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Tubman African American Museum

Christopher ChampagneMechanical Option2003 Senior Thesis

Christopher ChampagneMechanical Option

Tubman African American MuseumAtlanta, Georgia

Presentation Outline

Presentation GoalsExisting ConditionsExisting Mechanical SystemChiller OptimizationChilled Water PumpingLighting of Gallery SpaceConclusions and Recommendations



Presentation Goals

Investigation of the air-cooled water chillers:• Museums have low load profiles during the evenings when

only the exhibit spaces or anywhere artwork is stored needs to be cooled.

• A smaller chiller for off-hours cooling and a larger one for occupied mode.

• Staging of the chillers to see if an energy savings could be realized.

Investigation of switching from constant speed pumping to variablespeed pumping:• Advantages of primary-only, variable speed pumping.• Possibility of switching the chilled water pumps in this case.• Should the switch be made?

Investigation of current lighting system in gallery space



Existing Conditions

Location: Atlanta, GAUse: MuseumSize: 45,000 ft2

Two storiesConstruction Started:

October 2001Planned Completion:

Spring 2004Construction Cost:

$15.5 million



Design Team

The PRD Group, Ltd Exhibit Designer

Souza, True and Partners, Inc. Structural

Vanderweil Engineers M/E/P

Harmon-Piedmont Construction, LLC

CM/GC

E. Verner Johnson and Associates, Inc.

Architect



Existing Mechanical System

(2) 121.5 ton HCFC-22 air-cooled water chillers

(3) 290 GPM chilled water pumps

(2) 25,000 CFM constant volume and (1) 18,000 CFM variable volume custom air handling unit.



Chilled Water Equipment

(2) Trane Air-Cooled Water Chillers121.5 tons290 GPMEWT = 55 ˚FLWT = 45 ˚FHCFC-22 RefrigerantScrew compressor

(3) Bell & Gossett 1510 - 2 ½ BB Pumps290 GPM65 ft. head1750 RPM10.0 motor HP(1) Pump Standby



Chiller Optimization Technique

The maximum cooling load is 189.1 tons on July 15th at 2 pmusing Atlanta Bin Data and Carrier’s Hourly Analysis Program(HAP).

Engineering Equation Solver (EES) was used to simulate two equalsize air-cooled chillers

1. Trane Air-Cooled Series R Rotary Liquid Chillers Model RTAA 125 (Design Capacity = 120.1 ton)

2. Trane RTAA 110 (Design Capacity = 108.5 ton)3. Trane RTAA 100 (Design Capacity = 100.6 ton).

Upper capacity that one chiller would run before the second chillerwas run was varied from 85% to 100% of capacity to see which isthe most efficient. The lower capacity at which the second chillerwould turn off was set to 40%.



Chiller Optimization Equations

The optimization equations used in the EES simulation are from the California Energy Commission’s 2001 Non-Residential Alternative Calculation Methods (ACMs) document, specifically Chapter 2 entitled “Reference Method and Required Modeling Capabilities for Alternative Calculation Methods (ACMs).”

The following three terms are functions of chilled water supply temperature (Tchws) and the outdoor dry-bulb temperature (Toa). They are used to establish the efficiency of the chiller operation.

CAP_FT is the full load capacity as a fraction of rated capacity. It is a capacity correction that is a function of those terms.

EIR_FT is the full load efficiency (kW/ton) as fraction of ratedcapacity. It is an efficiency correction factor.

EIR_FPLR is the fraction of full load power as a function of fraction of full load output.



EES Model Cases

10040113.6100.6100L

10040108.5108.5110K

10040120.1120.1125J

9540113.6100.6100I

9540108.5108.5110H

9540120.1120.1125G

8540113.6100.6100F

8540108.5108.5110E

8540120.1120.1125D

9040113.6100.6100C

9040108.5108.5110B

9040120.1120.1125A

Cap. (%)Cap. (%)

UpperLowerkWTonModelCase



Electrical Utility Rates

6.910¢ per kWhNext 190,000 kWh

8.026¢ per kWhNext 7,000 kWh

8.757¢ per kWhFirst 3,000 kWh

All consumption (kWh) not greater than 200 hours200 hours times the billing demand.

$14.00Base Charge (includes first 25 kWh or less

The electricity would be provided by Georgia Power (a subsidiary of Southern Company).

PLM-3 rate which is for small to medium building size.

“Not less than 30 kW but less than 500 kW.”



Annual Operating Cost and Time

7214,12181,393929,304L

3313,58381,763934,654K

1112,67081,284927,718J

10714,90788,9641,038,866I

5513,96685,299985,828H

2413,13684,717977,400G

121115,35093,4951,104,441F

91214,76293,7941,108,762E

61014,03492,9811,096,997D

11815,01488,9641,038,866C

8914,33989,2911,043,601B

4613,61888,5721,033,188A

RankingsRankings(hrs)($)(kWh)

Operating TimeCost

Operating Time

Operating CostAECCase



Annual Operating Cost

75,000

80,000

85,000

90,000

95,000

Cost

($)

1

Annual Energy Cost

A B C D E F G H I J K L



Life Cycle Cost of Chillers

$75,000100.6100C

$84,000108.5110B

$96,000120.1125A

First Cost (FC)TonModelCase

Where:FC = first cost of plantUCj = plant utility cost for year jMCj = relative maintenance cost for year jd = discount rateN = number of years of analysis

MCj = $500d = 12 %N = 20

The following formula from CoolTools was used in the calculation of the LCC.

