Operation Of HVAC Systems Research Articles

Research on short-term and ultra-short-term cooling load prediction models for office buildings

Building cooling load predictions can be used to better understand energy demands and to improve the energy efficiency of HVAC systems. In this study, GA-SVR and GA-WD-SVR prediction models for short-term and ultra-short-term predictions for office buildings are established. The short-term cooling load prediction model is designed to outline an HVAC system’s operation strategies for the following day. The ultra-short-term cooling load prediction model is designed to inform building managers of the cooling load for the next hour and to adjust HVAC system operations in advance. An office building in Tianjin is used to train and evaluate the load prediction models. Meteorological data and one-day-ahead and one-hour-ahead cooling load records are used as model inputs. The prediction results indicate that the GA-SVR prediction model performs better for short-term cooling load prediction with MRE and R2 of 6.5% and 73.1%, respectively, while the GA-WD-SVR prediction model performs better for ultra-short-term cooling load prediction with MRE and R2 of 4.6% and 88.7%, respectively.

Energy conservation through flexible HVAC management in large spaces: An IPS-based demand-driven control (IDC) system

Abstract Buildings consume substantial amounts of energy and require sophisticated control strategies to fulfill occupants' comfort requirements. In large spaces, various occupancy patterns result in uneven load distributions, requiring high-resolution occupancy information for sufficient system control. In recent years, the development of indoor positioning systems (IPS) enabled the possibility of more scientific and precise occupancy detection systems, leading to better operation of buildings' HVAC systems. This paper proposes a demand-driven control system for air conditioner control in large spaces based on IPS. The proposed system focuses on optimizing the ventilation rate based on number of occupants and their spatial distribution in an experimental space. A dual-network (Wi-Fi network and BLE network) indoor positioning system is installed to collect the occupancy data and guide the operation of Variable-Air-Volume (VAV) boxes. The energy-saving potential of the proposed system is examined with a computational fluid dynamics (CFD) model in terms of temperature distribution and energy consumption. This study also explores the interrelationship between cooling load variation and occupancy pattern under different control mechanisms. The final results show the proposed system has significant energy-saving potential by avoiding over-cooling in unevenly distributed occupancy conditions.

Data analytics for occupancy pattern learning to reduce the energy consumption of HVAC systems in office buildings

In the last few years, the collecting and processing of occupancy data have become emerging issues since they can affect, either directly or indirectly, several energy operations in buildings. The application of data analytics-based methods makes it possible to exploit the potentialities of occupancy related knowledge to enhance the energy management in buildings. A methodology, aimed at implementing an occupancy-based HVAC system operation schedule, is presented in this article. The process is based on the convenience of displacing groups of occupants with similar occupancy patterns to the same thermal zone. An optimisation of the stop schedule of an HVAC system has been investigated, considering a typical week’s occupancy patterns. The methodology was used to analyse the Zaanstad Town Hall (The Netherlands), considering anonymous occupancy data for a monitoring period of four months. The resulting optimised schedule was tested, through an energy simulation approach, considering a model calibrated with real energy consumption data. The savings related to the energy consumption of the HVAC system, as a result of the implementation of the strategy, in comparison to an occupancy-independent operation schedule amounted to 14%. The proposed process can be generalized and drive energy managers in evaluating optimised occupancy-based HVAC system operation schedules.

Optimization of roof solar reflectance under different climate conditions, occupancy, building configuration and energy systems

