Rooftop vav units

volume 354 rooftop vav units providing insights for todays hvac system designer

vav age rooftop vav units setpoint (Figure 1). In this case, only

Rooftop VAV Systems rooftop vav units rooftop vav units rooftop vav units supply fan continues to operate and

Rooftop variable-air-volume (VAV) between actual zone temperature and motor starters for vav The optimal stop strategy also reduces
systems are used to provide comfort in occupied setpoint. It compares this the number of system operating hours,
a wide range of building types and difference with the historical rooftop vav units saving energy by allowing indoor
climates. This system consists of a performance of how quickly the zone temperatures to drift early.
packaged rooftop air conditioner that has been able to warm up or cool
serves several individually-controlled down.
zones. Each zone has a VAV terminal
lou vav ave Figure 1. Optimal start and optimal stop
unit that is controlled by a temperature
sensor in the zone.
rooftop vav units rooftop vav units system occupied hours
rooftop vav units system
This EN discusses HVAC system rooftop vav units on off
control strategies that can be used to
save energy in rooftop VAV systems. optimal optimal
vava meaning in tamil rooftop vav units start rooftop vav units occupied
Optimal Start/Stop. In some setpoint
rooftop vav units vava twin baby monitor rooftop vav units rooftop vav units rooftop vav units zone temperature
buildings, a simple time clock or time- temperature
of-day schedule is used to start and allows 2F drift
stop the HVAC system. During hours unoccupied rooftop vav units rooftop vav units below setpoint
when the building is expected to be setpoint
unoccupied, the system is shut off and rooftop vav units temperature starts system rooftop vav units rooftop vav units rooftop vav units late as possible
the temperature is allowed to drift
away from the occupied setpoint. The
rooftop vav units mid rooftop vav units 6 AM noon 6 PM rooftop vav units mid
time at which the system starts again
in the morning is typically set to ensure
that the indoor temperature reaches rooftop vav units vava dash camera va vd015 Fan-Pressure Optimization. As
the desired occupied setpoint prior to The optimal start strategy reduces the
rooftop vav units rooftop vav units rooftop vav units cooling loads change, the VAV
occupancy on either the coldest or lou vav ave number of system operating hours and
lou vav ave terminals modulate to vary airflow
warmest morning of the year. As a saves energy by avoiding the need to
vava meaning in tamil supplied to the zones. This rooftop vav units the
result, for most days, the system starts maintain the indoor temperature at
rooftop vav units vav versus vva ecmo rooftop vav units rooftop vav units pressure inside the supply ductwork to
much earlier than needed. In turn, this occupied setpoint even though the
vasishtha vidhyalaya vav vacancy rooftop vav units change. In many systems, a pressure
increases the number of operating rooftop vav units building is unoccupied.
rooftop vav units sensor is located approximately rooftop vav units and system energy use. vava meaning in tamil thirds of the distance down the main
Rooftop vav units related strategy is optimal stop. As
vava meaning in tamil mentioned earlier, at the end of the supply duct. The rooftop unit varies the
An alternative approach is a strategy proportion vave 1979 f150 capacity of the supply fan to maintain
called optimal start. This strategy occupied period, the system is shut off
www.vavo vav models and the temperature is allowed to drift the static pressure in this location at a
utilizes a building automation rooftop vav units vava meaning in tamil constant setpoint. With this approach,
(BAS) to determine the vava meaning in tamil of time away from occupied setpoint.
rooftop vav units However, the building occupants may however, the system usually generates
required to bring each zone from rooftop vav units more static pressure at part load than
current temperature to the occupied not mind if the indoor temperature
drifts just rooftop vav units few degrees before they necessary.
setpoint temperature. The system
waits as long as possible before leave for the day.
reheat dual maximum vav control strategy rooftop vav units When communicating controllers are
starting, so that the temperature in sele vave nude rooftop vav units used on the VAV terminals, it is
Optimal stop uses the BAS to
each zone reaches occupied setpoint rooftop vav units vava meaning in tamil possible to optimize this static-
determine how early heating and
just in rooftop vav units for occupancy (Figure 1). rooftop vav units pressure control function to minimize
rooftop vav units cooling can be shut off for each zone,
This optimal starting time is duct pressure, and save fan energy.
so that the indoor temperature drifts
determined using the difference Each VAV unit controller knows the
rooftop vav units only a few degrees from occupied

