Case History: Chilled Water System Optimization at Purdue

Hemant Mehta, P.E. WM Group EngineersMatthew I. High, P.E. Purdue University

BACKGROUND• Purdue first encountered WM Group at an IDEA conference in 2012.

• Purdue contacted WM Group to see if there were any opportunities to optimize the utility costs.

• WM Group performed a system health check analysis at no cost, no obligation and presented their findings in two weeks.

Background• Based on the initial observation Purdue retained WM Group for a

comprehensive analysis of the chilled water system.• The recommendations implemented to date are:

– Installation of side-stream sand filters on the chilled water system– Conversion of the chilled water pumping system from primary/secondary/tertiary to a variable volume

pumping system with primary pumps only– Installation of free and pre-cooling– Minimizing simultaneous heating and cooling for 70 air handling units– Removal of orifice plate on Chiller #6 which increased the entire system pump head requirements when

that chiller was in operation– Enhanced Operator Training

– Cooling system cost is 2.5 times more than heating system

– I have yet to see a perfectly efficient cooling system– At Purdue I am sorry to say that your system is very

sick– There are opportunities to save millions of dollars in

first cost as well as operating costs

This is a copy of our slide we presented to Purdue based on the preliminary FREE analysis on April 12, 2013

• No operators training• Poor and/or signature design• Lack of peer review• Division of responsibility for

– Generation– Distribution – Utilization

Major causes of inefficient Cooling system

• Collect design data of the existing system• Obtain operating logs of at least two to three days per

month for one year• Spend two to three days in operating room to understand

how the system is operated and gain their confidence• Provide guide lines to the operation changes to achieve

“No cost Savings” • Generate Energy Conservation measures for

implementation

System Analysis Approach for FREE System Health Evaluation

• Wade Plant– 22,700 ton installed capacity

• Satellite Plant– 14,100 ton installed capacity

• Total installed 36,800 tons• Operating capacity ~ 28,800• Operating capacity loss of around 8,000 tons

2013 Plant Data

4. Loss of operating capacity by 8,000 tonsMaster plan report stated the following:

Observations during the first visit to the site

5. Short temperature difference of all chillers was higher than normal6. Very high Equivalent Full load hours (EFLH) andWinter cooling load of almost 4,000 tons did not make sense.7. Poor Delta T 7.7 deg F for Wade plant, 9.2 deg F for the satellite plant. Chillers were Design for 15 degree

Observations during the first visit to the site

8. Equipment dispatching was based on decision by operators 9. Pressure drop through one of the old chiller was excessive

Observations during the first visit to the site

• Implementation of Zero/ Low cost savings based on system observation

• Development of Energy Conservation Measures (ECM) for both plants as well as for buildings

• Written Report• Power Point presentation summarizing the final

report

Let’s discuss what was done during the study period of about 16 weeks

• Observation 1 Constant speed electric motor driven pumps were operating parallel to variable speed steam turbine driven pump

Implementation of Zero/ Low cost savings based on system observation

• Throttling of Electric Pumps

Wade Plant Observation

• Simultaneous Operation of Elec and Steam Pumps

Wade Plant Observation

• Observation 2: Total design pumping head was much higher than a normal benchmark for the campus system– As indicated in the last slide plant shaved impeller to

lower TDH from 310 feet to 240 feet.– In addition to these plant pumps, Satellite plant had

primary/ secondary pumping and all the buildings had pump and a stand by pump and more.

Observation 2: Total design pumping head was much higher than a normal benchmark for the campus system

• Observation 2: Total design pumping head was much higher than a normal benchmark for the campus system– Pumping company really got Rich on Purdue and may

be you have the same issue.– If your total pumping head is more than 200 feet,

regardless of size of your campus, most likely something is wrong.

– So what did we do at Purdue during our study?

Implementation of Zero/ Low cost savings based on system observation

• We turned off all building pumps• 1MW power reduction• Zero cost

• How did we convince to shut off all building pumps?

Observation 2: Total design pumping head was much higher than a normal benchmark for the campus system

• Use of Building Pumping Unnecessary

We built a pressure distribution diagram

Observation 3: Balancing contractors had partially closed valves to prevent pumps from running out of the curves.

• My Judgement - Balancing is a crime

• Electric Chillers’ CHW and CW Throttled

Observation 3: Balancing contractors had partially closed valves to prevent pumps from running out of the curves.

