dynamic simulation of an air handling unit and validation through monitoring data

Abstract This paper presents the model for the simulation of the behavior of an air handling unit (AHU), consisting of two heating coils, a cooling and dehumidifying coil, and a vaporizer. The proposed model reproduces the behavior of its single components, using the suitable e-NTU relations for the heat exchangers on the basis of actual geometries (e.g., type of heat exchanger, number of tube rows, number of passes), and mass and heat balance equations for the vaporizer and dehumidifying coils. The routine is developed as a MATLAB script and it is linked to a TRNSYS model, which simulates the building. The model is applied to a real AHU, which provides fresh air for an exhibition room of a museum, varying the supply relative humidity based on the indoor set point. During a one-month monitoring campaign in the building, several data about the external and internal climate were acquired, together with specific parameters of the AHU system (e.g., temperature and water flow rate at the heat exchangers, supply temperature and relative humidity of the air flow). These monitored data were compared with the outputs of the MATLAB script, validating the AHU model in the error band of the monitoring system

Modellazione dinamica di un sistema pompa di calore - edificio

Lo scopo della tesi è creare un modello che simuli il funzionamento di una pompa di calore durante il periodo invernale. Dopo la parte iniziale, dedicata all’analisi delle pompe di calore, viene descritta la modellizzazione, creata in ambiente MATLAB, composta da più sotto-modelli (nell’ordine: circuito idronico con pannelli radianti, condensatore, evaporatore e compressore). In base ai dati inseriti (riguardanti potenza termica oraria da soddisfare, condizioni climatiche esterne, presenza o meno dell’accumulo), il modello è in grado di determinare le prestazioni della macchina. Queste vengono poi confrontate con dati sperimentali forniti da costruttori. In seguito viene analizzato un edificio preso come benchmark destinato ad uffici (implementato tramite il software TRNSYS), supponendo che venga riscaldato con utilizzo diretto della pompa di calore o passando attraverso un sistema di accumulo. I dati ottenuti sulle prestazioni dinamiche della pompa di calore vengono infine confrontati con quelli risultanti dall’applicazione delle normative tecniche in vigore

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

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: 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

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

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

Synthesis and Optimal Operation of Smart Microgrids Serving a Cluster of Buildings on a Campus with Centralized and Distributed Hybrid Renewable Energy Units

Micro-district heating networks based on cogeneration plants and renewable energy technologies are considered efficient, viable and environmentally-friendly solutions to realizing smart multi-energy microgrids. Nonetheless, the energy production from renewable sources is intermittent and stochastic, and cogeneration units are characterized by fixed power-to-heat ratios, which are incompatible with fluctuating thermal and electric demands. These drawbacks can be partially overcome by smart operational controls that are capable of maximizing the energy system performance. Moreover, electrically driven heat pumps may add flexibility to the system, by shifting thermal loads into electric loads. In this paper, a novel configuration for smart multi-energy microgrids, which combines centralized and distributed energy units is proposed. A centralized cogeneration system, consisting of an internal combustion engine is connected to a micro-district heating network. Distributed electric heat pumps assist the thermal production at the building level, giving operational flexibility to the system and supporting the integration of renewable energy technologies, i.e., wind turbines, photovoltaic panels, and solar thermal collectors. The proposed configuration was tested in a hypothetical case study, namely, a University Campus located in Trieste, Italy. The system operation is based on a cost-optimal control strategy and the effect of the size of the cogeneration unit and heat pumps was investigated. A comparison with a conventional configuration, without distributed heat pumps, was also performed. The results show that the proposed configuration outperformed the conventional one, leading to a total-cost saving of around 8 %, a carbon emission reduction of 11 %, and a primary energy saving of 8 %

Building Energy Simulation by an In-House Full Transient Model for Radiant Systems Coupled to a Modulating Heat Pump

Radiant heating coupled to a heat pump is a particularly energy-efficient system, recommended in new constructions. However, the potential energy savings associated with this high thermal inertia system can only be achieved with appropriate control laws, to be tested in a full building–plant simulation environment. The developed transient code concurrently solves three tailored dynamic models of each involved sub-system, namely: building envelope (a benchmark room defined by ISO 13791), radiant floor (designed in accordance with EN 1264-2), and heat pump (an air-to-water electrically-driven modulating unit). Different control strategies were implemented, such as variation of internal temperature set-point dead band, supply temperature to radiant panels, and heating modes. Among the examined variables, we found that the higher energy savings (up to 15%) can be obtained by a proper choice of the supply temperature: in particular, fixed supply temperature should be preferred to climate-based control for this case study. The developed model can be used for optimal design of new systems and associated controls and for accurate energy audits of existing buildings employing these technological solutions

Economic assessment of flexibility offered by an optimally controlled hybrid heat pump generator: a case study for residential building

Abstract The ongoing decarbonisation process of the current energy system, driven by the EU directives, requires that more renewable energy sources are integrated in the global energy mix, as well as policies promoting investments in new low-carbon technologies, energy efficiency and grid infrastructure. The technical integration of renewable energy sources into the existing power system is not straightforward, due to the intrinsic aleatory characteristics of renewable production, which make the power grid balance harder. To handle this issue, beside the traditional supply-side management, grid flexibility can also be provided by enabling the active participation of the demand-side in power system operational procedures, by means of the so-called demand-side management (DSM). The present paper is aimed at assessing the ability of a cost-optimal control strategy, based on model predictive control, to activate demand-response (DR) actions in a residential building equipped with a hybrid heat pump generator coupled with a water thermal storage. Hourly electricity prices are considered as external signals from the grid driving the demand response actions. It is shown that the thermal energy storage turns out to be an effective way to improve the controller performances and make the system more flexible and able to provide services to the power grid. A daily cost-saving up to 35% and 15% have been highlighted with a 1 m3 0.5.m3 tanks, respectively. Finally, the achievable flexibility is shown to be strictly dependent on the storage capacity and operations, which in turn are affected by the generators sizing