09 - 2024-11-27 Feasibility Study.pdf

05 PLANNING AND DESIGN

PROGRAM SUMMARY | SPACE REQUIREMENTS

35% SUBMISSION

OCTOBER 2018

PAGE

AIRPORT OFFICE

BUILDING RESTACK

Feasibility Study Final Report

October 27, 2024

Prepared for Denver International Airport

TEAM

A I R P O R T O F F I C E B U I L D I N G R E S T A C K - D E N V E R I N T E R N A T I O N A L A I R P O R T

Final Report October 27, 2024

DENVER INTERNATIONAL AIRPORT

Owner

THE ABO GROUP

Architectural

RMH GROUP

Mechanical/Electrical/Plumbing/Fire Protection Engineering

RLB

Value Analysis/Cost Estimating

F E A S I B I L I T Y S T U D Y

TABLE OF CONTENTS

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0 EXECUTIVE SUMMARY

0.1 Background 4

0.2 Primary Purpose, Drivers, and Scope 5

1 DESIGN PROGRAM

1.1 Introduction 10

1.2 General Requirements and Goals 13

1.3 Sustainability 13

1.4 Architectural Elements 14

2 BUILDING SYSTEMS

2.1 Introduction 18

2.2 DESIGN CRITERIA 18

2.3 ELECTRICAL, MECHANICAL, AND PLUMBING 19

3 APPENDIX

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0 Executive Summary

0.1 Background

The Airport Office Building (AOB I), located in Denver International Airport at 8500 Peña Blvd, Denver, Colorado, is owned by the City of Denver. Built in 1991, this structure consists of a five-story office building on top of a three-story parking garage. Construction is Type 1, Fire-Resistive. The original tenant build-out was completed in 1993. As of August 2024, it is occupied by 500 Full Time Employees in approximately 82,000 gross square feet. The Airport Office Building’s evaluated historic status is Not Historic. Most of The Airport Office Building programmatic spaces include office and office support spaces such as meeting rooms, break rooms, and the like.

Additional background as indicated in the Request for Proposals:

As DEN grows in workforce, facility assets and operations, the administrative office spaces (mainly at existing AOB) supporting the growth have not been increased proportionally. This office space deficiency has impacted DEN workforce efficiency and ability to grow to support the organizational visions. This feasibility study will validate the program, provide infrastructure cost data to support decision-making, and provide roadmap to strategize the initiation of future projects.

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0.2 Primary Purpose, Drivers, and Scope

0.2.1 Primary Purpose

The FEASIBILITY STUDY compares the current building spaces, systems, and infrastructure with DEN’s growing needs to optimize workplace efficiency in alliance with developing workplace trends. The FEASIBILITY STUDY includes provisions for the internal expansion of the current structure (AOB I) regarding interior space management, mechanical, plumbing, and electrical systems. Provisions are also included for a new, mirrored Airport Office Building (AOB II), as well as relocation of the Airport Operations Center (AOC) to a location elsewhere in the Airport Campus.

0.2.2 Drivers

The FEASIBILITY STUDY Report for DEN AOB I and AOB II is guided by compliance with current building codes, anticipated building code updates, and anticipated sustainability requirements. The report ensures adherence to building codes, emphasizes energy efficiency and occupant comfort, and evaluates the existing HVAC system, plumbing infrastructure, and electrical infrastructure. Sustainability and Energy Efficiency Requirements are guided by codes and standards as listed throughout this study.

The FEASIBILITY STUDY also addresses budget evaluation Rough Order of Magnitude (ROM) cost estimates for design and construction as well. Overall, the report aims to comply with regulations, enhance energy efficiency, optimize resources, and meet functional requirements to enable DEN’s future workforce needs.

0.2.3 Scope

a. AOB I Restack

The AOB I Restack will consist of a comprehensive reallocation of building spaces and services on five stories.

This feasibility report provides insight of disciplines as described below:

i. Architectural

The scope of work being undertaken architecturally is to evaluate the following:

limited to exterior walls/glazing, and the roof of the building.

ii. Life Safety

The existing Fire Alarm/Fire Suppression system as well as the Smoke Management system are evaluated in the life safety portion of the AOB I Restack study. Additionally, recommendations for required improvements for the AOB I Restack are provided in the life safety portion of this study.

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iii. Electrical

As occupancy would be increasing with the AOB I Restack, electrical systems are evaluated in this feasibility study. The following, critical aspects are evaluated to ensure a well powered building that meets energy and sustainability requirements:

iv. Mechanical

The existing mechanical system is examined for equipment and distribution, as well as capacity to heat, cool, and exhaust the building. In addition to the additional occupant load of AOB I Restack, multiple options are presented in this study to address the needed improvements resulting from the added occupants and sustainability requirements.

v. Plumbing

An Analysis of the AOB I plumbing system is given in the plumbing portion of this study to address the existing distribution, this includes the pump system, core layouts, and equipment. To achieve the AOB I restack goals, options are provided that include the use of low-flow plumbing fixtures, plumbing circulation, plumbing recirculation, and new equipment.

vi. Telecommunication

The telecommunication distribution is evaluated for existing capacity, as well as additional services that are recommended for an increase in occupancy. This includes the existing and proposed IDF space, Wi- Fi upgrades, and distribution for the various other requirements in an office tower.

vii. Sustainability

Sustainability for building systems are examined and recommendations are made for plumbing and electrical systems. Architectural sustainability provisions are made as an integral part of the architectural portion of this study.

viii. Cost Estimating

The cost estimate for this portion of work is provided in Appendix 3.

