chilled water loop capacity study chilled water loop capacity...2.1 overview of chilled water system...

Chilled Water Loop

Capacity Study

Minnesota State

University Mankato

SBA Project No. 250807.00

March 2014

Prepared by: Contact: John Carlson

1450 Energy Park Drive Suite 300

St. Paul, MN 55108 Main: 651-634-0775

Fax: 651-634-7400 email: [email protected]

Minnesota State University Mankato March 11, 2014 Sebesta Blomberg & Associates, Inc.

Chilled Water Loop Capacity Study Page 1 Project No. 250807.00

Section Page

1.0 Executive Summary ...........................................................................................................2

2.0 Report Scope and Campus Background ..........................................................................3

2.1 Overview of Chilled Water System ...................................................................................... 3

3.0 Ability to Add Chiller Capacity at Trafton .....................................................................5

4.0 Control Narrative - Interface of Trafton and Main Plant .............................................6

4.1 Interface with Trafton Control Points ................................................................................... 7

4.2 Trafton Chiller Operation Sequences .................................................................................... 7

5.0 Update Campus Chilled Water Model ...........................................................................11

5.1 Campus Chilled Water Loads ............................................................................................. 11

5.2 Scenario 1 – Summer 2013 ................................................................................................. 12

5.3 Secondary 2 – Proposed 3-5 Year Build-Out ...................................................................... 13

5.4 Secondary 3 – Proposed 5-10 Year Build-Out .................................................................... 13

5.5 Secondary 4 – Proposed 10-20 Year Build-Out .................................................................. 14

5.6 Scenario 5 – Building Coil Improvements (With Proposed 10-20 Year Build-Out) .......... 15

6.0 Energy Savings and Operational Improvements by Integrating Operation of

Trafton and Main Plant...............................................................................................................17

7.0 Review PBEEP Study Recommendations for Chilled Water System .........................18

8.0 Additional Chilled Water System Recommendations and Comments .......................23

8.1 Differential pressure control for secondary pumps: ............................................................ 23

8.2 Staging of Tower Fans ........................................................................................................ 23

8.3 Tower water supply temperature setpoint: .......................................................................... 24

8.4 Main Plant cooling tower water supply header pressure setpoint: ...................................... 24

8.5 Control system devices – check calibration: ....................................................................... 24

8.6 Chilled water supply temperature setpoints: ....................................................................... 25

8.7 Site differential pressure alarms: ......................................................................................... 25

8.8 Main chiller plant Annex: ................................................................................................... 25

9.0 Scope from Proposal ........................................................................................................27



1.0 Executive Summary

Sebesta Blomberg & Associates was retained by Minnesota State University, Mankato (MSU Mankato)

to 1) to evaluate the capacity of the campus chilled water distribution loop including future campus

chilled water loads, and 2) Trafton chiller operation including integration into campus-wide chilled water

control system, 3) ability to increase chiller capacity in Trafton or other locations on campus, and 4) other

miscellaneous chilled water system tasks.

The updated current and future building loads were inputted into the model that Sebesta has kept on the

MSU Mankato campus for many years. The model indicates a future diversified peak campus load of

4,700 tons versus the 2013 projected peak of 4,193 tons. With an installed capacity of 4,000 tons located

in the Main Plant and Trafton, the campus must consider locations for capacity expansion.

The hydraulic model shows that Armstrong is the critical load to serve. This is due to a large pressure

drop in the service line to the building. The installation of an inline booster pump on Armstrong will be

needed as the campus loads grow over the next several years. With the booster pump for Armstrong, and

without improvements to site ΔT, the distribution system allows the current pumps at the Main Plant and

Trafton to adequately pump water to all end users. We were asked to model the improvement if the

temperature differential across 13 buildings was improved from the current 10° - 12° to 15° ΔT through a

coil replacement effort. Overall flow was reduced by 1500 GPM and the operating head on the plant

secondary pumps was reduced 40’ at peak flows.

The Trafton plant was reviewed for expansion of capacity and was found that the existing two chillers did

not leave sufficient room to install any significant additional capacity. Sebesta suggests that MSU

Mankato consider a Main Chiller Plant “Annex” that could house one or two chillers for future growth. It

is suggested that these chiller(s) would be more efficient that existing chillers (new variable speed

technology) and would become base loaded chillers after installation. The Annex would be separately

connected to the existing campus distribution system since the current lines from the Main Plant are sized

for current capacity.

The integration of the Trafton chiller into the campus-wide control system was investigated. A narrative

was created that describes the two primary modes of operation: 1) discharged at a “fixed” flow rate based

on a signal from the Main Plant as a stage of overall campus cooling, or 2) able to operate separate from

the Main Plant to provide capacity and adequate differential pressures to the campus. Along with the

control narratives, a definition of what control and monitoring points and functions are needed to make

Trafton dispatchable as an active component of the overall campus chilled water system.

Several operational and energy savings opportunities are presented in the report. The primary energy

savings comes from optimizing the operation of the cooling towers and better control of pumping. For

the cost of programming and a differential pressure sensor in Trafton, savings of $25,000 - $30,000

annually is achievable from the operation of the Main Plant and Trafton.



2.0 Report Scope and Campus Background

Sebesta Blomberg & Associates (Sebesta Blomberg) provided a proposal to provide engineering services

for various chilled water tasks at Minnesota State University, Mankato (MSU Mankato) under a

deliverable titled Chilled Water Loop Capacity Study. The proposal was based on knowledge of the

site from previous projects and discussions with Steve Ardolf regarding several areas of the chilled water

system operation that required analysis. Sebesta Blomberg was to provide cost and potential savings

required for decision making, methods to upgrade controls and communication, and other items. The full

list of tasks that were included in the proposal is included in Section 9 of this report.

The focus of this Chilled Water Loop Capacity Study at MSU Mankato includes the following:

One day site visit with prep and follow up

Review increasing Trafton capacity

Narrative for communication and control upgrade from Main Plant to Trafton (improve operation

and integration)

Update chilled water system hydraulics including confirming current and future loads and

potential location of future capacity

Energy and operating cost savings from communication with Trafton

Review PBEEP CHW findings

Identify potential for further operation improvements and identify cause of several operational

concerns raised during site visit

Sebesta Blomberg visited the site on July of 2013. The morning was spent at the Main Plant, primarily at

the chilled water system control screen, and also discussing recent controls and system upgrades as well

as control system modifications. During the afternoon we adjusted some setpoints and opened up

discussion with plant and maintenance staff. We walked through the Main Plant as well as the Trafton

chiller plant.

2.1 Overview of Chilled Water System

The chilled water system at MSU Mankato was designed as a primary / secondary chiller plant with

tertiary pumps at each building. The design conditions for the chillers were 44° - 56° (12°ΔT) so primary

pumps were designed at 2 GPM/ton. Plant variable speed secondary pumps were sized for a campus load

that was much less than the current campus. Over time they were no longer able to deliver design flows

to the buildings.

