Overview heating systems: definitions, types, operation
A thermal heating consists essentially of four elements:
• Fuel Tank
• One or more heat generators
• Safety devices, control and measurement
• Circuits of use, sorting, and channeling heat radiation
A heating system can be divided according to the type of the heated fluid in several categories:
• hot air system
• hot water system
• Plant diathermic oil
• Steam Plant
The thermal plants are also characterized by system expansion into two broad categories:
• System with closed expansion tank
• System with open expansion tank.
The source of energy or fuel used divides the heat generators used in different types:
• Heat generators powered by electricity
• heat generators fed with liquid
• heat generators fed with gaseous fuels
• Heat generators using solid fuels
• Heat generators fired with pulverized
The system used for the disposal and the evacuation of fumes further subdivides the heat generators in two categories:
• Generators natural draft
• Generators forced draft
Hot water systems
Are installations in which the heating fluid is water heated to temperature of around 70-90 ° C, but never reach the boiling temperature.
In such installations are the burner, the boiler, the system in the expansion vessel, the circulation system and pumps, heating elements.
The system expansion tank serves to absorb the volume increases when the water temperature increases. In fact the increase in temperature causes an increase in water pressure and consequently a volume increase of about 4% with the passage of the water temperature from 15 ° C to 90 ° C. If it were not for the expansion tank that allows water to expand the system with the boiler would explode.
The hot water systems can be divided into four broad categories:
• Plant a rain natural circulation. Here the heat generator is installed at the lowest point of the plant, such as in a cellar.
The discharge pipe of the hot water which leaves from heat generator rises up to the highest point of the installation and is fed to the heating bodies from the top.
The hot water circulation is possible because during the heating phase, the water increases in volume and becomes lighter, allowing it to rise in a natural way to reach the highest point where it descends through the heating bodies and transferring heat , cools, it compresses and becomes heavier, until you get back to the boiler to be heated up again. This way you do not need to use as circulation pumps circulation is natural.
• Plant in spring. Here the hot water delivery pipe feeds the heating bodies starting from the bottom, with or without the addition of a circulation pump
• Plant-wide. In this case, the hot water distribution system is placed on the same plane of the heat generator, which is necessary for the installation of a circulation pump
• One-pipe systems. In this case the hot water distribution system is formed by a single pipe that carries the thermal fluid simultaneously to the various heating bodies and reducing it in the boiler.
The thermal plants can be distinguished in two large categories according to their expansion system:
• Plant Open Cup
• Sealed systems
Open vessel systems
An example of an open expansion tank installed in a heating system of a building. You can see the water tap coming from the aqueduct, the water supply hose to the heating system and the vent pipe and the overflow at the top.
In the open vessel systems the expansion of the heating fluid (usually water) takes place inside open tanks suitably dimensioned, in contact with the atmosphere through a vent pipe.
The tanks are connected to the boiler through an inlet hose and a safety tube suitably dimensioned according to the power of the boiler and which depart from the boiler and reach the expansion vessel placed in the highest point of the system. These tubes must be free and can not be intercepted by any type of valve or faucet.
From the expansion vessel then exits the overflow tube, while flows into the feed pipe coming from the aqueduct through a faucet and a float valve that serve to integrate the installation with water that is lost to evaporation.
The expansion tank must be dimensioned by thermo technician according to the capacity and size of the heating system so as to absorb the increases of volume that undergoes the thermal fluid when temperature increases. If the expansion tank is badly dimensioned you may have leakage of water from the overflow tube during the heating phase and subsequent replenishment of water from the aqueduct during the cooling phase.
These replenishment of water are harmful to the heat system because they can cause corrosion and scaling in addition to being a waste of water and heat.
It is therefore necessary to be very careful when you make downsizing thermal plant as the addition of a boiler or heating elements in the rooms to get hotter. In these cases, check that the expansion vessel is adequate to the new dimensions of the system and, if inadequate, it should be replaced with a proper. These checks must do the thermo-technical parameters suggest all'impiantista new sizing of the expansion tank.
Sealed systems
Closed expansion vessels. They are of three types:
• autopressurizzati. Where the pressure in the vessel is given by the water contained in the plant that entering into the vessel compresses the air contained in it until equilibration hydrostatic.
• pressurized. Compressed air is pumped into the vessel until it reaches the hydrostatic equilibrium
• membrane. Are preloaded into the pressure to equal or exceed the system pressure. An elastic membrane separates the water from the air cushion which is located within the vessel.
In the heating closed vessel, the expansion of the water takes place inside the hermetically sealed and pressurized, usually placed in the room where the boiler is located. These containers are tested to withstand the temperatures reached by the hot water and its pressures. In the closed vessel membrane is an elastic membrane that separates the water from the air which acts as a cushion.
