Integrated Building Control System

INTRODUCTION

A traditional approach to building automation includes a collection of independent control systems, one for each building end use, with limited or no communication among individual systems or devices. Independent control systems found in existing commercial buildings typically address security, electric lighting, shading, fenestration, some process loads and heating, ventilation and air conditioning systems. Dynamic building envelope systems help achieve daylighting and passive solar benefits by regulating incoming solar radiation and heat gain. Daylight sensors adjust electrical lighting fixtures and operable shading devices based on the amount of natural light. Also, HVAC system can be operated based on occupancy and air quality inside a building. While these individual systems can contribute to general building energy savings and occupant comfort, there is still a lack of integrated management of different building components and systems such as lighting, fenestration, and heating, ventilation and air conditioning systems (Shen et al., 2021; King and Perry, 2017). When the individual systems are not properly coordinated to respond to indoor and outdoor environmental factors, building occupants often experience visual and thermal discomfort that can also negatively impact building energy performance (Hirning et al., 2013 and 2014; Suk and Schiler, 2012; Suk et al., 2013; Konis, 2013). Therefore, successful integration of the individual building systems via a common communication platform is necessary. Integrated Building Control Systems (IBCS) can help maximize building energy saving and improve occupant well-being when various building systems are effectively coordinated to maintain optimized indoor environments (Ghaffarianhoseini et al., 2016; Shen et al., 2021; King and Perry, 2017; Choi et al., 2019; Montier et al., 2013; Wu, 2019). This paper describes installations of an IBCS with operable windows, automated shading device, electrochromic glazing, adaptive lighting, and HVAC in an office building and reports the pilot scale evaluation of the integrated system.

BACKGROUND

In order to maximize building system performance, the research team identified and tested commercially available technology appropriate to specify as components of the pilot-scale IBCS. Over the course of this effort, refinements were made to the preliminary IBCS by incorporating new commercial technologies that improved performance and/or expanded the IBCS capabilities. The IBCS conceptual structure consists of a collection of building systems connected to a system integrator. The system integrator is a high-level, overarching controller that facilitates communication between individual building systems. Individual building systems are comprised of a system-level controller, sensors, user-input, and system appliances such as electrical lighting, operable windows, etc. The controller controls connected appliances based on input from the sensors, user input, and the system integrator. This concept is shown in Figure 1.

Figure 1: Conceptual structure of an Integrated Building Control System.

Prior to the IBCS installation at the demonstration site, a small-scale IBCS was installed and tested in a CLTC laboratory space in Figure 2. The small-scale IBCS was commissioned and tested under controlled conditions to demonstrate the technical feasibility of using commercially available systems. The IBCS controlled the following building appliances, each with its own dedicated controller: 1) recessed 2’x2’ LED luminaires, 2) an in-room air-conditioning heat pump, 3) an actuated skylight with integrated shades, 4) windows with electrochromic glazing, 5) a window with an integrated roller shade, 6) an actuated, operable window. The space was equipped with a suite of various monitoring and control devices. Additional technologies that were not included at the campus demonstration site, such as electrochromic windows and venting skylights with a roller shade, were also installed and tested to demonstrate the system's versatility. To create repeatable, real-world simulations, additional HVAC vents were routed into the room for environmental control, and a wall of dimmable fluorescent lamps external to the room provided artificial "daylight".

Figure 2: Integrated Building Controls Laboratory.

For each system controller, the ability to communicate with the IBCS's system integrator was evaluated. Technical limitations were identified, such as a controller's inability to provide bi-directional communication, which is required for satisfactory integration. The research team worked with building system manufacturers to overcome these limitations by increasing each device's system readiness and availability for use as part of a commercial IBCS. The primary results of the IBCS laboratory testing were:

• Demonstration of the IBCS's technical feasibility in a controlled setting.

• Identification of individual device barriers that hampered its use as part of an integrated control system and development of solutions for overcoming those barriers.

• Demonstration of IBCS operation with a cross-section of commercial building controllers and subsystems.

