IMPROVEMENTS FOR RESIDENTIAL TANK WATER HEATERS TO DECREASE THERMAL INERTIA, INCREASE EFFICIENCY/SAFETY OPERATION

AMELIORATIONS AUX CHAUFFE-EAU RESIDENTIELS POUR DIMINUER L'INERTIE THERMIQUE ET AUGMENTER L'EFFICACITE ET LA SECURITE DE FONCTIONNEMENT

English Abstract

This invention mainly consists of a water tank with a conventional cylindrical

shape where water is heated in the traditional way using a Vertical Heating
Pipe
(VHP) (usually around 100 mm diameter) where combustion gases flow upwards
from the burner located at the bottom of the tank. The main innovation is the
addition of a water finned-tube concentric with the VHP that increases overall
heat transfer surface area in more than 70%. The special feature of this tube
is
that it transfers heat to the water promoting an exclusive flow circulation
from
bottom to top of the tank, reducing inconvenient cold and hot water mixing
inside
the tank. On this manner, cold water from the bottom of the tank flows inside
the
tube receiving heat from the finned-tube and exiting it to the to the upper
part of

the water tank. The circulation of the water inside the tank is also made in
an
ordered manner using a baffle that restricts water movement in the upper part.

This process creates temperature stratification inside the tank, where hotter
water
is kept at the upper part. This guarantees that the water initially consumed
from
upper part of the tank has much higher temperatures than the bottom. This
increases the water tank virtual capacity in more than 60% for the same water
tank volume. Another innovative process is that the combustion air used for
the
burner, located at the bottom at the tank, comes from the top of the tank,
through
a separate tube and a small fan. This provides a safety measure for virtually
eliminating the risk of vapour lock explosion issues. The increased surface
area
from the finned-tube guarantees an increase in heat transfer surface area with
a
corresponding increase in overall efficiency. The fins also serve to rotate
the
combustion gases around the tubes to increase the contact of the combustion
gases with the metal parts. The finned-tube increases further the water
temperature to the upper part of the tank so that it can provide virtually
endless
hot water as long as the burner operates.

Claims

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CLAIMS:


I claim:


1. The use of a finned-tube running vertically upwards concentric to the
conventional
vertical heating pipe that provides additional heat transfer surface area to
heat the
water.


2. The use of a finned-tube as described in claim I that creates a natural
convective
movement from the bottom of the tank to the top of it. I claim the idea of
using this
finned-tube located in the center of the tank so that this concept can be
easily be
incorporated in existing conventional water heater designs.


3. The use of a twisted fin in the finned-tube as described in claims I and 2
that direct
the gases in a circular and spiral way around both vertical heating pipe and
finned
tube increasing the contact between combustion gases and metal parts.


4. The potential use of a fan to aspirate air from the top of the tank to the
burner located
at the bottom. The fan also helps to overcome the higher pressure-drop across
the
Vertical Heating Pipe and the finned-tube. This cold combustion air coming
from the
top of the tank is a safety future against vapour lock safety issues in the
system.


5. The use of a water tank as described on claims 1, 2 and 3 that can be used
as a
limitless water supply system with the addition of the finned-tube as
described on the
mentioned claims.




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6. The use of baffles that minimize convective movement of water to the tank
in the
upper part of it. The upper part receives hot water flow from both the
Vertical
Heating Pipe and finned tube.


7. All the claims above contribute for creating temperature stratification in
the tank and
we claim that this allows more hot water available without mixing with
incoming
water as water is consumed.

Description

CA 02566458 2006-11-01
Application for Letters Patent

Improvements for Residential Tank Water Heaters to Decrease
Thermal Inertia, Increase Efficiency/ Safety Operation
Luiz Claudio Vieira Fernandes

Table of Contents

INVENTOR 1
ABSTRACT 2
BACKGROUND 3
SUMMARY OF THE INVENTION 4
FIGURES 6
CLAIMS 9


CA 02566458 2006-11-01
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INVENTOR:

Luiz Claudio Vieira Fernandes
30 Carlyle Ave
Ottawa, ON K 1 S 4Y3 Canada

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CA 02566458 2006-11-01
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Improvements for Residential Tank water heatess to Decrease
Thermal Inertia, Increase Efficiencyl Safety Operation

This invention consists of a high efficient water tank that uses an extra tube
that run
along the vertical axis of the vertical cylindrical water tank. The water is
heated in an
ordered manner, creating beneficial temperature stratification inside the
tank. .

Br1GKGRflUNl3-

Practically all residences in Canada utilize water heaters for comfort.
Consequently the
market size is superior to 4 million units with at least $ 300 each,
corresponding to a
market size well above $ 1 billion dollars. The North American market is much
larger

reaching more than 10 billion dollars. Despite this market size, the majority
of gas water
heaters available today are relatively bulky for their water capacity, have
low thermal
efficiency and produce relative high levels of harmful air emissions. On the
other hand,

instantaneous gas water heaters are relatively new in the North American
market with
smaller size with the claim that they can provide endless supply of hot water.
Traditional
tank water heatess are cheaper, less efficient, have simpler heat exchangers,
and are
capable of supplying much larger amounts of hot water at the first minutes of
operation.

