A mixed integer linear programming-based simple method for optimizing the design and operation of space heating and domestic hot water hybrid systems in residential buildings

Air-to-water heat pumps (AWHPs) are an efficient technology to provide thermal energy for space heating and domestic hot water production in residential buildings, which cover about 30% of the Italian overall energy consumption. Despite of a series of benefits, such as low investment costs and large availability of the external source (ambient air), air-source heat pumps are affected by several drawbacks, the most important of which is the frosting phenomena. Nowadays, the most widespread defrosting technique is reverse-cycle defrost (RCD): the indoor heat exchanger of the AWHP operates as an evaporator, extracting thermal energy from the heated space to melt the ice layer. For this reason, during the defrosting process no heating is provided and the indoor air temperature may significantly drop; therefore, the thermal comfort of building occupants is negatively affected. Very few studies demonstrating that the correct design of the hydronic distribution loop can mitigate the adverse effect of defrosting cycles on indoor thermal comfort can be found in literature; hence, the aim of this paper is to optimize position and size of a thermal storage tank inserted within the hydronic loop in order to minimize the impact of defrosting cycles on the heating system performance. This work analyses the performance of an inverter-driven AWHP coupled to a residential building located in Bologna (Northern Italy) by means of a simulation model developed with TRNSYS; furthermore, the heat pump dynamic model takes into account the reverse cycle operating mode during defrosting cycles and the energy losses linked to on-off cycling. Results show that defrosting cycles have a negative, significant impact on the seasonal performance factor of the system, which is reduced up to 10% with respect to an ideal case where frosting phenomena is not considered. Furthermore, defrosting transients cause a relevant decrease of the indoor air temperature (about 1°C), linked to the worsening of indoor thermal comfort conditions, in systems characterized by low thermal inertia (water volume lower than 5 l/kW); on the contrary, the influence of defrosting cycles on indoor conditions can be considered as negligible for a water content in the distribution loop larger than 10 l/kW, especially if the thermal storage is placed on the supply loop (i.e. between the heat pump and the terminal units).Air-to-water heat pumps (AWHPs) are an efficient technology to provide thermal energy for space heating and domestic hot water production in residential buildings, which cover about 30% of the Italian overall energy consumption. Despite of a series of benefits, such as low investment costs and large availability of the external source (ambient air), air-source heat pumps are affected by several drawbacks, the most important of which is the frosting phenomena. Nowadays, the most widespread defrosting technique is reverse-cycle defrost (RCD): the indoor heat exchanger of the AWHP operates as an evaporator, extracting thermal energy from the heated space to melt the ice layer. For this reason, during the defrosting process no heating is provided and the indoor air temperature may significantly drop; therefore, the thermal comfort of building occupants is negatively affected. Very few studies demonstrating that the correct design of the hydronic distribution loop can mitigate the adverse effect of defrosting ...

Optimal sizing design and operation of electrical and thermal energy storage systems in smart buildings

Space cooling energy consumption is a significant component of building energy consumption, and in recent years it has attracted much attention worldwide owing to its significantly increasing usage. The variable refrigerant flow (VRF) system is one common type of cooling equipment for buildings in China and is applied extensively to residential and office buildings. The performance of VRF systems significantly influences the cooling energy consumption of buildings. The system energy efficiency and electricity consumption are the main indicators employed to evaluate the performance of VRF systems. It is hard to obtain the actual energy efficiency and electricity consumption of VRF systems in buildings because of the high cost of the required complicated measurements. This study proposes a virtual sensor modeling method to determine the actual energy efficiency and electricity consumption of 344 VRF systems in residential buildings. Statistical and clustering analyses are conducted to determine the energy efficiency and electricity consumption to obtain distributions and typical operation load patterns of VRF systems in residential buildings in China. The main findings are as follows: the main range of the Seasonal Energy Efficiency Ratio (SEER) for the cooling season is from 2.9 to 4.4; the median SEER in the Hot Summer and Cold Winter zone is lower than in another climate zones; the longer cooling duration may lead to greater electricity consumption, and the electricity load for VRF systems electricity load is periodic for each day. The oversizing issue is common for VRF systems in the dataset, which also led to the lower energy efficiency of VRF systems. The high usage of VRF systems appeared from July 27th to August 26th. The findings provide recommendations for designing VRF systems in residential buildings.

