Multi-family Buildings Research Articles

Unintended Effects of Energy Efficiency Policy: Lessons Learned in the Residential Sector

The European Union has set an ambitious goal to tackle climate change, and energy efficiency in the residential sector is among the measures required to close the gap between targeted and actual greenhouse gas emissions. While different policy tools have been applied, the diffusion rate of these measures remains low. A system dynamics simulation model of the residential sector was developed to assess the advantages and drawbacks of energy efficiency policy in the multi-family building sector based on experience accumulated over the last twelve years in Latvia. The model was validated in expert group model building sessions and with historical trends. Simulating the model, a hypothesis was tested that supported the idea that seemingly positive policy tools set the stage for a series of unintended adverse effects due to the complex interactions between different system components. The common assumption that information and financial support should result in significant energy efficiency diffusion proved to be wrong. It instead results in unintended long-term consequences that hamper national energy efficiency goals. The model carried out an analysis and brought insights for improving the effectiveness of government energy efficiency policy. It is concluded that models that broadly describe complex systems are needed to identify effective policies and foresee unintended side effects.

Assessment of residential scale renewable heating solutions with thermal energy storages

Thermal energy storage technologies significantly increase the benefits of decentralized renewable energy production on residential scale. While many studies investigate singular applications of thermal energy storages or provide a broad overview about the current state of research in this field, there is no comprehensive assessment on market-ready solutions. This paper combines a system performance analysis for the combination of photovoltaic and solar thermal generation with storages based on building energy system simulations. Energy systems for single- and multi-family reference buildings with low energy consumption, representing the most common retrofit case in Switzerland, are designed on equal energy performance, and later evaluated for total costs of ownership and financial payback. The results highlight the operational difference in thermal energy storages, where some technologies act more like an energy source in their optimal sizing. Variation of renewable input versus storage size emphasize the individual optimal storage duration. Many solutions are capable of substantially increasing the degree of energy autarky while being competitive without subsidies. This assessment helps guiding future development and design of thermal energy storages.

Uncertainty analysis of climate change potential assessments of five building energy renovation measures in Sweden

The aim of this study is to assess the impact of the uncertainties of life cycle inventory (LCI) data for energy use and materials in life cycle assessments of standard energy renovation measures carried out in multi-family buildings in Sweden. Five energy renovation measures were assessed with regard to their climate change potential. Modules A1–A3 and module B6 were included in the assessment and the functional unit, 1 m2 heated floor area of a renovated building fulfilling the Swedish building regulations and with a calculation period of 20 years, was used. The uncertainty of LCI data for materials and energy were assessed using the Ecoinvent data quality system. This study shows that with two different energy mixes, all renovation measures result in a decrease in the climate change potential. The five renovation measures used in the simulations, with and without consideration to uncertainties, show a lower climate change potential when carried out than when not carried out. It is also shown in this study that the inclusion of the uncertainties of the input data did not have any impact on the overall decisions to renovate or not to renovate. However, this should not be regarded as a general conclusion. If a renovation measure were to have a higher level of material use, or if the “Future energy mix” were to be improved, uncertainty considerations could become much more important from a climate change perspective.Article HighlightsAll assessed energy renovation measures show a decrease in their climate change potential when carried out.The energy renovation measures with the largest decreases of climate change potential are also the measures with largest energy saving potential.When uncertainties are considered, there are no overlaps in the results when carrying out or not carrying out a renovation measure.

Towards Differentiated Energy Renovation Strategies for Heritage-Designated Multifamily Building Stocks

The historic building stock is not homogeneous, which implies a need for differentiated energy renovation strategies in order to balance energy efficiency requirements and building conservation goals. This paper presents a new method for developing a base for differentiated energy renovation strategies for heritage-classified multifamily building stocks. Our suggested method combines different building databases using an extract, transform and load (ETL) technology. The method for this study was tested on the available information for heritage-designated and -classified multifamily buildings in the municipality of Stockholm, Sweden, and in the county of Halland, Sweden. The two cases reflect the heterogeneity of the Swedish Building stock. An important achievement is that the results visualise the relationship, not detectable before, between energy use, energy performance, year of construction and heritage classification within each of the selected building stocks. A specific result is that the energy-saving potential in the older building stock is insignificant in relation to the entire stock. The results contribute to an improved understanding of relationships both within and between the two historic building stocks, which is useful for developing differentiated energy renovation strategies.