• For a hydronic system let control valves do the dynamic balancing.

• Get read of circuit setters, triple duty valves• Open all partially closed valves• Undo the crime of wasting energy for no reason

Please

• Why loss of capacity• Tons = (Flow x Delta T x 500)/12,000• Satellite plant is design as primary secondary

system maintaining constant flow through chillers• Chillers are design for 55 degree return and 40

degree supply i.e. 15 degree Delta T• Your Delta T is 9.2 degree for satellite plant and

Wade plant is 7.7 degree F

Observation 4- Loss of operating capacity

Satellite Chiller Plant• 1 primary pump, 1 chiller

and 3 secondary pumps in operation

• System ∆T of 9.2oF -CH Design is 15oF

• CH Flow = 3,860gpmDecoupler flow = 2gpmSystem flow = 4,246gpmFaulty instruments

Wade Chiller Plant• System ∆T of 7.7oF -

CH Design is 15oF

• Convert pumping system to a variable volume primary pumping

• My first primary pumping design was for a 30,000 ton chilled water plant– Six 5,000 ton chillers– Seven Chilled water pumps

Solution to regain capacity and simple operation

Oldest Primary only Pumping System

Primary only pumping system

Primary Pump

Primary/Secondary pumping system

Primary Pump

Primary with Booster pumps pumping system

Primary Pump

Booster Pump

• Short temperature difference is defined as–Help me out

• At Purdue all most all chillers had high short temperature difference

• Investigation releved that the chemical treatment did not keep up after major system leak

• Filtration system was not adequate

Observation 5- Short temperature difference of all chillers was higher than normal

• High Short Temperature Difference

General Observations

• Average of 6.4 DegF Approach (2-3 DegF design)

High Approach Temperature

High Approach TemperatureAverage of 6.4 DegF Approach (2-3 DegF design)

• Likely Candidate:– Tube fouling due to

insufficient filtration– Typically recommend 0.5

micron sand filtration– Current filtration >1 micron

cartridge filtration

High Evaporator Approach

• Case Study

High Evaporator Approach

Observation 6: Very high Equivalent Full load hours (EFLH) andWinter cooling load of almost 4,000 tons did not make sense.

• If your system EFLH is higher than 2000 you can hit a lottery by savings hundreds of thousands of dollars.

• Purdue EFLH was 3324– Yes, Purdue did save millions by fixing the system

• Main reason of high EFLH is simultaneous heating and cooling

High EFLH

• Red area represents 40% of Load!

Simultaneous heating and cooling

Variable Primary Pumping Conversion• Remove constant speed primary pumps and

rely on existing variable speed secondary pumps.

• Can the existing system pumps handle the head of the chiller and plant piping in addition to the entire campus?

• Replaced primary pumps with spool piece of pipe and ran one whole summer to confirm

• Provided configuration and floor space for free cooling heat exchangers

• Provided energy savings all year long

Refrigerant Head Pressure Control• New modulating

condenser valves• Chiller controls

upgrades for all six chillers would be over $200K

• Initially thought we could control the valve to maintain head pressure with existing Delta V

• Developed our own program to control condenser flow

Measurement & Verification (M&V)• NWCP – all electric producing only

chilled water.• Monitor total building power and

individual chiller power.• Outside air wet bulb temperature

determines potential efficiency.• Each year compare our actual

hourly efficiency and energy use to 2014 projected energy use.

y = 0.0036x + 0.5828

0.00

0.50

1.00

1.50

2.00

2.50

-20 0 20 40 60 80 100

Sat P

lant E

fficie

ncy (

kW/T

on)

O.A. Wetbulb Temperature (°F)

Sat Plant Efficiency vs Wetbulb 2014

How Are We Doing?• FY17 (July 1, 2017 - June 30, 2018)

will be our first full year.

• Heat Exchangers– Over 3.8 Million Ton-hrs with HX’s– Over 1.5 Million kWh saved

• Falling short of our estimated energy savings

• Mild Winter– Projected over 2400 hrs HX operation– This year right at 2000 hrs

• Commissioning / Operator Experience

• Low campus CHW Delta T’s

• HX approach higher than design

Where are we going?• Increase Automation

• Campus initiatives to reduce cooling loads and increase CHW delta T’s

• Heat Exchangers– Cleaning / Flushing procedures– Additional Plates