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Cover page of Artificial Intelligence for Efficient Thermal Comfort Systems: Requirements, Current Applications and Future Directions

Artificial Intelligence for Efficient Thermal Comfort Systems: Requirements, Current Applications and Future Directions

(2020)

In buildings, one or a combination of systems (e.g., central HVAC system, ceiling fan, desk fan, personal heater, and foot warmer) are often responsible for providing thermal comfort to the occupants. While thermal comfort has been shown to differ from person to person and vary over time, these systems are often operated based on prefixed setpoints and schedule of operations or at the request/routine of each individual. This leads to occupants’ discomfort and energy wastes. To enable the improvements in both comfort and energy efficiency autonomously, in this paper, we describe the necessity of an integrated system of sensors (e.g., wearable sensors/infrared sensors), infrastructure for enabling system interoperability, learning and control algorithms, and actuators (e.g., HVAC system setpoints, ceiling fans) to work under a governing central intelligent system. To assist readers with little to no exposure to artificial intelligence (AI), we describe the fundamentals of an intelligent entity (rational agent) and components of its problem-solving process (i.e., search algorithms, logic inference, and machine learning) and provide examples from the literature. We then discuss the current application of intelligent personal thermal comfort systems in buildings based on a comprehensive review of the literature. We finally describe future directions for enabling application of fully automated systems to provide comfort in an efficient manner. It is apparent that improvements in all aspects of an intelligent system are be needed to better ascertain the correct combination of systems to activate and for how long to increase the overall efficiency of the system and improve comfort.

Cover page of Ceiling-fan-integrated air conditioning: Airflow and temperature characteristics of a sidewall-supply jet interacting with a ceiling fan

Ceiling-fan-integrated air conditioning: Airflow and temperature characteristics of a sidewall-supply jet interacting with a ceiling fan

(2020)

Ceiling-Fan-Integrated Air Conditioning (CFIAC) is a proposed system that can greatly increase buildings’ cooling efficiency. In it, terminal supply ducts and diffusers are replaced by vents/nozzles, jetting supply air toward ceiling fans that serve to mix and distribute it within the room. Because of the fans’ air movement, the system provides comfort at higher room temperatures than in conventional commercial/ institutional/retail HVAC. We have experimentally evaluated CFIAC in a test room. This paper covers the distributions of air-speed, temperature, and calculated comfort level throughout the room. Two subsequent papers report tests of human subject comfort and ventilation effectiveness in the same experimental conditions. The room’s supply air emerged from a high-sidewall vent directed toward a ceiling fan on the jet centerline; we also tested this same jet on a fan located off to the side of the jet. Primary variables are: ceiling fan flow volumes in downward and upward directions, supply air volume, and room-vs-supply temperature difference. Velocity, turbulence, and temperature distributions are presented for vertical and horizontal transects of the room. The occupied zone is then evaluated for velocity and temperature non-uniformity, and for comfort as predicted by the ASHRAE Standard 55 elevated air speed method. We show that temperatures are well-mixed and uniform across the room for all of the fan-on configurations, for fans both within or out of the supply jet centerline. The ceiling fan flow dominates the CFIAC airflow, and even though non-uniform is capable of providing comfortable conditions throughout the occupied area of the room.

Cover page of A review of advanced air distribution methods - theory, practice, limitations and solutions

A review of advanced air distribution methods - theory, practice, limitations and solutions

(2019)

Ventilation and air distribution methods are important for indoor thermal environments and air quality. Effective distribution of airflow for indoor built environments with the aim of simultaneously offsetting thermal and ventilation loads in an energy efficient manner has been the research focus in the past several decades. Based on airflow characteristics, ventilation methods can be categorized as fully mixed or non-uniform. Non-uniform methods can be further divided into piston, stratified and task zone ventilation. In this paper, the theory, performance, practical applications, limitations and solutions pertaining to ventilation and air distribution methods are critically reviewed. Since many ventilation methods are buoyancy driving that confines their use for heating mode, some methods suitable for heating are discussed. Furthermore, measuring and evaluating methods for ventilation and air distribution are also discussed to give a comprehensive framework of the review.

