Building HVAC Systems Research Articles

The fieldwork and control engineering studies on thermal comfort of occupants in a conventional office building in the tropics

This paper presents the fieldwork and the control system studies to examine and improve the thermal comfort of the occupants in a typical office building in Malaysia. The proposed control system works as the basis of adjusting the thermostat setting at a certain period of time with the degree of using the fuzzy logic. The thermostat of the central AC system has its set point fixed between 21℃ and 22℃, slightly below the range of 23–26℃ as recommended by Malaysian Standard MS1525. In order to maintain the room comfort, the occupants choose to switch OFF the central AC system for a certain period of time before it is switched back ON. It has been repeated at least once per working days. Therefore, the proposed control system is designed to overcome this practice. Pre- and post-comfort surveys have been conducted where the thermal comfort level of the occupants throughout this study is investigated. The air temperature ( Ta), globe temperature ( Tg), air velocity ( V) and relative humidity ( RH) in the occupied area were data-logged for continuous five working days. These data are used to compute the operative temperature ( Top) before new thermostat set points are generated, which indicates possible adjustment from the recommended set-point (24℃). The proposed thermostat setting has an error tolerance of 2.9% or less. As a result, the simulation results show an adjustment of the thermostat setting from 24℃ to 25.5℃, which successfully maintained the room temperature of the main office between 23.3℃ and 25℃. The relative humidity is maintained between 54.3% and 59.8%. Also, these outcomes have indirectly promoted an average increase of 22.6% in the thermal comfort satisfactory level of the occupants. Practical application: The new conclusions from the simplified thermostat control strategy, which can be customised according to the environment variables in the air-conditioned space (in this case the operative temperature and the relative humidity) or based on the preferences of the occupants, such as the level of thermal comfort that suits the current thermal environment in tropical climates, could be applied as an important guide for building services engineers and researchers. Their aims are to reduce energy usage in HVAC systems in the non-green office buildings in tropical climates while maintaining an adequate thermal comfort level, and thus, the performance and well-being of the office workers are improved.

The energy saving potentials of zone-level membrane-based enthalpy recovery ventilators for VAV systems in commercial buildings

Enthalpy recovery ventilators exchange heat and mass between exhausted air and outdoor ventilation air to reduce mechanical ventilation loads for HVAC systems in buildings. This study demonstrates the energy saving potential of integrating membrane-based energy recovery ventilators at zone-level into the conventional variable air volume (VAV) systems for commercial buildings. Building energy simulations are used to evaluate various operation strategies and potential energy savings for four selected climates including Minneapolis, Atlanta, Baltimore, and Miami. A medium-size DOE reference commercial building model with conventional VAV systems was used as a baseline. Three cases implemented with energy recovery ventilators were simulated using EnergyPlus and their results were compared with baseline cases in compliance with ASHRAE standard 90.1. The annual HVAC energy saving potential can reach up to 18–49% with this technique for various climates. The challenges of implementing and operating the zone-level energy recovery ventilators are also discussed in this paper.

Effect of Building Orientation and Window Glazing on the Energy Consumption of HVAC System of an Office Building for Different Climate Zones

Building orientation, i.e the positioning of building on site, is an important and foremost step during the construction of building. The orientation decides the amount of daylight and natural ventilation which can enter the building. As these days, most of the office space is centrally air conditioned, this paper explores the role of building orientation and window glazing, on the energy consumption of HVAC system of an office building. This paper considers a mid-rise four floor office building in Bangalore, models the building in various geographical orientations and through simulations, and determines the best orientation of the building such that the energy expenditure in rms of cooling and ventilation is minimal. Further simulations are carried out in different temperature zones in India by simulating the same office space in different locations, across India vis New Delhi, Chennai and Ahmedabad and the best orientation for placing the building is found. On realizing the best orientation, the window glazing values are varied for four suitable values of glazing and the most energy efficient glazing providing the least load on the HVAC system is found. The paper concludes with recommendations to reduce the energy consumption of the HVAC system in different zone.