The building pump design was not consistent across the campus – they included constant and variable

speed pumps with design operating heads of 30’ – 100’ resulting in excessive or deficient building flows.

The building pumps were operating in series with the plant secondary pumps and were “pulling” water

from the plant. The buildings competed against each other for chilled water flow.

When Sebesta Blomberg first started analysis of the campus chilled water system in 2005, the actual site

operating conditions were at best 10°ΔT on a design day, with an average of approximately 7.5°ΔT.

Since the plant was a primary / secondary design, at low ΔT conditions it was not capable of providing



design or nameplate chiller capacity to the site. Peak plant production was perhaps 2600 tons out of a

nameplate 3,200 tons of installed capacity.

When the site loads exceeded the capacity of the main chiller plant, two 400 ton chillers were added at

Trafton in two phases bringing total campus nameplate capacity to 4,000 tons. The Trafton chillers had

design conditions of 54° – 42° and were configured with variable primary flow - each chiller directly

connected between return and supply mains with variable flow rates through the chiller. The chillers

currently are operated in a fixed flow mode, with operators manually setting the flow rate at the chiller

panel.

System performance has improved with the addition of new buildings that operate at 12° – 15°ΔT, the

removal of all building pumps, the replacement of secondary pumps with pumps with enough capacity to

flow the buildings as well as the site, and significant improvements to equipment operation at the plant.

The chillers are running better, with higher efficiency and more capacity than we have seen at this plant

before. Plant improvements have included:

Tube replacements, overhaul, and new touch screen control to Chiller #1 (McQuay 1000 ton unit)

Overhaul Chiller #2 (Trane 1000 ton chiller), replacement of tubes and install new touch screen

Rebuilt Chiller #3 (Trane 1200 ton chiller), new oil pump, replaced 60 tubes (touch screen wasn’t

added yet but should be funded and installed)

Cooling towers were clean, balanced and updated

Library chillers are still installed and capable of cooling the building and separating it from the

campus but those chillers are near end of life and future planning is based on them being removed

Site distribution piping has also been looped and upgraded to improve pumping hydraulics

Current peak site loads have increased to approximately 4,000 tons which is equal to the installed chiller

capacity. Site temperature differentials have increased to 11.3°ΔT and are expected to trend to 12° or

higher in the future. Actual site conditions vary throughout the year and site ΔT still drops to 7° – 8° at

times. Sebesta has included a model of the impact of increasing site ΔT to 15° in Section 5.6.

Chiller capacity exists at the Library that is capable of cooling that building during peak loads by isolating

it from its normal service by the campus chilled water system. This emergency procedure will not

continue since the chillers are nearing end of life and haven’t been used in several years. All future

capacity planning is done without considering further use of the Library chillers.



3.0 Ability to Add Chiller Capacity at Trafton

The study Sebesta Blomberg provided in 2005 estimated a future campus cooling load of approximately

4,800 tons. After getting updated information from staff for this report, projections in Section 5 project a

future diversified site load of 4,700 tons. The 2005 study recommended a satellite plant with capability of

providing 1600 tons of cooling be installed in addition to the 3,200 tons of capacity at the Main Plant.

The study assumed that the Library chillers would not be replaced when end of life was reached but were

a short term way of dealing with peak campus loads by removing the Library from the central system.

The Trafton location was considered and hydraulically modeled. The additional capacity at Trafton

would serve the Trafton load as well as exporting capacity into the campus distribution system.

The Trafton chillers were installed during recent projects, with two 400 tons chillers being installed with

primary variable flow configuration, which can be manually operated and but were not integrated into the

automatic operation of the campus chilled water system. The current footprint of the two chillers is about

33’ wide (with 36” - 42” electrical clearance on each side. The length of each chillers is about 35’ with

additional space required for access, tube pull, and chilled water and condenser water pumps and piping.

There is only 11’-3” of clearance between the chillers but a minimum of 14’ is needed to install a third

400 ton chiller. It is not possible to “insert” a chiller between the existing two units and there is no

acceptable space available in the lower level of Trafton for a reasonably sized chiller. A single 400 ton

unit would not cover the future shortfall of 700+ tons of capacity.

Beyond the lack of space for a new chiller inside the building, additional tower capacity can’t be installed

within the tower enclosure that had been constructed. An additional 400 ton tower requires a minimum of

13’ of free space and there is only 11’ available between last tower and the enclosure wall. Additionally,

the condenser water piping from the towers to the chillers was not sized to allow expansion of chiller

capacity. In fact, there have been some issues reported with existing piping and tower water pumping.

Further consideration of installing additional capacity at Trafton is not recommended.



4.0 Control Narrative - Interface of Trafton and Main Plant

The primary concern about the operation of Trafton is the lack of remote control of the chillers by the

Main Plant Operators through the Andover DDC system. This lack of communication and remote control

prevents the Trafton plant from being integrated into the campus chilled water system. The Main Plant

can monitor operation of the Trafton chillers (chilled water supply and return temperatures, flow, and

enable / disable are on the chiller plant system screen). The chiller enable / disable, as well setpoints for

both supply temperature and flow setpoint are set manually through the Local Chiller – Cooling Tower

DDC Control System. The chillers are interlocked locally with the appropriate pumps and towers – not

selectable from Main Plant. The towers also appear to have a local tower water supply temperature

setpoint that was shown in an early sequence of operation to normally be 70°F but from operating logs the

tower water temperatures are actually between 80° and 85° almost all the time. Towers also have sump

heaters energized from the local DDC controller.

An early sequence mentioned resetting the supply temperature based on maintaining a constant return

temperature. We don’t understand the purpose of doing this and don’t believe it is currently being used.

It is important to remember that the Trafton building HVAC was designed to operate at a higher ΔT than

most of the campus. When the Trafton chillers are in operation, a very high percentage of the cooling

produced remains within Trafton.

A problem reported by not being able to control the Trafton chillers from the Main Plant is distribution

system pressure spikes. When the Trafton chillers are in operation and the campus loads decrease, the

control sequences at the Main Plant will automatically drop Main Plant chillers as they unload. If the last

chiller at the Main Plant drops off with decreasing campus load, the Trafton chillers could remain in

operation at a fixed flow rate. As the campus loads further drop off and the control valves in the

buildings continue to close, the high flow rate from the Trafton chillers would create unacceptably high

differential pressures and lead to an operating pressure spike.

Sebesta Blomberg was asked to provide a control narrative, to be implemented by the control contractor,

to address these issues and to provide more flexibility in the operation of these two 400 ton chillers. The

Trafton chillers need to be integrated into the long term operation of the campus chilled water system.

The changes in sequence of operation and interface with the Main Plant will be done through the Utility

Plant FX Control System and required upgrades in Extended Architecture (by others).

The narratives in this Section require that the following items be controllable from the Main Plant control

panel for each chiller as stated below:

1. Status of chiller – enabled or disabled from the Main Plant versus locally. The Local Chiller –

Cooling Tower DDC Control System had enabled chillers based on ambient temperature.

