Optimization of indoor environmental quality and ventilation load in office space by multilevel coupling of building energy simulation and computational fluid dynamics

The fundamentals, implementation, and application of an integrated simulation as an approach for predicting the indoor environmental quality for an open-type office and for quantifying energy saving potential under optimized ventilation are presented in this paper. An integrated simulation procedure based on a building energy simulation and computational fluid dynamics, incorporated with a conceptual model of a CO₂ demand controlled ventilation (DCV) system and proportional integral control of an air conditioning system as the optimization assessment of conceptual model in the occupied zone, was developed. This numerical model quantitatively exhibits energy conservation and represents the non-uniform distribution patterns of airflow properties and CO₂ concentration levels in terms of energy recovery and indoor thermal comfort. By means of an integrated simulation, the long-term energy consumption of heating, ventilation, and air conditioning systems are predicted precisely and dynamically. Relative to a ventilation system with a basic constant air volume supply rate characterized by a fixed outdoor air intake rate from the ceiling supply opening, the optimized CO₂-DCV system coupled with energy recovery ventilators reduced total energy consumption by 29.1% (in summer conditions) and 40.9% (winter).     

Proposal of a modeling approach considering urban form for evaluation of city level energy management

The importance of developing a method to bridge the gap between the current increasing trend of CO₂ emission from the commercial sector and the reduced emission level for ensuring long-term sustainability has increased. Various concepts exist for managing the energy use and CO₂ emission. These concepts can be categorized into advancement in technologies, dissemination of energy saving measures in buildings, optimization of local energy generation and distribution systems, spatial building stock pattern management, and improvement in CO₂ emission factor of the grid electricity. In this paper, we propose a modeling approach for energy use in the commercial sector in order to evaluate the options involved in the abovementioned energy management concepts in an integrated manner. In this modeling approach, a district is dealt with as a basic unit. Districts are first classified into several categories according to the spatial building stock pattern, or urban form. The end-use energy consumption per unit floor area is then calculated for each district category using a simulation of energy use in buildings in a representative district; this is used for quantifying the total end-use energy consumption at the municipal level. We carried out a case study in order to demonstrate the simulation capabilities and features of the suggested modeling approach in contrast with the conventional modeling approaches. In this case study, certain scenarios of CO₂ abatement integrating the energy management concepts are applied in the commercial sector of Osaka city, Japan, in order to investigate alternative avenues toward which policy efforts must be directed.     

A methodology for estimating occupant CO2 source generation rates from measurements in small commercial buildings

It is necessary to know CO₂ source generation rates and system flow parameters, such as supply flow rate and overall room ventilation effectiveness, in order to evaluate cost savings for demand-controlled ventilation applied to commercial buildings. This paper presents a methodology for estimating schedules for generation rates and flow parameters using short-term testing. These parameters are used within a model that predicts return air CO₂ concentrations as part of an overall energy analysis model. As a first step in developing the methodology, two different parameter estimation techniques were evaluated using simulated data. Each method gave models that provide good predictions of return air CO₂ concentrations, but differed in terms of the identified parameters. The preferred parameter estimation method provides estimates of both average hourly source generation rates and day-to-day variations. This technique was applied to three different types of commercial buildings using field monitored data. The sites are small commercial buildings with packaged HVAC equipment and included modular schoolrooms, children's play areas in fast food restaurants and a pharmacy retail store. The impact of the length of model training data period on estimated CO₂ generation rates was investigated. Eight weeks of data is sufficient for training. Expressed in terms of the coefficient of variation, the errors in predicted CO₂ concentrations ranged from 4% to 15% depending on the sites. The predicted frequency of time that CO₂ concentrations were within a given range agreed well with the field measured data.     