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b. AOB II Interior and Systems Buildout

AOB II is to be located in Denver International Airport at 8500 Peña Blvd, Denver, Colorado on the opposite/East side of A-Bridge from the Airport Office Building (AOB I), which is owned by the City of Denver. The new tower structure consists of a five-story office building on top of the existing three-story parking garage that was built as part of AOB I. Construction is anticipated to be Type 1, Fire-Resistive, with approximately 82,000 gross square feet of building area. Most of The AOB II programmatic spaces are to include office and office support spaces.

This feasibility report provides insight of disciplines as described below:

i. Architectural

The architectural scope for AOB II is limited. Requirements are listed for guidance in the architectural design of AOB II.

ii. Life Safety

Recommendations for the Fire Alarm/Fire Suppression system as well as the Smoke Management system are provided in this portion of the study.

iii. Electrical

Electrical system requirements and recommendations are provided in this study. The following, critical aspects are evaluated for AOB II:

iv. Mechanical

Mechanical systems recommendations are provided in this section with options to achieve a system that meets the following criteria:

v. Plumbing

Recommendations for a new building plumbing system are provided address distribution, maintaining system pressure, equipment, and fixtures for AOB II.

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vi. Telecommunication

Telecommunication infrastructure recommendations include IDF provisions, Wi-Fi coverage and distribution for the various other requirements in an office tower.

vii. Sustainability

Sustainability requirements and recommendations are provided for AOB II. Criteria and building components provided to achieve sustainability requirements include the following:

other components/aspects.

• Building electrification strategies.

viii. Cost Estimating

The cost estimate for this portion of work is provided in Appendix 3.

c. Relocation of Airport Operations Center (AOC) elsewhere in the Denver Airport Campus

As the programmatic requirements of AOB I and AOB II are to increase occupant capacity, major data services are going to have to be relocated to a location away from their current location. The scope of work being undertaken for this is to evaluate the electrical, mechanical, life safety, and communications aspects of relocating the AOC.

i. Architectural

There is currently no architectural scope for the AOC as the AOC portion of the study focuses on infrastructure.

ii. Life Safety

Recommendations for Fire Alarm/Fire Suppression are provided in this portion of the study.

iii. Electrical

Electrical system requirements and recommendations are provided in this study. The following, critical aspects are evaluated for the AOC:

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iv. Mechanical

Mechanical systems recommendations are provided for heating, cooling, and airflow of the AOC, both as a standalone building and as an interior space

v. Plumbing

Recommendations for AOC plumbing services are described in this section.

vi. Telecommunication

Telecommunication infrastructure recommendations are provided that include include fiber optic lines and radio transmitting for the AOC.

vii. Sustainability

No sustainability provisions are provided for the AOC as the AOC portion of the study focuses on infrastructure.

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1 Design Program

1.1 Introduction

The current design program for the upgrade of interior office spaces has been provided by DEN as an updated version of the Level 07 restack, which is shown below. Architectural and systems evaluation for the AOB I Restack and AOB II New Tower are based on five floors (Levels 6-10) of that design.

Level 07 Restack Plan (Provided by DEN):

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Additional Provisions have been made to the provided plan that indicates locations of Gender-Neutral restroom in order to fulfill current plumbing fixture count requirements as well as the City of Denver’s Gender Neutral restroom Requirements.

Plumbing Fixture Count:

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Gender-Neutral Restroom Placement:

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1.2 General Requirements and Goals

1.2.1 General Requirements of The AOB I and AOB II

a. Align with industry trends and DEN Workplace Strategy

b. Increase density and improve efficiency

c. Verify and determine building system infrastructure capacity

1.2.2 Program Goals

a. Tenant Finish and Building Envelope program study of floors 6-10 the existing workplace at the Airport Office

Building (AOB)

b. Tenant Finish and Building Envelope program study of Future Airport II Office Building (AOB); mirrored on the east side of ‘A’-Bridge.

c. Building Systems (Refer to Section 2):

i. Life safety

ii. Electrical capacities for power and lighting

iii. Mechanical

iv. Telecommunication

v. Sustainability

d. MOC Relocation (Refer to Section 2)

1.3 Sustainability

1.3.1 Requirements

Requirements for sustainability are as follows:

Denver Internation Airport Design Standards Manual (DSM)

Denver Executive Order 123

Denver Green Code

Energize Denver

Denver Green Building Ordinance – Roof Requirements

1.3.2 Criteria

The main criteria for measuring architectural elements and systems will be different for AOB I and AOB II shall be the criteria required to achieve LEED Gold:

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AOB I SHALL BE evaluated under LEED v4 Interior Design and Construction (Id+c)

AOB II SHALL BE evaluated under LEED v4.1 building Design and Construction (Bd+c)

Additional Criteria

Policies Listed under 1.3.1 “Requirements” also provide their own criteria for Sustainable Development.