An agent-based exploration of the effect of multi-criteria decisions on complex socio-technical heat transitions

Natural gas for heating is widespread in the built environment of The Netherlands, where the government aims at limiting heat demand and reducing natural gas consumption over the coming decades. In the owner-occupied residential sector, this transition is complex and requires cooperation and coordination of individuals and groups that make investment decisions. We use agent-based modelling to explore the effect that various financial policies could have in an illustrative neighbourhood, given that households make multi-criteria and group decisions. In the scientific literature, this type of energy model seldom focuses on the adoption of competing technologies by households as individual and collective agents grouped in homeowner associations in multi-family buildings. To address the problem and knowledge gaps, we model individual preferences with a multi-criteria perceived lifetime utility submodel, and decisions as outcomes of individual preferences and a threshold voting system. We explore energy taxes (natural gas and electricity), regulated price of heat from networks, and subsidies (insulation and heat pumps). Under our assumptions, we found that combinations of fiscal policies, regulated heat prices, and subsidies can sometimes create incentives for households to disconnect from natural gas, but that steering the transition mainly with financial policies could prove ineffective. We also found that, in terms of collective CO2 reduction, some transitions in which only some households phase out natural gas could have results similar to some scenarios in which households only improve their dwellings’ insulation levels.

Neural Approach in Short-Term Outdoor Temperature Prediction for Application in HVAC Systems

An accurate air-temperature prediction can provide the energy consumption and system load in advance, both of which are crucial in HVAC (heating, ventilation, air conditioning) system operation optimisation as a way of reducing energy losses, operating costs, as well as pollution and dust emissions while maintaining residents’ thermal comfort. This article presents the results of an outdoor air-temperature time-series prediction for a multifamily building with the use of artificial neural networks during the heating period (October–May). The aim of the research was to analyse in detail the created neural models with a view to select the best combination of predictors and the optimal number of neurons in a hidden layer. To meet that task, the Akaike information criterion was used. The most accurate results were obtained by MLP 3-3-1 (r = 0.986, AIC = 1300.098, SSE = 4467.109), with the ambient-air-temperature time series observed 1, 2, and 24 h before the prognostic temperature as predictors. The AIC proved to be a useful method for the optimum model selection in a machine-learning modelling. What is more, neural network models provide the most accurate prediction, when compared with LR and SVR. Additionally, the obtained temperature predictions were used in HVAC applications: entering-water temperature and indoor temperature modelling.

Indoor Comfort, Thermal Indices, and Energy Assessment of Multi-Family Colonial Revival Style Buildings

Colonial Revival style residences have unique architectural features amongst others. They are common multi-family residences in the United States with no or limited information about their performance. The research purpose is to assess indoor comfort, energy performance, and thermal indices in multi-family Colonial Revival style residences. The research questions include (i) Do Colonial Revival style buildings perform better than other old buildings? (ii) Do the buildings consume additional electricity than typical and other old buildings? The research examined four case studies in Hartford County, Connecticut. The investigation explored comfort surveys, monitoring, collection of actual electricity usage, and assessed thermal indices using mathematical models. The average indoor temperature of 25.4 °C and relative humidity (RH) of 61.3% are reported. About 67% of the residents are thermally comfortable. The research noted significance between thermal sensation and other variables, excluding how occupants feel about the air movement. The average number of hours of temperature exceeds 28.0 °C and 30.0 °C marks for over 11.4% and 2.5% of the time, respectively, except in one of the buildings. The mean indoor temperatures are within the applicable bands of the adaptive comfort models. The averages of actual thermal sensation vote (TSV) ranged from 3.32 to 4.37 on a 7-point sensation scale. The mean neutral temperatures varied from 24.2–25.6 °C. The average monthly electricity bill is within the national average for residences in summer, excluding in August. The mean wet-bulb globe temperature (WBGT) of 21.1–22.3 °C and summer simmer index (SSI) of 30.1–32.4 °C are calculated as feasible bands for thermal indices in the buildings. The basements are more comfortable than other spaces within the case studies. The research outcomes can be used for future developments of Colonial Revival style and other similar buildings. The study recommends interventions such as retrofit to improve the performance of some existing Colonial Revival style buildings, especially the older ones that are less insulated with outdated equipment and appliances.