A performance comparison of passive and low-energy buildings

This paper compares apartments in two residential blocks in Vienna; one passive and the other one low-energy. These blocks were constructed simultaneously in the same location and with comparable building construction features and floor plans. The main difference between the two blocks (other than the higher thermal insulation level in the passive building) lies in the ventilation system: passive buildings deploy controlled ventilation, whereas the low-energy buildings rely mostly on user-operated natural (window) ventilation. We measured indoor environmental conditions (indoor air temperature, relative humidity, and CO₂ concentration) in two units of each block over a period of five months. Additionally, the buildings were compared in view of operation and embodied energy use, CO₂ emissions, and construction costs.     

Control of indoor CO2 concentration based on a process model

Air-tight buildings need to have ventilation systems, although the use of these systems results in heavy energy consumption within the building sector. For this reason they have to be adequately regulated in order to achieve good indoor air quality and lower operation costs. The main challenge is to optimize regulation in office buildings, theaters, museums, and schools, where there are large fluctuations and heavy operating costs. Each further optimization leads directly to a better indoor climate and a reduction in energy consumption. In the case of ventilation systems, PI or PID regulators are usually used. In the described research an internal model control (IMC) system was designed with an internal loop, which constantly checks the momentary CO₂ concentration, and makes the necessary adjustments to the air flow. The results showed a significant improvement in the CO₂ level when using an IMC controller, in comparison with PI controller. The desired indoor air quality is achieved more than 80% of the time, with lower operating costs.     

In-situ implementation and validation of a CO2-based adaptive demand-controlled ventilation strategy in a multi-zone office building

This paper presents the in-situ implementation and validation of a CO₂-based adaptive demand-controlled ventilation (DCV) strategy in a super high-rise building in Hong Kong. The adaptive DCV strategy employs a dynamic multi-zone ventilation equation for multi-zone air-conditioning systems, in which a CO₂-based dynamic occupancy detection scheme is used for online occupancy detection. This strategy is implemented in an independent Intelligent Building Management and Integration platform (IBmanager), which communicates with the main station of the Building Management System (BMS) through a communication protocol and interface. The performance of this DCV strategy is practically tested and validated by comparing with that of the original fixed outdoor air flow rate control strategy used in site. The implementation architecture and test results including energy and environmental performances represented. Since the accuracy and reliability of the major measurement instrumentations affect the actual performance of the DCV strategy significantly, the commissioning and calibration of major measurement instrumentations are presented as well.     

Life cycle primary energy analysis of residential buildings

The space heating demand of residential buildings can be decreased by improved insulation, reduced air leakage and by heat recovery from ventilation air. However, these measures result in an increased use of materials. As the energy for building operation decreases, the relative importance of the energy used in the production phase increases and influences optimization aimed at minimizing the life cycle energy use. The life cycle primary energy use of buildings also depends on the energy supply systems. In this work we analyse primary energy use and CO₂ emission for the production and operation of conventional and low-energy residential buildings. Different types of energy supply systems are included in the analysis. We show that for a conventional and a low-energy building the primary energy use for production can be up to 45% and 60%, respectively, of the total, depending on the energy supply system, and with larger variations for conventional buildings. The primary energy used and the CO₂ emission resulting from production are lower for wood-framed constructions than for concrete-framed constructions. The primary energy use and the CO₂ emission depend strongly on the energy supply, for both conventional and low-energy buildings. For example, a single-family house from the 1970s heated with biomass-based district heating with cogeneration has 70% lower operational primary energy use than if heated with fuel-based electricity. The specific primary energy use with district heating was 40% lower than that of an electrically heated passive row house.     

Impact of lifestyle on the energy demand of a single family house

The building sector is one of the highest energy consumers in Austria. The potential to save energy in existing buildings is very high. Current Austrian policy incentives encourage home owners to renovate buildings to meet the European requirements, reduce energy consumption, and reduce CO₂ emissions. Nevertheless, there are often discrepancies between the measured and calculated energy consumption results despite efforts to take parameters into account such as the exact geometry and thermal properties of the building, energy demand for hot water, heating, cooling, ventilation systems, and lighting in the planning phase for selecting the best reconstruction option. To find the answer to this problem, many buildings are carefully investigated with the help of measurements, interviews, and simulations. This paper presents the analysis and results of the investigation of the impact of lifestyle on the energy demand of a single family house. The impact on energy performance of the most important parameters was observed by systematically changing parameters such as changing from a decentralized to a centralized heating system, considering various technologies and fuels for producing electricity and heat, use of renewable energy sources. Different occupant behaviours were changed systematically. The effects of these measures are analysed with respect to primary energy use, CO₂ emissions and energy costs. The results of these investigations show that the lifestyle and occupants’ living standard is mainly responsible for the differences between the calculated and measured energy consumption.     

