Texas Laboratories, Inc. Fort Worth, Texas
TABLE OF CONTENTS
EXECUTIVE SUMMARY………………………………….. Page 2
ARCHITECTURE AND BACKGROUND…………………. Page 3
MECHANICAL……………………………………………… Page 8
ELECTRICAL……………………………………………….. Page 24
CONSTRUCTION MANAGEMENT ………………………. Page 28
SUMMARY AND CONCLUSIONS………………………… Page 33
APENDICES………………………………………………….. Page 36
EXECUTIVE SUMMARY
This thesis is a yearlong case analysis of the building systems of an existing laboratory located in Fort Worth, Texas. The 220,560 sq. ft. facility contains the fourth chiller plant on the corporation’s grounds. The plant was designed with the capability of future integration with the existing 44°F chilled water campus loop. Currently, the chiller plant services the chilled water demand of the building with the standard constant-flow primary/secondary variable speed pumping arrangement. This report summarizes the impact of converting the plant from constant primary/variable secondary flow to a variable primary flow chilled water configuration.
Currently, the system has four chillers. Three of the chillers operate at 2400 GPM and the other chiller was designed for off peak cooling at 1480 GPM. Since in a variable primary flow system, the flow rate can be reduced to 40% of the design flow or 960 GPM, the fourth 1480 GPM chiller was eliminated from the system.
Constant primary flow/variable secondary flow configuration consumes more pump energy than variable primary flow by maintaining a constant flow through the chiller. Variable primary flow pumping systems save pump energy by operating at lower system head and varying the flow rates through the chillers. At a flat electricity rate of $0.055 per kWh, the total energy savings for a variable flow primary system compared to a primary-secondary system converts into an annual operating cost savings of $18,112.
Converting the chilled water system from a traditional constant primary/variable secondary flow arrangement to a variable primary flow arrangement affects the electrical and mechanical first costs. The lower first cost for variable primary flow pumping is a result of reducing the plant size, equipment costs, labor costs, and material costs. The total cost savings including the cost of the chiller for a field fabrication application $241,637 and for a prefabrication system is $245,757.
BACKGROUND
Primary Project Team
v Owner
· Texas Laboratories, Inc is the owner expanding their current laboratory areas.
v Design
· Ewing Cole Cherry Brott completed the mechanical, electrical, structural, plumbing, fire protection, and lighting design.
v Construction Management
· Austin Commercial, Inc.
v Site Work
· Rone Engineers preformed all the site evaluation studies such as soil testing and surveying.
Building Statistics
v Dates of Construction
· Construction began August 2002 and is scheduled to be completed by October 2003.
v Cost Information
The guaranteed maximum price for the building is approximately 45 million dollars.
v Building Function
· The building functions as a laboratory that performs pharmaceutical and medical device research. Research includes the development of eye drops and contact lens solutions.
v Location and Site
· The building is located on the North side of the existing Texas Laboratories, Inc. facility in Fort Worth, Texas.
· The site was previously a parking lot that serviced the employees working in an adjacent building.
· The building area was excavated to the elevation which involved a cut greater than ten feet in some areas.
v Architecture
· The façade is a combination of brick and glazed curtain wall with varying sizes of square tinted windows.
· The conference rooms have full skylight ceilings that extend into the corridors.
· Since the laboratory replaced an existing parking lot, a corridor was incorporated into the design to link the new parking lot to the adjacent building. The hallway was added to the design to shield employees walking to work from the hot climate.
· The planned building elevation will match the elevation of the existing buildings immediately to the west.
v Project Delivery System
· The project is being completed under a traditional design-build method.
Building Systems
v Mechanical
· The building is divided into six zones to meet the varying air requirements. See Figure 1 for zone division.
· There are 10 air handling units total. Six of the five air handling units service the laboratory areas. Since these units use exhaust 100% of the air, heat pipes are used to recover energy from the exhaust air to the supply outside air. The other four air handling units condition the cage wash area, chiller room, mechanical mezzanine, and office areas.
