U.S. patent application number 09/875024 was filed with the patent office on 2002-08-29 for gas water heater.
This patent application is currently assigned to Aquabeat Pty Ltd. Invention is credited to Lindner, David.
Application Number | 20020117122 09/875024 |
Document ID | / |
Family ID | 3822285 |
Filed Date | 2002-08-29 |
United States Patent
Application |
20020117122 |
Kind Code |
A1 |
Lindner, David |
August 29, 2002 |
Gas water heater
Abstract
A domestic gas storage water heater utilizes a plastic non
pressure tank to deliver mains pressure hot water. The heater may
be external or internal of the tank and has a heat out put of about
4-10 Mega joules per hour. A pressure transfer module uses the
mains pressure of the incoming cold water to deliver hot water from
the tank at mains pressure. The tank may be of larger storage
capacity than conventional gas heaters and the arrangement ensures
that the heated water in the tank is stratified into layers of
different temperature. This enables an uninterrupted supply of hot
water to be achieved.
Inventors: |
Lindner, David; (Victoria,
AU) |
Correspondence
Address: |
Connolly Bove Lodge & Hutz LLP
1990 M Street, N.W., Suite 800
Washington
DC
20036-3425
US
|
Assignee: |
Aquabeat Pty Ltd
2174 Frankston-Flanders Road Hastings
Victoria
AU
3915
|
Family ID: |
3822285 |
Appl. No.: |
09/875024 |
Filed: |
June 7, 2001 |
Current U.S.
Class: |
122/13.3 ;
122/15.1; 122/18.1; 137/592 |
Current CPC
Class: |
Y10T 137/86372 20150401;
F24D 17/00 20130101 |
Class at
Publication: |
122/13.3 ;
137/592; 122/15.1; 122/18.1 |
International
Class: |
F24D 017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 19, 2000 |
AU |
PQ8218 |
Claims
1. a combustion water heater which includes a) a non-pressurised
water storage tank having a cold water inlet in the lower portion
of said tank and a heated water outlet in the upper portion of said
tank b) a low heat output combustion chamber having a flue for the
egress of combustion gases c) a heat exchange surface associated
with said flue d) means for contacting water from the lower portion
of said water storage tank with said heat exchange surface e) means
for conducting water heated at the heat exchange surface to the
upper portion of said water storage tank f) pump means associated
with the heated water outlet to increase the pressure of water
exiting from the non pressurised tank.
2. A water heater as claimed in claim 1 in which the water in the
tank is stratified by temperature with the hottest water adjacent
the hot water outlet.
3. A water heater as claimed in claim 1 wherein the heat exchange
surface is disposed within the water storage tank.
4. A water heater as claimed in claim one wherein the pump means is
a multi compartmented pressure transfer module adapted to release
hot water at near mains pressure by utilising the existing mains
pressure of the cold water inlet.
5. A water heater as claimed in claim 1 wherein the heat exchange
surface is disposed within the lower portion of the tank and the
tank incorporates a shroud which separates the water in the lower
portion of the tank, which surrounds the heat exchanger, from the
water in the remainder of the tank, and a water outlet allows water
from within the lower portion to rise to the upper section of the
tank.
6. A water heater as claimed in claim 1 or 2 in which the energy
out put of the combustion unit is 1 to 2 kilowatts.
Description
BACKGROUND TO INVENTION
[0001] Gas water heaters that are commercially available and
deliver mains pressure water are characterized as having a
stainless steel tank or a vitreous enamel lined mild steel tank
with a high rating gas burner. These heaters don't have a large
capacity water storage but can heat the water quickly.
[0002] The heat efficiency of such heaters is not high and the
output of Carbon dioxide, a green house gas, is quite high. Usually
the heat exchange is achieved by passing the hot combustion gases
up a flue through the centre of the tank or over the external
surface of the tank. Australian patent 720062 is an example of this
approach. This has the disadvantage of having to heat the total
volume of water in the storage tank to the desired temperature.
[0003] U.S. Pat. No. 4,503,810 discloses a combustion gas water
heater in which the hot combustion gases do not exchange heat with
the stored water but rather a small volume of water is quickly
heated in direct exchange with the combustion gases in an external
heat exchanger. Cold water is drawn from the bottom of the storage
tank heated in the external heat exchanger and then returned to the
upper or middle portion of the storage tank by convection.