METHOD

The project includes market analysis, product refinement and pilot-scale demonstration of a new technology that integrates heating, ventilation and air conditioning systems, electric lighting, shading and operable fenestration under a single control system to improve whole-building energy performance and indoor environmental quality. This integrated approach increases whole-building energy efficiency, demand flexibility and occupant comfort; is highly flexible in terms of building applications, location and geometry; and can be deployed using currently available, off-the-shelf control hardware and software at substantially lower cost than use of traditional building energy management systems.

Four primary research objectives were developed as follows: 1) refine an IBCS specification for commercial applications including necessary hardware and software components; 2) evaluate the IBCS in the laboratory under controlled conditions to ensure its readiness for real-world deployment; 3) install and evaluate the IBCS in an existing building to validate control system performance; and 4) document expected IBCS costs, energy use, non-energy benefits, and other relevant elements.

The UC Davis main campus provided a demonstration building and test site for IBCS installation and evaluation. The IBCS was deployed in 13 spaces throughout the first floor of the facility, informally called The Barn, for a total of 2,068 square feet (Figure 3), or 36 percent of the conditioned building floor space. The building was originally designed for campus architects and engineers but currently houses multidisciplinary and multi-institutional teams of researchers and stakeholders for the mission of the UC Davis Institute of the Environment. Six demonstration spaces were located along the West building façade and seven spaces along the East façade. These spaces were selected because they encapsulated complete HVAC zones, and allowed for a detailed evaluation of HVAC, lighting and fenestration connected to and controlled by the IBCS under typical real-world conditions. The Barn is equipped with a smart power meter, which monitors energy use at the whole building level. This data was used to produce the baseline energy usage numbers for the cost-effectiveness calculations. IBCS installation and commissioning was completed in the summer of 2020. The system is currently fully functional and in operation at the facility.

Figure 3 North façade of the demonstration building (left) and floor plan of the demonstration area (right).

LIGHTING

The lighting system included linear LEDs, fixture controllers, open and closed loop photosensors, occupancy sensors and various gateways to translate the lighting control signal into BACnet signals. The building has a total of 221 installed luminaires in 15 different fixture types that consume 11,730 Watts. The pre-retrofit lighting in the demonstration area consisted of twenty-four (24) 34W recessed 2’x2’, thirty-eight (38) 32W recessed 1’x4’, and sixty (60) 32W pendant-mounted 1’x4’ fluorescent luminaires. In order to integrate the retrofitted lights within the IBCS, a wireless lighting control system was installed. The use of lighting controls can reduce the total lighting load through personal tuning, daylight harvesting, and occupancy-based controls. The daylighting and occupancy-based lighting control strategies that these devices employ typically result in 38 percent energy savings as compared to uncontrolled lighting.

HVAC

The first floor is divided into four different HVAC zones and the second floor is divided into two different control zones. Each zone is controlled via a separate thermostat. The existing central HVAC of the demonstration building included a wireless thermostat as the main controller. Due to the various communication protocols supported by the IBCS, no modifications were needed to integrate with the existing thermostats. The HVAC appliances in the test site are constant-volume air handlers, packaged central air conditioning units, and a gas furnace for heating. The IBCS algorithm for the HVAC system was designed to include occupancy-based controls using the occupancy sensor from the lighting system to reduce HVAC usage while the space is unoccupied. Occupancy-based HVAC controls have been analyzed in multiple studies with saving estimates from 10 to 43 percent for HVAC with a median of 20 percent. In addition to the control savings, this study looked at improving the thermal insulation of the building by replacing the windows, adding variable VLT and SHGC characteristics through actuated roller shades, and including alternative cooling methods with actuated windows.

WINDOW GLAZING + DYNAMIC SHADING

The demonstration building is a designated historic building and maintaining the historic appearance was a critical design criterion. The research team worked with an automated window company to design, manufacture, and install the automated system that includes double panes with an internal roller shade and actuator. According to the US Department of Energy, the most important factors for window thermal performance are their U-Factor and Solar Heat Gain Coefficient (SHGC). The U-Factor is a measure of how well the window insulates the building from the outside environment, and SHGC is a measure of how much thermal energy from the sun comes through the window. The windows in the IBCS demonstration zone are east and west facing, so both the U-Factor and SHGC should be minimized for ideal energy savings. Representative values for these parameters of the pre-retrofit window are approximately 1.09 and 0.81, respectively, and actual the performance of the window is likely even worse when considering the air leakage present with the old framing and hardware of the windows causing imperfect seals. According to documentation from the manufacturer, the retrofit windows have a U-Factor of 0.29 and an SHGC of 0.28.

