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What does stubbing mean in programming? Software Engineering Stack Exchange

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What does stubbing mean in programming?

I often hear the term stub, stub out somethings, stubs, . etc. What does stubbing mean in programming, where the word come from? and in what contexts it can be used?(just examples)

A stub method is a method that just returns a simple but valid (though not necessarily correct) result.

They are typically made when building the infrastructure and you don't want to spend time on every method needed right now. Instead you create stubs so everything compiles and your IDE's auto-complete knows about the methods you are planning to use.

Another place where stubs are used is in mocking when testing, You supply stub methods that the code you are testing relies upon through dependency injection that return fixed results and then ensure that the code does the right thing with them. This isolates testing to the code you are trying to test and means you don't need to spin up a database just to run tests.

Perhaps this is best answered with a concrete example. Let's consider the case where you're creating a desktop application. You've decided to have a function named createMenubar , createToolbar and createMain so that your application constructor is neat and tidy.

Your main code will look something like this (this example is in python):

Until you have everything working, your main function will fail, so how can you test your app during development? For example, if you start out working on createMenubar , the initialization will fail after it creates the menubar since you haven't implemented the toolbar or main area of the GUI.

This is where stubs come in. You can create a function named createToolbar and createMain that satisfy the requirement of the app constructor (namely, that these functions exist), without having to actually implement them. These functions are stubs:

With those stubs in place you can begin to implement the main program and the menubar, without having to worry about the details of the toolbar or main part of the program. Eventually you'll move on to the toolbar, and replace the stub with the actual function. And finally, you'll remove the stub for createMain and give that a real implementation.

Note that stubs don't necessarily have to do nothing. These stub could, for example, create an empty container widget that the app constructor can lay out. The point is, you create dummy functions or objects that do just enough to let your other code run while you are developing it. Over time you replace the stubs one-by-one until your application is complete.

A "stub" is used in "top down" programming. That's when you are building your application from the general to the specific. In so doing, you will use "stubs" as "placeholders" for the specific applications that you haven't had time to build. They often return things like dummy or random values to the more general part of the program. That's all right, the stub feeds enough of a value to make the more "senior" part of the program work. Until it is time for the stub to be replaced or fitted with its true computation or value.

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What is VAV and how we control it?

What is VAV and how we control it? Register to Answer this Question

VAV is variable air volume (air damper)

it can increase or decrease the cfm as needed (by a motor connected to a thermostat)

it has two types

1-bypass : for higher cfm ( it bypass the excessive cfm to the plenum above false ceiling )

2-shut off type : for lower cfm rates (it simply close the area reach the required temp.)

you must use VFD fan with the shut off type

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VAV means Variable Air Volume

This is a device used on the ducts to change air flow as per the requirements. It has its own thermostate. It is used when we have different cooling zones.

This can be used with a VSD AHU. For example if we have a meeting room connected with ducted AHU and sometimes we need cooling in that room and some times not. When we put thermostates on cooling and the room temp is over that unit then VAV will open and cool air will start coming in that room and when the required cooling temp is achieved then the VAV will close slowly and completely.

Hope this will work

A VAV terminal unit is often called a VAV box , is the zone-level flow control device. It is basically a calibrated air damper with an automatic actuator . The VAV terminal unit is connected to either a local or a central control system.

VAV systems vary the airflow at a constant temperature.

The simplest variable air volume control (VAV) system controls air from a single supply duct and varies the airflow to each zone or room based upon the temperature in the room. A VAV system consists of four basic parts: a thermostat, a precision actuator controlled damper, an airflow sensor, and a controller.

When the thermostat senses the space temperature is at the temperature setpoint, the controller closes the damper until the airflow reaches a predefined lower limit. As the room temperature moves away from setpoint, the controller opens the damper until the airflow reaches a predefined upper limit.

As room temperature rises above setpoint, the VAV controller opens the damper to introduce the cool supply air into the room, which returns the temperature to setpoint. The exact position of the damper varies between minimum airflow and maximum airflow as the requirements for cooling in the room change.

VAV: variable air volume

signal in to controller : temperature sensor

signal out from controller : actuator connected with an air damper

amount of air needed Commensurate with temperature

sometimes it contains an electric heater

VAV is a Variable Air Volume, air delivery volume varies directly with the changing cooling or heating load, thus saving energy at part-load conditions.Often called a VAV box , is the zone-level flow control device. It is basically a calibrated air damper with an automatic actuator.

