[0001] The present invention relates to a boiler, preferably but not exclusively of the
so-called combined type, comprising a first gas-water heat exchanger for producing
primary hot water for space heating in heat exchange relationship with a second water-water
heat exchanger for producing hot sanitary water through a primary piping system.
[0002] In the following description and the appended claims, the term: boiler of the so-called
combined type, indicates a boiler capable of delivering both hot water for space heating
or primary water and hot water for sanitary use.
[0003] As is known, in the field of domestic boilers for home use and in particular those
of the so-called combined type, the need of ensuring a prompt delivery of sanitary
water at the desired temperature and producing ever more compact and lightweight boilers
continues to rise.
[0004] To meet this need, so-called accumulation boilers in which a certain quantity of
hot water ready for use, sanitary or for space heating, is stored in a tank provided
in the primary piping system of the boiler and employed to supply in relatively short
time hot water for sanitary use, have become more widely used in the art.
[0005] Although essentially meeting the purpose, however, accumulation boilers do not allow
to fully achieve the desired structural simplification of the boiler and to attain
the features of high compactness and small size ever more sought after by the market.
[0006] The technical problem underlying the present invention is accordingly that of conceiving
and making available a boiler, in particular but not exclusively of the so-called
combined type, which allows to fulfill in all its aspects the above mentioned need
to ensure a prompt delivery of hot sanitary water and to have at the same time a minimum
size and the minimum weight compatible with the services required to the boiler.
[0007] In accordance with the present invention, this problem is solved by a boiler of the
above mentioned type, which is characterized in that it comprises in said primary
piping system a storage and expansion unit for said hot water for space heating, means
being provided for putting said unit in fluid communication with the second water-water
heat exchanger.
[0008] In accordance with the present invention, the desired reduction in size and weight
of the boiler is achieved by providing in the primary piping system of the boiler
a combined unit wherein the reservoirs necessary to accumulate hot water and to compensate
the thermal expansion of the water circulating in the primary piping system (expansion
chamber) are combined in a single and common body.
[0009] In accordance with a preferred embodiment, the storage and expansion unit comprises
a single tank having appropriate means allowing both accumulation of primary hot water
and compensation of the thermal expansion which said water undergoes during the operation
of the boiler.
[0010] Advantageously, the above mentioned means comprises a bag membrane in which is defined
a hot water storage zone supported within the tank wherein it is free to expand or
shrink depending on the temperature of the accumulated hot water.
[0011] In accordance with a preferred embodiment, furthermore, the storage and expansion
unit is installed between the above mentioned primary and secondary heat exchangers
and inside the boiler body.
[0012] In this manner, it is possible to achieve optimal characteristics of compactness
and structural simplification of the boiler, while keeping essentially unchanged the
storage capacity of hot water ready to use.
[0013] Further characteristics and advantages of the present invention will be more readily
apparent by the detailed description of an embodiment thereof given below by way of
non-limiting example with reference to the annexed drawings. In the drawings:
Figure 1 shows a perspective view of a preferred embodiment of a boiler in accordance
with the present invention;
Figure 2 shows a perspective view of a second embodiment of the boiler of FIG. 1;
and
Figure 3 shows a simplified piping diagram of the boiler in accordance with the present
invention.
[0014] With reference to the above mentioned drawing figures, reference number 1 indicates
a boiler, in particular a wall boiler of the so-called combined type, in accordance
with a preferred embodiment of the present invention.
[0015] The boiler 1 comprises a vessel 2 essentially parallelepipedic in shape and having
at the front a control panel 3 comprising an electronic control unit, control panel
3 comprising an electronic control unit, known per se, for controlling and regulating
the boiler.
[0016] In the vessel 2, the various components of the boiler 1 - shown schematically in
FIG. 3 - are conventionally supported in a manner known per se.
[0017] More specifically, the boiler 1 comprises a gas-water heat exchanger 4 for producing
primary hot water for space heating (indicated hereinafter by the term: primary exchanger),
in fluid communication - through a primary piping system globally indicated by reference
5 - with a plurality of radiant elements 6 and with a second water-water heat exchanger
7 for producing hot sanitary water (indicated hereinafter by the term: secondary exchanger).
[0018] In the primary piping system 5 three fluid paths, closed in a loop and in mutual
parallel relationship, are defined to connect the primary heat exchanger 4 respectively
with the radiant elements 6, with a primary water storage and expansion unit 8 and
with the secondary heat exchanger 7.
[0019] A first path, indicated by 9 in figure 2, comprises a first branch 9a defined within
the boiler 1 and including ducts 10, 11 respectively for water delivery to and return
from the primary heat exchanger 4 and a second branch 9b located outside the boiler
1 and including deliver and return ducts 12, 13 connected to the radiant elements
6.
[0020] The above mentioned inner branch 9a and external branch 9b of the fluid path 9 are
mutually connected by means of a pair of fittings of conventional type not shown in
the figures.
