Hourly simulations of an hospital building for assessing the thermal demand and the best retrofit strategies for consumption reduction

In the framework of energy saving and environmental protection, the role of the energy consumption in buildings is crucial. For existing buildings and especially for public ones, it is mandatory to correctly select and realize suitable retrofitting interventions to reduce costs and increase the efficiency. In fact, innovative solutions for both the envelope and the plants renovation are often very expensive and the correct choice becomes critical for the sustainability from the economic point of view. The aim of the present paper is to propose a methodology to optimize the process of selection for the retrofit interventions, here applied to a case study of the Monoblocco Pavilion at the San Martino Hospital in Genova, Italy. The building thermal behaviour is dynamically simulated by means of an Energy Plus model in order to evaluate the energy needs for both heating and cooling purposes. The base case scenario is evaluated in terms of key performance indicators (KPIs) and compared with benchmark values in order to select the more suitable intervention actions. For the analysed case study, the innovative retrofit solutions are fa\ue7ade void insulated panels, smart rotating windows with different emissivity glass and sunlight carrying optical-fibres coupled with dimmed LED lighting system. The technologies are combined in different intervention packages that are then compared in term of energy saving and economic sustainability by means of the estimation of hourly values of energy consumption and the assessment of the Simply Pay Back Period (SPB) of the investment

Modelling Heat Pumps with Variable EER and COP in EnergyPlus: A Case Study Applied to Ground Source and Heat Recovery Heat Pump Systems

Dynamic energy modelling of buildings is a key factor for developing new strategies for energy management and consumption reduction. For this reason, the EnergyPlus software was used to model a near-zero energy building (Smart Energy Buildings, SEB) located in Savona, Italy. In particular, the focus of the present paper concerns the modeling of the ground source water-to-water heat pump (WHP) and the air-to-air heat pump (AHP) installed in the SEB building. To model the WHP in EnergyPlus, the Curve Fit Method was selected. Starting from manufacturer data, this model allows to estimate the COP of the HP for different temperature working conditions. The procedure was extended to the AHP. This unit is a part of the air-handling unit and it is working as a heat recovery system. The results obtained show that the HP performance in EnergyPlus can closely follow manufacturer data if proper input recasting is performed for EnergyPlus simulations. The present paper clarifies a long series of missed information on EnergyPlus reference sources and allows the huge amount of EnergyPlus users to properly and consciously run simulations, especially when unconventional heat pumps are present

Energy demand modeling and forecast of monoblocco building at the city hospital of genova according to different retrofit scenarios

Buildings are one of the major energy consumers. Thus, it is crucial to develop new solutions in order to retrofit existent buildings (especially for public buildings), achieving both energy saving and environmental protection. The proposed solutions are in many cases expensive and it is necessary to evaluate them case by case. The present analysis focuses on the development of a methodology useful to select and evaluate different energy retrofitting solutions and it is applied to energy simulations of the Monoblocco Pavilion at the San Martino Hospital in Genova, Italy. The model allows to evaluate the building heating and cooling loads and to predict the energy requests associated to different retrofit scenarios. The selected retrofit technologies include some innovative solutions such as fa\ue7ade super insulated void panel, smart rotating windows with different emissivity glass and sunlight carrying optic-fiber coupled with dimmed LED lighting system. Results have been analyzed in terms of hourly values of selected variables and the different effects related to the retrofit strategies have been compared in terms of energy saving. The comparison included also the Simple Pay Back Period (SPB) of the investment in order to identify the best technologies combination also from an economic point of view

Transient thermal resistance of borehole heat exchangers for hourly simulations of geothermal heat pumps systems

The correct design of borehole fields requires the correct evaluation of the transient ground thermal response in time, but also the accurate estimation of the borehole (BHE) thermal resistance, expecially the grout contribution. Generally, the borehole thermal resistance is considered as steady-state; however, when considering the borefield hourly response to the building variable thermal loads, also the transient behavior of the grout thermal resistance plays an important role, which is quite often neglected. This study analyzes, with a dimensionless approach, the transient grout thermal resistance, with particular attention devoted to the effect of the boundary condition imposed to the internal tubes, namely imposed heat flux, imposed temperature and imposed convective coefficient, the last being the real operating conditions. In addition, the effects of grout to ground thermophysical properties and of shank spacing are analysed. The steady state numerical results are also compared with literature correlations. Finally, numerical evidences are given to demonstrate that the usual approach of calculating the overall BHE resistance just summing the grout resistance, numerical obtained by imposing a temperature on the tube surface, to the convective one can lead to meaningful errors at low Biot numbers

Heat extraction distributed thermal response test: A methodological approach and in-situ experiment