A system cold, the area of air is pressurized to a value such as to be higher than the pressure existing in the heating due to the hydrostatic height difference. When the water is heated, there is an increase of volume of water that is absorbed by the expansion vessel compressing the air cushion pressure, deforming the elastic membrane and increasing the value of the air pressure.
All closed vessels must be connected to the boiler, the same prescription of open ones, ie without shut-off valves. In addition, you should insert a safety valve ISPESL approved that does the same function of the safety pipe in the open vessel systems.
News on the use of closed expansion tank for solid fuel generators.
Communication I.S.P.E.S.L.
Posted on: I.S.P.E.S.L. Department approval and certification
Subject: Heating systems with generators fueled by pulverized solid fuel is not self-loading, forced circulation and expansion vessel.
Source: I.S.P.E.S.L.
Subject: Heating systems with generators fueled by pulverized solid fuel is not self-loading, forced circulation and expansion vessel.
By some peripheral departments of the Institute as well as manufacturers and installers of heating systems hot water, several requests were received concerning the updating of the safety regulations pertaining to facilities with generators fueled by pulverized solid fuel is not automatic loading and expansion tank closed.
Already the Technical Committee ISPESL "Plant Pressure" at the meeting on 09.02.2000 to present a proposal for the revision of Collecting "R" in this study had inserted a new chapter "R.9" regarding these types of facilities.
The Technical Committee consider that these types of solid fuels are
commonly used to produce steam or superheated water, felt that it is no longer current and justified the ban on using these types of fuels for heating systems with generators fueled by pulverized solid fuel is not self-loading, circulation
forced and closed expansion tank.
The need to update and modify the existing provisions is also the need to be able to use fuels such as wood processing residues referred to as wood chips or other obtained from the cleaning of woods or forests and always derived from biomass for ecological and environmental purposes.
Moreover, the system's expansion type closed vessel is indispensable in some cases because the users served by the plants are generally spread over different quotas to each other and justified by the sheer size of the plants that can take the size of a real district heating.
From the above, taking account of the need to allow expansion systems of the type closed vessel for type of installations with generators that use non-pulverized solid fuel, also considered that these types of plants not yet widespread at the time of collection "R" and. 82 state can be used with the installation of appropriate devices that provide the same level of safety as open vessel systems, taking into account that systems with closed expansion tank are already accepted by other EU countries which comply with standards have been enacted in countries like Germany, Austria, etc, also taking into account that these types of facilities are already built and used in the country and which also need to be assessed as to their operating safety, heard about the opinion of the Technical "Plant Pressure" in the sitting of 19.06.2003 and the opinion of the Working Group Ispesl "Update Collection" R "in its meeting of 26/01/04, you have on demand installer the application of the attached available "R.9" that will be part of a future new edition of the Collection "R".
It is clear that for systems with open expansion tank always non-pulverized solid fuel-loading and forced circulation R.9 the provisions of point 3 of the Annex, while for other plants solid fuel open expansion vessel remains in force the arrangement of the existing R.3.C Collection "R".
For installations with a capacity greater than 450 kW copy of the complaint system will also be sent to the Central Department approval for a joint assessment, waiting for the uniform application of the law throughout the national territory.
Collection R
Heating systems with generators fueled by pulverized solid fuel is not automatic loading and forced circulation
Chapter R.9
1 Scope
These provisions shall apply to installations with heat generators fed by non-pulverized solid fuel-loading and forced circulation.
These provisions do not apply to sets specified in point C of paragraph 2 of art. 3 of Legislative Decree no. 25/02/2000 n ° 93
2 Definitions
2.1 Device temperature limitation
This is device that limits the supply water temperature from the generator to the system
2.1.1 Device Temperature Limit switch with automatic reset
Question of automatic means which, when it reaches the maximum allowable temperature of the water, cause the interruption of the contribution of heat to the generator. This gain is automatically restored only when the water temperature has dropped below a predetermined minimum value.
2.1.2 Device for limiting the temperature safety cut-out.
This is automatic means that when it reaches the
maximum permissible temperature of the water causes the interruption of fuel supply and / or adduction of combustion air.
The fuel supply and / or the combustion air supply can be
restored only when the water temperature has dropped below a predetermined minimum value and only after manual reset or with tool.
2.1.3 Safety exhaust heat.
A device that is activated when the temperature of the generator reaches the maximum allowable value, to enable the operation of the heat exchanger built into the generator designed to dissipate the residual power.
