12 CAVE Engineering Site Visit Report B.pdf

Carlsbad Caverns National Park Visitor Center

Engineering Site Visit Report

Prepared by Southern Arizona Office National Park Service

August 2, 2019

Version B

Carlsbad Caverns National Park

Engineering Site Visit Report

Table of Contents Executive summary

1 Assumptions and limitations

2 Definitions

3 Introduction

4 Background

5 NIOSH engineering control recommendations

6 Discussion

6.1 Existing elevator lobbies at ground level

6.1.1 Introduction

6.1.2 NIOSH findings

6.1.3 Potential to add airlocks to ground level lobbies

6.1.4 Preliminary concept for airlocks at ground level lobbies

6.2 Existing elevator lobbies at cave level

6.2.1 Introduction

6.2.2 NIOSH findings

6.2.3 Potential to add airlocks to cave level lobbies

6.3 Airlocks at other cave parks

6.4 Heating, ventilation, and air-conditioning systems

6.4.1 Introduction

6.4.2 Outside air monitoring and control does not appear to comply with the original design

6.4.3 Existing HVAC systems have mechanical issues affecting performance

6.4.4 Existing DDC system has issues that are affecting performance

6.4.5 System peak cooling capacity concerns

6.4.6 NIOSH findings

6.4.7 Potential to modify or replace existing systems

6.5 Radon mitigation effectiveness and threshold requirements

7 Summary of key findings

8 Project options

8.1 Airlock Projects

8.1.1 Option A – Design and construct airlocks at cave level

8.1.2 Option B – Design and construct airlocks at ground level

8.2 HVAC Projects

8.2.1 Option A – Immediate action to improve OSA delivery and thermal comfort

8.2.2 Option B – Modify existing HVAC and DDC systems to improve OSA delivery

8.2.3 Option C – Design and replace central HVAC equipment and modify DDC

9 Recommendations

Version Description Date A Internal draft for review 7/25/19 B Issue to stakeholders 8/2/19

Carlsbad Caverns National Park [1]

CAVE Engineering Site Visit Report [B].docx SOAR - NPS

Executive summary The National Park Service (NPS) Southern Arizona Office (SOAR) conducted a site visit at the Carlsbad Cavern National Park (CAVE) from July 9 – 12, 2019. This site visit was conducted at the request of CAVE executives. The primary purposes of the site visit were to review existing building system conditions at the CAVE Visitor Center (VC) and review the potential implementation of several recommended engineering controls following a Radon assessment conducted by the National Institute for Occupational Safety and Health (NIOSH) Health Hazard Evaluation Program (HHE). The purposes of this report are to present significant findings from the site visit, project options for implementing NIOSH recommendations, and recommendations for consideration by CAVE executives.

NIOSH engineering recommendations relate to installing airlocks to minimize cavern air entering the VC and modifying Heating, Ventilation, and Air-conditioning (HVAC) and Direct Digital Control (DDC) systems to help remove cavern air if it does get into the VC.

The following key findings are noted following the site visit.

1. Adding airlocks to the ground level of the VC will significantly impact the existing building and visitor flow.

They will also add significantly complex HVAC systems to the building.

2. Adding airlocks to the cave level of the VC appears to be less impactful to the existing building and visitor flow compared to ground level. It also appears to reduce complexity of associated HVAC systems.

3. Regardless of how or where airlocks are installed, management will be required to ensure that the airlocks are being used effectively.

4. The existing HVAC and DDC systems do not appear to have been installed per original design. These systems also have existing issues that are affecting their performance. Implementing NIOSH recommendations regarding outside air (OSA) is problematic without modifying or replacing existing systems.

5. There is little understanding at this stage which NIOSH engineering control recommendations will be more effective than others in reducing measurable or modeled Radon doses within the VC. In addition, it is also not understood what specific thresholds will ultimately be required to be achieved within the VC. CAVE may consider implementing lower cost/lower impact controls first and assessing their effectiveness through continuous monitoring before implementing higher cost/higher impact controls.

The following project options are presented for CAVE consideration.

Airlock Projects

Option Description Order of magnitude cost Range of time to implement A Design and construct airlocks at cave level $500,000 - $750,000 12 to 24 months B Design and construct airlocks at ground level $1,000,000 - $1,500,000 12 to 24 months

HVAC Projects

A Immediate action to improve outside air delivery, thermal comfort, and operations $50,000 - $100,000 3 to 6 months

B Modify existing HVAC and control systems to improve outside air delivery $150,000 - $300,000 6 to 18 months

C Design and replace central HVAC equipment and modify controls $500,000 - $750,000 12 to 24 months

The following recommendations are presented for CAVE consideration.

1. Establish clear Radon mitigation goals / benchmarks.

2. Establish a robust continuous monitoring program in order to evaluate the impacts of engineering control implementation.

3. Immediately implement HVAC project Option A. Especially critical in this option is training designated

CAVE staff in the operation and maintenance of the DDC system. Evaluate effectiveness utilizing monitoring program.

4. Solicit a design contract for airlocks at the VC. Design could include both cave and ground levels.

Construction options and decisions should be finalized during design.