Methods to reduce the CO2 concentration of educational buildings utilizing internal ventilation by transferred air

The aim of this study is to develop internal ventilation by transferred air to achieve a good indoor climate with low energy consumption in educational buildings with constant air volume (CAV) ventilation. Both measurements of CO₂ concentration and a multi‐room calculation model are presented. The study analyzes how to use more efficiently the available spaces and the capacity of CAV ventilation systems in existing buildings and the impact this has on the indoor air quality and the energy consumption of the ventilation. The temperature differences can be used to create natural ventilation airflows between neighboring spaces. The behavior of temperature‐driven airflows between rooms was studied and included in the calculation model. The effect of openings between neighboring spaces, such as doors or large apertures in the walls, on the CO₂ concentration was studied in different classrooms. The air temperatures and CO₂ concentrations were measured using a wireless, internet‐based measurement system. The multi‐room calculation model predicted the CO₂ concentration in the rooms, which was then compared with the measured ones. Using transferred air between occupied and unoccupied spaces can noticeably reduce the total mechanical ventilation rates needed to keep a low CO₂ concentration.     

A novel methodology for estimating space air change rates and occupant CO2 generation rates from measurements in mechanically-ventilated buildings

It is useful to know ventilation rates and carbon dioxide (CO₂) generation rates for evaluating indoor air quality and ventilation efficiency in mechanically-ventilated buildings. A strong limitation of the current models is either they focus solely on a whole building or they are too complicated for practical use in studies of individual spaces. This paper develops a new method for accurately quantifying ventilation rates (i.e. space air change rate) and CO₂ generation rates from measured CO₂ concentrations for individual spaces. The proposed method firstly determined space air change rate using Maximum Likelihood Estimation (MLE). Additionally, a novel coupled-method was initiated for further estimating CO₂ generation rates. Both simulated and experimental data were used to validate the model. Experiments were conducted in a school office by measuring indoor CO₂ concentrations and pressure differences between the return air vent and space. Excellent agreement was obtained. At least 0.998 R² values were obtained for fitting measured CO₂ concentrations when conducting MLE for estimating space air change rate, and the corresponding residual plots showed no pattern and trend. The estimated numbers of occupants were same as the actual ones. Furthermore, the predicted space air change rates showed great consistencies with those from CO₂ equilibrium analysis. The model is simple, handy and effective for practical use. Moreover, the model is also capable for dealing with time-varying space air change rates.     

Heat supply to low-energy buildings in district heating areas: Analyses of CO2 emissions and electricity supply security

In several housing development projects in Norway the requirements related to the mandatory connection to district heating plants have shown to be a barrier for building low-energy residential buildings. The developers have considered the costs related to both low-energy measures and a space heating system that can utilize district heat to be too high to give the project acceptable profitability. In these projects the developers wanted to use a cheaper electric space heating system. Based on models representative for the range of the Norwegian district heating plants, calculations show that the CO₂ emissions related to heating in residential buildings with an energy standard in accordance with the new building regulations and that are connected to the district heating grid, are lower than for similar buildings with a low-energy standard and with heating based on electricity. However, in a long term perspective the differences are marginal when considering the national annual CO₂ emissions. Similarly, increased peak power demand due to electricity-based heating may also be regarded as marginal when compared to the present maximum peak power capacity in Norway.     

