Lecturer: Hongqiangli

Email:lihongqiang2009@yahoo.com.cn

Unit Fifteen

Commissioning of Variable Air Volume Systems

What is Commissioning (Cx) ?

What is Commissioning (Cx) ?• Definition:

“A quality-focused process for enhancing the delivery of a project. The process focuses on verifying and documenting that the facility and all of its systems and assemblies are planned, designed, installed, tested, operated, and maintained to meet the Owner’s Project Requirements.” ASHRAE Guideline 0-2005, The Commissioning Process

– Commissioning is often performed by an independent third-party engineering company.

– Operates as an owner’s representative to insure the installed systems meet the owners requirements and the plans and specifications

– Usually hired by the owner, sometimes by the architect, or general contractor.

Commissioning Person

All participants in the construction project have a commissioning responsibility. Participants include the commissioning authority, owner, design professionals, construction manager, general contractor, subcontractors, operation and maintenance manager, suppliers, and equipment manufacturers.

Benefits of Commissioning

• Reduced change orders• Less warranty and callbacks for contractor• Smoother turnover to maintenance• Improved equipment reliability• Reduced IEQ problems

– Reduced occupant complaints– Improved productivity

• Correct system operation and installation• Facility meets Owner’s expectation and operational

needs• Reduced utility consumption and operational costs

Commissioning Objectives

• Ensure the facility meets the owner’s performance requirements

• Provide a safe and healthy environment

• Provide optimum energy performance

• Provide a facility that can be efficiently operated and maintained

• Provide complete orientation and training to facility staff and occupants

• Provide improved documentation of system characteristics

Commissioning - What did we use to do and why do we need it?• CX of mechanical and electrical systems was done by the installing contractors• No standardization, or clear approach• Most of the real CX occurred during the warranty period as warranty calls• Buildings operated less efficiently• First year of occupancy was frustrating for the owner• Contractors spent more money during the warranty periods• Contractors can be rushed without enough time to double-check their work• Design Engineers do not have enough budget to oversee the construction in detail• Owners have had bad experiences with prolonged project closeout, and see CX as a solution• Hold contractors accountable for the specifications

Commissioning Scope• Mechanical Systems

– All HVAC equipment– Building automation system and hardwired controls

• Electrical Systems– Switchgear, major disconnects, backup generators and UPS

(Uninterrupted Power Supply)• Fire Safety Systems• Security Systems• Kitchen equipment• Irrigation system• Laboratory Fume hoods, gas control

Commissioning and Construction Phases

Prepare,Design Intent,

CX Plan,and

Specifications

ReviewSubmittals,

Prepare Checklists

and Testing Plans

VerifyComponents,

Witness Start-Up

and Component

Testing

PerformFunctionalTesting, Resolve

Deficiencies,ReviewO&M

PrepareCX Report,

Staff Training,

DefineSeasonalTesting

Planning Design Construction OccupancyAcceptance

Other Types of Commissioning

• Retro-commissioning– Performed to existing buildings that have not previously been

commissioned, after they have been occupied– Usually instigated as a result of high energy bills or poor

occupant comfort• Recommissioning

– Performed 5 to 10 years after a building was previously commissioned

– Sometime used as a form of deferred maintenance

Variable Air Volume (VAV)

use of varying airflow to control the condition of air, in contrast to the use of constant flow (often) with varying temperature.

VAV system controls temperature in a space by varying the quantity of supply air rather than varying the supply air temperature. A VAV terminal unit at the zone varies the quantity of supply air to the space. The supply air temperature is held relatively constant: while supply air temperature can be moderately reset depending on the season, it must always be low enough to meet the cooling load in the most demanding zone, and to maintain appropriate humidity.

Typical VAV system

Air Handling Unit

buildingautomationsystem (BAS)

VAVterminal

units

supplyductwork

returnductwork

supply-airdiffusers

Typical VAV system

This variable air volume system brings outside air and return air to the Air Handling Unit (AHU) (3). where the incoming air (8.) temperature and humidity can be controlled.