Building retrofit hurdle rates and risk aversion in energy efficiency investments

Despite extensive empirical evidence of the environmental benefits of green buildings and the increasing urgency to reduce carbon emissions in cities, there has been limited widespread adoption of energy retrofit investments in existing buildings. In this paper, we empirically model financial returns to energy retrofit investments for more than 3600 multifamily and commercial buildings in New York City, using a comprehensive database of energy audits and renovation work extracted from city records using a natural language processing algorithm. Based on auditor cost and savings estimates, the median internal rate of return for adopted energy conservation measures is 21% for multifamily buildings and 25% for office properties. Logistic regression modeling demonstrates adoption rates are higher for office buildings than multifamily, and in both cases adopter buildings tend to be larger, higher value, and less energy efficient prior to retrofit implementation. The economically significant magnitudes of returns to adopted energy conservation measures raise important questions about why many property owners choose not to adopt. As such, we discuss incentive and regulatory mechanisms that can overcome financial and informational barriers to the adoption of energy efficiency measures.

Home environment and noise disturbance in a national sample of multi-family buildings in Sweden-associations with medical symptoms

BackgroundPoor acoustic conditions at home can have negative health impact. The aim was to investigate home environment factors and medical symptoms associated with noise disturbance.MethodsAll adults (≥18 y) registered in selected apartments in Sweden were invited to participate in a questionnaire survey including medical questions and personal factors. Totally 5775 adults participated (response rate 46%). Information on home environment was obtained through an indoor environment questionnaire. Two-level logistic regression models (individual, municipality) were performed to estimate associations.ResultsTotally 11.9% reported noise disturbance in general at home. Noise disturbance from voice/radio/TV/music/similar sounds from neighbours (13.2%), scraping sound/footsteps/thumping from neighbours (16.5%) and road traffic (16.1%) were common. Younger age and smoking were related to more noise disturbance and more medical symptoms. Noise disturbance was related to tiredness, headache and difficulty concentrating (OR = 1.70–8.19). Renting the apartment (OR = 2.53) and living above ground floor (OR = 1.37) were related to more noise disturbance in general. Living in newer buildings (constructed from 1986 to 2005) was related to less noise disturbance in general (OR = 0.40–0.59). A warmer climate (OR = 1.95), higher municipality population density (OR = 1.24), a longer living time (OR = 1.34), construction year (1961–1975) (OR = 2.42), renting (OR = 1.80–2.32), living above ground floor (OR = 1.45) and having a bathroom fan (OR = 1.84) were associated with increased noise disturbance from neighbours. Factors associated with increased noise disturbance from installations or ventilation/fans/heat pumps included a warmer climate, higher municipality population density, construction year (1961–1995), renting and any mechanical ventilation. Higher municipality population density, construction year (especially 1961–1985) and renting were associated with more noise disturbance from traffic (OR = 1.77–3.92). Renting the apartment (OR = 1.73) and living above ground floor (OR = 1.60) were related to more severe traffic noise disturbances. Noise disturbance in general was partly a mediator of the effects of old buildings, renting the apartment and lack of mechanical ventilation on medical symptoms (% of total effect mediated by noise disturbance: 19–44.8%).ConclusionsNoise disturbance can be associated medical symptoms. Younger age, smoking, a warmer climate, higher municipality population density and different building factors (e.g. renting the apartment, construction period 1961–1985) can be associated with noise disturbance.

