Domestic Central Heating Systems Research Articles

Measures for Assessing the Effectiveness of Investments for Electricity and Heat Generation from the Hybrid Cooperation of a Photovoltaic Installation with a Heat Pump on the Example of a Household

In recent years, one of the key postulates in the European Union’s policy has become the development of renewable energy sources. In order to achieve the desired synergy effect, the idea of combining two selected sources of energy appeared. This article presents a technical and economic analysis of a hybrid connection of a ground source heat pump with a photovoltaic installation. Taking into account the heat demand of the building, a ground heat pump with a catalog nominal heating power of 25 kW was selected. This article presents the problem of the economic profitability of using a hybrid combination of a heat pump and photovoltaic panels in domestic hot water and central heating systems. The justification for the use of such heat sources in these installations is due to global trends and the gradual departure from conventional energy sources such as oil or gas boilers. This paper presents the economic and ecological results of using the pump heat connected together with photovoltaic panels. In the economic analysis, with the assumed installation costs related to the use of the considered heat pump and PV, two parameters commonly used in the investment analysis (static and dynamic) were used, namely, the simple payback period and the net present value of the investment. For the adopted assumptions, the usable area of the facility and the number of years of use were indicated, at which the investment in question is competitive with other alternative investment interest methods and will start to bring tangible benefits. The performed analysis also has measurable environmental benefits in the form of a reduction in carbon dioxide emissions at the level of 2893 kg/year into the atmosphere. The presented solution will help future investors understand the investment profitability mechanism for their households.

Emission Factors for Biofuels and Coal Combustion in a Domestic Boiler of 18 kW

The differences in the pollutant emissions from the combustion of bituminous coal and biofuels (wood, straw, and miscanthus pellets) under real-world boiler operating conditions were investigated. The experiments were performed on an experimental installation that comprised an 18 kW boiler, used in domestic central heating systems, equipped with a retort furnace, an automatic fuel feeder, a combustion air fan, and a fuel storage bin. The emission factors of gaseous pollutants, particulate matter, organic carbon, elemental carbon, and polycyclic aromatic hydrocarbons (PAHs), as well as some PAH concentration ratios for coal and biofuel combustion, were determined. The obtained results indicate that fuel properties have a strong influence on the emission factors of gaseous and carbonaceous pollutants. The total particulate matter (PM) emissions from the biofuel combustion were about 5-fold lower than those from the coal burned in the same boiler. The emission factors of the total carbons from the biofuel combustion were between 10 and 20 times lower than those from the coal combustion. The mean organic carbon (OC) and elemental carbon (EC) emission factors, based on the burned fuel, were 161–232 and 42–221 mg/kg for the biofuels and 1264 and 3410 g/kg for the coal, respectively. The obtained results indicate that molecular diagnostic ratios, based on the concentration of PAHs, vary significantly, depending on the fuel type.

Quantifying the performance of a passive deaerator in a gas-fired closed loop domestic wet central heating system

In the UK, approximately 16% of the energy use can be attributed to domestic wet central heating systems. Government financial support and advances in technology have led to boilers becoming more efficient and a range of technologies are now available that claim to be able to improve the efficiency of domestic wet central heating systems. One such low cost technology is a passive deaerator. This article presents the results obtained from installing a passive deaerator on the closed loop of a gas-fired wet central heating system, under controlled conditions in the Salford Energy House. The results indicate that although marginally less heat output was required from the boiler when the passive deaerator was operating, these savings are more or less out weighted by the boiler short cycling more frequently. Consequently, the overall reduction is gas consumption achieved by utilising the passive deaerator device is only of the order of 0.5%; this scale of savings may just be a consequence of measurement noise. The implications are that although a marginal benefit may be attributed to these products, if short cycling takes place, then these savings may become insignificant. Practical application: This article describes a test method that has been used to quantify the energy savings that could be achieved by installing a passive deaerator on the closed loop of a wet central heating system. Although the results indicate that the energy savings associated with using such a device are likely to be marginal, the test method described could be used to test a range of other devices that claim to improve the performance of domestic wet central heating systems, to directly compare before and after performance.