2. Chiller control mode selectable as Local (local DDC panel) or Remote (controlled from Main

Plant). When in Remote, operation can be Automatic Fixed Flow or Automatic Variable Flow

(under automatic control from Main Plant sequence of operation) or Manual (under control of

Main Plant for manual add or subtract and setpoint changes). The Local / Remote switch should

be located at Trafton and the Automatic Fixed or Variable Flow / Manual software switch to be

activated from the Main Plant



3. Control of starting a chiller – selected as automatic or manual (limited by time between restarts)

4. Chiller flow setpoint (primary pump flow rate)

5. Condenser water flow setpoint

6. Chilled water supply temperature setpoint

7. Cooling tower supply water temperature setpoint

8. Site DP control can be assigned to Main Plant or to Trafton Plant

The existing Local Chiller – Cooling Tower DDC Control System will remain in control of condenser

pump, chilled water pump, cooling tower fans and isolation valves, and sump heater. Current sequences

indicate that tower fans are not run in parallel in response to tower temperature. We want that changed to

parallel operation – both fans ramping up and down at the same speed if both towers are enabled. If

desired, some of these local functions could be transferred to the Main Plant control panel (for example:

control of flow to each tower to enable and to flow one or both towers with a single chiller).

4.1 Interface with Trafton Control Points The following points should be monitored and available for display or view from the Main Plant control

panel for each chiller:

1. Status of chiller

2. Compressor motor amps or kW (or % full load amps (% FLA) or % design kW as available from

chiller panel)

3. Chilled water supply and return temperatures

4. Chilled water supply and return pressures

5. Chilled water flow and setpoint

6. Chiller summary alarm

7. Cooling tower supply and return temperatures

8. Cooling tower basin temperature

9. Cooling tower supply and return pressures

10. Condenser water flow and setpoint

11. Tower water makeup water flow

12. Cooling tower vibration alarm

13. Cooling tower fan VFD alarm

14. Chilled water pump VFD alarm

15. Condenser water pump VFD alarm

16. Refrigerant warning

17. Refrigerant alarm

4.2 Trafton Chiller Operation Sequences Provide a selector for the following chiller operating modes be provided on Main Plant screen:

1. Automatic Fixed Flow: dispatched remotely by Main Plant. Site DP maintained by Main Plant

pumps.

2. Automatic Variable Flow: provide capacity and flow to satisfy the site differential pressure

(assumes Main Plant is not in operation which would indicate a very low campus load or during

periods when the Main Plant is shutdown or in a manual fixed flow mode)



Note: control of the Trafton chillers will remain capable of reverting to local control with the existing

controls (Local Chiller – Cooling Tower DDC Control System) if switched from remote to local to

provide emergency operation or testing.

Each chiller has a design minimum and maximum flow rate that was provided in Trane data sheets. The

minimum is typically the setpoint for the minimum flow switch that allows the chiller to start when

sufficient chilled water flow exists (velocity of around 2 FPS with enhanced tubes). The minimum flow

for Trafton chiller 1 is 300 GPM and 350 GPM for chiller 2. To provide some cushion on minimum flow

switch setpoint, a minimum for chiller 1 of 350 GPM and 400 GPM for chiller 2 should be programmed

(to prevent confusion, it is acceptable to use 400 GPM as a programmed minimum flow for both chillers).

The maximum flow velocity through evaporator tubes is 10 – 11 FPS. 10 FPS would be 1500 GPM for

chiller 1 and 1725 GPM for chiller 2. The site would have to be operating at about 6° ΔT to fully load the

chillers at those flow rates. A more reasonable max is based on an 8° site ΔT or 1200 GPM max flow.

These flows (400 GPM – 1200 GPM) should be programmed as min and max flows through both chillers.

4.2.1 Narrative – Automatic Fixed Flow Mode, dispatched by Main Plant:

As with the Main Plant chillers, Trafton chillers 1 and 2 are assigned a stage in the sequence of adding

and subtracting chillers based on changing site load. Typically they will be Cooling Stage 4 and Cooling

Stage 5 after the three Main Plant chillers have become fully loaded or additional flow is needed based on

losing chilled water setpoint from the Main Plant. Trafton chillers can be added automatically based on

current “Need Setpoint” (if Automatic Fixed Flow is enabled for Trafton chillers) or they can be added or

subtracted manually by the operator if in Manual mode.

When the stages of cooling calls for Trafton chillers to operate, the default startup flow setpoint is the

minimum flow rate for each chiller at the chilled water supply temperature indicated on the Utility Plant

Chiller Staging Setpoints screen. Startup flow and supply temperature can be manually overridden from

Main Plant control screen. Five (5) minutes (adjustable) after the startup flow setpoint is reached, the

flow setpoint will be increased (adjustable rate of increase) to a default maximum flow of 800 GPM

(adjustable) or will stop increasing if the chiller % FLA reaches 95 % (adjustable). NOTE: this maximum

compressor load limits flow when the Trafton ΔT is greater than 12°. If FLA is reached, compressor inlet

vanes will close to unload the chiller and protect from overloading the compressor motor. Leaving

chilled water temperature will increase when chiller unloads. Target flow setpoints can be overridden

prior to units being staged on but will revert to the 800 GPM target default after they are staged off. If the

site is at a low ΔT, the operator can increase the target max flow setpoint at any time to more fully load

the chiller.

While in Automatic Fixed Flow, dispatched by Main Plant, the Main Plant secondary pump flow will

vary speed to maintain an adequate site differential pressure (see revisions to Main Plant DP control in

Section 8.1). As site loads drop off the Main Plant controls will drop chillers but maintain control of site

DP. If MSU Mankato wants to implement a control strategy to help prevent the pressure spikes that have

occurred, the following in italics can be programmed – but the existing control system should handle

pressure spikes if interfaced with the Trafton chillers.

If all remote building DP sensors exceed their minimum DP setpoint by 5 PSI, versus the 1 PSI as

described in Section 8.1, the flow setpoint for each active Trafton chiller will be reduced by 25



GPM (adjustable) and an alarm issued to the operator station as described in Section 8.7. This

will actively reduce the pressure spikes that have caused concern. Even when dispatched by the

Main Plant as level 4 (one Trafton chiller) or level 5 (two Trafton chillers) of capacity, issues

could develop with the Main Plant secondary pumping or equipment put in manual that would

trigger losing control of site DP. If both chillers reduce to minimum flow without the Main Plant

subtracting one of the Trafton chillers as it is supposed to, then drop the lag Trafton chiller

without increasing the lead chiller’s flow setpoint. The last active Trafton chiller should be

dropped by the Main Plant or manually but if not, the minimum flow rate that has to be

maintained to prevent tripping should have minimal impact on the site pressures.

4.2.2 Narrative – Automatic Variable Flow Mode when Trafton Chillers are lead units (Main Plant out of operation):

There are times when Operators may want to use the Trafton chillers to meet site chilled water loads and

would select Automatic Variable Flow Mode for Trafton Chillers. This could occur during spring or fall

with a low site load. It could also occur when maintenance is being done at the Main Plant the Trafton

Plant provides site cooling.

