1. Chilled Water Systems Total Cost of Ownership
April 17, 2008

2. Business Development Manager - Chillers
Todd Brown
Business Development Manager - Chillers

3. AGENDA
Low temperature, low flow
Primary-Secondary vs Variable Primary Flow
Chillers in Series-Series Counterflow
Chiller-Tower Optimization

4. Goal: Minimize Capital & Operating Costs
Without Sacrificing:
Reliability, Efficiency, & Comfort

5. High Performance Chilled Water Systems:
Good for Business...
Offers lower first cost and lower operating cost.
Good for the Environment:
Reduced utility generated greenhouse gas emissions.
The Earthwise System is more that a system it is a process of designing the best chilled water system using low flow, low temp, and high efficiency for both airside and waterside systems and optimized control algorithms for sustained performance. Simply stated, the Earthwise system is the ultimate in chilled water systems for the owner, the engineer, the contractor and for The Trane Company In addition to establishing new long-term relationships, it offers the potential to Double or Triple the success ratio on targeted applied projects.

6. Example: Low Flow/ High Delta T
Base Design: 450 Tons
Design wet bulb: 78 F(25.5C)
Entering condenser water temperature (ECWT): 85 F(29.4C)
Evaporator and condenser temperature differences: 10 F (5.6C)
Coil, valve and chilled water piping pressure drop: 80 ft
Condenser water piping pressure drop: 30 ft
Pump efficiency: 75%
Pump motor efficiency: 93%
ASSUMPTIONS
Our base design is a 450-ton chilled water system. This slide shows the assumptions made about about this system.
“Rule-of-thumb” numbers were used to select the chiller. The 10-degree temperature differentials shown equate to 2.4 gpm/ton in the evaporator and 3.0 gpm/ton in the condenser. We’ll refer to these flow rates often.

7. example chilled water plant … Chiller (2.4, 3.0 gpm/ton)
Consumption: 256 kW (0.569 kW/ton)
Evaporator pressure drop: ft
Condenser pressure drop: ft
The first thing we note about the chiller is that its performance is “pretty good.”
On the other hand, the evaporator pressure drop may seem rather high—it is!! But to obtain chiller performance of kW/ton, the evaporator approach must be very close. That’s why the selected chiller includes enhanced evaporator tubes. We’ll talk more about this pressure drop later.

8. example chilled water plant … Cooling Tower (3.0 gpm/ton)
Power rating: 30 hp
Tower static head: 10.0 ft
Here’s the cooling tower data for our base design.
Given the previous data, total condenser water pump pressure drop is:
30 ft ft ft = 69 feet
This is a fairly normal situation.
Using a motor efficiency of 93%, tower fan consumption is 24.1 kW.
30 x / 0.93 = 24.1

9. example chilled water plant … Design Formulas
ASSUMPTIONS
As we consider various design alternatives for our example chilled water plant, let’s make some assumptions to keep this presentation simple.
Here’s what we won’t alter from our basic design:
1. The pipes. (This would certainly be true for a retrofit application.) It also means we can calculate system pressure drop using the fan (pump) laws.
2. The chiller. Keeping the same chiller will give us a very close “apples-to-apples” comparison of how pumping power affects operating costs.
3. We’ll also use the same chilled water coil in each alternative.
Here’s what we will change from our basic design:
1. The evaporator and condenser water flows. This will change the pressure drops through the system, through the bundles and through the chilled water coil … but it won’t change how we calculate pump power (hp, kW).
In our example, we’ll change the flows to 1.5 and 2.0 gpm/ton, respectively, on the evaporator and condenser. This equates to a 16-degree Delta-T across the evaporator and a 15-degree Delta-T across the condenser. These aren’t “magic” numbers, but they often result in an efficient chilled water system design.
2. We’ll also change the cooling tower size as appropriate, since the larger temperature difference will permit us to use a smaller cooling tower.
1.85
DP2/DP1 = (Flow2/Flow1)
gpm œ rpm
Head œ (gpm)²
Power œ (gpm)³

