The built environment has a vast impact on the natural environment, human health, and the economy. As the environmental impact of buildings becomes more apparent, a new field called "green building" is gaining momentum. Green building (also known as sustainable or high performance building) is the practice of creating structures and using processes that are environmentally responsible and resource-efficient throughout a building's life-cycle from siting to design, construction, operation, maintenance, renovation and deconstruction. This practice expands and complements the classical building design concerns of economy, utility, durability, and comfort. Green building is also known as a sustainable or high performance building. (EPA, 2014)
Green buildings are designed to reduce the overall impact of the built environment on human health and the natural environment by:
Efficiently using energy, water, and other resources
Protecting occupant health and improving employee productivity
Reducing waste, pollution and environmental degradation
For example, green buildings may incorporate sustainable materials in their construction (e.g., reused, recycled-content, or made from renewable resources); create healthy indoor environments with minimal pollutants (e.g., reduced product emissions); and/or feature landscaping that reduces water usage (e.g., by using native plants that survive without extra watering). (EPA, 2014)
Recently and across the high performing buildings industry, a serious question have been raised about how “high performance” buildings are performing when they’re actually operating. (Hinge and Winston, 2009); (Bray and Natasha 2006) The good news is that most of this nonsense can be easily remedied. The bad news is that the failures are beginning to bubble to the surface, and we are in danger of ruining the “green brand.” (Lstiburek J.W., 2008)
Case Study- First Year Performance Evaluation of Building 661 Retrofit Project
The following sections report on the actual conditions and processes encountered so far in the occupancy and commissioning of Building 661. It is a rare occasion in the building industry to forensically examine a project, solicit feedback from those involved in building construction projects, and deliver the results back to the industry which makes it a value to the industry. All the information are collected from the interim reports of Consortium for Building Energy Innovation (CBEI).
Figure 1: Building 661, Philadelphia, PA
History
Building 661- Penn State Center for Building Energy Science and Engineering- was built in 1942 for the Navy as a recreation facility – there used to be a pool, a basketball court, and a bowling alley in this building. The building sat vacant and unused from 2005 until CBEI decided to retrofit this building in 2013 for their new headquarter rather than demolishing and rebuilding. This site is a great example of beneficial reuse. This deep retrofit involved some demolition, but much of the original building structure was preserved, keeping this material out of the landfill. The reuse also meant preserving the historical character of the building. The Navy Yard and the Philadelphia region is home to many of these historic brick buildings. That means that the lessons learned at this site can be transferred throughout the region. The building layout and renovation was guided by the intended use of the building- a collaborative work environment for a Department of Energy (DOE) funded program designed to overcome market barriers to routinely implementing energy efficiency in buildings. The design team decided to only use market-
Building 661 is aiming to gain LEED Gold credit with 63 points. Below comes the list of attempted points for this project.
Sustainable Site --------------------- 13 of 26
Water Efficiency --------------------- 6 of 10
Energy & Atmosphere -------------- 24 of 35
Materials & Resources ------------- 7 of 14
Indoor Environmental Quality --- 12 of 15
Innovation in Design ---------------- 6 of 6
Regional Priority ---------------------- 2 of 4
Heating, Ventilation, Air Conditioning (HVAC)
-Passive and active chilled beams -Under floor air delivery with displacement diffusers -Variable refrigerant volume system -Dedicated outdoor air unit with exhaust air energy recovery (enthalpy wheels) -Demand controlled ventilation -High efficiency condensing hot water boiler -Heat recovery chiller providing regenerative heating and reheat during cooling season
LIGHTING
-Automatic lighting controls in all non-utility spaces -Vacancy / occupancy control in enclosed spaces -Time of day controls in common areas -LED lighting
ENVELOPE
- Optimal levels of spray foam insulation added to walls (R-value 20) and roof (R-value 30) to reduce heat loss -New double glazed low-emissivity argon-filled units with thermally broken frames to replace existing windows, with higher performance glazing on the south facing windows and skylights
Building Condition
Since occupancy in November 2014, the building envelope continues to have air and vapor gaps at the doors (from a lack of weather-stripping) and where the arched laminated beams meet the exterior walls in the atrium ‘high-bay’ space. These envelope issues currently cause higher than anticipated sensible and latent loads on the building HVAC system serving that zone. The exterior of the top plate and window headers on the north wall above the high bay windows was left unwrapped and unfinished by a subcontractor, and provides another source of uncontrolled air and water infiltration. These punch list items were identified in Winter 2014/2015, but remain unresolved while contract issues are still being addressed. Inside, the north side of the high-bay space remains unfinished and unoccupied. Perimeter radiant heating was completed and is functioning, but no active chilled beams were installed. Mid-way through summer 2015, the facility maintenance contractor installed two temporary supply grilles in the space, which are delivering dehumidified air from the DOAS into the space. This partially conditioned space poses thermal and humidity gradients across the glass wall separating the high bay common area from the north space that were not anticipated when the design load was prepared.