In a manner similar to 4.2.1, the first Trafton chiller would be brought on at minimum flow rate. Without

the Main Plant to maintain site differential pressure, we will control Trafton flow similar to how the

secondary pump flows are controlled at the main plant as described in Section 8.1. A local Trafton DP /

differential pressure sensor must be installed at Trafton between supply and return mains to maintain site

DP. The default Trafton Startup DP setpoint will be 25 PSID adjustable (versus the Main Plant Startup

DP of 35 PSID). The variable primary pump would increase in speed until:

1. Chiller % FLA reaches 95 % (adjustable)

2. Flow reaches 800 GPM (adjustable up to 1200 GPM maximum flow)

3. Trafton DP sensor reaches 25 PSID.

4. If the lead chiller reaches 800 GPM (adjustable) or 95% FLA (adjustable) without the Trafton DP

sensor reaching Startup Setpoint, the second chiller is brought online at minimum flow.

a. If the Trafton DP reaches or exceeds Startup DP Setpoint as the lag chiller ramps up to

minimum flow the lead chiller flow is reduced to its minimum flow rate and then both

chillers ramp up in parallel to satisfy the DP setpoint.

b. If the Trafton DP does not reach or exceed Startup DP Setpoint as the lag chiller ramps

up to minimum flow, the lag chiller will continue to increase its flow rate to maximum,

but will stop if:

i. Chiller % FLA reaches 95 % (adjustable)

ii. Flow reaches 800 GPM (adjustable up to 1200 GPM) maximum flow

iii. Trafton DP sensor reaches Startup DP Setpoint

iv. If the Startup DP Setpoint is reached, the total flow of both chillers is then

equally split between the two online chillers. After the flows have been split, the

chiller flows will ramp up and down in parallel to meet Startup DP Setpoint. Site

DP is then maintained as stated in paragraph 5 below.

5. After stabilizing at Startup DP Setpoint, setpoint will be adjusted in a manner similar to the Main

Plant as discussed in Section 8.1. If any building’s DP is less than 1 PSI below its minimum

setpoint for 5 minutes (adjustable) the Trafton Plant DP setpoint is raised by 1 PSI (adjustable).



If all building DP’s are at least one PSI above their minimum setpoint for 5 minutes (adjustable)

the Trafton Plant DP setpoint is decreased by 1 PSI (adjustable).

6. If the flow rate of both chillers drops to minimum for 5 minutes (adjustable) when Trafton

chillers are in Automatic Variable Flow Mode, the lag chiller is dropped and the lead chiller

ramps up flow to satisfy DP Setpoint until:

a. Chiller % FLA reaches 95 % (adjustable)

b. Flow reaches 800 GPM (adjustable up to 1200 GPM maximum flow)

c. Trafton DP sensor reaches 25 PSID.

NOTE: if the operator decides to manually put a chiller online at the Main Plant at a fixed secondary

pump flow rate, the Trafton chillers will continue to follow the Automatic Variable Flow Mode sequence

described above to maintain site DP.



5.0 Update Campus Chilled Water Model

Sebesta Blomberg developed the campus chilled water hydraulic model and has periodically updated with

new information, adjustments for future loads, and for planning. The model was adjusted to more

accurately represent the current conditions and plans for future.

5.1 Campus Chilled Water Loads

Table 5.1 below provides a summary of the current campus loads (Summer 2013), the proposed

new buildings, and the proposed cooling upgrades to existing buildings. Note that the items

highlighted in blue have been either added or changed from Sebesta Blomberg’s prior analysis.

Table 5.1: Summary of Campus Chilled Water Loads

Building Name Area CooledPeak

Load

Diversified

Load

Diversified

FlowDT

SF Tons Tons GPM ºF

Memorial Library (w/Addition) 246,365 616 431 1,035 10

Armstrong Hall 143,966 340 238 571 10

Highland Center (w/Otto) 130,280 401 281 449 15

Highland North (w/Pennington) 54,630 216 151 285 13

Myers Field House 82,308 231 162 389 10

Morris Hall (w/Addition) 66,761 153 107 257 10

Nelson Hall (w/Addition) 40,246 115 92 221 10

Performing Arts, Andreas Theatre 107,356 293 181 434 10

Taylor Center 137,921 328 179 430 10

Trafton Science Center 224,864 1,203 962 1,925 12

Trafton East Addition 55,940 150 116 279 10

Wigley Administration Building 48,933 109 76 183 10

Wiecking Center 17,555 44 31 74 10

Wissink Building 65,725 149 104 250 10

Student Union 209,162 703 422 1,012 10

Carkoski Commons 33,918 85 57 137 10

Sears Residence Hall 150,275 304 186 297 15

Ford Hall 66,783 374 281 449 15

Preska Hall 109,773 222 136 217 15

Total Summer 2013 - Including Library 1,992,761 6,036 4,193 8,894 11.3

Total Summer 2013 - Excluding Library 1,746,396 5,420 3,762 7,859 11.5

Housing and Dining 60,614 134 83 132 15

Medical and Dental 57,440 136 95 152 15

Sub Total 3-5 Year Build-Out 118,054 270 178 284 15.0

Total 3-5 Year Build-Out Including Library 2,110,815 6,306 4,371 9,178 11.4

Total 3-5 Year Build-Out Excluding Library 1,864,450 5,690 3,940 8,143 11.6

College of Business 52,314 124 87 138 15

Wiecking Center East Wing 10,000 25 18 28 15




Armstrong Addition and Renovation 57,000 135 94 151 15

Wiecking Center South Wing 30,000 75 53 84 15

300 Bed Residence Housing 109,000 220 135 215 15

Carkoski Commons - REMOVED -33,918 -85 -57 -137 10




SUMMER 2013

PROPOSED 3-5 YEAR BUILD-OUT





The above data was entered into the campus’ chilled water distribution model. Three scenarios

were modeled:

Scenario 1 is an analysis of the current system using the campus loads from this past

summer.

Scenario 2 is an analysis of the proposed 3-5 year build-out of the chilled water system,

after the proposed loads (Housing and Dining, Medical and Dental) are added to the

distribution system.


after the proposed loads (College of Business, Wiecking Center East Wing) are added to

the distribution system.


after the proposed loads (Armstrong Addition and Renovation, Wiecking Center South

Wing, 300 Bed Residence Housing) are added to the distribution system.

Each of the above Scenarios was modeled with and without the Library chillers online. Also,

booster pumps were added to Armstrong for some Scenarios, when needed. Refer to the

discussion below for more information.

5.2 Scenario 1 – Summer 2013

Scenario 1 models the actual present operating conditions of the chilled water distribution system,

as shown in Table 5.1.

5.2.1 Scenario 1 Results

Refer to Table 5.2 for a summary of important output data from the hydraulic model for

Scenario 1.

