WO2003023288A1

WO2003023288A1 - Central heating installation

Info

Publication number: WO2003023288A1
Application number: PCT/DK2002/000562
Authority: WO
Inventors: Poul Erik Hansen; Jan Eric Thorsen
Original assignee: Danfoss A/S
Priority date: 2001-09-11
Filing date: 2002-08-28
Publication date: 2003-03-20
Also published as: DE10144595A1; DE10144595B4

Abstract

The invention relates to a central heating installation comprising heating bodies (9) arranged in separate rooms in a heating circuit, the latter having a thermal source whose thermal output can be regulated and a circulating pump (12). Each heating body (9) has a valve (10), which can be set in accordance with the ambient temperature by means of a thermostat (11), in order to maintain the ambient temperature at an adjustable desired value. In conventional heating installations, the flow temperature is regulated according to a predetermined function, depending on the external temperature and the setting of the respective thermostat. This necessitates a temperature measurement at numerous locations and requires a large number of sensors and transmission devices. According to the invention, to keep thermal losses to a minimum in a cost-effective manner, whilst maintaining the desired ambient temperature, the thermal output of the thermal source can be regulated in such a way that the operating point of the circulating pump (12) adopts a position on its characteristic curve, in which the reflux temperature (T1; T2) of the installation is at a minimum, whilst still maintaining the ambient temperature that has been set and taking into consideration the thermal load of the installation.

Description

Central heating system

The invention relates to a central heating system arranged in separate rooms radiators in a heating circuit having a heat source with controllable heat output and a circulation pump, wherein each of the radiators comprise a valve which in depen- • ^■ dependence adjustable from the room temperature by a temperature controller to keep the room temperature at an adjustable setpoint.

In known central heating systems of this type, the flow temperature is usually regulated according to a predetermined function as a function of the outside temperature. The heat requirement does not only depend on the outside temperature, but also on the setting of the setpoints on the temperature controllers. This can result in the current flow temperature being higher or lower than required. If the flow temperature is too high, a higher heat loss can result. Conversely, if the flow temperature is too low, the desired room temperature could not be reached.

To solve this problem, it is known (DE 19756104 AI), the temperatures of the radiators and possibly other variables, such as valve lift, pressure difference on a valve, temperature setpoint adjustment of the temperature regulators on the valves, the inlet and outlet temperatures. Ren the radiator and the room air temperature using appropriate sensors and include the measured values centrally in the flow temperature control. However, this requires a considerable amount of sensors and transmission devices for the measured values.

The invention has for its object to provide a central heating system of the type mentioned, in which the heat losses are kept low with little effort and still maintain the desired room temperatures.

According to the invention, this object is achieved in that the heat output of the heat source can be regulated in such a way that the operating point of the circulating pump assumes a position on its operating characteristic in which the return temperature of the system is minimal while maintaining the set room temperatures and taking into account the thermal load on the system ,

It is preferably ensured that the operating point of the circulation pump can be changed automatically as a function of the thermal load on the system. Here you get by with a minimum of sensors.

The heat source preferably contains a heat exchanger, the primary side of which is connected to a district heating plant. In this case, only the volume flow on the primary side needs to be regulated as a function of a few measurement variables so that the operating point of the Circulation pump corresponds to the current heat load.

In particular, it can be ensured that, at predetermined intervals of at least a few days, the flow temperature in the secondary circuit of the heat exchanger can be raised automatically by increasing the volume flow in the primary circuit of the heat exchanger and then gradually reduced to a value during a measuring cycle which the heat output is lower than the thermal load of the system, and that during each measurement cycle, measured values of the heat output and the pressure difference at the circulating pump can be stored at the lowest measured value of the return temperature and during operation of the system between the measurement cycles, the secondary supply temperature by means of appropriate readjustment of the primary-side volume flow at the instantaneous primary-side temperature, the pressure difference associated with the instantaneous heat output at the circulating pump by interpolation between those stored adjacent to the instantaneous heat output heat output measured values is adjustable.