Building Energy Analysis Conducted to Date
The work performed on this project has uncovered important findings that broadly impact the design and delivery of energy retrofits. Below is a brief description of the technical issues, identified and addressed through mid-September 2015, which explore the performance of the building ‘as delivered’.
Measurement and Verification Hardware, Software and Commissioning
Performance measurement and verification planning is a rapidly growing field largely stimulated by state and utility resource planning as a means to measure performance to justify incentive payments or regulatory compliance. USGBC, ASHRAE, ICC and other organizations and code officials are using M&V to deliver high performance buildings. Building 661 was instrumented to understand the performance of the whole building, the performance of the three discrete and different HVAC systems approaches, and, in some cases, equipment level performance. The additional M&V data points were specified as a do-no-harm overlay to be connected through the Building Automation System (BAS). The Johnson Controls Niagara BAS installation and Facility Explorer software, including M&V instrumentation specified in the construction documents, was provided by the mechanical contractor. The contractor has not provided validation or commissioning documentation. Because of this lack of documentation, an internal validation study of the M&V system was conducted by Project 5.4 Investigators, during which several sensors were found to be improperly installed or programmed, leading to ‘bad’ readings. Four of the sixteen liquid flow stations, nine RTU electrical meters, all submeters on pumps and motors, and several air flow stations needed re-installation or re-programming to properly read and trend building data. All of the above issues were discovered because of good data analytics. The M&V conditions were discovered by the CBEI team and not the mechanical contractor, consulting engineer or commissioning agent. In a conventional retrofit project, the outcome and ultimate utility of the M&V system as an operational tool would have been compromised. Clearly there is a need to improve the skill level of these trades and technical professionals. New professional training curriculum, broader awareness of best practices, and carefully placed case studies in widely distributed trade publications can serve to address this need.
Data Analytics and the Building Systems
Data from the building BAS, the M&V sensors, and the lighting control system have been labeled and ported into the OSISoft PI system and displayed with the PI CoreSight interface, which the project team uses alongside the Facility Explorer software as the primary tools for visualizing building data and evaluating system performance. In winter 2015, the CBEI data analytics team discovered the radiant heating loop flow was too high which resulted in low heat transfer from the radiant heaters into the conditioned spaces. It was this energy balance discovery that led the discussion away from a potentially undersized boiler to reducing the hot water flow which in turn increases heat transfer of the perimeter radiant heaters. By the end of the heating season, occupants had begun reporting comfortable inside conditions even on very cold days. The CBEI data analytics team also discovered performance issues within the Dedicated Outdoor Air System (DOAS). The DOAS is a complex air handling system which delivers air at a fixed temperature and humidity so as to avoid condensation on the chilled beams within the conditions space during the cooling season. The performance of this system is critical for maintaining comfort in the largest and most heavily occupied high-bay area of the building. As installed, during second stage dehumidification mode, the preheating coil valve opened to 100% instantly instead of modulating to maintain a discharge air setpoint. This condition overpowered the cooling coil and sent the conditioned space out of control while decreasing the efficiency of the DOAS. Studying the DOAS performance over time led to the discovery that this error was in the control logic programmed by the mechanical contractor. It has been observed that the importance of data analytics is not well understood in the construction industry. The project team believes that opportunities for well-executed data analytics will only grow over time as building operators attempt to utilize complex building energy data streams to inform energy management and code compliance, and to meet demand response and other utility program goals. It is anticipated that as states begin to implement the Clean Power Plan, opportunities for analytics to document energy efficient building management will become more important and prevalent. This will create a broad need to educate building energy retrofit specifiers, regulators and the engineering and contracting communities about the need to improve data analytic capabilities.
Energy Balance Requirements
A significant subset of data analytics is understanding energy balancing within the building context. Specifically this approach can be taken at the whole building level or simply to assess a single energy consuming/producing component. It is worth highlighting specific examples of solving real problems like the radiant heating system described above as an educational tool. For example, the DOAS BAS controls continually showed the energy (Btu) input into the preheat coil, reheat coil, and cooling coil to be significantly lower than design. In fact, there was a significant discrepancy between the chiller output (Btu) and the energy input into the DOAS. This was not uncovered by the building operator, the mechanical contractor, the commissioning agent (heating coil) or the engineer. This energy imbalance was detected by the research team and further investigation determined that three Btu meters were improperly programmed (the pipe diameter was set at 2 inches instead of 2.5 inches, and the paddles were not centered in the bore of the pipes).