The main AHU components are supply fan (2.) heating coil (5.) cooling coil (6.), filter (7.), and humidity control equipment (not in above). The temperature in the individual rooms is measure by thermostats (11.), which directly control the dampers in each room. The supply air fan is speed controlled by an AC drive (4.) and it delivers the air to individual rooms throughout the building by supply air ducts. The AC drive controls the air volume by keeping the air pressure constant. The pressure is measured by the sensor (13.).

The return air fan (1.) delivers the exhaust air (9.) out of the building or part of the air (10.) is returned back to the AHU. The fan is controlled by an AC drive (14.) which keeps the room pressure measured by sensor (12.) constant.

Characterstics of VAV systems

Constant air temperature off AC Unit

Vary the air volume as load requires

Why use VAV?

– Provides multiple zones of comfort

– Life cycle cost will be less than other HVAC Systems trying to accomplish similar comfort levels

– Load diversity

• Smaller equipment ( lower AC unit first cost compared to Constant Volume)

• Less supply air ( less energy consumption)

– Able to adapt to changes in building use

Why Not ??

–Higher first cost than comparable single zone • Controls, equipment, commissioning

– Increased maintenance cost• More pieces to look after

Constant volume - variable temperature system have been dominating the HVAC applications in the past for obvious reasons. The implementation of variable volume control has been done with dampers or other mechanical control methods.

The advantages of variable air volume system implemented with variable speed control are:

Fast control to keep the comfort zone limits

Low consumption of electrical energy

Lower consumption of heating and cooling energy than in constant air volume systems

Simpler to keep noise level down

1. Introduction

2. Commissioning method statement

3. System components 4. Preliminary checks

5. Commissioning sequence 6. Setting to work

7. Terminal units 8. Secondary air distribution

9. Return air spigots 10. System diversity

11. Fan design performance check 12. System performance checks

Frequently used words and phrases:

Variable air volume (VAV) system 变风量系统commissioning 试运行 调试 air volume flow rate 空气体积流量terminal unit 终端设备 flexible duct 柔性风管Pitot tube 毕托管 thermal anemometer 热线风速仪supply fan 送风风机 extract fan 排风机over-pressurization 压力过高 spigot 套管、栓、龙头

1. Variable air volume (VAV) systems are dynamic air distribution systems and, as their name implies, the air volume flow rate is varied according to various parameters to achieve the required design conditions.

2. The fact that VAV systems are designed to vary system performance imposes a number of specific tasks on the commissioning specialist, which must be carried out in order to achieve satisfactory overall performance.

3. Proprietary units may employ a variety of means of regulating air volume flow rate including motorized dampers, inflating bellows, restricting flexible duct sections or a combination of such devices.

Variable air volume (VAV) systems: 变风量系统 dynamic: 动态的air volume flow rate: 空气体积流率 design conditions: 设计条件

impose: 施加 带来 commissioning specialist: 调试人员

proprietary: 私人拥有的 inflating bellows: 静压箱 常用 plenum chamberflexible duct section: 柔性风管部件

plenum chamber 静压箱

acoustic plenum chamber 消声静压箱

静压箱是送风系统减少动压、增加静压、稳定气流和减少气流振动的一种必要的配件，它可使送风效果更加理想。

静压箱的作用 可以把部分动压变为静压使风吹得更远； 可以降低噪音 风量均匀分配 静压箱可用来减少噪声，又可获得均匀的静压出风，减少 动压损失。而且还有万能接头的作用。把静压箱很好地应用到通风系统中，可提高通风系统的综合性能。

plenum chamber

spigot

plenum chamber

spigot

flexible duct

flexible duct ＋ plenum

flexible duct ＋ plenum

4. Control sensors may measure air flow by means of pressure differential, Pitot tube, flow grid or thermal anemometer using spot or averaging sensors.

5. The guidance is not system-specific, because the detailed tasks associated with one system type may not be the same for another type.

6. VAV system technology offers such a wide range of design options and proprietary components that the resulting installations are likely to require different commissioning techniques.

pitot tube: 毕托管 flow grid: 流动网格thermal anemometer: 热线风速仪

option: 选择 选项

system-specific: 根据系统而特殊或不同的

7. To ensure that the appropriate commissioning procedures are employed, the commissioning specialist should carefully review the recommendations of the equipment suppliers.

