FIELD OF THE INVENTION
The present invention relates to an energy storage system. More particularly, the present
inventing relates to thermal storage systems for use with a boiler, for example a domestic
boiler.
BACKGROUND TO THE INVENTION
Storage combination or combi boilers combine central heating and domestic hot water
(DHW) in one device.
The storage-type device includes an internal water store, typically having capacity for
storage in the region of 42 to 54 litres. This corresponds to an average energy storage
capacity of approximately 2.70kWh per charge of the device. Examples of such storage
combination boilers are listed in the following table together with their main characteristics:
The hot water flow rate defined in the above table is based on a temperature increase of 35
degrees Kelvin, i.e. nominal hot water flow temperature of 45 degrees centigrade.
Flow rates from such devices range from 14.0 to 17.5 litres per minute.
Hot water storage within such combination boiler devices is used primarily to increase
efficiency of the device, in use, and to improve customer satisfaction when using a
combination boiler. This is achieved because energy wastage is reduced by reducing boiler
cycling, switching on at high power even for small draw offs. Water and energy wastage is
reduced because hot water is supplied instantly from the hot water store compared with a
delay of approximately 15 seconds for a conventional combination boiler to produce water at
a usable temperature above 40 degrees centigrade. A conventional combination boiler does
not include water storage facility, but instead heats water as it flows through the boiler. In
some cases a conventional combination boiler includes a keep hot facility to provide instant
hot water, but this feature is known to waste up to 900 kWh of heat energy per year.
Combination boilers have many moving parts that can lead to break down, and so can be
considered less reliable than boilers such as system boilers, heat only boilers etc. which are
generally associated with a storage tank.
It is desirable to provide an improved boiler based heating system.
It is further desirable to provide an improved energy storage system that provides an
improved alternative to a conventional storage means for boiler use.
SUMMARY OF THE INVENTION
A first aspect of the present invention provides an energy storage system for a use with a
boiler, the energy storage system comprising :
a plurality of thermal energy storage banks, wherein each thermal energy storage bank
comprises a phase changeable material having a predetermined phase transformation
temperature;
an extraction device configured to recover waste energy from the boiler, wherein the
extraction device is operable to extract waste energy from the boiler and feed that energy to
at least one of the thermal energy storage banks; and
a controller arranged, in use, to activate the extraction device in response to operation of the
boiler.
The system according to embodiments of the present invention can store energy for heating
a relatively small volume of water using phase change material having a suitable phase
change transformation temperature.
The phase change transformation temperature may be the same for all banks. Alternatively,
at least one bank may operate with a phase change transformation temperature lower than
the phase transformation temperature of the remaining banks.
Each thermal energy storage bank may be connected to one or more adjacent thermal
energy storage banks by thermal energy transfer connections.
The extraction device may comprise a pump. The pump may comprise a potable water mini
pump. Alternatively, the pump may comprise a micro heat pump.
The pump may be configured to recover waste heat from flue gases generated during boiler
operation. The controller may activate the pump in response to firing of the boiler, for
example upon demand for hot water.
The energy storage system may recover heat from the boiler, in particular from boiler
inefficiencies, such as waste heat from exhausted flue gases and from the boiler heat
exchanger assembly during the boiler pump overrun period at the end of a firing cycle. The
present invention provides means for efficient flue gas recovery and end of firing cycle
recovery that can be integrated with hot water storage. Therefore, a device according to
embodiments of the present invention will increase energy recovery compared with currently
available technology.
The system may comprise a cold water inlet. Cold water may be mains fed.
The system may comprise a thermostatic blending valve, wherein the blending valve may
combine mains fed cold water with water heated by the energy storage system to control
outlet temperature of potable hot water. The thermostatic valve may be configured to
regulate outlet water temperature in the region of 47 degrees centigrade.
The flow rate of the energy storage device according to embodiments of the present
invention may be at least 15.5 litres per minute.
The phase change material may comprise a phase transformation temperature in the region
of 58 degrees centigrade. The phase change material may comprise a phase transformation
temperature within the range of 50 to 55 degree centigrade.
At least one of the banks may comprise phase change material comprising a phase
transformation temperature in the region of 28 degrees centigrade. The benefits of using
28°C low temperature PCM are that heat recovery circuit can be maintained at lower
temperature for longer periods and there by increasing the amount of energy recovered.