Experimental analysis of performance, greenhouse gas emissions and economic parameters for two cooling systems in a public administration building

More than a quarter of the non-residential buildings in Europe are public buildings and their energy consumption is forty percent higher than that of residential buildings. Therefore, promoting a public policy to increase energy efficiency of the HVAC systems in public buildings will have a significant impact in reducing global energy consumption.In order to have a precise estimation of the impact of the substitution of the HVAC systems in a large number of public buildings, it is essential to have accurate data of the performance of these systems in specific buildings, beyond the technical specifications stated by the manufacturers. In this paper the substitution of the wide-spread, conventional air-condensed chiller (ACC) for a water-condensed chiller (WCC) with a dry-adiabatic cooler in a public administration building is analyzed in terms of energy efficiency, economic return of the required investment and environmental implications. The influence of external factors as well as the load effect are quantified. The results show that the seasonal Energy Efficiency Ratio of the WCC is near twice that of the ACC, making the replacement of the ACC for the WCC an interesting option. The results obtained in this study could be extrapolated to other non-residential public buildings.

Optimal Operation of ERV System Installed in the Apartment Houses in South Korea

High air-tightness and high heat-insulation of buildings cause lack of fresh air inside the buildings. Operating the ventilation system in an apartment house may improve the indoor air quality, but may generate the problems, such as high airconditioning load and cold draft. In order to improve the indoor air quality while maintaining pleasant heat environment to a certain level, it is necessary to consume energy for cooling and heating. Energy Recovery Ventilation system (here in after “ERVs”) is the typical way to minimize the consumption of energy. To solve the problem, the installation of ERVs has been made mandatory for new apartment buildings that are constructed in the Republic of Korea. The interest in ERVs has increased recently in that the System is viewed as helping to: 1. Reduce energy costs of heating and cooling apartment buildings, which costs claim a significant portion of apartment building management budgets, and 2. Secure appropriate levels of ventilation in such buildings. Despite the enthusiasm, the lack of efficient implementation of ERVs persists. Based on the rationale, this study realized the optimal operating algorithm for ERVs. The study took actual data on temperature and humidity; operation status on air conditioners and ERVs; electricity consumptions; and PMV. The study analyzed airconditioning ventilation loads and energy-saving effects related thereto according to the optimal operating algorithm for ERVs. The results showed statistically significant figures that contribute to the reduction of loads and energy costs. Implications of the study include: 1. Introducing the optimal ERVs to apartment buildings will likely help the residents and building managers to better respond to changes occurring to the outside environment and to the inside loads being applied to indoor HVAC systems; and 2. Implementation of ERVs would likely help reduce the loads being imposed on the HVAC systems in apartment buildings.

Smart grid coordination in building HVAC systems: Computational efficiency of constrained economic linear optimal control

In the context of day-ahead or real-time electricity prices, the method of economic model predictive control has been shown to provide expenditure reduction in building HVAC systems, specifically if coupled with active thermal energy storage. However, due to the diurnal nature of electricity prices, these expenditure reductions can only be achieved if the economic model predictive control prediction horizon is sufficiently large, typically greater than 12 h. This work develops an alternative controller known as constrained economic linear optimal control. This constrained economic linear optimal control policy is shown to yield economic performance similar to a large-horizon economic model predictive control policy but also possesses a virtual insensitivity to horizon size. Thus, application of the constrained economic linear optimal control policy will require a fraction of the computational effort while yielding nearly identical economic performance.