BAS Control versus Unit Control
Building Automation Systems can interface with HVAC equipment on many levels ranging from simply enabling/disabling a chiller to controlling all fans, dampers, and valves in an air handler. What needs to be noted is that the BAS control in each case is based upon component external parameters, e.g. outside air temperature or building static pressure. Where this interface can get into trouble is when the BAS is used to replace the (factory provided) internal controls of complex or uncommon system, like a DOAS. In such cases the system control will only be as good as the installation and programming by the contractor.
DOAS Systems
The DOAS was specified to be controlled by the unit controller and provided with occupied and unoccupied signals from the BAS. The DOAS was provided by the mechanical contractor without any sensors or controls and all sensors were field wired and controlled by the BAS. The bottom line for DOAS system control, like other sophisticated HVAC components, is that the sequence of operations was too complex and unfamiliar to the mechanical contractor to properly design a field control system. Going forward, the industry needs to become more aware of DOAS design, installation and operation to avoid real operational issues.
DOAS System Desiccant Wheel Operation
The Trane CDQ desiccant wheel is used to enhance the dehumidification performance of a traditional cooling coil. The wheel is configured in series with the coil such that the “regeneration” side of the wheel is located upstream of the coil and the “process” side of the wheel is located downstream of the coil. The CDQ desiccant wheel adsorbs water vapor from the air downstream of the cooling coil and then adds it back into the air upstream of the coil where the coil removes it through condensation. This process is accomplished without the need for a second regeneration air stream. The addition of the CDQ desiccant wheel to the system enhances the dehumidification performance of the traditional cooling coil. The CDQ wheel transfers water vapor, and the cooling coil does all the dehumidification work in the system. The latent (dehumidification) capacity of the cooling coil increases without increasing its total cooling capacity. The system can achieve a lower supply-air dew point without lowering the coil temperature. Unlike a system with a cooling coil alone, the dew point of the air leaving the system can be lower than the coil surface temperature. Preheat may be used to obtain lower supply-air dew points in applications in which there may be an ample supply of chilled water available, but it is not at a cold enough temperature for the system to achieve the required dew point. Figure 7 shows that for entering mixed-air conditions of 80°F dry bulb/55 percent RH, a 40°F leaving dew point can be achieved if the air leaves the cooling coil at 47°F. But what if the temperature of the available chilled water is only 45°F, and with this water temperature the coil can only achieve a leaving-air temperature of 50°F? Looking at Figure 7, if the relative humidity of the entering mixed-air could be lowered to 30 percent RH, then the 40°F supply-air dew point could be achieved with 50°F air leaving the coil. Using a preheat coil to raise the dry-bulb temperature of this entering mixed air by 19°F results in a reduction in the relative humidity of that air to 30 percent RH (see Figure 8). While preheating the mixed air does add to the cooling load, it allows the system to achieve a lower supply-air dew point with only 45°F water. Table 1 shows an example of the condition in Figure 8 and how it can be achieved in three different ways. In this example, a CDQ system with preheat requires the most cooling capacity, but the temperature leaving the cooling coil is the warmest. Preheat can be modeled and predicted with Trane CDQ Performance Software. The sequence of operation provided by the engineering plans assumed the manufacturer’s controller would be provided, which was not the case. However, the DOAS was delivered and programmed using “canned” sequence blocks taken from a standard air handler.
Chillers
Chillers are manufactured to be applied in multi-zone applications, where the chilled water is pumped out to multitudes of equipment, whether it is the chilled water coils of several large air handling units scattered about the facility in question, or out to dozens and dozens of fan coil units serving single-zone spaces throughout the building. Few control points are needed for chiller operation. The enable command and leaving water temperature can generally be programmed directly at the onboard controller but sending these values from the BAS adds flexibility to the control scheme. Adding M&V sensors to the chiller and chilled water system at building 661 allowed for advanced trouble shooting at the beginning of the cooling season when the chiller shut down frequently due to internal safety alarms. These sensors also provide critical data used to determine chiller efficiency, which has the largest impact on the building’s energy use. In the case of Building 661, the specified chiller was believed to have a minimum chilled water flow limit of 88 gpm. The manufacturer, in August stated that the actual minimum flow was 100 gpm and would not warranty the unit if the flow remained less than 100 gpm. This issue has obviously caused an operation change requiring the chilled water pumps to operate at full capacity and flow to be bypassed around the heat exchanger to meet this higher flow requirement. This issue will require further study to determine the cause of this design error.