1.4 Architectural Elements

1.4.1 AOB I Restack

a. Building Envelope Upgrade

The existing building envelope for The AOB I Restack will need to be upgraded from its original construction, which does not meet today’s energy requirements. This will include all vertical and horizontal building components that are exposed to the elements. Components include the roof of the building, exterior storefront wall, and solid wall systems. The figure below is a representation of the upgrades needed.

Building Envelope Upgrades needed:

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i. Roof

The roof system will need to be replaced as the R-Value of the roof will not support sustainability requirements based on evaluation of the existing CAD files. Roof insulation thickness is too shallow, with an approximate thickness of 2 inches in places. Roof insulation should be at least 6 inches thick to meet and International Energy Conservation Code of R-30. The following figure shows a comparison of what is built vs what would provide the thermal protection currently Required.

Existing vs Required Roof Construction:

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ii. Wall systems

The majority of the building walls are constructed with Glass/Aluminum storefront systems; and include both transparent glazing as well as spandrel glazing. Energy efficiency upgrades to these systems differ as follows:

• Transparent glass curtainwalls: the R-Values and Solar Heat Gain Coefficients need to be upgraded from those of the original construction. This can be achieved by replacing the system; however, this method would likely be cost prohibitive. The suggested course of action to upgrade the energy efficiency of these systems would be to utilize retrofit window inserts. These are applied to the inside of the curtainwall frames; substantially increase the U-value of the curtainwall assembly, converting a two-pane window system to a four-pane window system, and enable the building owner to apply coated glass that meets sustainability requirements. The figure below provides an example of this.

Retrofit Curtainwall Insert:

• Spandrel Panels Spandrel panels are opaque panels that fit into the curtainwall frame and conceal ductwork, structure, and other building components that are not desirable to see. The spandrel panels can be provided a greater R-value by adding insulation behind the panel.

The center portions of the east and west exterior walls consist of uninsulated aluminum panels over cavity wall framing with a minimal amount of insulation. To meet sustainability requirements, the existing aluminum panels should be removed and replaced with insulated metal panels, with R-21 batt insulation placed inside of the cavity walls.

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Metal Panel Wall Replacement:

b. Interior Building Materials

Interior construction practices and materials need to be chosen based on their sustainability qualities as well as durability and appearance. The manufacture and health safety of building materials will contribute to the LEED scoring of the overall restack.

1.4.2 AOB Tower II

Tower II, as a newly built building, would need to be constructed in accordance with the sustainability requirements listed in Section 1.3.

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2 Building Systems

2.1 Introduction

2.1.1 Purpose

The purpose of this section of the report is as follows:

2.1.2 Tower I Restack

To evaluate the existing building electrical, life safety, heating, ventilating and air conditioning (HVAC), and plumbing systems to determine if the existing capacities are adequate to serve the proposed Airport Office Building (AOB) Tower 1 remodel resulting in additional occupant load, advise to current code requirements, and analyze and proposed potential energy saving measures that are feasible. These goals are meant to support the Rough Order of Magnitude (ROM) cost estimate and to help DEN validate their program and strategize future projects.

2.1.3 Tower II

To evaluate and propose the building electrical, life safety, HVAC, and plumbing systems for the new AOB II tower which have similar use to and mirrors Airport Office Building (AOB) I. These proposed systems will also be used to create a preliminary rough cost and assist DEN in facility planning.

2.1.4 MOC Relocation

The purpose of the MOC evaluation is to evaluate the needs of the new location. Additional discussion for the MOC mechanical HVAC requirements is in paragraph 3.3.3.

2.2 DESIGN CRITERIA

2.2.1 Tower I Restack, Tower II, MOC

• DEN Design Standard Manuals (DSM), latest versions available at the time of permit design:

o Standards and Criteria o Life-Safety o Mechanical o Communications & Electronic Systems o Digital Facilities & Infrastructure/BIM o Electrical o Sustainability

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99.6% for heating and 0.04% for cooling. Equipment operational projection design at extreme temperatures is considered.

• Interior design criteria for occupied spaces will be 70°F (70°F unoccupied) for heating and 75°F (85°F unoccupied) for cooling,

• Regularly unoccupied spaces will be set to 60°F for unoccupied heating setpoint and have no unoccupied cooling setpoint per DEN Mechanical DSM Q2 2024.