Energy Efficiency Indicators for Water Pumping Systems in Multifamily Buildings

With the current concerns about sustainable development and energy consumption in buildings, water pumping systems have become essential for reducing energy consumption. This research aims to develop guidelines for the energy assessment of water pumping systems in multifamily buildings. The methodological procedures are: (i) definition of the efficiencies of electric motors; (ii) definition of pump efficiency levels; (iii) determination of energy consumption; and (iv) construction of the efficiency scale and guidelines for projects and assessments. The results obtained were that centrifugal pumps with 40% efficiency have higher energy consumption, regardless of the efficiency class of the electric motors, showing a 20% increase in electrical energy consumption. Lower efficiencies directly impact the energy efficiency rating of the water pumping system. Thus the 40% efficiency obtained energy efficiency rating “Very Low—VL” for all motor efficiency classes (between IE1 and IE5). At 60% efficiency, the energy efficiency level of the system was “Average—A”, gradually increasing to “Very High—VH”, as the energy consumption in the pumps decreased and the motors’ energy efficiency classes increased. It is concluded that designers and professionals in the area must consider the efficiency of the pumps, as they play a fundamental role in the classification of the system’s energy efficiency. It is also recommended to verify the energy efficiency of the water pumping system and implement design guidelines so that the pumping system achieves lower energy consumption, contributing to the building’s energy efficiency and sustainability.

Proposed Method of Distribution of Horizontal Loads on Stiffening Walls

Numerical methods are commonly used to determine internal forces in stiffening walls. Extreme internal forces can be easily generated not only in slab-and-wall structure, but also in the bar system. It is always time-consuming to build such a structure, thus it is not used in single- or multi-family buildings with a simple wall arrangement. Then, a simple analytical model can be used to calculate internal forces in walls. Eurocode 6 (prEN 1996-1-1:2017) does not contain specific guidelines to calculate internal forces in walls and to use numerical methods or other reliable methods. This paper presents the procedure for determining internal forces in a building with a simple wall arrangement. The proposed method is based on the division of a wall with openings into components. The results were compared with values of internal forces determined by the linear elastic FE shell model. Rotation centre (RC) of the wall plan was demonstrated to be a significant factor which, besides bending and shear stiffness, had an impact on load distribution.

Simulation-Based Comparative Study on Energy Efficiency Criteria for LEED and BREEAM Systems

Energy efficiency is regarded as one of the important elements of green building. Every Green Building Rating (GBR) system puts forward a set of criteria for energy efficiency and it is different for each system. A comparative study is done to distinguish between two GBR systems practiced worldwide-LEED and BREEAM, first on the criteria for energy efficiency and secondly on how efficient and effective each system in energy performance improvement. Building energy simulation tool, eQuest is used to obtain annual energy consumption of a case study multi-family dwelling residential building for its various design options. Different design cases were formulated by changing design parameters and the simulation results thus obtained are used for evaluating the performance improvement for energy, calculated as per the criteria for each system. This study primarily looks for the combinations which grab total achievable credits in energy efficiency for a particular system. For LEED, it was found that renewable energy allocation alone has the greater influence in achieving higher credits. For BREEAM, there requires specifically a considerable decrease in HVAC load which can be brought by the means of more natural ventilation or by adopting passive cooling techniques. BREEAM was also found more effective in reflecting any kind of improvement made in terms of awarding credits.

The effect of weighting factors on income-related energy inequalities: The case of Sweden’s new building code

To ensure building construction with low heating demand, efficient use of sustainable energy carriers, and neutrality between heating technologies, Sweden recently introduced weighting factors (WFs) for different energy carriers which are now used in Energy Performance Certificates (EPCs). As EPC ratings are gaining increased influence in Swedish energy policy and regulation, with recent examples of buildings’ EPC rating acting as base for imperative regulatory requirements, the introduction of WFs is likely to have significant effects on how policy and regulations are distributed in the multifamily building stock. As residents often are directly or indirectly affected by policy that either impose or trigger measures to be undertaken in their building, the aim of this paper is to analyse how WFs affect the assessed energy performance of buildings in different resident income groups. The results show that overall, reduced energy performance from WFs was more common in high-income areas than in low-income areas. However, although the total number of buildings in the lowest EPC ratings was reduced after introducing WFs, the resulting income distribution among worst-performing buildings was more skewed towards low-income households than before introducing WFs. As imperative regulatory requirements previously have targeted worst-performing buildings, these results indicate that energy-related inequalities in the housing stock have become more prominent and should be considered as to not disproportionately burden low-income residents in the energy transition of the housing stock.