An energy storage system according to embodiments of the present invention may reduce
boiler cycling. It will be appreciated that in a domestic setting the majority of hot water drawoffs,
for example hand washing, are of short duration and therefore may present highly
inefficient use of energy.
A second aspect of the present invention provides a boiler in combination with the energy
storage system according to the first aspect.
A suitable boiler for use with the energy storage system in accordance with the present
invention may be a system boiler. Alternatively, a suitable boiler for use with the energy
storage system may be a combination boiler, wherein the energy storage system according
to the first aspect is provided external to the boiler. A suitable boiler may be, for example,
but not limited to a gas-fired boiler or a gas-fired boiler.
The combination of a suitable boiler and an external energy storage system according to the
present invention may provide a comparable system to a storage combination boiler, but
with savings in development and certification costs.
An energy storage system used in combination with a system boiler is advantageous over
known system boilers because a storage cylinder, generally situated in an airing cupboard or
the like, is no longer required. As such the space required for water storage is reduced.
An energy storage system used externally in combination with a combination boiler is
advantageous over known conventional combination boilers because the external energy
storage system substantially eliminates a delay in producing hot water upon demand. In
addition an energy storage system used externally in combination with a combination boiler
reduces the storage vessel requirements and also reduces the number of operational parts
within the boiler device that can lead to break downs.
The potable water content of the energy storage system will be significantly less than 15
litres. As such, the device may not require safety devices and testing normally associated
with unvented storage vessels (40 - 80 litre) used in combination boilers.
Conventional storage combination boilers, generally require the stored potable water to be
pasteurised because of the volume of water stored within the vessel exceeds a
predetermined level which increases the stagnation time. As such, by reducing and
maintaining the volume of potable water in the system to a maximum level of around 10 litres
and heating it instantaneously on demand, the water should not require pasteurisation, such
as heating to above 60 degrees centigrade, to protect against legionella.
A system boiler together with the energy storage system provides improved boiler efficiency
compared with conventional system boiler arrangements and with storage combination
boilers. Average boiler circuit temperatures will generally be lower.
The combination of a system boiler and the energy storage system according to the present
invention reduces water and energy wastage because instant hot water can be provided
from the store provide by the energy storage system.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention are described below, by way of example only, with
reference to the accompanying drawings, in which:
Figure 1 illustrates a schematic representation of a storage boiler arrangement comprising
an energy storage system according to an embodiment of the present invention;
Figure 2 illustrates a schematic representation of a storage boiler arrangement comprising
an energy storage system according to an embodiment of the present invention; and
Figure 3 illustrates a schematic representation of suitable locations for an energy storage
system according to embodiments of the present invention.
BRIEF DESCRIPTION
Figure 1 is a representation of an energy storage system 10 according to an embodiment of
the present invention in combination with a system boiler 20 to provide, what can be
considered effectively a combination boiler 100 with external storage capacity.
The energy storage system 10 comprises a series or collection of banks, 10 1, 102, 103, 104,
which are used to collect and store thermal energy which is normally dissipated as flue gas
waste. The energy storage system 10 recovers heat from a heat exchanger 201 located
between the boiler 20 and the flue 202.
Each bank 101 , 102, 103, 104 contains phase change material. The first bank is the waste
heat recovery battery and contains a phase change material with a melting point at 28
degrees centigrade and storage capacity in the region of 1.5 kWh.
The other banks 102, 103, 104 each contain a phase change material with a melting point of
58 degrees centigrade and storage capacity of 2.0 to 10.0 kWh.
In the embodiment illustrated in figure 1, a pump 105 is provided to transfer waste heat
energy from a flue gas heat exchanger 201 to the waste heat recovery bank 101 . A
controller 106 is operable to activate the pump 105 when the boiler 20 is fired upon demand
for hot water, for example a tap is opened. Heat energy from the exhaust/flue gases are
therefore recoverable
Figure 2 is a representation of an arrangement of a boiler 20 and energy storage system 10
similar to the arrangement illustrated in Figure 1. As such, like reference numerals have
been applied. The difference between the arrangements illustrated in Figure 1 and Figure 2
is a micro heat pump 115 in the waste heat recovery circuit between the flue gas heat
exchanger 201 and the waste heat recovery bank 101 as illustrated in figure 2. A water to
water micro heat pump 115 will generally extract more energy from the boiler flue gases 202
than the potable water mini pump 105 illustrated in figure 1. In addition the micro pump 115
is capable of storing the extracted heat energy at a higher temperature than the mini pump
105 of figure 1.