The central heating system can have a volume flow regulator, through which the primary-side volume flow can be regulated via a control valve in the primary circuit of the heat exchanger, depending on the primary-side return temperature, the secondary-side supply and return temperature and the pressure difference at the circulating pump and their speed. The invention and its developments are described below with reference to the accompanying drawings of a preferred embodiment. In it represent:

1 is a block diagram of the embodiment of the invention central heating system,

2 shows the dependency of the pressure difference on a circulation pump in the heating circuit of the central heating system on the volume flow at constant speed of the circulation pump, i.e. the operating characteristic of the circulation pump, and two different operating characteristics of the remaining parts of the heating circuit through which the fluid conveyed by the circulation pump flows, i.e. the rest of the pipeline network without the circulation pump, for two different operating points of the circulation pump,

3 shows characteristic curves similar to that of FIG. 2, but for speeds of the circulating pump which are constantly regulated to different setpoints, with a straight control characteristic of the circulating pump at different speeds, 4a shows the time course of the flow and return temperatures T ₃ , T _x , T ₂ , the heat output Q of the heat source and the pressure difference ΔP at the circulation pump as a function of the outside temperature T _A ,

Fig. 5a the course of the flow temperature T ₃ and the up to o associated return temperatures T _{X /} T ₂ , the

Heat output Q of the heat source and pressure difference ΔP at the circulation pump when the central heating system is adapted to different outside temperatures for calibrating the central heating system and

Fig. 6 for the different in the calibration of

Central heating system determined measured values of the pressure difference at the circulation pump and the heat output of the heat source with linear interpolated intermediate values.

In the exemplary embodiment of the central heating system according to the invention shown in FIG. 1, a heat source in the form of a heat exchanger 1 is supplied with warm water from a primary heating system via a flow line 2 and a return line 3 from a district heating plant (not shown). The primary return temperature Ti is measured by means of a temperature sensor 4 and fed to a volume flow controller 5. In the return line 3 there is also a control valve S which is controlled by the volume flow controller 5 via a servomotor 6. In the secondary heating circuit of the heat exchanger Schers 1 are parallel between a flow line 7 and a return line 8 several radiators 9 in series, each with a valve 10. One or more radiators 9 are each arranged in separate rooms to be heated. The valves 10 are each controlled by a temperature controller 11 which adjusts the degree of opening of the associated valve 10 as a function of the room temperature and a temperature setpoint set on the temperature controller 11 so that the room temperature remains largely constant. In the return line 8 of the secondary circuit of the heat exchanger 1 there is a circulation pump 12, the speed of which is kept constant at an adjustable setpoint by an internal speed controller. A measure of the pressure difference ΔP at the circulation pump and the volume flow V is supplied to the volume flow controller 5 via a data bus shown in broken lines. The return temperature T ₂ in the return line 8 is measured by means of a temperature sensor 13 and the flow temperature T ₃ in the supply line 7 by means of a temperature sensor 14. The measured values of the return temperature T ₂ and the supply temperature T ₃ are also fed to the volume flow controller 5 via lines shown in broken lines.

The flow regulator 5 controls in dependence on the supplied thereto temperatures Tχ ₇ T _2, T _3, the pressure difference AP to the circulating pump 12 and the flow rate V in the secondary heating circuit of the heat exchanger 1 whose heat output Q = V • C _v • p (T ₃ - T ₂ ), where V is the volume flow per unit of time, C _{v is} the heat content of the water sers in the heating system, p the density of the water on the secondary side of heat exchanger 1 and T3-T2 the temperature difference on the secondary side of the

I

Heat exchanger is such that the return temperature T _x and thus also the return temperature T _{2 of} the central heating system is minimal while maintaining the set room temperatures and taking into account the thermal load on the system. Er and Er and p change little with temperature. If V and T ₃ -T _{2 are} measured, the energy provided by the heating systems can be calculated. C _v and p change little with temperature. If V and T ₃ -T _{2 are} measured, the heating system's energy output can be calculated. In this way, heat losses are kept as low as possible and the heat efficiency of the central heating system, in particular the district heating plant, is kept high.

With this regulation, the operating point of the circulating pump 12 shifts on the circulating pump operating characteristic shown in FIG. 2 for a constant pump speed depending on the respectively set mean opening degree of the valves 10 of the heating elements 9 between the working points in the intersection points of the circulating pump operating characteristic and the pipe network characteristic curve, which comprise the pressure drop at the pipes 7, 8, radiators 9 and valves 10 in the secondary-side heating circuit of the heat exchanger 1 as a function of the volume flow V, in accordance with the respective degree of opening of the radiator valves 10 according to FIG. 2. The characteristic curves according to FIG. 3 then apply to different constant speeds, the operating points lying on the control curve of the circulating pump corresponding to the respective opening degree of the radiator valves.

