Optimal integrated sizing and operation of a CHP system with Monte Carlo risk analysis for long-term uncertainty in energy demands

In this study a probabilistic approach for optimal sizing of cogeneration systems under long-term uncertainty in energy demand is proposed. A dynamic simulation framework for detailed modeling of the energy system is defined, consisting in both traditional and optimal operational strategies evaluation. A two-stage stochastic optimization algorithm is developed, adopting Monte Carlo method for the definition of a multi-objective optimization problem. An Italian hospital facility has been used as a case study and a gas internal combustion engine is considered for the cogeneration unit. The results reveal that the influence of uncertainties on both optimal size and annual total cost is significant. Optimal size obtained with the traditional deterministic approach are found to be sub-optimal (up to 30% larger) and the predicted annual cost saving is always lower when accounting for uncertainties. Pareto frontiers of different CHP configurations are presented and show the effectiveness of the proposed method as a useful tool for risk management and focused decision-making, as tradeoffs between system efficiency and system robustness

Cost-optimal sizing of solar thermal and photovoltaic systems for the heating and cooling needs of a nearly Zero-Energy Building: the case study of a farm hostel in Italy

In this paper, the second of two parts, we apply the cost-optimal design method illustrated in Part 1 to a case study. We select a farm hostel located in Enna, Italy, as the local climate and the required energy services are suitable for the development of a solar-assisted nearly zero-energy building. The system is connected to the electric grid and does not use any other thermal energy vector. Energy demand includes heating, cooling, domestic hot water production, lighting and other electric uses, viz. inductance cooking, food refrigeration, local dehumidification, household appliances, and office devices. The building-plant system is described in terms of both technical characteristics of each component and internal loads. According to the proposed simulation-based methodology, we investigate the best design configuration by minimizing the lifecycle cost after 20 years of operation. The results of the procedure identify the optimal solution, in terms of number of solar thermal and photovoltaic panels, volume and control strategy of the thermal storage. Other outputs are the dynamic and seasonal energy balance of each system component and of the whole system, and additional economic parameters. The results show that the proposed method leads to a very favorable design with relevant notable economic and energy benefits with respect to a no-solar design solution (ΔCTOT=11%, ΔEINTOT=67%). However, several nearly optimal configurations provide very similar outcomes in terms of lifecycle costs, with different initial investment and energy performances. Consequentially, we introduce a multi-objective optimization approach aimed at identifying the best solution in terms of investment availability and energy objectives

A Proposal for New Microclimate Indexes for the Evaluation of Indoor Air Quality in Museums

A correct artwork preservation requires strict values of several microclimate parameters, in particular temperature, humidity, and light. In existing museums, the evaluation of the effectiveness of current building plant systems and management is essential to avoid artwork deterioration. In this work, we propose the use of five simple performance indexes that use monitored data to estimate the suitability of the whole museum system in the maintenance of benchmark values of temperature, humidity, and light. The new indexes also take into account microclimate daily span and spatial homogeneity, which can represent a criticality in the preservative process. We apply these new indexes to the results of a monitoring campaign in Palazzo Blu, a museum in Pisa, which lasted for almost four months during a temporary exhibition on Toulouse-Lautrec works. The indexes show a mainly acceptable instantaneous microclimate, but HVAC (Heating, Ventilating and Air Conditioning) system improvement is necessary to avoid high thermo-hygrometric daily span. This methodology is useful for the identification of microclimate criticalities and can help the cooperation between conservation experts and professionals giving hints to improve museum internal microclimate. In case ofalready optimal microclimate, these indexes can be useful in more complex analyses, including simulations of possible retrofit actions, keeping microclimate suitability as a constraint

Cost-optimal sizing of solar thermal and photovoltaic systems for the heating and cooling needs of a nearly Zero-Energy Building: design methodology and model description

This paper deals with the cost-optimal sizing of solar technologies for thermal and electrical needs of residential or tertiary buildings. We consider a typical nearly Zero-Energy Building, whose requirements of thermal and electrical energy are evaluated on the basis of internal loads and external climate. The building is heated and cooled with radiant panels; a heat pump and a system consisting in solar thermal collectors and a thermal storage provide thermal energy, while PV modules supply electricity. The proposed design procedure finds the best number (i.e. the size) of solar thermal and PV modules to be installed, through a lifetime simulation of building loads and energy system according to proper cost-optimality considerations. The paper is divided in two parts. In this first part, we describe general features and principles of the methodology, together with the physical models of each component of the building-plant system. Then, in the second part, we present a case study implementing the illustrated procedure. Results show the notable benefits of the proposed design approach with respect to traditional ones, in terms of both energy and economic savings. We consider simulation-based technique a promising tool for engineering activity as its results can be used to compare different design alternatives and choose a proper cost-optimal solution according to the specific project, context and goals priority. Besides, the proposed methodology can be successfully applied in the more general framework of Net Zero Energy Buildings (NZEBs) in order to fulfill recent regulatory restrictions and objectives in building energy performances

Energy Intensity Reduction in Large-Scale Non-Residential Buildings by Dynamic Control of HVAC with Heat Pumps

One of the main elements for increasing energy efficiency in large-scale buildings is identified in the correct management and control of the Heating Ventilation and Air Conditioning (HVAC) systems, particularly those with Heat Pumps (HPs). The present study aimed to evaluate the perspective of energy savings achievable with the implementation of an optimal control of the HVAC with HPs. The proposed measures involve the use of a variable air volume system, demand-controlled ventilation, an energy-aware control of the heat recovery equipment, and an improved control of the heat pump and chiller supply water temperature. The analysis has been applied to an academic building located in Pisa and is carried out by means of dynamic simulation. The achieved energy saving can approach values of more than 80% if compared with actual plants based on fossil fuel technologies. A major part of this energy saving is linked to the use of heat pumps as thermal generators as well as to the implementation of an energy efficient ventilation, emphasizing the importance of such straightforward measures in reducing the energy intensity of large-scale buildings

Control of natural circulation loops by electrohydrodynamic pumping

The paper analyses the effect of electrohydrodynamic (EHD) pumping on the control of natural circulation loops (NCLs). The two major objectives of the investigation are: finding the optimal configuration of an EHD pump and demonstrating that the NCL flow direction can be inverted by exploiting the EHD phenomena. In the initial experimental set-up, we measured the static pressure rise given by an EHD pump made of three consecutive modules of point-ring electrodes for different dielectric fluids and electrode materials. When reversing the polarity of the applied DC voltage, we observed opposite pumping directions, suggesting the presence of two distinct EHD phenomena, inducing motion on opposite directions: ion-drag pumping and conduction pumping. The former was identified as a more efficient process compared to the latter. Based on these preliminary experiments, we built a NCL, operating with the fluid HFE-7100. Two oppositely mounted optimised pumping sections could be alternately activated, to promote clockwise or anticlockwise motion. In the first series of tests, alternately, the pumping sections were triggered prior to the heat input. In any case, the circulation followed the EHD pumping direction. In other tests, the electric field was applied when natural circulation was already present and the flow was reversed by means of opposite EHD pumping, at both polarities. Simply inverting the polarity of the applied voltage, we could alternate ion-drag and conduction pumping; in this way, we easily controlled the direction of motion by means of a single EHD pumping device

On Sustainable and Efficient Design of Ground-Source Heat Pump Systems

This paper is mainly aimed at stressing some fundamental features of the GSHP design and is based on a broad research we are performing at the University of Pisa. In particular, we focus the discussion on an environmentally sustainable approach, based on performance optimization during the entire operational life. The proposed methodology aims at investigating design and management strategies to find the optimal level of exploitation of the ground source and refer to other technical means to cover the remaining energy requirements and modulate the power peaks. The method is holistic, considering the system as a whole, rather than focusing only on some components, usually considered as the most important ones. Each subsystem is modeled and coupled to the others in a full set of equations, which is used within an optimization routine to reproduce the operative performances of the overall GSHP system. As a matter of fact, the recommended methodology is a 4-in-1 activity, including sizing of components, lifecycle performance evaluation, optimization process, and feasibility analysis. The paper reviews also some previous works concerning possible applications of the proposed methodology. In conclusion, we describe undergoing research activities and objectives of future works

Validation of SEAS, a Quasi-Steady-State Tool for Building Energy Audits

SEAS is an energy auditing software that can simulate residential, office, school, and hospital buildings, providing energy requirements for heating, domestic hot water production, ventilation, lighting, and other electrical uses. In order to validate this quasi-steady-state tool, we simulated in SEAS several reference cases (based on EN 15265 benchmark room) and a residential dwelling. We also used the dynamic simulation software TRNSYS and compared the results of the two software in terms of seasonal energy requirements for space heating and energy fluxes through the elements of the building envelope. Most of SEAS results are in good agreement with EN 15265 and with TRNSYS. Nonetheless, we pointed out that SEAS lacks in accuracy when it simulates high thermal inertia buildings with intermittent heating: for these particular cases, new correlations for dynamic parameters and reduction factors should be developed

Criticalities in the NZEB retrofit of scholastic buildings: analysis of a secondary school in Centre Italy

Abstract In Italy, the recast of the European Directive on Energy Performance of Buildings (2010/31/EU) is implemented with specific definitions and deadlines for Nearly Zero Energy Buildings. We focus our attention on schools, not only for their social importance and high visibility, but also because in the next future a significant share of these buildings is likely to undergo refurbishment for different purposes than the energetic one. We start to analyze the criticalities associated with the current Italian legislation on NZEBs by means of a bottom-up approach: we choose a benchmark secondary school (located in Pisa, hosting about 750 students) and perform an accurate energy audit of the building system, together with an energy and economic simulation of an NZEB retrofit. More in detail, we present the case study and explain its choice as an appropriate representative of the existing scholastic buildings in Centre Italy; besides, we build two concurrent energy models, based on tailored and asset rating methods, we propose technically-feasible actions for deep renovation, and simulate, for both models, the associated energy and economic savings after 20 years of use. We observe long payback periods of the retrofit measures, due to low yearly energy uses in the existing configuration. Based on these results, we attempt to extend to a more general level the considerations on strengths and weaknesses encountered in the present application of the Italian regulation on NZEBs

Environmental monitoring of a Sardinian earthen dwelling during the summer season

Increasing interest in earth architecture has led to the development of new international norms regarding these structures. Although Italy has no specific legislation for this building type, both national laws for the safeguard of rural architecture and regional norms regarding the conservation of historical centers have considerably slowed down the pace of their destruction. This is particularly true for Sardinia, which maintains a conspicuous heritage of "raw earth" architecture, mostly in the old town centers of the Campidano plain and in its adjacent valley. Due to the current legislation on energy efficiency in buildings, it has become essential – particularly for the Sardinian region – to define guidelines for the improvement of energy efficiency for this existing building heritage and identify the best parameters for their energetic classification. Currently, these constructions are heavily penalized by the gap that persists between the requirements of current energy balance evaluations, calculated upon heating and domestic hot water energy demands, and the actual year-round energy performance, which also includes the summer season. Moreover, this building type has a low lifecycle environmental impact, but this aspect is not properly "rewarded" by Italian regulations. The study proposed herein firstly took into account the simulation of the thermal transient characteristics of the adobe wall (brick made of clay, earth and straw, forged with wooden molds and sun dried). Analytical calculations were performed using a transient model, assuming sinusoidal behavior of all the parameters acting on the system. The results showed a high thermal inertia of the material and a good ability in dampening the external thermal wave. Next, we conducted an internal and external environmental monitoring of an existing earthen residential building in Sardinia ("Casa Mancosu", Serramanna, VS), which provided the experimental data for the evaluation of the whole building thermo-physical behavior. The measurements were taken during the 2010 summer season; the dwelling was not cooled by an air conditioning system. Thermal comfort analyses based on these experimental data indicate that the roof is the "weak" component, creating local discomfort due to radiant asymmetry. The described methodology is expected to be applicable also to the many buildings of this geographical area similar to the examined one