5. Implement HVAC project Option B in order to bring the existing system closer to original design, ensure correct operation, and allow full implementation of NIOSH outside air recommendations. Evaluate effectiveness utilizing monitoring program.

6. Plan for HVAC Option C as part of cyclical equipment replacement planning.

Carlsbad Caverns National Park [2]

1 Assumptions and limitations In forming the findings contained herein, the following qualifications apply. Actioning of items in this report should be made taking these limitations into account.

• All comments are made on the basis of our understanding of the existing Visitor Center (VC) building systems at the Carlsbad Caverns National Park (CAVE). A site visit was conducted from July 9-12, 2019 to review existing conditions. This site visit comprised visual review of building spaces, mechanical equipment, and Direct Digital Control (DDC) systems. No disassembly or testing of existing systems was conducted.

• Discussions were undertaken with CAVE staff and their assessments have been considered in preparing this report.

• The following additional documents were reviewed in preparing this report.

o Evaluation of Exposure to Radon and Radon Progeny in an Underground Tourist Cavern and Its

Connected Buildings – Health Hazard Evaluation Program (HHE) – Centers for Disease Control and Prevention (CDC) – National Institute for Occupational Safety and Health (NIOSH) – May 2019 o Cave Radon Assessment Management Report and Corrective Action Plan – National Park Service – May 2019 o Rehabilitate Visitor Center Carlsbad Caverns National Park – Design Documents – August 31, 2009 o Rehabilitate Visitor Center Carlsbad Caverns National Park – Design Report – June 30, 2006 o Rehabilitate Visitor Center Carlsbad Caverns National Park – Operation and Maintenance Manuals o Rehabilitate Visitor Center Carlsbad Cavern National Park – Various Construction Submittals o Service Reports – PC Automated Controls – Various Dates o York Technical Guide – Millennium Single Package Rooftop Units o York Technical Guide – V* Series Unitized Energy Recovery Ventilators

• In general, this report does not consider administrative controls recommended in the NIOSH report noted above.

• In general, the building heating system and associated control logic was not reviewed on site.

• Several NIOSH engineering control recommendations are discussed in this report. There is little understanding at this stage which recommendations will be more effective than others in reducing measurable or modeled Radon doses within the VC. In addition, it is also not understood at this time what specific thresholds will ultimately be required to be achieved within the VC.

• In general, assessments of Radon gas itself or statutory requirements related to Radon are outside the scope of this report and the Engineer’s area of practice.

• Existing maintenance records (except as noted), testing reports, etc were not reviewed nor are they considered in this report.

• Architectural, structural, environmental, hazardous materials, acoustic, and Occupational Hazard and Safety (OH&S) issues have not been addressed and are not considered in this report.

• Opinions of probable construction cost, where provided, are intended to provide rough magnitudes of cost only and would be subject to further project development.

• Opinions of time range required for project implementation are rough assessments only and would be subject to further project development.

• Some of the assessments provided in this report are based upon information made available to our office by others. This information has been taken in good faith for the purposes of the assessments made in this report.

Carlsbad Caverns National Park [3]

2 Definitions The following definitions are provided for terms commonly used in this report.

• American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE): The American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) is a professional society which publishes many technical standards referenced by building codes for design and operation of building systems. The National Park Service (NPS) utilizes several ASHRAE standards.

• British Thermal Unit (BTU) (BTUH) (MBH): A British Thermal Unit (BTU) is a common unit of heat. It is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. BTU per hour (BTUH) or thousands of BTUH (MBH) are common units of thermal power.

• Cubic Feet per Minute (CFM): Cubic feet per minute (CFM) is a common unit of airflow quantity.

• Electrical Horsepower (HP): Electrical Horsepower (HP) is a common unit of motor power and is equivalent to 746 Watts.

• Ton of Refrigeration (tons): A ton of refrigeration is a common unit of power used to describe heat-extraction of refrigeration and air conditioning equipment. One ton of refrigeration is equivalent to 12,000

BTUH.

Carlsbad Caverns National Park [4]

3 Introduction The National Park Service (NPS) Southern Arizona Office (SOAR) conducted a site visit at the Carlsbad Cavern National Park (CAVE) from July 9 – 12, 2019. This site visit was conducted at the request of CAVE executives. The primary purposes of the site visit were to review existing building system conditions at the CAVE Visitor Center (VC) and review the potential implementation of several recommended engineering controls following a Radon assessment conducted by the National Institute for Occupational Safety and Health (NIOSH) Health Hazard Evaluation Program

(HHE).

The purposes of this report are to present significant findings from the site visit, project options for implementing NIOSH recommendations, and recommendations for consideration by CAVE executives.

Important assumptions and limitations apply to the site visit conducted and this report. Refer to Section 1 for details.

4 Background The CAVE VC is a 39,600 square foot (sf) facility comprising exhibit, theater, retail, office, and support spaces. The facility includes two elevator shafts, approximately 755 ft in height, which connect the VC to tourist caverns below (cave).

At the request of the National Park Service (NPS), NISOSH conducted an investigation of Radon both within the caverns as well as in several buildings at CAVE, including the VC. NIOSH published its findings in a report, Evaluation of Exposure to Radon and Radon Progeny in an Underground Tourist Cavern and Its Connected Buildings in May 2019. This report includes several engineering and administrative control recommendations to help mitigate Radon exposure for visitors and staff at CAVE.

