Trane TRG-TRC014-EN Bedienungsanleitung

Air ConditioningClinicVAV SystemsOne of the Systems SeriesTRG-TRC014-EN

TRG-TRC014-EN 5period oneWhat Is Variable Air Volume?notesThe terminal reheat system uses a central air handler and cooling coil to deliver cool prima

6 TRG-TRC014-ENnotesperiod oneWhat Is Variable Air Volume?In contrast, a variable-air-volume (VAV) system delivers the primary air at a constant tempe

TRG-TRC014-EN 7period oneWhat Is Variable Air Volume?notesHowever, at part load, the VAV system produces a balance by modulating the volume of constan

8 TRG-TRC014-ENnotesperiod oneWhat Is Variable Air Volume?the air volume reduction creates an opportunity to reduce the fan energy required to move th

TRG-TRC014-EN 9period oneWhat Is Variable Air Volume?notesContrasting the three systems discussed in this example, the simple, constant-volume, variab

10 TRG-TRC014-ENnotesperiod oneWhat Is Variable Air Volume?There are some basic building characteristics that favor the application of VAV systems. We

TRG-TRC014-EN 11period oneWhat Is Variable Air Volume?notesAnother feature of the VAV system is the ability to efficiently satisfy the comfort require

12 TRG-TRC014-ENnotesNext, we will examine the individual components that compose a VAV system.A simple VAV system includes the following:n Central ai

TRG-TRC014-EN 13period twoComponents of a VAV SystemnotesVAV Terminal UnitsA VAV terminal unit is a sheet-metal assembly installed upstream of its res

14 TRG-TRC014-ENnotesperiod twoComponents of a VAV SystemThe simplest of all VAV terminal units is the single-duct, cooling-only terminal unit. It con

VAV SystemsOne of the Systems SeriesA publication ofThe Trane Company

TRG-TRC014-EN 15period twoComponents of a VAV Systemnotesdetermined by the design cooling load of the space and the minimum setting is normally determ

16 TRG-TRC014-ENnotesperiod twoComponents of a VAV SystemVAV reheat terminal units provide supply-air tempering or space heating by reheating the cool

TRG-TRC014-EN 17period twoComponents of a VAV SystemnotesDuring the heating mode, the primary airflow must often be greater than the minimum setting o

18 TRG-TRC014-ENnotesperiod twoComponents of a VAV SystemA parallel, fan-powered terminal unit consists of a primary airflow modulation device and a s

TRG-TRC014-EN 19period twoComponents of a VAV SystemnotesWhen in cooling mode, the supply airflow to the space equals the primary airflow. When in tem

20 TRG-TRC014-ENnotesperiod twoComponents of a VAV SystemIn the cooling mode, the primary airflow is reduced as the cooling load in the space decrease

TRG-TRC014-EN 21period twoComponents of a VAV SystemnotesMost designers also believe that series units offer improved acoustical conditions in the spa

22 TRG-TRC014-ENnotesperiod twoComponents of a VAV SystemA dual-duct terminal unit consists of two airflow modulation devices with controls packaged i

TRG-TRC014-EN 23period twoComponents of a VAV Systemnotes As before, this graph indicates how the air supplied to the space by the terminal unit varie

24 TRG-TRC014-ENnotesperiod twoComponents of a VAV SystemTo deliver a constant volume of supply air to the space in a two-fan, dual-duct system as the

Preface© 2001 American Standard Inc. All rights reservedTRG-TRC014-ENiiThe Trane Company believes that it is incumbent on manufacturers to serve the i

TRG-TRC014-EN 25period twoComponents of a VAV Systemnotesthe respective duct system to the modulation devices in the dual-duct VAV terminal units.Whil

26 TRG-TRC014-ENnotesperiod twoComponents of a VAV SystemVAV Terminal Unit ControlsNext we will explore the control of VAV terminal units. Before disc

TRG-TRC014-EN 27period twoComponents of a VAV Systemnotesduct static pressure, airflow to the space can vary even when the immediate modulation device

28 TRG-TRC014-ENnotesperiod twoComponents of a VAV SystemAccurate measurement of primary airflow is required to enable pressure-independent control. M

TRG-TRC014-EN 29period twoComponents of a VAV SystemnotesA pneumatically-controlled terminal unit has an airflow-modulation device operated by a pneum

30 TRG-TRC014-ENnotesperiod twoComponents of a VAV SystemAn electronically-controlled terminal unit has an airflow-modulation device operated by an el

TRG-TRC014-EN 31period twoComponents of a VAV SystemnotesA digitally-controlled terminal unit has an airflow-modulation device operated with an electr

32 TRG-TRC014-ENnotesperiod twoComponents of a VAV SystemSimilar to electronic control, an electronic pressure transducer enables pressure-independent

TRG-TRC014-EN 33period twoComponents of a VAV SystemnotesDiffusersEach VAV terminal unit is commonly connected to a downstream, sheet-metal duct that

34 TRG-TRC014-ENnotesperiod twoComponents of a VAV SystemLinear slot diffusers are generally preferred for VAV air distribution. They use a principle

TRG-TRC014-EN iiiContentsperiod one What Is Variable Air Volume? ... 1Why VAV? ...