NOTE: current Main Plant maximum capacity is 3,200 tons

Table 5.2: Summary of Scenario 1 Results

5.2.1 Scenario 1 Conclusions and Recommendations

The model results are not showing any significant causes of concern with the existing

chilled water distribution system.

Library

Chillers

On/Off?

Armstrong

Booster

Pumps?

Total

Campus

System

Tons

Total

Campus

System

Flow

Rate

Utility

Plant

Tons

Utility

Plant

Flow

Rate

Trafton

Plant

Tons

Trafton

Plant

Flow

Rate

Utility

Plant

Rated

Pump

DP

Utility

Plant

Pump

DP

Trafton

Plant

Rated

Pump

DP

Trafton

Plant

Pump

DP

Remote Users

On No3,762

Tons

7,859

GPM

2,962

Tons

6,259

GPM

800

Tons

1,600

GPM160 ft 148 ft 150 ft 119 ft

Armstrong,

Highland North

Off No4,193

Tons

8,894

GPM

3,393

Tons

7,294

GPM

800

Tons

1,600

GPM160 ft 153 ft 150 ft 118 ft

Armstrong,

Trafton East



The diversified tonnage calculation for the existing campus load (4,193 tons) indicates

that the current campus demand exceeds the 4,000 tons of installed chiller capacity with

the Library Chillers not in service. There were no complaints of lack of cooling during

the summer of 2013 so the apparent 193 ton shortfall hasn’t caused a problem.

5.3 Secondary 2 – Proposed 3-5 Year Build-Out

Scenario 2 models the future planned build-out of the chilled water distribution system over the

next 3-5 years, as shown in Table 5.1.



Scenario 2.



5.3.2 Scenario 2 Conclusions and Recommendations

The model results are not showing any significant causes of concern with the existing

chilled water distribution system.


that the proposed 3-5 year future campus demand exceeds the 4,000 tons of installed

chiller capacity. The Library chillers can be turned on to help offset this load during peak

periods (not a preferred or recommended alternative), or another chiller can be installed

adjacent to the central plant. Without the Library chillers, Table 5.3 indicates a 371 ton

shortfall (3,571 – 3,200 = 371 tons) at the Main Plant. Trafton is base loaded at 800 tons.






Scenario 3.

Library

Chillers

On/Off?

Armstrong

Booster

Pumps?

Total

Campus

System

Tons

Total

Campus

System

Flow

Rate

Utility

Plant

Tons

Utility

Plant

Flow

Rate

Trafton

Plant

Tons

Trafton

Plant

Flow

Rate

Utility

Plant

Rated

Pump

DP

Utility

Plant

Pump

DP

Trafton

Plant

Rated

Pump

DP

Trafton

Plant

Pump

DP

Remote Users

On No3,940

Tons

8,143

GPM

3,140

Tons

6,543

GPM

800

Tons

1,600

GPM160 ft 151 ft 150 ft 119 ft

Armstrong,

Highland North

Off No4,193

Tons

9,178

GPM

3,571

Tons

7,578

GPM

800

Tons

1,600

GPM160 ft 157 ft 150 ft 118 ft

Armstrong,

Highland North





5.4.2 Scenario 3 Recommendations

Adding a booster pump to Armstrong will result in the building no longer being the

hydraulically remote user and also allows the required head at the secondary pumps to be

met with the Main Plant pumps. If a booster pump is not added at Armstrong, there is an

increasing risk that the building will be starved for flow during peak demand periods.

As a result, Sebesta Blomberg’s recommendation is to install a booster/tertiary pump at

the Armstrong Building for the proposed chilled water expansion discussed in this write-

up. It should be noted that Sebesta Blomberg recommended several years ago that the

University bypass and/or remove the booster/tertiary pumps at each building. The

University has seen improved system operation (higher ΔT, reduced maintenance, and

consistent delivery of chilled water to end users) after implementing this

recommendation. However, a properly controlled booster pump (with a variable speed

drive) can provide a positive benefit to a chilled water distribution system in a situation

like Armstrong with an undersized service main.

Lastly, note that a crosstie from inside Trafton to the south campus 12” loop was also

modeled as an alternate to installing a booster/tertiary pump at Armstrong. This crosstie

did not alleviate the above mentioned pressure drop issues so it should not be considered.


that the proposed 5-10 year future campus demand significantly exceeds the 4,000 tons of

installed chiller capacity. The Library chillers could be turned on to help offset this load

during peak periods (if they are still operable or installed), or additional chiller capacity

can be installed adjacent to the central plant.




Library

Chillers

On/Off?

Armstrong

Booster

Pumps?

Total

Campus

System

Tons

Total

Campus

System

Flow

Rate

Utility

Plant

Tons

Utility

Plant

Flow

Rate

Trafton

Plant

Tons

Trafton

Plant

Flow

Rate

Utility

Plant

Rated

Pump

DP

Utility

Plant

Pump

DP

Trafton

Plant

Rated

Pump

DP

Trafton

Plant

Pump

DP

Remote Users

On No4,045

Tons

8,309

GPM

3,245

Tons

6,709

GPM

800

Tons

1,600

GPM160 ft 155 ft 150 ft 121 ft

Armstrong,

Highland Center

Off No4,476

Tons

9,344

GPM

3,676

Tons

7,744

GPM

800

Tons

1,600

GPM160 ft 161 ft 150 ft 119 ft

Armstrong,

Highland Center

Off Yes4,476

Tons

9,344

GPM

3,676

Tons

7,744

GPM

800

Tons

1,600

GPM160 ft 149 ft 150 ft 107 ft

Highland North,

Trafton East





Scenario 4.




Adding a booster pump to Armstrong will result in the building no longer being the

hydraulically remote user and also allows the required head at the secondary pumps to be

met with the Main Plant pumps. If a booster pump is not added at Armstrong, there is a

risk that the building will be starved of flow during peak demand periods.


that the proposed 10-20 year future campus demand significantly exceeds the 4,000 tons

of installed chiller capacity. An additional chiller will certainly be required at this time.

It is assumed that the Library chillers will be retired at this point, and even if they did

remain they would not be able to fully offset this load during peak periods.

5.6 Scenario 5 – Building Coil Improvements (With Proposed 10-20 Year Build-Out)

Scenario 5 models the effects of replacing chilled water coils at a number of buildings. The

buildings that have been modeled with coil improvements are:

Performing Arts

Wissink Hall

Nelson Hall

Armstrong Hall SF1 and SF2.

Memorial Library

Centennial Student Union

Trafton North

Library

Chillers

On/Off?

Armstrong

Booster

Pumps?