In response to the NIOSH report, NPS developed a Corrective Action Plan (CAP). The CAP includes critical findings from the NIOSH report and planned NPS action in response to these findings. One action states, “deploy in house [Mechanical Engineer] for site visit, create a PMIS and contract for a mechanical engineering firm to propose concept designs for capital improvements recommended by NIOSH including airlock improvements.” In response to this action, the SOAR office was requested to deploy its staff Mechanical Engineer to assist CAVE.

5 NIOSH engineering control recommendations The NIOSH report includes several engineering and administrative control recommendations to mitigate Radon in the CAVE VC. Engineering controls generally involve the construction of airlocks and modifications to existing Heating, Ventilation, and Air-conditioning (HVAC) systems. Engineering control recommendations are summarized below.1

Airlocks

1. Install double airlocks at the VC elevator entrances and exits [at ground level]2

2. Install dedicated ventilation system to serve space between airlocks. Balance to have neutral air pressure with respect to elevator side of airlocks. Provide a minimum of 20 air changes per hour (ACH) for the space between the airlocks. Coordinate system exhaust location to prevent re-introduction into the building.

3. Control humidity in the space between airlocks to match the cave environment.

4. Do not serve elevator side of airlocks from the VC HVAC systems

Door Seals

1. Isolate elevator machine room from the VC using closed doors with weather seals and gaskets

HVAC systems

1. Evaluate existing system capacity to provide additional outside air (OSA)

1 Refer to report for additional narrative and details.

2 The report does not state explicitly that airlocks be provided at ground level, but from the narrative it is implied.

Carlsbad Caverns National Park [5]

2. Install ducted returns instead of using existing plenum return

3. Improve maintenance and calibration of control systems

Other

1. Install solar shading on VC west side, consider integrating a photovoltaic (PV) system

The NIOSH report also includes several interim recommendations for implementation until capital improvements can be made to the VC HVAC system. These recommendations are summarized below.

Interim measures

1. Implement preventative maintenance on existing airlock gaskets and brushes at the bottom of the elevator shaft.

2. During VC operating hours, increase OSA as much as possible while maintaining thermal comfort

3. Overnight, when temperatures are between 40°F and 77°F, HVAC systems should be operated for at least four hours prior to opening with OSA dampers fully open.

4. As much as feasible, operate the HVAC system in accordance with ASHRAE 62.1-2016 Ventilation for

Acceptable Indoor Air Quality

6 Discussion

6.1 Existing elevator lobbies at ground level

6.1.1 Introduction

Figure 1 illustrates the layout of existing elevator lobbies at the ground level of the VC. The central elevator lobby serves the front doors of all elevators (#1 through #4). There are two additional lobbies that serve the rear doors of each elevator group.

Elevators #3 and #4 are the primary elevators for visitor access. They are the largest elevators and were recently renovated. Elevators #1 and #2 are smaller and are used primarily for service access when #3 and #4 are operational and the number of visitors to the cave is not too high. Elevators #1 and #2 are scheduled for renovation as part of a large capital improvement project.

During the site visit, visitor flow generally comprised the following:

• Doors to the central lobby were open. Entrance into the central lobby was controlled with a retractable stanchion.

• Visitors were let into the central lobby by CAVE staff in groups. CAVE staff briefed visitors in in the central lobby. Visitors entered elevators #3 and #4 through their front doors.

• Visitors returning from the cave departed elevators #3 and #4 from their rear doors and entered the #3/#4 rear lobby. This lobby is open to the VC book store.

CAVE staff indicate elevator operation and visitor flow in and out of the cave can change depending on elevator outages or visitor population.

Figure 1 – Existing elevator lobbies at cave level. Existing elevator lobbies are located at front and rear doors of each elevator group.

Carlsbad Caverns National Park [6]

6.1.2 NIOSH findings

The NIOSH report recommended installing airlocks at VC elevator entrances and exits at ground level.

The NIOSH report details tracer gas tests that were conducted to determine whether Radon gas was entering the VC via the “main” elevator shaft (elevators #3/#4) or a crawl space beneath the building. Their finding was that the primary pathway for Radon was from the main shaft into the VC. It is speculated that this finding was the primary reason that airlocks were recommended at ground level.

6.1.3 Potential to add airlocks to ground level lobbies

The NIOSH report provides several general design recommendations for airlocks at ground level elevator lobbies.

However, the report does not include any details on how these recommendations could actually be implemented. Based on review of the site and discussions with CAVE staff, installing airlocks at ground level would likely have significant impacts to the existing building as well as existing operations. The following key findings are noted.

1. Adding airlocks inside of existing elevator lobbies at ground level will have significant spatial and visitor flow impacts

CAVE staff indicate that visitor flow patterns are flexible in order to accommodate elevator outages and visitor population. However, the central lobby is generally used for visitor loading. It’s also used to brief visitors prior to entering the cave. Adding airlocks within the central lobby will have a significant impact on available lobby floor area and visitor flow. This would be especially critical at peak visitor periods when all four elevators are in operation. In addition, this space has both an entrance from the main VC lobby and an entrance to a first aid room. Integrating an airlock with both of these doors would likely not be feasible without significant complexity and impact to existing lobby floor area.

