•Long-term exergy analysis of a GSHP system with VGWHE, HGWHE or GAHE is performed.•Performance of ASHP and GSHPs with VGWHE, HGWHE or GAHE are compared.•Exergy destruction of each component of the ...simulated systems is evaluated.•GSHP with VGWHE has the highest COP value and exergy efficiency.•Exergy destruction of GSHP with VGWHE and HGWHE increases over a 30-year period.
Heat pumps as the only end-use cooling/heating technology with a Coefficient of Performance (COP) greater than one, have attracted a great deal of attention over the past decade. In this study, the long-term energy and exergy analysis of four different types of heat pump systems: a common Air Source Heat Pump (ASHP), an ASHP with Ground Air Heat Exchanger (GAHE), a Ground Source Heat Pump (GSHP) with Horizontal Ground Water Heat Exchanger (HGWHE), and a GSHP with Vertical Ground Water Heat Exchanger (VGWHE) is performed. It is considered that all systems are used for space cooling and heating of a residential building. A mathematical model that takes into account the variations of building loads, ambient air temperature, soil temperature and COP of the system is developed for this purpose. The COP, the compressor work, and the exergy efficiency of the simulated systems are evaluated and compared over a thirty-year operating period. The obtained results indicated that the GSHP with the VGWHE demonstrated the best performance followed by the GSHP with the HGWHE, the ASHP with the GAHE and the common ASHP. Furthermore, the exergy destruction of each component of the simulated systems is evaluated and compared over a thirty-year operating period.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•The review of recent studies on heat delivery above 80 °C using vapour compression heat pumps•Discussion on advances in natural fluids for its use as high temperature working fluids•Discussion on ...the component development for high temperature heat pump operation•The review of fluid mixture proposals, cycle variations and system design in high temperature domain
The use of high temperature heat pumps (HTHPs) operating with natural fluids has been shown to be a potential environmentally friendly solution to increase energy efficiency in industrial processes. Industrial processes release a significant amount of energy as low quality waste heat to the environment. This paper reviews the research and development of efficient and cost effective HTHP technology that can utilize this waste heat. Natural fluids are of focus with consideration given to the comparable technologies using synthetic fluids. This review reveals the different challenges from fluid selection, component development to system optimization. The various innovative solutions to these challenges and promising technologies for further studies are discussed. The purpose of this paper is to serve as a start point for research by bringing together ideas, simulations and experimental results as a resource or reference tool for future development in HTHP using natural working fluids.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Novel reversely-variable circuitry for finned-tube heat exchanger (FTHX) proposed.•Refrigerant flowpath of FTHX alters flexibly between evaporator and condenser modes.•Circuits are fewer for ...condenser but more for evaporator to match respective needs.•Fewer circuits enhance overall heat transfer coefficient for condenser.•Overall energy performance is improved for air source heat pump (ASHP).
The finned-tube heat exchanger (FTHX) is preferred to contain more circuits as an evaporator but fewer as a condenser, so as to obtain the desired performance in both heating and cooling operation of the air source heat pump (ASHP). However, the conventional FTHX has two-way fixed circuitry with the same refrigerant flowpath in the opposite direction. In this article, the reversely-variable circuitry is proposed for the FTHX to exhibit different flowpath in evaporator and condenser roles flexibly. The original 4-branch distributor in the outdoor FTHX of a nominal 3500-W ASHP is replaced with a 2-branch one and a 3-branch one successively to maintain 4 circuits as an evaporator. Two check valves, however, are added between the two distributors and inside the gas header to change the flowpath to two circuits merging into one as a condenser. Compared with the two-way fixed FTHX, the reversely-variable one yields 5.8% larger cooling capacity and 7.2% higher EER for the ASHP with similar heating performance under nominal conditions. Further simulation shows that fewer circuits of the reversely-variable FTHX increase the overall heat transfer coefficient as a condenser, dominating the increase in the capacity of the FTHX and the overall energy performance of the ASHP. This novel design provides new thoughts to the FTHXs and can be popularized to those with different circuits.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
5.
