1,721,025 research outputs found
Modelling and control optimization of a solar desiccant and evaporative cooling system using an electrical heat pump
No full textAbstractThe aim of this work is the control optimization of a new solar assisted air-conditioning concept which combines a desiccant and evaporative cooling (DEC) system with an electrical heat pump. The DEC air handling unit configuration had to prevent return air from mixing with supply air. Therefore, a flat plate sensible heat exchanger is used instead of a rotary. Moreover an additional stream of outdoor air is used for the desiccant wheel regeneration. A reversible water/water heat pump is also included in the system. In summer, the heat pump cools the supply air stream and pre-heats the regeneration air when dehumidification is needed; in winter, the heat pump provides auxiliary heat if a minimum temperature is available in the heat storage, otherwise a backup boiler is used. The depicted system has been modelled and an extensive simulation work has been carried out in order to verify the control capability during the different operation modes. As a result an optimal control strategy has been identified. According to simulations, the system can deliver primary air at the requested temperature and humidity while holding the overall electricity consumption at significant low levels compared to reference system solutions
Numerical investigation of the castle of Zena energy needs and a feasibility study for the implementation of electric and gas driven heat pump
Full text linkThe Italian buildings stock includes a large amount of historical buildings. The reduction of national building energy consumption necessarily implies their refurbishment as well as an effective use of appropriate HVAC technologies today available. In this work a numerical investigation of the historical building Castle of Zena (XXIII century) and a feasibility study for the retrofit of its HVAC plant is presented. The work followed three main steps: the definition of the numerical model and the simulation of the building energy performance using the software platform TRNSYS 16 (Transient System Simulation Tool); selection, design and simulation of three appropriate HVAC options; discussion of results from the energy, economic and environmental point of view. Two type of numerical analyses on the building envelope have been performed: a first one in free floating conditions (no temperature control), and a second one with an ideal temperature control. The free floating simulation has been used for a first evaluation of the building performance. The adaptive comfort approach (Adaptive Comfort Algorithm) has been implemented to compare internal temperature with an acceptability range. Results have shown that during almost the 50% of the summer season internal temperature is above the upper limit of the comfort range, therefore a cooling plant is needed. On the other end, the annual energy needs for space heating is around 164 kWh/m2/year, while the space cooling is around 5 kWh/m2/year. Results coming from this first analysis, together with data obtained with the simulation with controlled internal conditions, have been used to design the HVAC systems. Due to the historical constraints and the installation effort needed it has been decided to exclude the HVAC technologies belonging to the category of all-air systems. Water systems have been selected. In particular, among them two pipe fan coil units were chosen as emissions systems, characterized by easy integration despite the good emission efficiency. Given the environmental and landscape constraints, wind, photovoltaic and solar thermal technologies have been excluded. Therefore a heat pump system was chosen as generation system using renewable energy. In the present study, two different type of heat pump system (HP) are analyzed. The first one is an electric heat pump (EHP) based on a compression cycle electrically powered and the second one is an air source gas driven absorption heat pump (GAHP-AS). Moreover two types of EHP systems have been analyzed. The first one is an air-water heat pump (EHP-AS) characterized by a low initial investment cost, while the second one is a water source heat pump (EHP-WS) linked to the existing well of the Castle. Neglecting, the control, emission and distribution sub-system energy needs, the system with the lowest primary energy consumption is the EHP-WS (103 kWh/m2/year), followed by the GAHP-AS (150 kWh/m2/year) and the EHP-AS (180 kWh/m2/year). From the economic point of view the EHP-WS have the shortest pay-back time, 7 years, also thanks to the use of the existing well, against the 14 years of the GAHP-AS. However, excluding the water source, only the gas absorption heat pump is economically feasible. Finally we could obtain a significant reduction of greenhouse gas emission (CO2) replacing the EHP-AS with the GAHP-AS (-26%) or the EHP-WS (-38%)
Modelling and experimental analysis of a GAX NH3-H2O gas-driven absorption heat pump
Full text linkThe experimental analysis of a gas-driven NH3-H2O heat pump whose cycle approaches the GAX concept is carried out. Full load operation is investigated by varying hot water temperatures and partial load operation is investigated by decreasing gas input down to 50% of the full load value. Numerical simulations bolster measurements accuracy and provide insight on the variation of cycle COP and Gas Utilization Efficiency (GUE), based on gross calorific value. A nearly constant GUE of about 1.5 is found for hot water temperatures lower than 50°C. The GUE steadily decreases above 50°C, reaching about 1.33 at 60°C. The COP varies more smoothly, from 1.73 at 45°C to 1.60 at 60°C. The GUE and COP reduction at 50% of the nominal gas input is 6.8% and 6.4%, respectively. Simulations suggest that performances at partial loads can improve if active control of solution mass flow rate is implemented. © 2016 Elsevier Ltd. and International Institute of Refrigeration. All rights reserved
Energy, environmental and economic analysis of electric vapour compression and gas driven absorption heat pumps for single-family houses