Adding airlocks within the #3/#4 rear lobby would significantly impact to lobby floor area and visitor flow. In addition, this space has two exits (book store and lobby). Maintaining both exits would likely not be feasible without significant complexity and impact to existing lobby floor area.

Adding airlocks within the #1/#2 rear lobby would significantly impact lobby floor area and visitor flow. Although, based on discussions with CAVE staff, the peak population that could use this lobby would be significantly less than the other lobbies because it is only served by smaller elevators #1 and #2. Regardless, like other lobbies, this space has two entrance/exits (back of house corridor and VC main lobby). Integrating an airlock with both of these doors would also likely not be feasible without significant complexity and impact to existing lobby floor area.

2. Adding airlocks outside of existing elevator lobbies at ground level will have significant spatial and visitor flow impacts

Existing ground level elevator lobbies are generally located between the main VC lobby and back of house spaces.

Implementing airlocks outside of the lobbies would therefore likely require expansion of elevator lobby spaces out into the VC main lobby. This expansion would significantly impact the main lobby area. It would also significantly impact visitor flow both in and out of elevator lobbies. Visitor flow management, inclusive of briefing, would need to be re-designed.

3. Adding airlocks at ground level will have significant architectural impacts

Effective airlocks will require sealed barriers with an intermediary space. In order to seal these barriers, airlock partitions will need to either be continuous to the underside of the building roof deck, or they will need to be continuous with an enclosed ceiling element. Both approaches will likely have a significant impact on existing building architecture including ceilings, HVAC, Electrical, Life Safety, and Fire Protection. This impact could be further complicated if multiple entrances/exits are integrated.

Carlsbad Caverns National Park [7]

4. Implementing NIOSH HVAC recommendations for airlocks will add significant operation and maintenance complexity

The NIOSH report recommends that intermediary spaces between airlocks have dedicated exhaust systems that are “balanced to establish neutral air pressure with respect to the elevator side of the airlocks.” This recommendation would require actively controlled fan systems and associated sensors, control points, logic, etc. As discussed in greater detail in Section 6 of this report, CAVE has experienced difficulties with operation and maintenance of the existing building HVAC Direct Digital Control (DDC) system.

The NIOSH report recommends that “humidity should be controlled to match the cave environment” in intermediary spaces between airlocks. Active humidity control would require humidifiers and water sources that meet humidifier manufacturer requirements. Water sources may need to be treated to meet these requirements. These are all systems that CAVE does not currently have or operate. As discussed in greater detail in Section 6 of this report, CAVE has experienced difficulties with the operation and maintenance of existing building HVAC systems.

The two NIOSH report recommendations noted above are further complicated by the potential for at least three, if not more, airlocks being required at the ground level.

5. Effective airlock strategies will require both engineering and management

Ultimately, the effectiveness of any airlock system installed in the VC will not rely on engineering alone. Airlocks will only be as effective if they are used correctly. Ensuring that the airlocks are used correctly by visitors may require additional CAVE management controls or oversight.

6.1.4 Preliminary concept for airlocks at ground level lobbies

Implementing effective airlocks at ground level elevator lobbies in the VC would require significant building modifications. It would also require a collaborative design process in order to minimize expense, complexity, impact to the existing building, and impact to visitor flow management.

Despite this requirement, discussions were held with CAVE staff to develop a preliminary concept for implementing airlocks. As illustrated in Figure 2, the preliminary concept comprises the following.

• Construct airlocks for central and #1/#2 rear lobbies in the VC main lobby

• Add seals to first aid room and back of house corridor doors. Discussions with CAVE staff indicate these doors are used by staff only and generally infrequently.

• Construct airlock for #3/#4 rear lobby at bookstore interface. Discussions with CAVE staff indicate that a pathway from this lobby to the bookstore should be maintained.

• Delete door between #3/#4 rear lobby and VC main lobby (subject to code compliance)

• Install HVAC systems for each airlock

• Potentially implement best practices from industrial, clean room, or other applications where airlocks are more commonplace. This may include automatic controls to help ensure airlocks are used effectively.

Figure 2 – Preliminary concept of airlocks at ground level. A preliminary concept for airlocks at ground level would require significant building modifications.

Carlsbad Caverns National Park [8]

The feasibility of this preliminary concept would be subject to further project development.

6.2 Existing elevator lobbies at cave level

6.2.1 Introduction

Figure 3 illustrates the layout of existing elevator lobbies at the cave level. The central elevator lobby serves the front doors of all elevators (#1 through #4). There are two additional lobbies that serve the rear doors of each elevator.

Each of the elevator lobbies has doors separating them from the cave environment. The central and #3/#4 rear lobbies have revolving doors as illustrated in Figure 4. The #1/#2 rear lobby has glazed storefront doors in a vestibule configuration.

6.2.2 NIOSH findings

The NIOSH report only provides a single recommendation regarding elevator lobbies at the cave level, specifically that a preventative maintenance program be implemented for existing revolving door gaskets and brushes as an interim measure.