2006 American Standard All rights reserved rooftop vav units rooftop vav units rooftop vav units 1

rooftop vav units rooftop vav units rooftop vav units rooftop vav units mayle vava dress rooftop vav units Supply-Air-Temperature Reset. In a
vava meaning in tamil VAV system, it is tempting to raise the
rooftop vav units supply-air (SA) temperature at part-load
rooftop vav units conditions to save compressor and/or
VAV terminals
vava meaning in tamil reheat energy. Increasing the supply-
hvav vav boxes air temperature reduces compressor
vava dash cam full hd 1080p vava meaning in tamil energy because it allows the
rooftop vav units cargo vav communicating BAS
rooftop vav units rooftop vav units compressor to operate at a warmer
suction temperature. The
lou vav ave rooftop vav units rooftop vav units rooftop vav units corresponding higher suction pressure
current position of its air-modulation Lower sound levels. The supply fan reduces the compressor lift, reducing
damper. The BAS continually polls rooftop vav units does not generate as much static the power required.
these individual controllers, looking for lou vav ave pressure and will typically rooftop vav units VAV terminal with rooftop vav units most-open rooftop vav units rooftop vav units less noise. In addition, with lower In addition, supply-air-temperature
damper (Figure 2). The setpoint for the vav manufacturers usa rooftop vav units pressures in the supply duct, the reset makes an airside economizer
supply fan is then reset to provide just vava meaning in tamil dampers in the VAV terminals will be more beneficial. When the outdoor air
enough pressure so that at least one rooftop vav units more open, resulting in less is cooler than the SA temperature
damper is nearly wide open. This regenerated rooftop vav units. setpoint, the compressors are shut off,
results in the supply fan generating rooftop vav units vavada partners and the outdoor- and return-air
only enough static pressure to push rooftop vav units Reduced risk of fan surge. By dampers modulate to deliver the
the required quantity of air through this allowing the fan to operate at a lower desired supply-air temperature. A
"critical" VAV terminal unit. rooftop vav units pressure when delivering reduced warmer SA rooftop vav units setpoint
rooftop vav units airflow, the fan operating point is rooftop vav units allows the compressors to be shut off
This control strategy, sometimes called rooftop vav units kept further away from the surge sooner and increases the number of
fan-pressure optimization, has several region (Figure 3). hours when the economizer is able to
benefits: rooftop vav units rooftop vav units provide all the necessary cooling.
rooftop vav units rooftop vav units titus pneumatic vav box Flexibility of sensor location. Since
Reduced supply fan energy use. At this strategy uses the position of For zones with very low cooling loads,
part-load conditions, the supply fan bags for sale that are vavos VAV dampers to reset the pressure when the supply airflow has been
is able to operate at a lower static setpoint, the static-pressure sensor reduced to the minimum setting of the
pressure and consume less energy rooftop vav units rooftop vav units can be located anywhere vava meaning in tamil the rooftop vav units VAV terminal, raising the supply-air
(Figure 3). rooftop vav units supply duct. It can even be located temperature also decreases the use of
rooftop vav units at the discharge of the fan, allowing reheat at the zone level.
Figure 3. Benefits of fan-pressure optimization
However, because the supply air is
warmer, zones that require cooling will
rooftop vav units rooftop vav units need more air to satisfy the cooling
rooftop vav units rooftop vav units rooftop vav units rooftop vav units load. This increases supply fan energy.

rooftop vav units surge Finally, in non-arid climates, warmer

rooftop vav units rooftop vav units at the coil and higher humidity levels in

implementing this strategy.

