CA2566458A1 - Improvements for residential tank water heaters to decrease thermal inertia, increase efficiency/safety operation - Google Patents

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.

Description

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:

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

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 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 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.

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 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.

Claims (7)

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.

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.