Cool roofs have been widely proved to represent an effective strategy for building thermal-energy performance improvement during the cooling season. However, their effectiveness along the whole year can be affected by building features and other boundary conditions. The present work aims at assessing the energy performance of high solar reflectance roof solutions in different climate zones, when implemented in a variety of building typologies. Therefore, an optimization study was carried out to select the optimum roof solar reflectance able to minimize building annual HVAC energy consumption. In this work, Italian climate zones were considered as case study conditions. The analysis was performed through dynamic simulation of validated standard ASHRAE building reference models. Moreover, the role of (i) type of HVAC system operating, (ii) presence and intensity of internal gains, and (iii) roof thermal insulation level was evaluated on the resulting optimum roof reflectance capability. Results show that the optimum roof solar reflectance varies under different climate conditions, mainly depending on heating or cooling dominated conditions. However, all further analyzed boundary conditions, i.e. building typology, HVAC system, internal gains, and roof insulation level, affect building energy performance and, therefore, the optimum roof reflectance identification. In the hottest climate, the optimum roof solar reflectance resulted to be consistently equal to the maximum considered, i.e. 0.8, also with varying the other parameters. Moreover, the annual HVAC energy need is more sensitive to roof reflectance in the apartment building, showing 17% of energy savings with standard model characteristics. On the other hand, in heating dominated climates, the optimum roof solar reflectance is more variable, ranging over all the considered values, because it is affected by the additional boundary conditions. On the contrary, the variability of HVAC need due to roof solar reflectance variation is generally lower.

Thermal Load Reduction with Green Building Envelope

Various studies have confirmed that high thermal resistance in roof & wall can reduce the heat transfer load of the buildings. In this study, experimental investigation of the effects of some sustainable features (such as green roof, reflective coated roof & Fly ash brick (FAB) etc.) on the building has been conducted in the Indian context. For the purpose, two scaled building models i.e. Model I (conventional design) & Model II (green design) have been examined with different design configurations. The sensible heat transfer (SHT) load of the building is reduced by 21% - 29% through the use of FAB with cavity wall in place of Fired clay brick (FCB) wall. The load reduction increases to 26% - 44% by using FAB cavity wall with reflective coating on the roof. This reduction further increases to 64% - 68% with FAB cavity wall along with green roof. In this final scenario, the monthly electrical energy saving for air-conditioning is approximately 5.1 kWhe/m2 per unit envelope area, with associated reduction in GHG emissions up to 6.36 kg CO2eq/m2 per unit envelope area, assuming continuous operation of HVAC systems.

IMPACT OF RETROFITTING ENERGY-EFFICIENT DESIGN STRATEGIES ON ENERGY USE OF EXISTING COMMERCIAL BUILDINGS: COMPARATIVE STUDY OF LOW-IMPACT AND DEEP RETROFIT STRATEGIES

This article discusses energy-efficient retrofitting design strategies for commercial office buildings, and examines their effect on energy consumption. The objective of the research was to study how to integrate passive design strategies and energy-efficient building systems to improve building performance, and reduce the energy consumption of existing buildings in three different climate types (cold, mixed and hot climates). First, properties of existing buildings were analyzed based on national CBECS database to determine typical characteristics of office buildings located in Chicago, Baltimore and Phoenix, including size, building envelope treatment and building systems. Then, fourteen different prototypes were developed, varying the building shape and orientation to represent different building stock, and energy modeling was conducted to establish energy usage baseline. Multiple design considerations were investigated based on extensive energy simulations and modeling, where low-impact and deep retrofits were considered. Low-impact strategies included improvements to the building envelope, lighting systems and optimization of HVAC systems operation (without upgrading heating and cooling equipment). Deep energy retrofits also included improvements to building envelope and lighting, and considered changes and improvements to HVAC systems (specifically, integration of radiant systems). Energy modeling was conducted for all prototypes, and results were obtained for the baseline (current energy usage), and energy usage considering low-impact design strategies and deep retrofits. A total of 126 energy models was developed, simulated and analyzed, providing a dataset that captured energy usage for investigated scenarios. The comparative analysis of simulation results was used to determine how specific techniques lead to energy savings in different climate types, as well as for buildings of various shapes and orientations.

Thermal Comfort and HVAC Systems Operation Challenges in a Modern Office Building – Case Study

Abstract The aim of the study is to evaluate the indoor environment conditions in the new-built office building, Energetikum, and consequently suggest the control strategies, which can lead to determination of critical areas and elimination of thermal discomfort. Representative offices have been selected and equipped with portable sensor groups for monitoring of the indoor environment parameters. Contribution is presenting the data obtained from 6 selected rooms during 3 reference weeks - heating, transition and cooling period. The measured results indicate overheating of the rooms, particularly in the ones with the large glazed areas with higher solar gains. The values of indoor air temperature during heating and transition period could not meet the normative criteria according to standard EN 15251:2007 (the cat. II.) during 13 % - 49 % of evaluated time intervals. Consequently, the simulation model of the selected office was created and is pointing to the possibilities of the control system improvement, which can lead to an elimination of the problem with overheating.