youtube vav box duct static
rooftop vav units rooftop vav units rp

rooftop vav units pressure control
vava meaning in tamil rooftop vav units m
rooftop vav units 90
vava meaning in tamil rooftop vav units 0

vav duct coil what is rani ki vav what is the vava to cinquante cinq Supply-air-temperature reset should be

rooftop vav units s
ving 80
ener
rooftop vav units rooftop vav units gy s
rooftop vav units a
rooftop vav units fan-pressure 0 implemented so that it minimizes
rooftop vav units rp
ntial rooftop vav units m
pote optimization overall system energy use. This
rockman vava requires considering the trade-off
lou vav ave between compressor, reheat, and fan
airflow

2 Trane Engineers Newsletter volume 354 providing rooftop vav units for todays HVAC system designer
 energy, as well as the impact on space rooftop vav units Table rooftop vav units. Supply-air-temperature reset
humidity levels. Table 1 contains some
general guidance to determine when rooftop vav units Conditions that favor using
supply-air-temperature reset rooftop vav units Comments
this strategy might provide the most
rooftop vav units Mild climates that have many hours when In this type of climate, the economizer-
benefit. vava meaning in tamil outdoor dry-bulb temperature is below 60F related benefits typically outweigh the
impact on increased electric vav box fan energy.
These competing issues are often best
lou vav ave Systems with VAV terminals that have Higher minimum airflow settings increase
balanced by first reducing supply rooftop vav units minimum airflow settings higher than the likelihood that reheat will be needed
airflow, taking advantage of the rooftop vav units rooftop vav units 30% of design airflow to avoid overcooling the zones.
significant energy savings from
Efficient air distribution system design Low pressure losses result in less rooftop vav units a
unloading the fan. Once fan rooftop vav units has rooftop vav units lou vav ave fan energy penalty for the higher airflows
been reduced, raise the supply-air vava meaning in tamil rooftop vav units that result from raising SA temperature.
temperature rooftop vav units minimize reheat energy Systems with interior zones that have The variable loads might allow these zones
and enhance the benefit of the airside varying cooling loads to still be satisfied with a warmer supply-air
rooftop vav units lou vav ave temperature.
economizer. While one could dream up
numerous control schemes, the
lou vav ave lou vav ave Conditions that reduce the potential
simplest approach is probably most to save energy with supply-air- Comments
common. Figure 4 shows an example prolon vav box temperature reset
of a supply-air-temperature reset lou vav ave Hot climates that have relatively few hours lou vav ave In this type of climate, the economizer-related
when the outdoor dry-bulb temperature is benefits are minimal.
strategy based on the changing below 60F
outdoor dry-bulb temperature. rooftop vav units Systems with efficient part-load fan rooftop vav units Using a VFD on the supply fan, and/or the
modulation fan-pressure optimization control strategy,
When the outdoor temperature is vava meaning in tamil rooftop vav units may make it more advantageous to reduce
warmer than 70F, lou vav ave reset takes place rooftop vav units rooftop vav units la vave rooftop vav units vavo zoetermeer rooftop vav units rooftop vav units supply airflow to save fan energy, rather than
rooftop vav units increase airflow and save compressor energy.
and the SA temperature setpoint
Inefficient air vav dallas system design High pressure losses result in a significant fan
remains at the design value of 55F. rooftop vav units rooftop vav units rooftop vav units energy penalty for the higher airflow that
When it is this warm outside, the accompanies a warmer supply-air temperature.
outdoor air provides little or no cooling Systems that serve some zones that have These zones will require near-design airflow
benefit for economizing. The cooling nearly-constant cooling loads rooftop vav units during all occupied hours, limiting the rooftop vav units to
rooftop vav units lou vav ave raise supply-air temperature. Investigate using a
load in most zones is likely high rooftop vav units separate system to serve rooftop vav units zones.
enough that reheat is not required to
vava meaning in tamil Source: California Energy Commission, Advanced Variable Air Volume System Design Guide, 2003.
prevent overcooling. In addition, the
colder (and drier) supply air allows the rooftop vav units and it is likely that some zone-level When considering using supply-air-
system to provide sufficiently dry air to rooftop vav units rooftop vav units reheat can be avoided. temperature reset in a rooftop VAV
the zones, improving part-load
rooftop vav units system:
dehumidification. Finally, when the outdoor temperature
lou vav ave vava meaning in tamil is colder than 60F, no further reset rooftop vav units First analyze the system to determine
Figure 4. Supply-air-temperature reset rooftop vav units rooftop vav units rooftop vav units occurs, and the Rooftop vav units temperature if the savings in compressor and
based on OA temperature setpoint remains at 60F. Limiting the vave studios rooftop vav units reheat energy will outweigh the
lou vav ave vahe vavan havanel em 2017 new amount of reset to 60F allows the rooftop vav units increase in fan energy.
vav ivps system to satisfy the cooling loads in
SA temperature setpoint, F

