Haviland- Chiller Plant Design Considerations

Chiller Plant Design Chiller Plant Design ConsiderationsConsiderations

Jon R. Haviland, P.E., CEMAssistant Vice PresidentMarx/Okubo Associates

[email protected]

Better Buildings by Design 2005 Chiller Plant Design 2

Plant design optionsEquipment optionsNew plant design considerationsRetrofit design considerationsRetrofit project case study


Plant Design OptionsPlant Design Options


Single Chiller SystemSingle Chiller System

Loads

Tower

Chiller

TWP

CWP


Single Chiller SystemSingle Chiller SystemAdvantages– Lower first cost– Simple system for installation and control

Disadvantages– Inefficient at low load conditions– Lack of back-up and redundancy


Parallel Chiller SystemParallel Chiller SystemTower

Chiller 1

Chiller 2

Loads

TWP1

CWP1

TWP2

CWP2


Parallel Chiller SystemParallel Chiller SystemAdvantages– More efficient at low load conditions– Provides back-up and/or redundancy

Disadvantages– Increased first cost– More difficult to control effectively, especially with

different size chillers (should have computerized system)

– More equipment to maintain


Series Chiller SystemSeries Chiller System

CWP

TWP

Tower

Loads

Chiller 2 Chiller 1


Series Chiller SystemSeries Chiller SystemAdvantages– Easier to control with simple control systems– Effective with different size chillers– Utilize one stand-by pump– Good for large temperature differential systems

Disadvantages– Increased pumping requirements for chilled water– Chillers may not be interchangeable


PrimaryPrimary--Secondary Chilled Secondary Chilled Water SystemsWater Systems



Advantages– Uncouples chillers and loads to allow variable flow in

loads– Can be used with large temperature differential systems– Can be used with thermal storage systems– Can be used with water-side economizer systems– Improved control– Reduced operating costs



Disadvantages– Higher first costs– Requires more, sophisticated equipment– Requires sophisticated control system


Variable Flow PrimaryVariable Flow Primary

New chillers can operate with variable flowSimplifies system designBypass with modulating control valve required to maintain minimum flowSystem can be parallel or series design


Equipment OptionsEquipment Options


Electric ChillersElectric Chillers

Reciprocating chillersRotary screw chillersCentrifugal chillersAir-cooled chillers


NonNon--electric Chillerselectric Chillers

Absorption chillers– Single-effect absorption chiller

Low pressure steamHot waterUse in CHP applications

– Double-effect absorption chillersMedium pressure steamDirect-firedHeat recovery


NonNon--electric Chillerselectric Chillers

Centrifugal or screw chiller without electric motor– Natural gas engine– Steam turbine– Dual drive – engine and electric motor


Other Cooling SourcesOther Cooling Sources

Air-side economizerWater-side economizerThermal energy storage


New Plant Design New Plant Design ConsiderationsConsiderations

Determine requirementsDesign processAfter construction considerations


Determine RequirementsDetermine Requirements

Capacity required– Current load– Potential future loads– Redundancy requirement– Provisions for special loads


Determine RequirementsDetermine Requirements

Operating profile– Hours per day– Days per week– Continuous loads– Load diversity


Design ProcessDesign Process

Schematic design of possible options– Chiller sizing– Chiller Performance– Cooling sources– Operating temperatures– Cooling tower selection– Basic plant layout


Chiller SizingChiller Sizing

Benefits of different size chillers– Fewer total operating hours– More operation above 50% load

Depends on load profile


Even Chillers - 8,463 operating hours


Uneven Chillers - 7,624 operating hours


Chiller SizingChiller Sizing

Use of different size chillers may eliminate need for pony chillerVariable speed chillers provide improved part load performance and minimum capacity


Chiller Performance RatingsChiller Performance RatingsAmerican Refrigeration Institute Standard 550/590-98Standard conditions– Full load– Chilled water temperatures - 54 F to 44 F– Condenser water temperatures - 85 F to 95 F

Efficiency rating - kW/Ton


Chiller Performance RatingsChiller Performance RatingsPart load efficiency– Integrated Part Load Value (IPLV)