Benchmarking Analysis of Energy Consumption in Supermarkets

The energy performance of buildings needs to be monitored and maintained. A well-developed energy management system in the building can help to identify failures in a timely manner and reduce excessive energy consumption. This study attempts to introduce awareness on potential energy savings in supermarkets. A supermarket in Latvia is analysed as a case study. The largest consumption of energy in supermarket was determined to derive from operation of refrigeration systems, HVAC systems and lighting. The methodology used in this study is based on benchmarking analysis. Using benchmarking analysis, the specific energy amount in function of the amount of customer in supermarket is studied in this work. The specific energy consumption shows wide dispersion: from 1.06 kWh per customer up to 1.73 kWh per customer. This leads to a variance of 48% of consumed electricity for one customer. The variance can be explained by various technological and climate factors, but even more importantly - behavioural factors.

Demand response control of residential HVAC loads based on dynamic electricity prices and economic analysis

During peak hours, electrical loads of residential HVAC systems can cause imbalance between electricity supply and demand. Demand response control has the potential to facilitate supply–demand balance. The demand side load control can help reduce electricity consumption through demand response programs. Since HVAC loads are the major contributors to peak loads, reducing HVAC load at peak hours is an objective of many demand response technologies. This article analyzes performance of the dynamic thermostat controller of HVAC systems in homes that have dynamic price of electricity. Based on a price signal, the dynamic thermostat controller sets back the thermostat temperature to save electricity consumption and costs. The consumers choose participation in the demand response program based on the real-time price of electricity and set a threshold price that the thermostat uses to set the temperature during peak power price period. The performance of dynamic thermostat controller was analyzed for two cities, Austin TX and Chicago IL, and historical market price data were used to generate hourly based real-time price. In addition to different climate zones, two different types of residential buildings were modeled. Based on detailed energy simulation, the changes in HVAC system operation were analyzed when considering electric energy saving, peak power reduction, cost saving, as well as the potential thermal discomfort. The specific results show that dynamic pricing combined with dynamic thermostat controller results in 12% annual energy cost savings for HVAC operation with the energy saving of up to 6%, but without significantly changing the thermal comfort.

Thermal performance and cost analysis of mortars made with PCM and different binders

The high energetic consumption is one of the biggest concerns of modern society. The incorporation of phase change materials (PCM) in construction materials allows regulates the temperature inside the buildings. The main objective of this study was the characterization of the thermal performance of PCM mortars based in different binders. It was possible to observe that the incorporation of PCM in mortars leads to a decrease of the maximum temperatures, increase of the minimum temperatures, significant lag time delay, reduction of the heating and cooling needs, and consequent decrease of the cost of HVAC systems operation, for all tested seasons.

Simplified dynamic neural network model to predict heating load of a building using Taguchi method

Prediction of heating and cooling loads is necessary for building design and HVAC system operation, in order to reduce energy consumption. This study intended to develop a method for the prediction of the instantaneous building energy load, depending on various combinations of input parameters using a dynamic neural network model. The heating load was calculated for a typical apartment building in Seoul for a one-month period in winter using the Energy-Plus software. The data sets obtained were used to train neural network models. The input parameters included dry-bulb temperature, dew point temperature, direct normal radiation, diffuse horizontal radiation, and wind speed. The Taguchi method was applied to investigate the effect of the individual input parameters on the heating load. It was found that the outdoor temperature and wind speed are the most influential parameters, and that the dynamic model provides better results, as compared with the static model. Optimized system parameters, such as number of tapped delay lines and number of hidden neurons, were obtained for the present application. The results of this study show that Taguchi method can successfully reduce number of input parameters. Moreover dynamic neural network model can predict precisely instantaneous heating loads using a reduced number of inputs.