Another benefit that makes VAV a popular choice in HVAC design is its capability to control temperature in multiple zones. Compared to a conventional constant volume system, a VAV system has multiple VAV terminal boxes, each serving a zone controlling air flow to that zone and maintaining the set-point temperature.

In Short VAV is variable air volume ( Electromechanical device ) , Which sense the return air temperature of specific room & if target temp is achieved it close the supply air damper ,which results in pressure difference with in the main supply duct and this pressure difference is sensed by VFD driven Fan to operate accordingly, and cycle continues.

Hope above is brief actual description.

VAV box terminal is controlled by room space temperature thermostat by varying the flow of condition air into room space. When the room is warmed the thermostat will sense the increase of temperature in the room thus giving signal to VAV control system to increase the flow of condition air into the room VAV box terminal will continuously varying the flow of condition air until the room temperature setting is satisfied.

The goal of any HVAC system is to maintain a temperature within a space or zone. When the space is large, such as an auditorium or open factory space, the HVAC system delivers tempered supply air based on a single setpoint and space temperature. However, when the system must maintain the comfort level in several zones the problem becomes more complex. For example, an office area system must maintain a comfortable temperature based on multiple setpoints in individual rooms. This complex problem is often solved by installing a system of variable air volume controls on branch outlets.

The simplest variable air volume control (VAV) system controls air from a single supply duct and varies the airflow to each zone or room based upon the temperature in the room. A VAV system consists of four basic parts: a thermostat, a precision actuator controlled damper, an airflow sensor, and a controller.

Variable Air Volume controled by Damper

Variable air volume VAV is the air flow terminal device upstream main of air outlets installed for individual rooms or zones.

In experience there are two areas of applications out of many, they are:

1) Under a central HVAC system supplying conditioned air to more than one to many zones or rooms, individual temperature controls is possible for each zones or rooms as the occupants need. Since the VAVs are devices able to control the air flow rate to rooms with the help of a room/zone thermostat.

2) Under a central HVAC system supplying conditioned air to many zones or rooms, hourly heat gains varies from room to room, that is they will not be uniform. However the central HVAC equipment shall be sized based on the calculation of the peak cooling load referring to the month, hour, and the maximum outside ambient temperature and solar and internal heat gains. Hence cooling requirements varies from room to room or zone to zone, the comfort cooling for individual rooms shall be achieved by using the VAV with the help of individual thermostats.

There are three types of VAVs: byepass type, pressure independant and induction type.

VAV (Variable air volume),this used in duct for control the air flow throug the duct but now days i am researching for automatic controlled sensor device, the name of this product VAQ.

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Variable Air Volume Systems - Principles, Applications & Acceptance Testing - a PDH Online Course for Engineers

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Variable Air Volume Systems - Principles, Applications & Acceptance Testing

Air conditioning systems can be categorized according to the means by which the controllable cooling is accomplished in the conditioned space. The design of air distribution system must combine a proper choice of engineered products efficiently providing conditioned air to the space while low on energy consumption and with the ability to provide individual control.

This 4-hr course discusses the HVAC air distribution system with focus on Variable Air Volume (VAV) systems. The course is entirely based on US Corps of Engineers Construction Engineering Research Laboratory (USACERL) technical report 99:20, May 1999. This course lists the Appendix A of the report and other appendices have been separately listed.

At the conclusion of this course, the student will:

  • Understand how the VAV system operates with its advantages and limitations;
  • Learn the different classifications of VAV systems including pressure dependent, pressure independent and volume limiting boxes;
  • Understand basic type of fans used in air handling systems including forward curved, backward curved, radial and aerofoil construction;
  • Understand fan laws, fan sizing , fan curves and system curves;
  • Understand different means to control the fan capacity;
  • Learn different type of cooling coils including face split, vertical split and interwined coils;
  • Understand different approaches to duct design;
  • Learn different duct design methods;
  • Understand different types of VAV terminal boxes;
  • Understand VAV controls including direct digital controls;
  • Learn about the instruments used in acceptance testing and monitoring; and
  • Understand the initial and final steps to testing, adjusting and balancing for performance verification.

This course is aimed at beginners, novice engineers, building services design engineers, end users, service technicians, architects, maintenance supervisors, contractors, energy auditors, layout professionals and general audience.