10. example chilled water plant … Chilled Water Pump (2.4 gpm/ton)
System conditions …
System head: 80 ft
Bundle head: ft
Flow rate: gpm
Pump power …
36.7 hp
29.5 kW
Here are the power requirements for the chilled water pump at the system conditions shown; that is …
(80 ft ft) x 1080 gpm / (3960 x 0.75) = 39.9 hp
36.9 hp x / 0.93 = 32.0 kW
Forget the pump selection equations already? Here they are again …
hp = (gpm x PD) / (3960 x pump efficiency)
kW = (hp x 0.746) / motor efficiency

11. example chilled water plant … Condenser Water Pump (3.0 gpm/ton)
System conditions …
System head: ft
Bundle head: ft
Tower static: ft
Flow rate: 1350 gpm
Pump power …
26.0 hp
20.8 kW
And here are the power requirements for the condenser water pump …
(30 ft ft ft) x 1350 gpm / (3960 x 0.75) = 31.4 hp
31.4 hp x / 0.93 = 25.2 kW

12. example chilled water plant … System Energy Consumption
With 2.4, 3.0 gpm/ton flows …
(0.043, L/S/KW)
2.4/3.0
Chiller 256.0
Chilled Water Pump 29.5
Condenser Water Pump 20.8
Cooling Tower 24.1
Total kW 330.4
Let’s look at the system totals (since we remember that the meter is on the building.)
The question is this: Since the meter is on the building, is there anything we can do to make the system better?

13. example chilled water plant … Low Flow System
Base Case Low Flow……………….
ARI , 16dT F, 14dT F, 14dT; 83.3 F F, 16dT
2.4/ / / / /2.0
Chiller
Chilled Water Pump
Condenser Water Pump
Cooling Tower
Total kW
So, we get the “best” full-load system performance with low flow in both the evaporator and the condenser. (You could say that it’s a “low-flow” system from an energy standpoint as well as water!)
What else can we discover by examining this chart?
1. Oh my gosh—the chiller’s consuming more power in the low-flow alternatives than in our base design … we’d better not do that! I equate this to the Wizard of Oz saying, “Pay no attention to that man behind the curtain.” Of course you pay attention to him! Of course you need to pay attention to the tower and pumps! (The meter is on the building, remember?!)
2. Reducing water flow really cuts pump kW.
3. Looking only at full-load system operation, which plant design should we choose?
Yes, the one with low evaporator and condenser flows. In fact, it’s full-load power consumption is almost 4% less than that of the base design. Said another way, it cuts system power by almost 0.03 kW/ton! (Some chiller manufacturers would kill to be able to do that!)

14. What About Part Load Operation?
We’ll use …
Chiller kW values for NPLV
Derived from the selection program
Cooling tower kW
Tower energy at part load based on being linear with speed reduction
And constant kW values for the …
Chilled water pump
Condenser water pump
ASSUMPTIONS
What happens at part load? For simplicity’s sake, we’ll use the APLV relief numbers from the chiller selection program to find out. You can use lower values, if you’d like, but you’ll see that the chiller is not the limiting factor here. Apart from the chiller APLV values, we’ll use what’s on the chart.

15. Part Load Operation

16. Experienced designers use pump, piping and tower savings to select an
you ’
ve got more …
System Design Options
Either •
Take full energy (operating
cost) savings Or
Reduce piping size and cost
Experienced designers use pump,
piping and tower savings to select an
even
more
efficient chiller

17. Decoupled Systems
moving to…
Variable Flow Systems

18. Primary– Secondary design 58.0°F 44.0°F 58.0°F 44.0°F 58.0°F 857 gpm
(each)
44.0°F
857 gpm
primary pumps
2571 gpm
58.0°F
bypass (decoupler)
44.0°F gpm
58.0°F 2571 gpm
secondary pumps

