GB2127529A

GB2127529A - Hot water heating installation

Info

Publication number: GB2127529A
Application number: GB08325536A
Authority: GB
Inventors: Jens Jorgen Molbaek; Peter Jorgensen; Poul Steffen Dam
Original assignee: Danfoss AS
Current assignee: Danfoss AS
Priority date: 1982-09-24
Filing date: 1983-09-23
Publication date: 1984-04-11
Also published as: FI833403A; FI833403A0; DE3235364C2; GB2127529B; GB8325536D0; DK419883D0; NL8303277A; SE8305070L; DE3235364A1; JPS59135516A; FR2533673A1; SE8305070D0; DK419883A

Abstract

In a hot water heating installation comprising a heat generator (1), circulating pump (4) and radiators (6, 6a, 6b) regulated by thermostatic valves (7, 7a, 7b), wherein the supply temperature is variable, a regulator (11) is influenced by the supply and return temperatures and so changes the supply temperature that the difference between the supply and return temperatures is kept at a predetermined desired value. The desired value need not be constant but may be predetermined as a function of the return temperature. An electronic regulator or a differential thermostat may be employed as the regulator (11). In this way, the efficiency of the heating installation can be improved in dependence on the load. <IMAGE>

Description

SPECIFICATION Hot water heating installation This invention relates to a hot water heating installation comprising a heat generator, circulating pump, and radiators controlled by thermostatic valves, wherein the supply temperature is variable.

In known installations of this kind, changes in the supply temperature such as produced by a change in the boiler temperature, adjustment of a mixing valve or the like, are brought about by hand, in relation to time or depending on the weather. Within each room, the dissipation of heat is regulated by thermostatic valves depending on the actual requirements. If the heat demand drops in a room, the thermostatic valve associated with that room closes. A smaller amount of hot water flows through the associated radiator and this water cools to a lower temperature as it passes through. Consequently, the logarithmic mean temperature of the radiator which is decisive for the dissipation of heat decreases. At the same time, the arithmetic mean temperature which is decisive for the heat loss in the pipes also changes but not to the same extent as the logarithmic mean temperature.

Consequently, the heat loss increases as a percentage of the dissipated heat and the efficiency of the heating installation decreases.

If, in the case of a condensation boiler, (for example, as disclosed in British Patent Specification 2073383 A (No.81/00611)) the return temperature assumes excessively high values, as is the case when the supply temperature remains the same and the load is heavy, it may no longer bring about condensation of the flue gases in the boiler and therefore also fails to asbsorb heat of condensation. This likewise reduces the efficiency of the heating installation.

An object of the present invention is to provide a hot water heating installation of the aforementioned kind which permits a reduction in the sacrifices made in the efficiency depending on the demand.

This object is achieved according to the invention by a regulator which is influenced by the supply and return temperatures and so changes the supply temperature that the difference between the supply and return temperatures is kept at a predetermined desired value.

Throughout this Specification the term "heat generator" is intended to cover all types of heat producers, that is to say not only boilers but also, for example, heat pumps, the heat in the generator being transmissible to the water in the heating installation either directly, by way of a heat exchanger, by way of a condenser or the like, or indirectly by way of a condenser or the like.

In the construction according to the invention, the supply temperature is regulated depending on the load on the installation. This is because the return temperature, on which the supply temperature is dependent, can be regarded as a parameter defining the load on the installation.

Within the system there is, therefore, information feedback which permits the supply temperature to be made dependent on the load.

In addition, there is the advantage that the relationship between the supply and return temperatures can be selected at will within wide limits. Accordingly, depending on the form of the desired value, one can have a load-dependent influence on factors that reduce the efficiency, as will hereinafter be explained.

In the simplest case, the desired value is a constant. This leads to the supply temperature dropping together with the return temperature.

This gives a reduction in the arithmetic mean temperature and thus a reduction in the heat losses in the pipes. However, it is particularly advantageous if the desired value is predetermined as a function of the return temperature. Any desired relationship can then be achieved between the supply and return temperatures. It is favourable for the desired value to increase with a rise in the return temperature, particularly linearly. This achieves the least possible arithmetic mean temperature in the pipes and thus the lowest heat loss. Since the desired value is in this case predetermined approximately directly proportionally to the load on the installation, the best achievable result will be that the amount of water circulated per unit time is approximately constant.This provides the additional advantage that the P-deviation (the difference between the temperature setting and the sensor temperature) of the thermostatic valves is likewise substantially constant.

