Review of existing schemes of the heating part of the ITP

Heat supply is one of the fundamental parts of modern infrastructure, providing comfortable living and working conditions for millions of people. Individual heating points (IHP) are designed to connect heating systems, hot water supply, ventilation and technological heat-using installations of one building or its part, are responsible for the effective distribution of thermal energy in buildings and structures. The thermal part of the IHP includes various schemes and technologies aimed at optimizing the heat transfer process, reducing energy losses and ensuring the reliability of the system. This material was prepared by us, a scientific group from the Moscow Power Engineering Institute. In it, we will consider the existing schemes of the thermal part of the IHP, their operating principles, areas of application and what features these schemes have.

The connection diagram for hot water supply systems is selected depending on the ratio of the maximum heat flow to hot water supply and the maximum heat flow to heating according to the following ratios:

$0.2\ \geq\ \frac{Q_{hmax}\ }{Q_{omax}\ }\geq1$ $0.2\ <\ \frac{Q_{hmax}\ }{Q_{omax}\ }<1$

Single-stage parallel connection scheme of hot water heaters and dependent connection of heating systems

The operation according to this scheme is carried out as follows: network water from the supply pipeline enters the heating point, having passed through the heat meter, then the network water flow is divided in the required ratio into the heating and hot water supply systems. To ensure the required temperature, a corrective mixing pump is installed in the heating system. In the hot water supply heater, cold tap water is heated, the constancy of the temperature of which is maintained by the flow regulator. If the water-drawing devices are closed, then the flow of hot water through the circulation pipeline again enters the hot water supply heater. After passing the heat exchanger, the network water enters the return pipeline, mixes with the water flow from the heating system and returns to the heat supply source. Thus, the network water consumption is equal to the sum of its costs for heating and hot water supply.

The features of a single-stage parallel circuit are simplicity and relatively low cost, but the high consumption of hot coolant and irrational use of return water, which has a temperature of about 40-70 °C, make it possible to use this circuit in cases where the load on the DHW exceeds the heating load or is too small compared to it. Such circuits are also used with standard temperature graphs of network water.

In a two-stage scheme, DHW heaters are divided into 2 stages.

Two-stage connection diagram of hot water heaters and dependent connection of heating systems

One of the heaters is installed on the return pipeline after the building heating system, the second on the supply pipeline of the heating network before the heating system. Preliminary heating of water in the lower stage heater is carried out due to the heat of the return water, which allows to reduce the consumption of network water for hot water supply. With such a connection, both systems have a significant impact on each other. The unevenness of the pressure when passing the maximum flow of tap water through the DHW heaters at different times of the day is large, therefore water with a temperature lower than required can enter the heating system, which can lead to “underheating” in the building. Such a scheme is used with increased temperature graphs of network water.

A two-stage connection system of heaters with independent heating connection allows avoiding the disadvantages of previous schemes.

Two-stage scheme of connection of hot water heaters and independent connection of heating systems

The considered scheme allows to reduce the consumption of network water by unloading the second stage of the heater at an average load of hot water supply and positive temperatures of the outside air, since in this case the temperature of the return water from the heating system will be increased and its heat will be sufficient to heat the water in the first heater to the required parameters. Such a feature makes it possible to level the daily load schedule. In addition, the specific combined energy production at the CHPP increases due to the lower temperature of the return network water compared to other schemes. Also, connecting systems in this way allows to maintain a stable hydraulic mode in the heating network due to the constant consumption of network water in the heating point.

Connection of ventilation and air conditioning systems in premises
is carried out in several ways:

directly – if there is no need to change the calculated parameters of the coolant;
through mixing pumps – when it is necessary to maintain a constant temperature of water entering the second heating air heaters of air conditioning systems, to reduce the temperature of the water before entering the ventilation systems, to ensure that the water does not boil at the highest points of pipelines and air heaters;
through heat exchangers – when the hydraulic modes of external networks and heat consumption systems differ.

Authors of the material: Temrina D.N., Guzhov S.V.