Lighting and Daylighting
Building 661’s lighting is a digitally addressable system operated by a Lutron Quantum software-based control system, with BACNet integration providing data to CBEI’s OSISoft PI CoreSight analytics software. The lighting system is not directly tied to the BAS. Estimated electric usage data is calculated by combining the data available on the status of each addressable light fixture ballast with factory-provided ‘cut-sheet’ data on the rated wattage of the installed fixtures. All lighting fixtures in the building have been assigned to one of the three HVAC zones and will be evaluated alongside the sub-metered data available for the major HVAC and electrical systems in the building. As initially installed and commissioned, the system is not yet optimized to minimize energy use by controlling the interior lights and skylight shades to ambient daylight conditions, or to implement a customized demand response program to shed loads on high usage days. A more refined set of calibration and control sequences using existing capabilities will be identified by the project team, and proposed for future implementation by the building owner.
Indoor Environmental Quality
Investigators from the Center for Building Performance and Diagnostics (CBPD) at Carnegie Mellon University (CMU) conducted an initial ‘swing season’ Post Occupancy Evaluation (POE) for Building 661 on March 25th and 26th, 2015. The full report for that POE included: examination of drawings and records describing the technical attributes of building systems (TABS); spot measurements using the National Environmental Assessment Toolkit (NEAT) instrument cart; 24-hour continuous measurements using GrayWolf system for the thermal and air quality in the workplace; and short-term user satisfaction questionnaires in the sampled workstations. The report documented issues and made recommendations for the HVAC and lighting and daylighting systems, as well as spatial and acoustical quality. Additional IEQ measurements were made during summer 2015 by CBEI interns, after restoring to operation two portable data carts built for CBEI early in the program which were removed from our former headquarters in Building 101. The carts were deployed throughout the building during the summer, with emphasis on monitoring acoustics and potential indoor air temperature stratification in the high bay area and below the skylights.
Building 661 Preliminary Energy Performance
Low-energy buildings do not always operate as they were designed and they used more energy and produced less energy than predicted in the design/simulation stage. The design community rarely goes back to see how their buildings perform after they have been constructed. Some documented reasons are listed below: (Pless. et.al. 2006)
There was often a lack of control software or appropriate control logic to allow the technologies to work well together.
Design teams were too optimistic about the behavior of the occupants and their acceptance of systems.
Energy savings from daylighting were substantial, but were generally less than expected.
Plug loads were often greater than design predictions.
Effective insulation values are often inflated when comparing the actual building to the as-designed building.
PV systems experienced a range of operational performance degradation. Common degradation sources included snow, inverted faults, shading, and parasitic standby losses.
Building 661 provides a unique opportunity for the industry to better understand the issues impacting design and delivery of advanced HVAC performance in building renovations. With the M&V system now essentially commissioned, it is possible to actively explore the historic data and utilize it to develop building and area level performance metrics. Building 661 has an occupied square footage of ~36,230 sq. ft. Table below presents preliminary estimates of whole building energy usage and intensity, based on 7 months of energy consumption data.
Table 1: Current Whole Building Performance
Conclusion
The result of this study shed light on the importance of Operation and Maintenance (O&M) in green building success. The most effective way of advancing the building construction industry towards a sustainable balance is through rational analysis of the actual performance. By continuing to disclose performance data and lessons learned about projects, we can help to move each other forward on the road to high performing buildings—with good intentions and high performance. As more actual energy performance data become available on high performing buildings, clearer and more realistic expectations will help to establish confidence within the building design and construction industry about costs and savings. (Adam, 2008)
Bibliography
Adam W. (2008). Documenting Performance: Does it need to be so hard? High Performing Buildings
Adam W. (2008). The proof is performance. High Performing Buildings
Bray, J., & McCurry, N. (2006). Unintended consequences: how the use of LEED can inadvertently fail to benefit the environment. Journal of Green Building, 1(4).
Lstiburek, J. W. (2008). Why green can be wash. ASHRAE Journal, 50(11).
Luther, Mark B. (2009) "Developing an'As Performing'Building Assessment." Journal of green building 4.3.
Pless, S., Deru, M., Griffith, B., Long, N., & Judkoff, R. (2006). Lessons learned from case studies of six high-performance buildings. Golden, Colorado: National Renewable Energy Laboratory.
