In winter, the corresponding heat is continuously supplied to the room to maintain the necessary temperature of the room to improve the indoor working and living conditions.
Composition of the heating system:
Heat source – a heat medium preparation facility that enables the fuel to generate heat energy and heat the heat medium, such as a boiler.
Heating pipes - heat medium delivery systems, which refer to the pipes between the heat source and the heat dissipation equipment. The heat medium transports the heat energy from the heat source to the heat dissipation equipment through a piping system.
Heat dissipation equipment - indoor heat medium utilization facilities, equipment that dissipates heat into the room, such as radiators, heaters, radiant panels, etc.
Pipeline Accessories - Heat Medium Conditioning, System Maintenance Facilities.
Classification of heating systems:
Classification of heating systems:
1. According to the classification of heating medium (heat medium: the medium substance that transfers heat):
(1) Hot water heating system: The heating system with hot water as the heat medium is mainly used in civil buildings.
(1) Low-temperature hot water heating system: the water supply and return temperature is 95 °C/70 °C or 85 °C/60 °C, which is generally used in civil buildings.
(2) High-temperature hot water heating system: the water supply temperature is higher than 100 °C. Generally, it should be applied in production plants. The design supply and return temperature is mostly 120~130°C/70~80°C.
(2) Steam heating system: The heating system with water vapor as the heat medium is mainly used in industrial buildings.
(1) Low-pressure steam heating system: the relative pressure of steam is less than 70kPa
(2) High-pressure steam heating system: the relative pressure of steam is 70~300kPa
(3) Hot air heating system: The heating system uses hot air as the heat medium to heat the air to 30~50 °C and send it directly into the room. It is mainly used in large industrial workshops. For example, heaters, hot air curtains, etc. are typical equipment for hot air heating.
Hot air heating uses air as the heat medium, its density is small, the specific heat capacity and thermal conductivity are very small, so the heating and cooling are relatively fast. However, the specific volume is large, and the required pipeline section area is relatively large.
(4) Flue gas heating system: The high-temperature flue gas generated by fuel combustion is used as the heat medium to bring heat to the heat dissipation equipment. For example, the forms of stoves, fire walls, fire pits, and fire fields are widely used in the vast villages and towns in the north of the mainland.
Although flue gas heating is simple and practical, because most of them belong to the local combustion fuel in simple combustion equipment, the fuel can not be used reasonably, the combustion is insufficient, the heat loss is large, the thermal efficiency is low, the fuel consumption is more, and the temperature is high, the sanitary conditions are not good enough, and the danger of fire is large.
2. According to the different heating areas:
(1) Local heating system
Heat sources, pipes, and heat dissipation equipment are combined into a single unit and dispersed in various rooms, which is called local heating. For example, stoves, fire walls, ondols, electric infrared heating, electric heating, gas or natural gas heating (wall-hung boilers) are all local heating.
Features: simple, poor sanitary conditions, high energy consumption.
(2) Central heating system
The heating system in which the heat source and the heat dissipation equipment are set separately, and the heat source supplies heat to each room or each building through the heat medium pipe, which is called a centralized heating system.
Features: large heat supply, fuel saving, low pollution.
The central heating system with hot water and steam as the heat medium can better meet the requirements of people's life, work and production for indoor temperature, and has good sanitary conditions, reduces environmental pollution, and is widely used in building heating projects.
(3) District heating system
A heating system that uses a regional boiler house as a heat source to heat many buildings in an area.
Hot Water Heating System:
1. Classification of hot water heating system
1. According to the different hot water heating cycle power, it is divided into natural circulation system and mechanical circulation system.
Circulatory power: The natural circulation system relies on the density difference of water for circulation; The mechanical circulation system relies on the pressure of the water pump for circulation.
Single-pipe system: Hot water flows sequentially through risers or horizontal supply pipes and cools in each radiator sequentially.
Double-pipe system: Hot water is distributed to multiple sets of radiators in parallel through the water supply riser or horizontal water supply pipe, and the cooled return water flows from each radiator directly along the return riser or horizontal return pipe back to the heat source.
3. According to the different ways of laying the pipeline of the system, it can be divided into vertical and horizontal systems.
4. According to the different temperature of the heat medium, it can be divided into low-temperature water heating system and high-temperature water heating system.
Vertical :
Single-tube upper and lower return type: (1) downstream type; (2) Leapfrogging.
Horizontal: Horizontal tandem type.