Hygiene guideline for the planning, installation, and operation of ventilation and air-conditioning systems in health-care settings - Guideline of the German Society for Hospital Hygiene (DGKH).

Since the publication of the first “Hospital Hygiene Guideline for the implementation and operation of air conditioning systems (HVAC systems) in hospitals” (http://www.krankenhaushygiene.de/informationen/fachinformationen/leitlinien/12) in 2002, it was necessary due to the increase in knowledge, new regulations, improved air-conditioning systems and advanced test methods to revise the guideline. Based on the description of the basic features of ventilation concepts, its hygienic test and the usage-based requirements for ventilation, the DGKH section “Ventilation and air conditioning technology” attempts to provide answers for the major air quality issues in the planning, design and the hygienically safe operation of HVAC systems in rooms of health care.

Global Optimization of the Production and the Distribution System for Typical European HVAC Systems

European countries have agreed on a new 2030 Framework with a 30% improvement in energy efficiency compared to projection and a 40% cut in greenhouse gas emissions compared to 1990 levels. With an estimated 11% of all the electrical energy used in Europe consumed by HVAC systems, the improvement of their efficiency is a key element to reach these targets. When looking at the energy flow in typical European HVAC systems, one can observe important degradation in efficiency associated to heating and cooling energy transportation systems together with a non-optimal use of the production plant. These inefficiencies are direct consequences of the system design with, quite often, a lack of consideration of the system part load or its off-design operation. This research attempts to identify the sensitivity of both cooling and heating HVAC systems to these conditions and to propose an approach to optimize the design and the operation of HVAC systems integrated in buildings considering trade-off between primary systems efficiency, distribution losses and auxiliaries consumption.

Application of a simplified thermal network model for real-time thermal load estimation

Heating and cooling loads are the major reasons for energy use in buildings. Buildings are usually subject to schedules and set-points which are not optimized in response to the dynamic weather conditions, internal loads, and occupancy patterns. The thermal network model has been widely applied for real-time building load estimation, which is crucial for optimizing the operation of the HVAC system. However, there has been limited exploration of the capabilities of the thermal network model due to constraints imposed by the solution method adopted. In this paper, the exponential matrix method was adopted to simplify the state space equations and solve the thermal network model analytically. This enhances the applications of a simplified thermal network model for investigation of multiple scenarios of HVAC system operations and equipment sizing, and for more accurate estimation of heating and cooling loads. This study also proves that the analytical solution method is asymptotically stable regardless of time step. A typical office was used as a case study and the predicted building loads are compared with measured data and numerical results from EnergyPlus. For the case study, the model demonstrated better accuracy and is seen to be robust for thermal load estimation for cooling season.

Thermal comfort in air-conditioned buildings in hot and humid climates--why are we not getting it right?

While there are plenty of anecdotal experiences of overcooled buildings in summer, evidence from field studies suggests that there is indeed an issue of overcooling in tropical buildings. The findings suggest that overcooled buildings are not a consequence of occupant preference but more like an outcome of the HVAC system design and operation. Occupants' adaptation in overcooled indoor environments through additional clothing cannot be regarded as an effective mitigating strategy for cold thermal discomfort. In the last two decades or so, several field studies and field environmental chamber studies in the tropics provided evidence for occupants' preference for a warmer temperature with adaptation methods such as elevated air speeds. It is important to bear in mind that indoor humidity levels are not compromised as they could have an impact on the inhaled air condition that could eventually affect perceived air quality. This review article has attempted to track significant developments in our understanding of the thermal comfort issues in air-conditioned office and educational buildings in hot and humid climates in the last 25 years, primarily on occupant preference for thermal comfort in such climates. The issue of overcooled buildings, by design intent or otherwise, is discussed in some detail. Finally, the article has explored some viable adaptive thermal comfort options that show considerable promise for not only improving thermal comfort in tropical buildings but are also energy efficient and could be seen as sustainable solutions.