Simulation and experimental demonstration of model predictive control in a building HVAC system

This article presents the framework and results of implementing optimization-based control algorithm for building HVAC systems and demonstrates its benefits through reduced building energy consumption as well as improved thermal comfort along with lessons learned. In particular, a practically effective and computationally efficient model predictive control algorithm is proposed to optimize building energy usage while maintaining thermal comfort in a multi-zone medium-sized commercial building. This article has two themes. Driven by the challenge of fully evaluating the benefit of the proposed model predictive controller against baseline control, a model predictive control design framework is first presented with its performance benchmarked based on a high-fidelity building HVAC simulation environment to verify its effectiveness and feasibility. Following the same model predictive control design framework, the experimental results from the same building located at the Philadelphia Navy Yard are then presented. For the simulation study, the performance of the model predictive control algorithm was estimated relative to baseline days with exactly the same internal loads and outdoor conditions, and it was estimated that model predictive control reduced the total electrical energy consumption by around 17.5%. For the subsequent experimental demonstration, the performance of the model predictive control algorithm was estimated relative to baseline days with similar outdoor air temperature patterns during the cooling and shoulder seasons, and it was concluded that model predictive control reduced the total electrical energy consumption by more than 20% on average while improving thermal comfort in terms of zone air temperature.

Fault-tolerant optimal control of a building HVAC system

This article presents the development and application of a fault-tolerant control technology, its online implementation, and results from several tests conducted for a large-sized HVAC system. By integrating model-based model predictive control and data-driven fault detection and diagnosis algorithms, the technology automatically adapts the HVAC control laws to a set of subsystem faults and can therefore reach and maintain the largest energy consumption reduction levels that are achievable at any point throughout a building lifecycle. The model predictive control algorithm generates optimal set-points that minimize energy consumption for the HVAC actuator loops while meeting equipment operational constraints and occupant thermal comfort constraints. The fault detection and diagnosis algorithm uses probabilistic graphical models to detect and classify in real time potential faults of the HVAC actuators based on data from multiple sensors. The fault-tolerant control system is realized by executing the two algorithms on the same platform, within the same framework, and by using the fault detection and diagnosis algorithm's output to continuously update the model predictive control algorithm constraints. The proposed integrated technology is executed at the supervisory level in a hierarchical control architecture as an extension of a baseline building management system. The performance and limitations of the fault detection and diagnosis, model predictive control, and fault-tolerant control algorithms are illustrated and discussed using measurement data recorded from multiple tests.

Experimental and Simulation Study on the Performance of Counter Flow Closed Cooling Tower Systems

Cooling towers are required in building HVAC systems that use water as the cooling condenser fluid. Cooling towers used in this study are of the forced draft, counter flow, indirect/closed evaporative type. This study sought to demonstrate the performance characteristics of a closed system cooling tower by its effectiveness value, Number of Transfer Units (NTU), cooling capacity, and overall heat transfer and mass coefficient of the cooling tower. Experiments were performed on a heat exchanger coil intercrossed with ⅜ inch diameter intersections on parallel lines. Results of the experiment were then compared with the heat and mass transfer correlations taken from previous studies, and also combined with Computational Fluid Dynamics (CFD) simulations to examine the physical processes that occur in the cooling towers. All the experimental results, theoretical calculations and CFD simulations used variations of warm water mass, cold air, and water spray to present a clear description of the performance characteristics of a closed system cooling tower. The results of this study have shown that an increase in the amount of water spray mass flow causes an increase in the effectiveness value, heat transfer and overall mass transfer, as well as the cooling capacity of the cooling tower. The waste heat typically utilizes up to 80% of latent evaporation heat, and 20% of sensible air heat; however, waste heat in the closed system cooling tower utilizes 100% of latent evaporation heat. The mass transfer coefficient rate tends to be stable for a small mass of water spray.

Control strategies for integration of thermal energy storage into buildings: State-of-the-art review

Thermal energy storage (TES), together with control strategies, plays an increasingly important role in expanding the use of renewables and shifting peak energy demand in buildings. Different control strategies have been developed for the integration of TES into building-related systems, mainly including building envelopes, HVAC systems and hot water tanks (HTWs). A systematic survey of control strategies using TES in the building-related systems is still lacking. This paper presents a comprehensive review of these control strategies. It provides a summary of the applied strategies and makes recommendations for future studies. Considering that control techniques serve as a basis for the implementation of control strategies, typical control techniques utilized in the building systems, as well as their strengths and weaknesses associated with the application, are also introduced to help users gain a better understanding.

