Constructing a new Department of Public Works Field Headquarters
Milwaukee DPW addresses energy efficiency, reduces costs, and increases operating efficiency
Michael W. Krause, AIA, Project Architect, Buildings & Fleet Services, Department of Public Works, City of Milwaukee, Wisconsin
Venu J. Gupta, P.E., Superintendent, Buildings & Fleet Services, Department of Public Works, City of Milwaukee, Wisconsin; Chair, APWA Facilities & Grounds Committee
Most government agencies find their budgets squeezed by a steady increase of regulatory and legislative burdens. Skyrocketing construction costs, a tight labor pool and ever-increasing competitive pressures make it more critical than ever before to increasingly reach the ideal where design strategies and construction methods are cost effective, ecologically sound, cost less to operate and are socially beneficial.
When we discuss facilities, the conversation covers both an organization's most valuable physical assets and one of its biggest expense items—whether they realize it or not.
In 2004, Milwaukee Mayor Tom Barrett gave the green light for the construction of a new field headquarters building at a former manufacturing location that had been sitting vacant for quite some time. The site once was a thriving automotive frame business operated by A.O. Smith Corporation. It was critical to relocate the current field headquarters building so as to vacate the land by the end of February 2006 to allow construction of the Harley Davidson Museum. In addition to the time constraints, the budget also proposed various challenges. The funding was established several years ago and the construction costs, like in the rest of the country, were fast increasing.
The construction offered the department the opportunity to consolidate various field operations to one site which would offer operational efficiency and streamline various functions. Resources could be shared by many departments offering additional savings in operating costs.
A staff team was put together to work with the City Project Architect, Mike Krause, to come up with a conceptual layout utilizing "Lean Principles" in designing the most efficient layout while eliminating and reducing any duplicated procedures.
Lean Systems Thinking promotes doing more with less—less square feet of space, less machinery, a lot less inventory, less waste of resources, less energy consumption, less human effort—and therefore the systematic assessment results in a smaller building but one that is more efficient, and therefore costs less to both construct and ultimately to operate.
The Briohn Building Construction Company hired by the Real Estate Development, LLC, Samuel D. Dickman, was provided a copy of the APWA publication Getting it Right! A Guide to Planning & Constructing Public Works Yards so as to better understand the activities that would be carried on at the new public works facility.
Design Program/Project Challenge
The challenge was to construct a new Public Works Field Headquarters Facility on a current brownfield site (24 acres), not to exceed the $24 million budget; and move staff from 10 satellite locations and consolidate field operations from 10 scattered sites while constructing this new 230,000-square-foot facility in 14 months, including time for design and construction. The building would house a staff of approximately 500, and 390 pieces of light and heavy equipment would be pulling out from this location, including approximately 102 trailers, backhoes and utility equipment. The contract for construction was executed in January 2005. As the contract was being finalized, Krause worked with representatives from all departments in developing a building program to address all activities and needs of the city while using Lean Principles.
The Ignition Meeting
On February 11, 2005, an Ignition Meeting was called of experts in the field of Sustainable Building Concepts and Energy to collectively develop various energy alternatives and to undertake Life Cycle Costing for the building systems. The goal of a Life Cycle Cost Analysis is to determine which combination of systems and equipment offers the lowest cost of ownership. This group of experts included the following:
Energy modeling was completed using Tran Trace 700, Version 4.1.7 Software Program. The following alternatives were evaluated using Life Cycle Cost Analysis.
Alternative 1: Code. According to the guideline specification, the building can be divided into the following zones: (1) offices and assembly areas, (2) lockers and lavatories, (3) shop offices, (4) repair bays, (5), warehouse, (6) shop areas, and (7) vehicle storage. Offices and assembly areas will be heated and cooled with a rooftop unit using gas-fired preheat, direct-expansion (DX) cooling, and variable air volume with electric reheat terminals. Lockers and lavatories will be heated and cooled with a constant volume rooftop unit using gas-fired heat and DX cooling. Shop offices will use a constant volume rooftop unit using gas-fired heat and DX cooling. Repair bays will be heated only with direct-fired makeup air units. The warehouse will be heated only with gas-fired unit heaters. Shop areas and vehicle storage will be heated only by gas-fired makeup air units.
Based on the guideline specification and code requirements, we assumed the following U-Values for the building envelope: floor = 0.12, roof = 0.053, exterior walls = 0.063 and windows = 0.57. We also assumed a window shading coefficient (SC) of 0.55.
According to the model results, MDPW, built to Wisconsin Building Code standards and baseline lighting power densities specified by WE Energies, would consume 1,400,000 kilowatt-hours (kWh) of electric energy and 13,500 therms of natural gas each year at an estimated cost of $145,000. Peak overall electric demand would be 520 kilowatts (kW). See the attached Annual Energy Use and Energy Use Reduction tables (page 69).
Alternative 2: Upgrade Envelope to High-Performance. We evaluated upgrading the building envelope to the following U-Values set forth in the Advanced Buildings Energy Benchmark, Version 1.0, dated October 2003: floor = 0.10, roof = 0.033, exterior walls = 0.053 and windows = 0.35. We also assumed a better window shading coefficient (SC) of 0.40 and a highly reflective roof (reflectivity of 60%). If the entire building envelope were upgraded to this level, MDPW would consume 1,250,000 kWh and 13,000 therms each year at an estimated cost of $135,000 yielding an annual savings of $10,000, only $0.043 per square foot. Peak overall electric demand would be 440 kW.