( ) ( )( )∑=

+÷++=N

j

jjj dMCUCFCLCC

1

1



Life Cycle Cost of Chillers

$706,880.98

$698,458.84

$686,695.15

500,

000.

00

550,

000.

00

600,

000.

00

650,

000.

00

700,

000.

00

750,

000.

00

Cost ($)

RTAA 125

RTAA 110

RTAA 100Tr

ane

Mod

el

Num

ber

LCC of Different Size Chillers



Chiller Optimization Recommendation

• The RTAA 100 has the smallest life cycle costbased on the assumptions stated above.• However given its tonnage being only slightlyabove the design cooling load, this might not be awise selection.• The RTAA 110 would still provide cost savingsover the RTAA 125 (LCC savings = $10,422.14), alongwith some added safety to the designer.• The staging should be set to 100% of capacityof the first chiller before the second chiller is turned on.



Chilled Water Pumping

One method of saving energy used by a building is changing the primary pumps of a primary-only, chilled water system from constant speed to variable speed.

Important Considerations:

Does the chilled water system meets the requirements for being switched from constant speed to variable speed pumps?

What is the overall economic benefit along with benefits that are not quantifiable?



Advantages of Variable Speed Pumps

• Improved efficiency (motor and pump) and consequently energy savings.

• Reduced system noise.• Improved control of system flow to respond to flow

and pressure requirements of the system.• Extended motor life due to soft stops & starts

which puts less wear and tear on the parts of the pump.

• Lower installation cost.• The control valve in the bypass ensures that

neither of the chillers would become “starved” during a low load situation, as flow is diverted directly from the supply back to the chillers.



Possibility of Switching Pumps

Trane mentions four situations where variable primary flow should notbe used (Trane, 1999). They are for system where:

System chilled-water temperature is critical. Examples are a “cleanroom” or computer chip making plants.• Although there are specific temperature and humidity guidelines

for a museum, they are not critical. Slight temporary fluctuations will not cause permanent damage to the artifacts.

The system flow rate, and consequently the load, does not vary.• The load does vary in the Tubman Museum, between the occupied

hours and the unoccupied hours. Also, due to the large transient load of occupants, the location of the load varies frequently within the inside of the building during the occupied hours.

It is unlikely that the owner/operator will run the plant as designed.• This is a slight area of concern, but something that doesn’t

eliminate the use of variable speed pumps for the system.Existing chiller controls are old and inaccurate.• This is a new construction project, so this also is not a concern.



Current Piping Schematic

CHILLER 1 (CH-1):CAPACITY = 121.5 TONSHCFC-22 REFRIGERANT (2) SCREW COMPRESSORS (10) CONDENSER FANS 1.0 HP EACH 850 RPMAMBIENT MAX = 95°FAMBIENT MIN = 23°F


AFTER CHILLER:LWT = 45°F290 GPM


BEFORE CHILLER:EWT = 55°F290 GPM


CHWS

CHWR

CHWS

CHWR

AIRSEPARATOR

EXPANSIONTANK

CS PUMP (P-4):

FOR ALL PUMPS:290 GPMWATER TEMP. = 55°FNPSHR = 8.4 FTHEAD = 65 FTPUMP RPM = 1750BHP = 7.25MOTOR HP = 10

CS PUMP (P-3):

CSPUMP (P-6):(STAND BY)

SHOT CHEMICALFEEDER

PRESSURERELIEF VALVE

BALL VALVEBUTTERFLY VALVEBUTTERFLY VALVE WITH MEMORY STOP (BALANCING VALVE)CHECK VALVESTRAINER W/BALL VALVE, HOSE BIBB & CAP

AUTOMATIC CONTROL VALVE, MODULATING ACTUATOR

COMBINATION FLOWMETER/SHUT OFF/BALANCING VALVE (CIRCUIT SETTER)

UNION OR FLANGE

LEGEND:

AHU-1A&1B(LOAD)

AHU-2(LOAD)



Proposed Piping Schematic


BALL VALVEBUTTERFLY VALVEBUTTERFLY VALVE WITH MEMORY STOP (BALANCING VALVE)CHECK VALVESTRAINER W/BALL VALVE, HOSE BIBB & CAP

AUTOMATIC CONTROL VALVE, MODULATING ACTUATOR

COMBINATION FLOWMETER/SHUT OFF/BALANCING VALVE (CIRCUIT SETTER)

UNION OR FLANGE


FOR ALL PUMPS:290 GPMWATER TEMP. = 55°FNPSHR = 8.4 FTHEAD = 65 FT

VS PUMP (P-3):

VS PUMP (P-4):

VSPUMP (P-6):(STAND BY)

EXPANSIONTANK

LEGEND:

CHWR

AIRSEPARATOR

CHWS

SHOT CHEMICALFEEDER PRESSURE

RELIEF VALVE

CHWS

CHWR




AHU-1A&1B(LOAD)


AHU-2(LOAD)



Chilled Water Bypass Control

Normally closed control valve.