Alternative ventilation strategies in U.S.offices:Comprehensive assessment and sensitivity analysis of energy saving potential

Mature technologies exist to reduce the heating,ventilation,and air-conditioning(HVAC) energy associated with ventilation and use ventilation proactively to save energy.This study investigated the energy use impacts in U.S.office buildings of multiple alternative ventilation strategies that combined:economizing,demand controlled ventilation(DCV),supply air temperature reset(SR),and/or a doubled ventilation rate.We used energy simulations in a Monte Carlo analysis,sampling 17 building inputs and varying locations to match the climate zone distribution of the U.S.office stock.Results indicated the possibility for significant savings compared to a baseline that ventilated constantly at a minimum rate in both a small office type with a constant air volume(CAV) HVAC system and a medium office type with a variable air volume(VAV) system.In 95%of instances,HVAC source energy savings were 5-25%in the small-CAV office(median:11%) and 6-42%in the medium-VAV office(median:27%).In the small-CAV office,DCV typically saved the most energy,usually from heating,and heating degree days and occupant density were decisive influences.In the medium-VAV office,economizing and SR were most important,DCV usually only had minor impacts,and zone temperature setpoints,along with climate indicators,were the critical influences.Other than infiltration,envelope characteristics did not strongly influence energy impacts.The untapped primary energy savings of alternative ventilation strategies over the 74%of U.S.office floorspace reasonably represented by our modeling was estimated at 36 TWh per year,with an annual value of U.S.$ 1.25 billion.     

Ein Vergleich von Passiv‐ und Niedrigenergie gebäuden am Beispiel zweier Wohnhäuser in Österreich

Die Bezeichnungen “Niedrigenergie”‐ und “Passiv”‐Haus beschreiben verschiedene Grade der Energieeffizienz von Gebäuden im Zusammenhang mit Richtlinien und Standards unterschiedlicher europäischer Länder. In den letzten Jahren gab es viele Diskussionen über die Vor‐ und Nachteile von Niedrigenergie‐, Passiv‐ und neuerdings auch Plusenergiehäusern. In diesem Kontext zeigt der vorliegende Beitrag eine detaillierte Bewertung von Wohnungseinheiten in zwei Wohnhäusern in Wien, Österreich. Eines dieser Gebäude ist ein Niedrigenergiehaus, während das andere die Kriterien eines Passivhauses erfüllt. Da beide Gebäude gleichzeitig von denselben Baufirmen am selben Grundstück errichtet wurden und sich in Konstruktion und Grundrissen gleichen, bieten sie ein geeignetes Beispiel für eine vergleichende Performance‐Einschätzung: Der Hauptunterschied zwischen den Gebäuden liegt (abgesehen von stärkerer Dämmung des Passivhauses) im Lüftungssystem: Passivhäuser verwenden kontrollierte Lüftungssysteme, während in Niedrigenergiehäusern der Luftaustausch hauptsächlich durch Fensterlüftung vonstatten geht. Der Vergleich der Gebäude basiert auf gemessenen innenklimatischen Bedingungen (Lufttemperatur, relative Luftfeuchte und CO₂‐Konzentration) in jeweils zwei Einheiten jedes Gebäudes über einen Zeitraum von fünf Monaten aufgezeichnet. Außerdem wurden die Gebäude hinsichtlich Energieverbrauch (Heizung und Strom), grauer Energie für die Bauteile, CO₂‐Emissionen (sowohl für Bauteile als auch im Betrieb) und Konstruktionskosten verglichen. A comparison of passive and low‐energy buildings using the example of two apartment blocks in Austria. The terms “low‐energy” and “passive” denote different levels of energy performance of buildings in the context of guidelines and standards in a number of European countries. In the last few years, there have been many discussions as to the benefits and drawbacks of low‐energy and passive (and recently, energy‐plus) buildings. In this context, the present contribution includes a detailed assessment of apartment units in two building blocks in Vienna, Austria. One of these blocks may be characterized as low‐energy, while the other one adheres to the benchmarks for passive buildings. As these blocks have been erected on the same site and at the same time (with many similar construction and layout features), they provide a proper case in point for a comparative performance assessment: the main difference between the two blocks is, setting aside the higher insulation level of the passive building, the ventilation system. Apartments in the passive block use controlled ventilation, whereas the low‐energy apartments use mainly window ventilation. The comparative assessment of these buildings was based on measured indoor parameters (indoor air temperature, relative humidity, and CO₂ concentration) in two units of each block over a period of five months. Moreover, the apartments were assessed regarding actual energy use (heating, electricity), embodied energy for construction, CO₂ emissions (both for construction and operation), and construction costs.     