2.2 Combustion System Quick Disconnect.
A combustion system is considered Quick Disconnect if, in every operating condition, the heat generation can be stopped so quickly that dangerous operating states will not occur, both on the water side is the side combustion.
For state of dangerous operation shall mean any increase in water temperature at the exit of the generator above 100 ° C and each formation of explosive gas-air mixtures in the combustion chamber and / or in the passages of the fumes.
2.3 Combustion system in partial shutdown.
A combustion system is considered a partial cutout if a large portion of the generation of color can be quickly interrupted by the action of adjusting devices and security without triggering operating states of dangerous side combustion.
2.4 Power residual
And 'the portion of thermal power that is transferred to the water again after the interruption of the power supply to the generator. The residual power is defined by the manufacturer of the generator
2.5 Device Power Dissipation
This is device consisting of a heat exchanger of safety and / or other
devices to dissipate the residual power, in order to ensure that not exceeded the maximum allowable temperature of 100 ° C water to the generator output.
3 Plant to open expansion vessel
3.1 The heat generators fed with solid fuel not pulverized in type plants in open expansion vessel must be equipped with:
a. open expansion tank;
b. safety tube;
c. alarm device audible and / or optical;
d. thermometer with thermometer well for monitoring
and. pressure gauge, pressure gauge with flange for control;
f. temperature limiting device with automatic reset;
g. limiting device temperature safety cut-out
In addition to the provisions in paragraph 3.1 for maximum operating pressures
the plant above 2 bar must be equipped with a device dissipation of the residual power.
4 plants in closed expansion tank
4.1 The heat generators fed with solid fuel not pulverized in installations of the type with closed expansion vessel must be equipped with:
a. expansion vessel
b. safety valve
c. thermometer with thermometer well for monitoring
d. pressure gauge with flange for pressure gauge
and. pressure switch block with manual reset
f. acoustic and / or optical
g. a temperature limiting device with automatic reset
h. a device for limiting the temperature safety cut-out
i. for combustion systems must be installed on a partial switch-off device power dissipation residual, referred to in paragraph 4.3
4.2 For systems up to a nominal power of 100 kW at partial shutdown, the device power dissipation of residual can be formed by the sun temperature relief valve. The relief valves shall be as specified by the manufacturer of the generator and be installed according to the instructions of the manufacturer.
4.3 Device dissipation of residual power.
The device of the residual power dissipation must be constituted by a discharge of thermal safety in combination with a heat exchanger integrated in the boiler. Among exchangers are allowed including water heaters accumulation or circulation, provided it is designed and configured so that heat can be transferred without additional auxiliary and external energy. Heaters fixed water circulation integrated into the generator can not be used such as water heaters operating but only as
heat exchangers safety.
In addition, the following conditions must be met:
• the discharge of thermal safety and security of the heat exchanger must be suitable for the project and the thermal characteristics of the generator and be able to dissipate in the case of combustion systems partial shutdown, the residual power;
• if the heat exchanger as security is used to build a water heater, this must be dimensioned so that it meets the above conditions to its maximum operating temperature, in the case of heat exchangers security exclusively used to dissipate the heat in the case of malfunctions, the safety relief valve must be installed upstream of the heat exchanger in the stream of cold water at the inlet.
Other solutions are not excluded provided they comply with equivalent level of
safety, the objectives of protection and safety requirements described above.
4.4 Combustion system switch-off
Any assessment of the combustion systems shutdown, both fast is partial, it will be based not only on combustion as an isolated phenomenon, but also as part of the design of the generator, the storage capacity, the fuel system, the air circuit and fumes, and of the safety device and adjustment.
5 Systems with expansion system pressurization pump
5.1 In the case in which the pressure in the generator is secured by means of pumps, the same generator must be connected to a closed vessel at constant pressure and variable level, by means of a relief valve suitable to download the expansion volume. The pressurization pumps must draw from the pot when the water volume is contracting.
5.2 In each case must be at least one level switch security to protect the generator.
Advantages and Disadvantages
Open cup, advantages:
• Increased safety because the system is not under pressure
• Cheaper and easier
Open Cup disadvantages:
• Increased consumption of water and fuel for evaporation and dispersion of heat from the expansion vessel
• corrosion and fouling of the internal piping of the system because the water coming in contact with the air, and having to be reciprocated due to evaporation, is oxygenated and loads of calcium salts that are deposited on the pipe, if it is not treated with appropriate filter.
Closed cup, advantages:
• Lower water consumption and fuel
• Longer service life of the pipes due to lower scale and corrosion
Closed cup, disadvantages:
• Less security because the system is under pressure
• Lower cost because it requires safety devices that make more complex the system and its realization
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Source:
Italian version of CercaGeometra.it