Horizontal Leap:
2. Natural circulation of hot water heating system
1. Working principle: Before the system is running, the whole system should be filled with cold water. When the system is working, the water is heated in the boiler, the density becomes smaller, the hot water rises along the water supply pipeline and flows into the radiator, the hot water releases heat in the radiator, the temperature decreases, the density becomes larger, and then flows back to the boiler along the return pipe.
2. Features of natural circulating hot water heating system:
Advantages: simple device, easy operation, labor-saving maintenance and management, no power consumption, no noise, etc.
Disadvantages: Due to the limited pressure of the system, the flow rate of the pipeline is small, resulting in a large pipe diameter, resulting in a high initial investment. Due to the small circulating pressure, the radius of the natural circulation system should not exceed 50m, and it can only be used in a single building.
3. Mechanical circulation of hot water heating system
1. Working principle: using the forced circulation of the water pump, the popular resistance of the water flow in the whole annular pipeline is overcome by the power provided by the water pump, and the head size of the water pump is determined by the flow resistance.
2. Features: The circulating water pump is set up, which increases the regular operation electricity cost and maintenance workload of the system, but the pressure generated by the water pump is very large, so the heating range can be expanded, not only for single building heating, but also for multiple buildings, district heating, and widely used.
3. The difference between the two systems:
(1) The cycle power is different; (2) The connection points of the expansion tank are different.
4. Commonly used pipe network forms
1) Double-tube upper and lower return type
(1) Structural form
The water supply main pipe is located at the top of the system, the return water main pipe is located in the lower part of the system, generally located in the trench, the water supply pipe and the return pipe of the radiator are set up separately, each group of radiators can form a circulating loop, the water supply temperature of each group of radiators is basically the same, and each group of radiators can adjust the flow of heat medium by themselves, and they are not affected by each other.
The main water supply pipe should be set up with an upward slope according to the direction of the water flow, so that the bubbles flow with the direction of the water flow to the highest point of the system, and the air will be discharged out of the system by setting an exhaust device at the highest point.
The slope direction of the backwater main pipe is the same as that of the natural circulation system, and the slope should be 0.003.
(2) Features:
The circulation of hot water mainly depends on the action pressure of the water pump, and there is also a natural action pressure, the upper layer action pressure is large, the flow rate through the radiator is more, the lower action pressure is small, and the flow through the radiator is less, thus causing the "vertical imbalance" phenomenon of upper heat and lower cold, the more floors, the more serious the imbalance phenomenon.
(3) Occasions of use: In buildings with less than 4 floors.
2) Double pipe lower for lower return type
(1) Structural characteristics:
(1) The main pipe of water supply and the main pipe of return water are laid in the trench or basement, and the pipe insulation effect is good and the heat loss is less.
(2) The main pipes for water supply and return are laid under the bottom radiator, and it is difficult to remove air in the system. There are two main methods of exhausting; One is to manually disperse the exhaust through the exhaust valve of the top radiator; The other is through a special air pipe, manual or centralized automatic exhaust.
2) Mechanical circulation single tube upper supply and lower return type
(1) Structural form
The water supply and return risers of the radiators of the single-pipe system share a single pipe, and the radiators on the risers are connected in series to form a circulating loop. The inlet water temperature of the radiators on each floor from top to bottom is different, and the temperature decreases in turn, and the heat medium flow rate of each group of radiators cannot be adjusted individually.
According to the different structural forms, it can be divided into a single pipe for the upper and lower flow of the downstream type, and a single pipe for the upper and lower back of the leapfrog type.
(2) Features
For single-tube systems, because the radiators of each layer are connected in series on a circulating pipeline, the pressure generated by the gradual cooling process from top to bottom can be superimposed to form a total pressure, so there is no vertical misalignment problem of double-pipe system in single-tube systems. Even if the lowest radiator is lower than the center of the boiler, the water can be circulated. Due to the low temperature of the heat medium at the inlet of the lower radiator, the area of the lower radiator is more than that of the upper layer.
(3) Applicable occasions
In multi-storey and high-rise buildings, a single-pipe system is preferable.
4) Middle-fed system
(1) Structural form
The horizontal water supply main pipe is laid in the middle of the system, and the upper system can be used for the lower supply and lower return type, and the lower system can be used for the upper supply and lower return type.
(2) Features
It alleviates the phenomenon that there are too many upper and lower circulation floors and is prone to vertical misalignment, and at the same time, it can avoid the low height of the bottom of the top beam and cause the water supply main pipe to block the top window and hinder its opening.
(3) Applicable occasions
It can be used for the addition of floors to the original building or when the upper floor area is smaller than the lower floor area.