In one embodiment, the desired valuels constant below a limiting value of the return temperature. This takes into account that for low return temperatures the desired value could become too small to result in useful regulation.

Another possibility is that the desired value first drops to a lower limiting value with a rise in the return temperature and then increases again.

This feature is recommended if, when starting a cold installation, uniform starting is desired until normal operation is achieved. In particular, the regulator can be so designed that the supply temperature is held constant below the limiting value of the return temperature.

The course of the desired value can also be selected so that particularly good heat transfer conditions obtain in the heat generator (e.g. boiler or heat pump). In this case, it is of interest that the return temperature should be as low as possible.

This can be achieved in that the desired value increases sharply above a predetermined return temperature. Particularly when using a condensation boiler, it is recommended that the desired value increases so rapidly if the return temperature rises to approach the condensation temperature, that the return temperature cannot exceed a limiting value which is less than the condensation temperature. One therefore always ensures that the returning water can absorb heat of condensation (that is to say, the temperature of the return water is always such (low enough) that the flue gases in the boiler will condense as they are brought into heat exchange relationship with the return water).

In practice, desired value behaviours can be prescribed which, on the one hand, keep pipe losses low (in the region of low and medium loading) and also keep the return temperature low (in the region of medium and high load). A compromise may be necessary in the overlapping zones.

In an installation with a return mixing conduit and a valve influencing the mixing ratio, the regulator may control the valve to maintain the desired temperature difference. One can then employ a conventional construction for the installation and change only the nature of the valve control.

In particular, the return mixing conduit may have a throttling point and the valve may be connected between the heat generator and return mixing conduit. In this way, a simple two-way valve will be adequate.

In an installation with heat generator-radiator means of variable heat output, the regulator may control the heat generator-radiator means to maintain the desired temperature difference.

Here, again, a conventional installation may be employed in which only the control of the heating installation is altered.

In one example, an electronic temperature difference regulator is used which is connected to a supply temperature sensor and a return temperature sensor by way of conduits carrying electric signals. Such an electric regulator has the advantage that additionai variables may be introduced without difficulty, for example control of an upper limit for the supply temperature in relation to the external temperature.

In another embodiment, the regulator is a differential thermostat with two oppositely operative working elements which are each connected to a supply temperature sensor and a return temperature sensor to form one system.

Such a regulator has a very simple construction and is independent ofthe electric mains.

In particular, the differential thermostat may be provided instead of a heat generator thermostat and actuate a switch to switch the heat generator heating on and off. The desired dependence on regulation can therefore be achieved by way of simple replacement of the thermostat.

It is also favourable for the differential thermostat to be an attachment on the valve and to actuate its closing member. Since such valves are often provided with a removable attachment, the desired result can be achieved by using this special differential thermostat attachment.

Advantageously, the systems have a liquidvapour filling and the desired temperature difference is determined by temperature and position-dependent forces of the two working elements. By means of a suitable combination of filling media, pressure-subjected areas of the working elements, stressing and characteristic curves for the springs used and resilient working elements, positions of equilibrium are obtained which are defined by a desired value dependent on the return temperature.

In a preferred embodiment, the pressure faces of the two working elements are equal but the vapour pressure of the liquid-vapour filling of the system associated with the return temperature is higher than that of the system associated with the supply temperature. The construction of the working elements can therefore be the same, which is rational. These working elements of equal size can also be arranged in a space-saving manner. A compensating spring can possibly be dispensed with.

In many cases it is favourable for the regulator to hold the supply temperature substantially constant in a lower range of the return temperature and, in a higher range thereof, to hold the temperature difference at the desired value. In this way one achieves that the stated regulation is switched off on low heating demand so that a certain minimum value of the supply temperature is maintained. A subsequent increase in the heating demand can then be satisfied rapidly.

From a constructional point of view, this can for example be achieved in that the working element of the system associated with the supply temperature is fixed to the actuating element and the working element of the system associated with the return temperature is connected thereto by way of a compression spring, that the compression spring is bridged by a non-positive clutch when the biassing force of the compression spring is overcome, and that both working elements are resilient.

In a further embodiment, the two working elements are formed by two capsules which are fixed with respect to the attachment and contain corrugated bellows. Between the confronting bellows bases there is a strut acting on the closing member by way of a driver which projects radially outwardly between the capsules, extends axially along the outside of one capsule and, beyond said capsule, is radially inwardly guided.