The NIOSH report doesn’t provide any direct discussion about the effectiveness of existing doors at the cave level elevator lobbies. NIOSH tracer gas was released inside the main shaft (bypassing existing lobby doors) and was then measured inside the building. Although not discussed explicitly in the report, there appears to be an implicit assumption that motive forces that moved the tracer gas from inside the shaft to inside the VC were generated by pressure differences created due to the ineffectiveness of the existing cave level lobby doors. In other words, it appears that the NIOSH position is that their tests show that the existing doors are ineffective.3

The existing central elevator lobby serves a place for visitors to either board or discharge from any of the existing elevators. At the time of the site visit, this lobby was used for visitors to gather prior to leaving the cave. CAVE staff indicate that this is a typical visitor flow approach, but always subject to change depending on outages and visitor volume.

Regardless, discussions with CAVE staff indicate that high winds have been witnessed bypassing the existing revolving doors and there is a shared opinion that they are generally ineffective as airlocks. Figure 5 illustrates the condition of brushes at the top an existing door. Gaps were witnessed for many of the doors.

6.2.3 Potential to add airlocks to cave level lobbies

The NIOSH report does not include a recommendation to modify existing cave level elevator lobby doors or add additional airlocks at this level. However, following discussions with CAVE staff, as well as reviewing the existing VC, 3 NISOH did not test the secondary elevator shaft (elevators #1/#2), and there is no evaluation/data available for the existing airlock at the #1/#2 rear lobby at this time.

Figure 3 – Existing elevator lobbies at cave level.

Existing elevator lobbies at the cave level incorporate revolving doors and vestibules.

Figure 4 – Existing revolving doors. There are existing revolving doors between elevator lobbies and the cave.

Carlsbad Caverns National Park [9] adding airlocks at the cave level appears to be feasible and potentially much less impactful than adding airlocks at the ground level. The following key findings are noted.

1. Adding airlocks inside of existing elevator lobbies at cave level is problematic

Installation of airlocks within existing lobby footprints would likely have a significant impact on available lobby floor area and therefore have a direct impact on visitor flow. In addition, CAVE Resources staff indicate that the existing central lobby may have historical challenges to any significant interior renovations. These challenges make adding airlocks within existing lobby footprints problematic.

2. There is more flexibility to expand into the cave

Despite challenges to adding airlocks within existing lobby footprints, there appears to be a lot more flexibility to adding airlocks outside of the lobbies and into the cave itself. First, there is additional open space outside of existing lobbies.

Second, as illustrated in Figure 6, there is precedent for constructed elements in these areas such as railings, information stands, restroom, and retail and food service areas. Finally, CAVE resources staff indicate that both historical and natural resource issues are likely more manageable for construction outside of the existing lobbies than within them.

3. Airlocks at cave level add an engineering control point before the shaft

The NIOSH report indicates that the primary pathway for cave air to enter the VC is from the main elevator shaft.

Adding airlocks at cave level would add an engineering control point before the shaft. Discussions with CAVE staff indicate that this approach would be preferred to having an engineering control point after the shaft.

4. Designs can be selected that minimize impact to visitor flow

Constructing airlocks outside of existing lobbies would minimize impact to existing lobby space and visitor capacity. In addition, the availability of open space outside of the lobbies would allow flexibility for airlock designs that minimize impacts to visitor flow in and out of airlocks.

5. HVAC design for airlocks could be simplified

The NIOSH report provides several HVAC design recommendations for airlocks at ground level, including comfort conditioning, humidity control, pressure control, and exhaust design. Several of the recommended approaches would not be required for airlocks at cave level, or they could be simplified.

6. Effective airlock strategies will require both engineering and management

Although providing airlocks at the cave level offer a number of advantages, ultimately their effectiveness will not rely on engineering alone. Airlocks will only be effective if they are used correctly. Ensuring that the airlocks are used correctly by visitors may require additional CAVE management controls or oversight.

Figure 5 – Existing revolving door brushes. Existing revolving door brushes have inconsistent gaps.

Figure 6 – Existing constructed elements in the cave.

There are a number of existing constructed elements within the cave.

Carlsbad Caverns National Park [10]

6.3 Airlocks at other cave parks

Brief discussions were conducted with facility management staff at Jewell Cave National Monument (Jewell), Mammoth Cave National Park (Mammoth), and Wind Cave National Park (Wind). Each of these sites have tourist caverns. Access to the caverns are typically by elevator or a natural entrance. “Airlocks” between tourist caverns and buildings or the exterior vary throughout the parks, ranging from single manual doors to double doors with a vestibule.

Jewell does have elevator access to its tourist caverns from a visitor center. The single shaft is approximately 330ft in height. As illustrated in Figure 7, the elevators have separate doors immediately in front of the elevator entrance doors. The effectiveness of this approach in mitigating cave air from entering the visitor center is not known to us at this time. This approach was not described in the NIOSH recommendations.

Mammoth and Wind have elevators for access to their tourist caverns. But these elevators are located in separate elevator buildings. These buildings incorporate “airlocks” typically comprising single or double doors with vestibules.

Airlocks at all three parks are manual only, with no active airlock control systems or dedicated HVAC systems.

Of note from discussions with facility management staff was the issue of white-nose syndrome for cave bats. At least one of the parks has implemented visitor washing stations in response to the issue. It is unknown to us whether such washing stations would need to be considered at CAVE or in the design of airlock systems there.