Philadelphia, Pennsylvania- 2015
Mahsa Safari, PhD Candidate, Pennsylvania State University, 2015
Table of Contents
Introduction
The built environment has a vast impact on the natural environment, human health, and the economy. As the environmental impact of buildings becomes more apparent, a new field called "green building" is gaining momentum. Green building (also known as sustainable or high performance building) is the practice of creating structures and using processes that are environmentally responsible and resource-efficient throughout a building's life-cycle from siting to design, construction, operation, maintenance, renovation and deconstruction. This practice expands and complements the classical building design concerns of economy, utility, durability, and comfort. Green building is also known as a sustainable or high performance building. (EPA, 2014)Green buildings are designed to reduce the overall impact of the built environment on human health and the natural environment by:
- Efficiently using energy, water, and other resources
- Protecting occupant health and improving employee productivity
- Reducing waste, pollution and environmental degradation
For example, green buildings may incorporate sustainable materials in their construction (e.g., reused, recycled-content, or made from renewable resources); create healthy indoor environments with minimal pollutants (e.g., reduced product emissions); and/or feature landscaping that reduces water usage (e.g., by using native plants that survive without extra watering). (EPA, 2014)Recently and across the high performing buildings industry, a serious question have been raised about how “high performance” buildings are performing when they’re actually operating. (Hinge and Winston, 2009); (Bray and Natasha 2006) The good news is that most of this nonsense can be easily remedied. The bad news is that the failures are beginning to bubble to the surface, and we are in danger of ruining the “green brand.” (Lstiburek J.W., 2008)
Case Study- First Year Performance Evaluation of Building 661 Retrofit Project
The following sections report on the actual conditions and processes encountered so far in the occupancy and commissioning of Building 661. It is a rare occasion in the building industry to forensically examine a project, solicit feedback from those involved in building construction projects, and deliver the results back to the industry which makes it a value to the industry. All the information are collected from the interim reports of Consortium for Building Energy Innovation (CBEI).History
Building 661- Penn State Center for Building Energy Science and Engineering- was built in 1942 for the Navy as a recreation facility – there used to be a pool, a basketball court, and a bowling alley in this building. The building sat vacant and unused from 2005 until CBEI decided to retrofit this building in 2013 for their new headquarter rather than demolishing and rebuilding. This site is a great example of beneficial reuse. This deep retrofit involved some demolition, but much of the original building structure was preserved, keeping this material out of the landfill. The reuse also meant preserving the historical character of the building. The Navy Yard and the Philadelphia region is home to many of these historic brick buildings. That means that the lessons learned at this site can be transferred throughout the region.The building layout and renovation was guided by the intended use of the building- a collaborative work environment for a Department of Energy (DOE) funded program designed to overcome market barriers to routinely implementing energy efficiency in buildings. The design team decided to only use market-
Building 661 is aiming to gain LEED Gold credit with 63 points. Below comes the list of attempted points for this project.
Sustainable Site --------------------- 13 of 26
Water Efficiency --------------------- 6 of 10
Energy & Atmosphere -------------- 24 of 35
Materials & Resources ------------- 7 of 14
Indoor Environmental Quality --- 12 of 15
Innovation in Design ---------------- 6 of 6
Regional Priority ---------------------- 2 of 4
Heating, Ventilation, Air Conditioning (HVAC)
-Passive and active chilled beams-Under floor air delivery with displacement diffusers
-Variable refrigerant volume system
-Dedicated outdoor air unit with exhaust air energy recovery (enthalpy wheels)
-Demand controlled ventilation
-High efficiency condensing hot water boiler
-Heat recovery chiller providing regenerative heating and reheat during cooling season
LIGHTING
-Automatic lighting controls in all non-utility spaces-Vacancy / occupancy control in enclosed spaces
-Time of day controls in common areas
-LED lighting
ENVELOPE
- Optimal levels of spray foam insulation added to walls (R-value 20) and roof (R-value 30) to reduce heat loss-New double glazed low-emissivity argon-filled units with thermally broken frames to replace existing windows, with higher performance glazing on the south facing windows and skylights
Building Condition
Since occupancy in November 2014, the building envelope continues to have air and vapor gaps at the doors (from a lack of weather-stripping) and where the arched laminated beams meet the exterior walls in the atrium ‘high-bay’ space. These envelope issues currently cause higher than anticipated sensible and latent loads on the building HVAC system serving that zone. The exterior of the top plate and window headers on the north wall above the high bay windows was left unwrapped and unfinished by a subcontractor, and provides another source of uncontrolled air and water infiltration. These punch list items were identified in Winter 2014/2015, but remain unresolved while contract issues are still being addressed. Inside, the north side of the high-bay space remains unfinished and unoccupied. Perimeter radiant heating was completed and is functioning, but no active chilled beams were installed. Mid-way through summer 2015, the facility maintenance contractor installed two temporary supply grilles in the space, which are delivering dehumidified air from the DOAS into the space. This partially conditioned space poses thermal and humidity gradients across the glass wall separating the high bay common area from the north space that were not anticipated when the design load was prepared.Building Energy Analysis Conducted to Date
