Maurizio Sasso

Micro-combined heat and power in residential and light commercial applications

Abstract The cogeneration is worldwide considered as the major option to achieve considerable energy saving with respect to traditional systems. This paper deals with the application of micro-cogeneration (electrical power

Assessment of micro-cogeneration potential for domestic trigeneration

Cogeneration is worldwide considered as the major option to achieve considerable energy saving with respect to traditional systems. This paper deals with the application of micro-cogeneration, Micro-Combined Heat and Power (MCHP) (electrical power &;60;15 kW) to small-scale (residential application) users for the assessment of its use in trigeneration; the state of art of this technology is considered, a test facility designed and built to evaluate the performances of MCHP-Electric Heat Pump (EHP) system itself is described and the Energetic, Economic and Environmental (3-E) analysis in some operation mode to match the users loads is proposed.

Determining the optimal configuration of a heat exchanger (with a two-phase refrigerant) using exergoeconomics

Abstract In this paper, the exergoeconomic theory is applied to a heat exchanger for optimisation purposes. The investigation was referred to a tube-in-tube condenser with the single-phase fluid to be heated flowing in the inner annulus and the two-phase refrigerant flowing in the external annulus. First, the irreversibility due to heat transfer across the stream-to-stream temperature-difference and to frictional pressure-drops is calculated as a function of two design variables: the inner-tubes diameter and the saturation temperature of the refrigerant, on which the heat-exchange area directly depends. Then, a cost function is introduced, defined as the sum of two contributions: the amortisation cost of the condenser under study and the operating cost of the conventional electric-driven heat-pump in which this component will have to work. The latter contribution is directly related to the overall exergy destruction rate in the plant, whereas the amortisation cost mainly depends on the heat-exchange area. So, design optimisation of the device can be performed by minimising this cost function with respect to the selected design variables. The so-called structural approach (Coefficient of Structural Bond) is used in the optimisation, in order to relate the local irreversibility in the condenser to the overall exergy destruction rate in the heat-pump plant. A numerical example is discussed, in which, for a commercial heat-exchanger, the design improvements needed to obtain a cost-optimal configuration are investigated. The results show that significant improvements can be obtained with respect to devices based on conventional values of the design parameters.

Model Predictive Control-Based Optimal Operations of District Heating System With Thermal Energy Storage and Flexible Loads

Operating heating power plant (DHPP) with fluctuating load is a complex problem. Thermal energy storage (TES), flexible loads, and operating constraints compound this complexity further. This investigation focuses on the design of a model predictive controller (MPC) that reduces the operating and maintenance cost in a DHPP, considering TES and flexible loads. The MPC accomplishes this task by scheduling boilers, TES units, and flexible loads. To handle the fluctuating demand, the MPC uses forecasts and combines it with a constrained optimization problem. The objective function reflects the cost, whereas the generator limits, TES dynamics, thermal loads, including supply temperature, power plant layout, and reliability, are the constraints. The resulting optimization problem is modeled as a mixed-integer linear program with both continuous and logic variables. Here the logic variables model the operating modes of the boiler and storage units. The use of receding horizon approach enhances the robustness to the forecast errors. The constraints modeling plant layout, supply temperature, and grid reliability lead to a more realistic solution. The MPC is illustrated using simulation on historical data and experiments on a DHPP at Ylivieska, Finland. Our results demonstrate the cost benefits of the proposed approach.

Optimum performance of heat engine-driven heat pumps: A finite-time approach

Abstract Classic thermodynamics, assuming the Carnot machine as the upper comparison limit in energy conversion systems analysis, considers thermal equilibrium during heat transfer interactions. Such an assumption requires either infinitely slow cycles or infinitely large heat exchanger surfaces. More realistic limits on the optimal operation of energy systems can be provided by finite-time thermodynamics, which takes into account the constraints represented by finite operation time and limited heat interaction area. This paper focuses on the search for the optimum heating performance of a heat engine-driven heat pump in which the waste engine heat is used for heating purposes. At first, only thermal irreversibilities are considered; then, in order to obtain a more realistic model, the so called “internal” heat leak irreversibilities are taken into account too. Finally, a comparison between the performances of the irreversible model and those of actual plants is carried out.

