Ioan Sarbu

Optimal design of urban water supply pipe networks

This paper approaches the optimisation of looped water distribution networks supplied from one or more sources, according to demand variation. The pipe networks have concentrated outflows or uniform outflow along the length of each pipe. An optimisation model coupled with a computational iterative procedure of optimal discharges through pipes is developed on the basis of linear programming for the design of new or partially extended water distribution networks. The optimum solution obtained by this model consists of one or two pipe segments of different discrete sizes between each pair of nodes. The improved linear optimisation model guarantees a high reliability. Also, it is possible to take into account the network pipes with variable discharge on route. Additionally, the paper compares the linear optimisation model to some others, such as the classic model of economical velocities, the Moshnin model and a nonlinear model. This shows a good performance of the proposed model.

Ground-Source Heat Pump Systems

This chapter presents a detailed description of ground characteristics, ground-source heat pumps (GSHPs) and GSHP development. This chapter also discusses the most common simulation models and programs of the vertical ground heat exchangers (GHEs) or borehole heat exchangers (BHEs) currently available and describes different applications of the models and programs (i.e. simulation of ground thermo-physical capacity, a one-dimensional transient BHE model, modelling the interactions between ground temperature variations and performance of ground-coupled heat pumps (GCHPs), and a vertical GHE design based on hourly load simulations). Additionally, the chapter presents a new groundwater heat pump (GWHP) using a heat exchanger with special construction, tested in a laboratory, has the potential to obtain better energy efficiency with combined heating and cooling by GCHP. Finally, the advanced engineering applications of hybrid GCHP systems and environmental performance are also briefly analysed.

Thermal Energy Storage

This chapter is focused on the analysis of thermal energy storage (TES) technologies that provide a way of valorizing solar heat and reducing the energy demand of buildings. The principles of several energy-storage methods and calculation of storage capacities are described. Sensible heat-storage technologies including the use of water, underground, and packed-bed are briefly reviewed. Latent heat-storage systems associated with phase-change materials (PCMs) for use in solar heating and cooling of buildings, solar water-heating and heat-pump systems, and thermochemical heat storage are also presented. Additionally, a three-dimensional heat-transfer simulation model of latent heat TES is developed to investigate the quasi-steady state and transient heat transfer of PCMs. The numerical simulation results using paraffin RT20 are compared with available experimental data for cooling and heating of buildings. Finally, outstanding informations on the performance and costs of TES systems are included.

Solar Thermal-Driven Cooling Systems

This chapter provides a detailed review of different solar thermal-driven refrigeration and cooling systems. Theoretical basis and practical applications for cooling systems within various working fluids assisted by solar energy and their recent advances are presented. The first aim of this chapter is to give an overview of the state-of-the-art of the sorption and thermomechanical technologies that are available to deliver cooling from solar energy. The second aim is to compare the potential of these technologies in delivering competitive sustainable solutions. The topics approached in present chapter is similar to that of the other work but it is focused on solar closed-sorption refrigeration systems providing useful information updated and more extensive on their principles, development history, applications and recent advances. The application areas of these technologies are categorized by their cooling temperature demands (air-conditioning, refrigeration, ice making). Additionally, the thermodynamic properties of most common working fluids and the use of ternary mixtures in solar-powered absorption systems are reviewed. A mini-type solar-absorption cooling system using both fan coils and the radiant ceiling as terminals was designed and installed. The system performance as well as the indoor thermal comfort is analyzed. Finally, some information on design, control, and operation of hybrid cooling and heating systems are included. The study also refers to a comparison of various solar thermal-powered cooling systems, and to some use suggestions of these systems.

Solar-Assisted Heat Pumps

This chapter presents the operation principle of a heat pump (HP), discusses the vapor-compression-based HP systems, and describes the thermodynamic cycle and the calculation, as well as operation regimes of a vapor-compression HP with electro-compressor. The calculation of greenhouse gas (GHG) emissions of HPs and energy and economic performance criteria that allow for implementing an HP in a heating/cooling system is considered. A detailed description of the HP types and ground-source HP (GSHP) development is presented and important information on the selection of the heat source and HP systems are discussed. Additionally, other approach is to integrate the solar thermal system on the source side of the HP so that the solar thermal energy is either the sole heat source for the HP or provides supplementary heat. Additionally, the operation principle and calculation of the thermodynamic cycle for a solar-assisted absorption HP are also briefly analyzed. Finally, analytical and experimental studies are performed on a direct-expansion solar-assisted heat pump (DX-SAHP) water heating system. The effects of various parameters, including solar radiation, ambient air temperature, collector area, storage volume and speed of compressor, are been investigated on the thermal performance of the DX-SAHP system. A novel heating, ventilating and air-conditioning system consisting of a solar-assisted absorption ground-coupled HP is also described, and some of the influence parameters on its energy efficiency is analyzed. A model of the experimental installation is developed using the TRNSYS software and validated with experimental results obtained in the installation for its cooling-mode operation.