The work performed on this project has uncovered important findings that broadly impact the design and delivery of energy retrofits. Below is a brief description of the technical issues, identified and addressed through mid-September 2015, which explore the performance of the building ‘as delivered’.Measurement and Verification Hardware, Software and Commissioning
Performance measurement and verification planning is a rapidly growing field largely stimulated by state and utility resource planning as a means to measure performance to justify incentive payments or regulatory compliance. USGBC, ASHRAE, ICC and other organizations and code officials are using M&V to deliver high performance buildings. Building 661 was instrumented to understand the performance of the whole building, the performance of the three discrete and different HVAC systems approaches, and, in some cases, equipment level performance. The additional M&V data points were specified as a do-no-harm overlay to be connected through the Building Automation System (BAS). The Johnson Controls Niagara BAS installation and Facility Explorer software, including M&V instrumentation specified in the construction documents, was provided by the mechanical contractor. The contractor has not provided validation or commissioning documentation. Because of this lack of documentation, an internal validation study of the M&V system was conducted by Project 5.4 Investigators, during which several sensors were found to be improperly installed or programmed, leading to ‘bad’ readings. Four of the sixteen liquid flow stations, nine RTU electrical meters, all submeters on pumps and motors, and several air flow stations needed re-installation or re-programming to properly read and trend building data. All of the above issues were discovered because of good data analytics. The M&V conditions were discovered by the CBEI team and not the mechanical contractor, consulting engineer or commissioning agent. In a conventional retrofit project, the outcome and ultimate utility of the M&V system as an operational tool would have been compromised. Clearly there is a need to improve the skill level of these trades and technical professionals. New professional training curriculum, broader awareness of best practices, and carefully placed case studies in widely distributed trade publications can serve to address this need.Data Analytics and the Building Systems
Data from the building BAS, the M&V sensors, and the lighting control system have been labeled and ported into the OSISoft PI system and displayed with the PI CoreSight interface, which the project team uses alongside the Facility Explorer software as the primary tools for visualizing building data and evaluating system performance. In winter 2015, the CBEI data analytics team discovered the radiant heating loop flow was too high which resulted in low heat transfer from the radiant heaters into the conditioned spaces. It was this energy balance discovery that led the discussion away from a potentially undersized boiler to reducing the hot water flow which in turn increases heat transfer of the perimeter radiant heaters. By the end of the heating season, occupants had begun reporting comfortable inside conditions even on very cold days. The CBEI data analytics team also discovered performance issues within the Dedicated Outdoor Air System (DOAS). The DOAS is a complex air handling system which delivers air at a fixed temperature and humidity so as to avoid condensation on the chilled beams within the conditions space during the cooling season. The performance of this system is critical for maintaining comfort in the largest and most heavily occupied high-bay area of the building. As installed, during second stage dehumidification mode, the preheating coil valve opened to 100% instantly instead of modulating to maintain a discharge air setpoint. This condition overpowered the cooling coil and sent the conditioned space out of control while decreasing the efficiency of the DOAS. Studying the DOAS performance over time led to the discovery that this error was in the control logic programmed by the mechanical contractor. It has been observed that the importance of data analytics is not well understood in the construction industry. The project team believes that opportunities for well-executed data analytics will only grow over time as building operators attempt to utilize complex building energy data streams to inform energy management and code compliance, and to meet demand response and other utility program goals. It is anticipated that as states begin to implement the Clean Power Plan, opportunities for analytics to document energy efficient building management will become more important and prevalent. This will create a broad need to educate building energy retrofit specifiers, regulators and the engineering and contracting communities about the need to improve data analytic capabilities.Energy Balance Requirements
A significant subset of data analytics is understanding energy balancing within the building context. Specifically this approach can be taken at the whole building level or simply to assess a single energy consuming/producing component. It is worth highlighting specific examples of solving real problems like the radiant heating system described above as an educational tool. For example, the DOAS BAS controls continually showed the energy (Btu) input into the preheat coil, reheat coil, and cooling coil to be significantly lower than design. In fact, there was a significant discrepancy between the chiller output (Btu) and the energy input into the DOAS. This was not uncovered by the building operator, the mechanical contractor, the commissioning agent (heating coil) or the engineer. This energy imbalance was detected by the research team and further investigation determined that three Btu meters were improperly programmed (the pipe diameter was set at 2 inches instead of 2.5 inches, and the paddles were not centered in the bore of the pipes).