5) Bottom supply and upper return type (reverse flow type)
(1) Structural form
The water supply main pipe is located above all radiator equipment, the return water main pipe is located under all radiators, and the expansion tank is connected to the return water main. The return water flows back to the boiler room through the expansion tank, and is then pumped into the boiler by the circulating water pump.
(2) Features:
(1) The flow direction of water in the system is from bottom to top, which is consistent with the direction of air flow, and the air can be discharged through the expansion tank, and there is no need to set up exhaust devices such as centralized exhaust tanks.
(2) For the ground floor room with large heat loss, due to the high water supply temperature of the bottom floor, the area of the bottom radiator is reduced, which is convenient for arrangement.
(3) The main pipe of water supply is in the lower part, and the main pipe of return water is in the upper part, so the ineffective heat loss is small.
6) Horizontal tandem type
(1) Structural form
One riser connects multiple sets of radiators horizontally in series. When there are many radiators in series, the horizontal misalignment phenomenon of overheating at the front end and overcooling at the end is prone to occur during operation. 8-12 groups of radiators per loop are appropriate.
According to the connection between the water supply pipe and the radiator, it can be divided into downstream type and leapfrog type.
(2) Features
Advantages: simple system, simple installation, less wear floor slabs, convenient construction; The total cost of the system is lower than that of the vertical type; Buildings with different use functions and different temperature requirements for each floor are convenient for layered adjustment and management.
7) Heterogeneous system and co-programming system
In the layout of the main pipes of the heating system for water supply and return, the arrangement form of unequal total length of the circulating loop through each riser is called a heterogeneous system. The arrangement of the total length of the circulating loop through the individual risers is equal to that of the same programmatic system.
Different formula: the total length of the circulating loop through each riser is not equal, the flow distributed by the near riser is more, the room is overheated, and the flow distributed by the far riser is less, and the room is too cold.
Same formula: The total length of the circulating loop through each riser is equal, the pressure loss of the loop is easy to balance, and the pipe material is consumed.
9) Household metering hot water heating system
It is an important technical measure for building energy saving, improving indoor heating quality and intelligent management of heating system.
For the new residential hot water central heating system, the household heat metering and room temperature control devices should be set up, and the heat metering and charging should be implemented.
Household heat metering: Separately measure the heating heat supplied to the household in the unit of household (set).
(1) Single-tube system with spanning tubes
It can be used in new residential buildings, the main pipe is buried in the ground floor, the system is simple, but the radiator temperature control valve needs to be added.
(2) Double-tube upper supply upper return type
Features: The amount of pipes is large, which affects the appearance, but it can control a certain group of radiators separately, which is conducive to energy saving.
(3) Double-pipe lower for lower return type
It is suitable for new residential buildings, and the main pipe for water supply and return is buried in the ground floor, and the maintenance of water leakage is complicated.
(4) Double-tube upper and lower return type
(5) Horizontal double-tube radial type
For new residential buildings, the water supply and return pipes are buried in the ground floor, and the buried pipes have no joints. However, the amount of pipes is large, and water separators and water collectors need to be set.
Fourth, high-rise building hot water heating system
5. Radiant floor heating system
Radiant heating is a heating method that uses the heat emitted by radiant radiator equipment on the roof, ground, wall or other surfaces in the building to meet the heating requirements of the room or local working point.
It is a combination system of radiative heat transfer and convective heat transfer of air that uses low-temperature hot water or high-temperature water to heat the surrounding walls and ground temperatures.
1. The principle of floor hot water heating
Low-temperature hot water floor radiant heating is low-temperature radiant heating with hot water not higher than 60°C as the heat medium, and the heating pipe is buried in the floor.
2. Analysis of the characteristics of radiant floor heating
Compared with ordinary radiator heating, underfloor heating has the following advantages:
(1) Improve the comfort of indoor heating
(2) Effectively save energy
(3) The effective usable area of the room has been expanded
(4) Improve the sanitary conditions of heating
(5) Reduced floor noise
(6) Wide selection of heat sources: the water supply ≤ 60 °C, and the temperature difference of the return water ≤ 10 °C. Such as industrial waste heat boiler water, various air conditioning return water, geothermal water, etc.
Disadvantages of underfloor heating:
(1) Floor heating is a buried concealed project, which has potential safety hazards.
(2) The height of the space to be occupied is at least 60-80cm, and the height difference is formed with other indoor spaces without radiant heating, and the ground load needs to be increased by about 120kg/m2.
(3) The requirements for the temperature and flow of the heat medium are different from those of the original radiator heating system, and a separate heat source system needs to be set up.