Cover page of Side-by-side laboratory comparison of radiant and all-air cooling: How natural ventilation cooling and heat gain characteristics impact space heat extraction rates and daily thermal energy use

Side-by-side laboratory comparison of radiant and all-air cooling: How natural ventilation cooling and heat gain characteristics impact space heat extraction rates and daily thermal energy use

(2019)

For radiant cooling to maintain equivalent comfort conditions as all-air cooling it must remove more heat from a space, the peak space heat extraction rate must be larger, and the peak must occur earlier. In this article, we assess how the magnitudes of these differences are influenced by heat gain characteristics and by the use of natural ventilation night precooling. We present measurements from a series of multi-day side-by-side comparisons of radiant cooling and all-air cooling in a pair of experimental testbed buildings, with equal heat gains, and maintained at equivalent comfort conditions. In a five-day experiment with mixed internal heat gains, solar gains, and natural ventilation night precooling, radiant cooling had to remove 35% more heat than the all-air system in equivalent circumstances; and the peak heat extraction rate was 20% larger (median difference on multiple days). In a similar experiment with highly convective internal gains the differences were smaller (26% more thermal energy, 12% larger peak), while in an experiment with highly radiant gains the differences were larger (40% more thermal energy, and 21% larger peak). The differences were much smaller in an experiment without natural ventilation night precooling (7% more thermal energy, 5% larger peak). These findings have consequences for the choice, design, and control of mechanical cooling systems, especially in buildings that also use passive cooling strategies such as natural ventilation night precooling.

Cover page of Ceiling fans: Predicting indoor air speeds based on full scale laboratory measurements

Ceiling fans: Predicting indoor air speeds based on full scale laboratory measurements

(2019)

We measured indoor air speeds generated by ceiling fans in 78 full-scale laboratory tests. The factors were the room size, fan diameter, type, speed, direction (up or down), blade height, and mount distance (i.e. blade to ceiling height). We demonstrated the influence of these factors, showing that the most significant are speed, diameter and direction. With other factors fixed, the average room air speed in the occupied zone increases proportionally with fan air speed and diameter. Blowing fans upwards yields lower but far more uniform air speeds than downwards. We show that for the same fan diameter and airflow, fan type has little effect on the air speed distribution in the region outside the fan blades. We developed several new dimensionless representations and demonstrate that they are appropriate for comparisons over a wide range of fan and room characteristics. Dimensionless linear models predict the lowest, average, and highest air speeds in a room with a median (and 90th percentile) absolute error of 0.03 (0.08), 0.05 (0.13), and 0.12 (0.26) m/s respectively over all 56 downwards tests, representing common applications. These models allow designers to quickly and easily estimate the air speeds they can expect for a given fan and room. We include all measured data and analysis code in this paper.

  • 9 supplemental PDFs
  • 2 supplemental images
  • 4 supplemental files
Cover page of Eliminating Overcooling Discomfort While Saving Energy

Eliminating Overcooling Discomfort While Saving Energy

(2019)

A large percentage of commercial buildings in North America use variable air volume (VAV) systems with reheat, and this system type is also common around the world. Summertime overcooling is widespread in such buildings and has received considerable media attention over the past few years. ASHRAE Research Project RP-1515, reported in this article, shows that much of today’s overcooling originates in unsubstantiated engineering assumptions about the performance of VAV boxes and diffusers at low-flow setpoints. These assumptions are that low flows will cause diffusers to dump cooled air and create drafts around occupants, ventilation air will be poorly mixed, and VAV airflow control will become unstable or inaccurate. Together, they have resulted in VAV minimums being commonly set at 20% to 50% of maximum. ASHRAE RP-1515 and other recent research have shown each of these assumptions to be unwarranted, and that far lower minimums are desirable.

