HVAC Systems

Alfred Woody, PEVentilation/Energy Applications, PLLCNorton Shores, Michigan231 798 3536

HVAC System Functions

Control space temperature HeatingCooling

Control space humidityControl airborne contaminates

Exhaust systemsAir filtration

Provide outdoor air for occupantsProvide space pressurization

HVAC System Components

Air handling unitAir distributionExhaust air equipmentSystem controlsCentral energy equipment

BoilersChillersDistribution equipment

Air Handling Unit (AHU)

Air intakeReturn air/outdoor air mixing boxFiltersHeating deviceCooling deviceFanHumidifier

Air Handling Unit

Air Handling Unit Con’t.

FiltersPressure drop depends on level of cleanliness desiredUsed to protect air tempering coils and maintain space cleanlinessReplacement when dirty needed to avoid excessive pressure loss and assure cleanliness

Air Handling Unit Con’t.

Heating deviceRaises air temperature 20 F to 100 FHeating options

Hot water, electric resistance or steam coilGas fired heat exchangerDirect fired gas burnerHeat recovery device

Heating Equipment Efficiency

Direct fired gas90% efficient

Indirect fired gas 80% efficient

Air Handling Unit Con’t.

Cooling deviceReduces air temperature 10 F to 20 FCooling options

Chilled water coilRefrigerant coilEvaporative coolerHeat recovery device

Air Handling Unit Con’t.

FansMoves air through AHU and distribution system with minimum noise and pressure lossOptions

CentrifugalAxialPropeller

Air Handling Unit Con’t.

HumidifierProvides moisture for heating season humidity controlOptions

Wetted padSteam Ultrasonic

Types of AHU’s

Constant volume variable temperatureVariable air flow or variable air volume (VAV)Multizone – several flows of constant volume variable temperatureDual duct – flow of warm air and a flow of cool air that mixes at each zone

Air Distribution Components

Duct systemsDampersThermostats and zone control devices

VAV boxesReheat coils Flow dampersFan powered boxes

DiffusersInsulation covering components

Types of Air Distribution Systems

Mixing – jets of air introduced into the room often at the ceiling that quickly mix with room air for desired temperatureDisplacement – low velocity air introduced into room that tries to avoid mixing often low to allow warmer room air to rise for removal at ceiling

Air Mixing

Uniform temperatureUses high velocity jetsGood for dilution ventilation, bad for hood exhaust

Displacement Ventilation

Warm air with airborne contaminants will riseLow air velocity in space with workersCooler space temperatures

Exhaust Air Systems

General exhaust where air is removed from space used in dilution ventilationLocal exhaust for contaminant removal

HoodsClose capture hood - Specially designed fixture for capture and removal of contaminantCanopy hood – air removal device localed above contaminant

Booths – Enclosure that surrounds contaminant source that is at lower pressure than surrounding space

Close Capture Hood Exhaust

Hood designed for application to capture & contain contaminantCan be single or multiple dropsWith proper air cleaning device can recirculateexhaust air.

Enclosures and Booths

Airborne contaminants containedApply exhaust for contaminant removalAir exhaust depends on openingsBest protection for workers

Exhaust Air System Components

Hood Type influences required air flow for contaminant control

Duct systemAir cleaning deviceFanStack

Exhaust Air System Components Con’t.Duct System

Flow determine by system dampers or pressure loss of components in systemFlow needs to be fast enough to carry contaminants to air cleaning device

Heavy particulate like wood chips need high velocity –3500 FPM velocityGases have the most economical flow considering duct size and pressure loss

Exhaust Air System Components Con’t.Air cleaning device

Mechanical dry type - good for big particulate Filters - good for particulate but ineffective for gasesElectrostatic precipitators -good for particulate but ineffective for gasesScrubbers - good for particulate and gases

Exhaust Air System Components Con’t.Fans

Centrifugal – good for high pressure systems with airborne particulateAxial - good for high pressure systems with no airborne particulatePropeller - good for general exhaust systems

Stack – high enough to send discharged air from local building environment

System ControlsThe HVAC system performs in a dynamic world

having varying conditions. It responds to these changing conditions by adjusting the operation of its components so that the desired environment is maintained. Conditions monitored and/or maintained include:TemperaturePressureHumidityCO2Air velocityEnergyTime

System Control ComponentsSensors

TemperatureHumidityPressure Flow rateLighting levelsElectrical powerPosition switchSmoke Time

ControllersValves – adjust hot water flowDampers – adjust outdoor air flowElectrical relay/switches – start a fan

System Control Components Con’t.Controllers

Pneumatic Normally combined pneumatic elementTypically proportional control

Electric/ElectronicOn/off or proportional control

Digital Uses microprocessors to execute software programsMore precise and accurate controlCan include time integration, demand setback, data collection, diagnostics and trouble shooting