The Thermal Response Test (TRT) is a worldwide adopted in-situ methodology able to estimate the ground thermal conductivity and borehole thermal resistance. During the test the carrier-fluid exchanges a constant heat flux with the ground while circulating in a pilot Borehole Heat Exchanger (BHE). During a Distributed Thermal Response Test (DTRT) the ground thermal conductivity and borehole thermal resistance are determined at different vertical sections along the borehole. The measured fluid temperature values are analysed with numerical or analytical approaches based on mathematical models which typically approximate the BHE. Those models are based on some strict assumptions, including pure conduction and constant heat transfer rate. During a heat extraction TRT the operating conditions to the ground are similar to the "winter mode" conditions of a working BHE system. In such case the estimated thermal behaviour of the borehole can differ from the result obtained by means of a heat injection TRT. This issue is of peculiar interest for water-filled boreholes, where the BHE thermal resistance is related to the water temperature and density gradient in the borehole filling-space. In this operating mode a heat pump is usually employed and the constant heat transfer rate condition required by the models can be difficult to be respected since the efficiency of the cooling-machine is dependent on the inlet carrier-fluid temperature to the evaporator. In this paper a methodology to perform a heat extraction DTRT with constant heat transfer rate to the ground is presented. The approach described has been applied in a real water-filled borehole installed in Stockholm, Sweden. Data analysis results are presented and the outcomes regarding the evaluation of the local borehole thermal resistance are discussed and compared with those from an erlier heat injection test performed in the same borehole

Investigation on the effects of different time resolutions in the design and simulation of BHE fields

The correct design of a field of Borehole Heat Exch angers (BHE) requires the knowledge of ground thermal properties, heat pump performance and building heating and cooling demand. The sequence o f heat pulses from (to) the ground by the heat pump can be described according to different time steps , from hours to months and even years. The monthly time step approach is often the preferred design choice which involves recursive calculations (temporal superposition techniques) and the availability of precalculated temperature response factors (or g-functions) for given BHE field geometries. Such a complex computing task is usually performed thanks to commercial codes in order to fulfil a carrier fluid temperature at the end of a given time horizon, typically 10 or 25 years. In this paper the monthly design approach (EED code and TecGeo proprietary code) is compared with the three thermal pulse approach (modified ASHRAE Method Tp8) and it is demonstrated that for a representative series of case studies the three pulse calculation, easy to be performed at engineering level, is able to provide the correct BHE field overall length with 8% accuracy with respect to the reference monthly calculations

Extending the Ashrae Tp8 method for vertical borefield design to uniform BHE temperature boundary conditions

The Ashrae method is a fast algorithm for calculating the overall length of closed-loop borehole heat exchangers, considering the ground thermal response and the building thermal load profile. The method includes a corrective variable called Temperature Penalty (Tp) to account for the thermal interaction between boreholes. Several authors proposed different approaches for calculating this parameter, but the majority is inaccurate or too complex. Recently, the same Authors suggested a very simple method, called Tp8. The coefficients included in the original formula were optimized against g-functions obtained by spatial superposition of a single source always working at the same heat rate. In this paper, the early Tp8 method is improved by the calculation of new constants based on g-functions calculated for uniform temperature borehole conditions. A large dataset of 300 borefield configurations have been considered for optimization and validation purposes. In this case, all the BHEs are at the same temperature and the overall heat transfer rate of the field is constant in time. Compared with EED software outputs, the results from present Tp8 method show a good accuracy (within 3% for the overall BHE field length) while maintaining a great simplicity in applying the method at engineering design level

Pulsated Thermal Response Test experiments and modelling for ground thermal property estimation

The Thermal Response Test (TRT) is a well known experimental technique for estimating both the ground thermal conductivity and the effective borehole heat exchangers (BHE) resistance in ground coupled heat pump (GCHP) applications. The usual experimental approach for the TRT measurements is to inject (and even extract) a constant heat rate in the ground while the carrier fluid is circulated inside a reference heat exchanger. In this paper the TRT approach is applied with reference to non constant heat rate condition during a several day measuring session at the SEB building site of the University of Genova, Italy. A constant heat injection has been operated for the first 100 hours of the experiment and then a series of 8 hour square pulses (on/off mode) have applied for about 11 days. The ground and BHE thermal properties have been here estimated according to different algorithms developed either at the University of Genova and Polytech Montreal, where either the ILS and FLS (Infinite and Finite Line Source) theories or a Resistance/Capacitance approach are implemented to reconstruct the measured temperature evolution from parameter estimation

Thermal response of helix ground heat exchangers

This paper is devoted to the thermal analysis of shallow ground heat exchangers with pipes arranged in a helix configuration. The pipes where the carrier fluid is circulated typically embrace a cylindrical volume that is filled by ground or concrete, the latter being the case of the so called geopiles. Other pipes dispositions include conic helices that can be easily inserted in proper excavations. The analysis of the transient thermal behavior of a helix/ground assembly is here carried out according to different approaches, including the exploitation of superposition techniques, the finite element modelling and experiments in a reduced scale mock up. Different geometrical configurations have been taken into account and also the variability of ground and concrete thermal properties have been considered. A detailed description of the experimental set up is provided and the model results have been processed in order to develop suitable temperature response factors (or g -functions) to be employed for predicting the ground heat exchanger behavior in different operating conditions