Total

Campus

System

Tons

Total

Campus

System

Flow

Rate

Utility

Plant

Tons

Utility

Plant

Flow

Rate

Trafton

Plant

Tons

Trafton

Plant

Flow

Rate

Utility

Plant

Rated

Pump

DP

Utility

Plant

Pump

DP

Trafton

Plant

Rated

Pump

DP

Trafton

Plant

Pump

DP

Remote Users

On No4,270

Tons

8,622

GPM

3,470

Tons

7,022

GPM

800

Tons

1,600

GPM160 ft 160 ft 150 ft 122 ft

Armstrong,

Highland North

Off No4,701

Tons

9,657

GPM

3,901

Tons

8,057

GPM

800

Tons

1,600

GPM160 ft 167 ft 150 ft 121 ft

Armstrong,

Highland North

Off Yes4,701

Tons

9,657

GPM

3,901

Tons

8,057

GPM

800

Tons

1,600

GPM160 ft 155 ft 150 ft 109 ft

Highland North,

Highland Center



Trafton East

Trafton Center

Trafton South

Meyers Field House

Highland Center

Taylor Center

The coil improvements are assumed to have no effect on building tonnage, but they would

decrease the required flow rate at each building by increasing the differential temperature. For the

purpose of this study, the differential temperature at these buildings would be increased from

their current value (10ºF in most cases) to 15ºF.

This scenario models the future planned build-out of the chilled water distribution system over

the next 10-20 years, as shown in Table 5.1.



Scenario 5. This scenario no longer needs the Armstrong booster pumps, so they have

been removed from consideration.




The lowered building flow rates from the coil improvements reduce the velocity and

pressure drop through the chilled water distribution mains. As a result, the required head

at the Utility Plant secondary pumps drops by approximately 40 feet, and the required

head at the Trafton Plant secondary pumps drops by approximately 18 feet, both in

relation to full build-out described in Scenario 4. These are very significant reductions in

pump head, and would free up capacity in the existing distribution system for future

expansions and chilled water load increases and save considerable pump energy.

Library

Chillers

On/Off?

Armstrong

Booster

Pumps?

Total

Campus

System

Tons

Total

Campus

System

Flow

Rate

Utility

Plant

Tons

Utility

Plant

Flow

Rate

Trafton

Plant

Tons

Trafton

Plant

Flow

Rate

Utility

Plant

Rated

Pump

DP

Utility

Plant

Pump

DP

Trafton

Plant

Rated

Pump

DP

Trafton

Plant

Pump

DP

Remote Users

On No4,270

Tons

7,006

GPM

3,470

Tons

5,726

GPM

800

Tons

1,280

GPM160 ft 121 ft 150 ft 104 ft

Highland North,

Highland Center

Off No4,701

Tons

7,696

GPM

3,901

Tons

6,416

GPM

800

Tons

1,280

GPM160 ft 125 ft 150 ft 103 ft

Highland North,

Highland Center



6.0 Energy Savings and Operational Improvements by Integrating Operation of Trafton and Main Plant

The primary impact of integrating the operation of the Trafton chillers into the Main Plant controls is

operational and not economic. The operation improvements were described in the Narrative in Section 4.

Having to send staff to the Trafton chillers to make any changes in flows or setpoints has not allowed

MSU Mankato to get full value from the chillers. It could be said that sending someone to make manual

changes in the way the chillers or towers are operating is an acceptable way to operate that capacity, but

that approach has caused problems and prevents the type of significant improvements that have been

made in the operation of the Main Plant. Whenever quick actions need to be taken in a chilled water

system, a significant delay in reacting can cause problems. The pressure spikes that have been

experienced is an example of this. Since the operators for the campus chilled water system are stationed

at the Main Plant, they can only take ownership and control of the Trafton chillers if they are integrated

into the system.

The primary areas of energy savings opportunities are discussed in Section 8. The savings apply as much

to the operation of the Trafton chillers as the Main Plant chillers. Realistically, MSU Mankato has to

realize that the total electrical energy usage of the chilled water system isn’t huge. Based on prior work

and data gathering, we assume that total annual production is in the neighborhood of 4 million ton-hours.

If an average total energy of 0.80 kW/ton and $0.10 per KWH is used, the cost of electricity to run the

chilled water system would be about $320,000 annually.

The two major energy savings opportunities in Section 8 are tower water supply temperature setpoints

(8.3) and differential pressure control for pumping (8.1).

1. Tower Water Setpoints: Considering that the tower temperatures in the operating logs are

consistently in the 80° - 85° range, we estimate a 10° reduction in annual average tower

temperature is achievable resulting in a 0.07 kW/ton energy reduction as described in Section 8.3.

The annual savings would be $20,000 - $25,000 and would be shared by both the Main Plant and

the Trafton chillers.

2. Differential Pressure Control modifications: With the DP setpoint for pump control not being

reset based on actual site DP at monitored buildings, a conservative savings of 0.02 kW/ton is

expected by implementing what is described in Section 8.1. To put in perspective, pump energy

is less than 0.10 kW/ton of total system energy usage. The annual savings would be $6,000 -

$7,000 and would again be shared by both the Main Plant and the Trafton chillers.

There are energy savings available from the other items in Section 8 but many are just good practice and

ways to improve the way the plant operates.

An operational improvement discussed in Section 8.8 describes a method of adding chilled water capacity

with an “annex” constructed next to the Main Plant. This is a logical location to add capacity now that

plans are under way for the Housing and Dining Facility.



7.0 Review PBEEP Study Recommendations for Chilled Water System

Sebesta Blomberg was asked to comment on chilled water recommendations from a PBEEP Study that

was dated May 22, 2012. The two recommendations, summary and details, are located at the end of this

Section. The following Energy Conservation Opportunities (ECOs) were listed:

ECO 1 - Chillers are staged based on percentage of load in lieu of actual demand

ECO 13 - Chiller Condenser Water Pump CP-3C

ECO-1 Recommendation: The “Finding” stated the opportunity was “Equipment is enabled regardless of

need, or such enabling is excessive”. The calculations for the ECO involved looking at the campus load

(tons) and determining the appropriate number of chillers that should have been enabled and active. The

recommendation is to enable the next stage of cooling (add a chiller) when 90% of the enabled chiller

capacity is being used (assuming this is based on the chiller’s % load data point which is actual amps

divided by rated amps. Subtracting a chiller would be done when the campus load is less than 20% of the

combined enabled chiller tons.

Comment: The current control sequence is very similar to the recommended action with a few

modifications that reflect the actual site conditions. Actual site conditions at Mankato include

times where the system ΔT is below design conditions. From Section 2 “Overview of Chilled

Water System”, the annual site ΔT can be as low as 7° - 8° from its peak of approximately 11.3°.

When the site ΔT is low in a primary secondary configuration (constant flow primary pumps

designed for 12° ΔT) there is no way that a chiller’s loading can exceed say 85% if the site is at a

10° ΔT. Waiting for a 90% trigger to add a chiller will cause operational problems. The plant

has set up an “Add” chiller trigger at 70% – 80% load and also included code that will allow the

chilled water supply to campus temperature to only exceed chiller setpoint by 3°adjustable. A

chiller is currently subtracted (aggressively) when the percent loaded of the combined chillers on

line is 15% - 18% less than the trigger to add the last chiller (approximately 50% loaded) and then

the remaining on line chillers become almost fully loaded again. Allowing the chillers to drop to

20% loaded as recommended puts them all at less efficient operating points.

