Elevator units have been used in heating centers of apartment buildings since the middle of the last century, and individual instances continue to work successfully until now. Residents are not in a hurry to change outdated elements to new fittings equipped with modern automation, and this reluctance is completely justified. To clarify the essence of the issue, we suggest that you understand what an elevator, its device and basic functions in a heating system are.
Purpose and functions of the node
Water in the district heating networks reaches a temperature of 150 ° C and moves along the external pipelines at a pressure of 6-10 bar. Why are such high heat carrier parameters supported:
- In order for high-temperature boilers or other heat-power equipment to function with maximum efficiency.
- For the delivery of heated water to areas remote from the boiler room or CHP, network pumps must create a decent pressure. Then, at the thermal inputs of nearby buildings, the pressure reaches 10 Bar (pressure testing - 12 Bar).
- Transportation of superheated coolant is economically viable. A ton of water, brought to 150 degrees, contains significantly more thermal energy than a similar volume at 90 ° C.
Reference. The coolant in the pipes does not turn into steam, because it is under pressure, which keeps water in a liquid state of aggregation.
According to the current regulatory documents, the temperature of the coolant supplied to the water heating system of a residential or administrative building should not exceed 95 ° C. And the pressure of 8-10 atmospheres is too great for a house heating system. So, the indicated water parameters need to be adjusted in a smaller direction.
An elevator is a non-volatile device that reduces the pressure and temperature of the incoming coolant by mixing chilled water from the heating system. The element shown above in the photo is part of the circuit of the thermal unit, it is installed between the supply and return pipes.
The third function of the elevator is to provide water circulation in the house circuit (usually a one-pipe system). That is why this element is of interest - with external simplicity it combines 3 devices - a pressure regulator, a mixing unit and a water-jet circulation pump.
Elevator Operation Principle
Externally, the design resembles a large tee of metal pipes with connecting flanges at the ends. How is the elevator inside:
- the left nozzle (see drawing) is a tapering nozzle of the design diameter;
- behind the nozzle is a mixing chamber of a cylindrical shape;
- the lower pipe serves to connect the return line to the mixing chamber;
- the right pipe is an expanding diffuser that directs the coolant into the heating network of a multi-storey building.
Note. In the classic version, the elevator does not require a connection to the home electrical system. An updated version of the product with an adjustable nozzle and electric drive is connected to an external power source.
The steel elevator unit is connected by the left pipe to the supply line of the centralized heat network, and the lower one to the return pipe. On both sides of the element shut-off valves are installed, plus a strainer - a sump (otherwise - a sump) at the feed. The traditional scheme of a heating station with an elevator also includes pressure gauges, thermometers (on both lines) and a meter for energy consumption.
Now let's see how the elevator jumper works:
- Superheated water from the heat supply network passes through the left pipe to the nozzle.
- At the moment of passage through a narrow section of the nozzle under high pressure, the flow is accelerated according to the Bernoulli law. The effect of a water-jet pump begins to act, providing circulation of the coolant in the system.
- In the zone of the mixing chamber, the water pressure is reduced to normal.
- A jet moving at high speed into the diffuser creates a vacuum in the mixing chamber. There is an ejection effect - a fluid flow with a higher pressure carries through the jumper the coolant returning from the heating network.
- In the chamber of the heating elevator, chilled water is mixed with superheated, at the outlet of the diffuser we obtain the coolant of the desired temperature (up to 95 ° C).
The main condition for the normal operation of the elevator is a sufficient pressure difference between the main supply and the return line. The indicated difference should be enough to overcome the hydraulic resistance of the house heating and the injector itself. Please note: the vertical jumper cuts into the return line at an angle of 45 ° for better separation of flows.
Specifications for Standard Products
The line of factory-made elevators consists of 7 sizes, each assigned a number. When selecting, 2 main parameters are taken into account - the diameter of the neck (mixing chamber) and the working nozzle. The latter is a removable cone, which changes if necessary.
The nozzle is replaced in two cases:
- When the cross section of a part increases as a result of normal wear and tear. The reason for the development is the friction of the abrasive particles contained in the coolant.
- If it is necessary to change the mixing coefficient, increase or decrease the temperature of the water supplied to the home heating system.
The numbers of standard elevators and the main dimensions are shown in the table (compare with the symbols on the drawing).
Please note: the nozzle flow area is not indicated in the technical specifications, since this diameter is calculated separately. To select the number of the finished elevator tee for a specific heating system, it is also necessary to calculate the required size of the mixing and injection chamber.
Calculation and selection of the elevator by number
We’ll immediately clarify the procedure: first, the diameter of the mixing chamber is calculated and the appropriate elevator number is selected, then the size of the working nozzle is determined. The diameter of the injection chamber (in centimeters) is calculated by the formula:
The indicator Gpr participating in the formula is the real heat carrier consumption in the apartment building system, taking into account its hydraulic resistance. The value is calculated as follows:
- Q - the amount of heat spent on heating the building, kcal / h;
- Tcm - temperature of the mixture at the outlet of the elevator tee;
- T2o - water temperature in the return line;
- h is the resistance of the entire heating distribution with radiators, expressed in meters of water.
Reference. To insert incomprehensible kilocalories into the formula, you need to multiply familiar watts by a factor of 0.86. Meters of water are converted into more common units: 10.2 m of water. Art. = 1 bar.
An example of elevator number selection. We found out that the real consumption of Gpr will be 10 tons of mixed water in 1 hour. Then the diameter of the mixing chamber is 0.874 √10 = 2.76 cm. It is logical to take mixer No. 4 with a 30 mm chamber.
Now we find out the diameter of the narrow part of the nozzle (in millimeters) according to the following formula:
- Dr is the previously determined size of the injection chamber, cm;
- u is the mixing coefficient;
- Gpr - our flow rate of the finished heat transfer medium to the system.
Although outwardly the formula seems cumbersome, in reality the calculations are not too complicated. One parameter remains unknown - the injection coefficient, calculated as follows:
We have decoded all the notations from this formula, except for parameter T1 - the temperature of hot water at the entrance to the elevator. If we assume that its value is 150 degrees, and the supply and return temperatures are 90 and 70 ° C, respectively, the desired size Dc will be 8.5 mm (at a flow rate of 10 t / h of water).
When the magnitude of the pressure Нр at the entrance to the elevator from the central side is known, an alternative formula for determining the diameter can be used:
Comment. The result of the calculation according to the last formula is expressed in centimeters.
In conclusion, the disadvantages of elevator mixers
We found out the positive aspects of using elevators in home heating stations earlier - non-volatility, simplicity, reliability and durability. Now about the disadvantages:
- For the normal functioning of the system, it is necessary to ensure a significant pressure difference between the return and supply.
- An individual selection of a node to a specific heating network is required, based on the calculation.
- To change the parameters of the outgoing heat carrier, it is necessary to recalculate the diameter of the nozzle opening under new conditions and replace the nozzle.
- Infinitely variable temperature control is not provided.
- The unit cannot be used as a circulation pump for a local circuit (for example, in a private house).
Clarification. There are advanced elevator models with adjustable bore. Inside the pre-chamber, a cone is mounted, moved by a gear transmission, the drive is manual or electric. True, the main advantage of the unit is lost - independence from electricity.
Single-tube home systems operating in conjunction with elevators are quite difficult to put into operation. First you need to squeeze the air out of the return riser, then from the supply, gradually opening the main valve. The master plumber in the video will tell you more about injection units and the method of starting: