Central Heating and Chilling Plant Conservation Measures
UW-Milwaukee’s central plant is unique. As one of the most efficient and well running operations in the state of Wisconsin, this plant utilizes condenser heat rejection by pumping water from Lake Michigan for chilling. The use of cool lake water (42-70 deg.F.) takes the place of cooling towers and dramatically improves the energy efficiency of the chilling system.
With a well trained and experienced staff, UWM’s Central Heating and Chilling Plant has made many strides over the years to implement conservation measures. The outcomes of these measures have been well documented and are one of the finest examples of sustainability at UWM.
Campus and Central Heating and Chilling Plant Combined Fuel Savings
Campus Related Savings
Cooling-Building Control Installation and Setback Programming
The Building Cooling Control Setback report calculates savings in fuel used to air condition campus buildings that has resulted from the installation of cooling controls and ongoing programming of the Metasys building management system.
Savings result from the set back or shutdown of building cooling equipment for building spaces that are not in use. Projected setback tons is based on a 4 year (1996-2000) average of past Daily/Monthly cooling load setback tons which comprised of 16.5% of the maximum chilling load.
Reheated projected tonnage is based on a 5 year (1996-2001) percentage where (40.4%) of the total chilled water tons produced was reheated. Current cooling set back is usually over 50% of the maximum daily cooling load. Savings are calculated daily during hours of most set back 9:30 PM to 7:30 AM.
Total Combined Savings: Cooling Months Only, Years 2000 through October 2010 = $1,518,064
Heating-Building Control Installation and Setback Programming
The Building Heating Control Setback report calculates savings in fuel used to heat campus buildings that has resulted from the installation of HVAC controls and ongoing programming of the Metasys building management system.
Savings result from the set back or shutdown of building heating equipment for building spaces that are not in use. The report is based on a comparison of current year 10^ 3 BTUs used, per 1000 square feet of heated space, per degree day, as compared to that used prior to the installation of these controls (an average of 1996, 1997 and 1998).
Cost savings are calculated using current year/month cost per million BTUs, but does not include the savings acquired in set back of buildings during cooling months which are covered in the Building Cooling Control Setback report.
This report only takes into account the dollars saved in natural gas and fuel oil consumed at the Central Plant and does not include the substantial savings in electrical costs that result from reducing the run time of large heating and air conditioning ventilating fans or the savings from conversion of these fans to variable speed drives.
Total Combined Savings: Heating Months Only, Years 2000 through December 2010 = $4,962,524
Total Campus Related Savings1= $6,480,588 (up to 2010)
Central Plant Related Savings
The following are some of the on-going fuel savings generated from efficiency improvement projects implemented at the UW-Milwaukee Central Heating and Chilling Plant. They do not include countless other improvements being made at the plant that do not have a large or obvious pay back, but are made just the same, to continually improve plant efficiency and reliability.
Chilled Water Secondary/Primary Loop Pump
This project consisted of the installation of two variable speed chilled water distribution pumps at the Central Heating and Chilling Plant and the removal of chilled water pumps from campus buildings.
This converted the campus chilled water building systems from constant flow variable temperature to constant temperature variable flow, allowing each building to take only the amount of water needed to satisfy its cooling needs.
Savings are acquired in a reduction in electrical power used by pumping all chilled water from the Central Plant and eliminating excess pumping of water at each building. Savings are also realized in the elimination of keeping spare parts and maintaining numerous pumps throughout campus.
Total savings from May 1991 through October 2010: $2,233,684
Boiler Controls Installation
This project consisted of replacing the 21 year old fuel oil and gas controls on the Central Plant’s four large utility boilers. The savings are achieved primarily by the monitoring and adjusting of the fuel air ratio on each boiler to improve burner overall combustion efficiency.
Total Saving from March 1991 through December 2010: $2,527,427
Steam Chiller Operational Improvements
These savings were/are realized from the implementation of a combination of improvements in equipment and equipment maintenance procedures. Improvements primarily consist of the installation of chiller condenser inlet strainers, resizing chiller turbine air ejectors to increase steam turbine efficiency, removing chiller water box scale deposits to reduce plugging of tubes, annual opening of chiller water boxes to clean 16,000 evaporator and condenser tubes and replacement of original chiller tubes with high efficiency tubes.
Total savings from May 1991 through October 2010: $3,044,633
Chilled Water De-Coupler Valve Installation
These savings were realized through the installation of a 20″ valve in the chilled water primary secondary loop De-Coupler line. Valve was used to put chilled water distribution pumps in series with chilled water pumps to force more water through chillers. Savings were acquired by loading up the more cost efficient electric chiller and unloading the less cost efficient steam chillers.
Total savings from 1991 through 2000: $399,575
(Operation of the De-Coupler valve was made obsolete in 2001 by the installation of larger chilled water pumps with AFD controls freeing up the plant’s distribution pumps to pump more water out to campus buildings.)
Chiller Pump GPM Increase and Variable Speed Control
This project increased the size of the Plant’s three chilled water pumps from 60 HP to 150 HP and installed alternating frequency drives to allow increased loading of 3000 ton Carrier electric chiller. Savings are acquired by loading up the more cost efficient electric chiller and unloading the less cost efficient steam chillers.
Total savings from May 2001 through October 2010: $1,292,641
Total Central Plant Savings= $9,497,960 (up to 2010)
Combined Campus and Central Plant Savings= $15,978,547 (up to 2010)
Even though the campus total heated square feet has increased by 38.5% since 1990, in 2010 it consumed 8.1% less fuel per degree day than it did prior to 1990.
1 This report does not represent all of the cost saving projects initiated on campus. BTUs used and saved pertains to heating fuels only, natural gas and fuel oil.