Storage of thermal solar energy Stutz, Benoît; Le Pierres, Nolwenn; Kuznik, Frédéric ...
Comptes rendus. Physique,
September-October 2017, 2017-09-01, 2017-09, Volume:
18, Issue:
7-8
Journal Article
Peer reviewed
Open access
Solar thermal energy storage is used in many applications, from building to concentrating solar power plants and industry. The temperature levels encountered range from ambient temperature to more ...than 1000 °C, and operating times range from a few hours to several months. This paper reviews different types of solar thermal energy storage (sensible heat, latent heat, and thermochemical storage) for low- (40–120 °C) and medium-to-high-temperature (120–1000 °C) applications.
Le stockage thermique de l'énergie solaire touche de très nombreuses applications, qui vont du bâtiment aux centrales solaires à concentration en passant par l'industrie. Les niveaux de température rencontrés vont de la température ambiante à plus d'un millier de degrés, et les durées d'utilisation de quelques heures à plusieurs mois. Cet article passe en revue les différentes familles de stockage d'énergie solaire thermique (stockage sensible, latent et thermochimique), pour des applications à basses (40–120 °C) et moyennes–hautes températures (120–1000 °C).
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•The system used R290 (an environment-friendly refrigerant).•The results showed that the COP of an HSHP mode is better than GSHP, ASHP, SAHP for most environmental conditions.•The best payback was ...obtained using a SAHP mode.•A case study was also performed considering the climate of three Brazilian cities.
This work presents a study for examining the viability of Solar Geothermal Hybrid Source Heat Pump systems to produce domestic hot water in Brazilian-type climates. The system considered has an open-loop ground-water (aquifer) and an uncovered solar collector that can be used in a separate or connected in series topology. The refrigerant chosen for the heat pump was R290 (propane). This theoretical analysis was made using lumped models for each component of the system. The influence of ambient temperature, solar radiation, water well depth and ground water temperature in the COP, payback and collector efficiency were analyzed. The results showed that the COP of a Hybrid Source Heat Pump was better than other types of heat pump configurations for most environmental conditions, but the best payback was obtained using a Solar-Assisted Heat Pump. A case of study was performed for three different cities in Brazil and the paybacks found were in the range of 2.28 and 4.45 years. The results of COP and payback were compared with other papers and the maximum difference was 10% and 12%, respectively. Considering the scenario of a house that already has a water well, thereby eliminating the drilling cost, the best payback is obtained using a Ground-Source Heat Pump.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
lDefrost performance of heat pump system using MCHX and FTHX was studied.lEnergy supplies and consumptions were calculated and quantitatively analyzed.lThe drainage performance of MCHX is worse than ...that of FTHX.lThe experimental results can provide guidance for the design optimization of MCHX.
The frosting behavior of microchannel heat exchangers (MCHXs) has been studied extensively, but little is known about their defrosting performance in heat pump systems based on heat transfer characteristics analysis. In this study, the defrosting performance of heat pump systems using MCHX and finned tube heat exchanger (FTHX) was studied experimentally. Three types of energy supplies and four types of energy consumptions were calculated and quantitatively analyzed during defrosting processes. Although the indoor fan was turned off, the indoor air source provided more than 60% of the energy in both heat exchanger heat pump systems. The defrosting time and the energy consumption of FTHX heat pump system were 59.6% and 55.1% less than those of MCHX heat pump system, respectively, even though its frosting mass was 17.2% more. In contrast, the retained water mass and the vaporized water mass on the MCHX were 99.7% and 123.1% higher than those of FTHX, respectively. This is mainly due to the poor drainage performance of MCHX, which increases the melted frost contact time on the heat exchanger surface and therefore prolonging the defrosting time. Therefore, the defrosting efficiency of the MCHX heat pump system was 22.9% lower than that of the FTHX heat pump system. The contribution of this study is that the defrosting energy supplies and consumptions were quantitatively studied, and the reason of low defrosting efficiency of MCHX was analyzed.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Realization of an absorption/compression heat pump of more than 40 kW heating power.•Internal temperature lift of 45 K is reached at maximum.•Absorption takes place at pressure between 11.5 and 16 ...bar.•Cavitation problems inside solution pump were overcome using PI-controller.
The full potential of hybrid absorption-compression heat pumps, which can cover heating demands at temperatures of around 100 °C and provide additional cooling in industrial processes, has yet to be exploited. Although research has also been conducted on alternative systems, the natural working pair NH3 and H2O still has numerous advantages, being a very economic and thermodynamically well-suited refrigerant for this application. Striving for the development of a heat pump system that can cover a large range of heating demands at a temperature of about 80 °C and create useful cooling power in industrial processes, a test rig was designed and built at the Institute for Thermodynamics at the Leibniz University in Hanover. According to the targeted heating power of 50 kW, the components of the system are chosen based on a simulation model that solves mass, energy and component-specific balance equations for each of the parts simultaneously. This simulation is later used to compare and evaluate experimental data. Constant parameters are water-inlet temperatures at the heat source of 59 °C and at the heat sink of 50 °C. Depending on the mass flow of ammonia-poor solution and the condensation pressure, the heating capacity and the COP of the test rig are investigated. The range of the poor solution mass flow is from 0.21 kg/s to 0.31 kg/s, while the absorption pressure is varied between 13.5 bar and 16.5 bar. The COP of heating reaches a maximum of 2.5, providing more than 40 kW of heating power at a maximum internal temperature lift of 43 K.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Air-to-air heat exchange (AHX) likely to be economic but limited to less than 20% of air heating.•AHX plus heat pump (HP) could provide up to 40% of air heating with 20% lower energy ...cost.•Refrigerants with critical temperatures between 70–110 °C and evaporating 25–30 °C are most promising.•HP options attractive if capital costs are less than NZ$300 kW−1 of heating.
Air heating by heat recovery using air-to-air heat exchangers (AHX) and heat pumps (HP) was analyzed for a typical spray dryer with inlet ambient air heated to 200 °C and exhaust air with dry bulb of 76 °C and dewpoint of 38.5 °C. The HP design is a tradeoff between greater heat recovery and lower COP as evaporation temperature decreases. With an evaporation temperature of 25–30 °C, it was possible to provide up to about 40% of the air heating load with more than 20% lower energy cost. The transcritical cycle, with dehumidification of exhaust air at a constant temperature and inlet air heating in the supercritical region, is thermodynamically well-matched to the drying process. The ideal critical temperature is between 70 °C and 110 °C, so a trade-off between efficiency, cost and safety may be needed with respect to refrigerant choice. Refrigerants R134a looks most promising while R32 and R290 also have good energy efficiency but are flammable. Economically for the typical spray dryer in New Zealand, only use of an AHX is attractive but is limited to about 20% of the air heating. Combining with an R134a HP to get higher heat recovery than an AHX alone would only be attractive if HP capital costs could be reduced significantly to less than about NZ$300 kW−1 heating capacity.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
A large fraction of the energy demand is due to space heating. Direct solar heating might reduce the need of fossil fuels. However the poor solar collector efficiency when outside temperature and ...solar radiation are low, as in the heating season, limit most of solar collectors application to domestic hot water heating. Similarly air source heat pumps are penalized just when the heating demand is higher. Then a possible solar contribution to the outside air as a heat pump cold source was first analyzed, evaluating different integration modes of the two sources. Subsequently the coupling of a ground source and a solar section appeared a more favourable application, also because solar heat could recharge the ground in periods of low or no heating demand. At the same time the solar section might reduce the length of the expensive boreholes. Solar assisted absorption heat pumps were successfully experimented. Recently studies were devoted to a solar assistance of heat pumps by PV/T collectors, that offer both a fraction of the electricity to drive the heat pump and a solar assistance to the heat pump cold source, be it the ground or the outside air.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