In the illustrated examples, the boiler 20 is a conventional system boiler, which in
combination with the energy storage system 10 dispenses with a hot water storage tank.
The combination of a system boiler 20 and the energy storage system 10 provides a heating
system that can operate more efficiently than a comparable storage combination boiler.
The boiler 20 is a typical system boiler, which does not form part of the present invention as
such. The main components of the boiler 20 associated with the energy storage system are
described below. It will be appreciated that other boiler types can be used with the system
according to embodiments of the present invention, including for example a gas-fired boiler
or an oil-fired boiler.
In both figures 1 and 2, the boiler 20 comprises a hydro-block 207. Upon opening a hotwater
tap the boiler 20 generally responds to the demand and the boiler fires-up and hot
water is supplied to the tap via a three port valve located on the hydro-block 207. In the
illustrated example the output flow at the hydro-block 207 is directed through the energy
storage system 10. Therefore, the demand on the boiler 20 is reduced due to the heat from
the flue gases 201 being recovered and used by the energy storage system 10 to heat water
that is stored in the energy storage system 10. As such, upon demand for hot water, the
system according to embodiments of the present invention supplies hot water immediately
the tap is opened.
The hot exhaust/flue gases are generally exhausted to the atmosphere via the boiler flue
202after the heat has been extracted by the boiler gas to water heat exchanger from the
combustion of gases within the combustion chamber 208. In the illustrated example a heat
exchanger 201 is located between the combustion chamber 208 and the boiler flue 202 and
act together with the energy storage system 10 to recover heat from the exhaust gases, as
described further below.
Flue gases are generally corrosive especially below the dew point and therefore a stainless
steel bespoke gas to water heat exchanger 201 for the waste heat recovery circuit may be
most suitable.. To keep the development simple, flexible and cost effective a pumped circuit
is used to transfer heat from the heat exchanger 201 to the waste heat recovery bank 10 1.
The system 100, comprising a boiler 20 and an energy storage system 10 includes a hot
water outlet 209, mains cold water supply 2 10, a condensate drain 2 11, central heating hot
water flow output 2 12, and central heating return 2 13.
In the system according to embodiments of the present invention, the potable water content
in the energy storage system 10 will be less than 15 litres. Therefore, the water content
should not require pasteurisation i.e. heating above 60 degrees centigrade, to protect
against legionella. However, if pasteurisation of potable, domestic, hot water is a
requirement, for example as set by a regulations, bank 10 1, as illustrated in figure 1 can be
heated to an elevated temperature periodically, for example once per week.
In known storage combination boilers the water is normally heated to around 65 degrees
centigrade to increase storage capacity and to reduce the risk of legionella. The average
energy storage capacity of a vessel of a storage combination boiler is 2.7 kWh, which
corresponds to around 25 litres of potable water. Typically, such volume requires
pasteurisation of the water and therefore requires heating in excess of 60 degrees
centigrade.
During normal operation of a boiler 20, at the end of the heating cycle, the boiler pump
generally continues to run for a further five to ten minutes to prevent overheating of the
boiler. The energy in the boiler, due to the overrun, is normally dissipated to central heating
radiators or through the casing of the boiler appliance. In the configuration of a boiler 20 and
energy storage system 10 according to embodiments of the present invention, the energy
storage system 10 can utilise the overrun period of the boiler 20 by recovering this energy
during the overrun period because stratification in the banks 101 , 102, 103, 104 can be
managed.
The flow temperature from a comparative combination boiler is in the region of 45 degrees.
To achieve the same flow temperature from the boiler 20 and the energy storage system 10
as illustrated in figures 1 and 2 suitable phase change material is material comprising a
melting point or phase transformation temperature of 50 to 55 degrees centigrade. In
addition a thermostatic blending valve 110 is included in the energy storage system 10 such
that the temperature of hot water at the outlet 209 is regulated at around 47 degrees
centigrade
The energy storage system is configurable such that the space it requires for
mounting/locating is minimised. For example, as illustrated in figure 3, the energy storage
system 10 may be located adjacent the boiler 20, for example behind or below 300 the boiler
20. Alternatively, the energy storage system 10 may be located remotely from the boiler 20,
with suitable conduit or pipework connecting the two. For example, a boiler 20 may be
mounted in a wall or within a cabinet in a kitchen and the energy storage system 10 may be
located discretely in a space or void, for example above wall cabinets 310, in a cavity behind
base cabinets 320 or in a space between a cabinet and a wall 330 .