Energy-related occupant behaviour is crucial to design and operation of energy and control systems in buildings. Occupant behaviours are often oversimplified as static schedules or settings in building performance simulation ignoring their stochastic nature. The continuous and dynamic interaction between occupants and building systems motivates their simultaneous simulation in an efficient manner. In the past, simultaneous simulation has relied on co-simulation approaches or customized source code changes to building simulation programmes. This paper presents Buildings. Occupants, an open-source package implemented in Modelica, for the simulation of occupant behaviours of lighting, windows, blinds, heating and air conditioning systems in office and residential buildings. Examples were presented to illustrate how the models in the Occupants package are capable to simulate stochastic occupant behaviours. The major contribution of this work is to introduce the equation-based modelling approach to simulate occupant behaviours in buildings and to develop an open-source Occupants package in the Modelica language.

Multi-objective optimization of solar energy systems for electricity and hot water generation in collective residential buildings considering the power-to-heat concept

In this work, a mixed integer linear programming (MIP) approach for the optimal design of energy systems in residential buildings is presented. The optimization model considers the economic criteria of the guideline VDI 2067. The objective of the MIP is to minimize the annual costs which comprise the investment as well as demand- and operation-related costs. Conventional boilers, electrical heaters, combined heat and power (CHP) units, heat pumps (HPs), photovoltaic (PV) systems and thermal storages as well as local heating networks (HNs) are defined as options. The investigation on a building level shows that a boiler is the economically optimal solution for small buildings, followed by a HP unit. In multi-family buildings, both boilers and CHP units hold an economical advantage over HPs. For apartment buildings, CHP is identified as the economically optimal system. In the neighbourhood analysis of six buildings, the solver establishes a local HN which allows for both economical and CO2-emission reductions.

A predictive and adaptive control strategy to optimize the management of integrated energy systems in buildings

Investigation of VRF system cooling operation and performance in residential buildings based on large-scale dataset

Purpose The purpose of this paper is to examine the variables that impact the adoption of energy management systems in residential buildings, focusing on the main motivations behind their acceptance. Design/methodology/approach The study used the Delphi technique and analyzed the data quantitatively. Quantitative data was collected by administering a well-structured research questionnaire to 20 Delphi experts knowledgeable in energy usage, energy management and energy efficiency. The obtained data was analyzed using descriptive analysis. Findings The study highlights that the most significant drivers for adopting energy management systems (EMS) in residential buildings are predominantly economic and operational factors. Reduction of energy costs and the ability to track energy consumption from sensors, which promotes energy-saving behavior, were strongly agreed upon by respondents, reflecting their importance in influencing adoption decisions. Energy consumption reduction also emerged as a key driver, emphasizing the critical role of reducing operational expenses. Other drivers, such as economic factors like rising energy prices and the reduction of energy demand, underscore the economic pressures encouraging EMS adoption. Environmental considerations, such as reducing environmental degradation and improving environmental conditions, were ranked lower, showing a lesser but still meaningful emphasis on sustainability. Factors like enhanced energy security, reduction of global warming and commitment from top management were among the least prioritized, reflecting potential challenges in awareness, investment or policy support. Practical implications The study offers policymakers and industry stakeholders useful data for developing targeted strategies and incentives to encourage homes to use energy-efficient devices. It also provides useful direction for residential developers and utility providers in designing and promoting energy management systems that are consistent with customer preferences and habits, resulting in more sustainable living environments. Originality/value The study provides a comprehensive look at the key factors driving the adoption of energy-saving technologies in homes, giving new insights into consumer behavior and industry trends. The value of it is highlighted by giving empirically supported advice to policymakers and industry leaders on how to promote more effective and broad adoption of sustainable energy practices in the residential sector.

Factors influencing the airflow rate of kitchens in cooking exhaust shaft system of high-rise residential buildings

Comparative research on different air conditioning systems for residential buildings

Energy performance of buildings: The evaluation of design and construction measures concerning building energy efficiency in Iran

Renewable energy systems (RES) in buildings should be designed carefully, not only because of the need for an optimal design, but also to comply with related laws. Therefore, the design of RES in the buildings requires close collaboration between architects and engineers from the beginning of the design process. To support such collaboration, this study proposes a simplified design method for RES in buildings during the early design stage. By using the proposed design method, design alternatives that meet the required energy standards as suggested by law are first generated. Further designs are made to evaluate the performance and cost of the design alternatives and to find the optimal types of RES for the building. The study also uses a case study to verify the applicability of the design method to the early design stage. Although the performance and cost of the different design alternatives are similar, the implementation of each type of RES in each design alternative is different. Nonetheless, by analyzing performance patterns and the cost ratio of each type of RES in each design alternative, the study allows the most suitable type of RES to be chosen for the building.

Optimization and evaluation of CCHP systems considering incentive policies under different operation strategies

Delta-T-based operational signatures for operation pattern and fault diagnosis of building energy systems