6.4 Heating, ventilation, and air-conditioning systems

6.4.1 Introduction

Existing VC HVAC systems were installed as part of a large scale rehabilitation project circa 2009 (PMIS 023336).

As illustrated in Figure 8, existing VC HVAC systems are variable air volume (VAV) systems generally comprising the following.

• Packaged VAV rooftop units (RTU) with direct expansion (DX) cooling (scroll type compressors).

Note that RTU have no heating section.

• VAV terminal units (VAV boxes) with hydronic re-heat coils.

• Fuel oil fired heating hot water boilers and associated pumps.

• Direct Digital Control (DDC) system

Figure 7 – Jewell cave doors at elevator entrances. Jewell cave elevators have doors directly in front of elevator entrances.

Figure 8 – Existing VC HVAC systems. The existing VC HVAC systems comprise VAV equipment and a DDC system.

Carlsbad Caverns National Park [11]

The RTU are located at roof level. They provide supply air (SA) to the building. SA is mixture of Return Air (RA) from the building and Outside Air (OSA) for ventilation.

SA is delivered at a quantity and temperature as determined by the HVAC DDC system to meet the building comfort conditioning needs. The RTU have refrigerant, or DX, coils to lower SA temperature. But they do not have heating sections. Heating is primarily accomplished downstream of the RTU at VAV boxes.

Each zone has a VAV box that uses the zone’s thermostat to determine what is needed for comfort conditioning.

The VAV boxes vary the quantity of SA to each zone as needed for cooling. When heating is required, VAV boxes vary both quantity of SA as well as its temperature through the use a re-heat coil. Re-heat coils are provided heating hot water from the building’s boilers. As zone requirements change throughout the day and season, correct delivery of SA quantity and temperature to each zone is controlled by the DDC system. The DDC system utilizes sensors to measure parameters in the system, control elements such as valves or airflow dampers to affect these parameters, and logical sequences to determine how and when a parameter should be affected.

As noted, the SA from the RTU is a mixture of RA and OSA. OSA is introduced into the building to provide adequate ventilation. OSA, while needed for ventilation, is often much warmer or much cooler than RA from the building. Processing this temperature difference requires energy from the RTU. To reduce this energy, the CAVE VC HVAC systems incorporate Energy Recovery Ventilators (ERV) at each RTU. As illustrated in Figure 9, ERV utilize heat exchangers, known as heat wheels, to transfer energy from RA leaving the RTU and OSA entering the RTU. This energy exchange includes both sensible thermal energy (change in temperature) and latent thermal energy (change in absolute humidity). The net effect is that the energy required to process OSA at the RTU is reduced through the use of ERV.

While the ERV are designed to reduce the energy required to process OSA, existing RTU also include airflow dampers that allow the ERV to be bypassed as part of an air side economizer. As illustrated in Figure 10, OSA can be used directly to meet the cooling needs of the building (either totally or in part) when conditions are favorable. When the economizer is enabled, the ERV are bypassed and OSA enters the RTU directly.

The VC DDC incorporates graphic based software. This software is hosted on a standalone computer located in a maintenance office. The software has a Graphical User Interface that can be used to troubleshoot HVAC systems, modify system set points, create and review data trends, or review existing control logic.

Figure 9 – Energy recovery ventilators. Existing energy ventilators exchange energy between OSA and RA in order to reduce the energy required to process OSA.

Figure 10 – Air side economizer. An air side economizer uses OSA to meet some or all of the cooling load when outdoor conditions are favorable. When enabled, ERV are bypassed.

Figure 11 – Existing DDC logic. The VC DDC system has graphic based logic.

Users can use these graphics to review and operate the DDC system.

Carlsbad Caverns National Park [12]

As a graphic based system, logic sequences are displayed schematically. Users can interact with these sequences and adjust input or output variables. Figure 11 illustrates graphic based logic for the DDC system.

Table 1 provides a summary of existing key equipment and systems at the CAVE VC.

Table 1 – Existing RTU and ERV equipment at CAVE

Equipment Make Model Serves Nominal Capacity RTU-1 York Z23AC04N6KB2BL VC – West 30 tons RTU-2 York Z23AC04N6KB2BL VC – East 30 tons ERV-1 York VR122A40V4AL21 RTU-1 8,000 – 13,000 CFM ERV-2 York VR122A40V4AL21 RTU-2 8,000 – 13,000 CFM DDC Automated Logic WebCTRL

6.4.2 Outside air monitoring and control does not appear to comply with the original design

Based on a review of existing HVAC systems on site and design documents for the VC rehabilitation project, there are several critical areas where existing systems do not appear to comply with the original design. In the context of the NIOSH report, these differences have a significant impact on OSA quantity and management capabilities of the existing systems.

Available construction submittals from the rehabilitation project were reviewed for mechanical and DDC systems. The DDC systems were submitted at least twice during construction.

Comments from the reviewing consulting engineer requested components and control sequences as described in the design documents.