The above design criteria are given with the assumption that this building will be designed within the period of the adoption of these future codes and regulations; the criteria will be updated during the design process to the current additions at that time. The City and County of Denver (CCD) Amendments for the 2024 International Codes are expected to be extensive and are unknown at this time.

There are several Administrative Modification Requests associated with multiple disciplines for this building which were approved by the CCD, Community Planning & Development (CPD) which would need to be reevaluated in conjunction with CPD for any major renovation of affected systems to verify compliance when approved to proceed with full design. The Administrative Modification Request that impacts consideration at this stage of analysis is discussed below.

2.3 ELECTRICAL, MECHANICAL, AND PLUMBING

2.3.1 Tower I Restack

a. Life Safety

FIRE ALARM

The existing fire alarm system is a zoned system with voice evacuation. It serves level 3 through the penthouse.

The fire alarm control panel is located on level 4 in room #04A05.

Speaker and strobe coverage is provided throughout corridors, lobbies, and most open offices. Speaker cov-erage is provided in locker rooms and some break rooms. Strobe coverage is provided in conference rooms, restrooms, and some records areas. Duct detectors are provided on the ductwork mains for each level. Smoke detection is installed in elevator lobbies, electrical rooms, and telephone terminal board closets.

The extensive floor plan changes associated with the restack would require new fire alarm speaker and strobe devices throughout levels 6-10, with the exception of the restrooms. Additionally, the existing system does not

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F E A S I B I L I T Y S T U D Y meet the current DSM, which requires a digital, addressable system. It is recommended to provide a new fire alarm system for levels 6-10 as a part of the restack program. This system could be networked into the DEN Terminal Complex system to provide enhanced monitoring and voice communication from the Emergency Communication System.

Specific requirements for the new system would be determined by a design consultant creating a Fire Alarm System Basis of Design per the DSM. The system would be required to comply with NFPA 72.

FIRE SUPPRESSION

The fire suppression system consists of a dual fed 10” fire line connected to fire department connections.

This system feeds dry pipe systems (in the garage/ loading dock areas) and a wet system which serves lev-els 6 through 10 and the mechanical penthouse on level 11. Each level is a separate sprinkler zone served by a 4” branch and has fire department valve cabinets. The fire water system has a diesel-powered fire pump (FP-1) and a jockey pump (JP-1) located in the fire pump room on level 4. The fire sprinkler system is monitored by flow and tamper switches on each level. The Maintenance Control Center (MCC) and Communications Center are equipped with double-interlock pre-action systems with nitrogen generators.

Specific requirements for a revised fire suppression system would be determined by a design consultant creating a Fire Suppression System Design per the DSM and performance specifications. The system would be required to comply with NFPA 13 and Denver Community Planning & Development, Fire Preven-tion Bureau (FPB). This high-rise building classification requirements will adhere to CCD Amendments.

SMOKE MANAGEMENT

The existing smoke management systems consist of the use of the building relief air fans, RF-1 through RF-6 for smoke removal through the return air shaft, designed with sheet metal lining. The stairwell pressurization system consists of supply fans SF-8 and SF-10 located on level 5B, area 2A, taking outside air from intake louvers and discharging it into their respective stair wells. This air is then relieved out of the building at level 11 through louvers with control dampers. Elevator hoistway and refuge area pres-surization are provided by fan SF-12 located on level 5B , area 2A, taking outside air from intake louvers and discharging into hoistways then into the refuge area in front of the elevator car doors. This air is then exhausted by fan EF-8 located in the penthouse on level 11 through louvers to the outside. Sequences of operation or recent test data for the smoke management and pressurization systems were not available at the time of this report. Please see fan system capacity table below.

The recommendations below are related to the corresponding HVAC system options based on the depth of construction for each option, i.e., if shafts are accessed and modified, the smoke management system should be modified correspondingly. For further information and a more in-depth description of the exist-ing system and its performance reference the Annual Smoke Control Test Report – 2023 accomplished and authored by Jensen Hughes, a copy of which will be included in the appendix.

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i. Smoke Management Impacts Associated With HVAC Option 1

It is anticipated a new smoke exhaust/ level depressurization duct riser will be routed to all occupied levels. Each level branch will be provided with fire/smoke dampers having command-able actuators. A new rated smoke exhaust fan and riser will be sized for 5 air changes per hour (ACH) from a single level in accordance with the Denver Fire Code prescriptive approach (or current requirement at the time of design). The fan will be located on the roof adjacent to the penthouse. Inlets will be arranged to reduce the amount of test smoke over the test period in accordance with the Denver Fire Code prescriptive approach.

An additional fan(s) is recommended for make-up air. Fire/Smoke dampers at the shaft will have com-mand-able actuators. Dedicated dampers, duct branches and outlets will be arranged to distribute the make-up air in order to flush the space, reducing the amount of test smoke over the test period in accordance with the Denver Fire Code prescriptive approach. Components will be specified to UL UUKL as appropriate.