19. Variable Primary design 58.0°F 44.0°F 58.0°F 44.0°F 58.0°F 44.0°F DP
857 gpm
Variable Primary
design
58.0°F
44.0°F
857 gpm
58.0°F
44.0°F
857 gpm DP
(typical)
2571 gpm
58.0°F
44.0°F gpm
58.0°F 2571 gpm

20. Variable Primary part load
off
off
56.0°F
44.0°F
1050 DP
(typical)
1050 gpm
56.0°F
Maximum Flow = 1300 gpm
Minimum Flow = 244 gpm
Selection Flow = 750 gpm
44.0°F gpm
56.0°F 1050 gpm

21. Variable Primary part load
off
56.0°F
44.0°F
525
56.0°F
44.0°F
525 DP
(typical)
1050 gpm
56.0°F
Maximum Flow = 1300 gpm
Minimum Flow = 244 gpm
Selection Flow = 750 gpm
44.0°F gpm
56.0°F 1050 gpm

22. Primary– Secondary design off 51.2°F 44.0°F 51.2°F 857 gpm 44.0°F
(each)
44.0°F
857 gpm
primary pumps
1714 gpm
51.2°F
44.0°F
664 gpm
44.0°F gpm
56.0°F 1050 gpm
secondary pumps

23. Lower Capital Cost Variable Primary advantages
Fewer …
Pumps
Motors
Pump bases
Starters and wiring
Fittings and piping
Controls
Less labor

24. More Available Space
Opportunity to …
Add other equipment
Select larger, more efficient chillers
Improve service access

25. Simplified Control
Unfetters chillers from flow-based control
Operates distribution pumps to transport water
… not to start/stop chillers

26. Improved Reliability
Provides system with …
Fewer pumps and accessories
Fewer chiller recovery options
Fewer pump recovery options
Better balance between pumps and chillers online

27. Chiller Selection Considerations
Evaporator flow limits
Rate-of-change tolerance
Flow “range-ability”
Difference between selection flow rate and evaporator minimum flow limit

28. What are other’s saying???
Variable Primary Flow Chilled Water Plant Design …

31. Reduces total annual plant energy 3-8% Reduces first cost 4-8%
VFP systems:
Reduces total annual plant energy 3-8%
Reduces first cost 4-8%
Reduces life-cycle cost 3-5%*
*Relative to conventional Decoupled chilled-water systems.

32. VPF System More information
“Don’t Ignore Variable Flow,” Waltz, Contracting Business, July 1997
“Primary-Only vs. Primary-Secondary Variable Flow Systems,” Taylor, ASHRAE Journal, February 2002
“Comparative Analysis of Variable and Constant Primary-Flow Chilled-Water-Plant Performance,” Bahnfleth and Peyer, HPAC Engineering, April 2001
“Campus Cooling: Retrofitting Systems,” Kreutzmann, HPAC Engineering, July 2002
Over the past 18 months we have received more questions concerning Variable Primary Flow systems than anything else. It is obvious that there is a huge interest in these systems. For more information you may refer to the three articles mentioned above -- they are generic and do not mention manufacturer’s names.
As a system designer or engineer I would caution you to critically read any article that doesn’t cover both benefits and drawbacks. VPF systems are not a panacea.

33. unsuited for Variable Primary Flow
Inadequate control capability
Insufficient chiller unloading
Vintage chiller controls
Poor financial return
(Consider chilled water reset instead)

34. Series Evaporator Systems
Parallel VPF Systems
moving to…
Series Evaporator Systems

35. VPF system configurations Series-Counter Flow
VFD

36. VPF system configurations Series-Counter Flow
Upstream Chiller
Single
Compressor
Chiller
Lift
62.82° F
Downstream Chiller
Lift
54.86° F
Series-Counter flow
Arrangement
Lift
55.63° F
48.96° F
41° F
41° F
Upstream chiller: = 54.86
Downstream chiller: = 55.63
Average lift: (vs for single compressor (12%))
Better chiller efficiency, but high P

37. Chiller–Tower Optimization … Do It Right!

38. chiller–tower optimization The Question …
What’s the “right” condenser water temperature?