Evaluation of the performance of enclosed balconies based on temperature monitoring

Enclosed, glazed balconies influence the energy balance of the flats thanks to the temperature rise caused by solar gains in unheated sunspaces. The potential benefits, however, may differ depending on the inhabitants’ behaviour. To evaluate these effects, internal temperature in multi-family buildings located in Zamość (a city in the eastern part of Poland) was monitored at the turn of the years 2017 and 2018. The temperature was registered with the use of iButton sensors located in flats and sunspaces. Three dwellings with the same orientation were included in the research – two with glazed balconies, differing by the area of the living space, the number of the inhabitants, and their behaviour (flats no. 1 and 2), and one with an open balcony, used for comparison (flat no. 3). Air temperature within the glazed balconies was usually higher than the external air temperature, and the sunspaces helped to reduce heat losses from the adjoining rooms by 10.7% (flat no. 1) and 26.6% (flat no. 2). The apartments also showed some differences as far as the comfort of use during summer is concerned, flat no 1 being the most prone to overheating.

Four years monitoring of heat pump, solar thermal and PV system in two net-zero energy multi-family buildings

This work presents four-year monitoring results of two new multi-family houses in Innsbruck aiming to be net-zero energy buildings (NZEB). The project combines high-performance buildings designed in Passive House standard, highly-efficient HVAC systems i.e., low-temperature distribution and emission, a double-stage ground-water source heat pump including a desuperheater and mechanical ventilation with heat recovery, and maximum possible renewable sources i.e., roofs fully covered with photovoltaic panels (PV) and solar thermal collectors. The design goal of NZEB was to balance on an annual basis, the electricity consumption of the technical systems and the electricity production of the PVs, and later on the evaluation by means of a monitoring campaign. With a combination of high-performance technologies with respect to the building envelope, HVAC, and renewables, the measured annual onsite produced PV electricity is 6% (4-year average) higher than the one consumed by the heat pump. However, it was not sufficient to cover the consumption of all the technical systems (auxiliary and appliances). Concerning the building envelope, Passive House quality is recommended, concerning the HVAC, complex configuration seems not beneficial in practice and there was no clear indication of the benefit to implementing a desuperheater in this project. Solar thermal collectors produced 20% (4-year average) more heat per unit area than a PV-driven heat pump, however, the combination of both and the corresponding system complexity tends to show more negative aspects, and thus, a decision should be taken with care. Finally, it could be shown that reducing thermal losses and minimization of the auxiliary energies is of major importance to reach NZEB.

Efficiency of Different Balcony Slab Modernization Method in Retrofitted Multi-Family Buildings

Many buildings have considerable thermal bridges at the junction of balcony slabs with walls. To achieve the new EU directive targets related to energy efficiency, greater attention should be paid to such design details. This study analyzes the efficiency of traditional balcony slab modernization methods, the use of modern insulation materials and a new alternative system: an added self-supporting light balcony system (LKBD) in retrofitted large-panel buildings. The main objective was to capture cost-effective renovation methods from both the heat loss reduction perspectives and risk of surface condensation. The analyses, carried out in four buildings, have shown that at current costs, the thermal modernization of balconies is not economically efficient (SPBT > 98.4 years). However, it is necessary because leaving the balcony slabs without insulation or only insulating them from the bottom carries the risk of surface condensation. The most cost-effective renovation method is to insulate the balcony slabs from below and above with the thickest possible XPS layer (SPBT = 98.4 years; 107.4 years). Replacing XPS with modern material increases SPBT by almost 50%, for the LKBD system, SPBT = 269.2–281.5 years. More favorable energy and economic effects related to the reduction of balcony thermal bridges were achieved in the wall with lower insulation.

Efficient, effective and fair allocation of costs and benefits in residential energy communities deploying shared photovoltaics

Deployment of rooftop solar photovoltaics on multi-family buildings lags behind other residential buildings sectors, despite the benefit of significantly higher self-consumption achievable by applying on-site generation to aggregated building load. This is, in part, because of challenges in developing suitable business models to ensure the fair allocation of costs and benefits between different stakeholders. Embedded networks can provide a mechanism for consumers to co-ordinate their engagement in the energy market, as well as to distribute on-site generation between multiple households. However, to succeed, an embedded network must deliver benefits to all households as well as providing returns to investors. This paper uses a case-study of a 72-apartment complex in Sydney Australia to explore different ways to distribute the costs and benefits of a potential shared photovoltaic system between apartment owners and residents. A range of tariff structures, including demand or capacity charges as well as fixed and time-varying volumetric charges, are compared for their ability to recover investment costs, incentivise efficient energy behaviour and achieve customer acceptance through fairness and transparency. The analysis demonstrates the tension between these desired outcomes and the significant challenge of designing a mechanism to deliver them all. In particular, tariff structures incorporating peak demand charges, while cost-reflective and efficient, are unable to deliver benefits to all stakeholders and thereby ensure the sustainability of the embedded network. The findings have implications for market design and for policy approaches to support embedded networks and energy communities.