Type Energy SourcePneumaticElectric

Control ActionsTwo positionModulatingProportional

control device positioned proportionally in response to change in controlled variable

Proportional plus Integral (PI)Improves proportional control by reducing over-shooting the adjustment to the response

Proportional-Integral-Derivative (PID)Improves PI control by adding anticipation action to the controller

Adaptive

System Controls -

LevelsLocalSystem

Combines all elements of system for optimum resultsBuilding

Combines several systems into one operationSite

Optimizes all building systems for most economical performance considering energy costDiagnostic function useful in early trouble shooting by DPW personnelCan collect energy use information

Central Energy Equipment

Heating BoilersHeat exchangers

CoolingChillersRefrigeration equipment

DistributionWaterSteamRefrigerant

Central Heating Equipment

BoilersOutput

Hot waterSteam

Fuel Natural gasOilSolid fuel

Burner typeOn/offHigh/low/offModulating

Central Cooling EquipmentChiller

Compressor typeReciprocatingScrewCentrifugal

AbsorptionHot water/steamGas fired

CondenserCooling tower waterAir cooled

Distribution System

Water – hot & chilledValves - balancingConstant flow – three way control valvesVariable flow – two way control valves

SteamPressure reducing valvesTrapsCondensate receivers/pumps

RefrigerantGas - to condenser & from evaporator coilsLiquid – condenser to evaporator coils

Other Cooling Systems

Evaporative coolingGood for dry climatesEvaporating water into air lowers air temperature

Radiant coolingIn ceiling

Other Heating Systems

Unit heatersPoor efficiency

RadiatorsFin Tube ConvectorsRadiant heaters

At ceilingIn floor

System Size Considerations

Heating and cooling loads Desired space conditionsClimateBuilding Shell performanceBuilding processes and operating equipment

Heating and Cooling Loads

Heat sink

Internal Heat source

InternalHeat source

InternalHeat source

Heat leaving with Exfiltration

Heat gains/lossesdue to infiltration

Heat gains due to solar radiation

Heat exhchange with outdoor air

Heat exchange with a ground

Heat gain /loss with cascading air in/out of adjacent space

Heat Leaving with Process Exhaust

Heat Leaving with Local Exhaust

Heat added or removed by AHU

HVAC Energy Waste & Inefficiency

AHU Waste & Inefficiency

Air intake location poor bring in contaminants

Return air/outdoor air mixing boxExcess outdoor airNo economizer cycle

FiltersExcessive pressure dropToo dirty

Heating deviceHigh flowsDirty heat exchange surfaces dirtyWater too hot

AHU Waste & Inefficiency Con’t.Cooling device

High flowsDirty heat exchange surfaces dirtyChilled water too cold

FanPoorly selected fanOperating when not required

HumidifierOperating when not required

Cabinet - poorly insulatedLeaking control valves

Air Distribution Waste & Inefficiency

Duct systemsExcessive air velocityLeaks

DampersThermostats and zone control devices

VAV boxesReheat coils Flow dampersFan powered boxes

DiffusersInsulation covering components Excess air velocity

Exhaust Air Equipment Waste & Inefficiency

Poor contaminant captureExcessive air flowsOperating equipment when not requiredFailure to recover heat from hot exhaustsPoor duct designExcessive damper use

System Controls Waste & Inefficiency

Lack of calibration and good maintenanceFailure to turn off when not neededFailure to react to occupancy changes

Temperature resetVentilation air adjustment

Lack of economizer/enthalpy controlNo central EMCS

System-wide optimizationDiagnostic and performance evaluations

Central Energy Equipment Waste & Inefficiency

Failure to reset temperatures when possibleLack of water treatment leading to fouling of heat transfer surfacesFailure to recover energy from waste streamsNot using high performance controlsUse of oversized equipment

Heat Recovery

Using waste heat to reduce energy use in some systemThere must be a heat source to recoverThere must be a simultaneous heat useIt must be cost effective

Heat Recovery Systems

From AirSensible heat exchangers

Run-around systemPlateHeat wheel

Latent heat exchanger

Heat wheelAbsorbing solution

From FluidsHeat exchangers

Shell & tubePlate

Heat pumpsRaise temperature to 180 FDouble bundle condensers can provide 140 F water

Run-Around Coils

No cross contaminationCan recover energy from multiple sourcesLow efficiencySuited for dirty air applicationsAir streams can be removed from each other

Plate Heat Exchanger

No cross contaminationNo moving partsLow maintenanceExhaust and supply airstreams must be adjacent and parallel to each otherPreheat coil needed to prevent of exhaust condensate

Thermal WheelsHigh efficiencyLow first and operating costCross contamination possibleHigh maintenance costExhaust and supply air streams must be adjacent and parrell to each otherPreheat coil required to prevent freezing of exhaust condensate

Common HVAC System ECM’s

Following will be several slides of ECM’sfound during site surveys

Thank you

Questions?