Abstract
The document considers the use and conservation of energy in domestic dwellings using heating systems, specifically water heated boilers, which is the cheapest solution in the market for home heating systems in Ireland and Europe. The document starts with a literature review of the available home heating systems and focuses on boilers due to its availability and price. The literature review includes a standard boiler array for a typical house, the radiators materials, and key concepts to understand the use of boilers for heat generation in homes. Later, it is necessary the calculation of heat transference for a given room or house gets the energy transference. In the current example, the heat transference is -4202W, the negative value is because the room is considered the control volume and the output of energy has a negative value. In the calculation, there are positive partial values, but at the end, they reduce the requirement for the boiler, and the final value did not represent the worst case conditions for the boiler work, that is, in the evening and when the room or house is unoccupied.
With the energy transference calculation, it is possible to select the best boiler to meet the energy requirements. The homeowner must select the available boiler in the market with a value higher than calculation; in this case, a boiler with a power of 5275W meets the requirements of the calculation and gives to the owner the ability to operate the boiler in 75%-80% of its capacity. The capacity of the boiler should be controlled by flow valves in each radiator or by control instruments directly to the boiler. After the selection of the boiler, it is possible to improve the home conditions with the addition of insulation, reducing the energy requirements to 3911W. To finish the document, there are several recommendations for installation, operation, and energy consumption to reduce the energy bills and improve the operations of the boiler.
Introduction
The heating is essential to deal with the low temperatures in the countries where the four seasons are observed: summer, autumn, winter, and spring. Households in countries with winter, such as Ireland, must have a heating system that can maintain the internal temperature of the building or house within the temperature and humidity comfort range, that is, between 21 ° C and 26 ° C and humidity between 40% and 60%. However, not all homes need the same system. The choice of one or the other will depend on the location of the house, the weather and isolation, the size and distribution of the house, the number of inhabitants of the house and the cost associated with it.
The types of heating can be divided according to the energy source (biomass, geothermal, solar, electric and gas) or according to the apparatus or system from which the heat is obtained (radiant floor, air pump, electric by accumulators, electric By convectors, thermoelectric emitters and boilers with water radiators). For research purposes, boiler technology with water radiators is considered the most used by households in Ireland and Europe.
Boiler technology with radiators heat is produced, by burning fuels such as natural gas, in a boiler located in a specific place and distributed to terminal elements (radiators) through the water, emitting heat to those spaces that they require it.
The choice of water as a heat carrier is because it is a cheap substance, common in all buildings and its specific heat is greater than that of other substances, so it requires a lower flow rate to transport the same amount of heat.
As the boiler is located in another space, it can be freely aerated without problems. This can serve a single user (individual central heating) or the housing building (collective central heating).
Energy costs (electricity, gas) represent challenges for citizens, government and companies to increase the efficiency of systems, consume less energy while maintaining the comfort of temperature and humidity required in homes.
Objective
The objective of the paper is to know what are the best practices and procedures to increase the efficiency of a heating system in agreement with national and regional regulations. The heating system considered in the paper is the water-boiler due to the cost acquisition, availability and the use of water as the energy transference element.
Methodology
The method starts with a review of literature considering a theory framework of heating systems. The theory of heating systems is analog to air conditioning (cold) systems with the difference in the efficiency considerations and heat sources. The heating system to be considered in the document is the boiler and radiator array. The used flow is water.
After the theory framework is ready, starts the calculation of the energy (heat) transference in a typical house considering all the external areas of the house, later the selection of the boiler according to with the energy calculation.
The document finishes with recommendations for the correct use of boiler and radiators and strategies to the homeowner to increase the efficiency of the heating system.
Review of literature
The boiler is a thermodynamic component that works together with radiators to increase the temperature of a closed space. The logic in the use of boilers is different to air conditioning systems that have the function to reduce the temperature of a room, home or building. The use of boiler-radiation arrays have a sense when the outside temperature is below the room temperature, and that temperature is below 21°C. It is possible to add other components to the heating system as central heating feed tank, hot water feed tank, vented hot water cylinder and thermostats.
The boiler, as a thermodynamic machine, transforms the chemical (gas, diesel) or electric energy to caloric energy using water as the energy transport mean due to its availability, cost, and heat capacity. The water is supplied by the municipal water company, but it must be demineralized and treated before the use in the home heating system. According to the required power, the boiler could require a full room of the house or could have a portable size located in the kitchen or a bathroom (Worcester Bosch, 2017).
Types of Radiators
Aluminum Radiators
It is the most requested radiator, since it can be installed in modules and adapts to all corners. The great advantage is that it heats very fast when the system starts, but similarly, the heat lasts very little when the boiler stops working
Iron Radiators
These types of radiators that work with water can also be made of iron. As a point of favor say that this class of thermal emitters manage to conserve the heat even when two hours have passed since the heating system went out. Of course, iron radiators take longer to reach the right temperature and are very heavy (Woodford, 2016).