Cover page of Optimizing Radiant Systems for Energy Efficiency and Comfort

Optimizing Radiant Systems for Energy Efficiency and Comfort

(2019)

Radiant cooling and heating systems provide an opportunity to achieve significant energy savings, peak demand reduction, load shifting, and thermal comfort improvements compared to conventional all-air systems. As a result, application of these systems has increased in recent years, particularly in zero-net-energy (ZNE) and other advanced low-energy buildings. Despite this growth, completed installations to date have demonstrated that controls and operation of radiant systems can be challenging due to a lack of familiarity within the heating, ventilation, and air-conditioning (HVAC) design and operations professions, often involving new concepts (particularly related to the slow response in high thermal mass radiant systems). To achieve the significant reductions in building energy use proposed by California Public Utilities Commission’s (CPUC’s) Energy Efficiency Strategic Plan that all new non-residential buildings be ZNE by 2030, it is critical that new technologies that will play a major role in reaching this goal be applied in an effective manner. This final report describes the results of a comprehensive multi-faceted research project that was undertaken to address these needed enhancements to radiant technology by developing the following: (1) sizing and operation tools (currently unavailable on the market) to provide reliable methods to take full advantage of the radiant systems to provide improved energy performance while maintaining comfortable conditions, (2) energy, cost, and occupant comfort data to provide real world examples of energy efficient, affordable, and comfortable buildings using radiant systems, and (3) Title-24 and ASHRAE Standards advancements to enhance the building industry’s ability to achieve significant energy efficiency goals in California with radiant systems. The research team used a combination of full-scale fundamental laboratory experiments, whole-building energy simulations and simplified tool development, and detailed field studies and control demonstrations to assemble the new information, guidance and tools necessary to help the building industry achieve significant energy efficiency goals for radiant systems in California.

Cover page of Codes and standards report

Codes and standards report

(2018)

The goal of this study was to (1) propose changes to Title 24 to support improved modeling capabilities and help achieve significant energy efficiency goals for radiant systems in California, and (2) propose changes, as needed, to relevant ASHRAE Standards, Handbooks, and Guidelines to provide new information and guidance on radiant systems. The current version of California Building Energy Efficiency Standards, Part 6 of the California Building Standards Code (Title 24) does not address factors specific to high thermal mass radiant systems within the body of the Standards. The alternative compliance method references some limited aspects relating to radiant systems but it is incomplete and not practically applicable, and has not yet been implemented in the associated compliance software. In addition, there are some modeling limitations for radiant systems in EnergyPlus, which is the simulation engine underlying the compliance software for the Title 24 performance approach. Updates to the Title 24 alternative compliance method are needed to ensure that modeled performance accurately reflects proposed designs, and to properly allow buildings with radiant systems to take appropriate credit for their performance. This study provided a background and roadmap of the steps needed to provide effective coverage of radiant systems for Title 24 compliance. Listed below are topics that are recommended to be added to the ASHRAE Standards and Handbooks.

• Provide consistent definitions for different radiant system types in ASHRAE Handbook System and Equipment, Chapter 6 (Radiant Heating and Cooling).

• Provide comfort data in real radiant buildings in ASHRAE Handbook System and Equipment, Chapter 6 (Radiant Heating and Cooling).

• Provide revised cooling load definitions and calculations in ASHRAE Handbook Fundamentals, Chapter 18 (Nonresidential Cooling and Heating Load Calculations) and ASHRAE Handbook Fundamentals, Chapter 19 (Energy Estimating and Modeling Methods).

• Provide revisions to account for effect of night cooling for buildings conditioned by radiant system in ASHRAE Handbook Fundamentals, Chapter 18 (Nonresidential Cooling and Heating Load Calculations), ASHRAE Handbook Fundamentals, Chapter 19 (Energy Estimating and Modeling Methods), ASHRAE Guideline 36-2018 (High-Performance Sequences of Operation for HVAC Systems), and ASHRAE Handbook Systems & Equipment, Chapter 6 (Radiant Heating and Cooling).

