Demand Side Management analysis of a commercial Water Loop Heat Pump system

Demand side management (DSM) can be defined as a set of measures adopted to modify customers\u2019 energy demand with the aim of improving the efficiency of the overall energy system. Indeed, DSM strategies can be used to reduce customers\u2019 demand at peak times, reduce energy consumption seasonally/yearly, change the timing of end-use consumption from high to low-cost periods, and increase consumption during off-peak periods. DSM strategies can be implemented by using the energy flexibility available in the final users\u2019 applications, e.g. the thermal inertia of the building mass, the presence of additional energy storage systems enabling load shaping or the use of control systems to turn on/off end-users\u2019 devices when required. Being intensive energy consumers because of a high electric energy demand (mainly for refrigeration, which accounts for about 40 % of the yearly energy consumption), supermarkets are ideal candidates for energy use optimizations obtained through a DSM approach. This work shows the results of a DSM analysis carried out for a refrigeration and HVAC plant in a supermarket coupled with a Water Loop Heat Pump (WLHP) system. The water loop is used as a heat source/sink for the refrigeration unit supplying the cooling capacity required by food preservation and for several heat pumps that provide heating/cooling inside the supermarket building. The system is modelled in TRNSYS and the role of the water loop and its thermal inertia to provide energy flexibility is investigated. The system design and control strategy are modified in order to reduce the electricity costs in presence of demand response programs based on real-time price mechanisms

Ejector characterization for refrigeration applications with natural refrigerants

Employing natural fluids in refrigerating plants at warm climate conditions sometimes impacts negatively on the system performance. Ejectors can play a key role in configurations aiming at improving the efficiency of such systems, however their geometry has to be optimized in order to gain the best benefit. Scope of this work is a numerical investigation on the geometry of the ejector in a cascade plant configuration with natural refrigerants, aiming at identifying the influence of various geometry aspects on the performance of the system. A one-dimensional model is employed for the ejector, while the performance of the refrigerating plant is evaluated in different operating conditions in order to seek the optimal configuration

Water storage to improve the efficiency of CO2 commercial refrigeration systems

Carbon dioxide is being more and more widely used in commercial refrigeration, due to its negligible environmental impact. However up to now its application as the only refrigerant is especially devoted to cold climates, which allow for the best exploitation of this refrigerant. Several solutions are being identified to extend a convenient application of CO2 also to mild climate conditions, through modifications of the refrigerating cycle and the adoption of various innovative configurations. Quite often such configurations require significant extra costs or involve the adoption of solutions not yet well established in the market. In some cases the promotion of interactions between the refrigeration systems and other systems available in the building could allow for the exploitation of simple solutions which could be easily adopted with low extra costs. In this paper a basic CO2 transcritical/subcritical commercial refrigeration system is considered, applied to cold rooms and display cabinets in a supermarket located inside a large shopping mall. Subcooling of the refrigerant is performed, taking advantage of a large fire prevention water tank. The whole refrigeration system has been modelled in Trnsys environment. Simulations have been carried out taking into account the hourly weather data and the daily profile of the cooling load demand from the refrigerated food storage equipment. Different configurations are examined, for the best exploitation of this cold storage. The technical feasibility of this solution is investigated

Porous media modeling of compressible flow in micro heat exchangers

An efficient equivalent porous media model designed to simulate the heat and fluid flow in a gasgas micro heat exchanger is presented. Although similar models are common in macroscale environment, the present implementation takes into account several issues typical of microscale applications. In particular, three coupled solutions provide the hot fluid temperature, cold fluid temperature, and solid temperature, thus including conjugate heat transfer effects. Proper source terms incorporate the pressure loss effects and provide the coupling among the domains via the mutual heat transfer computation. Furthermore, since for gaseous, compressible flows no fully developed flow is attained, specific local based microscale correlations are used for the determination of heat transfer coefficients and friction factors, using only local values and properly taking into account both rarefaction and compressibility effects