39. Or Said Another Way … kW Condenser Water Temperature
This is a 1,000-ton centrifugal chiller at half load. At the wet bulb this hour, the coldest water the tower can produce is 72°F.
A couple of things to note:
The tower’s power is a cube of the speed, so that’s why you see the difference between 72° and 78°F.
The reduction for the chiller actually starts turning up at some point.
There is about an 11% difference in power consumption between running the towers as hard as possible (72°F) and the optimal condition.
As a rule of thumb, we’ve found that most times, if you can reduce your tower speed to half without going above the design condenser water temperature, it’s most often worth it for centrifugal chillers.
Helical-rotary chillers tend to fare better at colder tower temperatures. The amount of head pressure relief is dependent on compressor type and design.
Condenser Water Temperature

40. chiller–tower optimization How Do You Do It?
The optimization control strategy can be programmed into our BAS energy management systems. So the “rule” is that the chillers and the control system both must be McQuay.
With real-life controls!

41. How do you do it? MicroTech II and BAS Combination
The optimized method requires auto-adaptive controls. This control logic constantly adjusts the condenser water supply temperature to the value that uses the least amount of power. The controller measures the power requirement for the chiller and cooling tower. The condenser water temperature setpoint then is altered and the power consumption is checked again. If the total power consumption goes down, a similar adjustment is made and the total power is checked again.

42. What’s good for the component … may NOT be good for the system!
What’s good for the chiller (or the tower) may not be good for the system. Let’s look at a few control options, then examine the effect of those options.

43. where’s the meter? The Only Possible Response …
On the building!
The only possible question to ask the owner, designer, whoever is this—”Where’s the meter?”
Said another way, “How many chiller plants have you been involved in where the meter was on the chiller?”
In 17 years, I’ve seen some on the chiller PLANT. If we want to reduce the owner’s operating costs, we need to examine the meter’s location. It’s on the building or at a minimum the chiller plant.

44. chiller–tower optimization In Summary …
Defines the optimal entering condenser temperature
Optimal control is the right thing to do … AND it saves money
Savings are real and can be quantified
The control strategy is available NOW!
Besides the fact that we’re working to expand the portion of the system that’s optimized, the important points to remember are these:
Colder is NOT better.
Optimal control saves money.
It’s available NOW.

45. Lowest Total Cost of Ownership
Exploit technology!
Low flow
Low temperature
High efficiency
Controls
Leverage:
Optimized Controls
Variable Primary Flow
Series Evaporators
First
Cost
Operating
Cost
In summary, the EWS is a design process that looks at the entire system and features low flow low temperature and high efficiency on both the waterside and the airside.
In addition we must take advantage of the latest controls technology to provide the optimum system level controls.
It is about changing today’s design parameters and lowering both first cost and operating cost to provide the ultimate value for the building owner.

46. Questions or Comments?
Ask for questions about optimization. Possible answers:
To a certain point, we’ve found that it’s best to reduce the tower fans to low speed and let the water temperature elevate. Be careful. Hotter is not always better either.
At this point, we will not be releasing the control algorithm. However, CPL is available that can be used in Tracer Summit®. Let’s just say that data available in BAS systems is used to find the minimum tower-plus-chiller energy consumption. (May want to refer back to the “component models” slide.)
In general, the optimal water temperature for helical-rotary compressors is lower than for centrifugal compressors. This is inherent in their respective designs. The less head it pushes, the better it likes it.
The system was first installed and working at a 5,750-ton job site. The initial control installation was difficult BECAUSE IT WAS THE FIRST TIME. However, since then it has been implemented in Tracer Summit and can be “used.”
We’ve considered looking at optimization for variable condenser water flow and water temperature, but don’t have a date for tackling this project yet.
This is applicable to both existing and new construction. We believe it will be especially valuable in existing buildings where the owner is interested in operating cost savings.