Optimal operation of a district heating power plant with thermal energy storage

This paper presents an optimal control strategy for a district heating power plant with thermal energy storage. The main goal of the control strategy is to reduce the operation costs of the power plant, by scheduling the boilers, the operation of the thermal energy storage and the curtailment on the loads. The problem is stated as a constrained optimization in the form of a Mixed Integer Linear Program (MILP), embedded on an Model Predictive Control (MPC) framework. Particular attention is paid to modeling of boilers operating constraints, including the outlet water flow temperature, to the energy exchanged with the thermal energy storage and to the operating modes of the power plant layout, including the constraints related to the supply water temperature needed from the network. The results are performed using the data and the layout of the power plant located in the city of Ylivieska, in Finland. The cost analysis performed shows the advantages of using the predictive control strategy.

3-E Analysis of a Heat Pump Driven by a Micro-Cogenerator

The cogeneration, or the combined production of electric (and/or mechanical) and thermal energy, is a well established technology, which has important environmental benefits and it has been noted by the European Community as one of the first elements to save primary energy, to avoid network losses and to reduce the greenhouse gas emissions. In particular, our interest will be focused on the micro-cogeneration, MCHP (electric power ≤ 15 kW), which represents a valid and interesting application of this technology which refers, above all, to residential and light commercial users. This article reports the Energetic, Economic and Environmental (3-E) analysis of a natural gas fuelled micro-cogenerator combined with an electric heat pump (EHP), MCHP/EHP, starting by the results of an intense experimental activity developed in a simulation station [1] in a wide range of conditions. The MCHP/EHP, is fuelled by chemical energy and it can be considered as a thermally activated heat pump, a very interesting alternative to the conventional electric inverse machines. There have been simulated two operating conditions: a heating mode with coproduction of electric and thermal energy, and a cooling mode with co-production of electric, thermal and cooling energy (trigeneration). The performances during a year of functioning are evaluated too.

Exergetic cost and exergoeconomic evaluation of vapour-compression heat pumps

An application of the theory of exergetic cost and the exergoeconomic evaluation of a conventional vapour-compression heat pump are described. Included are effects of malfunctioning by plant components. Evaluation of the achievable exergy saving by restoring the original efficiency of a single device is included. A vapour-compression heat pump is used in a numerical example.

Experimental analysis of small scale cogenerators based on natural gas fired reciprocating internal combustion engine

The European Union recently established an ambitious target by 2020 that consists of increasing the utilization of renewable energy up to 20%, reducing its overall pollutant emissions to at least 20%, and achieving a primary energy saving of 20% compared to reported 1990 levels. This aim could be reached only with strong effort in different sectors, such as residential, commercial, industry, tertiary, transportation, .... In particular in the European Union a remarkable contribution to energy consumption and CO2 emissions is concentrated in residential and commercial sector. The introduction of more efficient technologies in these sectors could help in achieving the results expected by 2020. An option is given by cogeneration, defined as the combined “production” of electric and/or mechanical and thermal energy starting from single energy source, that could be considered one of the first elements to save primary energy, to avoid network losses and to reduce the greenhouse gas emissions. In particular, our interest will be focused on the microcogeneration (electric power ≤ 15 kW), which represents a valid and interesting application for residential and light commercial users. The energetic, economic and environmental implications due to the use of small scale cogeneration systems were reported, starting by an experimental research activity performed by the authors and other researchers.© 2010 ASME

Cogeneration for Energy Saving in Household Applications

During the last decade, small-scale combined heat and power systems are becoming a viable alternative to conventional power supply and boiler-based heating system in many types of applications. With regard to domestic sector, the use of combined Heat and Power generation on micro scale (< 15 kW electric output), micro-CHP for short, is currently relatively uncommon, but the market availability of gas-fuelled generating equipment, together with a significant number of current R&D projects, confirms the large potential for micro-CHP development, that was up to now limited to niche applications. In this paper attention is paid to the problems derived by the transfer of this technology, well known in the industrial field, to small-scale applications. One of the greatest obstacle is the match between thermal and electric energy outputs of the micro-CHP and the load profiles of end users. Consequently, some energy residential appliances such as dishwasher, clothes washer, water heater, will be considered in the paper, both in their traditional configuration (electricity driven) and in alternative more efficient configurations (thermal and electricity driven). Some energetic and economic analyses are presented. Finally an experimental apparatus set up to study the integration of a micro-CHP system with usual household appliances and heating equipment is shown.