The former cannot be installed by modules, are the most economical radiators and are used little (although their performance is good). For their part, steel emitters heat quickly and retain heat better than devices made of aluminum.
Other terms and definitions
Flow rate: The flow rate is the volume of water per unit of time of water used by the boiler. The power of the boiler is proportional to the flow rate and the temperature difference. The boiler has a maximum capacity of flow rate. Each boiler has a standard value of flow rate, if the flow rate from the municipal provider is higher than the standard flow rate, the boiler did not deliver more power.
System filter: The filters remove contaminants from the water using magnetic and non-magnetic techniques. The filter avoids early failures to the boiler, pipes, and radiators removing minerals and contaminants from the water increasing its heat capacity and avoiding mineral deposits in the heating system components (USwitch, 2016).
Thermostatic Radiator Valves: The TRV is a valve that controls the water flow through the individual radiator to regulate the temperature of the room. An open valve increases the flow rate of hot water through the radiator, increasing the temperature change speed in the room. A closed valve reduces the hot water flow and the speed in the temperature change of the room.
Causes of energy losses
According to energy conservation, the energy has not created either loss but transformed. The energy loss in a house consists in the energy transference between the house and the external environment increasing the work of the heating system more than the design. The most important energy losses causes are:
Leaks and loss of insulation
There are three ways of heat and energy transference: conduction, convection, and radiation. A higher area of non-insulated materials increases the heat transference by the floor, roof, walls, windows and doors (Sustainable Energy Authority of Ireland, 2016).
Figure 1: Energy loss distribution in house
The logic of energy transference in the heating system is that the energy goes from inside the house to the outside, due to the fact the temperature outside the house is lower than the inside temperature. For calculation purposes, the control volume is the house and energy output has negative values.
Raw Data for energy transference calculations:
Windows: 3.35 m2
External walls area: 39 m2
Floor: 27.87 m2
Roof: 27.87 m2
Specific energy per person: 58W
Energy transference by the windows
The energy transference by the Windows considers the external radiation of the home windows. The considered energy transference by the window is proportional to the area of the window and the load factor of the glass (Table 1).
For example, a house may have a load factor between 75 and 150, according to the orientation of the windows: north, south, east, and west. A rounded value of 100 works for the example. A house with 3.35 m2 of windows will have energy transference of +1055 W. The effect of radiation occurs in the day when there is sun radiation. In the evening there is no radiation effect (The Radiator Shop, 2016).
Energy transference by the walls: The effect of the roof is by conduction by the walls thickness. The average factor of the wall is 7. For the previous example, the area of the wall is 20x12 + 12x15 = 420 ft2= 39 m2. The total energy transference is -861 W. The example considers that the walls are un-insolated. For an insulated wall, the total energy transference will be near zero.
Energy transference by the roof: The effect of the roof is by conduction by the roof thickness. The average factor of the roof is 34. For the previous example, the area of the roof is 27.87 m2. The total energy transference is -2989 W.
Energy transference by the floor: The effect of the roof is by conduction by the roof thickness. The average factor of the roof is 4. For the previous example, the area of the roof is 27.87 m2. The total energy transference is -352 W.
Energy transference by the room air for the people or occupants: The energy by the occupants is generated inside the control volume that means the energy has a positive value. For an example of six people and a specific energy of 58 W/person, the total energy is +348 W.
Energy transference inside the house:
W = +1055 W + (-861 W) + (-2989 W) + (-352 W) + (348 W)
Positive values reduce the required power by the boiler. Due to the fact, the design requires the worst case scenario, the positive values will not be considered in the calculation.
W = (-861 W) + (-2989 W) + (-352 W) = -4202 W
Analysis of the results
The calculation of energy transference has different interpretations according to the design goals. It is not useful for the design to consider the natural energy providers that increase the temperature of the room, for example, sun radiation or people's heat. The previous is because that reduces the energy requirement from the boiler. Using that criterion, it is not useful in the evening when the number of people is lower, and the boiler has not the capacity for that situation. It is preferable to consider all the output energy transferences that increase the energy output of the boiler. For that reason, the sun radiation through the windows and people's heat are not considered in the calculation for the boiler selection.
With the highest value calculated in the energy output, then the homeowner selects the best boiler adapted to its necessities and considered the investment for insulation.
Design of boiler
The boiler and heating components meet the standard array showed in Figure 2. The boiler receives cold water from the municipal provider, transforms chemical or electric energy to an increase in the water temperature. The hot water flows through radiators in different places of the house increasing the temperature of the house.
Figure 2: Regular arrangement of heating system (Worcester Bosch, 2017)
Boiler and radiators installation considerations:
■ space the homeowner is going to heat (Reilly, 2014).
■ The measurement of the space where the radiator will be placed (what measures has the physical space where it is going to be located, if there are any window and the height to which it is so that the radiator can be placed underneath without being an obstacle).
■ In the case that the homeowner will renew the radiators, it is advisable that the installation is developed by a professional since small works will have to be done to adapt the old sockets to the new radiators.
