The cost-effectiveness of heat pumps in specific buildings in South Africa

Water heating heat pumps are extremely energy efficient and large savings can be realized when they are compared to direct electrical resistance heaters. In spite of the energy efficiency of heat pumps, a large number of residential buildings in South Africa still use electrical heaters to heat water. The reason for this is that heat pumps are considerably more expensive than electrical heaters. Building owners tend to choose the system with the smallest initial cost and do not compare the two systems on the basis of life-cycle cost. It is also difficult to calculate the life-cycle cost of a heat pump because it depends on many factors like climatological conditions and water temperature. In this paper a methodology is developed to calculate the life-cycle cost of a heat pump hot water installation. The model is used to investigate the effect of daily runtime, electricity tariff, hot water consumption and geographical location on the cost-effectiveness of heat pumps. The cost-effectiveness of heat pumps increases with daily run time, water consumption and electricity tariff. Heat pumps are more cost-effective near the coast than in the interior. If sized correctly, heat pumps are more cost-effective than electrical heaters for all major cities in South Africa. The cost-effectiveness of heat pumps for two specific buildings, one a university student hostel in Potchefstroom and the other a hotel in Durban, is also investigated. For both cases it was found that heat pumps are more cost-effective than direct electrical resistance heaters.     

Experimental studies on a ground coupled heat pump with solar thermal collectors for space heating

This paper presents experimental studies on a solar-assisted ground coupled heat pump (SAGCHP) system for space heating. The system was installed at the Hebei Academy of Sciences in Shijiazhuang (lat. N38°03′, long. E114°26′), China. Solar collectors are in series connection with the borehole array through plate heat exchangers. Four operation modes of the system were investigated throughout the coldest period in winter (Dec 5th to Dec 27th). The heat pump performance, borehole temperature distributions and solar colleting characteristics of the SAGCHP system are analyzed and compared when the system worked in continuous or intermittent modes with or without solar-assisted heating. The SAGCHP system is proved to perform space heating with high energy efficiency and satisfactory solar fraction, which is a promising substitute for the conventional heating systems. It is also recommended to use the collected solar thermal energy as an alternative source for the heat pump instead of recharging boreholes for heat storage because of the enormous heat capacity of the earth.     

An experimental analysis of a solar assisted absorption heat pump with earth seasonal storage

A plant composed of an energy roof, a seasonal earth storage and an absorption heat pump has been experimented. The purpose was to study the behaviour of the various components and their interaction. The surveys were carried out over a two year period. The following operations were considered: the charging of the earth storage by the energy roof and the working of an absorption heat pump connected either to the energy roof or to the earth storage.     

Energy savings for solar heating systems

In this paper the realistic behaviour and efficiency of heating systems were analysed, based on long term monitoring projects. Based on the measurements a boiler model used to calculate the boiler efficiency on a monthly basis was evaluated. Comparisons of measured and calculated fuel consumptions showed a good degree of similarity. With the boiler model, various simulations of solar domestic hot water heating systems were done for different hot water demands and collector sizes. The result shows that the potential of fuel reduction can be much higher than the solar gain of the solar thermal system. For some conditions the fuel reduction can be up to the double of the solar gain due to a strong increase of the system efficiency. As the monitored boilers were not older than 3 years, it can be assumed that the saving potential with older boilers could be even higher than calculated in this paper.     

Numerical and experimental analysis of convection heat transfer in passive solar heating room with greenhouse and heat storage

In this paper, heat transfer and air flow in passive solar heating room with greenhouse and heat storage are studied. Thermal insulation of solar heating room has significant effects on temperature distribution and airflow in the heating chamber of this solar system. Heat transfer and air flow in a rock bed, which is used as solar absorber and storage layer, are also studied. If porosity is kept within certain range, increasing the rock size causes an increase of the capability of thermal storage and heating effects; increasing the porosity of thermal storage materials results in an increase of the bed temperature but a decrease of the rock mass. The specific heat capacity and thermal conductivity have a remarkable effect on the average temperature of rock bed. All these factors should be taken into account when designing a solar heating system.     