TRG-TRC014-EN 35period twoComponents of a VAV SystemnotesBecause variable-air-volume systems are installed in, and distribute air along the surfaces o

36 TRG-TRC014-ENnotesperiod twoComponents of a VAV SystemThe linear slot diffuser is placed on the structural T-bars with the mounting feet resting on

TRG-TRC014-EN 37period twoComponents of a VAV SystemnotesSupply Duct SystemThe supply duct system transports the primary air from the air handler to t

38 TRG-TRC014-ENnotesperiod twoComponents of a VAV SystemDesigners commonly use two methods to engineer the supply duct system:n Equal friction n Stat

TRG-TRC014-EN 39period twoComponents of a VAV SystemnotesOther publications contain more complete details related to duct design, but here are a few g

40 TRG-TRC014-ENnotesperiod threeSystem ConfigurationsTo permit a complete understanding of the VAV system, we must look at it from a system level. In

TRG-TRC014-EN 41period threeSystem Configurationsnotesand equipment. Interior spaces on the top floor of a building often need to be treated as a peri

42 TRG-TRC014-ENnotesperiod threeSystem ConfigurationsIf the heat loss of the perimeter space exceeds 450 Btu/hr per linear foot [430 W per linear met

TRG-TRC014-EN 43period threeSystem ConfigurationsnotesIf the heat loss of the perimeter space is less than 450 Btu/hr per linear foot [430 W per linea

44 TRG-TRC014-ENnotesperiod threeSystem ConfigurationsWhen overhead heating is acceptable, VAV reheat, fan-powered, or dual-duct terminal units can be

iv TRG-TRC014-EN

TRG-TRC014-EN 45period threeSystem ConfigurationsnotesSimilarly, fan-powered terminal units can be used in perimeter spaces that require seasonal cool

46 TRG-TRC014-ENnotesperiod threeSystem ConfigurationsInterior SpacesBecause an interior space is surrounded by spaces at the same temperature, it doe

TRG-TRC014-EN 47period threeSystem ConfigurationsnotesTypically, either VAV reheat or fan-powered terminal units are used to provide the tempering nee

48 TRG-TRC014-ENnotesperiod threeSystem ConfigurationsAny unneeded air is diverted to the return air stream, allowing individual comfort control of th

TRG-TRC014-EN 49period threeSystem ConfigurationsnotesIn a typical commercial building, the occupied mode occurs during daytime operation. The buildin

50 TRG-TRC014-ENnotesperiod threeSystem ConfigurationsIn a typical commercial facility, the unoccupied mode occurs at night. The building does not req

TRG-TRC014-EN 51period threeSystem ConfigurationsnotesThe morning warm-up/cool-down mode typically occurs as a transition from the unoccupied mode to

52 TRG-TRC014-ENnotesperiod fourFan ModulationTo accommodate the variable-volume requirements imposed by a VAV system, the system supply fan must be s

TRG-TRC014-EN 53period fourFan Modulationnotesplot performance on the basis of the static pressure component only. Performance curves published for so

54 TRG-TRC014-ENnotesperiod fourFan ModulationWhen the system resistance curve is superimposed on the fan curve, the intersection predicts the airflow

TRG-TRC014-EN 1notesperiod oneWhat Is Variable Air Volume?A variable-air-volume (VAV) air-conditioning system varies the volume of constant-temperatur

TRG-TRC014-EN 55period fourFan ModulationnotesThis “riding the fan curve” method of modulation can be used with any centrifugal fan. However, it is mo

56 TRG-TRC014-ENnotesperiod fourFan ModulationFan Modulation Curve The fan modulation curve illustrates the static pressure requirement of the VAV sys

TRG-TRC014-EN 57period fourFan ModulationnotesTo achieve this balance, a simple control loop is used. First, the static pressure is sensed from a part

58 TRG-TRC014-ENnotesperiod fourFan ModulationThe system static pressure controller senses this higher pressure and sends a signal to the supply fan t

TRG-TRC014-EN 59period fourFan ModulationnotesAs the VAV terminal units modulate shut, the system resistance curve shifts upwards. The fan begins to “