This provides a particularly simple and spacesaving construction.

In particular, the strut may be tubular, lie against the bellows base of the system associated with the supply temperature, and guide in its interior the compression spring which extends between a transverse wall of the strut and the other bellows base. The height of this arrangement is only a little more than the sum of the two capsule heights.

Further, for night time control and to reduce the running temperature (and the demand on the heat generator) the supply temperature sensor may be provided with a heater for maintaining the temperature sensed by that sensor at an artificially high level irresepective of the actual supply temperature.

The present invention also provides a hot water heating installation comprising a heat generator, a circulating pump, radiators controlled by thermostatic valves, and a regulator, which is influenced by the supply and return temperatures, for so controlling the supply temperature that the supply and return temperatures have a regulated difference.

How water heating installations constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, wherein: Fig. 1 is the circuit diagram of a first hot water heating installation; Fig. 2 is a temperature diagram; Fig. 3 is the circuit diagram of a modified hot water installation; Fig. 4 is the circuit diagram of a third hot water installation; Fig. 5 shows the constructional form of the Fig.

4 installation; Fig. 6 is a diagram showing the relationship between the desired value and the return temperature, and Fig. 7 is a similar diagram for a different relationship.

Referring to the accompanying drawings, the hot water heating installation of Fig. 1 comprises a boiler 1 of which the outlet 2 is connected by way of a three-way mixing valve 3 to a supply conduit 5 having a circulating pump 4. The supply conduit leads to several radiators 6, 6a, 6b connected in parallel and each preceded by a thermostatic valve 7, 7a and 7b, respectively. The common return conduit 8 is connected on the one hand to the boiler inlet 9 and on the other to a return mixing conduit 10 leading to the three-way valve 3.

An electronic regulator 11 receives temperature signals from a supply temperature sensor 12 by way of a signal line 13 and from a return temperature sensor 14 by way of a signal line 1 5.

A desired value for the difference between the supply and return temperatures is predetermined by means of a desired value setting apparatus 1 6.

The desired value setting can be made manually but depends particularly on the return temperature. Apart from the desired value setting, some other influence may be provided, for example setting an upper limiting value for the supply temperature. This maximum permissible supply temperature could possibly be controlled in relation to the external temperature. An actuating apparatus 1 8 for the three-way valve 3 is controlled by way of a further signal line 17.

Fig. 2 shows the supply temperature tv and the return temperature tr, both measured in the vicinity of the radiator. The mean temperature tmr of the pipes, i.e. the arithmetic mean resulting from the temperature of the supply conduit and the temperature of the return conduit, is entered in dotted lines. The mean temperature tmh at the radiators, i.e. the logarithmic mean of the supply temperature and the withdrawal temperature, is entered in broken lines. The condition a represents the starting position in which the difference between the supply and return temperatures is equal to the desired value S,. The mean temperature tmh of the radiators is only slightly below the mean temperature tmr of the pipes because, on account of comparatively large amounts of circulated hot water, the arithmetic mean temperature approaches the logarithmic mean temperature.The condition b shows the corresponding temperatures when a higher heat demand has arisen but there is no supply temperature regulation in accordance with the invention. The thermostatic valve throttles; the amount of flow drops; the two mean temperatures tmr and tmh therefore also drop, as does the return temperature tr. It should be noted that, because of the slower flow, considerable cooling takes place in the radiator and its mean temperature tmh is considerably less than the mean tempeature tmr of the pipes. The condition c shows the position upon a reduced heat demand but with supply temperature regulation. As a result of a drop in the return temperature tr, the desired value S2 is likewise somewhat reduced.

For a heat demand corresponding to the mean temperature tmh of the radiators in condition b, the supply temperature is considerably less and the return temperature higher. As a result, the mean temperature tmr of the pipes is only insignificantly higher than the mean temperature tmh of the radiators. The heat loss in the pipes is therefore correspondingly low.The following table gives temperature in OC as they could occur in the aforementioned three conditions:

a b c ty 90 90 60 tr 70 34 50 S 20 - 10 tmr 80 62 55 tmh 79 54 54 In the Fig. 3 arrangement, reference numerals increased by 100 are used for corresponding parts. A return mixing conduit is here omitted. The change in the supply temperature is brought about by appropriate control of the boiler heating device 1 9 illustrated in the form of an oil burner.

For this purpose, a switch 23 is provided in the electric leads 20 and 21 to the burner motor 22.

The switch is actuated by a regulator 111 in the form of a differential thermostat. The movable contact of the switch is seated on a linkage 24 engaged by two oppositely operative working elements 25 and 26 as well as a compensating spring 27. By way of a capillary tube 113, the working element 25 communicates with a supply temperature sensor 11 2 which detects the temperature of the boiler water. The system 28 so formed has a liquid-vapour filling. The other working element 26 communicates by way of a capillary tube 11 5 with a return temperature sensor 114. The system 29 so formed likewise has a liquid-vapour filling. In the present case, both systems have the same filling. When the return temperature rises as a result of a higher heat demand, the pressure in the working element 26 increases.The switch 23 is closed until the boiler temperature has risen to a value sufficient for opening the switch 23 again.

Reference numerals increased by 200 are used for corresponding parts in the Figs. 4 and 5 arrangement. In this case, a throttling point 30 is provided in the return mixing conduit 210 and a valve 31 in the outlet conduit 202. When its closing member 32 is moved, in the case of the supply water there is a change in the ratio between the water passing through the boiler 201 and the water supplied by way of the return mixing conduit 210 and thus the supply temperature. The working element 225 associated with the supply temperature comprises a capsule 33 containing corrugated bellows 34 of which the base 35 is connected to the closing member 32 by a strut 36. The return temperature working element 226 comprises a capsule 37 containing corrugated bellows 38 of which the base 39 is provided with an abutment element 40.Between the strut 36 and the abstinent element 40 there extends a compression spring 41. When the latter has been compressed by a predetermined amount, it is bridged by a non-positive clutch 42. The two bellows 34 and 38 have a spring characteristic.

In this case, both systems 228 and 229 are again provided with a liquid-vapour filling.

However, the filling of system 229 associated with the return temperature has a vapour pressure curve lying above that of the system 228 associated with the supply temperature. Upon a low heat demand, the pressure in the working element 225 predominates. The base 39 is near its lower limiting position. The valve 31 is actuated in the sense of keeping the supply temperature constant, the value being subsantially predetermined by the prestressing of the spring 41. However, when on account of a higher heat demand the return temperature rises, the pressure in the working element 226 finally becomes so large that the spring 41 is compressed and the non-positive clutch 42 is closed. One now obtains regulation in dependence on the difference between the supply and return temperatures.The difference is determined by the characteristic spring curve of the two bellows 34 and 38 as well as the temperature-dependent forces of the working elements. Further, an element may be included, e.g. in the form of a weighted lever, by which the resulting force-position equilibrium and thus the differential value can be altered.

As is shown in Fig. 5, the valve 32 has a valve housing 43 of conventional construction and an attachment 44 which contains the regulator in the form of a differential thermostat. The two working elements 225 and 226 are accommodated in a housing 45 placeable on the valve housing 43 with the aid of a clamping device 46. The strut 36 is tubular and receives the compression spring 41 which extends between a transverse wall 53 of the strut 36 and the bellows base 39. A driver 47 on the strut 36 has a radially outwardly extending section 48, a section 48a extending axially outside the capsule 37, and a radially inwardly extending section 49. The latter acts on a pin 50 for actuating the closing member 32. The driver 47 is guided in the housing 45.

The supply temperature sensor 212 is associated with a heating device 51 which is energised through a cable 52. Energisation of the device 51 can be effected, for example at night time to produce a reduction (in running temperature).

The graph of Fig. 6 shows the desired value S against the return temperature tr. In a lower zone up to a limiting value at about 350C, the temperature difference is constant, namely 50C.

With a rising return temperature, the desired value S increases substantially linearly.

In a different arrangement, as shown in the graph of Fig. 7, the supply temperature ty is held constant up to a return temperature of 400 C. This meons that the temperature difference, represented by the desired value S, decreases linearly. Thereafter, the desired value S rises linearly with an increase in the return temperature, i.e. with increasing load.

In the installations as described, the real load, i.e. the one registered by the radiator thermostats, determines, the temperatures in the installation by way of the regulator. Supplementary heat, for example sun rays, heat stored in buildings and the like, which influence the load, are automatically taken into account when setting the supply temperature.