On the Use of Base Temperature by Heat Cost Allocation in Buildings

Heat cost allocators (HCAs) have a high market share in existing buildings, which may cause problems, especially with variable heat cost allocation due to wrong readings from HCAs and/or the method used in the heat cost allocation process. That is why we proposed two easily applicable and clear methods, which may be used with two types of HCAs commonly used in the billing practice. The proposed methods were presented on the example of the actual allocation of variable heating costs for a multi-family building located in Poland, and the results of billing were compared with three other methods of variable heating costs allocation. Owing to the proposed methods, higher (K = 0.5260 for schema A, K = 0.4468 for schema B) values of the correlation coefficient between heating costs and the average indoor temperature were obtained than for the methods commonly used in accounting practice. Additionally, the use of the proposed method allows for the elimination of defective indications of heat cost allocators in the billing process and discrepancies in the indications of HCAs in individual flats, which do not have technical justification and violate the norms of social coexistence.

Optimal system design for energy communities in multi-family buildings: the case of the German Tenant Electricity Law

Involving residential actors in the energy transition is crucial for its success. Local energy generation, consumption and trading are identified as desirable forms of involvement, especially in energy communities. The potentials for energy communities in the residential building stock are high but are largely untapped in multi-family buildings. In many countries, rapidly evolving legal frameworks aim at overcoming related barriers, e.g. ownership structures, principal–agent problems and system complexity. But academic literature is scarce regarding the techno-economic and environmental implications of such complex frameworks. This paper develops a mixed-integer linear program (MILP) optimisation model for assessing the implementation of multi-energy systems in an energy community in multi-family buildings with a special distinction between investor and user; the model is applied to the German Tenant Electricity Law. Based on hourly demands from appliances, heating and electric vehicles, the optimal energy system layout and dispatch are determined. The results contain a rich set of performance indicators that demonstrate how the legal framework affects the technologies’ interdependencies and economic viability of energy communities with multi-energy systems. Certain economic technology combinations may fail to support national emissions mitigation goals and lead to lock-ins in Europe’s largest residential building stock. The subsidies do not lead to the utilisation of a battery storage. Despite this, self-sufficiency ratios of more than 90% are observable for systems with combined heat and power plants and heat pumps. Social CO2 mitigation costs range between 147.5–272.8 €/tCO2. Finally, the results show the strong influence of the heat demand on the system layout.

Domestic hot water design and flow measurements

In this study, the sizing of primary side components for preparation of domestic hot water are analysed, both qualitatively and based on measurements of domestic hot water demand in one multi-family building with 268 apartments. The collected data spans a period of 18 days during the end of 2020 and is collected in 15-min, 1-min, and 6-s intervals. An overview of the historic development for the design of domestic hot water flow in Sweden is also presented. There is a long-standing argument in Sweden, that the current district heating guidelines result in an overdesign of the flow for domestic hot water. The consequence of this is oversizing heat exchangers and valves in the substations. This study assesses, qualitatively, the issues related to overdesigned primary side valves for preparation of domestic hot water. A revised design for domestic hot water flow for the Swedish context is also conceptualised. The study suggests that an improved design flow for domestic hot water in multi-family buildings can be derived based on empirical measurements. The 15-min intervals are observed to tone down information of peaks to a degree where it is unsuitable to use as basis for a new design flow. The 1-min data does appear to preserve information to a degree where it can be used to assess a design flow when related to data with a 6-s interval. The 6-s data is expected to constitute a resolution that may be less available, and in this study, it constitutes a representation of the real domestic hot water demands. However, to find a fitted curve to empirical data, for the design flow based on number of apartments per multi-family building, the population of datasets needs to be increased.