· The building contains it own chiller plant with three 1300 ton water cooled centrifugal chillers and one 800 ton chiller. Condenser water is cooled through four induced flow cooling towers.
· In the laboratory area, negative air pressures are maintained in the lab and positive air pressures are maintained in the hallways.
v Structural
· The structural system is steel frame with vertical cross bracing.
· The floor system is concrete slab on metal deck construction.
· Lateral moment connections account for wind and seismic factors
v Lighting
· Lab areas use 8” diameter aperture incandescent downlights and 2x2 recessed fluorescents with 0.125” acrylic lens.
· Offices are lighted with 4” linear (2) lamp fluorescent indirect pendants.
· Animal holding rooms have dimming control systems
v Fire Protection
· The building is equipped with a five zone sprinkler system.
· Steel beams are encased with 1 ½” fiber board for two hour fireproofing protection
· The building is split into zones which are divided by two hour fire walls.
v Transportation
· The building has one 13’x9’ freight elevator located at the northwest section of the building.
· The second floor is primarily the mechanical mezzanine therefore; there are only two stairways on opposite sides of the building connecting the two floors.
v Telecommunications
· The data communications room is located in the mechanical mezzanine.
· All the fire protection, security, control systems, and telecommunications are wired to the data communications room.
MECHANICAL
Design Criteria
v Plant Integration
· The building is a part of a series of facilities on the Texas Laboratories, Inc. Campus. Building E contains the fourth chiller plant on the grounds. The plant was designed with the capability of future integration with the existing 44°F chilled water campus loop.
v Redundancy
· To avoid the loss of costly research due to the malfunction of the mechanical components, system redundancy was a priority to the owner
· The plant is designed to handle the peak cooling demand in the facility without the energy recovery of the heat pipes or the post cooling. During the design of the six laboratory air handling units, post-cooling coils were added to the design at the request of the owner. The post cooling coils are serviced by a separate chilled water loop than the pre-cooling coils. Four air cooled glycol chillers located outside to the west of the main plant service the post-cooling coils.
v Future Expansion
· In the future, the plant must have the capacity to provide chilled water to the adjacent building and another small expansion.
v System
· Building requires multiple systems to satisfy the varying air requirements of each zone. Refer to Table 2, to review each space requirement and Figure 1.to view zone spaces.
· Design Outdoor Air Temperatures are from ASHRAE Fundamentals. See Table1 for requirements.
ASHRAE FUNDAMENTALS OUTDOOR AIR CONDITIONSWinter / Summer
Design / Design Dry Bulb and / Mean / Design
Dry Bulb / Wet Bulb / Daily / Wet Bulb
99% / 97.50% / 1% / 2.50% / 5% / Range / 1% / 2.50% / 5%
17 / 22 / 101/74 / 99/74 / 97/74 / 22 / 78 / 77 / 76
Table 1. Design Outdoor Air Conditions for Fort Worth, Texas
DESIGN REQUIREMENTS FOR CFM AND ZONE TEMPERATURES
Minimum Outdoor / Summer Indoor / Winter IndoorZONE / Function / Maximum / Air / Design Temp. / Design Temp.