In addition to the improvements attributed to upgrading the window glazing, each window is equipped with actuated roller shades that provide an additional energy savings opportunity by rejecting solar radiation that enters the conditioned space of the building through the windows. Integrated between glass panes of the window, these shades have a transmittance of 3 percent, which means that they prevent 97 percent of solar radiation from entering the building when deployed. Utilizing roller shades with metalized films is a recent development and the research team expects as more studies show the energy saving potential the product costs will be optimized based on energy economics to improve sales volume. Previous research by Eleanor S. Lee, and Stephen Selkowitz indicates that dynamic shading can reduce daily cooling loads by 22 to 24 percent compared to a daylit space with static blinds positioned horizontally on clear sunny days throughout the year (Lee and Stephen, 1997).

PRECOOLING THROUGH NATURAL VENTILATION

The last feature of the windows installed in this retrofit package is natural ventilation. The specified window is equipped with a single-chain motor that can open the window to a maximum length of 13.8 inches. The goal of this feature was to offset HVAC loads by utilizing natural ventilation when outside environmental conditions are favorable. While there are multiple situations in which natural ventilation can be advantageous for reducing energy loads, the most noted example is precooling the building through natural ventilation. By opening the windows at night to let the cooler air into the building, the start of the building’s mechanical cooling is delayed so that the daily HVAC usage can be decreased. Precooling using natural ventilation has the potential to significantly outperform precooling strategies that utilize air handlers. Multiple studies have modeled buildings to determine the potential energy savings by utilizing precooling through natural ventilation. These figures range potential energy savings from 5 percent to 23.5 percent when considering various parameters such as relative humidity, the duration of venting, whether using actuated windows or the building’s air handlers, and/or the thermal mass of the building. A 2015 modeling study by Christopher Iddon and Nikhil ParasuRaman that closely matches the control algorithm used in this implementation found precooling through natural ventilation reduces annual cooling energy usage by 15.7 percent (Iddon and ParasuRaman, 2015).

PRE-RETROFIT BUILDING OPERATION PATTERN

Building energy consumption was carefully monitored throughout the entire year. The total electrical energy use includes all electrical systems in the building, i.e. electric lighting, HVAC, and plug loads. The data is not disaggregated by building sub-system. The monthly pre-retrofit electricity consumption ranges from 5,330 kWh in November to 9,007 kWh in June (Figure 4). The average electrical energy use during this period was approximately 6,900 kWh per month. The demonstration building shows above average energy use in the months of June, July and August due to the Sacramento valley summer climate and therefore an increased HVAC load.

Figure 4 Pre-retrofit electricity usage of the building.

During a site visit of the demonstration building, occupants were asked to describe the typical operating hours of the building. Based on this information, the building is typically occupied 8:00 AM – 6:00 PM, Monday – Friday. Occasionally, there are occupants in the building during the weekend. To confirm this, the hourly load profile and energy use of the building were examined for weekdays (excluding holidays). The average hourly load profile begins to increase starting between 7:00-8:00 AM and decreases starting between 4:00-6:00 PM. The increased energy use between these hours is attributed to an increase in occupancy and the associated use of lighting, HVAC and plug load appliances. The average weekday load profile varies on a monthly basis (Figure 5). The highest load observed was in July 2017 during the hour of 2:00 PM - 3:00 PM with an average of 27.2 kW.

Figure 5 Weekday load profile for The Barn from October 2017 through October 2018.

The highest load observed for the average weekend profile was in June 2017 during the hour of 3:00 PM - 4:00 PM with an average of 15.6 kW. Additionally, during the weekends the load profile does not increase around 8:00 AM as it does during weekdays. This is likely due to the presence of fewer occupants, and therefore lesser use of the lighting, HVAC and plug-load appliances.