[0004] Another problem with water heater storage tanks is corrosion
of the tank which occurs with unlined and also vitreous enamel
lined tanks. The use of non-corrodible stainless steel tanks is an
expensive solution to the problem. Plastic tanks are cheaper but
these are unsuitable for storing mains pressure hot water.
[0005] One proposal has been to use plastic lined metal tanks as
proposed in U.S. Pat. No. 4,338,888. The combustion chamber has
water walls for heat exchange. Water from the bottom of the tank is
heated in the water walled combustion chamber and the heated water
is returned to the lower portion of the tank.
[0006] Another approach for electric heated tanks is USA patent
4437484 which uses an un-pressurised plastic tank and a pump.
[0007] It is an object of this invention to provide a storage water
heater which overcomes these problems.
BRIEF DESCRIPTION OF THE INVENTION
[0008] To this end the present invention provides a combustion
water heater which includes
[0009] a) a non-pressurised water storage tank having a cold water
inlet in the lower portion of said tank and a heated water outlet
in the upper portion of said tank
[0010] b) a low heat output combustion chamber having a flue for
the egress of combustion gases
[0011] c) a heat exchange surface associated with said flue
[0012] d) means for contacting water from the lower portion of said
water storage tank with said heat exchange surface
[0013] e) means for conducting water heated at the heat exchange
surface to the upper portion of said water storage tank
[0014] f) pump means associated with the heated water outlet to
increase the pressure of water from the non pressurised tank.
[0015] By using a non-pressurised tank a plastic tank can be
utilised with the resultant advantages of longer service life due
to less corrosion. By returning the heated water from the heat
exchanger to the upper portion of the tank, temperature
stratification of the water in the tank is established. This has
the benefit that water extracted from the upper portion of the tank
is always the hottest water in the tank. The plastic used can be
any structural polymer that is heat resistant and suitable for the
application. Stratification of heated layers of water is achieved
by introducing the hot water to the top portion of the tank and
separating any hotwater being heated in the bottom of the tank from
cold water by using a separate chamber or a shroud.
[0016] The use of a low joule burner in combination with a heat
stratified tank means that the stored water can be cost effectively
heated over a longer period of time. Because the hottest layers are
adjacent the outlet there is little risk that the supply of hot
water will be interrupted. The low joule burner is preferably rated
at 1 to 2 kw.
[0017] The pump adjacent the outlet ensures the that the water
pressure from the hot water taps will be at a pressure equivalent
to mains pressure. Preferably the pump is a multi compartment
pressure transfer module that utilises the mains particularly high
density polypropylene. The tank can be formed by any suitable
moulding technique although for high density poly propylene blow
moulding is preferred. The storage volume of the tank may be
greater than that which is conventional for gas heaters but
equivalent to that of electric storage heaters intended to supply
similar daily volumes. A domestic size tank would be 315 litres
storage capacity but smaller or larger sizes are feasible. A large
tank is required when the power rating of the combustion chamber is
selected to provide a time to heat the whole tank of about 12 to 20
hours. The dimensions of such a tank are typically about 660 mm
diameter and 1700 mm height. For smaller tanks a higher rating
burner could be used to provide a larger proportion of the tank
with hot water.
[0018] The tank 1 is provided with an outer skin 2 and a layer 3 of
insulation to limit heat losses from the tank. The outer skin is
preferably of a hard wearing, tear resistant and weather resistant
plastic such as high density polyethylene, low density
polyethylene, ABA, ABS or even sheet metal. Sheet metal has the
advantage of having lower thermal expansion characteristics and may
also be less expensive. The insulation material can be any suitable
material with low heat conductivity with polyurethane foam being
the preferred material.
[0019] The removable lid 4 also has an insulation layer between an
inner and outer skin. Because the tank is not intended to operate
at mains water pressure the seal between the tank and the lid need
not be particularly strong. This means that access to the interior
of the tank for manufacturing and maintenance purposes is much
easier than for mains pressure tanks. The lid 4 is arranged to seat
on the tank above the operating water level 9 of the tank.