It is not known if this work will trigger revisions to the existing hoistway, area of refuge, or stairway smoke management systems. Interaction with Denver CPD-FPB will be required for this determination.

The most conservative case is that the entire smoke management system would be replaced to conform to current requirements along with the extensive HVAC modifications in this option.

The Firefighters Smoke Control Panel will be revised or replaced as required to reflect the new level by level smoke management system.

ii. Smoke Management Impacts Associated With HVAC Option 2

This option does not directly impact the Smoke Management system. The existing system could contin-ue to operate as it does currently. However the design is based on older codes, it uses HVAC components for smoke management functions, and it is operating under an Administrative Modification from Denver CPD to allow the use of standard building automation controls.

This administrative modification was granted in 2023 for what was anticipated to be a long-term proj-ect. It is not known if Denver Fire Prevention Bureau will require any upgrades to this system. It should be noted that most components used for smoke management are of 1990s vintage and the reliability is likely diminished. For projection of anticipated modifications for this system, new listed and rated fans would be required to replace the existing exhaust and intake.

It is not known if this work will trigger revisions to the existing hoistway, area of refuge, or stairway smoke management systems. Interaction with Denver CPD-FPB will be required for this determination.

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iii. Smoke Management Impacts Associated With HVAC Option 3

This option would limit any modifications to anything required to accommodate the increased occu-pant load on each level. The impacts associated with Option 2 are also valid for this option.

b. Electrical Capacity

EXISTING NORMAL POWER

The existing Tower 1 normal power system has a dual electrical service, fed by Xcel. It is fed by Transformers 902/987 and 887/987. Both transformers feed Main Switchgear 4-2ASG1 in a dual-ended switchgear ar-rangement with an electrical interlock. 4-2ASG1 is a 480/277 volt, 3 phase, 4 wire, 4000A with a 65,000 AIC rating. It has 4000A main circuit breakers with GFI protection on each end. Xcel meters are located within the switchboard and serve the two services. DEN-owned electronic meters are also provided on each ser-vice. 4-2ASG1 feeds Bus Riser 2A; Bus Riser 2B; and Distribution Panels 10-2AD1, 3-2AD1 and 3-2BD1. It also has a connection to the standby generator system via an automatic ‘tap box’. That connection is through a 1600A circuit breaker in the distribution section. The utility transformers, 4-2ASG1, and generator are locat-ed outdoors on level 4 of Tower 1, in area 2W. 4-2ASG1 has a metered peak demand load of 528 kW, which is 635A. This leaves an available capacity of 3,365A.

General power for levels 5A through 10 is distributed through Bus Riser 2A, a 1000A bus duct that is fed from a 1000A circuit breaker in 4-2ASG1. Each of levels 6 through 10 have at least two bus plugs on the bus riser: one 100 amp feed to a 480/277V panelboard for lighting and HVAC loads, and one 100 amp feed to a 75 kVA step down transformer and 120/208V panelboards. The bus riser and this electrical equipment are located in stacked electrical rooms on each level. Meter data for the 120/208 systems on the 7th and 8th lev-els indicated a peak demand load of approximately 40A, which leaves 185A of spare capacity. Due to similar use and occupancy, it is assumed peak loads would be similar for levels 6, 9, and 10. Level 6 has an addition-al 225A bus plug which feeds the 6th level UPS system. Level 10 has an additional 60A bus plug which feeds Panel 10-2AL5 at 120/208V through a 45 kVA transformer.

Distribution Panel 10-2AD1 is a 480/277V, 3 phase, 4 wire, 800A main-lug-only distribution panel fed directly from an 800A circuit breaker in 4-2ASG1. It is located on level 10 and feeds the 10th level UPS system, roof loads, and several unknown loads.

EXISTING STANDBY POWER

The tower emergency standby power system is served by additional feeds from the same pair of Xcel trans-formers that feed the normal power system. The pair of Xcel transformers feed Switchgear 4-2AESG1, a 480/277 volt, 3 phase, 4 wire, 4,000A switchgear with a 65,000 AIC rating. It has 2000A main circuit breakers with GFI protection on each end. Xcel meters each service within the switchboard. DEN-owned electronic

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Final Report October 27, 2024 meters are also installed on each service. 4-2AESG1 is also fed by a 1600 kVA, 480/277V standby generator via a generator tap box. The generator feeds 4-2AESG1 directly into the distribution section via a 1600A circuit breaker. The generator tap box also has a 1600A connection to 4-2ASG1. A PLC provides controls that prevent accidental energization of both switchgear from generator and utility sources. This equipment sits next to 4-2ASG1 and the Xcel transformers on level 4. 4-2AESG1 feeds distribution panels 3-2AED1 and 3-2BED2 on level 3.

3-2AED1 feeds several panelboards on levels 3 through 5, as well as 11-2AEH1, 11-2AEH2, and 11-2AEL1, which feed mechanical equipment serving levels 6-10. 3-2BED1 feeds several panelboards on levels 3 through

5. Notably, it feeds automatic transfer switch 5A-2AATS on level 5, which feeds a UPS system that serves panel-boards on levels 6, 8, and 9. This transfer switch is also fed from Bus Riser 2B on the normal system.

