An all-in-one machine coupled with a horizontal ground heat exchanger for the air-conditioning of a residential building

Heating, ventilation and air conditioning (HVAC) systems are considered of great importance in the building sector, as they represent a significant part of the energy demand in buildings. Moreover, they are deeply related to indoor environmental quality, which strongly affects occupants' quality of life. This paper presents the analysis of a compact all-in-one and plug-and-play machine providing heating, cooling and controlled mechanical ventilation to a low energy residential building. In particular, the system is composed of an air-to-air heat pump coupled to a heat recovery unit which can pre-heat the fresh air and contribute to domestic hot water production. In the present work, an additional heat exchanger embedded in the building's foundations has been included in the system to pre-heat or pre-cool the outdoor air before it enters the heat recovery unit. The compact energy system has been mathematically modelled, and its operations have been monitored in a real residential building recently constructed in Udine (North-East of Italy). The annual energy performance of the all-in-one machine has been obtained, and the system layouts with and without ground heat exchangers have been compared. The use of the ground heat exchanger helps to decrease the primary energy consumption and the operating costs (in heating, 14% and 11% respectively), improving, at the same time, the thermal comfort conditions inside the building

Analysis of a double source heat pump system in a historical building

This work presents the case study of the retrofitting of a historical building of the University of Padua, equipped with a hybrid heat pump system, which uses as heat source/sink the ground and ambient air. The building is located in Padua (Italy) and it is a historical complex of the late 1800, previously used as a geriatric hospital, in which a retrofit process is occurring in order to build the new humanistic campus of the Padua University reaching the highest energy efficiency. The refurbishment is in progress and regards both the building envelope and the plant-system. The building is equipped with two types of heat pumps: the first one is coupled to the ground with borehole heat exchangers and the second is a common air-to-water heat pump. The entire building plant system has been investigated through integrated computer simulations making use of EnergyPlus Software. A new control strategy in order to manage the two types of the heat pumps has been developed in order to increase the energy efficiency. The results outline the potential of the computer simulations in order to control the hybrid heat pump system. In fact, a suitable switch temperature was found in order to move from ground to air source/sink for the heat pumps. In addition, this strategy allows the control of the thermal drift of the ground temperature throughout the years

At the roots of the energy performance gap: Analysis of monitored indoor air before and after building retrofits

The growing concern about climate change and energy security has fostered energy efficiency measures to reduce building consumption in many European countries. The policies and incentives behind these improvements typically rely on pre-calculated expected energy savings. However, evidence shows that the actual energy performance after such interventions often falls short of the expected targets. People’s behavior is one of the causes of the energy performance gap between measured and predicted building energy performance. This study contributes to this discussion by analyzing data on air temperature, relative humidity, and Volatile Organic Compounds monitored in eleven apartments in Milan (Italy) before and after building renovation. These data were then used to simulate two representative flats, thus obtaining their energy demand for space heating. The analysis of the measured data shows that users adapt differently to building retrofits. Under the assumption of constant moisture generation during the periods monitored, some occupants appear to increase air change rates and reduce indoor air temperatures, while others show the opposite behaviour. These trends could be related to the fact that some users prioritize air quality over thermal comfort and vice versa. Energy simulations suggest that the former behaviour leads to a larger energy performance gap

Analysis and application of a lumped-capacitance model for urban building energy modelling

Buildings are one of the major responsible of energy consumption and carbon emissions worldwide. Due to the continuous growth of cities, researchers moved their focus from single buildings to urban scale analyses. The present work aims at demonstrating the reliability of a lumped-capacitance model in the evaluation of heating and cooling demand at urban level. The model presented extends a previous one with different modules for solar radiation pre-processing, HVAC systems and photovoltaic production estimation. A case-study district of 13 buildings in Padua (Italy) has been analysed, considering detailed single buildings simulations with EnergyPlus as benchmark. Results show that the model leads to good accuracy in the evaluation of the district energy demand for both space heating and cooling. The major sources of error are geometrical simplifications, shadowing and thermal zoning effects, thus showing the importance of high-quality input data in urban modelling. However, results highlight how simple corrections may enhance the accuracy when detailed geometrical information is not available. Finally, the model has been used to assess the cost and energy saving potential of several building retrofit measures and PV installations on the considered district, providing an important indication in the investment priority for decision makers

Comparative analysis between dynamic and quasi\u2010steady\u2010state methods at an urban scale on a social\u2010housing district in Venice

The residential building stock represents one of the major players in energy use and greenhouse gas emissions; thus, it is fundamental to reduce the energy used. Simulation tools are becoming more and more accurate in compliance with the new requirements both at the singlebuilding and at the district scale, although they are not affordable by non\u2010specialist users such as policymakers. The research concerns the evaluation of the energy demand for space heating for a historical district that is representative of the Italian building stock. The work compares dynamic and specialist\u2010oriented urban scale tools such as Energy Urban Resistance Capacitance Approach (EUReCA) and City Energy Analyst (CEA)) as well as a quasi\u2010steady\u2010state calculation method (Excel spreadsheet), which is more affordable for non\u2010specialist users. The work was carried out to assess the possible deviation of the results between the dynamic and quasi\u2010steady\u2010state calculation methods, as well as to identify any limits and opportunities in the application of the latter procedure, which is currently the official national calculation tool for the implementation of Directive 2010/31/EU. The study shows how the quasi\u2010steady\u2010state method predicts a reliable building energy demand, in line with the results obtained by the two dynamic tools, when considering only geometry and infiltrations as input. However, the limits of the quasi\u2010steady\u2010state method emerge when introducing internal loads, significantly underestimating the energy demand compared to CEA and EUReCA simulations. The results underline the potential application of the quasi\u2010steady\u2010state method to predict energy demand, although dynamics tools are more reliable but far more complex. Major findings through two methods concern the impact of solar heat gains on the overall heating demand at both the single building and the district scale. The different results between the tools provided evidence of a gap in the use of the simplest tool and demonstrated the accuracy and reliability of the proposed approach with a lower computational effort

Lumped-capacitance models to evaluate the urban cooling energy consumptions: analysis on a case-study district in the University of Padua

The growth of urban population and consumption has boosted research about Urban Building Energy Modelling (UBEM). This paper proposes an analysis of the cooling energy demand of a real district with a new UBEM platform, EUReCA (Energy Urban Resistance Capacitance Approach). EUReCA consists of a Python-based tool to predict cities' energy demand based on simplified physical models. The article compares the hourly temperature and humidity profiles to those calculated with EnergyPlus, used as a benchmark. Moreover, hourly and seasonal cooling demand are verified and peak load difference is highlighted. Finally, the effect of several retrofit actions on building envelopes and HVAC plants is discussed and compared to the current scenario

Analysis of the thermal inertia of historic buildings and related advantages for retrofit strategies applied for urban energy modeling

Since the beginning of this century Italian legislation focused on historic and existing buildings’ retrofit, as they represent a large part of the national building stock. In this context the most difficult challenge is preserving heritage and obtaining energy saving at the same time. Energy Plus software is used for the detailed dynamic simulation and is compared to simplified resistance-capacitance models. A sensitivity analysis is performed to evaluate the input parameters and their influence on the thermal behaviour of an historic building in Padua (Italy), highlighting the effect of high thermal mass to flatten the temperature trends and optimizing systems’ operation