In the embodiments described and illustrated the energy storage system 10 comprises four
banks 101 , 102, 103, 104. However, it will be appreciated that the number of
banks/batteries are provided by way of example only, as is the melting point temperatures of
the phase change material in each bank. As such fewer or more banks may be applicable
and also higher or lower phase transformation temperatures may apply.
The system comprising phase change material provides a system capable of storing and
releasing energy, where heat is absorbed or released when the physical state of the material
changes from solid to liquid or liquid to solid.
The system has been described in combination with a system boiler. However, it will be
appreciated that the system can be used with other types of boiler to improve system
performance and reduce waste heat, for example, but not limited to oil-fired boilers and gasfired
boilers.
Whilst specific embodiments of the present invention have been described above, it will be
appreciated that departures from the described embodiments may still fall within the scope
of the present invention.

Claim
An energy storage system for a use with a boiler, the energy storage system
comprising:
a plurality of thermal energy storage banks, wherein each thermal energy storage
bank comprises a phase changeable material having a predetermined phase
transformation temperature;
an extraction device configured to recover waste energy from the boiler, wherein the
extraction device is operable to extract waste energy from the boiler and feed that
energy to at least one of the thermal energy storage banks; and
a controller arranged, in use, to activate the extraction device in response to
operation of the boiler.
An energy storage system according to claim 1, wherein the phase-change
transformation temperature is the same for all banks.
An energy storage system according to claim 1, wherein at least one bank may
operate with a phase-change transformation temperature lower than the phase
transformation temperature of the remaining banks.
An energy storage system according to any preceding claim, wherein each thermal
energy storage bank may be connected to one or more adjacent thermal energy
storage banks by thermal energy transfer connections.
An energy storage system according to any preceding claim, wherein the extraction
device comprise a pump.
An energy storage system according to claim 5, wherein the pump comprises a
potable water mini pump.
An energy storage system according to claim 5, wherein the pump comprises a micro
heat pump.
An energy storage system according to claims 5, 6 or 7, wherein the pump is
configured to recover waste heat from flue gases generated during boiler operation.
An energy storage system according to claim 8, wherein the controller activates the
pump in response to firing of the boiler.
10. An energy storage system according to any preceding claim, further comprising a
cold water inlet.
11. An energy storage system according to any preceding claim, further comprising less
than 15 litres of potable water.
12. An energy storage system according to claim 11, further comprising a thermostatic
blending valve operable to blend inlet cold water with the potable water heated by the
energy storage system to control outlet temperature of potable hot water.
13. An energy storage system according to claim 12, wherein the thermostatic valve is
configurable to regulate outlet water temperature.
14. An energy storage system according to claim 13, wherein outlet water temperature is
in the region of 47 degrees centigrade.
15. An energy storage system according to any preceding claim, wherein the flow rate of
the energy storage system is at least 15.5 litres per minute.
16. An energy storage system according to any preceding claim wherein the phasechange
material comprises a phase transformation temperature in the region of 58
degrees centigrade.
17. An energy storage system according to any preceding claim, wherein the phase
change material comprises a phase transformation temperature within the range of
50 to 55 degree centigrade.
18. An energy storage system according to any preceding claim, wherein at least one of
the banks comprises phase change material comprising a phase transformation
temperature in the region of 28 degrees centigrade.
19. A boiler in combination with the energy storage system according to any preceding
claim.
20. A boiler according to claim 19, wherein the boiler is a system boiler.
2 1. A boiler according to claim 19, wherein the boiler is a combination boiler.
22. A boiler according to claim 19, wherein the boiler is a gas-fired boiler.
23. A boiler according to claim 19, wherein the boiler is an oil-fired boiler.
24. A boiler according to any of claims 19 to 23, wherein the energy storage system is
located externally to and in fluid communication with the boiler.
25. A boiler according to any of claims 19 to 24, further comprising a heat exchanger
configured to receive exhaust gases and to deliver captured heat energy to at least
one bank of the energy storage system.
26. An energy storage system hereinbefore described and with reference to the
accompanying drawings.
27. A boiler as hereinbefore described and with reference to the accompanying drawings.