Future use of heat pumps in Swedish district heating systems: Short- and long-term impact of policy instruments and planned investments

Heat pumps constitute one of the major technologies used in district heating systems in Sweden. Totally about 6 TWh of heat are supplied annually by heat pumps, equivalent to 12% of the heat supplied in district heating systems. New policy instruments that have recently been introduced will change the conditions for technologies in the district heating systems. It is likely that the incentives for waste incineration and combined heat and power will be improved. This study estimates how different policy instruments, and new investments in waste incineration and combined heat and power, affect heat pumps in Swedish district heating systems. The results indicate that heat pumps are affected in both a short-term and a long-term perspective, and that heat pumps will play a less important role in district heating systems in the future. Depending on the policy instruments applied in the district heating sector, the long-term use is between 18% and 71% lower than current use. In a long-term perspective, it is in the systems which currently use heat pumps during a large part of the year that new investments in waste incineration and combined heat and power can be expected, resulting in a convergence between different district heating systems regarding how much heat is supplied by combined heat and power and waste incineration, and regarding the annual operating hours for heat pumps.     

First and second law analysis of a solar assisted heat pump based heating system

We propose a model for the heating system of an ecological building whose main energy source is solar radiation. The most important component of the heating system is a vapour compression heat pump. Both the first law and the second law were used to analyse the heat pump operation. The state parameters and the process quantities were evaluated by using, as input, the building thermal load. The second law analysis emphasised that most of the exergy losses occur during compression and condensation. Preliminary results show that the photovoltaic array can provide all the energy required to drive the heat pump compressor, if an appropriate electrical energy storage system is provided.     

Validation of a computer model for solar assisted district heating systems with seasonal hot water heat store

The TRNSYS XST-model for the calculation of the thermal behaviour of ground buried hot water heat stores was validated. For the validation procedure measured data of the seasonal hot water heat store in Hannover (Germany) were used. In contrast to previous investigations the temperatures of the surrounding ground were also taken into consideration. The determination of the heat store parameters was carried out using TRNSYS in combination with the parameter identification software DF. The deviation between measured and calculated temperatures is less than ±3%. The measured and calculated heat quantities are also in good agreement (annual deviation less than 2%). The validated XST-model was integrated into a TRNSYS model to calculate the thermal behaviour of the solar assisted district heating system in Hannover in 2002. The deviations between measured and calculated heat quantities do not exceed 5%.     

Heat pumps and energy storage - The challenges of implementation

The wider implementation of variable renewable energy sources such as wind across the UK and Ireland will demand interconnection, energy storage and more dynamic energy systems to maintain a stable energy system that makes full use of one of our best renewable energy resources. However large scale energy storage e.g. pumped storage may be economically challenging. Therefore can thermal energy storage deployed domestically fulfil an element of such an energy storage role? Current electricity pricing is based on a ½ hourly timeframe which will be demonstrated to have some benefits for hot water heating from electrical water heaters in the first instance. However heat pumps linked to energy storage can displace fossil fuel heating systems and therefore the question is whether a renewable tariff based on “excess” wind for example is sufficient to operate heat pumps. An initial analysis of this scenario will be presented and its potential role in challenging aspects of fuel poverty.     

Performance of commercially available solar and heat pump water heaters

Many countries are using policy incentives to encourage the adoption of energy-efficient hot water heating as a means of reducing greenhouse gas emissions. Such policies rely heavily on assumed performance factors for such systems. In-situ performance data for solar and heat pump hot water systems, however, are not copious in the literature. Otago University has been testing some systems available in New Zealand for a number of years. The results obtained are compared to international studies of in-situ performance of solar hot water systems and heat pump hot water systems, by converting the results from the international studies into a single index suitable for both solar and heat pump systems (COP). Variability in the international data is investigated as well as comparisons to model results. The conclusions suggest that there is not too much difference in performance between solar systems that have a permanently connected electric boost backup and heat pump systems over a wide range of environmental temperatures. The energy payback time was also calculated for electric boost solar flat plate systems as a function of both COP and hot water usage for a given value of embodied energy. The calculations generally bode well for solar systems but ensuring adequate system performance is paramount. In addition, such systems generally favour high usage rates to obtain good energy payback times.     

