Thermal energy storage is a functional strategy to minimize the sizing of air conditioning systems and reduce their primary energy consumption. The approach is well known also in groundsource heat pump systems (GSHPs), especially in coupling boreholes as ground heat exchangers (GHEs) with tanks filled with phase change materials (PCMs). The application is quite rare in coupling with horizontal GHEs, that are commonly used in mild climates into shallow trenches. Normally, their low energy performance does not justify an extra-cost for reaching a further thermal benefit. Moreover, the underground thermal energy storage (UTES) would not be viable due to the seasonal energy balance occurring over the soil surface, that depletes what has been stored. Nevertheless, novel and profitable horizontal GHEs have recently appeared in the market, such as flat-panel, baskets and radiators, whose heat transfer efficiency seems very interesting. So, to advance in UTES by shallow GHEs, we have proposed to mix PCMs directly with backfill material for a flat-panel type GHE. Two PCMs have been chosen with different melting points to match the working temperatures for space heating and cooling modes. The application has been evaluated through numerical modelling to solve transient heat transfer using effective heat capacity method. Yearly performance has been simulated taking into account the estimated energy requirement for a residential building located in Northern Italy. According to hourly time series boundary conditions, the simulation results show that PCMs employment is able to smooth the thermal wave in the ground due to the frequent on/off operation of a GSHP. As a result, the consequent temperatures of the working fluid would improve the coefficient of performance of a heat pump (COP). Moreover, the whole year performance analysis indicates that the proposed ground thermal storage using PCMs could be suitably sized to preserve the soil thermal depletion in winter by charging the PCMs naturally in the summer with a shallow GHE.
Numerical Analysis of A Novel Ground Heat Exchanger Coupled with Phase Change Materials
BOTTARELLI, Michele;BORTOLONI, Marco;
2014
Abstract
Thermal energy storage is a functional strategy to minimize the sizing of air conditioning systems and reduce their primary energy consumption. The approach is well known also in groundsource heat pump systems (GSHPs), especially in coupling boreholes as ground heat exchangers (GHEs) with tanks filled with phase change materials (PCMs). The application is quite rare in coupling with horizontal GHEs, that are commonly used in mild climates into shallow trenches. Normally, their low energy performance does not justify an extra-cost for reaching a further thermal benefit. Moreover, the underground thermal energy storage (UTES) would not be viable due to the seasonal energy balance occurring over the soil surface, that depletes what has been stored. Nevertheless, novel and profitable horizontal GHEs have recently appeared in the market, such as flat-panel, baskets and radiators, whose heat transfer efficiency seems very interesting. So, to advance in UTES by shallow GHEs, we have proposed to mix PCMs directly with backfill material for a flat-panel type GHE. Two PCMs have been chosen with different melting points to match the working temperatures for space heating and cooling modes. The application has been evaluated through numerical modelling to solve transient heat transfer using effective heat capacity method. Yearly performance has been simulated taking into account the estimated energy requirement for a residential building located in Northern Italy. According to hourly time series boundary conditions, the simulation results show that PCMs employment is able to smooth the thermal wave in the ground due to the frequent on/off operation of a GSHP. As a result, the consequent temperatures of the working fluid would improve the coefficient of performance of a heat pump (COP). Moreover, the whole year performance analysis indicates that the proposed ground thermal storage using PCMs could be suitably sized to preserve the soil thermal depletion in winter by charging the PCMs naturally in the summer with a shallow GHE.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