The desired value S for each installation is set so that optimum conditions are obtained as far as the heat loss is concerned. Useful values lie between 50C and 300 C. Favourable regulating conditions were obtained for S=200C at a load of 100% and was reduced linearly with the load conditions. The curves in Figs. 6 and 7 are so designed that adequately high supply temperatures still obtain in the lowermost load range and the pipe losses are kept as low as possible in the medium load range. If it is important to keep the retum temperature low at high load, the characteristic curve may, starting with the limiting value for the return temperature, undergo a still steeper course than is shown.

A heat pump may be used instead of the illustrated boilers 1,101,201.

Claims

1. A hot water heating installation comprising a heat generator, a circulating pump, radiators controlled by thermostatic valves, and a regulator, which is influenced by the supply and return temperatures, for so controlling the supply temperature that the supply and return temperatures have a regulated difference.

2. An installation as claimed in Claim 1, in which the difference is a function of the return temperature.

3. An installation as claimed in Claim 2, in which the difference increases with a rise in the return temperature.

4. An installation as claimed in any one of Claims 1 to 3, in which the difference increases linearly with a rise in the return temperature.

5. An installation as claimed in Claim 3 or Claim 4, in which the difference is constant below a limiting value of the return temperature.

6. An installation as claimed in any one of claims 2 to 4, in which the difference first drops to a lower limiting value with a rise in the return temperature and then increases again.

7. An installation as claimed in any one of Claims 1 to 6, in which, when using a condensation boiler, the difference increases so rapidly when the return temperature increases to approach the condensation temperature, that the return temperature cannot exceed a limiting value which is less than the condensation temperature.

8. An installation as claimed in any one of Claims 1 to 7, and including a return mixing valve having a valve closure member influencing the mixing ratio, wherein the regulator controls the valve to provide the regulated difference.

9. An installation as claimed in Claim 8, in which the return mixing conduit has a throttling point and the valve is connected between the heat generator and return mixing conduit.

10. An installation as claimed in any one of Claims 1 to 7 and including heat generator heating means of variable output, wherein the regulator controls the heating means to provide the regulated difference.

11. An installation as claimed in any one of Claims 1 to 10, wherein an electronic temperature difference regulator is used which is electrically connected to a supply temperature sensor and a return temperature sensor.

12. An installation as claimed in any one of Claims 1 to 10, wherein the regulator is a differential thermostat with two oppositely operative working elements which are each connected to a supply temperature sensor and a return temperature sensor to form a closed system.

13. An installation as claimed in Claim 10 and Claim 12, wherein the differential thermostat is provided instead of a heat generator thermostat and actuates a switch to switch the heat generator means ON and OFF.

14. An installation as claimed in Claim 8 or Claim 9 and Claim 12, wherein the differential thermostat is an attachment on the valve housing and actuates its closure member.

1 5. An installation as claimed in any one of Claims 12 to 14, wherein each system has a liquid-vapour filling and the regulated difference is determined by temperature and positiondependent forces of the two working elements.

1 6. An installation as claimed in Claim 15, wherein the pressure faces of the two working elements are equal but the vapour pressure curve of the liquid-vapour filling of the system associated with the return temperature is higher than that of the system associated with the supply temperature.

17. An installation as claimed in any one of Claims 1 to 16, wherein the regulator holds the supply temperature substantially constant in a lower range of the return temperature and, in a higher range thereof, maintains the regulated difference.

18. An installation as claimed in any one of Claims 12 to 16 and Claim 13, wherein the working element of the system associated with the supply temperature is fixed to the actuating element and the working element of the system associated with the return temperature is connected thereto by way of a compression spring, the compression spring being bridged by a non-positive clutch when the biassing force of the compression spring is overcome, and both working elements being resilient.

19. An installation as claimed in any one of Claims 14 to 18, wherein each working element is formed by a respective one of two capsules which are fixed with respect to the attachment and contain corrugated bellows, and between the confronting bellows bases there is a strut acting on the closure member by way of a driver which projects radially outwardly between the capsules, extends axially along the outside of one capsule and beyond said capsule, is radially inwardly guided.

20. An installation as claimed in Claim 1 8 and Claim 19, wherein the strut is tubular, lies against the bellows base of the system associated with the supply temperature, and guides in its interior the compression spring which extends between a transverse wall of the strut and the other bellows base.

21. An installation as claimed in any one of Claims 1 to 20, wherein the supply temperature sensor is provided with a heater for achieving a night-time reduction in running temperature of the installation.

22. A hot water heating installation substantially as hereinbefore described with reference to, and as illustrated by, Fig. 1 or Fig. 3 or Fig. 4 and/or Fig. 5.