Experimental evaluation of occupancy-based energy-efficient climate control of VAV terminal units

Results are presented from a nearly week-long experimental evaluation of a scalable control algorithm for a commercial building HVAC system based on real-time measurements of occupancy obtained from motion detectors. The control algorithm decides air flow rate and amount of reheat for each variable air volume terminal box based on real-time measurements of occupancy and space temperature. It is a rule-based controller, so the control computations are simple. The experiments showed that the proposed controller resulted in 37% energy savings over baseline on average without sacrificing indoor climate. In contrast to prior work that reports energy savings without a careful measure of the effect on indoor climate, it is verified that the controller indeed maintains indoor climate as well as the building's baseline controller does. This verification is performed from measurements of a host of environmental variables and analysis of before/after occupant survey results. A complete system required to retrofit existing buildings with the controller is presented, which includes a wireless sensor network and a software execution platform. Two useful observations from this work are: (i) considerable energy savings—along with compliance with ASHRAE ventilation standards—are possible with simple occupancy-based control algorithms that are easy to retrofit; and (ii) these savings are attained with binary occupancy measurements from motion detectors that do not provide occupancy-count measurements. Results also show that there is a large variation in energy savings from zone to zone and from day to day.

Strategies and technology solutions for the optimal management of building - HVAC system

Despite increasing attention is paid to the development of strategies and innovative technology solutions for the energy efficiency of building components and systems, especially in the residential sector not much has been deepened on the optimal management of the building-HVAC system. In relation to the specific Mediterranean climatic context of the city of Bari, and in reference to a singlefamily-residential buildings type, different solutions for the energy efficiency and its optimal management have been evaluated through dynamic energy and economic analyzes.

A convex approach to a class of non-convex building HVAC control problems: Illustration by two case studies

In this paper, a convexification approach is presented for a class of non-convex optimal/model predictive control problems more specifically applied to building HVAC control problems. The original non-convex problems are convexified using a convex envelope approach. The approach is tested on two case studies: a benchmark building HVAC system control problem from the literature and control of a hybrid ground-coupled heat pump (HybGCHP) system. For the first application, convexified model predictive control was used and results were compared with fuzzy and adaptive control results. For the HybGCHP system, convexified optimal control was applied and the results were compared with dynamic programming based optimal control. In the first case superior performance was observed over the corresponding fuzzy and adaptive control results from the literature. For the HybGCHP system the associated convexified optimal control gave almost global optimal results in terms of responses and cost criteria. The suggested method is especially useful for optimal building HVAC control/design problems which include non-convex bilinear or fractional terms. Since a polynomial expression can be recursively expressed as a system of bilinear equations, the proposed method, in principle, can be applied to all systems where polynomial non-convexities exist.

RATING OF INDOOR ENVIRONMENTAL QUALITY IN SYSTEMS OF SUSTAINABILITY ASSESSMENT OF BUILDINGS

Indoor environmental quality (IEQ) has an important impact on health and wellbeing of building users. In order to maintain an acceptable IEQ, policies, strategies and guidelines on achieving the required IEQ have been developed. Control and evaluation of indoor air factors is needed for ensuring the sufficient air quality. Impact of emmisions from building materials, furnishings and HVAC systems to indoor air quality should be included in the assessment of indoor environmental quality. In many systems for sustainability assessment of buildings is put a great emphasis on indoor environmental quality. This paper provides an overview of sustainability assessment systems for rating of indoor environmental quality. The criteria included in LEED, BREEAM and other well known systems for assessment of indoor environmental quality are presented. Building environmental assessment system (BEAS) developed for application in Slovakia is also introduced. Worldwide used rating systems were based on the development of BEAS. This is multi-criteria system contained six main fields such as site selection and project planning; building construction; indoor environment; energy performance; water and waste management. System consist from 53 indicators of assessment.