Is there a future for tank water heaters? This invention improves tank water
heaters
keeping some of its advantages: simplicity, capable of supplying large amounts
of water
for short periods of time, virtually maintenance free and low capital costs.
The
improvements with this invention are overall thermal efficicncy improvements,
thermal

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storage reduction losses, safety operation enhancement and endless supply of
hot water,
similar to tankless water heaters operation.

SUMMARY OF THE INVENTION:

It is the object of the present invention to provide a more efficient, safer
and with
15 virtually same production cost as a conventional vertical cylindrical gas
fired water
heaters.

This novel water heater uses a cyiindrical shape water tank that has baffles
1(see Fig 1
next page) that separate water in individual compartments so that as water is
consumed,
there will be less mixture between new incoming water with pre-heated water in
the tank
in the upper part. Additionally, this novel water tank utilizes an additional
water finned-
tube 2 in the center, concentric to the conventional Vertical Heating Pipe
(VHP) 3 that
provides additional heat transfer surface area to heat the water (see Fig 1).
This tube
carries cold water from the bottom of the tank, heats it up and leaves hot
water on the
upper part, enhancing even further the water thermal stratification inside the
tank. This
fact and the larger heat transfer area with the additional finned-tube will
guarantee higher
thermal efficiency rates, superior to 85% mark. The stratification water
effect due to the
internal baffles and the water finned-tube substantially increases the total
water tank
capacity. For instance, with a similar size for a conventional 50 gallons this
design can
provide at least 80 gallons or 64% more of hot water at virtually constatrt
temperature.
Conventional water heaters are limited in this respect due to the intense
mixing process
that occur as the cold water penetrates the tank, stirring the flow and
subsequently

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mixing with the hot water. The natural convection mechanism promoted by the
hot
vertical heating pipe (VHP) also creates a circular flow motion inside the
tank that
reduces the water stratification process and increases mixing. The new design
uses
baffles to minimize mixing and the water finned-tube (Fig 1) also brings hot
water to the
upper part also minimizing mixing. Additionally safety features such as
combustion air
inlet at the top of the tank 4 minimizes the risk of explosions/ fire
associated with
flammable vapours that can be present in the water tank surroundings. The
combustion
air is admitted through a small fan 5 that also compensates for the higher
pressure-losses
that occur with the insertion of the finned-tube. The burner can operate under
low/ high
intensity mode (between 20,000 and 120,000 BTU/ h capacity) so that it can
operate at
ionger periods of time under less transient conditions that contributes to
lower thermal
efficiencies. The construction of the tank is relatively simple and the water
finned-tube is
easily welded to both the bottom and top of the cylindrical water tank as
shown by figure
1. Ignition can be achieved with a piezoelectric igniter.



CA 02566458 2006-11-01
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1.0 Technical Approach
1.1 Capacity

The new designer allows a substantial reduction on the mixing of cold and hot
water
inside the tanks for three reasons: a) The use of water tubes that take water
from the
bottom of the tank to the upper part minimizing natural convective movernent
caused by
density differences. The movement of water during the heating process is
limited inside
the tubes and their ends. In conventional water tanks this movement occurs
inside the
entire tank so that the mixing process is intense. b) Use of baffles inside
the water tank c)
Reducing heat transfer from the center tube (VHP) to the water tank with the
addition of
the finned-pipe.

1.2 Installed Cost

A traditional water heater manufacturer can easily build this novel water tank
since the
basic geometry is kept. The water finned-tube is welded at both ends of the
cylinder.. The
baffles can be spot welded in the central cylindrical part. The additional
cost associated
with the finned-tube is compensated for the smaller tank size (at least 50%
less volume)
if a similar water capacity (50 gallons) is desired.

1.3 Efficiency

The new design has thermal efficiencies above 80% mainly due to the heat
exchanger
design that uses both the conventional Vertical Heating Pipe (VHP) and the
finned-
tube.surfaces. The electrical power necessary to move the fan represent less
than 1% of

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CA 02566458 2006-11-01
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the total power delivered by the heater.
1.4 Safety

This design allows combustion gases to be admitted from the top of the tank
minimizing
risks associated with possible flammable gases heavier than air present in the
surroundings.

2.0 Economics

2.1 Manufacturing Costs

As explained earlier, for a 50 gallons capacity water heater, it is expected
that the new
design will reduce the total volume by at least 60%. This is due to the
stratification
process that occurs inside the heater, minimizing diffusion of cold incoming
water. Also,
the heating mechanism that uses a finned-tube to transport the hot water to
the upper part
of the tank is also responsible for a significant reduction of convective
water movements
(and therefore mixing) inside the tank.

2.2 Distribution and Retail Costs

Since both designs are not radically different than the traditional
cylindrical water heater
design, any existing water heater manufacturer can adapt its manufacturing
line to these
geometries. Retail cost is expected to be lower than $ 400,00 and installation
cost below
$ 180.00. Total product cost is expected to be between $ 100 to $ 130 dollars
per unit.

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