The energy use during weekday work hours (8:00 AM – 6:00 PM) and weekend days was compared for the same time span (Figure 6). This showed that the weekend electricity use is approximately 53 percent less than weekday energy use. This significant decrease in energy use is related to the decrease in building system use during the weekend when occupancy is lower.

Figure 6 Comparison of the Energy Use for Weekdays and Weekends.

ANALYSIS

IBCS economic performance is highly dependent on the existing conditions, the use type, and the specific implementation of IBCS deployed. While IBCS can consist of any number of controllable building systems such as lighting, HVAC, fenestration or plug load controls; IBCS cannot happen without some level of building integration work being done. This work may consist purely of programming a site-specific sequence of operations or it may also include physical installation of communications hardware such as cabling, wireless transceivers, or protocol gateways.

Due to this variability in possible IBCS embodiments, four scenarios were modeled to understand the cost benefit of the most common incremental steps of IBCS as estimated by the research team. Modeled scenarios considered combinations of lighting, HVAC, and shading integration. Savings due to natural ventilation were not considered in the modeling. Code-compliant and legacy construction scenarios were both considered. The energy savings and project costs were determined considering a mix of existing publications, site conditions at the project demonstration site, and energy modeling. All energy savings and cost numbers are specific to the 5,744 square foot demonstration building on UC Davis campus using a flat rate of $0.18 per kW-hr. Results are summarized in Table 1.

SCENARIO A: LIGHTING + HVAC INTEGRATION IN A CODE-COMPLIANT BUILDING

The first IBCS scenario modeled consisted of adding building integration hardware to an existing code-compliant building and implementing temperature and ventilation setbacks based on occupancy signals from the lighting controls. This scenario is titled “Lighting + HVAC Integration in a Code-Compliant Building”. Energy savings were modeled in Energy Plus using weather data from Sacramento CA and resulted in an annual savings of 27 percent of the HVAC energy usage for a total of 11 percent savings of whole building energy usage. Project costs were determined using information collected from the field demonstration construction project. Total project cost including materials and labor are estimated to be $5,474. This scenario has an estimated simple payback of 3.0 years.

SCENARIO B: LIGHTING + HVAC + SHADING INTEGRATION IN A CODE-COMPLIANT BUILDING

The second IBCS scenario modeled consisted of adding building integration hardware and metalized film roller shades to an existing code-compliant building and implementing seasonal shade control and temperature and ventilation setbacks both based on occupancy signals from the lighting controls. This scenario is titled “Lighting + HVAC + Shading Integration in a Code-Compliant Building”. Energy savings were modeled in Energy Plus using weather data from Sacramento CA and combined with existing shading case studies. This resulted in an annual savings of 38 percent of the HVAC energy usage for a total of 16 percent savings of whole building energy usage. Project costs were determined using information collected from the field demonstration construction project. Total project cost including materials and labor are estimated to be $47,099. This scenario has an estimated simple payback of 18.2 years.

SCENARIO C: LIGHTING + HVAC INCLUDING LIGHTING RETROFIT

The third IBCS scenario modeled consisted of adding building integration hardware and a lighting and lighting controls retrofit to an existing building and implementing temperature and ventilation setbacks both based on occupancy signals from the lighting controls. This scenario is titled “Lighting + HVAC including Lighting Retrofit”. Energy savings were modeled in Energy Plus using weather data from Sacramento, California and combined with existing lighting case studies. This resulted in an annual savings of 27 percent of the HVAC energy usage and 63 percent of lighting energy usage for a total of 37 percent savings of whole building energy usage. Project costs were determined using information collected from the field demonstration construction project and RS Means for construction cost estimates. Total project cost including materials and labor are estimated to be $72,579. This scenario has an estimated simple payback of 12.3 years.