A novel and dynamic demand-controlled ventilation strategy for CO2 control and energy saving in buildings

Although conventional CO₂-based demand-controlled ventilation strategies, such as proportional and exponential controls, can ensure buildings/spaces meeting the minimum requirements of outdoor air by industry standards, they are operated under the assumption of equilibrium condition which can hardly be reached in practice and therefore there is still much space to improve on conventional strategies in terms of energy saving. In this paper, a novel and dynamic control strategy was developed for hourly scheduled buildings. The strategy utilized schedules by setting a base ventilation rate for unoccupied periods and calculating ventilation rate dynamically at each occupied period by solving the CO₂ mass balance equation to keep indoor CO₂ near the set point during the occupied period. Experimental simulations were made over a sports training center using both simulated and experimental CO₂ generation rates. Results show that the new strategy can save +34% of energy related to ventilation air compared to proportional control. The new strategy was also extended to common buildings which are occupied for almost all opening hours. In the case of common buildings, the new strategy can save about +26% of energy related to ventilation air compared to proportional control. The new strategy is simple, dynamic, flexible and efficient.     

Life cycle primary energy use and carbon emission of an eight-storey wood-framed apartment building

In this study the life cycle primary energy use and carbon dioxide (CO₂) emission of an eight-storey wood-framed apartment building are analyzed. All life cycle phases are included, including acquisition and processing of materials, on-site construction, building operation, demolition and materials disposal. The calculated primary energy use includes the entire energy system chains, and carbon flows are tracked including fossil fuel emissions, process emissions, carbon stocks in building materials, and avoided fossil emissions due to biofuel substitution. The results show that building operation uses the largest share of life cycle energy use, becoming increasingly dominant as the life span of the building increases. The type of heating system strongly influences the primary energy use and CO₂ emission; a biomass-based system with cogeneration of district heat and electricity achieves low primary energy use and very low CO₂ emissions. Using biomass residues from the wood products chain to substitute for fossil fuels significantly reduces net CO₂ emission. Excluding household tap water and electricity, a negative life cycle net CO₂ emission can be achieved due to the wood-based construction materials and biomass-based energy supply system. This study shows the importance of using a life cycle perspective when evaluating primary energy and climatic impacts of buildings.     

A new methodology for renewable and rational use of energy policy in building sector: Case study for the island of Crete

This paper discusses the future development of efficient energy policies with respect to building sector, using a new simulation computer model called INVERT. The building sector incorporates supply side systems (heating, domestic hot water (DHW) and cooling systems) and Demand Side Management (DSM) measures. Simulation runs have been carried out up to 2020 for the Greek island of Crete based on sensitivity analyses for different building types, heating/cooling technologies and DHW systems. Promotion schemes for renewable energy sources (RES) and rational use of energy (RUE) are also implemented in the simulation model, since they have a strong impact on long-term financial investment strategies. Transfer costs and CO₂ emissions of various hypothesis scenarios about new or additional promotion schemes for energy conservation in residential buildings have been compared with a reference scenario for the island of Crete. The outcome of this case study is presented and discussed in this paper.     