Characterization and concentrations of polycyclic aromatic hydrocarbons in emissions from different heating systems in Damascus, Syria

Traffic has long been recognized as the major contributor to polycyclic aromatic hydrocarbon (PAH) emissions to the urban atmosphere. Stationary combustion sources, including residential space heating systems, are also a major contributor to PAH emissions. The aim of this study was to determine the profile and concentration of PAHs in stack flue gas emissions from different kinds of space heaters in order to increase the understanding of the scale of the PAH pollution problem caused by this source. This study set out to first assess the characteristics of PAHs and their corresponding benzo[a]pyrene equivalent emissions from a few types of domestic heaters and central heating systems to the urban atmosphere. The study, enabled for the first time, the characterization of PAHs in stationary combustion sources in the city of Damascus, Syria. Nine different types of heating systems were selected with respect to age, design, and type of fuel burned. The concentrations of 15 individual PAH compounds in the stack flue gas were determined in the extracts of the collected samples using high-performance liquid chromatography system (HPLC) equipped with ultraviolet-visible and fluorescence detectors. In general, older domestic wood stoves caused considerably higher PAH emissions than modern domestic heaters burning diesel oil. The average concentration of ΣPAH (sum of 15 compounds) in emissions from all types of studied heating systems ranged between 43 ± 0.4 and 316 ± 1.4μg/m(3). Values of total benzo[a]pyrene equivalent ranged between 0.61 and 15.41μg/m(3).

Bubble shape and breakage events in a vertical pipe at the boiler flow line

The theoretical and experimental aspects concerning the typical bubble shape at the flow line of a standard domestic central heating system are investigated. This is done in support of the on-going research on two-phase flows in domestic central heating systems. Bubble nucleation and detachment at the primary heat exchanger wall of a domestic central heating boiler results in a bubbly two-phase flow in the system pipe work. Bubbly flow results in undesired cold spots at higher points in the system, consequently diminishing system performance. An experimental analysis was done on the bubble shape at the exit of the boiler through the application of photographic techniques. The results are presented in terms of the measured bubble aspect ratios at some principal system operating conditions. The dimensionless Eotvos and bubble Reynolds number were calculated and tabulated with the measured mean diameters. The data was subsequently correlated to the bubble shape regime diagram. Results suggest that most bubbles are quasi-spherical in shape with a noticeable elongation at lower bulk fluid Reynolds numbers.

Investigation of bubble behaviours in wet central heating systems

A series of experimental measurements has been conducted in order to investigate the bubble behaviours through the horizontal pipe line of the domestic wet central heating systems. Obtained results exposed the effect of 90 degree bend, buoyancy forces on bubbly two phase flow patterns and effect of velocity on void fractions and bubble diameters. Distance chosen for the first sight glass (HSG0) was sufficient enough to note the effect of 90 degree bend on void fraction patterns. Due to the effect of 90 degree bend, position of the peak void fractions across the pipe section lowers, with an increase in bulk fluid velocity. Bubbles tend to flow for longer distance at the bottom of the pipe section. Buoyancy force effect is demonstrated with figures for highest bulk fluid velocity at three different positions. Analysis of four different flow rates at two different saturation ratios show reduction for average bubble diameters and void fractions when bulk fluid velocity increases. An attempt to predict bubble dissolution rates across the horizontal pipeline of the system is made, however results show some uncertainties.

Twitter Controls the Household Heating System

The home is composed of many different devices, services and related technologies. These have a lack of communication with one another. A challenge within domestic central heating system is being able to exploit the functionality and offer a common means of monitoring and controlling, either locally or remotely. This paper introduces a domestic central heating system design for householders to control it through twitter, either locally or remotely. We believe by enabling householders to monitor and control domestic central heating system could contribute to make a smart home.

A naturally aspirated convector for domestic heating application with low water temperature sources

The introduction of low temperature renewable energy sources such as geothermal heat pumps into domestic central heating systems will demand that new technologies be developed to dissipate the required heat loads into homes. The main reason for this is the lower operating temperatures associated with these energy sources, which can be as low as 35°C and rarely exceed 55°C. Unless the appropriate heat exchanger is deployed, expensive and intrusive alternatives such as forced air convectors, under floor heating and home insulation retrofitting must be considered. This work details the development of a turn-key heat pipe based naturally aspirated convector for domestic central heating applications. The results show that the heat pipe convector design has a power density of nearly 3 times that of a popular off the shelf panel radiator as well as a finned-serpentine convector. Furthermore, the low water content associated with the heat pipes results in a unit with a much reduced thermal response time which could be advantageous in the context of building thermoregulation.