Correct use of radiators and heating system to contribute to efficient energy use:
■ Drain radiators at least once a year, as over time the heat decomposes in the air, and that decreases the performance of the radiators. It is best to purge them at the beginning of winter. In this way, the homeowner will ensure a better performance of heating thus reducing energy consumption.
■ Place radiators under the windows. The location is the ideal place to favor the diffusion of hot air and a more efficient operation. Do not cover the radiators and close them when they are not in use.
■ Do not cover the radiators by placing anything on them or placing extremely close furniture, sofas, curtains, etc. Covering the radiators implies limiting the heat emitting capacity and can cause domestic accidents.
■ Close the radiators that are not necessary. Remove the heating completely if the house is going to be unoccupied for weeks or months.
■ Install programmers with thermostats.
■ Take care of security. Radiators are a source of heat that, at all costs, must be kept from touching children. Therefore, there are covers, protectors for these areas that not only prevent burn but also hit the radiator in case of a fall. The homeowner also has to cover the radiator tubes, which also heat up when in operation.
■ To help ensure that the heat generated by the radiator does not escape through the wall; it is recommended to place a reflective element behind. In this way, the heat is reflected towards the room avoiding losses to the outside and obtaining up to 10% of energy saving.
Recommendations to save on heating
1. In winter put the heating to 19-21ºC, and lower it at night to 15-17ºC. Energy consumption increases by 7% for each grade the homeowner raise.
2. Use thermostats and chrono-thermostats and saves up to 25% energy by programming the temperature according to the homeowner schedule. They are economic devices that the homeowner can install himself.
3. The homeowner must insulate the walls, roof, and floor. The home economy and the environment will benefit. A building with optimum insulation can reduce energy consumption by up to 90%.
4. The homeowner must consider the energy label; it will take him to know the energy efficiency of the heating systems. The green color and the symbol A + distinguish the most efficient equipment: the ones that consume less energy.
5. First, ventilate, and then turn on the heating. 10 minutes are enough to ventilate a room fully.
6. Close the blinds and curtains at night, the homeowner will avoid significant heat losses and save energy.
7. Place weather-strips and under doors on the edges of doors and windows. They help to insulate the house better and save up to 30% energy. It is a very economical and easy solution.
Walls insulation
For the determination of the insulation which should be placed adjacent to the wall, it is necessary to calculate the area on which the insulation material will be placed.
3 * (20 * 15) * - (6 * 4) * 3= 828 ft2 = 76.92 m2
The heat transfer coefficient of the building materials are given as:
Assuming the wall is made of bricks, the heat transfer coefficient is of 0.523W/(m*K), and the roof of concrete with K= 0.11. With the previous information it is possible to calculate the heat transfer through the wall by using the formula:
Q= - KA/L*(To-Ti)
Q = wall 1 + wall 2 + wall 3 + wall 4 + roof
Q = 65.511 + 65.511 + 65.511 + 72.3+ 22.42
Q = 291 watt
The value of 291 watts represents the energy flow that is avoided thanks to the use of insulation in the house. Figure 3 shows a typical standard procedure of the application of insulation material between the face brick and the masonry block.
Figure 3: Procedure of insulation installation
Using the previous value of energy transference (-4202W) and the use of insulation, the ultimate value of energy transference for the house is:
W' = -4202 W + 291 W
W' = - 3911 W
The new energy value may benefit to the homeowner with less energy consumption in the house, lower bills or the selection of a smaller (and cheaper) boiler.
Discussion and analysis
The energy calculation allows the homeowner to know how much energy is required by the boiler to heat a room or house. The use of boiler accessories as valves allows the control of water flow by the system. With a closed valve, the flow of hot water is near zero and the heat transference to the room by the boiler is zero, but when the valve is 100% open the hot water flows through the radiators increasing the temperature in the room or house.
The calculation of the energy transference from the conditioned environment (room or house) to the exterior atmosphere is -4202 W without insulation. This is the most critical scenario, necessary for the boiler selection and acquisition by the homeowner. After improvements to the house by the installation of insulations, the value of heat transference is reduced to 3911W giving to the homeowner enough space to configure the boiler.
The installation of the insulation is executed between the masonry block and the face brick for two reasons: protect the isolation from sun and weather conditions and to facilitate the energy insulation in the air chamber between the two layers of walls, roof and floor. The application of the insulation is using a hose that sprays polyurethane foam thought a hole between the masonry and the brick wall.
Conclusion
The report brings the reader the best strategies and recommendations for the use of boilers in domestic dwellings. The theory framework gave the basic information to support the selection of the technology of the heating system, which are the boiler and radiator. The use of water is convenient due to its availability and the heat capacity. Each part of the heating system is studied and analyzed.
The selection of the power boiler is the consequence of the energy transference calculation of a typical house. It was necessary to take considerations according to the energy generation inside and outside the house.
In the end, there were installation and efficiency recommendations to improve the operation of the boiler and the energy consumption.
Reference List
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