[0021] A second fluid path is indicated by 14 and comprises exchanger 4, a pair of ducts
15, 16 respectively for feeding to and withdrawing primary water from the storage
and expansion unit 8, a hydraulically controlled 3-way valve 17 and a pair of ducts
18, 19 for returning the primary water to the heat exchanger 4.
[0022] A third fluid path 20 comprises the duct 10 for water delivery to the primary heat
exchanger 4, the ducts 15, 16 for feeding to and withdrawing primary water from the
storage and expansion unit 8, the 3-way valve 17 and a pair of delivery and return
ducts 21, 22 connected to the secondary heat exchanger 7.
[0023] In accordance with the present invention, the above mentioned duct 22 is connected
in a known manner to the duct 19 for returning the primary water to the heat exchanger
4.
[0024] In a preferred embodiment of the boiler, illustrated in figure 1, the fluid paths
14 and 20 are entirely supported within the vessel 2.
[0025] In accordance with a feature of the present invention, the primary water flow in
each of the fluid paths 9, 14 and 20 is promoted by a variable-speed pump 23 of known
type and incorporating a 3-way valve.
[0026] The primary water flow is also directed towards one or the other of the parallel
fluid paths 14 and 20 provided inside the boiler by means of the 3-way valve 17 as
will be clarified in more detail hereinbelow.
[0027] More specifically, the 3-way valve 17 is driven in a known manner by an actuator
31, incorporating a flow sensor, mounted on a duct 24 provided for feeding cold sanitary
water taken from the water mains to the secondary heat exchanger 7.
[0028] Reference numeral 25 indicates a duct extending from the secondary heat exchanger
7 and designed for delivering hot sanitary water to the users.
[0029] In a manner equivalent to that set forth for the ducts 12 and 13, the above mentioned
ducts 24 and 25 are also equipped with fittings of conventional type - not shown -
for connection with an external system for distribution of the hot sanitary water
to the users which system is in turn equipped with corresponding fittings, also not
shown, designed to be inserted in a water-tight manner thereon.
[0030] In accordance with a preferred embodiment, the storage and expansion unit 8 for hot
primary water comprises a tank 26 in which is conventionally supported a membrane
27 of the so-called bag type.
[0031] In accordance with the present invention, in the membrane 27, provided for compensating
the thermal expansion of the primary water, a zone 28 is defined for storing a predetermined
quantity of hot primary water temperature of which is constantly measured and controlled
by a thermostat 30 of conventional type.
[0032] Between the membrane 27 and the tank 26 is also defined a variable-volume airspace
29 including air, optionally under pressure, or another appropriate gas.
[0033] The operation of the boiler 1 described above is as follows.
[0034] In the absence of any sanitary water withdrawal and in space heating mode, the pump
23 promotes circulation of the fluid from the duct 13 to the duct 10 for water delivery
to the primary heat exchanger 4 and cuts off the duct 19 while the 3-way valve 17
closes the duct 16.
[0035] In accordance with this operating mode, the hot primary water circulates exclusively
in the fluid path 9 so as to give away to the radiant elements 6 part of the heat
supplied thereto by the primary heat exchanger 4.
[0036] In the absence of any sanitary water withdrawal, furthermore, the temperature of
the hot primary water accumulated in the unit 8 is kept at a constant value thanks
to the intervention of the thermostat 30.
[0037] Whenever the temperature of the stored water falls below a preset thresold value,
this thermostat drives the burner of the boiler so as to deliver the maximum thermal
power to the primary heat exchanger 4, stops any fluid flow in the path 9 by means
of the pump 23 and switches the 3-way valve 17 on so as to allow a primary water flow
from the duct 16 to the duct 18.
[0038] In this way, the primary water flows only in the fluid path 14 and by-passes both
the radiant elements 6 and the secondary heat exchanger 7.
[0039] As soon as hot water for sanitary use is drawn, the actuator 31 incorporating the
flow sensor drives the pump 23 and the 3-way valve 17 so as to allow a primary water
flow from the duct 16 to the duct 21, i.e. from the storage and expansion unit 8 to
the secondary heat exchanger 7 and therefrom to the primary heat exchanger 4.
[0040] In this operating mode, therefore, the primary water flows exclusively in the fluid
path 20 while by-passing the radiant elements 6.
[0041] In this way, the hot primary water stored in the unit 8 is immediately sent to the
secondary heat exchanger 7 where it releases its heat to the cold water drawn from
the water mains and thus allows quick delivery of hot water from the boiler 1.
[0042] In accordance with the present invention, the primary water heated by the primary
heat exchanger 4 is fed by the pump 23 to the unit 8 in order to replace the stored
hot water delivered to the secondary heat exchanger 7.
[0043] In accordance with an advantageous feature of the present invention, by adjusting
the flow rate delivered by the pump 23 it is possible to withdraw from the unit 8
the minimum quantity of hot primary water necessary to reach the desired temperature
level of the sanitary water.
[0044] Advantageously, this adjustment may be performed by means of a thermostat, not shown,
provided on the duct 25 and which regulates the flow rate delivered by the pump 23
and, optionally, also the thermal power delivered by the burner to the primary heat
exchanger 4.
[0045] When the sanitary water witdrawal is terminated and depending upon the temperature
detected by the thermostat 30, the boiler returns to the pre-existing operating conditions
or accumulates new hot primary water in the unit 8 as disclosed hereinabove.
[0046] Understandably, in all the operating modes described the unit 8, in addition to fulfilling
the important function of heat accumulator able to supply ready-to-use hot water to
the secondary heat exchanger 7, compensates all the thermal expansions/contractions
of the primary water thus ensuring a correct operation of the boiler 1.
[0047] In each of the above mentioned operating modes the burner of the primary heat exchanger
4 and/or the pump 23 are started - by known procedures - if and when they are in stand-by
status.
[0048] In accordance with a second embodiment of the invention, shown in figure 2, the boiler
1 allows a prompt delivery of hot sanitary water with spaces reduced to a minimum
even when the storage and expansion unit 8 is installed outside of the vessel 2.
[0049] In another embodiment of the boiler 1, not shown, both the storage and expansion
unit 8 and the secondary heat exchanger 7 with associated inlet and outlet ducts may
be installed outside of the vessel 2.
[0050] These additional variants allow - where required - installation in separate rooms
of the boiler vessel and the unit 8 and, optionally, of the secondary heat exchanger
7 and achieve, even if to a lesser degree, the desired reduction of the overall size
of the boiler.
[0051] From the above description and discussion the several advantages achieved by the
present invention are evident.
[0052] From a functional viewpoint, the boiler of the present invention allows to achieve,
in addition to a prompt delivery of hot sanitary water with waiting times reduced
to a minimum, a gradual and in any case reduced use of the primary water stored in
the storage and expansion unit 8.
[0053] The boiler of the present invention thus allows an optimal use of the accumulated
heat which can be metered to face in an extremely flexible and durable manner the
most varied requirements of hot sanitary water withdrawals.
[0054] Integrating the storage and expansion functions in the same unit also allows to obtain
the desired prompt delivery of hot sanitary water while using a boiler of extremely
small size and weight.
[0055] In a preferred embodiment, the size of the boiler is reduced to a minimum by incorporating
the storage and expansion unit 8 inside the boiler vessel.
[0056] Advantageously, furthermore, the airspace 29 between the bag membrane 27 and the
tank 26 contributes to the thermal insulation of the membrane 27, thus allowing to
reduce and in some cases to eliminate the insulation layers normally provided on the
outer surface of the accumulation tanks of the prior art.
[0057] By integrating the storage and expansion functions in a single structure, the unit
8, the further considerable advantage of a "self-regulation" of the primary water
storing capacity in the membrane 27 is achieved.
[0058] In winter, when the primary water reaches its maximum temperature and hence also
its maximum volumetric expansion, the storage capacity in the zone 28 is at its highest
level and thus allows ample compensation for the heat loss in the various ducts.
[0059] Conversely, in summer when the boiler 1 operates in the mode of hot sanitary water
delivery and the primary water falls to the lowest degree of volumetric expansion,
the storage capacity in the zone 28 is at its lowest level and in perfect alignment
with the lesser thermal inertia of the secondary heat exchanger 7 and the lesser heat
loss due to the various ducts.
1. Boiler, in particular of the so-called combined type, comprising a first gas-water
heat exchanger (4) for producing hot primary water for space heating, said heat exchanger
(4) being in heat exchange relationship, through a primary piping system (5), with
a second water-water heat exchanger (7) for producing hot sanitary water,
characterized in that it comprises in said primary piping system (5) a storage and
expansion unit (8) for said hot water for space heating, means being provided for
putting said unit (8) in fluid communication with said second water-water heat exchanger
(7).
2. Boiler according to claim 1, characterized in that said storage and expansion unit
(8) for hot primary water is placed between said first gas-water heat exchanger (4)
and said second water-water heat exchanger (7).
3. Boiler according to claim 1, characterized in that said unit (8) comprises a tank
(26) for storage and expansion of said hot primary water.
4. Boiler according to claim 3, characterized in that said tank (26) comprises a bag
membrane (27) in which a storage zone (28) for said hot primary water is defined.
5. Boiler according to claim 1, characterized in that said means for putting said storage
and expansion unit (8) for the hot primary water in fluid communication with said
second water-water heat exchanger (7), comprises at least one duct (16, 21) having
respective valve means (17).
6. Boiler according to claim 5, characterized in that said valve means (17) are driven
by an actuator (31), incorporating a flow detector, mounted on a duct (24) for feeding
cold sanitary water to said second water-water heat exchanger (7).