Permits the operation of a single chiller below its low flow limit.

Programmed to maintain only the minimum flow for each chiller that is on as opposed to constant flow, which would waste energy.

Located near to the chillers so that the pressure drop throughout the system can drop as the coil loads drop.



Additional Costs

Savings:The three-way valves are replaced with two-way valves at the AHU’s.Less piping needs to be around the load with the elimination of the three-way valves.Steel schedule 40 piping, which costs $97 per linear foot for 6” piping for 100 feet of piping, meaning a savings of $9,700.Costs:A control valve in the bypass has to be added in the bypass line, which would typically cost $1950.Three variable frequency drives must be purchased each costing $5,800.Additional cost = $9,650.



Cost Savings – Energy

There are several different techniques available forcalculating the energy savings (kWh) for variablespeed pumps.

Carrier’s Hourly Analysis Program (HAP)Bell & Gossett ESP-Plus Online ProgramEngineering Equation Solver (EES)

The results from EES will be presented further.



Engineering Equations Solver (EES)

The following terms were created using lookup tables:Flow Rate vs. HeadFlow Rate vs. Pump EfficiencyPercent of Nameplate Load vs. Motor EfficiencyPercent of Design Speed vs. Drive Efficiency (for theVariable speed pumps only)Individual functions were created for:Total PowerPump EfficiencyPump Model CurvePercent of Nameplate LoadDeciding Number of Pumps Operating Based on the LoadSpeed the Variable Speed Pumps Operate At



Engineering Equations Solver (EES)



Life Cycle Cost of Pumps

Where:FC = first cost of equipmentUCj = utility cost for year jMCj = relative maintenance cost for year jd = discount rateN = number of years of analysis

The following formula from CoolTools was used in the calculation of the LCC.

( ) ( )( )∑=

+÷++=N

j

jjj dMCUCFCLCC

1

1

In this example:FCconstant = $0FCvariable = $9,650MCj = $500d = 12%N = 20 yearsUCj constant speed = $4,092UCj variable speed = $2,369



Payback Period of Pumps

Initial Additional Cost for Variable Speed Pumps = $9,650

Yearly Savings= $1,723.53

Payback Period= $9,650 / $1,723.53= 5.6 years



Chilled Water Pumping Conclusion

Based solely on cost, it makes sense to switch from constant speed pumps to variable-speed pumps.

The LLC is $3,219.85 less for variable speed.

The payback period is slightly lengthy, but realistic.



Lighting of Gallery Space

The lighting system for a gallery space in the museum (Collection Gallery 255) was designed using industry guidelines.

The IESNA Lighting Handbook – Ninth Edition (2000)



Placement of Luminaries

X = (Ceiling height – eye level) * 0.577= (15’-0” – 5’6”) * 0.577= 66” = 5’-6”



Lightscape Renderings

Southeast corner of room from above

South of the room from above



Target Illuminance

The IESNA Lighting Handbook target illuminancefor:

Flat displays and 3-dimensional objects is 300 lx (30 fc)

Lobbies, general gallery areas and corridors is 100 lx (10 fc).



Photometric Data

Southeast corner of room from above



Photometric Data

South of the room from above



Lighting of Gallery Space Conclusion

The new lighting design is compliant with the lighting requirements stated in the IESNA Lighting Handbook for illuminance.

Artwork and artifacts are accentuated.



Conclusions and RecommendationsThe RTAA 110 would still provide cost savings (LCC savings = $10,422.14) over the RTAA 125, along with some added safety to the designer and should be selected.

The staging should be set to 100% of capacity of the first chiller before the second chiller is turned on.

The primary-only, chilled water pumps should be switched from constant speed pumps to variable-speed pumps. The LCC is $3,219.85 less for variable speed. Variable speed control also has some advantages that are not quantifiable in economic terms.

The new lighting design is compliant with the lighting requirements stated in the IESNA Lighting Handbook.



Acknowledgements

I would like to thank the following people who have made my thesis possible:• The Pennsylvania State University Department ofArchitectural Engineering faculty including:

• My advisor, Dr. James Freihaut• Dr. William Bahnfleth and Dr. Stanley Mumma• Jonathan Dougherty, Moses Ling, M. Kevin Parfitt and Kenneth Davidson

• Vanderweil Engineers, especially Heather Tsatsarones and Ron Edwards

• Fellow architectural engineering students who have lent their knowledge and expertise

• Mom, Dad and Jen who are always there for me• My friends who have been understanding and helpful



Questions

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