Heat Distribution Systems in Buildings

This chapter presents the heat distribution systems in buildings, including hot-water radiators, radiant panels (floor, wall, ceiling, and floor-ceiling) and room air heaters. First objective of this study is the analysis of the energy savings in central heating systems with reduced supply temperature, for different types of radiators taking into account the thermal insulation of the distribution pipes and the performance investigation of different types of low-temperature heating system with different methods. Additionally, a mathematical model for numerical modeling of the thermal emission at radiant floors is developed and experimentally validated, and a comparative analysis of the energy, environmental and economic performances of floor, wall, ceiling and floor-ceiling heating using numerical simulation with Transient Systems Simulation (TRNSYS) software is performed. Finally, important information for control and efficiency of solar heating systems (SHSs) is included, an analytical model for energetically analysis of the SHSs is developed, and some economic analysis indicators are presented to show the opportunity to implement these systems in buildings.

Solar Electric Cooling Systems

This chapter covers solar electric cooling systems including the solar photovoltaic (PV) and thermoelectric (TE) systems. Thus, the utilization of solar PV panels coupled with a vapor-compression air-conditioning system is described, and a good amount of information regarding ecological refrigerants trend is included. Additionally, this chapter presents details referring to TE cooling parameters and formulations of the performance indicators and focuses on the development of TE cooling systems in the recent decade with particular attention on advances in materials and modeling approaches and applications.

Using Ground-Source Heat Pump Systems for Heating/Cooling of Buildings

This chapter mainly presents a detailed theoretical study and experimental investiga‐ tions of ground-source heat pump (GSHP) technology, concentrating on the groundcoupled heat pump (GCHP) systems. A general introduction on the GSHPs and its development, and a description of the surface water (SWHP), ground-water (GWHP), and ground-coupled heat pumps are briefly performed. The most typical simulation and ground thermal response test models for the vertical ground heat exchangers (GHEs) currently available are summarized. Also, a new GWHP using a heat ex‐ changer with special construction, tested in laboratory, is well presented. The second objective of the chapter is to compare the main performance parameters (energy effi‐ ciency and CO2 emissions) of radiator and radiant floor heating systems connected to a GCHP. These performances were obtained with site measurements in an office room. Furthermore, the thermal comfort for these systems is compared using the ASHRAE Thermal Comfort program. Additionally, two numerical simulation models of useful thermal energy and the system coefficient of performance (COPsys) in heating mode are developed using the TRNSYS (Transient Systems Simulation) software. Fi‐ nally, the simulations obtained in TRNSYS program are analysed and compared to ex‐ perimental measurements.

Substitution Strategy of Non-Ecological Refrigerants

This chapter presents a study on the recent development of possible substitutes for non-ecological refrigerants for heating, ventilating, air-conditioning and refrigeration (HVAC&R) equipment based on thermodynamic, physical and environmental properties and total equivalent warming impact (TEWI) analysis. This study contains information regarding the environmental pollution produced by the working fluids of heat pumps (HPs), air conditioning (A/C), and commercial refrigeration applications and the ecological refrigerant trend. Overall, the study is useful for those readers who are interested in the current status of alternative refrigerant development related to vapour compression-based systems. The study describes the selection of refrigerants adapted to each utilisation based on the thermodynamic, physical and environmental properties, the technological behaviour, and the use of constraints as the principal aspect of environmental protection. This chapter also explores the studies reported with new refrigerants in HPs, domestic and commercial refrigerators, chillers and A/Cs.

Types of Compressors and Heat Pumps

This chapter presents a detailed description of the refrigeration compressor types (reciprocating, rotary screw, centrifugal and scroll compressors) and the heat pump (HP) types. Important information on the selection of the heat source and HP systems and domestic hot-water production for nearly zero-energy buildings are discussed. In addition, some installation instructions for HPs and examples of HP utilisation are presented. Finally, the HP sales’ contribution to renewable energy sources in the European Union is shown.