Regulating device for a central heating plant containing a hot water supply

Regulating device for a central heating plant containing a hot water supply, comprising a boiler for heating a heating medium, a pipe for feeding the heating medium to space heating elements, a distribution device which is accommodated in the feed pipe and has a connection to a flow-through heat exchanger which is also connected to a return pipe from the space heating elements to the boiler. A pipe for tap water being provided in the flow-through heat exchanger and said flow-through heat exchanger being provided with a thermostat which operates the distribution device in order to change from circulation through the space heating elements to circulation through the flow-through heat exchanger and vice versa. The thermostat being adjustable to permit setting of the minimum temperature in the flow-through heat exchanger at which the distribution device switches over from space heating to circulation through the flow-through heat exchanger.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a regulating device for a central heating 
plant containing a hot water supply, comprising a boiler for heating a 
heating medium, a pipe for feeding the heating medium to space heating 
elements, a distribution device which is accommodated in the feed pipe and 
has a connection to a flow-through heat exchanger, which is also connected 
to a return pipe from the space heating elements to the boiler, while a 
pipe for tap water is provided in the flow-through heat exchanger, and 
said flow-through heat exchanger is provided with a thermostat which 
operates the distribution device and at a particular temperature switches 
the distributicn device to circulation of the heating medium through the 
flow-through heat exchanger and at another temperature to circulation of 
the heating medium through the space heating elements. 
2. Description of the Prior Art 
Such a regulating device is known for example from Dutch Pat. No. 148.697. 
in the heating plant described in this patent the thermostat in the 
flow-through heat exchanger at a temperature of about 55.degree. C. 
switches the three-way valve to circulation the flow-through heat 
exchanger and, when a temperature of about 65.degree. C. is reached, 
switches the three-way valve back to circulation through the space heating 
elements. This means that the water in the flow-through heat exchanger is 
kept constantly at an average value of about 60.degree. C. 
On the one hand this temperature in the flowthrough heat exchanger means 
that, apart from heat losses in the pipe between the flow-through heat 
exchanger and the draw-off point, hot running water is always available 
immediately; on the other hand, maintaining this high temperature in the 
flow-through heat exchanger gives rise to considerable energy consumption, 
particularly during periods when no hot running water is being drawn off. 
SUMMARY OF THE INVENTION 
The object of the present invention is to produce a regulating device for 
the hot water supply of a central heating plant, in which there is the 
possibility of limiting energy losses during the periods when no hot 
running water is required. 
This object is achieved according to the invention through the thermostat 
being adjustable, in order to permit setting of the minimum temperature in 
the flow-through heat exchanger at which the distribution device switches 
over from space heating to circulation through the flow-through heat 
exchanger. 
The use of an adjustable thermostat gives the user the possibility of 
setting the temperature as desired in the flow-through heat exchanger. 
Setting at a high temperature has the disadvantage of a high energy loss 
during long standstill period such as at night, while a lower temperature 
means that the user has to put up with a longer waiting time before the 
tap gives hot water at, say, 60.degree. C. 
The setting finally selected by the user will be a compromise between 
energy consumption and the desired comfort.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As can be seen from FIG. 1, the central heating plant comprises a boiler 1, 
which is provided with a heat exchanger 2 for heating the heating medium, 
is pipe 3 to supply heating medium to space heating elemenls 4, a 
three-way valve 5 which is accommodated in the pipe 3 and is connected via 
a pipe 6 to a flow-through heat exchanger 7, which is also connected to a 
return pipe 8 running from the space heating elements to the boiler and 
having therein a circulating pump 9. The flow-through heat exchanger 7 
contains a tap water pipe 10, which enters the flow-through heat exchanger 
at 11 and leaves the flow-through heat exchanger again at 12. The tap 
water pipe runs with a number of helical windings through the flow-through 
heat exchanger 7. Positioned inside the flow-through heat exchanger 7 is 
the sensing element 13 of a thermostat 14, which is placed in the known 
way in the tap water pipe 10 some distance away from the inlet 11. The 
sensing element "observes" when water is drawn, and on the basis of this 
the thermostat switches over the three-way valve 5, so that heating medium 
is conducted through the flow-through heat exchanger 7. 
Accordingly, hot heating medium always flows through the flow-through heat 
exchanger when hot water is drawn, in order to heat the tap water. 
Although the flow-through heat exchanger is insulated, the temperature 
inside the flow-through heat exchanger will gradually decrease if no hot 
water is drawn for long periods, such as at night. When the temperature 
falls to below a predetermined level, the thermostat 14 switches over the 
three-way valve or distribution device 5, so that hot heating medium is 
fed to the flow-through heat exchanger. When the temperature inside the 
flow-through heat exchanger reaches a predetermined value again, the 
thermostat 14 switches the distribution device back again to space 
heating. 
The thermostat 14 is designed so as to be adjustable and in the embodiment 
described has a switch with six settings. By means of this switch, it is 
possible to set the temperature at which the distribution device is 
switched over from circulation through the space heating elements to 
circulation through the flow-through heat exchanger and with a switching 
difference of a fem degrees Celsius to put it back tc circulaticn through 
the space heating elements. 
The heating plant is also provided with regulating equipment for ignition 
of the burner and for safety purposes, said equipment not forming part of 
the present invention and therefore not being discussed in any further 
detail here. 
FIG. 2 shows the relationship between the setting of the thermostat 14 and 
the energy consumption in m.sup.3 gas per 24 hours. It can be seen clearly 
in this graph that at the lowest setting 1 of the thermostat the energy 
consumption is about 0.03 m.sup.3 gas, a consumption which inconsumption 
creases exponentially to 0.4 m.sup.3 at the highest setting 6. 
The graph in FIG. 3 shows the waiting time in sec. before running water at 
60.degree. C. is obtained, depending on the setting of the thermostat 14. 
For example, with a tap pipe 2 meters long, at setting 1 one would have to 
wait 35 sec. for running water at 60.degree. C. At the highest setting of 
the thermostat 14 the waiting time is reduced to 10 sec. it is clear from 
this graph that as the tap pipe increases in length, the difference in 
waiting time between the lowest and the highest setting becomes relatively 
smaller. For example, with a tap pipe 12 meters long at setting 1 of the 
thermostat, the waiting time would be 50 sec., and at the highest setting 
of the thermostat the waiting time would be about 38 sec. It can therefore 
be seen clearly from the graph that with longer tap pipes there is only a 
relatively small loss of comfort if the temperature in the flow-through 
heat exchanger 7 is kept at a low value. 
It will be clear that the temperature going with the lowest setting 1 of 
the thermostat must always be higher than the temperature of the cold 
inflowing tap water, otherwise the thermostat can no longer "observe" when 
water is being drawn and will thus become thermally inoperative. 
If hot water is required frequently, despite a low setting of the 
thermostat 14 a relatively higher temperature will still obtain in the 
flow-through heat exchanger 7. The saving therefore takes place only when 
no water is drawn for a long time, for example at night, and the user can, 
if desired, lower the setting of the thermostat only at night for example 
by connecting it to a time switch. 
The regulating device according to the inventicn therefore enables the user 
to save energy, at the expense of lengthening the waiting time. Since it 
can also be seen that with long tap pipes it is pointless to maintain the 
temperature of the flow-through heat exchanger 7 at a high value, the 
regulating device according to the invention also provides the opportunity 
to set the optimum temperature in the flow-through heat exchanger 7, 
depending on circumstances.