However, most of the building envelope (230,000 square feet) covers heated-only spaces including the repair bays, warehouse, shop areas and vehicle storage. All of these spaces will be heated to only 50 to 65 F so envelope upgrades, in these areas, will have minimal value. When we focused our envelope analysis on the heated and cooled areas which include the office and assembly areas, and lockers and lavatories (29,000 square feet), the savings were $7,000 or $0.24 per square foot. Therefore, an upgrade in the envelope for the heated and cooled areas yields a much better payback than the heated-only areas. Furthermore, since the cooled areas would be affected by this upgrade, the peak overall electric demand would still be 440 kW (same peak reduction benefit as upgrading the entire building envelope).
Alternative 3: Add Air-To-Air Heat Recovery. Many zones will have a high exhaust air requirement: lockers and lavatories will have a combined exhaust rate of 4,400 cubic feet per minute (cfm), repair bays will have an exhaust rate of 1,900 cfm, shop areas will have an exhaust rate of 5,500 cfm, and vehicle storage will have an exhaust rate of 55,000 cfm. For every cubic foot of air exhausted, one cubic foot of outdoor air must enter MDPW and this air must be conditioned to the proper temperature and humidity, requiring energy use.
Air-to-air heat recovery equipment uses the tempered exhaust air as a source of energy to precondition the outdoor air before it enters the ventilation system. Exhaust air from the lockers and lavatories (4,400 cfm) can be processed through a heat-wheel device that can precondition 4,400 cfm of outdoor air entering the offices and assembly areas. This preconditioned outdoor air will provide sufficient ventilation for 220 occupants at the recommended level of 20 cfm per occupant. A heat-wheel device will also recover humidity, during the heating season, so the interior humidity levels remain higher, reducing static electricity and improving occupant comfort and health. Exhaust air from the repair bays, shop areas, and vehicle storage (62,400 cfm) can be processed through a run-around loop that can preheat 62,400 cfm of outdoor (makeup) air entering these spaces. During the cooling season, this system can be bypassed. Run-around loops are ideal for recovering heat from exhaust air contaminated with vehicle emissions, paint fumes, and particulate.
If air-to-air heat recovery units are added, MDPW would consume 1,400,000 kWh and 9,600 therms each year at an estimated cost of $120,000 yielding an annual savings of $25,000. Peak overall electric demand would be 510 kW.
During the Life Cycle Cost Analysis it was determined that most of the energy savings was captured by the heat wheel. The high cost of the run-around loop was not as effective due to the exhaust cycle times and ultimately not included in this project.
Alternative 4: Reduce Lighting Density and Add Sensors. Wisconsin Building Code allows lighting densities (watts per square foot) that are higher than recommended practices for an energy-efficient building. Lower lighting densities save on first cost and energy cost. We reduced lighting power densities from those used as a baseline by WE Energies to those listed in the Advanced Buildings Energy Benchmark, Version 1.0, dated October 2003.
Additional savings could be achieved by installing occupancy sensors on non-emergency lights not required for egress. Some corridor lights and some of the parking garage lights should remain on at all times. All other lights can be controlled through occupancy sensors with manual overrides.
If lower lighting power densities are installed and most of the lights are controlled by occupancy sensors, MDPW would consume 930,000 kWh and 14,400 therms each year at an estimated cost of $134,000 yielding an annual savings of $11,000. Peak overall electric demand would be 440 kW.
Alternative 5: Combine Measures. Reduce lighting density and add occupancy sensors, add air-to-air heat recovery, and upgrade envelope in the spaces. In addition, upgrade the air-cooled rooftop units from a code-minimum energy efficiency ratio (EER) of 9 to an EER of 11. If all of these measures are implemented, MDPW would consume 730,000 kWh and 10,000 therms each year at an estimated cost of $97,000 yielding an annual savings of $48,000. Peak overall electric demand would be 340 kW.
Alternative 6: Upgrade Heating System. Provide boilers and hot water heat as an alternate to the planned gas-fired and electric reheat system. Hot water can be provided to the rooftop units for preheat, the reheat coils in the office area, and the unit heaters in the repair bays, warehouse, and vehicle storage areas. If built as specified, MDPW will consume 260,000 kWh for reheat and 13,500 therms at an estimated cost of $26,000 each year. A high-efficiency hot water boiler system (82% efficient) could provide all of this heat using 24,000 therms each year at a cost of $15,000 yielding an annual savings of $11,000. Peak overall electric demand would be unchanged from the base of 520 kW.
Alternative 7: Upgrade Cooling System to Chilled Water. Provide water-cooled chilled water cooling as an alternate to DX cooling. This upgrade would only affect the areas that are cooled: offices and assembly areas, lockers and lavatories, and shop offices. A typical rooftop DX cooling system will require 1.38 kW of electric power to produce one ton of cooling. A water-cooled chilled water system will require 35% less electric power. If built with DX cooling, MDPW will consume 150,000 kWh each year for cooling. By reducing this 35%, 53,000 kWh will be saved each year, reducing annual electric energy costs by $5,000. Peak overall electric demand would be 480 kW.
While the construction contract was being negotiated, the demolition of existing buildings was started in December 2004 to enable the developer in meeting the fourteen-month fast-track design/build schedule. In addition, due to this brownfield site which was once used for steel fabrication, the site would require a hard surface cap.
Demolition was performed in keeping with LEED (Leadership in Energy and Environmental Design) in an environmentally-conscious way:
Upon completion, this new facility will be highly energy efficient. It is estimated that based on Life Cycle Costs, it would cost $87,117 for various energy initiatives while saving approximately $48,000 per year, offering a simple payback of two years. Part of the savings is expected from a waste oil boiler to heat the four-bay vehicle maintenance shop using drained vehicle oil for fuel.