CFM / CFM / °F / °F
1 / Laboratory / 175,000 / 175,000 / 66 / 66
3 / Cage Wash / 20,000 / 20,000 / 72 / 72
4 / Offices / 35,000 / 7000 / 75 / 75
5 / Chiller Plant / 7000 / 4500 / 80 / 65
6 / Mech. Mezz. / 30,000 / 3000 / 80 / 65
Table 2. Texas Laboratories, Inc. zone design air flow rates and temperature requirements
Figure 1. Texas Laboratories, Inc. zone space requirements
Existing Conditions
Constant Primary/Variable Speed Secondary Chilled Water Plant Design
v Chillers
· (3) 1400 ton water cooled centrifugal chillers
o (1) for standby
o (2) for peak load cooling
· (1) 800 ton water cooled centrifugal chiller
o Part-load cooling
v Primary Constant Speed Pumps
· (3) 2400 GPM, (1) 1480 GPM Horizontal Splitcase
o 50 HP motor
o 55 ft. Head
v Secondary Variable Speed Pumps
· (3) 4800 GPM Horizontal Splitcase
o 200 HP motor
o 115 ft. Head
v Decoupler
· 14” diameter pipe
o Connects return and supply chilled water piping
o Installed Flow meter signals chillers on and off
v Sequence of Operation
Texas Laboratories supplies chilled water to the load with a constant-flow primary/secondary variable speed pumping arrangement, show in Figure 2. The system operates by delivering variable flow chilled water to the cooling coils while maintaining a constant flow rate across the chillers. To maintain a constant flow rate across the chillers, the unused chilled water from the chillers is bypassed. An installed flow meter in the decoupler senses direction of the flow controls the sequencing of the chillers. When the flow through the decoupler is reversed and the return system water mixes with supply chilled water, the system signals another chiller to energize. As the cooling load decreases, a chiller will be shutdown when the flow rate through the chiller is equivalent to the flow rate sensed in the bypass. The secondary chilled water pump adjusts its speed to maintain a set point determined by the differential pressure at the end of the loop.
Figure 2. Constant Primary Flow/Variable Secondary Flow Pumping Arrangement
When a chiller is energized, its associated primary water pump is energized and the valve will open. Then the DDC system energizes a condenser water pump with the respective condenser water valve. A sensor in the condenser water temperature to the chiller modulates the tower bypass valve to fully open to the tower. As the temperature rises the valve will modulate to provide flow to the tower. A signal is sent to the tower fan to maintain the set point temperature of 85°F after the valve is open. See Figure 3 to view a schematic of the condenser water loop.
Figure 3. Condenser Water Flow Diagra
Since the animal holding areas are more critical than the office space, the chilled water valves to the air handling units that serve the office and cage wash spaces will be closed in the case of very high outdoor air temperatures or system complications.
Alternative Design
Variable Primary Flow Chilled Water Plant
v Chillers
· (3) 1400 ton water cooled centrifugal chillers
o (1) for standby
v Primary Variable Speed Pumps
· (3) 2400 GPM Horizontal Split case
o 150 HP motor
o 170 ft. Head
v Bypass
· 12” diameter pipe
o Connects return and supply chilled water piping
o Installed high performance butterfly valve modulates the flow to provide the minimum flow rate through the chiller
v Sequence of Operation
Chilled water is supplied to the load with a variable primary flow pumping arrangement, show in Figure 4. Unlike a constant flow primary/variable flow secondary system configuration which maintains a constant flow rate through the chiller, a variable primary flow arrangement varies the flow according to the load demand. The primary variable speed chilled water pumps modulate their flow to maintain a preset differential pressure at the end of the load loop between the supply and return valves. The differential pressure set point should be set equal or slightly greater than the sum of the pressure drops of the control valve, coil, pipe fittings, and piping friction of the branch circuit between the supply and return mains. As the supply air temperature rise or falls below the design set point, the cooling coil valve is signaled to open or close until the water flow rate through the coils is adequate to meet the load requirements. When the load demands a flow rate below the rated capacity of the chillers, chilled water is bypassed from the supply to the return piping. If the flow rate through the chillers falls below the recommended minimum, there is a risk of freezing water and damaging the evaporator.
Figure 4. Variable-flow primary pumping arrangement
The condenser and cooling towers operate similarly to the constant flow primary/variable flow secondary system.
v Elimination of the Part-Load Chiller
For Variable Primary Flow, it is not desirable to operate varying sizes of chillers in parallel. Inconsistent chillers complex the bypass valve controls that maintain the minimum flow rate through the chiller. The chiller energy consumption is proportional to the flow rate through the evaporator. The small chiller was eliminated in the variable primary flow design because it takes less pumping energy to operate the 1400 ton chiller with a minimum flow rate of 960 GPM at part loads than operating an 800 ton chiller at low loads with a constant flow rate of 1480 GPM.