Full text linkThe aim of this paper is to compare energy consumptions, CO2 emissions, and operative costs of condensing boilers, electric vapour compression heat pumps and gas driven absorption heat pumps to provide space heating and domestic hot water. The analysis is performed for 140 m2 single-family houses in five different Italian cities whose envelope features depend on the location. For each location, two different envelope conditions are considered. The first one is a non-insulated building, while the second one is the same building, but an external thermal insulation is added on vertical walls and roof. To avoid internal renovation, radiators are maintained as emission system. Combined dynamic simulations are performed to appreciate building and system interactions. A 6 second time step is set to evaluate properly interactions and the DHW profile demand. In addition, the GHP dynamic model is a grey box model experimentally validated. The results show that electric vapour compression heat pumps reach the highest non-renewable primary energy savings (>32%) compared to condensing boilers, but their operative costs are higher due to the higher specific cost of electricity in Italy. Gas driven absorption heat pumps achieve a lower consumption reduction than electric heat pumps (>22%), but they have also the minimum operative cost among the three technologies
Dynamic modelling and comparison between transient step response of capacitive hygrometers and chilled mirrors for delay compensation
No full textAbsorption and compression heat pump systems for space heating and DHW in European buildings: energy, environmental and economic analysis
Full text linkThe selection of the proper device for space heating and domestic hot water for a building is crucial to achieve good energy and economic performances. For a single-family house, the most common heating device is the condensing boiler. Solar systems, electric heat pumps and gas driven sorption heat pumps represent suitable alternatives for improving the efficiency. Although the performances of each technology are well known, their ability to operate efficiently in bivalent heating plants depends on several variables and the choice of the most suitable heating system for a specific building is not straight-forward. The aim of this paper is to compare, under conditions typical of the European region, the seasonal performances of six system configurations that are obtained by combining the most commonly used heating technologies. The comparison is carried out in terms of primary energy consumption for three climatic conditions, changing the quality of the building envelope and the emission system typology. Although the results are sensitive to the primary energy factor for electricity, electric heat pumps generally result the most promising technology for conditions with low thermal lift, while gas heat pumps have the higher performances at high lift. Additionally, the systems are compared in terms of yearly CO2 emissions and economic feasibility, finding scattered results among countries, due to large differences in the local energy mix and energy prices
A Continuous Commissioning Analysis and its Application to a New Installed Solar Driven DEC System Coupled with Heat Pump
Full text linkAbstractThe aim of this paper is to define and implement a continuous commissioning methodology that can be effectively applied to a solar driven desiccant and evaporative cooling (DEC) system. The objective is to assess the energy performance of the system's components and identify possible operation faults. The methodology consists in the breakdown and analysis of the DEC into sub-systems; for each of them a simplified dynamic mathematical model based on experimental data has been developed. A possible fault is detected when the difference between the theoretical and measured performances is higher than the accuracy of the methodology. The proposed methodology has been successfully implemented for a hybrid solar DEC system comprising a non-conventional DEC air-handling unit, a solar thermal system and an electrical heat pump.The results of the methodology's application to the first experimental data of summer 2014lead to the following conclusions: the solar sub-system operated as expected whereas the heat pump and the desiccant rotor did not. In particular, the electrical heat pump has a higher cooling capacity than the one predicted at partial load but with a similar COP value, this deviation is mainly due to the assumed partial load performance coefficient. The desiccant rotor presents a much lower performance than the one expected. However, the rotor inefficiency is difficult to highlight due to the high measurement uncertainties on the air side
Analysis of HVAC retrofit layouts including solar cooling system with adsorption heat pump - Modelling, dynamic simulation and multi-criteria evaluation
No full textMinimalist RC network for building energy simulations: a case study based on OpenBPS
Full text linkRobust and fast dynamic simulation tools are crucial for the sizing of the components of complex HVAC system and for the definition of the optimal control strategy. In this work, a first step towards the extension of OpenBPS, a new building energy performance simulation tool, to the dynamic simulation of HVAC systems is presented. In particular, the building model has been reduced to a Resistors-Capacitors (RC) network and OpenBPS has been used for the identification of the parameters of the grey-box model. Indeed, the reduction and identification of the building energy model is the fundamental step for extension of the tool to perform dynamic simulations of complex HVAC systems with the advantage of low computational load, thus suitable for parametric yearly simulations and control strategy analyses. The toolkit of identification and cross validation of a minimalist RC network is presented in this paper, discussing the results obtained for a case study building under study in the European project Heat4Cool founded by Horizon 2020 programme. The identified model demonstrated a good accuracy in the estimation of the room temperature under different tests settings representative of the actual operating conditions
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