Emergency lighting on levels 6 through 10 is backed by DualLite Spectron LSN inverters located in the electrical room ton each level. Each is fed by a 277V circuit from panel 3-2AEH1.

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UPGRADES REQUIRED BY RESTACK PROGRAM

The Restack Program would seek to increase the density of use on levels 6 through 9. This would entail addi-tional workstations and meeting rooms, which in turn would require additional power circuits. The following table indicates the type and number of programmed spaces envisioned for each of these levels, and assump-tions for typical equipment and number of circuits required to serve each space. The total number of normal power circuits required to serve these office and support spaces on each level is 103.

The 120/208V normal power panelboards on the existing levels are mostly full. Each has several existing loads that will continue to be in use with the Restack Program. These, combined with the estimated 103 circuits re-quired for the new program, will require an additional 42 circuit panelboard on levels 6, 7, and 8. Level 9 has

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Final Report October 27, 2024 more existing 120/208V panelboards, which contain the necessary circuits for the program.

The existing electrical rooms have little spare wall space. The new subpanels may need to be installed remote-ly on the floor, which is an opportunity to reduce branch circuit lengths. They will be fed from the existing 120/208V panelboards.

A summary of the existing circuits and the need for future circuits is shown in the following table:

The 120/208V system on the 7th level had a metered peak demand load of 41.7A. The table below indicates the NEC-required 125% factor for metered loads and the estimated electrical load added by the net gain in space types. Despite having an existing break room, additional break room appliances are included because of the increased density of occupants. The panelboard is adequate for the restack with 93.3 amps of estimated spare capacity. The step down transformer feeding the panelboard is adequate, with 33.6 kVA of estimated spare capacity. As the program has an identical space count on each level, this capacity is assumed to be sufficient for those levels as well.

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Lighting systems and mechanical equipment are largely fed from the 480/277V normal power panelboard on each level. Existing fluorescent lighting systems have already been converted to LED, using retrofit kits or LED replacement lamps. However, compliance with the City of Denver Building Code will require a lighting power density of 0.62 W/SF (per table C405.3.2(1) of IECC 2024). This, combined with the extent of the renovations, will require new lighting and controls systems to be installed throughout the renovated areas on each level.

The lighting demand load will decrease as a result. See the Sustainability section for details on plug and lighting controls.

Three HVAC system options are considered in this study. See the HVAC section for a description of the systems.

For Option 1, a new 480/277V distribution panel would be installed on the 5th level, dedicated to serving the new heat pumps and hydronic pumps. This would be fed from bus riser 2A. 120V power for the fan coil units will come from branch panelboards on each level. The load for these items is expected to be a net decrease in electrical load from currently installed units. Existing penthouse electrical panelboards will remain to serve the DOAS, fans, and other miscellaneous rooftop HVAC equipment. These existing panelboards will require meter-ing to verify capacity.

For Options 2 and 3, the existing penthouse electrical infrastructure would be reused to feed rooftop equip-ment. Existing branch panelboards on each level would power the new VAV boxes and other miscellaneous equipment. These existing panelboards will require metering to verify capacity.

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The 8th and 9th levels are expected to require an additional 48 port data switch to serve the additional worksta-tions and meeting rooms. This will require a new 120V circuit from the UPS-backed panelboard in their IDF. The power requirement for the additional switch is 6-12 amps. Capacity for this load on each UPS will need to be verified during design.

The 7th level does not have an existing IDF. One will be added as a part of the restack. This room will require a new 100A, 120/208V panelboard with a 60A main circuit breaker. It will be fed from existing Panel 5A2AUPS1, which is backed by an existing UPS and the generator system. The capacity of this existing system will need to be metered and verified in design. Eight 20A, 208V twist lock receptacles will be installed to power the IT racks.

The following table is a load calculation for the Main Switchgear 4-2ASG1 with the net gain of spaces and appliances added to the metered peak demand load. Conservatively, loads removed are not included in this calculation, as it is not known if they were running when the peak demand was measured. The switchgear is lightly loaded, with more than 3000A of spare capacity remaining. The choice of mechanical system will affect the loading on 4-2ASG1. However, the metered peak load contains the existing HVAC electrical load. The large amount of excess capacity on 4-2ASG1 is sufficient for additional load due to increased occupancy and system changes.

