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Controlling the AHU by the BMS

   

Added on  2021-04-22

9 Pages2067 Words101 Views
MSc BuildingServicesEngineering–Building ManagementSystemsBrunelUniversityMScin BuildingServicesEngineeringBuildingManagement and ControlSystemsBuildingManagement SystemsAssignment2017/18 Part1Part1.1Indicateinatable howyouwould specifytheinputsandoutputstoachieve effective controloftheAHU bytheBMS. An example of thetypeoftable requiredisillustratedbelow.ControllerinterfacePointsFielddevicee.g.sensor type/actuatoretc.Inputvalueor controlactionUniversal Input1Inlet Low temperature sensorDetecting low temp values and activate the actuatorUniversal Input2High temperature sensorDetecting high temp values Universal Input3Hot water Flow sensor Excites flow in the hot water lineUniversal Input4Volume sensor Detects volume of air allowed in the chambers Universal Input5Voltage controllerControls source voltage hence optimized performance Universal Input6AHU damper inlet actuatorRegulates the amount of air entering damperUniversal Input7Air pressure control at inlet Regulates air pressure at the inlet Universal Input8Self adjusting valve actuatorAutomatic closing and opening of valvesUniversal Input9Chilled water flow sensorExcites the flow in the chilled water lineUniversal Input10Fan actuator Allows fan to draw in air when requiredAnalogueOutput1Voltage sensor in input 1Regulated current to sensor 1AnalogueOutput2Voltage sensor 2Regulated current to sensor 2AnalogueOutput3Voltage sensor 3Regulated current to sensor 3AnalogueOutput4Voltage sensor 4Regulated current to sensor 4AnalogueOutput5Voltage sensor 5Regulated current to sensor 5AnalogueOutput6Voltage sensor 6Regulated current to sensor 6AnalogueOutput7Voltage sensor 7Regulated current to sensor 7AnalogueOutput8Voltage sensor 9Regulated current to sensor 9Part1.2(10%)ThisAHU isusedtoimplement anoptimumstartand stop energysavingstrategyforthe building.Describehowthiswould beimplemented and howtheBMS outstation/controller would interact with theAHU,i.e.thesensordataused, thecontrol actionsoverthecourseof a workingday inthewinter months(northern hemisphere) to implement thisstrategy. Itis important to alsodescribe thewayinwhich theBMS outstation/controllermightbe programmedtoallowitto decidewhen to operate plant.Optimum performance is often desired such that the system is only used when needed. And this is implemented as follows: -During extreme weather conditions, when temperatures are very low, the low temperaturesensor detects this change and transmits signal to the BMS. Necessary control actions

MSc BuildingServicesEngineering–Building ManagementSystemssuch as sending of information to the high temperature sensor to allow more heat and air into the space are activated(Electronic design, 2018).Part1.3(5%) Akeyfield device in thisBMS is thetemperaturesensor. Atypical sensor typeused inthisapplicationis theplatinum resistancethermometer(PRT) that canbeusedin theform ofaprobe intotheAHU orthe associatedductwork.

Therelationship between temperaturesensedand resistancegeneratedforaPRT canbe defined bythefollowingequationoveralimited range:Rt= Ro(1+αt)R0=Resistanceat 0°C (Ω) given as 100 Ωα = temperaturecoefficient forplatinum(K-1)= 3.9 x10-3t = temperature sensed(°C)= 109oCIfthePRT is definedasa PT100(Resistanceat0°C = 100Ω) andthevalueoftemperature coefficientforplatinumis3.9x10-3perdegreeK.Ifa PRTPT100sensorisusedtomeasuretheair temperature inthereturn airductof theair handlingunit and it reads109Ωat thesensor,whatistheair temperaturein theductas measuredbythe PRT tothenearest degreeCelsius?Solution: We simply substitute in the given equation: Rt =100(1+3.9x10-3 x 109) = 143oC Part4Thedampersusedto divert airintheAHU would beoperatedbyanactuatorcontrolledby theBMS outstation/controller.List and describethe elementsof thespecification that you wouldconsiderin selectinga suitableactuatortocontroltheinlet airdamper.-The damper inlet valve must control air inflow appropriately and in real time fashion -

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