Countless instances are occurring where building owners are upset about the performance of the HVAC system in a part or in all of their building or buildings, and rightfully so. They complain about discomfort, air quality concerns, inability to control their systems, lack of understanding how the systems are supposed to operate, displeasure with the amount of time their maintenance staff must spend to address apparent comfort problems or complaints from occupants. These issues quickly transfer to the design problems and the investigation and resolution of theses issues because owners automatically assume the problems are design related.

In this course, you are required to study the US Army Corps of Engineers Construction Engineering Research Laboratory (USACERL) technical report 99:20, May 1999 Appendix A.

You need to open or download above document to study this course.

The HVAC equipment configuration and variants available in the market today provides many options. If conditioning is transferred only by means of heated or cooled air, the system is termed an all-air system. If conditioning is transferred only by means of hot or chilled water, the system is termed an all-water system. If conditioning is transferred by a combination of heated/cooled air and hot/chilled water, then the system is termed an air-water system.

Once you finish studying the above course content , you need to take a quiz to obtain the PDH credits .

VAV box minimum postion and ventilation equirments

VAV box minimum postion and ventilation equirments VAV box minimum postion and ventilation equirments VAV box minimum postion and ventilation equirments

I am reading ASHRAE 62, 2007, multiple zone calculation and trying to apply on an example from my imagination.

three zones, A, B , and C, served by three VAV boxes.

let us say all efficiencies mentioned in the standard equal to 1,

Supply air rates are 2000, 3000, and 4000 cfm with total of 9000 cfm.

outdoor air in breathing zone requirement 100, 150, and 250 cfm with total of 500 cfm.

minimum VAV position 25% each (500, 750, and 1000 cfm)

Standard says ventilation should be available under any operation condition.

Now if all boxes are in minimum, each zone would get his outdoor requirement, but,if zones A&B were in minimum and zone C was in full load, then the total cfm would be 5250 cfm, the outdoor is still 500 cfm

the outdoor coming to zone A in this case would be 500x500/5250 = 47 cfm.

to reach 100 cfm in zone A in this case, we need either a total outdoor air of 1166 cfm, means double of full load requirement, or to increase the minimum position to 1052 cfm instead of 500 cfm, then we have to recalculate again.

this is for three simple zones only, what about 40 zones or more?

am I right, or reading the standard in a wrong way?

RE: VAV box minimum postion and ventilation equirments

Voz is the zone outdoor airflow

To answer your question about maintaining individual VAV box OA rates, you do not worry about this. Set up your AHU to handle Vot and allow it to distribute in your building as loads change. OA is held constant at 500 CFM no matter if your AHU is supping your minimum 2250 CFM or the maximum 9000 CFM. We can do this a variety of ways. but most common is directly measuring OA flow rate with a OA measuring station and modulating the OA and RA dampers to maintain a constant OA, reliving at excess airflow to exhaust.

RE: VAV box minimum postion and ventilation equirments

I mentioned in my post that with full /minimum load, each zone will get its OA requirement, my concern was when two zones were in minimum and the third one was in full load.

RE: VAV box minimum postion and ventilation equirments RE: VAV box minimum postion and ventilation equirments

All zone at full load the ratio of OA is 500/9000 = 0.055

zone A 2000*0.055 = 111 cfm of OA

zone B 3000*0.055 = 165 cfm of OA

zone C 4000*0.055 = 220 cfm of OA

zone A 500*0.222 = 111 cfm of OA

zone B 750*0.222 = 166.5 cfm of OA

zone C 1000*0.222 = 220 cfm of OA

zone A 500*0.095 = 47 cfm of OA

zone B 750*0.095 = 71 cfm of OA

zone C 4000*0.095 = 380 cfm of OA

when we say " in VAV systems, when a zone reach its set point, the VAV box damper will close to a minimum position that ensure ventilation requirement", the question here is: what does mean ventilation requirement her,?

does it mean zoen OA requirement, or just any amount of SA we can introduce it into a zone just to keep air circulation,? usually we use 25% of full load zone SA.

Am I reading the standards in a wrong way?

RE: VAV box minimum postion and ventilation equirments

Am I reading the standards in a wrong way?"

Having trouble following your thought process.

zone A 500*0.095 = 47 cfm of OA

zone B 750*0.095 = 71 cfm of OA

zone C 4000*0.095 = 380 cfm of OA"

RE: VAV box minimum postion and ventilation equirments

"VAV systems, when a zone reach its set point, the VAV box damper will close to a minimum position that ensure ventilation requirement", the question here is: what does mean ventilation requirement her,?"

I mean what the meaning of ventilation if it is not the OA that should come to a zone. hop this is clear.

I agree building will receive 500 cfm of OA under any operation mode and you idea is very logic for this point, but if we use this approach and we do not care about zones level, then why do we do zoning at first place.

as an example, an office in office building could stay at minimum position for whole occupation hours and this zone has 5 employee need 50 cfm of OA (example) now if this zone in minimum position receives only 25 cfm for whole occupation period, does this zone comply with the standard?

RE: VAV box minimum postion and ventilation equirments RE: VAV box minimum postion and ventilation equirments

"I agree building will receive 500 cfm of OA under any operation mode and you idea is very logic for this point, but if we use this approach and we do not care about zones level, then why do we do zoning at first place."

"as an example, an office in office building could stay at minimum position for whole occupation hours and this zone has 5 employee need 50 cfm of OA (example) now if this zone in minimum position receives only 25 cfm for whole occupation period, does this zone comply with the standard?"

RE: VAV box minimum postion and ventilation equirments RE: VAV box minimum postion and ventilation equirments RE: VAV box minimum postion and ventilation equirments

if we have more than one ventilation zone then we have to provide required OA to each breathing zone in each ventilation zone to meet with 6.2.2.1 as you mentioned.

RE: VAV box minimum postion and ventilation equirments RE: VAV box minimum postion and ventilation equirments RE: VAV box minimum postion and ventilation equirments RE: VAV box minimum postion and ventilation equirments RE: VAV box minimum postion and ventilation equirments RE: VAV box minimum postion and ventilation equirments RE: VAV box minimum postion and ventilation equirments

"if we consider whole building as a one ventilation zone then we are ok with it, and we do not have to use multiple zone procedure since we have only one zone"

You can't do that to your example because "ventilation zone" is similar with your "AC zone", zone are controlled by a single thermostat. If you don't have VAV box, and directly introducing the FA to each space then you can consider it as one ventilation zone.

RE: VAV box minimum postion and ventilation equirments

I gave an example for multiple zone and found out that under a certain operation case, some zones will not receive their OA requirments, but whole system is receiving required amount of OA.

Random said it is enough to introduce the calculated OA (500 cfm in our example) to the rooftop to comply to the standard regardless what each zone is receiving and he supported his opinion by the standard.

You said it is a system level not a zone level.

let me ask this in a different way, if we have multiple zones VAV project that need a total of X cfm of OA, we introduced this X cfm to the VAV rooftop unit that serves the project, do we conform to standard 62,Randoom said Yes, what do you think? yes or No.

RE: VAV box minimum postion and ventilation equirments

You are missing the point. The answer to your question is Yes. VAV rooftop unit does not necessarily mean it has a VAV box on the zone. Your example has VAV box which means it has multiple zone. If you would just spend time on analyzing the std. 62, for multiple zone system, your OA might be the same regardless of the SA (if Zp<0.15 Ev=1.0) or it may not. Zp computation is at the system level.

RE: VAV box minimum postion and ventilation equirments

so your answer is "Yes" that was what I would like to know, thank you for your help

RE: VAV box minimum postion and ventilation equirments

VAV rooftop (used as DOA) with FCU for zone cooling is an example.

RE: VAV box minimum postion and ventilation equirments RE: VAV box minimum postion and ventilation equirments

"How do we consider the VAV box minimum position.?" was the first line in my original post.

you said we need to increase OA damper and we may get 100%, I told you this was not the question, you didn't like that and started to attack, anyway thank you for your help and I will try to improve my knowledge.

RE: VAV box minimum postion and ventilation equirments

Your calculation of Zp is incorrect.

Voz is the zone outdoor airflow

ASHRAE 62.1-2007 section 6.2.5.1 & Table 6-3 notes

ASHRAE 62.1-2010 User Manual Section 6.2.5

IMC-2012 section 403.3.2.3.1

RE: VAV box minimum postion and ventilation equirments RE: VAV box minimum postion and ventilation equirments Red Flag Submitted

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