SCENARIO D: LIGHTING + HVAC + SHADING INTEGRATION INCLUDING LIGHTING RETROFIT

The fourth IBCS scenario modeled consisted of adding building integration hardware, metalized film roller shades and a lighting and lighting controls retrofit to an existing building and implementing seasonal shade control and temperature and ventilation setbacks both based on occupancy signals from the lighting controls. This scenario is titled “Lighting + HVAC + Shading Integration including Lighting Retrofit”. This resulted in an annual savings of 38 percent of the HVAC energy usage and 63 percent of lighting energy usage for a total of 41 percent savings of whole building energy usage. Total project cost including materials and labor are estimated to be $114,203. This scenario has an estimated simple payback of 17.2 years.

Table 1: Cost-effectiveness results

The economic performance discussed only includes cost savings from conservative flat electrical rates. IBCS enables the future realization of advanced building control strategies that not only improve whole building energy usage and occupant comfort but also consider and adjust appliance operation based on real-time pricing signals and demand events. The research team anticipates the future broad adoption of time-of-use based tariffs to significantly improve the economic performance of the IBCS.

Based on the field deployment and energy modeling analysis, the final IBCS specification diagram was developed in Figure 7. It includes hardware components and communication protocols. Three fenestration types such as venting windows with roller shades, venting skylights with roller shades, and electrochromic glazing are included in the proposed IBCS. The venting window and skylight components include a BMS interface unit, roller shade motor, venting controller, venting actuator, I/O device, and interface unit. The electrochromic glazing components include an electrochromic glazing controller and in-glass unit (IGU) that receives a control signal to change the level of tint of the glazing in response to the amount of daylight entering the space. The lighting system control utilizes a hierarchical star network topology where devices are connected to one another with multiple devices acting as hubs. The lighting system components include a network bridge, lighting load controller, occupancy sensors, daylight sensors, lighting control user interface, and luminaires. The network bridge makes the occupancy status, lighting sensor values and state of the lighting system available to the system integrator. The HVAC system components used in the IBCS include a field server gateway, cloud server, wireless gateway, wireless thermostat, and the HVAC units themselves. The auxiliary inputs provide data that the system integrator can use to expand the capabilities of the IBCS. The auxiliary system inputs include OpenADR device, indoor CO2 sensor, outdoor CO2 sensor, and a weather station (gateway, console, and sensors).

Figure 7 Final Specification for IBCS Hardware and Communication Platform.

CONCLUSION AND FUTURE WORK

Overall, the field deployment and building energy modeling outcomes support the project goals and objectives to develop new technologies and system integration strategies that improve building system performance while saving energy. Field deployment and evaluation results verified system design, procurement, installation and commissioning under real-world conditions for the new technology at scale. Project outcomes show that the IBCS can reduce HVAC, lighting and shading loads by 10 to 40 percent over typical baseline systems in an office building in the given climate condition. Estimated electricity savings will translate directly to cost savings of $7.9M to $31.6M annually if there is a one percent adoption rate throughout California’s commercial buildings.

For the selected demonstration site, analysis showed that basic HVAC and lighting system integration using occupancy-based control are relatively inexpensive and is expected to result in simple payback periods of less than three years. Peak demand reductions ranged from less than five percent for lighting and HVAC systems integration to as much as 15 percent for an IBCS incorporating natural ventilation and building precooling. The addition of integrated shading and operable fenestration can significantly reduce peak demand associated with cooling loads and was shown to reduce annual energy use by up to 30 percent depending on conditions and climate zone.

Based on this range of energy savings, estimated statewide emission reductions associated with a one percent adoption rate of IBCS in California’s commercial buildings range from 35,687 to 142,748 metric tons of carbon dioxide equivalent annually. This is equivalent to removing 7,710 to 30,840 typical gasoline-fueled passenger vehicles (as defined by the US Environmental Protection Agency) from California roads each year.

Non-energy benefits of the IBCS include improved building performance, air quality management, and building safety features. The project team worked closely with multiple fenestration and lighting control manufacturers to refine their products for inclusion in the field deployment. These new products are commercially available and ready for use in today’s integrated building control systems by system designers, installers, and system integrators. Outcomes from this project set the groundwork for additional research that, if successful, may support the adoption of more aggressive energy standards related to integrated building control systems.

This project was supported by the California Energy Commission's Energy Research and Development Division.

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