The controls contractor, PC Automated Logic, addressed some of these comments in the submittals reviewed. However, many of the components and sequences noted in the submittal drawings were not actually installed.4

1. There is no way to tell how much OSA is being delivered to the VC.

The original design included HVAC components and control sequences to continuously monitor OSA being delivered to each RTU and make necessary adjustments based on RTU operation or building occupancy. However, several of these components and control sequences were not actually installed. Figure 12 includes two cross sections of VC RTU. The cross section on the top illustrates exiting RTU configurations on site. OSA is delivered through the ERV.5 RA comes from the building and is either exhausted through the heat wheel or mixed with OSA in a plenum to create Mixed Air (MA). MA then goes through a pre and final filter and the DX cooling coil. From here, MA becomes SA (now filtered and conditioned).

It then enters the fan section of the unit and is supplied to the building.

4 It is not understood whether other decisions were made during construction that would have superseded the submittals. It is also not understood whether there is any actual re-course available for installation not complying with construction submittals.

5 When the economizer is not enabled.

Figure 12 – Existing VC RTU vs design. The top image illustrates the existing VC RTU configuration. The bottom image illustrates the original design intent for the VC RTU. This design included components and logic to monitor and control the amount of OSA being delivered to the VC.

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The problem with the existing RTU configuration is that there are no measurement or control components in the OSA airstream. In other words, there is no real way to measure the quantity of OSA being delivered or change this quantity based on RTU operation. The existing RA dampers are manual and are in the fully open position. As air will travel the path of least resistance, the quantity of OSA delivered to the unit will be a function of the differences in static pressure of the return air path (from the ceiling plenum) and the OSA path (through the heat wheel).

The ERV have variable speed exhaust fans, which are currently controlled to operate at 80% of the SA fan speeds for building pressure relief. A general assumption could be made that the quantity of OSA provided to the RTU would be equal the quantity of exhaust air; but with a fully open RA damper, no OSA damper, and each fan having its own operational fan curve, it is speculated that the fan interaction here is more complex. Regardless, with the current configuration there is no way to measure the actual OSA being delivered or actively control the quantity.

The bottom cross section of Figure 12 illustrates the original design intent for the RTU. This intent included automated RA and OSA dampers to control each of these air pathways as well as an airflow monitoring station to measure the actual quantity of OSA being delivered. The original design intent was that the RA damper would operate inversely with the SA damper; meaning, if the SA damper was fully open, the RA damper would be closed. In addition, the ERV exhaust fans would operate to maintain positive pressure in the building based on measuring building pressure relative to outside.6 The key differences here are that the original design intent included components to actively measure and control the OSA pathway.

2. The existing system does not actively control OSA

The existing RTU are VAV systems. This means that the quantity of SA delivered to the building will vary to meet building comfort conditions. The comfort conditions required actually vary by zone, with each VAV box also varying airflow to meet the requirements at the zone level. Per ASHRAE standard 62.1-2016, this type of system is referred to as a “Multiple-Zone Recirculating System.” To comply with the standard, the minimum amount of OSA required at the RTU will be a function of both the zones themselves (area and occupancy) and the amount of air being provided to the zones by the VAV boxes (referred to as “primary air”). In short, the minimum OSA required at the RTU changes depending on what is happening in the system.

The original design monitored zone occupancy, which was either fixed or estimated using carbon dioxide sensors. It also monitored the primary airflow delivered to each zone. Using this data, the design specified that the DDC calculate OSA requirements in accordance with ASHRAE 62.17 and adjust dampers to meet these requirements at the RTU.

The current system has no control logic to monitor zones or update minimum OSA requirements at the RTU. Some zones do have carbon dioxide sensors. However, these sensors are used essentially as high limits for VAV airflow. In other words, VAV either provide airflow based on zone temperature or “more” airflow if the carbon dioxide levels are above a set-point.

6.4.3 Existing HVAC systems have mechanical issues affecting performance

CAVE has recently engaged a company from El Paso, PC Automated Logic8, to provide maintenance on existing RTU equipment. Immediately prior to the site visit, it is our understanding that PC Automated Logic replaced a condenser fan motor on RTU-2. A review of service reports for the last 12 months also indicate that repairs were made to compressors 1, 2 , and 4 on RTU-1 last year. Despite recent repairs, several key mechanical issues were noted during the site visit, including the following.

6 Equipment and control logic to achieve this does not appear to have been installed.

7 2004 version at the time.

8 Note that this is the same contractor that originally installed the DDC system.

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RTU – 1

• There is a note dated 6/18/18 in the DDC system stating there is a problem with the DDC controller. The DDC technician lowered discharge air temperature set-point to 50°F as a work around to ensure that all unit compressor stages were being used. It is unclear whether this issue has been resolved.

• The heat wheel is not functioning. The DDC is providing an enabling signal, but the wheel itself is not functioning. This reduces the effectiveness of the ERV and adds load on the RTU.

• Economizer dampers are taped shut as illustrated in Figure 13.

This prevents the unit from being able to use its air side economizer.

RTU-2

• The SA smoke detector is locked “off” in the DDC. This means that it is essentially bypassed. This issue has life safety implications.

• This unit is operating at approximately 50% cooling capacity with only two of four compressor / refrigeration circuits functional.

o There is a note dated 8/8/17 in the DDC system stating there is a problem with compressor 3. The DDC technician locked out this compressor as a work around. It is unclear whether this issue has been resolved.

o Compressor 4 is failed with a low pressure alarm in the DDC

• The heat wheel is not functioning. The DDC is providing an enabling signal, but the wheel itself is not functioning. This reduces the effectiveness of the ERV and adds load on the RTU.