BAS Control versus Unit Control
Building Automation Systems can interface with HVAC equipment on many levels ranging from simply enabling/disabling a chiller to controlling all fans, dampers, and valves in an air handler. What needs to be noted is that the BAS control in each case is based upon component external parameters, e.g. outside air temperature or building static pressure. Where this interface can get into trouble is when the BAS is used to replace the (factory provided) internal controls of complex or uncommon system, like a DOAS. In such cases the system control will only be as good as the installation and programming by the contractor.DOAS Systems
The DOAS was specified to be controlled by the unit controller and provided with occupied and unoccupied signals from the BAS. The DOAS was provided by the mechanical contractor without any sensors or controls and all sensors were field wired and controlled by the BAS. The bottom line for DOAS system control, like other sophisticated HVAC components, is that the sequence of operations was too complex and unfamiliar to the mechanical contractor to properly design a field control system. Going forward, the industry needs to become more aware of DOAS design, installation and operation to avoid real operational issues.DOAS System Desiccant Wheel Operation
The Trane CDQ desiccant wheel is used to enhance the dehumidification performance of a traditional cooling coil. The wheel is configured in series with the coil such that the “regeneration” side of the wheel is located upstream of the coil and the “process” side of the wheel is located downstream of the coil. The CDQ desiccant wheel adsorbs water vapor from the air downstream of the cooling coil and then adds it back into the air upstream of the coil where the coil removes it through condensation. This process is accomplished without the need for a second regeneration air stream. The addition of the CDQ desiccant wheel to the system enhances the dehumidification performance of the traditional cooling coil. The CDQ wheel transfers water vapor, and the cooling coil does all the dehumidification work in the system. The latent (dehumidification) capacity of the cooling coil increases without increasing its total cooling capacity. The system can achieve a lower supply-air dew point without lowering the coil temperature. Unlike a system with a cooling coil alone, the dew point of the air leaving the system can be lower than the coil surface temperature. Preheat may be used to obtain lower supply-air dew points in applications in which there may be an ample supply of chilled water available, but it is not at a cold enough temperature for the system to achieve the required dew point. Figure 7 shows that for entering mixed-air conditions of 80°F dry bulb/55 percent RH, a 40°F leaving dew point can be achieved if the air leaves the cooling coil at 47°F. But what if the temperature of the available chilled water is only 45°F, and with this water temperature the coil can only achieve a leaving-air temperature of 50°F? Looking at Figure 7, if the relative humidity of the entering mixed-air could be lowered to 30 percent RH, then the 40°F supply-air dew point could be achieved with 50°F air leaving the coil. Using a preheat coil to raise the dry-bulb temperature of this entering mixed air by 19°F results in a reduction in the relative humidity of that air to 30 percent RH (see Figure 8). While preheating the mixed air does add to the cooling load, it allows the system to achieve a lower supply-air dew point with only 45°F water. Table 1 shows an example of the condition in Figure 8 and how it can be achieved in three different ways. In this example, a CDQ system with preheat requires the most cooling capacity, but the temperature leaving the cooling coil is the warmest. Preheat can be modeled and predicted with Trane CDQ Performance Software.The sequence of operation provided by the engineering plans assumed the manufacturer’s controller would be provided, which was not the case. However, the DOAS was delivered and programmed using “canned” sequence blocks taken from a standard air handler.