8. VAV systems typically comprise the following components, some of which may require specialist commissioning by the manufacturer in addition to general commissioning as part of a complete air distribution system

9. A particular check should be made to ensure that distribution ductwork internals are clean throughout. If there is any doubt regarding the state of system cleanliness, the commissioning specialist should formally draw attention to this.

review: 查阅 复习 equipment suppliers: 设备提供商

how to translate???

internal: 内部 draw attention to…: 对…注意

10. With the supply and extract fans operating simultaneously, the running speed should be increased gradually. Motor running current checks should be made at various increments, and the results recorded for each fan, to assess performance and prevent overloading of the motor.

11. The fans should then be stopped and made safe so that the cause of the static pressure irregularity can be investigated and rectified by the appropriate personnel before proceeding further.

12. during the commissioning of the individual VAV terminals, it may be necessary to further fine-tune the fan speed to compensate for any system pressure variations.

current: 电流 increment: 增量 overloading: 过载

irregularity: 无规律 ( 的变化 ) rectify: 修正 调整personnel: 人员 proceed: 继续进行

terminal: 终端 终点 terminal station fine-tune: 微调

13. All procedures and techniques to be applied in checking terminal unit volume flow rates should be in accordance with the manufacturer’s instructions and should be incorporated into the commissioning method statement.

14. Verification of these arrangements is necessary, and the number of VAV terminal units to be checked should be defined within the project commissioning specification.

15. at the outset of the VAV terminal checks, the commissioning specialist should select a number of units with inlet duct configurations suitable for in-duct flow measurements to be taken.

instruction: 指示 说明 instruction book specificationincorporate: 合并 结合 incorporated: 组成公司的 Inc. DELL Inc.statement: 说明 陈述

verification: 确认 查证 define: 详细说明

outset: 开始 inlet duct configuration: 风管入口结构in-duct flow: 风管入口流动

16. Volume flow rate checks by pitot-static duct traverse should be conducted on these terminals to validate the method of flow rate measurement adopted within the commissioning method statement,

17. With such an arrangement, the commissioning specialist must balance proportionally each of the secondary terminals by the methods detailed in section A3.2 so that they discharge the specified proportion of the volume of air delivered by the VAV terminal, within the specified (or appropriate) tolerances.

18. For all the above arrangements, regulation of the return air inlets must be carried out to achieve a proportional balance within the specified tolerance limits.

pitot-static duct traverse: 风管横截面布置毕托管conduct: 进行

carry out: 执行

secondary terminal: 二次终端设备 tolerance: 公差 允许的误差specified: 指定的

19. It may be necessary to impose a reduced air flow condition on a number of terminals to achieve the required design diversity.

20. Where necessary, guidance should be obtained from the unit supplier or manufacturer and close liaison with the designer is recommended to take account of any particular arrangements that may be required.

21. With the required design system diversity applied, total flow rates should be measured and recorded by pitot traverse.

diversity: 差异 多样性

How to translate???

guidance: 指导 liaison: 联络 联系

22. In conjunction with this, the static pressure at the least favored unit should be monitored and the system operating pressure set to its optimum point, i.e. the lowest system operating pressure that still satisfies the least favored unit.

23. With the system in this mode, the pressure drop across each component of the air handling unit should be measured and recorded.

24. Indicative positioning should be specified by the designer, based on the distribution ductwork system layout and the calculated system resistance characteristics.

the least favored unit: 处于最不利条件下的设备

indicative: 指示性的 指导性的 layout: 规划 布局resistance characteristic: 阻力特性

pressure drop: 压力降

25. It is, therefore, necessary to set up the fan performance controls for checking both maximum and minimum volumes, in addition to checking the equivalent performance at other intermediate points.

26. The setting of the automatic control system should be finalized by the controls specialist in liaison with the commissioning specialist.

27. With the supply and extract fans delivering their design maximum air volumes, adjust the outside air damper until the required design volume flow rate is achieved. With the system in its fully turned down condition, the minimum outside air quantity should be checked to ensure that the correct ratio has been maintained.

equivalent performance ：类似的性能 intermediate: 中间的

turned down: 关小，减弱，降低

finalize: 最终确定

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