60 TRG-TRC014-ENnotesperiod fourFan ModulationInlet vanes modulate the capacity of a fan by “pre-swirling” the air in the direction of fan wheel rotat

TRG-TRC014-EN 61period fourFan ModulationnotesFan-speed control modulates fan capacity by varying the speed of rotation. This is commonly accomplished

62 TRG-TRC014-ENnotesperiod fourFan ModulationFinally, the capacity of vaneaxial fans can be modulated by adjusting the pitch angle of the actual fan

TRG-TRC014-EN 63period fourFan ModulationnotesIn response to reduced airflow and rising system static pressure, the variable-pitch vaneaxial fan respo

64 TRG-TRC014-ENnotesperiod fourFan ModulationSystem Static-Pressure ControlEach of these fan-capacity control methods requires a signal from a contro

2 TRG-TRC014-ENnotesperiod oneWhat Is Variable Air Volume?This equation describes the performance of a constant-volume, variable-temperature system at

TRG-TRC014-EN 65period fourFan Modulationnotesincluded in the supply duct, this method ensures that the sensor is on the fan side of the damper so tha

66 TRG-TRC014-ENnotesperiod fourFan ModulationThe optimized static-pressure control method combines the location-related benefits of fan outlet contro

TRG-TRC014-EN 67period fourFan ModulationnotesA comparison of these static-pressure control methods demonstrates the energy savings potential. At this

68 TRG-TRC014-ENnotesperiod fiveApplication ConsiderationsWhen designing a VAV system for a building, there are several considerations to address:n Sy

TRG-TRC014-EN 69period fiveApplication ConsiderationsnotesSystem-Level VentilationDuring operation, a typical VAV system delivers a mixture of outdoor

70 TRG-TRC014-ENnotesperiod fiveApplication ConsiderationsWith all three components, DDC controls on the VAV terminal units and air handler, a method

TRG-TRC014-EN 71period fiveApplication ConsiderationsnotesFreeze Protection for CoilsAs mentioned, proper VAV system ventilation often leads to a high

72 TRG-TRC014-ENnotesperiod fiveApplication ConsiderationsCoils can be protected from freezing in many ways, such as:n Draining the coils during cold

TRG-TRC014-EN 73period fiveApplication ConsiderationsnotesMinimum space ventilation requirements often dictate minimum primary airflow settings on VAV

74 TRG-TRC014-ENnotesperiod fiveApplication ConsiderationsBuilding Pressure ControlMaintaining a slightly positive pressure inside buildings, especial

TRG-TRC014-EN 3period oneWhat Is Variable Air Volume?notesRearranging the equation and using the constant supply airflow of 1,840 cfm [0.87 m3/s], the

TRG-TRC014-EN 75period fiveApplication ConsiderationsnotesA sensitive static-pressure controller directly compares the variations between the space st

76 TRG-TRC014-ENnotesNow, we will review some of the main concepts from this clinic on variable-air-volume (VAV) systems.A variable-air-volume (VAV) a

TRG-TRC014-EN 77period sixReviewnotesA simple VAV system is comprised of the following components:n Central air handlern Supply ductn VAV terminal uni

78 TRG-TRC014-ENnotesperiod sixReviewA simple building has two types of spaces: perimeter and interior. These two space types require different types

TRG-TRC014-EN 79period sixReviewnotesFinally, when applying a VAV system to a building, there are several considerations that must be addressed. They

80 TRG-TRC014-ENnotesperiod sixReviewVisit the ASHRAE Bookstore at www.ashrae.org.For information on additional educational materials available from T

TRG-TRC014-EN 83Questions for Period 11 Given a space sensible load of 30,000 Btu/hr [8,793 W], a space dry-bulb temperature of 78°F[25.6°C], and a pr

84 TRG-TRC014-ENnotesQuiz11 What method of static-pressure control provides the greatest power-savings potential for a VAV system?Questions for Period

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86 TRG-TRC014-EN1a 1,382 cfm [0.65 m3/s]1b 63°F [17.2°C]1c 829 cfm [0.39 m3/s]2 The reduced airflow across the cooling coil at part load causes the re

4 TRG-TRC014-ENnotesperiod oneWhat Is Variable Air Volume?However, because this type of system can respond to the demands of only one thermostat, it c

TRG-TRC014-EN 87changeover/bypass VAV system A system that allows variable supply air to the spaces but uses a constant-volume central supply fan. Th

88 TRG-TRC014-ENGlossaryfan speed control Method of supply-fan modulation that affects the capacity of a fan by varying the speed of rotation—commo

TRG-TRC014-EN 89Glossaryconstant-volume fan, packaged so that the airflow paths are in series. This provides a constant volume of supply air to the sp

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