Standard temperature conditionsWeighted average of kW/ton at various loads

– Non-standard Part Load Value (NPLV)Specific application temperaturesSame weighting as IPLV


Chiller Performance RatingsChiller Performance RatingsIPLV/NPLV rating scale– A = kW/ton at 100% load– B = kW/ton at 75% load– C = kW/ton at 50% load– D = kW/ton at 25% load

ARI Standard 550-98– IPLV = 1/(0.01/A + 0.42/B + 0.45/C + 0.12/D)


Cooling SourcesCooling Sources

Use of different fuel sources provides flexibility and reliabilityTypes to be considered depend on several factors– Utility rates and structure– Load profile– Air quality considerations– Maintenance considerations


Cooling SourcesCooling Sources

Economizer cycle– Air-side generally most effective– Water-side use

Building configuration does not allow air-sideCooling for special load requirementsClimatic considerations


Operating TemperaturesOperating Temperatures

Chilled water supply temperature– Lower supply temperature

Reduced air flow requirementsImproved dehumidificationIncreased chiller operating cost versus reduced fan operating costs, especially with a VAV system



Chilled water ∆T– Higher ∆T means reduced pipe size and

pumping requirement, increased coil size, and reduced fan energy

– Optimum temperature depends on amount of piping in system


Chilled Water Chilled Water ∆∆T T ComparisonComparison



Condenser water supply temperature– Lower supply temperature improves chiller

efficiency– Approach temperature can be 6 – 10 ºF above

design wet bulb– Use 0.4% design temperature data



Condenser water ∆T– Normal 10ºF works well in most cases– Larger ∆T common with absorption chillers

due to higher load and should be considered for large systems or when the cooling tower is remote from the chiller plant

– Reduced chiller efficiency versus smaller pipes and reduced pumping horsepower


Cooling Tower SelectionCooling Tower Selection

Selection should be based on required water flow, optimum approach temperature and ∆TAllowance for potential tenant equipment loadSelection should based on water-side economizer conditions if that is part of system


Cooling Tower SelectionCooling Tower Selection

Increasing size of the cooling tower is generally the least expensive way to improve the efficiency and provide some safety margin in the systemUse of variable speed drive on the fan motor minimizes any operating cost penalty


Determine Basic Plant Determine Basic Plant LayoutLayout

Select system that will best fit needs of projectFor simpler systems, parallel system with different size chillers is probably best choice



Systems with different occupancy schedules or load requirements need more complex system– Primary-secondary plant offers most flexibility– Variable primary flow works with new electric

chillers with less complexity than a primary-secondary system



Large chilled water ∆T– Series plant– Primary-secondary with primary flow greater

than secondary flow



Analyze options– Opinion of probable costs– Operating cost estimates

Screening measuresEnergy simulation

– Life cycle costs



Complete design of chosen option– Peer review– Operator review– Determine sequence of operations


New Plant Design New Plant Design ConsiderationsConsiderations

After construction activities– Commissioning– Training


Chiller Plant Retrofit Chiller Plant Retrofit ConsiderationsConsiderations

Don’t Simply Replace; Don’t Simply Replace; ReRe--engineerengineer



Basic process should follow same steps as outlined aboveAdditional considerations– Engineer and contractor should have experience

with this type of project



Additional considerations– Engineer needs to familiarize himself with

existing plantRecord drawingsOperator interviewObservation of plant



– Constructability should be considered during design phase

Operator reviewContractor review

– Coordination critical during construction phase

Retrofit Project Case StudyRetrofit Project Case Study


BackgroundBackground

Vacated single tenant building26 years oldAdjacent buildings under same ownership with sale of one or all unlikelyBuilding to be taken to shell condition and renovated for multi-tenant useDue diligence based on these assumptions


Site PlanSite Plan


ParticipantsParticipants

OwnerProject managerProperty managers (2 firms)– Contract maintenance staff

Construction managerConsultants– Architect– Engineer


Existing Central PlantExisting Central Plant

Located in penthouseTwo 360-ton single effect absorption chillers Two low pressure steam boilers– Modified to meet AQMD requirements– Also provides heating and domestic hot water