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F E A S I B I L I T Y S T U D Y

c. Mechanical

HVAC

i. Existing conditions

AOB-1 conditioning consists of a variable air volume (VAV) system which is composed of one large built-up air handling unit (AHU) serving levels 6 through 10. The medium pressure supply air from the AHU is conveyed via ductwork from the mechanical penthouse into a fire rated shaft located at the core of the building where branches are ducted to the distribution systems on each level. At each level, air is distrib-uted to zone VAV terminal boxes and VAV fan powered (FPVAV) boxes. Fan-coil units (FCU) are utilized for some localized conditioning. The return air travels from each level’s ceiling plenum space to the fire rated return air shaft where it is ducted back to the inlet of the AHU to mix with outside air. Relief fans (RF-6 through RF-9) draw from the return air duct to remove air from the system when the AHU is in economizer mode. Economizer mode occurs when the ambient conditions can maintain building re-quired setpoints without input from heating or cooling systems. The total airflow of these fans is 97,500

CFM.

The AHU consists of (in order of air flow) filters, hydronic heating coils, hydronic cooling coils, two supply fans (SF-3 and SF-4), backdraft dampers (to enable single fan operation), and sound attenuators. The hy-dronic coils are supplied by the main airport heating and cooling plants from piping in the utility tunnel.

The hydronic building systems are supplied by pumping systems in the level 3 mechanical room which are the building level pumps from the primary area plant systems. The AHU is capable of suppling a total of 112,000 CFM.

The general exhaust system entailing all toilet and janitor closet air removal is by EF-2 located on roof level 11. The main level electrical rooms, located in the core area on each level, are exhausted at a rate of 250 CFM each through EF-4 located on level 11. Tenant exhaust was added at tenant level buildout through EF-20.

Additional cooling was added for a computer/ server/ communications area room on level 6.

Much of the mechanical systems and components are well beyond their expected service life according to the 2019 ASHRAE Handbook – HVAC Applications – Chapter 38 Owning and Operating Costs - Table 4 Comparison of Service Life Estimates. Before and during the proposed renovation, the contractor should be tasked with evaluation of expected equipment life beyond completion and replacement needs to be considered during the project.

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The following table has relevant airflows for major systems:

Equipment/ System

Air Flow – cubic feet per minute (CFM)*

Notes

Main AHU

SF-3 and SF-4

112,000 Total, 56,000 Each

Hard copy drawing in Mech.

Room SOO indicates duct pressure controlled by fan inlet vanes.

General Exhaust

EF-2

-6,125

Electrical Room Exhaust

EF-4

-1,250

Relief Fans (Main AHU)

RF-6 through RF-10

-19,500 Each (Economizer mode) totaling 97,500

According to the drawings fans are also for smoke management in emergency operation.

Stairway Pressurization

SF-8 and SF-10

19,000 Each (Emergency)

Elevator Hoistway and Refuge Area Pressurization

SF-12

33,000 (Emergency)

Refuge Exhaust

EF-8

-18,000 (Emergency)

Smoke Exhaust

EF-16

-20,000 (Emergency)

Tenant Exhaust

EF-20

-4,300

*Values obtained from drawings: no balance reports were available at the time of this report.

The elevator machine room is conditioned by a separate AHU (AHU-3) with CUP chilled and heating water.

DEN has a project in place to update all HVAC BAS control systems with new software and hardware to bring current building operations to DEN DSM standards. This project will include implementing control strategies to optimize energy consumption with the current systems. The project Contract Number is 202161068. The project is slated to start construction in the winter of 2024.

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F E A S I B I L I T Y S T U D Y

ii. Basis of HVAC Analysis

A building assessment was completed to evaluate the mechanical building systems currently in operation and determine whether or not they could support the proposed remodel on levels 6-10. The analysis is based off of limited site visits and available documents and drawings.

Load calculations were performed for the proposed occupant load change on level 7. Levels 8-10 are an-ticipated to approximately reflect that of level 7 with the exception of level 10 which is assumed to have an increased load of approximately 10-15% due to the roof exposure.

The following values were assumed for these calculations:

1) Occupant load increased by approximately 40 people per level (occupant diversity factor included).

2) New LEDs at .64 W/SF will be provided throughout

3) Each workstation has (2) monitors and one computer at approximately 120 watts each

4) Wall R=12; Windows = Double Pane Low E with Green Tint U=0.345 Shading Coefficient = 0.69 (Determined in conjunction with original specifications)

The calculation results suggest that the existing system can support the additional cooling loads resulting from the additional equipment and people. It should be noted that this assumes both supply fans are running simultaneously, and each level may receive approximately 22,400 CFM. It should be noted that the velocity of the existing supply main ductwork located within the shaft is greater than recommended by ASHRAE. The velocity of this ductwork, assuming full peak flow, is approximately 4,000 feet per min-ute (FPM). Velocities greater than 3,500 FPM (in a shaft or above solid drywall ceiling) are not recom-mended and can lead to noise problems. Velocities at 3,500 FPM result in an noise criteria (NC) rating of 45 in the shaft. Typically offices are required to stay at an NC of 35 or less which would be velocities closer 2,500 FPM or less in shafts. The return air shaft free area appears to be sufficiently sized.