Summary: The current control sequences already capture the savings of controlling adding and

subtracting chillers. The addition of monitoring the supply temperature to the site, which is the

primary function of the plant, is an improvement to ECO-1. Current sequences also respond to

the real changes in site ΔT which always happen. No changes to current sequences are

recommended.

ECO-2 Recommendation: The “Finding” stated the opportunity was “Pump Speed Doesn’t Vary

Sufficiently”. The calculations for the ECO involved looking at the variable speed condenser water pump

CP-3 and have a balancing contractor compare pump HP and flow to design conditions and the different

flow requirements of the chillers. There was mention that the pump was designed for 4920 GPM which

does not match any combination of chillers. It was then assumed that CP-3 was overpumping the cooling

tower system. Through functional testing and recording flows the speed of the pump for various



combinations of chillers could be determined. Evidence of implementation method was suggested to be

condenser water supply and return temperatures.

Comment: CP-3 operates in conjunction with constant speed pumps when high condenser water

flows are required. CP-3 is always the lead pump and the other pumps are added as chillers are

added. The 4920 GPM design flow of the pump is somewhat irrelevant since the operating heat

at that design flow seldom if ever is actually experienced on site. All chillers have flow meters

for condenser water flow measurement (periodically compare flows to pressure drop across

condenser bundle to calibrate). The current control sequence has been set up for a single supply

header pressure setpoint to be maintained. That 20 PSIG setpoint is a carryover from the original

sequence of operation. The plant has had a “To Do” list of monitoring the flow meter readings of

each active chiller or combination of chillers to develop a look-up table with seven conditions

(Chiller numbers in operation: 1, 2, 3, 1&2, 1&3, 2&3, and 1&2&3) and the required header

pressure setpoint. This allows design flows to be met without throttling pumps and only using the

more efficient VFD on CP-3. The initial setting was to be developed by putting all three chillers

on line and balance to design flows by minimal throttling only at the chillers that are overflowing.

The other 6 combinations would then be done under actual operating conditions and recording the

header setpoint needed for design flows. It is very likely that reasonable control of flows could

be accomplished with as few as 3 setpoint for one or two or three chillers online.

Summary: The plant should complete the previously suggested modifications to the control

sequence to build the table that provides the actual design flows the chillers require. Using the

flow meters on the chillers as confirmation of required flow rates will be an operator function.

The suggestion to use temperature rise across the condensers is not recommended since flow

meters already exist and ΔT across condenser is load dependent. All actions are capable of being

done by the plant operators and the programming changes are minor.



8.0 Additional Chilled Water System Recommendations and Comments

Beyond the defined scope of this project, additional items to improve campus chilled water system

operation and efficiency were discussed and noted. The following are provided for consideration:

1. Differential pressure control for secondary pumps

2. Staging of tower fans

3. Tower water supply temperature setpoint

4. Main Plant cooling tower water supply header pressure setpoint

5. Control system devices – check calibration

6. Chilled water supply temperature setpoints

7. Site differential pressure alarms

8. Main chiller plant Annex

8.1 Differential pressure control for secondary pumps:

Currently there is not automatic reset of the Main Plant differential pressure setpoint that controls the

VFD on the secondary pumps. The current default Main Plant DP setpoint is 35 PSID and adjustable by

the operator. The advantage of controlling a VFD with a direct connected local DP sensor and setpoint is

the elimination of the “refresh” time of typical scanning DDC systems. Not having an automatic reset of

the setpoint for the secondary pumps can lead to over-pumping the site (having a DP setpoint that results

in remote building DP’s that are higher than required.

It is recommended that the DP control of the secondary pumps be reset based on the comparison of

building remote DP’s to a unique setpoint for each building. If any building’s DP is less than its

minimum setpoint for 5 minutes (adjustable) the current plant DP setpoint is raised by 1 PSI. If all

building DP’s are at least one PSI above their minimum setpoint for 5 minutes (adjustable) the current

plant DP setpoint is decreased by 1 PSI. The time delays are provided to ensure that excessive

adjustments of setpoints are not done.

8.2 Staging of Tower Fans

During the site visit it was noted that when two chillers were on line and all three cells were “flowing”,

only four fans were in operation. It is recommended that when towers are flowing water all fans (2 cells

and each has a fan) should be in operation. The VFD’s for each fan should receive the same increase or

decrease in speed based on the relationship between supply temperature versus setpoint. A typical staging

of towers is based on maintaining a minimum of 50% of design flow to ensure the tower fill is fully

covered and there are no short circuiting of air (air pulled through the tower without cooling incoming

water. If adequate fill coverage is maintained a single chiller would run on two covers and once two or

three chillers are in operation all towers and fans would be enabled.



8.3 Tower water supply temperature setpoint:

Regardless of what the control sequences say, plant operating logs show that condenser water supply

temperatures almost always are between 80° and 85°. Trane chillers with R123 refrigerant are capable of

operating at temperatures as low as 65°. It was reported that there were issues at some time in the past

with cold tower water setpoints but that would indicate that chiller setup should be checked. A reduction

of lift of 5 degrees (difference between chilled water supply setpoint and tower water inlet temperature)

will result in a decrease of roughly 1% of energy usage per degree of lift reduction (or 5%). The

additional tower fan energy required to provide that colder temperature is typically 1/3 of a percent of

energy usage per degree of lift reduction (or 1.67%). Definitely is a change worth trying. It is

recommended that the setpoint be reduced by a couple degrees at a time to confirm that chiller operation

is not impaired. The primary items to watch out for are compressor surge and problems with refrigerant

from condenser to evaporator (watch refrigerant liquid levels in condenser). The lowest achievable tower

temperature can be used as a constant setpoint or a reset schedule established based on ambient wet bulb.

A typical reset schedule is a 7° approach at a 78° wet bulb providing an 85° tower setpoint, increasing to

a 12° approach at 53° wet bulb providing a 65° tower setpoint.

8.4 Main Plant cooling tower water supply header pressure setpoint:

This modification was discussed in Section 7. All chillers have flow meters for condenser water flow

measurement (to confirm calibration periodically compare flows to pressure drop across condenser

bundle). The current control sequence has been set up for a single supply header pressure setpoint to be

maintained. That 20 PSIG setpoint is a carryover from the original sequence of operation. The plant has

had a “To Do” list of monitoring the flow meter readings of each active chiller or combination of chillers

to develop a look-up table with seven conditions (chiller numbers in operation: 1, 2, 3, 1&2, 1&3, 2&3,

and 1&2&3) and the required header pressure setpoint. This allows design flows to be met without

throttling pumps and only using the more efficient VFD on CP-3. The initial setting was to be developed

by putting all three chillers on line and balance to design flows by minimal throttling only at the chillers

that are overflowing. The other 6 combinations would then be done under actual operating conditions and

recording the header setpoint needed for design flows. It is very likely that reasonable control of flows

could be accomplished with as few as 3 setpoint for one or two or three chillers online.