The impact of auxiliary energy on the efficiency of the heating and cooling system: Monitoring of low-energy buildings

This paper presents a detailed meta-analysis of end and primary energy use for heating, cooling and ventilation of 11 low-energy non-residential buildings and one residential building in Germany that belong to the EnOB research program launched by the German Federal Ministry for Economy. In particular, the analysis emphasizes the substantial impact of auxiliary energy use on the efficiency of heating and cooling performance. The investigated buildings employ environmental energy sources and sinks - such as the ground, ground water, rainwater and the ambient air - in combination with thermo-active building systems. These concepts are promising approaches for slashing the primary energy use of buildings without violating occupant thermal comfort. A limited primary energy use of about 100 kWh_prim/(m²_neta) as a target for the complete building service technology (HVAC and lighting) was postulated for all buildings presented. With respect to this premise, a comprehensive long-term monitoring in high time resolution was carried out over the course of two to five years, with an accompanying commissioning of the building performance. Measurements include the energy use for heating, cooling, and ventilation, as well as the auxiliary equipment, the performance of the environmental heat source and sink, and local climatic site conditions.     

Calculation of the yearly energy performance of heating systems based on the European Building Energy Directive and related CEN standards

According to the Energy Performance of Buildings Directive (EPBD) all new European buildings (residential, commercial, industrial, etc.) must since 2006 have an energy declaration based on the calculated energy performance of the building, including heating, ventilating, cooling and lighting systems. This energy declaration must refer to the primary energy or CO₂ emissions.The European Organization for Standardization (CEN) has prepared a series of standards for energy performance calculations for buildings and systems. This paper presents related standards for heating systems. The relevant CEN-standards are presented and a sample calculation of energy performance is made for a small single family house, an office building and an industrial building in three different geographical locations: Stockholm, Brussels, and Venice.The additional heat losses from heating systems can be 10-20% of the building energy demand. The additional loss depends on the type of heat emitter, type of control, pump and boiler.     

Modeling energy efficiency of bioclimatic buildings

The application of bioclimatic principles is a critical factor in reducing energy consumption and CO₂ emissions of the building sector. This paper develops a regression model of energy efficiency as a function of environmental conditions, building characteristics and passive solar technologies. A sample of 77 bioclimatic buildings (including 45 houses) was collected, covering Greece, other Mediterranean areas and the rest of Europe. Average energy efficiency varied from 19.6 to 100% with an average of about 68%. Environmental conditions included latitude, altitude, ambient temperature, degree days and sun hours; building characteristics consisted in building area and volume. Passive solar technologies included (among others) solar water heaters, shading, natural ventilation, greenhouses and thermal storage walls. Degree days and a dummy variable indicating location in the Mediterranean area were the strongest predictors of energy efficiency while taller and leaner buildings tended to be more energy efficient. Surprisingly, many passive technologies did not appear to make a difference on energy efficiency while thermal storage walls in fact seemed to decrease energy efficiency. The model developed may be of use to architects, engineers and policy makers. Suggestions for further research include obtaining more building information, investigating the effect of passive solar technologies and gathering information on the usage of building.     

A holistic utility bill analysis method for baselining whole commercial building energy consumption in Singapore

The methodology for baseline building energy consumption is well established for energy saving calculation in the temperate zone both for performance-based energy retrofitting contracts and measurement and verification (M&V) projects. In most cases, statistical regression models based on utility bills and outdoor dry-bulb temperature have been applied to baseline monthly and annual whole building energy use. This paper presents a holistic utility bills analysis method for baseline whole building energy consumption in the tropical region. Six commercial buildings in Singapore were selected for case studies. Correlationships between the climate data, which are monthly mean outdoor dry-bulb temperature (T₀), relative humidity (RH) and global solar radiation (GSR), and whole building energy consumption are derived. A deep prediction study based monthly mean outdoor dry-bulb temperature (T₀) and whole building energy consumption is stated. The result shows that variations of the energy consumption in most of these buildings are contributed by T₀ and can be well predicted at 90% confidence level only with it. The analysis of such kind of model is especially useful for building managers, owners and ESCOs to track and baseline energy use during pre-retrofit and post-retrofit periods in the tropical condition.