Additionally, assuming 22,400 CFM per level, the individual level distribution supply duct maintains this high velocity and also has a higher than recommended static pressure loss. Velocities in ductwork above acoustical ceilings are recommended to be at 1,750 or less to maintain a NC level of 35. Each level distribution main duct static pressure loss is 0.484” W.C. / 100 feet of duct. Standard practice is to keep this value at 0.25” W.C. / 100 feet of duct or less. Higher static pressure losses result in more fan energy usage.

In addition to the loads, the ventilation was reviewed. The coil schedules on the existing drawings were reverse engineered to come up with an approximate operational outside air value. From this, it is as-sumed the building is operating between 15-20% outside air. The calculations show 22,900 CFM (20.4%) of outside air is required to meet current code. This value does not take diversity into account which could lower the code required outside air value. The proposed redesign provides for additional people to occupy each level. This addition is anticipated to increase the required ventilation air by approximate-ly 3,000 CFM increasing the code required outside air to approximately 25,900 (23.2%). Review of the cooling and heating coils suggests there is sufficient existing capacity to support this increase in ventila-tion air.

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According to the approximate median service life spans of the internal components of an air handling units (AHU) as well as other system components serving this building according to the 2019 ASHRAE Handbook – HVAC Applications – Chapter 38 Owning and Operating Costs - Table 4 Comparison of Ser-vice Life Estimates are well beyond operational expectancy. It should also be noted that the building and its equipment are approximately 33 years old Below are three options based on a mix of construction cost and mechanical systems driven by the Energize Denver Ordinance Energy Use Intensity (EUI) target requirements which are discussed in the Sustainability section. Discussed below, in this section, are two mechanical system options to meet these requirements and one with minimal construction to achieve occupancy as soon as possible. All options will include design and operational requirements per ASHRAE Standard 241, Control of Infectious Aero-sols to reduce the risk of airborne disease transmission.

Option 1 offers the possibility to incorporate LEED® innovation credits and will have a higher probability of achieving the EUI target requirements along with relieving the CUP heating load building consumption almost entirely, cooling reduction will require further analysis of CUP operations and temperature data.

An additional possible subjective benefit of this option is that it could be an airport and City of Denver showcase project.

Option 2 is anticipated to have a lower installation / first cost but is not expected to generate as many LEED® Energy and Atmosphere or Innovation credits and meeting minimum EUI requirement requires additional envelope thermal resistance as discussed in the Architectural section of this report. However, specific energy modeling will be required to validate the entire building system.

Option 3 is based on minimum cost of renovation while providing enough modifications to accommodate the changes in the level plan. This option is not expected to meet either the final EUI target or receive enough credits to achieve LEED status. This approach will keep the building running for a time period until funding priorities can be utilized to revise enough of the systems to comply with City and County of Denver (CCD) and DEN DSM requirements.

Options 1 and 2 listed below are designed to reduce demand on the existing boiler plant or any proposed expansions of the CUP system. The options are projected to be more energy efficient than current CUP operations and will eliminate products of combustion from building usage. Options 1 and 2 are intended to be in common with the suggested new systems of AOB 2 so that maintenance activities, knowledge, and spare parts will have parallel application. Option 3 is intended to be the lowest cost to achieve occu-pancy.

iii. Tower 1 - Option 1

This proposed option will be composed of a system that makes use of new heat pump technology and takes advantage of energy exchange possibilities via the heat available in the chilled water system. This will require a near complete removal of the existing 1990s era HVAC systems and enhancement of the building envelope such as window inserts and added insulation to the spandrel sections as discussed in the Architectural portion of this report.

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F E A S I B I L I T Y S T U D Y

The first component for this option is a dedicated outdoor air system (DOAS) unit which will supply ventilation air (primary air) to four-pipe heating and cooling, active and passive chilled beam units distributed in zones for precise local temperature control. This DOAS unit will be located within the Penthouse. Individual IDF/IT rooms will be cooled with independent low profile fan-coil units (FCU) to comply with DSM IDF requirements. Dedicated data / communications spaces with large heating loads will be cooled with low profile FCUs depending on the final loads. Each chilled beam zone can be shut-off when unoccupied. A DOAS with zone dampers provides a simple way of separating zones when some are 24/7 and others are unoccupied. Outside air volume will be controlled by carbon dioxide and occupancy sensors. The systems will be specified so that turndown can be achieved efficiently for the project while having one floor occupied 24 hours a day, while other areas are unoccupied. This type of system can be changed within the BAS to modify operations to occupancy hours on a zone level.

The production of both heating and cooling will be from water source heat pumps and system inertia buffer tanks located on level 5 within added or existing mechanical space close to existing piping to be reused. An alternative space would be on the roof near the DOAS unit within the penthouse; however this would decrease construction efficiency and make major maintenance more difficult. The heat pumps will be a modular six-pipe water source system with a process water loop tied into and decoupled from the chilled water return and chilled water supply (a switch over will be designed and controlled to reject or sink heat depending on the process loop temperature). Utilizing multiple units in a modular configuration will provide a level of redundancy, continuous operation during routine maintenance and high efficiency turndown at low load conditions.