Bubble dissolution in horizontal turbulent bubbly flow in domestic central heating system

In a domestic central heating system, the phenomenon of microbubble nucleation and detachment on the surface of a boiler heat exchanger finds its origins in the high surface temperature of the wall and consequential localised super saturation conditions. If the surrounding bulk fluid is at under-saturated conditions, then after exiting the boiler, the occurrence is followed by bubbly flow and bubble dissolution. A comprehensive understanding of the fundamentals of bubble dissolution in such a domestic wet central heating system is essential for an enhanced deaeration technique that would consequently improve system performance. In this paper, the bubble dissolution rate along a horizontal pipe was investigated experimentally at different operating conditions in a purpose built test rig of a standard domestic central heating system. A high speed camera was used to measure the bubble size at different depths of focal plane using two square sectioned sight glasses at two stations, spaced 2.2m apart. A dynamic model for bubble dissolution in horizontal bubbly flow has been developed and compared with experimental data. The effects of several important operating and structural parameters such as saturation ratio, velocity, temperature, pressure of the bulk liquid flow, initial bubble size and pipe inside diameter on the bubble dissolution were thus examined using the model. This model provides a useful tool for understanding bubble behaviours in central heating systems and optimising the system efficiency.

Two-phase distribution in the vertical flow line of a domestic wet central heating system

The theoretical and experimental aspects of bubble distribution in bubbly two-phase flow are reviewed in the context of the micro bubbles present in a domestic gas fired wet central heating system. The latter systems are mostly operated through the circulation of heated standard tap water through a closed loop circuit which often results in water supersaturated with dissolved air. This leads to micro bubble nucleation at the primary heat exchanger wall, followed by detachment along the flow. Consequently, a bubbly two-phase flow characterises the flow line of such systems. The two-phase distribution across the vertical and horizontal pipes was measured through a consideration of the volumetric void fraction, quantified through photographic techniques. The bubble distribution in the vertical pipe in down flow conditions was measured to be quasi homogenous across the pipe section with a negligible reduction in the void fraction at close proximity to the pipe wall. Such a reduction was more evident at lower bulk fluid velocities.

Bubble nucleation on the surface of the primary heat exchanger in a domestic central heating system

The theoretical and experimental aspects of heterogeneous bubble nucleation are reviewed in the context of the micro bubbles present in a domestic gas fired wet central heating system. Such systems are mostly operated through the circulation of heated standard tap water through a closed loop circuit which often results in water supersaturated with dissolved air leading to micro bubble nucleation at the primary heat exchanger wall. This study will report the micro bubble nucleation in a standard domestic central heating system at typical operating conditions. Bubble nucleation rates have been calculated in the range of 0.3–4 bubbles/cm2 s with total system bubble production rates measured in the range of 784–6920 bubbles per second. Bubble nucleation rates have been calculated through the consideration of the heat exchanger surface under super saturation conditions. The lack of experimental research in this area is evident from the non-existence of experimental correlations developed for similar physical scenarios where low levels of super saturation predominate. Hence, the classical nucleation models are considered inadequate for adaptation to the present study. A correlation through the application of the model for non-classical heterogeneous nucleation is proposed, based on the experimental data of the present study.

Micro bubble formation and bubble dissolution in domestic wet central heating systems

16 % of the carbon dioxide emissions in the UK are known to originate from wet domestic central heating systems. Contemporary systems make use of very efficient boilers known as condensing boilers that could result in efficiencies in the 90-100% range. However, research and development into the phenomenon of micro bubbles in such systems has been practically non-existent. In fact, such systems normally incorporate a passive deaerator that is installed as a ‘default’ feature with no real knowledge as to the micro bubble characteristics and their effect on such systems. High saturation ratios are known to occur due to the widespread use of untreated tap water in such systems and due to the inevitable leakage of air into the closed loop circulation system during the daily thermal cycling. The high temperatures at the boiler wall result in super saturation conditions which consequently lead to micro bubble nucleation and detachment, leading to bubbly two phase flow. Experiments have been done on a test rig incorporating a typical 19 kW domestic gas fired boiler to determine the expected saturation ratios and bubble production and dissolution rates in such systems.

Measurement of bubble detachment diameters from the surface of the boiler heat exchanger in a domestic central heating system

Abstract Wet central heating systems are used throughout the world and the domestic variants are known to account for 16% of the carbon dioxide emissions in the UK. It is an industry wide fact that significant quantities of air leak into the system’s closed loop circuit, mostly due to thermal cycling during routine use. The water in the system results in high dissolved gas saturation levels thus resulting in microbubble nucleation and detachment at the boiler wall. An in depth knowledge into the behaviour of microbubbles in such systems could result in better deaeration systems thus improving the overall system efficiency. In this study, we will report a measurement of the bubble detachment sizes in this system at different operating conditions, these being, the system flow rate, pressure, heating load and saturation ratio. The Winterton models for zero and finite contact angles for the prediction of the bubble detachment diameters in supersaturated solutions were used as a comparison with the test results. The model for the prediction of bubble detachment diameters at finite contact angles in round pipes has yielded good predictions. A new correlation has been proposed so as to include the effects of pressure and heat flux on the bubble characteristics which were not represented through the Winterton model.

