why is water used in central heating systems
In central heating systems, heat is supplied by a single unit and ducted to outlets in the floor or ceiling of rooms/spaces inside the house. Most central heating systems use hot air, though heated water passing through radiators or underfloor pipes can also be used. For homes, separate room heaters are more common than central heating. Most central heating systems use gas or electricity, but some use energy-efficient sources such as, waste heat recovery, or the absorption of passive heat (for example, solar radiation). Though both air and water have reasonable heat storage capacity, there are always some energy losses between the heating unit and the room. These heat losses can be reduced by minimising the length of duct/pipe run, minimising cross-section area, maximising flow rate, improving insulation, and running the ducts/pipes through spaces with warmer temperatures. A central heating system has a slower response to changes in room heating requirements. The delay will increase with longer duct/pipe runs and will be greater in systems using water to transfer heat from the plant to the rooms. Central heating involves a significant upfront capital cost compared with room heating options. An efficiency of 7090% (depending on the system specified) can be achieved. Central heating suits families with small children, elderly people and people with a disability or long-term illness. The lower-temperature heat sources in each room are safer than high-temperature appliances, with a reduced risk of burns. energy-efficient heat sources can be used to power the central unit (for example, solar panels or
the combustion of gas, oil or solid fuel is isolated from the heated space. limited control over heat output within each individual space without suitable feedback from each space (for example, separate thermostats) the need for suitable routes for pipes and ducts.
All central heating systems have three components: a heat (or energy) source (for example mains gas), a distribution medium (for example the water that flows through the radiators), and a heat emitter (for example, the radiator). Heat sources include: gas (most common in UK), oil, LPG, electricity (from the grid or renewable sources), biomass, coal, combined heat and power, solar thermal and heat pumps. The most common distribution medium for heating in the UK is water (called a БwetБ system), which can be high or low temperature. Heat can also be distributed using air, steam, or electricity. The most common heat emitter in the UK is a radiator, but several others are discussed below. Low or high temperature central heating? Traditionally, radiators fed by central heating systems operate at higher temperatures (from 60 to 80 degrees C). A lower temperature flow (as low as 35 degrees) is becoming more common, and is desirable because it is more efficient. Low temperature heating is common in underfloor heating, which can operate at around 35 degrees C, but is also possible and increasingly common with a radiator system.
Your buildingБs heat loss value: If your building suffers from significant heat loss that cannot be corrected, it may not be practical to switch to lower temperature heating. How much space you have: low temperature system will require more surface area of radiator (or other heat emitter) to work as effectively. You may need to install new radiators. With a heat pump, the efficiency increases as the temperature decreases. So a lower temperature system is preferred. These are commonly installed with underfloor heating,. Generally speaking, for a lower temperature heating system, it is more efficient to leave the heating on continuously, and for a higher temperature system it is more efficient to turn it on around key demand periods. Heat loss from a building is proportional to the inside/outside temperature difference, but the more airtight and well-insulated your building is, the less this becomes important. This explains why in well-insulated buildings using low-temperature heating (for example many houses in Scandinavia) it becomes efficient to leave heating on 24 hours a day. Underfloor heating Underfloor heating works like having a big radiator under the floor: hot water is passed through coils under the floor, which rises to heat the room. Because underfloor heating usually operates between 35-45 degrees C, they are ideal for condensing boilers which require a lower return water temperature to condense.
Underfloor heating is also suitable for heat pumps, which provide lower temperature water. Because underfloor heating is a form of, it is most suitable to spaces that are well insulated and with less air exchange. It is most effective left on for extended periods rather than heating at key times, so is ideal in environments with continual occupancy. Types of heat All heat emitters give off heat in some combination of convection (movement of heat through the air) and radiant heat (heats objects directly - like the sun). Where there is a lot of air exchange, poor insulation or high ceilings, the use of higher radiant heat becomes more efficient, because the heat is not lost in draughty air. Fan convectors and natural convectors have a very high convection to radiant ratio, of around 80%, and they are most suitable for use in homes with low air exchange rates, low ceilings, and good insulation, or heating small closed spaces. Radiators have a convective/radiant ratio of 50-70%. Passive solar heating takes advantage of the sunБs warmth and stores and releases heat back into the home in the evening. This happens to some extent in every home, as sunlight passes through windows and is absorbed by walls. But there are steps you can take in design which will increase the passive solar gain. Image:
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