties, or you can either talk to your manufacturers, or you can go to this PNNL document to look for more stuff, okay. I'm going to save this model, again, before I move to the next component. The next one is DX heating coil. Again, very close to what cooling coil component is. Hard sizing, COP,air flow rate, rated supply fan power per volume flow rate, and different kind of curves. Function of temperature, function of flow fraction, energy input ratio, function of temperature, and so on, okay, all right. Let's move to the next one, which is, set point schedule, set point manager. Again, this is the simplest set point manager that I have used, which justtalked about a constant value of supply air temperature from the air loop, okay. But, there are different kinds of set point managers.

Let's say if you want to bring something like, you know, they're different kind of options. Seriously, there are so many of them. For example,if you want to bring an outdoor air reset temperature, you can always do that. Generally we use those outdoor air reset temperatures for chillers as well as for boilers. You can have dual set point temperature set. For example, if I bring it here, let me just do it again. And, now you can see the color changed to gray. You can change the control variable to temperature. I mean, there is only one option. Then you can change the high setpoint schedule name, as well as the low set point schedule name. You can vary the supply air temperature between these two values. Again, this is one of the complicated setpoint manager. In case you have this kind of set point for your system, please go ahead and change these properties. But, for now I'm just going to use the easiest one, which is set point manager schedule. Again, deck temperature 1. And, it controls the supply air temperature to 55 degree Fahrenheit all year long, it's the constant value, okay. Which I find very reasonable, okay.

I think we are done with supply side, for now. We can move to the next one, which is demand side. Again, we have this VAV weather reheat box, which is electrical heat. You can rename it if you want. You can hard size it. A lot of times you will see those hard sizing values in your mechanical layouts. Do you want to have a constant zone minimum air flowinput method? If not,you can change it to either fixed flow rate or scheduled. For nowit's constant, which is 30%. In case you change this input method with schedule, you need to provide a schedule here, in this minimum air flow fraction schedule name section. Do you have any hard size value for maximum hot water or a steam flow rate? Well, it shouldn't be, because it's electric reheat box.

Then, what else? Like, if you want to control for outdoor air, if yes, change it to yes. Then you
have other properties, like efficiency. If it's an electric reheat box efficiency of 100%, seemsreasonable. But, a lot of times people use it as like, 98%. People still assume that there is a 1 or 2% loss somewhere here and there. And, in case you want to provide a schedule, you want to make sure when you want to make this system available. Please provide a schedule, here. Like, either an on/off schedule. I think on/off schedule works best for these kind of schedules, okay. In case you have a capacity, please provide it here, for electric reheat coil, okay. We are in electrical heat coil section. I should have mentioned it earlier, okay. Now, in case you just want to go ahead and connect the thermal zones to demand-side, what you need to do is, either click on the mixer side or a splitter side, here. And then, you can select the thermal zones from this right hand side list. Let's assume that you want to connect this air loop only with floor 1. Click select only floor 1 thermal zones. I can see the rename, I have renamed them as thermal zone floor 1 underscore conference room 3, blah, blah, blah.

I know now, like, which, what thermal zones that I need to connect to this, to this air loop, okay. Select all of them. And, you can see,you need not to provide the VAV reheat boxes again and again. If you just do it once, you can see OpenStudio automatically provides all those thermal or these a terminal boxes automatically for you, okay. Let's just do it real quick. And, that's it, okay.

Once you are done with this, you can either run this simulation. If you run the simulation now you will get the errors, because these, I mean, if you,I'm sorry. I should have made it more clear. You can get errors, only if you need to have a plant loop here, connected to your heating and cooling coil. Since this is a DX coil system, you need not to worry about having a plant loop, okay. You can still run the simulation, and, unless there is a specific error,you'll be fine. At the end you will get some results, you'll be able to understand the energy consumption for heating and cooling as well, okay. I think we are good for now. We can save the system. Save it, here. And, we can do something else.

For example, you want to have a dedicated outdoor system, okay. Instead of this air loop serving as a primary heating and cooling system, you want to change it to dedicated outdoor system. What you need to do is, you need to click on this dotted line, again. And, change the sizing ratios, sizing properties, I'm sorry. You need to change this 100% outdoor air in cooling and heating option to, yes, okay. When you do it, go up, change this type of load to size 1 option 2 ventilation requirement. In case you need to hard size it, do it please,okay. Then you can provide the, what do you say, the heat exchanges, as well, at the outdoor air site. For example, if I just scroll down and try to find something like, heat exchanger, let me just try to find it here, okay. You can see this heat exchanger air to air sensible and latent. If I bring like, ERV heat exchanger and drop it in the, in these auto air nodes, you can see there is a heat exchanger between the return air,or the outdoor air.I'm sorry, the supply of outdoor air, as well as the node, which is throwing out the unnecessary air in the atmosphere, okay.

There is a heat exchanger between these two nodes. If you click on this heat exchanger component, you can make changes, here. You can hard size this component. You can provide the effectiveness ratio of heating, as well as cooling, in sensible and latent options. If you scroll down, you can change the heat exchanger time to,let's say, rotary instead of plate. You can change the frost control type to,let's say, exhaust on only, or exhaust air recirculation. And, do you want to lock it, block this a heat exchanger with economizer. The default option is, yes. But, if you want to change it no, that's much easier here, right. Like, just select for this no option, here. Again,it's a very simple air loop system that we have created. I would suggest you to practice this for this class. I know we haven't spent a lot of time today, but, again, as I mentioned earlier I don't want to confuse you with a lot of information in one class on HVAC systems.

HVAC systems are the most complicated components in any energy modelling process. I would suggest you to digest whatever we have done so far, today. Practice,again and again, and like, create some systems by yourself. Instead of DX single-speed, you can provide something like, DX multiple speed, double speed, I'm sorry, two speed. You can bring electric heating coils instead of DX single speed coil. And, run the simulation. Try to understand how these systems work. A lot of times, you don't even have plants loops for your buildings. For example, if you have a residential buildings with PTACs, with electric heating and cooling coils. Chances are you won't even need to create a plant loop in your energy model, okay. I can run this simulation, now. If I go to the result tab and run the simulation, it should work fine, okay. I think that's enough for today. I know it's, again, as I mentioned, it's a short session, but, please practice.

In next class we'll do a lot of stuff. We'll create the plant loops, we talk about how to create OpenStudio HVAC components using the measures. We'll talk about some complicated systems, as well as domestic hot water systems, okay. Please practice guys. Again, this class was very important. I'm giving you two weeks to practice on it. And, in case you have any questions, please don't hesitate to write me an email. Or, you can always comment under the videos, okay. Well, thanks so much guys. Take care. Bye.