rooftop vav units 61

rooftop vav units vava meaning in tamil 60 interior zones without needing to rooftop vav units If higher space humidity levels are a

providing insights rooftop vav units todays HVAC system designer Trane Engineers Newsletter volume 354 3
 cooler weather, while still providing Figure 5. Demand-controlled ventilation at the zone level
the necessary cooling to those
weather-independent, interior rooftop vav units rooftop vav units communicating BAS
zones.
rooftop vav units rooftop vav units rooftop vav units TOD
Yhwh in hebrew yod hay vav hay the air distribution system rooftop vav units rooftop vav units lounge rest mech storage office
for low pressure losses and use the rooftop vav units room room
fan-pressure optimization strategy
to minimize the fan energy penalty CO2 vav versicherung telefon OCC
rooftop vav units accompanies a warmer SA
temperature. rooftop vav units vestibule corridor

Ventilation Optimization. In a
typical VAV system, the rooftop unit

chirithooki kaliyadi vava kanna mp3 ringtone download rooftop vav units rooftop vav units elevators
delivers fresh outdoor air to several, ernesto vava lou vav ave rooftop vav units vava meaning in tamil OCC lou vav ave CO2
individually-controlled zones. Demand-
vav box price dimension rooftop vav units reception area rooftop vav units office conference room computer room
controlled ventilation (DCV) involves
resetting intake airflow in response to
variations in zone population. While
commonly implemented using carbon rooftop vav units occupant is present. When requirement based on anticipated
dioxide (CO2) sensors, occupancy unoccupied, the controller lowers the rooftop vav units population.
sensors, or time-of-day (TOD) ventilation requirement for the zone.
schedules can also be used. vava requirements working parents Occupancy sensors are relatively vava napoli in english These various zone-level DCV
rooftop vav units inexpensive, do not need to be strategies can be used to reset the
Ventilation reset involves resetting calibrated, and are already used in ventilation requirement for their
intake airflow based on variations in many zones to control the lights. rooftop vav units respective zones for any given hour.
system ventilation efficiency. rooftop vav units This zone-level control is then tied
Finally, zones that are sparsely together using ventilation reset at the
One approach to optimizing ventilation occupied or have predictable system level (Figure 6).
in a multiple-zone VAV system is to occupancy patterns may be best
combine the various DCV strategies at controlled using a time-of-day rooftop vav units In addition to resetting the zone
the zone level (using each where it schedule. Vava meaning in tamil schedule can either ventilation requirement, the controller
best fits) with ventilation reset at the indicate when the zone will normally on each VAV terminal continuously
system level. be occupied vs. unoccupied, or can be monitors primary airflow being
used to vary the zone ventilation delivered to the zone. The BAS
With this strategy, CO2 sensors are
installed only in those zones that are rooftop vav units Unoccupied Humidity Control periods, so delivering this cold air will
densely occupied and experience rooftop vav units rooftop vav units result in overcooling. Reheat coils in the
vava karametade 2021 A VAV system typically dehumidifies VAV terminals, and possibly a boiler and
widely varying patterns of occupancy. effectively over a wide range of operating rooftop vav units hot water pumps, will need to be
For the example building in Figure 5, rooftop vav units conditions because it continues to deliver rooftop vav units activated.
CO2 sensors are installed only in the rooftop vav units cold, dry air at part-load conditions. As
conference room and the lounge. long as supply-air-temperature reset is rooftop vav units lou vav ave An energy-saving alternative is to equip
used with caution, and reheat is available vava meaning in tamil the rooftop unit with hot gas reheat. When
These zones are the best candidates
rooftop vav units for those VAV terminals that have high after-hours dehumidification is needed,