Building design and operational choices that impact indoor exposures to outdoor particulate matter inside residences

Much of human exposure to particles of outdoor origin often occurs inside homes where we spend most of our time. This work (1) reviews existing literature on the important parameters governing the infiltration and persistence of particles of outdoor origin in residences, (2) re-analyzes portions of data from recent experimental investigations of submicron particle infiltration and central HVAC system operation in single-family homes, and (3) combines these data to highlight particularly stark differences in particle infiltration factors and human exposures to submicron particles of outdoor origin that are driven by building envelope design, filter choice, and HVAC system design and operation (with an additional focus on data from one low-energy home). Results reveal that envelope design and construction, HVAC filter selection, and HVAC system operation can lead to variations in infiltration factors for submicron particles ranging by a factor of 60 or more from the most protective homes to the least protective homes. Moreover, an additional experiment performed in the most protective low-energy home (when relying on infiltration for ventilation air) was also responsible for the highest amount of outdoor particle infiltration when tested again while using an energy recovery ventilator connected to an outdoor air supply for ventilation air, suggesting that residential mechanical ventilation systems can adversely influence outdoor particle infiltration if improperly installed.

Assessment of condensation of water vapor in the mixing chamber by CFD method

The analyzed topic belongs to the field of design and operation of HVAC systems, focusing mainly on mixing chambers. The paper deals with problems of condensation and freezing of water vapour on walls of mixing chambers in a special case, when the partial pressure of the final resulting state of the mixture of warm moist air and colder air is located above the saturation limit. Experimental in situ methods and computer computational fluid dynamics (CFD) modelling method were used for processing. The main contribution of this work is the finding that partial condensation and freezing of water vapour may occur in local parts of the mixing chamber. It causes problems in terms of hygienic safety and service life of these devices. In particular it has been found that condensation and freezing of water vapour may occur even if relative humidity of the resulting mixture is about 70 %.

A knowledge based approach for selecting energy-aware and comfort-driven HVAC temperature set points

HVAC systems are responsible for providing acceptable thermal conditions and indoor air quality for building occupants. Increasing thermal comfort and reducing HVAC related energy consumption are often seen as conflicting goals. Few researchers have investigated the feasibility of reducing HVAC related energy consumption by integrating occupants’ personalized thermal comfort preferences into the HVAC control logic. In this study, we introduce a knowledge-based approach for improving HVAC system operations through coupling personalized thermal comfort preferences and energy consumption patterns. In our approach, thermal comfort preferences are learned online and then modeled as zone level personalized comfort profiles. Zone temperature set points are then selected through solving an optimization problem for energy, with comfort, indoor air quality, and system performance constraints taken into consideration. In the case that acceptable comfort levels for all occupants of a zone were not achievable, the approach selects set points that minimize the overall thermal discomfort level. Compared to an operational strategy focusing on comfort only, evaluation of our approach, which aims for both maintaining or improving comfort and reducing energy consumption, showed improvements by reducing average daily airflows for about 57.6m3/h (12.08%) in three target zones.

Thermal comfort: Design and assessment for energy saving

Thermal comfort is one of the most important aspects of the indoor environmental quality due to its effects on well-being, people's performance and building energy requirements. Its attainment is not an easy task requiring advanced design and operation of building and HVAC systems, taking into account all parameters involved. Even though thermal comfort fundamentals are consolidated topics for more than forty years, often designers seem to ignore or apply them in a wrong way. Design input values from standards are often considered as universal values rather than recommended values to be used under specific conditions. At operation level, only few variables are taken into account with unpredictable effects on the assessment of comfort indices. In this paper, the main criteria for the design and assessment of thermal comfort are discussed in order to help building and HVAC systems designers and operators to navigate the complex and varied world of standards in the field of thermal environment for improving indoor environmental quality and energy saving. The examples discussed in the paper will also be useful for the standardization, leading to harmonized documents more readable for all users.

초고층 사무소 건물 엘리베이터 홀에서의 연돌현상 저감을 위한 공조가압 방안의 적용

초고층 사무소 건물 엘리베이터 홀에서의 연돌현상 저감을 위한 공조가압 방안의 적용