(4) Due to the small temperature difference of the heat medium and the large corresponding flow rate, the cross-section of the heat medium transmission pipeline and the energy consumption of the transmission are about twice as large as that of the radiator heating system.
(5) The material and construction market is worrisome, and the construction, commissioning and acceptance procedures are difficult; The technical principles and basic data of the design are still in the process of understanding and lagging behind the application.
3. The composition and form of the system
(1) Floor construction
The floor structure of low-temperature hot water radiant floor heating is shown in the figure below:
(2) The structure and installation of the water divider (collector).
(1) The structure of the water collector
It is made of ≮25mm steel pipe, the diameter of the pipe is 2 specifications larger than the thickest branch loop, the length is determined by the number of branch loops, the spacing between the center of the branches is 100mm, and the end is also 100mm.
(2) Installation of water distribution (collector).
Location: Placed in the middle of the house as much as possible to avoid hydraulic imbalance, and the residential building is permanently located in the kitchen. Valves and filters should be set in front of the water separator, and valves should be set up after the water collector. A release valve should be set on the water collector and water divider.
Laying: Surfaced or concealed installation in the interior wall wall groove or tube well.
4. The material and arrangement of the heating tube
(1) Material: cross-linked polyethylene pipe (PE-X)
Anti-aging, high temperature resistance (-70~110°C), high pressure resistance (burst pressure 6Mpa), easy bending, corrosion resistance, no scaling, good hydraulic conditions.
(2) Layout: see figure
Purpose: The hot water pipes with high transmission temperature should be arranged under the window and the outer wall as far as possible, which is conducive to the uniformity of indoor temperature.
5. Installation of low-temperature hot water ground radiant heating system
The construction process of low-temperature hot water ground radiant heating system is as follows: ground cleaning - installation of insulation layer - installation of water separator and water collector - installation of heating pipe - hydraulic test - filling layer - surface layer.
1) Ground cleaning: remove the accumulated soil and all kinds of debris on the ground, keep the ground clean, and prevent damage to the insulation board.
2) Insulation layer installation: The insulation layer is generally made of polystyrene foam board. The insulation layer is made on the leveling layer, the insulation board should be smooth, the plate joints should be tight, and there should be no hollowing and protrusions in the lower part. Leave expansion joints between them and the surrounding walls.
3) Install the water separator and water collector The installation of the water separator and water collector should be installed before starting to lay the heating pipe. It is advisable to install the water separator on the top and the water collector on the bottom, the center distance should be 200mm, and the center of the water collector should not be less than 300mm from the ground.
4) Install the heating pipe: pay attention to the distance between the pipes and the pipes, the spacing of the pipe clamps, add the casing pipe out of the ground, and the casing is 150-200mm higher than the decorative surface to protect the heating pipe.
Laying steel wire mesh, steel wire mesh is also laid on the reflective film, and also on the coil, and the above must be laid when reinforced.
Connect the pipeline and the water divider, the exposed part of the coil is sleeved with a pipe sleeve to avoid sunlight, and the white wire is the connecting wire between the electric heating actuator and the room thermostat (automatic temperature control is available, manual is not).
A steel wire mesh is placed on aluminum foil to secure the electric heating pipe above and increase the adhesion of the surface concrete.
Lay the electric heating pipe on the steel wire mesh and tie it firmly with a plastic cable tie.
5) Hydrostatic test: Before the floor heating system is pressed, the pipes must be flushed in advance. The hydrostatic test is carried out twice, and the test pressure of the floor heating system is 1.5 times of the working pressure, and should not be less than 0.6MPa. The pressure drop of lh should not be greater than 0.05 MPa when the pressure is stabilized at the test pressure. The hydrostatic test should be slowly boosted by a hand pump.
6) Filling layer and surface layer practice:
The construction of concrete filling layer should meet the following conditions:
(1) All expansion joints have been laid according to the design requirements;
(2) The heating pipe is installed and the water pressure test is qualified, and the heating pipe is under pressure;
The construction of the concrete filling layer shall be undertaken by the civil construction party; The installation unit should cooperate closely to ensure that the water pressure in the heating pipe is not less than 0.6MPa, and the system should be kept at least 0.4MPa during the maintenance process. 5% anti-cracking additives must be added to the filled bean stone concrete, and the curing cycle of the concrete filling layer should not be less than 21 days.
Construction of the surface layer:
The following materials should be used for low-temperature hot water ground radiant heating:
(1) Cement mortar, concrete floor;
(2) Stone floors such as tiles, marble, granite, etc.;
(3) Laminate flooring, parquet flooring and heat-resistant solid wood flooring in line with national standards.
Wall-hung boiler + fan coil unit: