DE29908367U1 - Device for operating a heat supply system with a limited return temperature in variable-volume networks - Google Patents

Description

27-0Ä.99

Device for operating a heat supply system with limited return temperatures in variable-volume networks

Description

Technical area

The present invention relates to a technical solution for the construction and operation of a heat supply system for rooms with a heat generator unit, a

Distribution network with flow and return and heating surfaces.

The typical configuration underlying the invention is

a) a district heating station connected to a
district heating supply network, which meets the technical connection conditions of the
District heating supplier with a return temperature limitation, most often supplies residential units and usually also produces domestic hot water by water heating.

b) a condensing boiler whose return temperature should not be exceeded for economical operation and which supplies similar residential units.

Both a district heating station with a converter as the core for heat transfer between the primary and secondary network and a condensing boiler are generally characterized by the fact that these systems have a low heat capacity compared to their heating output and heating processes of an apparatus with a static or low-flowing secondary medium can very quickly lead to overheating or the heating process can be blocked by the control system. A minimum flow rate on the secondary side is necessary for proper operation.

State of the art

Known heat supply systems, especially district heating systems, with a dimensioning - especially of the primary-side control valve -

According to the grid connection data and the nominal heat output, due to the operating behavior of the consumers, there is a tendency to operate unstably at times, which cannot be controlled by conventional controller dimensioning alone.

The causes are due to the sum of the individual saving behaviour of the consumers - in the usual case the residents of the apartments to be heated, which

on the one hand by manually temporarily reducing the setpoint of thermostat valves on heating surfaces or room temperature controllers, e.g. when you are away,

on the other hand, a necessary increased flow temperature for the

Needs of individual customers

and in case of presence to compensate for the self-inflicted energy deficiency with reduced heating operation,

is marked.

Practical experience shows that it is not possible to force consumers to implement a balanced mode of operation. The consequence of this mode of operation is a temporarily unstable behavior of the control of the heat generator due to insufficient flow rates, which is evident in district heating stations through the frequent opening and closing of the control valve in the primary circuit.

In this situation, a high switching frequency with short burner running times is unavoidable for condensing boilers.

In district heating substations, this causes increased wear of the controller output contacts and the valve actuators, as well as overheating phenomena in the secondary flow with frequent triggering of the safety thermostats and thus more frequent activation of the safety function of the primary control valves, which can also lead to increased failures of the valve actuators and converter defects due to thermodynamic stresses and, depending on the design of the primary circuits, to pressure surges/cavitation.

The behaviour of the throttled consumers causes a subcooled return temperature in the heat supply network.

Due to the maximum limitation of the primary return temperature in accordance with the technical connection conditions of the district heating suppliers, fixed bypass sections in the secondary heating network, which cause an uncontrolled increase in the return temperature, are not sensible or are not permitted.

Description of the invention

The invention is based on eliminating the above-mentioned disadvantages without significantly increasing the cost, the most important goal being to extend the service life of the equipment in the given situation. The description refers to district heating stations as the main area of application.

The problem is to be solved in such a way that the flow and return lines, in addition to their distribution function, are given a further definitive function as heat storage.

An additional improvement of the effect is achieved by the

This can be achieved by over-dimensioning the distribution lines (main flow and return lines) or by inserting a storage vessel into the flow line.

The illustration refers to the drawing "Fig. 1".

The district heating house station is connected to a district heating network on the primary side, is pre-regulated via a control valve 1 (often with a safety function) and supplies one or more heating circuits on the secondary side, here heating network outlet 3 and the hot water heating system outlet 4.

These secondary-side outlets can be freely designed as mixed or unmixed heating circuits with or without differential pressure-controlled pumps.

On the distribution lines - in the most effective case at the ends - there are one or more controllable bypass sections with actuators 6,7, the flow of which can be regulated when opened.

can additionally be determined by throttle valves 8,9.

During low load times with low flow through the consumer branches 5 with a cumulative low flow of the heating medium through the heat generator (converter 2), the control elements/actuators (e.g. valves) 6,7 are opened according to an algorithm and a predetermined minimum flow is established. The heating medium is heated with a flow temperature according to the outside sensor 11 and control sensor 12 until the return temperature 14 has reached a value that represents a switch-off condition due to the specified return temperature limit on sensor 13.

The actuators 6, 7 are then closed and the control with the primary control valve is terminated until the stored heating medium has been discharged via the consumers 5. The charging process is then repeated.

If the flow is sufficient as a result of sufficient consumption, the system switches to continuous control operation.

The controller must be designed to identify an operating condition with naturally generated, sufficient flow rate and the low-load condition with insufficient flow rate.

Detection can be achieved by measuring the flow rate itself, by obtaining a signal using an electronically controlled pump or by evaluating the status of the controller, e.g. based on temperatures or stability criteria.

Claims (1)

A heat supply system, such as district heating stations or condensing boilers, which are defined as heat generators and have at least 1. are equipped with one or more heating groups or consumer branches and the necessary control technology, each with a connected network for supplying heat consumers, which represent variable-flow supply systems in which temporary phases of low flows occur, hereinafter referred to as low-load phases. 2. Requirements for maximum return temperatures must be met, is characterized by the fact that 3. the supply network can, in addition to the distribution function, also be used as a controllable heat storage facility if required, whereby the additional connection of storage tanks or expansions in the pipe run is optional, in which one or more remote-controlled actuators 6 , 7 (e.g. valve or pump) create a bypass function to the consumers 5 if required, thus ensuring definitive operating conditions by fulfilling a minimum flow rate and a minimum transmission power in the heat generator 2 and heating the supply network up to a certain return temperature or within a unit of time or charging the heat storage facility.
During the low load phase, after the end of the charging phase with the removal of the bypass function, the heat contained in the heat storage is cooled or discharged to a certain extent via the consumers 5 , while the heat generator system 2 can temporarily stop generating heat. 4. during a phase of sufficient throughput on the part of the consumer, normal operation can take place without the heat storage function 5. a suitable control system identifies the low-load phase and then coordinates heat generation and heat storage.