The performance of heat pumps in service-comparison of a computer model with a real installation

A comparison is made between a computer model which was developed in an earlier paper and experimental results in which a heat pump was used to heat a house during the heating season 1978–1979. The heat pump used was an air-to-water machine, and it is found that the radiator temperature in the experiment varies according to the heat demand of the house because of the effect of thermal inertia of the water and other thermal masses in the heat transfer system. The computer model simulates this effect, using hourly weather data to calculate the heat demand of the house and assuming that the radiators run at the temperature necessary to supply the heat demand during each hour. The model also calculates the coefficient of performance of the heat pump, and hence calculates the running cost in kilowatt-hours for each hour. The calculated running cost is compared with daily readings of kilowatt-hour meters. It is found that the comparison is very accurate during normal operation of the heat pump, with an accuracy of better than 1 per cent over a period of four months of the heating season, although the accuracy is not always quite so good. A comparison is also made between hourly calculated radiator temperatures and continuous recordings of flow and return temperatures. The comparison in this case is satisfactory, but there is a time lag due to the effect of thermal inertia of the building fabric which the computer model is not intended to simulate.     

Performance of a natural circulation solar air heating system with phase change material energy storage

The design, construction and performance evaluation of a passive solar powered air heating system is presented. The system, which has potential applications in crop drying and poultry egg incubation, consists of a single-glazed flat plate solar collector integrated with a phase change material (PCM) heat storage system. The PCM is prepared in modules, with the modules equispaced across the absorber plate. The spaces between the module pairs serve as the air heating channels, the channels being connected to common air inlet and discharge headers. The system was tested experimentally under daytime no-load conditions at Nsukka, Nigeria, over the ambient temperature range of 19–41 °C, and a daily global irradiation range of 4.9–19.9 MJ m⁻². Peak temperature rise of the heated air was about 15 K, while the maximum airflow rate and peak cumulative useful efficiency were about 0.058 kg s⁻¹ and 22%, respectively. These results show that the system can be operated successfully for crop drying applications. With suitable valves to control the working chamber temperature, it can also operate as a poultry egg incubator.     

集中供暖换热站扩容供热方式的选择

通过对某换热站新增区域的供热方式与原采暖用户进行系统分析,建议新增区采用间接连接和混水直接连接两种方案,并对两种方案给出详细的设计说明;通过对两种方案进行整体比较分析,综合得出混水直供换热方式运行经济,供热效果良好,尤其是区域供热新增区或新建区采暖用户的供热选择方式。     

Solar and geothermal heating and cooling of the European Centre for Public Law building in Greece

The European Centre for Public Law in Legraina near Athens in Greece is heated and cooled by a combined solar and geothermal system. The main components of the system are a saline groundwater supplying well, water storage tank for 6 h autonomy, inverter for regulating geothermal flow, heat exchanger, two electrical water source heat pumps placed in cascade, fan coils, air handling units, as well as solar air collectors for air preheating in winter. In addition, hot water is supplied to the building hostel by solar water heaters. Monitoring of the energy system during heating showed excellent energy efficiency and performance.     

Experimental and theoretical study on a solar assisted CO2 heat pump for space heating

In this paper, a solar combi-system which consists of solar collector and a CO₂ heat pump is investigated experimentally and theoretically. Two experiments are primarily conducted to show the performance of this solar combi-system under different operation conditions. A system model is developed and validated in TRNSYS to analyze the influence of main components parameters. Subsequently, a multi-parameter optimization is carried out in GENOPT to obtain a final optimal result. The simulated results show that the optimized system can save 14.2% electricity and improve the solar fraction by 8%. The solar fraction of the optimized system can reach 71.1%. Finally, the optimized system performance is studied with the weather and load characteristics in Shanghai. Compared with the CO₂ HP heating system alone, the solar assisted system can save 1790.8 kWh electricity on the basis of year round operation.     

Modeling the impact of integrating solar thermal systems and heat pumps for domestic hot water in electric systems – The case study of Corvo Island

The use of solar thermal systems with electricity backup and heat pumps as hot water suppliers in residential buildings seems to be a very promising way to increase energy efficiency. Nevertheless, the massive adoption of such solutions in small networks (neighborhood, village) may induce problems in the electric grid management. This study explores the impact of such systems in small electric grids, using an hourly electricity backup load model. To test and validate the model, we used the island of Corvo (Azores), a small isolated community where it is being implemented a project of electrification of domestic hot water systems (DHW). We consider different load scenarios to manage the backup of DHW systems and analyze its consequences on the peak load and overall energy demand. For Corvo, for the best case where the backup is limited and distributed along off-peak hours, we observed an increase of 24% in the peak load and 7.5% in the annual energy demand. Critical values of peak load are found in winter, when daily solar irradiation is lower than 2000 Wh/m²/day. We conclude that the solar thermal systems are responsible for most of the peak load increase, but since they have the flexibility to adjust the electric backup hours due to the thermal storage capacity, the use of these systems can minimize the impact on the grid. Heat pumps on the other hand, albeit being more efficient in terms electric backup, are less flexible to contribute to the grid management as they operate continuously.     

German central solar heating plants with seasonal heat storage

Central solar heating plants contribute to the reduction of CO₂-emissions and global warming. The combination of central solar heating plants with seasonal heat storage enables high solar fractions of 50% and more. Several pilot central solar heating plants with seasonal heat storage (CSHPSS) built in Germany since 1996 have proven the appropriate operation of these systems and confirmed the high solar fractions.Four different types of seasonal thermal energy stores have been developed, tested and monitored under realistic operation conditions: Hot-water thermal energy store (e.g. in Friedrichshafen), gravel-water thermal energy store (e.g. in Steinfurt-Borghorst), borehole thermal energy store (in Neckarsulm) and aquifer thermal energy store (in Rostock). In this paper, measured heat balances of several German CSHPSS are presented. The different types of thermal energy stores and the affiliated central solar heating plants and district heating systems are described. Their operational characteristics are compared using measured data gained from an extensive monitoring program. Thus long-term operational experiences such as the influence of net return temperatures are shown.     

Comparison of the modeling of a solar absorption system for simultaneous cooling and heating operating with an aqueous ternary hydroxide and with water/lithium bromide

This paper compares the theoretical performance of the modeling of a solar absorption system for simultaneous cooling and heating operating with water/lithium bromide and alternative aqueous ternary hydroxide mixtures. Aqueous ternary hydroxide working fluid consists of sodium, potassium and cesium hydroxides in the proportions 40 : 36 : 24 (NaOH : KOH : CsOH). Plots of Carnot coefficients of performance and enthalpy-based coefficients of performance are shown against the evaporator temperature. The results showed that, in general, the system with the hydroxide mixture may operate with higher coefficients of performance than the system with the lithium bromide mixture. Also it was shown that the system with the hydroxide may operate with a higher range of temperatures.     

Feasibility study of the application of solar heating systems in Iran

This study outlines the economic feasibility for utilization of solar heating systems for some buildings in the selected typical cities in different climatic regions of Iran. The feasibility of application of the solar heating systems has been determined by means of proper economic criteria and a life time of 25 years for capital investment. It has been found that utilization of such systems could be feasible in some of the regions for specific applications.