Energy Saving Effect of Integrated Piping in Building HVAC System

Energy Saving Effect of Integrated Piping in Building HVAC System

Wireless sensors system for the chillers fault diagnostic based on characteristic Petri net modelling

The chillers are important refrigeration components of building air-conditioning systems and their operational status is directly related to the building's HVAC system performance and stability. The issue of fault diagnosis of chillers has received wide attention. This paper will feature Characteristic Modelling Technology in fault diagnosis for chillers and modelling with fuzzy Petri net technique. Using fuzzy Petri nets knowledge representation and inference algorithm for matrix operations describes the characteristic parameters of chiller fault indication and relationships. Using the proposed diagnostic systems can take full advantage of the information resources of characteristic parameters for fault diagnosis, and according to chiller efficiency indexes of COP a comprehensive diagnosis of fault diagnosis and chiller can run efficiently. The test results of plant running show the feasibility and accuracy of the fault diagnostic system.

Energy performance modelling and heat recovery unit efficiency assessment of an office building

This paper investigates and analyzes a typical multi-zone office building?s annual energy performance for the location and climate data of central Belgrade. The aim is to evaluate the HVAC system?s and HR unit?s performance in order to conduct the most preferable heating and cooling solution for the typical climate of Belgrade city. The energy performance of four HVAC system types (heat pump - air to air, gas-electricity, electrical and fan coil system) was analyzed, compared and evaluated on a virtual office building model in order to assess the total annual energy performance and to determine the efficiency of the HR unit?s application. Further, the parameters of an energy efficient building envelope, HVAC system, internal loads, building operation schedules and occupancy intervals were implemented into the multi-zone analysis model. The investigation was conducted in EnergyPlus simulation engine using system thermodynamic algorithms and surface/air heat balance modules. The comparison and evaluation of the obtained results was achieved through the conversion of the calculated total energy demand into primary energy. The goal is conduct the most preferable heating and cooling solution (Best Case Scenario) for the climate of Belgrade city and outline major criteria in qualitative enhancement.

Computational Fluid Dynamic Modeling of Horizontal Air-Ground Heat Exchangers (HAGHE) for HVAC Systems

In order to satisfy the requirements of Directive 2010/31/EU for Zero Energy Buildings (ZEB), innovative solutions were investigated for building HVAC systems. Horizontal air-ground heat exchangers (HAGHE) offer a significant contribution in reducing energy consumption for ventilation, using the thermal energy stored underground, in order to pre-heat or pre-cool the ventilation air, in winter and summer, respectively. This is particularly interesting in applications for industrial, commercial and education buildings where keeping the indoor air quality under control is extremely important. Experimental measurements show that, throughout the year, the outside air temperature fluctuations are mitigated at sufficient ground depth (about 3 m) because of the high thermal inertia of the soil, the ground temperature is relatively constant and instead higher than that of the outside air in winter and lower in summer. The study aims to numerically investigate the behavior of HAGHE by varying the air flow rate and soil conductivity in unsteady conditions by using annual weather data of South-East Italy. The analysis shows that, in warm climates, the HAGHE brings a real advantage for only a few hours daily in winter, while it shows significant benefits in the summer for the cooling of ventilation air up to several temperature degrees, already by a short pipe.

Green Building Studio Test Result Comparison with Test from ANSI ASHARE Standard 140-2011

Computer simulation is an important and proven method to help understand and analyze the thermal performance of buildings, and predict their operational energy consumption. Building energy simulation is widely used to help design energy efficient building envelopes and HVAC systems, develop and demonstrate compliance of building energy codes, and implement building energy rating programs. However, large discrepancies exist between simulation results from different building energy modeling programs. This leads many common users lack confidence in the results from building simulation methods.

A case study of a high end residential condominium building acoustical design and field performance testing

A high end multi-owner condominium building complex consists of 314 units configured in a central tower with a 39-story central core, as well as 21 and 30 story side towers. A series of project specific acoustical design considerations related to condominium unit horizontal and vertical acoustical separation as well as background noise control for building HVAC systems were developed for the project construction documents and later field tested to confirm conformance with the acoustical design criteria. This paper presents the results of these building wide field tests as well as a discussion of pitfalls encountered during design, construction, and post-construction.