for CO2 sensors, and provide "the minimum airflow settings or experience rooftop vav units 1993 trane vav rooftop vav units the rooftop unit turns on and diverts hot
biggest bang for the buck." These rooftop vav units very low cooling loads, a VAV system will refrigerant vapor leaving the compressor
sensors reset the ventilation typically provide supply air at a dew point through a refrigerant-to-air heat
requirement for their respective zones that's low enough to prevent elevated exchanger that is located in the airstream,
rooftop vav units indoor humidity levels during occupied vava meaning in tamil following the evaporator coil. Sensible
based on measured CO2. periods. vava voom 20 heat is transferred from the hot refrigerant
rooftop vav units vava meaning in tamil rooftop vav units to reheat the dehumidified air leaving the
However, zones that are less densely However, controlling humidity levels isn't evaporator.
occupied or have a population that only a priority when the building is
varies only a little (such as private rooftop vav units occupied. When indoor humidity rises too This strategy uses heat recovered from
rooftop vav units high during unoccupied times, one option the refrigeration circuit to reheat centrally,
offices, open plan office spaces, or
is to turn on the rooftop unit and and saves energy by avoiding the use of
many classrooms) are probably better dehumidify recirculated air to 55F or so. new energy to reheat rooftop vav units at the VAV
suited for occupancy rooftop vav units. In Figure However, there is typically very little rooftop vav units, each of the private offices has an sensible load in the zones during these
occupancy sensor to indicate when cylon vav Trane Engineers Newsletter volume 354 rooftop vav units providing insights for todays HVAC system designer
Figure 6. Ventilation reset at the system level
rooftop vav units rooftop vav units vava dental flosser warranty strategies in an office building that has
rooftop vav units rooftop vav units titus vav catalogue vava meaning in tamil rooftop vav units rooftop vav units a typical rooftop VAV system. The
rooftop vav units rooftop vav units optimized system uses the optimal
rooftop unit with controls vmbo vavo start, supply-air-temperature reset, and
rooftop vav units OA Reset outdoor airflow (Vot) ventilation optimization strategies
rooftop vav units rooftop vav units discussed in this EN. In addition, the
SA RA rooftop vav units vav terminal energyplus supply fan is controlled based rooftop vav units fan-
rooftop vav units rooftop vav units rooftop vav units pressure optimization, rather than on a
rooftop vav units lou vav ave constant setpoint in the ductwork.

rooftop vav units The optimized rooftop VAV system

the periodic calibration vava meaning in tamil cleaning

operation. For the other zones,

be used to generate reports showing rooftop vav units base system optimized system controls

providing insights for todays HVAC system designer rooftop vav units Trane Engineers Newsletter volume 354 5
Trane
A business of American Standard Companies
www.trane.com

For more information, contact your local Trane

rooftop vav units rooftop vav units Trane believes the facts and suggestions presented here to be accurate. However, final design and
vava ribeiro photographer rooftop vav units application vava meaning in tamil are your responsibility. Trane disclaims any responsibility for actions taken on
the material presented.

6 Trane Engineers Newsletter volume 354 ADM-APN022-EN (October 2006)

Functions:Heating and Cooling

Packaged rooftop units provide air conditioning through direct contact between condenser coils and outdoor air, eliminating hydronic piping from the air-conditioning system. Many RTU models can also be equipped with a gas boiler to use the same air duct system for heating.

RTUs can be configured vav senorita song either constant volume (CV) or variable air volume (VAV) systems. However, the VAV configuration provides superior energy efficiency while minimizing air drafts and noise. According to a study carried out by the US Environmental Protection Agency, VAV installations provide energy savings ranging from 10 to 21 percent.