8.5 Control system devices – check calibration:

During the site visit, viewing the chiller plant screens identified at least four readings that were out of

calibration:

Flow meter for Trafton Chiller #1 indicated a setpoint of 480 GPM but chiller loading and inlet /

outlet chilled water temperatures indicated a probable flow of 565 GPM.

Flow meter on Chiller 2 at Main Plant wasn’t reading correctly – often negative flows when

online.

Primary combined supply flow temperature sensor reading was higher than any chiller’s supply

setpoint



Plant supply to campus temperature sensor was approximately two degrees higher than indicated

by plant operation

Temperature sensors should be checked “regularly” in ice bath for calibration. Flow meters should be

compared to pressure drops across condensers and evaporators or calibrated against a portable ultrasonic

flow meter.

8.6 Chilled water supply temperature setpoints:

When on site, the two Trane chillers had a 42.5° setpoint and the McQuay had a 45 degree setpoint. The

plant had recently rebuilt the McQuay and there was no reason why it couldn’t provide the same 42.5°

supply temperature. The setpoint was reset while on site without issue. NOTE: the current 3° deadband

for exceeding setpoint as a trigger to add capacity is often changed on other sites based on weather

conditions, usually when wet bulb temperatures are high. . During hot and humid conditions the lower

supply temperature can cause humidity issues in critical buildings. During periods when wet bulb

exceeds say 65° (adjustable) the deadband can be reduced to 2° or even 1°.

8.7 Site differential pressure alarms:

As an indication of a system problem, variations from the parameters in the sequences for control of

secondary pumps in Section 8.1 should be alarmed. If any building’s DP is less than its minimum

setpoint by 5 PSI for 5 minutes (adjustable) a low building DP alarm will be given. If all building DP’s

are at least five PSI above their minimum setpoint for 5 minutes (adjustable) a high building DP alarm

will be given.

8.8 Main chiller plant Annex:

The analysis in Section 5 shows that the current plus future loads will bring the total campus load to

roughly 4900 tons. The current installed capacity is 4000 tons – 3200 at the Main Plant and 800 at

Trafton. This indicates a 900 ton long term capacity shortfall. Earlier in this report we noted that there

really isn’t a good way to increase the installed capacity at Trafton. The two 400 ton chillers have taken

up usable space and it would be difficult and expensive to add chiller or tower capacity. The Main Plant

is also built out to capacity within the existing building (current space and pipe capacity is limited).

There are planned changes in the area of the existing plant when roadways are modified with the

construction of the Housing and Dining facility. A very workable location for a chiller plant annex or

addition would be between the Main Plant and the generation building with a separate piping connection

to the campus distribution loop. There is room near the existing cooling towers to install additional tower

capacity to the west of the chiller plant annex. The annex could be connected to the existing Main Plant

to allow operators to go between the facilities. We recommend that a minimum of 1000 ton of chiller

capacity be installed in the annex to allow full retirement of the Library chillers to meet the future 4900

ton load. The chiller(s) should have a variable speed drive compressor motor to provide extremely

efficient performance at low loads and at low condenser water temperatures.



The maximum single unit sizing would be based on staff’s comfort level with the current estimate of long

term campus loads and the knowledge that the annex is probably the best long term location for even

more capacity if needed. If the 4900 tons is really the maximum for the next 20 years then 1000 tons is

adequate. However, adding a couple hundred tons of “cushion” could be done very cost effectively. We

are assuming that the Trafton chillers will remain a long term part of chilled water system operation based

on their positive contribution to campus distribution system hydraulics. There appears to be room two

bays in the annex. A bay could provide room for future capacity, but used for other purposes (currently

unidentified) in the short term if additional flexibility is desired. Between the two bays MSU Mankato

could stage the additional capacity or hold a space open “just in case”.



9.0 Scope from Proposal

Many tasks listed below overlap in effort. The following summarizes our understanding of these general

areas that need to be evaluated and analyzed:

1. One day site visit to gather data and meet with staff:

General trouble-shooting and operational discussions

Discuss reported spikes in distribution pressure

Review plant records to establish current peak CHW loads and operating conditions – as well

as data from several times of the year showing chiller operating

Get updated projections for future campus chilled water loads and confirm the location and

reasonable schedule of those loads

Revisit Library chiller installation and future operation

Data on cooling and operation of new Preska Dorm along with T&B comments.

Sequences of operation for latest Trafton Chiller.

Walk-down at Trafton plant, discuss condition and operation and expansion of capacity

Discuss current Central Plant control sequences / operations

2. High level evaluation of the potential to increase the installed capacity of Trafton from the current

800 tons. It was reported that the space required for the installation of the first two units may have

limited the ability to install additional capacity in Trafton

3. OMITTED, Mankato to work directly with control contractor: Discuss the capabilities and

limitations of current Metasys/Andover controls and their ability to control the campus chilled water

system. This will be a discussion of the perceptions of Steve and operators and Sebesta Blomberg as

well as documenting conversations with control system providers. This is not a detailed analysis and

will be our high level opinion. It will also include a discussion of the proposed Utility Plant FX

Control System Upgrade versus an Extended Architecture upgrade.

4. Provide a control upgrade narrative for controls contractors to establish communication and specified

controls between the Main Plant and the Trafton Plant. Provide an analysis of what apparently is

happening without this capability and discuss with Mankato the impact on system operations

(pressure spikes and chiller staging) and approach to receiving proposals from qualified controls

contractors. The narrative will be performance based versus prescriptive for approach. Contractors

will use their knowledge of the Mankato system to provide a working solution. Our deliverable is the

narrative, Mankato will get proposals using standard campus RFP documents.

5. Upgrade current campus chilled water hydraulic model and develop a scenario for a chiller plant

addition/annex constructed north of the existing central plant to include a new connection to the main

campus distribution loop for 800 – 1200 tons (will work with Mankato on final capacity).

Eliminating the road between chiller plant and generator plant opened up this possibility. We would

also update the current model with updated information of current loads (plant loads and performance



of new buildings) and future loads provided by Mankato staff. Model would include the following

scenarios

Updated current loads showing performance of the central plant and Trafton, review

performance of new facilities (Preska and Sears).

Project future loads including projections for buildings, locations, and schedule.

Review and discuss opportunities for Main Plant annex, added capacity from Trafton if

viable, isolation of Library on its own chillers, and export of Library extra capacity.

Provide a model for current loads plus approximately four models for future loads

considering existing plant, expanded Main Plant, Trafton export at current or maximum

future capacity if feasible to expand, and Library taken off the loop.

6. Provide an estimate of energy savings from the addition of communication between Main Plant and

Trafton (and possibly the Library Chillers) and the ability to control and optimize the operation of

these satellite plants. This would include pumping, chiller staging, and improvement in system

efficiency available with the upgrades.

7. Review and comment on the PBEEEP Study chilled water system recommendations sent by Steve.

These include staging chillers on percent load and operation of the chiller condenser water pumps.

Provide a recommendation to implement, modify or not to implement.

chilled water loop capacity study chilled water loop capacity...2.1 overview of chilled water system...

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