Two cell cooling tower– Replaced three years earlier– Capacity for single effect absorption chillers


Possible OptionsPossible Options

Electric chillersAbsorption chillersEngine-driven chillersThermal storageIndependent or with adjacent building


Alternatives ConsideredAlternatives Considered

Stand-alone alternatives– Two 350-ton electric chillers– Two 350-ton absorption chillers– Two 350-ton engine-driven chillers– Electric chillers with 4500 ton-hour thermal

storage



Integrated alternatives– Provide piping between two buildings – Utilize one of the four options above for the

stand-alone plant



Single plant alternatives– Abandon plant in Building 2 and expand plant

in Building 3 with piping between the buildings– Existing Plant in Building 3

Three 250-ton electric chillers in plant on parking level P-2Cooling tower on roof



Single plant alternatives– New Equipment possibilities

600-ton electric chillerTwo 350-ton engine-driven chillersTwo low temperature chillers plus 4500 ton-hour thermal storage


ConstructibilityConstructibility IssuesIssues

Building 2 options– Electric capacity– Cooling tower and structure– Existing chilled water riser size– Noise considerations


ConstructibilityConstructibility IssuesIssues

Building 3 options– Cooling tower capacity– Condenser water riser size– Thermal storage space requirements– Engine exhaust routing– Electrical capacity


AnalysisAnalysis

Opinion of probable costsScheduleOperating costs– DOE-2 simulations– Nine options considered


AnalysisAnalysis

Other considerations– Electricity riser problem in Building 2– Impact of utility deregulation


Economic AnalysisEconomic Analysis

Based on estimated impact of deregulationFinal options– Integrated system with new chillers in Building

2 connected to Building 3 plant700-tons electric700-tons absorption



First Cost– 700 ton electric

$929,223$1,109,273 with potential bus duct repair

– 700 ton absorption$1,395,247



Annual energy cost– 700 ton electric - $778,160– 700 ton absorption - $680,769

Simple Payback– Without bus riser repair – 4.5 years– With bus riser repair – 1.9 years


Final ChoiceFinal Choice

Absorption chillers in Building 2 with connection to Building 3– Proactive ownership with long term outlook– Support from local natural gas utility– Optimum conditions for new plant in Building

2– Significant problems with expanding plant in

Building 3


Chiller PurchaseChiller Purchase

Chiller pre-purchased by owner– Maintain control over final selection and

options– Delivery critical

Potential full building tenant wanted early availabilityCity rigging restrictions – Saturday night only


Chiller PurchaseChiller Purchase

Bid to major manufacturersBid specified conditions of capacity, giving cost, efficiency, delivery and willingness to accept penalty clauseAllow manufacturers to suggest alternatives of capacity and/or efficiency and additional cost for this


New Central PlantNew Central Plant

Two 360-ton direct fired absorption chillers with lower supply temperatureOne 120-ton rotary screw chiller for off hours use (minimum effective absorption chiller capacity)Primary-secondary piping systemPiping between the two buildings with transfer pumps and metering


Single Line DiagramSingle Line Diagram


Sequence of OperationsSequence of Operations

Seven modes of operation identified with written sequenceIndependent versus integrated operationElectric or gas chiller base loadOccupied versus unoccupied


Phase IIPhase II

Building 1 central plant– Originally absorption chillers and boilers– Reciprocating chillers installed in 1987

Noise complaintsReliability issues

– Small chiller in Building 3 plant for Fitness Center after hours use with piping to lower level air handling unit


New Building 1 PlantNew Building 1 Plant

Two centrifugal chillers and new cooling tower– Tower selected for maximum capacity for space

available– Chillers selected to match cooling tower

capacity– Use existing connection (increase size to

maximize transfer capacity) with new riser


New Single Line DiagramNew Single Line Diagram


SummarySummary

Project illustrates choices available and retrofit process discussedOwnership with long term outlookCooperation by all participantsLife is easier with a vacant building

Documents

Haviland- Chiller Plant Design Considerations