[0020] The pressure transfer module 5 is of the type described in
WO97/46805. The contents of that patent are incorporated herein by
reference. Cold water passes into the module through mains pressure
cold water inlet 10 and after being reduced in pressure the water
flows through cold water outlet 12 into the lower portion of the
tank.
[0021] The PTM is either positioned in the top of the tank or draws
hot water from the top layer of water in the tank. Hot water is
drawn into the PTM 5 and exits at mains pressure through the hot
water outlet 11.
[0022] In the embodiment shown in FIG. 1 cold water from the bottom
of the tank is drawn into the heat exchanger 7 and passes up the
heated water delivery pipe into the upper section of the tank. The
external heat exchanger 7 comprises a gas flame 6 mounted in a
chamber with an associated air inlet. The hot combustion gases are
caused to circulate around pipes or water walls in the heat
exchanger and then to exit via the flue outlet 8. In FIG. 1 the
flue is shown as balanced with the flue outlet 8 being adjacent the
air inlet for gas flame 6.
[0023] The embodiment of FIG. 2 is a first version of a tank with
the gas flame 6 and heat exchanger 7 disposed in the lower portion
of the tank. A shroud or convection flume 13 confines the cold
water entering the bottom of the tank through inlet 12 so that it
is in heat exchange relation ship with the external surface of the
heat exchanger 7. The arrangement of heat exchanger 7 within the
shroud 13 may be in accordance with the well known principals of
heat exchangers in increasing the heat transfer surface area
without impeding the flow of flue gases from the flame 6 to the
flue outlet 8. In FIG. 2 the flue outlet 8 is disposed in the lid 4
of the tank. To maximise the heat transfer the hot water delivery
pipe 14 surrounds the vertical flue 16 up into the upper portion of
the tank to terminate just below the water level 9.
[0024] In the embodiment of FIG. 3 which is a variation of the
embodiment of FIG. 2 the flue is balanced with the flue outlet 8
being adjacent the air inlet for flame 6. As shown in FIG. 3 the
heat exchanger 7 provides a path for the flue gases which traverses
the base of the tank and then doubles back . The arrangement of
heat exchanger 7 can be designed to provide maximum heat transfer
area between the conduits for the combustion gases and the water
contained within shroud 13. In the embodiment of FIG. 3 the hot
water delivery tube 14 can be of smaller diameter.
[0025] In all three embodiments the operation of the gas flame may
be fan assisted to ensure complete combustion of the fuel and to
assist in the positive flow of the flue gases to the outlet 8. In
the embodiment of FIGS. 2 and 3 the fan and gas mixing valve may be
situated on the top of the tank to avoid having them attached to
the external wall of the unit which would increase the floor
imprint of the unit. This has the additional advantage of keeping
the fan away from dust accumulation near the bottom of the unit.
The fan and gas valve can be a unit in which the speed of the fan
controls the gas inlet valve to maintain the correct air/gas
mixture required for clean combustion. A pre-mix burner with a DC
fan is preferred. In a simple unit with on temperature sensor a one
speed fan would be suitable. A two speed fan would need two
temperature sensors one higher than the other.
[0026] The burner used with a 315 litre tank in accordance with any
of the above 3 embodiments is rated at 5-6 Mega-joules/hour which
given the efficiency of the stratification in the tank and the
insulation on the tank gives a heating out put of about 1.1-1.3 Kw.
The efficiency rating is about 80%. The burner may be a simple
flame into the heat exchanger or may be a flame supported on a
thimble like mesh shroud or even a longer mesh burner to extend
within the tank for the embodiments of FIGS. 2 and 3.
[0027] The burner can be controlled by a control unit which
includes one or more temperature sensors within the tank. With one
sensor placed near the bottom of the tank a temperature above the
set temperature for the tank would trigger the switching off of the
burner. With two sensors one near the top and one near the bottom
variable heating rates can be utilised. A low temperature at the
upper sensor would trigger a higher input rate for the fan to
increase the heat out put until the upper sensor exceeded the set
temperature.
[0028] For domestic dwellings, the water heater of this invention
provides an uninterrupted supply of mains pressure hot water at low
energy cost and low green house emissions. In addition the tank has
a longer useful life than conventional gas water heaters of
equivalent capital cost.
* * * * *