How the elevator unit works in a district heating scheme

Envision your house on a chilly winter’s day, feeling toasty and comfortable because of your district heating system. However, have you ever wondered how that heat enters your apartment? The elevator unit is useful in this situation. This fundamental part of a district heating scheme acts as the system’s heart, circulating hot water throughout the structure to keep you comfortable.

What precisely is the elevator unit then? Consider it a heat-traffic controller. In a multi-story building, it controls the hot water flow from the central heating plant to each individual apartment or unit. The entire system would come to a complete stop without this essential component, leaving the residents freezing.

However, how does the elevator unit function? Imagine that hot water from the central boiler is distributed throughout your building via a network of pipes. The elevator unit operates when the thermostat in your apartment is raised. It turns on a valve that lets hot water rise to your floor, providing warmth at your door.

You may now be asking yourself, what makes it an elevator unit? Well, this device raises the water’s temperature as it passes through the system, much like an elevator raises people to different floors of a structure. No matter how cold it is outside, it makes sure that every floor has the proper amount of heat to maintain a comfortable indoor climate.

Take a moment to recognize the elevator unit, the unsung hero of your district heating system, the next time you enjoy the cozy warmth of your home. You would literally be left out in the cold without it. This compact yet powerful technological device maintains a steady heat flow, guaranteeing that you

Purpose and function of the unit

In district heating networks, water is heated to 150 °C and is pushed through external pipelines at 6–10 bar of pressure. Why are coolant parameters kept so high?

1. To ensure that high-temperature boilers or other heat-power equipment to function with maximum efficiency.
2. To deliver heated water to areas far from the boiler house or CHPP, network pumps must create a decent pressure. Then at the heat inputs of nearby buildings the pressure reaches 10 bar (pressure test – 12 bar).
3. Transportation of superheated coolant is economically advantageous. A ton of water brought to 150 degrees contains significantly more thermal energy than a similar volume at 90 °C.

Reference: Because the heat transfer medium in the pipes is under pressure to maintain the liquid aggregate state of water, it does not evaporate.

Current regulatory documents state that coolant supplied to a residential or office building’s water heating system cannot be hotter than 95 °С. Furthermore, the in-house heating network cannot withstand pressures of eight to ten atmospheres. This indicates that a downward adjustment to the specified water parameters is necessary.

The elevator is a low-energy device that mixes cooled water from the heating system to lower the temperature and pressure of the incoming coolant. The component of the thermal unit scheme that is positioned between the supply and return pipes is the one that is seen in the above photo.

Ensuring water circulation in the house circuit—typically through a single-pipe system—is the elevator’s third purpose. This makes the element interesting because, despite its simplicity, it combines three devices: a water-jet circulation pump, a mixing unit, and a pressure regulator.

Principle of operation of the elevator

From the outside, the design looks like a big metal tee with connecting flanges at the ends. The layout of the elevator inside:

• the left branch pipe (see drawing) is a tapered nozzle of the designed diameter;
• behind the nozzle there is a cylindrical mixing chamber;
• the bottom socket is used to connect the return line to the mixing chamber;
• The right-hand pipe is an expanding diffuser that directs the heat transfer medium into the heating network of a multi-storey building.

Note: The elevator in the classic version can operate without being connected to the home’s electrical system. The product has been updated and now has an electric actuator and an adjustable nozzle. It is powered by an external source.

The left pipe of the centralized heating network connects the steel elevator unit to the supply main, and the bottom pipe connects it to the return pipe. Shut-off valves are located on both sides of the element, and on the supply side, there is a sump, also referred to as a strainer. A device for measuring the amount of energy used, pressure gauges, and thermometers on both lines are also part of the conventional design of a heating station with an elevator.

Let’s now examine the operation of the elevator jumper:

1. Superheated water from the heating network passes through the left pipe to the nozzle.
2. At the moment of passing through the narrow nozzle cross-section under high pressure, the flow accelerates according to Bernoulli"s law. The effect of a water-jet pump starts to work, which ensures circulation of the heat carrier in the system.
3. In the zone of mixing chamber the water pressure is reduced to the norm.
4. The jet moving at high speed into the diffuser creates rarefaction in the mixing chamber. The ejection effect occurs – a higher-pressure fluid flow entrains the coolant returning from the heating network through the jumper.
5. In the chamber of the heating elevator there is mixing of cooled water with superheated water, at the outlet of the diffuser we get the coolant of the required temperature (up to 95 °C).

To be clear. It should be mentioned that the elevator unit also makes use of the injection principle, which is the simultaneous energy transfer and mixing of two jets. The pressure of the resulting flow decreases relative to the original, but increases relative to the pressure drawn from the return. In the video, the procedure is demonstrated more clearly:

There must be a sufficient pressure differential between the main supply and return lines for the elevator to operate normally. The hydraulic resistance of the injector itself and the home heating system should be overcome by this difference. For improved flow separation, a 45° angle is cut into the return of the vertical jumper.

In a district heating system, the elevator unit plays a crucial role in regulating the flow of hot water from the main heating plant to individual buildings. Essentially, it acts as a bridge, lifting the hot water to higher levels in tall buildings where gravity alone can"t carry it. This unit ensures that every floor receives the necessary amount of heat by controlling the pressure and flow of water. It operates using pumps and valves, which work together to maintain the right balance throughout the system. By efficiently distributing heat, the elevator unit helps keep buildings warm and comfortable while maximizing energy efficiency. Understanding how this component works is key to optimizing the performance of district heating schemes and ensuring reliable heating for residents.

Technical data of standard products

There are seven standard sizes in the line of factory-made elevators, and each has a number. The working nozzle and the throat diameter (mixing chamber) are the two primary factors considered in the selection process. The latter is a changeable, detachable cone that can be used as needed.

Two situations require replacing the nozzle:

1. When the passage section of the part increases due to natural wear and tear. The reason for this is the friction of abrasive particles in the thermal fluid.
2. If it is necessary to change the mixing ratio – to increase or decrease the temperature of the water supplied to the house heating system.

The table provides the main dimensions and the number of standard elevators (compare with designations in the drawing).

Please take note that since this diameter is calculated independently, the nozzle cross-section is not included in the technical data. It is necessary to compute the required size of the mixing and injection chamber in addition to the number of ready-made elevator tees for a given heating system.

Calculation and selection of elevator by number

To make the sequence of events clearer, the diameter of the mixing chamber is calculated first, followed by the appropriate elevator number selection and the size of the working nozzle. The following formula is used to get the injection chamber’s diameter (in centimeters):

The actual heat carrier flow rate in the apartment building system, accounting for hydraulic resistance, is represented by the formula’s Gpr. This is how the value is computed:

• Q – the amount of heat consumed for 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 – resistance of the entire heating system with radiators, expressed in meters of water column.

Citation. The familiar watts must be multiplied by the coefficient 0.86 in order to add incomprehensible kilocalories to the formula. Water column meters are converted to the following more widely used units: 1 Bar is equal to 10.2 m of water.

An illustration of choosing an elevator number. It has come to our attention that the actual Gpr will be 10 tons of mixed water in an hour. The mixing chamber’s diameter is therefore 0.874 −10 = 2.76 cm. It makes sense to use a mixer #4 with a 30 mm chamber.

Now, we use the following formula to determine the nozzle’s narrow section’s diameter (in millimeters):

• 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 fluid at the supply to the system.

The calculations are not too difficult, despite the formula’s initial seeming complexity. There’s still one parameter we don’t know: the injection coefficient, which is determined as follows:

With the exception of parameter T1, which indicates the hot water temperature at the elevator’s inlet, we have figured out all of the designations in this formula. When the supply and return temperatures are 90 and 70 °C, respectively, and its value is 150 degrees, the required size Dc will emerge as 8.5 mm (at a flow rate of 10 t/h of water).

An alternative formula for the diameter can be used if the head HP at the elevator inlet on the central side is known:

Note: The computation’s outcome, as determined by the final formula, is given in centimeters.

In conclusion about the disadvantages of elevator mixers

The advantages of employing elevators in home heating units—energy independence, ease of use, dependability, and durability—were previously discovered. Now for the drawbacks:

1. For normal operation of the system it is necessary to ensure a significant difference in water head between return and supply.
2. Individual selection of the unit to the specific heating network is required, based on calculation.
3. In order to change the parameters of the outlet heating medium, the nozzle orifice diameter must be recalculated for the new conditions and the nozzle must be replaced.
4. Smooth temperature regulation is not provided on the elevator.
5. The unit cannot be used as a circulation pump for local circuits (e.g. in a private house).

To be clear. Elevator models have been improved with movable cross-sectional area. A cone inside the pre-chamber is driven by an electric or manual gear transmission. But the unit’s primary benefit—its independence from electricity—is gone.

It is challenging to start up single-pipe house systems that are used in conjunction with elevators. Squeezing air out of the return riser and supply riser first is required before progressively opening the main gate valve. The master plumber in the video will learn more about the launching technique and injection units:

For homeowners looking for cost-effective heating options, it is crucial to comprehend how the elevator unit operates within a district heating system. In order to distribute heat from the centralized heating plant to individual homes, the elevator unit is essential. Residents can make knowledgeable decisions about their insulation and heating needs by understanding how it operates.

Fundamentally, the elevator unit acts as a go-between for the individual homes and the district heating network. It controls the flow of steam or hot water, making sure that every home gets the right amount of heat for its needs. This procedure helps save money and preserve the environment by maximizing energy use and preserving cozy interior temperatures.

The elevator unit’s capacity to regulate the circulating fluid’s temperature is a crucial component of its operation. It modifies the heat output through advanced sensors and valves according to variables like the outside temperature and the needs of the home. The system is very efficient because of this dynamic response mechanism, which also reduces energy waste while improving comfort.

Moreover, the elevator unit makes it easier for the district heating network to incorporate renewable energy sources. It makes it possible to seamlessly integrate solar, biomass, or geothermal heat into the overall system by accounting for variations in supply and demand. This adaptability encourages the shift to more environmentally friendly heating options, lowering reliance on fossil fuels and lessening environmental effect.

To sum up, the elevator unit is the central component of a district heating system that ensures efficient heat distribution to each individual home. Maximum comfort, energy savings, and environmental sustainability are guaranteed by its effective operation. Homeowners can improve their homes’ insulation and heating by making educated decisions based on their understanding of how this component operates, helping to create a more sustainable and resilient future.

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