The influence of thermal bridge calculation method on the building energy need: a case study

The goal of the paper is to compare two different methods of calculating the linear transmittance of thermal bridges in order to evaluate the building energy need for heating. As a case study, it was considered an existing non-isolated residential building of '70 years consisting of 30 housing units. All the construction details of the building are known. The energy analysis of the building was carried out using a commercial software. The linear transmittance of the thermal bridges was determined both by the catalogue, provided by the software itself, and by the numerical finite-element evaluation according to UNI EN ISO 10211 standard using a 2-D numerical simulator. Through numerical analysis it is possible to evaluate in a detailed way all the thermal bridges present in the building and therefore it is possible to evaluate the approximation induced by the use of the catalogue. Results show that the detailed analysis leads to a transmission heat exchange through thermal bridges about eight times greater than that estimated through the catalogue and consequently to a higher building energy need of about 12%. The heating energy needs per unit area of the individual housing units were also compared

Energy Audit of a \u201860 Residential Building Served by a Steam Heating System

The present paper deals with an energy audit of a residential building served by two central systems for heating and domestic hot water production respectively. The heating service is obtained by a low pressure and natural circulation steam system. These types of plants show lots of problems: low energy efficiency due to the high operating temperatures and to the poor insulation of pipes, lack of comfort within the building units due to the high inertia and to the inefficiency of the regulation. In order to calculate the energy performance of the building, a model based on the UNI/TS 11300 standards and validated on the basis of the real consumption has been used. The current building state has been simulated and different actions to improve energy performance have been examined. For each of them, using cost-benefit analysis, the simple payback time has been rated

Performance analysis of a liquid desiccant and membrane contactor hybrid air-conditioning system

ABSTRACT The present study examines the performances of a hybrid air-conditioning system in which a vapour-compression inverse cycle is integrated with an air dehumidification system working with hygroscopic solution and hydrophobic membrane. This model may be a valid alternative to traditional summertime air-conditioning system, in which the air is cooled to below its dew-point temperature and subsequently reheated. The proposed hybrid system involves simultaneously cooling and dehumidifying the air conveyed to the conditioned ambient in an air-solution membrane contactor. An LiCl solution is cooled by means of a vapour-compression inverse cycle using the refrigerant KLEA 407C. The solution is regenerated in another membrane contactor by exploiting the heat rejected by the condenser. A SIMULINK calculation programme was designed in order to simulate the system under examination in steady-state conditions. The performances of the system were analysed on varying a few significant operating parameters, and were compared with those of a traditional direct-expansion air-conditioning plant in typical summertime conditions. The results of the simulations revealed significant energy savings, which, in particular operating conditions, may exceed 50%

Validation and calibration of dynamic energy models: energy audit of a public building.

Detailed buildings energy audits require dynamic simulation models based on hourly input data. This paper presents the calibration and validation of an office building energy model for the heating and cooling services. Simulations are carried out by DesignBuilder software. Measured hourly heating and cooling energy supplied by the generation system are used for the calibration of the model. Employee behaviour with reference to occupancy profiles and indoor temperature settings is also considered. A good agreement between measured and simulated data is obtained for both heating and cooling seasons

On the performances of a hybrid air-conditioning system in different climatic conditions

ABSTRACT In previous papers the authors demonstrated that significant energy savings can be achieved in air-conditioning through the use of a hybrid plant in which a vapor-compression inverse cycle is integrated with an air dehumidification system working with hygroscopic solution and hydrophobic membrane. The advantage of this system lies in the fact that the refrigeration device operates at a higher evaporation temperature than that of a traditional system, in which dehumidification is achieved through condensation. In the proposed hybrid system the supplied air is simultaneously cooled and dehumidified in an air-solution membrane contactor. The LiCl solution is cooled by means of a vapor-compression inverse cycle. The solution is regenerated in another membrane contactor by exploiting the exhaust air and the heat rejected by the condenser. The paper reports a study of the steady-state behavior of the system in summer climatic conditions on varying some significant climatic parameters, such as the latent load of the conditioned space and the outdoor and indoor relative humidity. The performances of the hybrid system are compared with those of a traditional direct-expansion air-conditioning plant. Results of the simulations reveal that energy saving may exceed 60% when the latent load in the conditioned environment is high

Heat Transfer via Unconditioned Spaces: The Influence of the Adjustment Factor Evaluation Method

The aim of the paper is to determine the influence of the evaluation method of the heat transfer via unconditioned spaces in building energy need calculation procedure, taking into account the dispositions of the UNI/TS 11300-1 standard. Two different calculation methods for the adjustment factor btr,U are compared with reference to a case study of a '70 years condominium building: the simplified method, based on the tabulated values, available only for existing buildings, and the detailed one, based on the analytical calculation of the heat transfer coefficient Hue between unconditioned spaces and external environment, available for both new and existing buildings. In the latter case, the influence of thermal bridges between unconditioned rooms (cellars, attics, stairwells) and the outside and the ground is also considered. Results are discussed in terms of both btr,U factor and temperature Tu of the unconditioned spaces. The energy need of single apartments has also been calculated in order to evaluate the influence of the calculation procedure on heating millesimal table of the condominium. Results of simulations reveal significant differences on single units energy needs between the detailed and simplified method; the contribution of thermal bridges in Hue coefficient calculation is negligible

Appunti di termoigrometria e impianti

Il volume \ue8 rivolto principalmente agli studenti dei corsi laurea in Ingegneria e Architettura, ma si pone anche come strumento di supporto per i professionisti che operano nel campo dell\u2019energetica e degli impianti di climatizzazione degli edifici. Il testo, corredato da numerose figure ed esempi, affronta gli argomenti in modo semplice e sintetico e si propone come continuazione dei volumi Appunti di Termodinamica (Aracne 2007) e Appunti di Trasmissione del Calore (Aracne 2012), pubblicati dagli stessi autori. Dopo alcune nozioni di base di psicrometria, vengono affrontati i problemi termoigrometrici delle strutture e i concetti di benessere e di qualit\ue0 dell\u2019aria indoor connessi con la progettazione degli impianti di climatizzazione degli edifici. Il dimensionamento degli impianti \ue8 trattato in modo sintetico con riferimenti dettagliati alla legislazione e alla normativa tecnica vigenti

L'incidenza del coefficiente medio globale di scambio termico per trasmissione nelle ristrutturazioni importanti di primo e secondo livello alla luce del DM 26/06/2015

Vengono presentate alcune considerazioni circa l'applicazione del recente DM 26/06/2015 riguardante i requisiti minimi da rispettare in materia di risparmio energetico nell'edilizia. In particolare vengono discusse, con riferimento alle ristrutturazioni importanti di primo e secondo livello, le problematiche riscontrate e le possibili soluzioni pratiche per il rispetto dei limiti imposti sul coefficiente medio globale di scambio termico per trasmissione H'T. Dall'analisi di alcuni semplici casi di studio, si deduce che i limiti imposti sono spesso di difficile applicazione nelle ristrutturazioni degli edifici esistenti

Riqualificazione energetica di un edificio unifamiliare alla luce del Superbonus 110%

Il presente articolo sintetizza la tesi di Laurea Magistrale [1] in Architettura discussa nella sessione di Dicembre 2020 presso il Dipartimento di Architettura e Design (DAD) della Scuola Politecnica dell\u2019Universit\ue0 di Genova riguardante l\u2019applicazione della recente normativa in tema di efficienza energetica degli edifici e detrazioni fiscali, nota come Superbonus 110%. Il Superbonus 110% nasce a supporto della ripresa del settore edilizio, a fronte della grave crisi economica derivata dall\u2019epidemia di Covid-19. Il caso di studio riguarda il miglioramento della prestazione energetica di un edificio unifamiliare, attraverso la riqualificazione dei componenti edilizi ed impiantistici. L\u2019analisi \ue8 stata condotta applicando la regolamentazione introdotta dall\u2019articolo 119 del D.L. 19 maggio 2020, n. 34 [2], noto come Decreto Rilancio, convertito in Legge 17 luglio 2020, n. 77, e dalle successive modificazioni e integrazioni, nonch\ue9 dal D.M. 6 agosto 2020 [3], recante i requisiti tecnici per l\u2019accesso alle detrazioni fiscali per la riqualificazione energetica degli edifici. Il lavoro segue il percorso che deve affrontare il tecnico per quantificare l\u2019effetto del Superbonus 110%, partendo dall\u2019analisi dello stato di fatto dell\u2019immobile, procedendo nella progettazione degli interventi migliorativi in materia di isolamento ed impianti nel rispetto della normativa tecnica vigente in materia di efficienza energetica degli edifici e detrazioni fiscali, per concludersi con cenno sulla verifica dei massimali di spesa e della congruit\ue0 dei costi