Feedback quality and environmentally friendly use of domestic central heating systems

The study examined the influence of system-embedded feedback on user behaviour during the environmentally friendly operation of a central heating system. A PC-based simulation, called CHESS, was developed to model the critical features of a central heating system. After having received 30 min of training on the simulation task, 60 participants worked on a series of operational scenarios under different levels of system feedback. In addition to the collection of various performance measures (e.g. energy consumption, energy wastage), a range of user variables was collected (e.g. environmental concern). As hypothesized, the results showed that increased feedback resulted in improved environmentally friendly performance and, more importantly, the specific feedback indicator influenced the type of strategy used to improve human – machine system performance. A major implication is that system designers need to develop feedback indicators that are chiefly influenced by user behaviour and are largely immune to factors that are beyond the user's control (e.g. weather conditions).

Circulation pumps as structure-borne sound sources: emission to semi-infinite pipe systems

Circulation pumps are an important source of noise from domestic central heating systems. Pumps can generate airborne, liquid-borne and structure-borne sound and although standards exist for airborne and liquid-borne sources, none do for structure-borne sources. This is primarily because the structure-borne acoustic power delivered by the pump not only depends on the pump but also on the connected receiving system, which can be a complicated combination of pipes, valves and radiators. Also pumps deliver liquid-borne and structure-borne acoustic power simultaneously and their relative contributions to the sound radiated from the pipe system is not obviously obtainable. The approach proposed is to estimate the emission from the pump into semi-infinite pipes of material and cross-section typical of heating systems. Then to estimate the ‘mixing’ effect of bends, joints and other pipe discontinuities, due to wave mode conversion, as described in a companion paper. In the present paper, it is demonstrated that the structure-borne power can be calculated from the measured free velocity and mobility of the pump for each component of vibration and from receiver mobilities of idealized pipe systems. The structure-borne power is compared with the liquid-borne power measured directly by intensimetry.

Domestic central heating radiators: a cause for concern in all age groups

A retrospective analysis of all burns admitted to the Welsh Regional Burns and Plastic Surgery Unit, Chepstow, in the period 1 January 1990 to 1 October 1993, highlighted a group of 50 patients who had sustained contact burns from the radiators of domestic central heating systems. There was a male prevalence, with an average age of 43.4 years (range 6 months to 100 years). The mean TBSA burned was 1.58 per cent (range 0.13–6.0 per cent) and half of the injuries were full thickness depth. The forearm and hand were predominantly injured. Although the literature has indicated that the incidence of contact burns peaks at the extremes of the age spectrum, this study has shown that contact radiator burns can be sustained by all age groups. The aim of the audit was to investigate the mechanism of injury and link precipitating factors. The contribution of the high surface temperature of the radiator to the burn injury is alluded to. The various methods available to reduce this risk are discussed and the use of the low surface temperature radiator, already routinely used in health care premises, is advocated.

Boiler efficiency and gas consumption: Effects of cycling and pump speed

This brief note sets down some results on the effects of decoupling the room thermostat and cylinder thermostat from the pump and boiler in a 'wet' domestic gas-fired central heating system. Decoupling means that the boiler and pump operate continuously, as opposed to coupled control in which the control thermostats switch off the pump and boiler when no heat is required. The results showed that, for decoupled control, the boiler cycling rates were increased by 62%, the mean boiler efficiency was reduced from 68% to 62% and the gas consumption was increased by about 3% across the 1990/91 winter season. In mild weather the deterioration was much worse and it is important that the controls be properly coupled in these conditions. Lower pump speeds also increase boiler cycling and slow down the heating-up rates for space and hot water heating.

Short-term thermal energy storage as a means of reducing the heat pump capacity required for domestic central heating systems

The effects upon the economics, size and performances of domestic central heating heat pumps by the incorporation of some thermal energy storage between the heat pump and the heat distribution system are studied with the aid of computer simulation programs. It is demonstrated that significant reductions in the capacity of the heat pump and system annual running costs can be made by using moderate quantities of heat storage without causing any detriment to the overall performance of the heating system. The results are being validated in the laboratory, where a phase-change material thermal energy store is linked to a heat pump and heat distribution system, and the performance of this system is being monitored.

Prevention of Corrosion in Domestic Hot Water Central Heating Systems

The corrosion reactions that are likely to occur when bare steel is exposed to water in domestic central heating systems are discussed and the resultant effects are related to corrosion of radiators per se, and to the ancillary occurrence of hydrogen gas-locking in. radiators and to blockage of pumps by loose magnetite.The suggested remedial measures include care in installation to prevent air ingress into and water leakage from central heating systems and the use of corrosion inhibitors.