• The ERV exhaust fans are not functioning. The DDC is providing an enabling signal but the fans themselves are not functioning. This can have an adverse impact on building pressurization.

Exhaust Fan (EF)-2

• Fan is not functioning. The DDC is providing an enabling signal, but the fan is not functioning. This will impact restroom and kennel exhaust.

6.4.4 Existing DDC system has issues that are affecting performance

In general, CAVE staff are not familiar with the existing DDC system; nor do they regularly access the system other than to occasionally change zone temperature set-points. CAVE staff indicate they have not been trained on how to use the system. This unfamiliarity can have a significant impact on the operation of the VC HVAC systems. The existing DDC system was reviewed during the site visit. The following key findings are noted in addition to those discussed previously.

1. There appear to be errors in the system that are affecting performance

• Errors in flow control settings for VAV boxes. For example, cooling maximum airflow for VAV-1 was set at

200 CFM. Original design was 2,500 CFM. This error was preventing the VAV box from opening. Corrected on site.

• Heating request polling for RTU-2 appears to be missing. This will affect heating performance.

Figure 13 – RTU-1 economizer dampers. RTU-1 economizer dampers are currently taped shut. This prevents the unit from using its air side economizer.

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• Airflow request polling appears to be missing. Zone airflow calculation does not work. Despite these errors, this information is not used in the logic. Refer to discussion on original OSA control design.

• Several control inputs from equipment are misconfigured, including several from Variable Frequency Drive

(VFD).

2. Several original design sequences are missing

• This is no optimal start / morning warm-up logic. This can lead to comfort issues at the beginning of occupancy.

• There is no night cooling logic. This can lead to comfort issues at the beginning of occupancy.

• There is no static pressure set point re-set logic. This can lead to higher fan energy and/or comfort issues.

3. Temperature set points are beyond design and affect performance

• CAVE staff edits to occupied zone temperature cooling set points are well beyond design. Most set points were found to be between 60°F and 62°F while on site at outdoor air temperatures over 100°F. This essentially creates false load in the system, creates false alarms, and drives all variable components to 100% for most of the day. This causes excessive energy use. It can also starve zones that are further down the SA ductwork.

• Unoccupied zone temperature set points were generally inconsistent and should be rationalized.

• Set-point dead bands, differences between cooling and heating set points, were found to be generally too narrow. Dead bands as low as 2°F are currently in the system. Dead bands of at least 5°F are recommended for system stability.

4. There are errors in the graphics

• Several key equipment and systems were found to be in alarm. However, alarm statuses were generally not visible in the graphics

• Elements, such as carbon dioxide sensors, are missing from the graphics for several zones.

6.4.5 System peak cooling capacity concerns

Discussions with CAVE staff indicate a concern with the existing HVAC system cooling capacity. Developing HVAC load estimates for the VC is outside the scope of this report. However, some limited design data was available for review. Table 2 summarizes cooling load capacities for the VC system from several sources.

The first source is a design report that appears to have been developed for the VC rehabilitation project. This report provided design tonnage for cooling for the VC by hour and month. It is assumed that this data is meant to show total tons (sensible and latent). Sensible capacity is the ability to change the dry-bulb temperature of the SA. Latent capacity is the ability to remove moisture from the SA. This source showed a peak capacity requirement estimate of 54.1 tons.

The second source is from the design drawings for the VC rehabilitation project. The drawings contain an equipment schedule which showed a total sensible capacity requirement of 51.5 tons. This schedule showed an equivalent total capacity requirement, which appears to be a typo.

The final source is from the York Millennium technical guide capacity tables. This is the series of equipment that was actually installed at the VC. Outdoor and indoor conditions were assumed as shown in Table 2 and data was interpolated from the technical guide capacity tables. These tables showed an available total and sensible capacity of

63.1 and 48.0 tons respectively.

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Table 2 – VC HVAC cooling capacity design vs installed

Source Total

Capacity (Tons)

Sensible Capacity

(Tons)

OSA Dry-bulb Temperature

(F)

OSA Wet-bulb Temperature

(F) Notes

Design Report

54.1 ? 96.3 68.7 Assumed as total load estimate; July 5pm

Design Schedule

51.5 51.5 100 ?

Not typical that total and sensible are equal Installed

Equipment

63.1 48.0 100 67

Per York technical guide capacity tables using 12,000 CFM and 80F RA Temp

Based on a review of the sources noted, there appears to be a minor capacity shortfall when comparing estimated installed capacity against the original design report and schedule. An important note is that the original design schedule assumed that the majority of OSA load was met by the ERV. If ERV are not functioning correctly, then this load must be met by the RTU. At peak conditions, RTU may not have sufficient capacity to handle both building and OSA load.9

A rough take-off of the rehabilitation project documents shows that the VC has approximately 29,000 sf of conditioned space. The design report estimated a peak capacity requirement of 54.1 tons, this equates to roughly 525 sf per ton, which is higher than would be expected for a building of this type.

In addition, both the…