Chillers
Chillers are manufactured to be applied in multi-zone applications, where the chilled water is pumped out to multitudes of equipment, whether it is the chilled water coils of several large air handling units scattered about the facility in question, or out to dozens and dozens of fan coil units serving single-zone spaces throughout the building. Few control points are needed for chiller operation. The enable command and leaving water temperature can generally be programmed directly at the onboard controller but sending these values from the BAS adds flexibility to the control scheme. Adding M&V sensors to the chiller and chilled water system at building 661 allowed for advanced trouble shooting at the beginning of the cooling season when the chiller shut down frequently due to internal safety alarms. These sensors also provide critical data used to determine chiller efficiency, which has the largest impact on the building’s energy use. In the case of Building 661, the specified chiller was believed to have a minimum chilled water flow limit of 88 gpm. The manufacturer, in August stated that the actual minimum flow was 100 gpm and would not warranty the unit if the flow remained less than 100 gpm. This issue has obviously caused an operation change requiring the chilled water pumps to operate at full capacity and flow to be bypassed around the heat exchanger to meet this higher flow requirement. This issue will require further study to determine the cause of this design error.Lighting and Daylighting
Building 661’s lighting is a digitally addressable system operated by a Lutron Quantum software-based control system, with BACNet integration providing data to CBEI’s OSISoft PI CoreSight analytics software. The lighting system is not directly tied to the BAS. Estimated electric usage data is calculated by combining the data available on the status of each addressable light fixture ballast with factory-provided ‘cut-sheet’ data on the rated wattage of the installed fixtures. All lighting fixtures in the building have been assigned to one of the three HVAC zones and will be evaluated alongside the sub-metered data available for the major HVAC and electrical systems in the building. As initially installed and commissioned, the system is not yet optimized to minimize energy use by controlling the interior lights and skylight shades to ambient daylight conditions, or to implement a customized demand response program to shed loads on high usage days. A more refined set of calibration and control sequences using existing capabilities will be identified by the project team, and proposed for future implementation by the building owner.Indoor Environmental Quality
Investigators from the Center for Building Performance and Diagnostics (CBPD) at Carnegie Mellon University (CMU) conducted an initial ‘swing season’ Post Occupancy Evaluation (POE) for Building 661 on March 25th and 26th, 2015. The full report for that POE included: examination of drawings and records describing the technical attributes of building systems (TABS); spot measurements using the National Environmental Assessment Toolkit (NEAT) instrument cart; 24-hour continuous measurements using GrayWolf system for the thermal and air quality in the workplace; and short-term user satisfaction questionnaires in the sampled workstations. The report documented issues and made recommendations for the HVAC and lighting and daylighting systems, as well as spatial and acoustical quality. Additional IEQ measurements were made during summer 2015 by CBEI interns, after restoring to operation two portable data carts built for CBEI early in the program which were removed from our former headquarters in Building 101. The carts were deployed throughout the building during the summer, with emphasis on monitoring acoustics and potential indoor air temperature stratification in the high bay area and below the skylights.Building 661 Preliminary Energy Performance
Low-energy buildings do not always operate as they were designed and they used more energy and produced less energy than predicted in the design/simulation stage. The design community rarely goes back to see how their buildings perform after they have been constructed. Some documented reasons are listed below: (Pless. et.al. 2006)- There was often a lack of control software or appropriate control logic to allow the technologies to work well together.
- Design teams were too optimistic about the behavior of the occupants and their acceptance of systems.
- Energy savings from daylighting were substantial, but were generally less than expected.
- Plug loads were often greater than design predictions.
- Effective insulation values are often inflated when comparing the actual building to the as-designed building.
- PV systems experienced a range of operational performance degradation. Common degradation sources included snow, inverted faults, shading, and parasitic standby losses.
Building 661 provides a unique opportunity for the industry to better understand the issues impacting design and delivery of advanced HVAC performance in building renovations. With the M&V system nowessentially commissioned, it is possible to actively explore the historic data and utilize it to develop building and area level performance metrics. Building 661 has an occupied square footage of ~36,230 sq. ft.
Table below presents preliminary estimates of whole building energy usage and intensity, based on 7 months of energy consumption data.
Conclusion
The result of this study shed light on the importance of Operation and Maintenance (O&M) in green building success. The most effective way of advancing the building construction industry towards a sustainable balance is through rational analysis of the actual performance. By continuing to disclose performance data and lessons learned about projects, we can help to move each other forward on the road to high performing buildings—with good intentions and high performance. As more actual energy performance data become available on high performing buildings, clearer and more realistic expectations will help to establish confidence within the building design and construction industry about costs and savings. (Adam, 2008)Bibliography
Adam W. (2008). Documenting Performance: Does it need to be so hard? High Performing BuildingsAdam W. (2008). The proof is performance. High Performing Buildings
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EPA. (2014). Green building. Retrieved from http://archive.epa.gov/greenbuilding/web/html/
Lstiburek, J. W. (2008). Why green can be wash. ASHRAE Journal, 50(11).
Luther, Mark B. (2009) "Developing an'As Performing'Building Assessment." Journal of green building 4.3.
Pless, S., Deru, M., Griffith, B., Long, N., & Judkoff, R. (2006). Lessons learned from case studies of six high-performance buildings. Golden, Colorado: National Renewable Energy Laboratory.