• Provide new design guidance to account for the impacts of direct solar radiation on chilled radiant floors in ASHRAE Handbook Applications, Chapter 54 (Radiant Heating and Cooling), and ASHRAE Handbook System and Equipment, Chapter 6 (Radiant Heating and Cooling).

• Provide new design guidance to account for the impacts of acoustical ceiling panels and clouds on cooling capacity of radiant ceiling slabs in ASHRAE Handbook System and Equipment, Chapter 6 (Radiant Heating and Cooling).

• Provide new design guidance to account for the impacts of air movement from ceiling and other fans on cooling capacity for both radiant ceilings and floors in ASHRAE Handbook System and Equipment, Chapter 6 (Radiant Heating and Cooling).

Cover page of Cooling Load and Design Sizing Report

Cooling Load and Design Sizing Report

(2018)

The current standard procedure for design sizing of cooling systems is not well suited for design of buildings with radiant cooling. There are several reasons that the standard design procedure for radiant cooling systems (ASHRAE Systems & Equipment 2016 Chapter 6: Radiant Heating and Cooling) is flawed, including that the current standard definition of space cooling load (ASHRAE Fundamentals 2017 Chapter 18: Nonresidential Cooling and Heating Load Calculations) omits fundamental principles that are essential to the operation of radiant cooling. This report identifies several specific shortcomings with the current standard cooling load definition and with the standard cooling system design sizing procedure. We explain the fundamental flaws with each, discuss why addressing these shortcomings is especially important to the optimal design and operation of radiant cooling systems, and provide general recommendations for how the procedures ought to be improved. The issues and recommendations presented in this report have been informed by several research projects conducted as part of the CEC EPIC research program Optimizing Radiant Systems for Energy and Comfort (EPC-14-009). In addition to identifying specific flaws with standard cooling load and design sizing procedures, we also discuss how each aspect of our research has provided evidence about or potential solutions to each issue.

Cover page of Comparison of construction and energy costs for radiant vs. VAV systems in the California Bay Area

Comparison of construction and energy costs for radiant vs. VAV systems in the California Bay Area

(2018)

The goal of this study was to perform a design stage cost analysis comparing a selected radiant building against an identical building with a traditional variable air volume (VAV) system. Major findings from the cost estimates include:

• The radiant HVAC design has a total cost of $38.9/ft2 compared to $29.9/ft2 for the VAV design, representing a $9.0/ftpremium for the radiant design.

• The higher costs for the radiant system can largely be attributed to higher piping labor costs for piping and radiant equipment, which itself is $9.8/ft2 higher than that for the VAV design.

• Since labor rates are higher in the San Francisco Bay Area, for the estimated national average labor rate, the premium for radiant is $6.8/ft2, compared to the VAV system. The high installed cost for the radiant equipment is partly a reflection of the current radiant manufacturers’ pricing strategies and the contractors’ bidding practices. The radiant market is relatively small and immature in the United States, especially compared to the well-established VAV market. Alternative design approaches are discussed that may reduce first costs and/or energy costs. Energy models of the two designs (radiant and VAV) were developed in EnergyPlus to evaluate the corresponding energy and comfort performance. In the VAV system model, the controls are generally based on the recently published ASHRAE Guideline 36 (ASHRAE, 2018), which provides high performance sequences of operation for VAV systems. However, for the hybrid radiant slab and DOAS system, there are no well-established control sequences readily available. The annual simulation results show that the total site HVAC energy use is 16.2% higher for the radiant system (2.9 kBtu/ft2) than the optimized VAV design (2.5 kBtu/ft2). The report contains further discussion of opportunities to improve the energy performance of radiant systems. For example, in mild climates, such as the Bay Area in California, radiant designs should take advantage of the benefits of free cooling as much as possible either with airside or waterside economizers.