4a to 4c illustrate the dependency of the respective temperatures t _lr t ₂ and t ₃ , the thermal output Q of the heat source and the pressure difference ΔP at the circulation pump 12 as a function of a fluctuating outside temperature T _a (lower curve in FIG 4a). 4b and 4c only indicate qualitative profiles of the curves. This also applies to FIGS. 5b and 5c.

In order to regulate the heat output of the heat source or of the heat exchanger 1 in the manner mentioned, the central heating system is first automatically calibrated by the volume flow controller 5 according to FIGS. 5 and 6 for different heat loads or outside temperatures at regular intervals of at least a few days. A measuring cycle extending over a few hours proceeds according to FIG. 5a as follows: At the beginning, the flow temperature T ₃ in the secondary heating circuit is greatly increased by increasing the volume flow in the primary circuit of the heat exchanger 1 by opening the control valve S further. Thereafter, the flow temperature T _{3 is} always constant after the temperatures T _{X /} T ₂ and T ₃ and the operating point of the pump

Have set value - with the valves 10 by the Temperature controller 11 are closed further because of the increase in the flow temperature T _{3 in order to} continue to maintain the set temperature setpoint - by one level is reduced to a value at which the thermal output Q is lower than the thermal load on the system. This lowest value of the flow temperature T ₃ and thus the heat output is achieved in that the valves 10 are finally all open. During this step-by-step measuring cycle, the return temperatures Ti and T _{2 reach} a minimum, which in the example shown in FIG. 5 a lies at the intersection of the vertical dashed line with the course of the temperatures Ti and T ₂ . The measured values of the thermal output Q and the pressure differences ΔP at the circulating pump 12 determined in each measurement cycle in a corresponding minimum of the temperatures Ti and T ₂ in the volume flow controller 5 are stored in the volume flow controller 5. During the operation of the system between the individual measuring cycles, the secondary-side flow temperature T ₃ is then, by corresponding readjustment of the primary-side volume flow V at the instantaneous primary-side return temperature T _x , the pressure difference ΔP associated with the instantaneous heat output Q at the circulating pump by linear interpolation between the current heat output adjacent stored heat output measured values, which are indicated in FIG. 6 by three measurement points each determined in one of three measurement cycles.

Claims

claims

1. Central heating system with radiators (9) arranged in separate rooms in a heating circuit which has a heat source with controllable heat output (Q) and a circulation pump (12), the radiators (9) each having a valve (10) which depending on the room temperature can be adjusted by a temperature controller (11) in order to keep the room temperature at an adjustable setpoint, characterized in that the heat output

(Q) of the heat source can be controlled so that the operating point of the circulation pump (12) assumes a position on its operating characteristic (ΔP = f (V)) in which the return temperature (Ti; T ₂ ) of the system while maintaining the set one Room temperatures and taking into account the thermal load on the system is minimal.

Central heating system according to claim 1, characterized in that the operating point of the circulation pump (12) can be changed automatically as a function of the thermal load on the system.

Central heating system according to claim 1 or 2, characterized in that the heat source has a heat exchanger (1), the primary side of which is connected to a district heating plant.

4. Central heating system according to claim 3, characterized in that the flow temperature (T ₃ ) in the secondary circuit of the heat exchanger (1) by increasing the volume flow (V) in the primary circuit of the heat exchanger (1) can be raised automatically and at predetermined intervals of at least a few days thereafter, during a measuring cycle, it can be gradually reduced to a value at which the thermal output (Q) is lower than the thermal load of the system, and that during each measuring cycle measured values of the thermal output (Q) and the pressure difference at the circulation pump (12) at the lowest Measured value of the return temperature (Ti; T ₂ ) can be saved and during operation of the system between the measuring cycles, the secondary-side flow temperature (T ₃ ) by corresponding adjustment of the primary-side volume flow (V) at the current primary-side temperature (Ti) for the instantaneous heat output (Q) belonging pressure difference ΔP at the circulation pump (12 ) can be set by interpolation between the stored heat output measured values adjacent to the current heat output.

5. Central heating system according to claim 4, characterized in that it has a volume flow controller (5) through which via a control valve (S) in the primary circuit of the heat exchanger (1) whose primary-side volume flow (V) as a function of the primary-side return temperature (Ti ), the second därseiten flow and return temperature (T ₃ , T ₂ ) and the pressure difference (ΔP) on the circulation pump (12) and their speed is adjustable.