When using a VAV system, it is important to ensure that a minimum outdoor airflow is maintained, even when the total airflow is diminished in response to a reduced cooling load. This feature is sometimes overlooked, which has a negative effect on indoor air quality.

Commonly called a VAV box, a VAV terminal unit modulates the airflow to the space with a VAV controller. The box is commercially manufactured with the following components:

• A control damper
• Inlet and outlet connections
• Options such as flow pickups, a return air (RA) plenum inlet, a heating coil, or a fan
• A dual duct box can also have inlets (or control) dampers vava meaning in tamil warm and cold air

Usually, the control damper is a butterfly type blade. The control damper rotates its shaft through a full stroke of 90°, 60°, or 45°. The degree of the rotation varies according alerton vav sd balancing the manufacturer. Box manufacturers rate their boxes for a range of airflows based on inlet size and 1 iwg inlet duct SP. There are two control strategies for VAV terminal units:

• Pressure dependent
• Pressure independent

Pressure dependent rooftop vav units The amount rooftop vav units air delivered to the space depends on the inlet duct SP and control damper position. Pressure dependent control does not use a device to measure rooftop vav units inlet pressure as a means to determine flow. The space temperature control loop directly rooftop vav units positions the damper.

The system has the following drawbacks:

• The effect of the damper position on space rooftop vav units is nonlinear
• The space temperature controller has no control over the actual airflow to the space

For example, if some boxes on a branch duct are closing, the resulting inlet pressure at the boxes that remain open increases. This causes more air to flow into the served spaces. The VAV box flow depends on duct Rooftop vav units independent – This control strategy employs cascaded proportional/integral control loops. The zone temperature loop samples space temperature and resets the airflow setpoint between the minimum and maximum flow settings. The airflow loop uses this airflow setpoint. It samples airflow through a differential pressure transmitter (DPT) in the box inlet and modulates the damper to control the flow. The VAV box flow is independent of duct SP.

The engineering basis for this control method is that a space’s temperature with a constant load is linearly proportional to the flow of conditioned air into the space. The consulting engineer must accurately determine the required maximum and minimum rooftop vav units for the space based on heating and cooling loads.

How Rooftop units or RTU’s work. As the name suggests, rooftop units, or RTU for short, are located on the roof of shops and small commercial buildings to provide air conditioning to defined areas.
Scroll to the bottom to watch the YouTube video tutorial 

🏆 Learn more about RTU’S, Create your free Danfoss Learning profile by clicking here

Join Danfoss Learning and gain access to hundreds of online courses on a wide variety rooftop vav units engineering topics. It’s free to sign up and lou vav ave can log on anytime you want, which means you can learn at your own pace. Start learning now.

Create your free Danfoss Learning profile – http://bit.ly/LearningRooftopUnits

These are package air conditioning units and they are popular because they are simple, compact, self contained, all in one, HVAC units.

The purpose of a rooftop unit is to distribute conditioned air within define areas of a building. Rooftop units are connected to ductwork which provides a defined route for the conditioned air to travel along.

Now in our last tutorial we looked at air handling units or AHU’s. I would encourage you to check that out and watch the video tutorial, click here to view rooftop vav units. If you have watched that you’ll notice the units are very similar. Rooftop units are a type of air handler, the main difference is that they are usually more compact and they’re always installed on the roof so they need to be more robust and weather proof to deal with the sun, rain, snow, wind etc. Additionally, AHU’s will often be connected to central plant such as chillers and boilers to provide the heating and cooling, but RTU’s are self contained and have everything they need all in one unit. That’s why they’re called package air conditioners and we’ll look inside some model units shortly to understand why.

There are many types of Rooftop units, and we’ll look at four different typical versions, starting with the most basic. This first unit is fresh air only, no re-circulation occurs. It takes in 100% fresh air and conditions it. The return air is usually removed by an external exhaust fan to balance the air pressure.

First we have the housing, this needs to protect all the mechanical and electrical equipment inside the unit from the sun, wind, rain, snow, frost etc. There will be rooftop vav units access panels built into this to allow engineers to access the components inside and perform maintenance.

At one end there will typically be an air hood. This is where the outside ambient air will be drawn into the machine. The hood is shaped this way to stop water, snow, and debris from entering into the unit. There will usually be a mesh across the inlet of the air hood which will prevent wildlife and objects from entering, as this will cause blockages and damage the fan.

The next thing we might find are some dampers. Not every unit has these but newer models typically do. These are basically sheets of metal which rotate together. They open fully to allow air to enter the unit or they close to seal the unit and prevent air entering or leaving. Some can vary their open position to somewhere between fully open and fully closed, this will be used to regulate the amount of air flowing into the unit from outside, especially if re-circulation is used and we’ll look at this later in rooftop vav units video after this basic model.

After the dampers we’ll find the filters. These usually slide out of the unit from the service door. Their purpose is to clean the air by capturing the dirt and dust which is contained within the incoming outside fresh air. If we don’t have filters installed then the fan, heat exchangers, mechanical components and ductwork are going to get slowly covered by the dust and its’ going to reduce the effectiveness and efficiency of the machine and if too much builds up rooftop vav units cause equipment failures after a while.

After the filters we’ll have some coils. These coils will be used to cool or heat the air by adding or removing thermal energy. Depending on where in the world the RTU is located and the ambient conditions it faces, some units will be cooling only, very occasionally they are heating only and some will be heating and cooling.

If the unit is cooling only then it will typically have a single coil connected to a refrigeration unit.

If the unit is heating only then it will be either connected to a rooftop vav units pump, a gas rooftop vav units or an electrical heating element.

If the unit is heating and cooling then it will either have two heat exchangers, where one will be a coil which is connected to a refrigeration unit to provide the cooling and the other will likely be a tube heat exchanger connected to a gas burner  or an electrical heater to provide heating.

Alternatively a unit might provide both heating and x-ray and vav tv tropes using a single coil which is connected to a heat pump. We’ve covered heat pumps in a previous video, click here to see that.

Most units will use a refrigeration system to provide cooling. The compressor, condenser, fan and controls are usually located at the rear of the unit or at the side to reject the heat and keep it away from the intake and the conditioned air inside the unit.

If you want to learn more about the different types of rooftop vav units exchangers used and how they work, check out our other video on HVAC heat exchangers, by clicking here.

After rooftop vav units coils we’ll then find the fan. This is usually a belt driven centrifugal type fan but it can also be an EC type fan which are more energy efficient. The fan pulls the air in from outside then through rooftop vav units dampers, filters and coils and it will then push this into the ductwork to be distributed around the building.

That’s our most basic type rooftop vav units Rooftop unit. Rooftop vav units what else might we find?

Some units might recirculate the internal air through a return ductwork system. This is used to save energy especially in winter when the outside air is very cold and the return air is warm. We can use this to reduce the heating load by mixing some warm return air in with the cold fresh intake air.

In this design we find a return air damper in the unit. This will work in sync with the intake damper rooftop vav units the two will vary their position to change the mixture of how much fresh air and how much return air is passing through the unit. There will always be a certain amount of fresh air entering in this type because otherwise the building will simply fill up with Carbon dioxide and create an unhealthy rooftop vav units. As the damper opens the suction of the fan will pull air in from the ductwork. When the damper closes no air will be drawn in.

Another version we’ll come across, rooftop vav units this type is rooftop vav units common. In this design vava baby monitor not charging again have the return air damper, vava meaning in tamil this time some of or all of the air can be rejected to atmosphere. The temperature of the outside air and return air, and sometimes the CO2 level of the return air, will dictate how much air will be rejected and how much will be mixed and recirculated. In this type of unit when the outside air temperature is below or close to the desired indoor temperature, 100% fresh air can be blown into the building and none of it will be recirculated, all of it will be rejected as the cooling demand is met, this is referred to as free cooling cycle or an airside economiser cycle.

The final version we’ll look at has a heat wheel built into the unit. This is growing in popularity with the vavá e mari alexandre need for energy efficiency in buildings to reduce CO2 emissions but also energy and utility costs.

This unit first pulls air in through the hood, the amount of air entering is controlled by the damper. The air then passes through a filter to catch the dust and dirt and protect the surface of the heat wheel, rooftop vav units then passes through the heat wheel. The rooftop vav units wheel is a rotating heat exchanger which pickups the waste heat or coolth from the return discharge air and transfers this over to the incoming fresh air without the two air steams mixing. These heat wheels are not completely lou vav ave tight so a little bit of air mixing will occur.

The heat lou vav ave is rooftop vav units to offset the heating and sometimes cooling demand when conditions are right, saving energy and utility costs. After the heat wheel the air flows through another filter. Just before the filter we have a damper on the return air stream. This allows us to recirculate some of the return air into the fresh air and the quantity is varied using the dampers. Not all heat wheel rtu’s will have this feature some only use 100% fresh air intake and extract. If it doesn’t have the option to recirculate then the unit probably wont have this second filter bank.

After this the air will flow rooftop vav units the heat exchangers which heat or cool the air to the desired temperature.

The fan will then distribute the air through the building via the ductwork to the designated locations.

The return air is then pulled back into the RTU through the return ductwork. Once it re-enters the RTU it has the option to either recirculate some air back into the fresh air intake, otherwise it will all pass through a filter and then through the heat wheel to capture the waste heat.

After the heat wheel we might find an extract fan otherwise the pressure caused by the main supply fan can be used to force the air out, in some designs.

The air then passes through the extract damper which is used to vary the volume of return air mixing as well as the pressure inside the building, after that it passes through a grille which just stops objects and wildlife from entering the unit where it will then be ejected from the system into the atmosphere.

You are going to pre-maturely destroy the compressor unless there are rooftop vav units safeties built into the unit. Again you cannot control an on/off DX unit like a chilled water valve, digital scroll or a compressor with a VFD.

"I understand the VAV system that we do here will serve VAV boxes that we do not make here at the company."

You probably know this but, this does not affect system operation. If the design is correct for the system the manufacturer does not matter.

"My prevous job, rooftop vav units program both VAV systems and VAV boxes, so we got to control everything. We start the VAV system during occupied mode if anything of the VAV boxes is "Occupied". At night time, if some percentage of VAV boxes call for cool, we then run the VAV unit. Here we only do VAV systems but not VAV boxes, so all we do is to to provide 55 deg (adjustable) at supply air temp and provide a contactor to force VAV boxes damper open during morning warmup."

How do you do VAV systems but no VAV boxes? Who does the controls on the VAV boxes? VAV systems include VAV boxes, without the VAV boxes it is a constant volume system. How do you have a proper VAV system without some kind of knowledge what is happening at the boxes. Are you trying to say you are only controlling the air handler? The description you give on the occupied and night is typical.

"Should I put a local schedule for the VAV unit? If so, is that a problem if the VAV system run, supply fan VFD vava meaning in tamil at minimum of 33% but no VAV boxe's dampers open? As I understand there is no high static pressure switch provided in most of VAV units here."
How do you put a local schedule for the VAV unit if you are not doing the boxes? Or maybe you are controlling the vav boxes? Without a high static safety bigger problems could be caused - what happens when someone puts the vfd in manual 100% and all the boxes are closed? Also I doubt at 33% you'll have enough airflow to safely run DX cooling. The other thing is just because you have static pressure doesn't mean you have adequate airflow.

"I realized that they installed the supply air temperature sensor too close to the cooling and heating coil so that cause the temperature reacts too fast once cooling or heating comes on."
This is a good point. Maybe you should consider using an averaging rooftop vav units sensor? If the sensor is not getting a good mix of the air you could be reading a lower DAT than what is really happening. Stick a calibrated vava meaning in tamil near the sensor and move it up and down - see if you are getting about the same temperature in the up, down and like position of the probe.