GB2521610A

GB2521610A - Point-of-use water heater

Info

Publication number: GB2521610A
Application number: GB1322847.3A
Authority: GB
Inventors: Ronnie Paterson; Lee Higginbottom
Original assignee: Ebac Ltd
Current assignee: Ebac Ltd
Priority date: 2013-12-23
Filing date: 2013-12-23
Publication date: 2015-07-01
Also published as: GB201322847D0

Abstract

A water heater includes a water tank 1 having a water inlet 2, a water outlet 3, and a heating element 4. A tap or faucet T is connected to the water outlet 3, and a supply pipe 10 for connection to an ambient water supply is arranged to supply fresh water to the water inlet 2 via an expansion vessel 15. The expansion vessel has first and second connections 16 and 17 connected respectively to the supply pipe 10 and the water inlet 2 so that water flows through the expansion vessel 15 before entering the water tank 1. A waste outlet 21 is connected to the expansion vessel via a pressure release valve (PRV) 20 to conduct water to waste in the event that the pressure in the expansion vessel exceeds a predetermined maximum figure. In use, the expansion vessel prevents hot water from entering the waste outlet 21 assisted by separation of the first and second connections 16 and 17.

Description

POINT-OF-USE WATER HEATER

TECHNICAL FIELD OF THE INVENTION

This invention relates to point-of-use water heaters of the kind which are often installed in a kitchen cabinet under a sink to provide a source of boiling water on demand.

BACKGROUND

Point-of-use water heaters which provide an immediate supply of boiling water are becoming increasingly popular in new builds and kitchen refits. Water is stored under pressure and heated above the temperature at which water boils at atmospheric pressure so that when the hot water is dispensed it immediately starts to boil.

When water is heated in a pressure tank, expansion of gases dissolved in the water may typically cause the volume of the water to expand between 2 and 5%. In one known system a non-return valve is included in the water supply pipe and a pressure release valve is placed between the non-return valve and the tank. When a predetermined pressure is exceeded the pressure release valve will open allowing boiling water to escape into a waste pipe. This arrangement has a number of drawbacks, one being that a quantity of hot water, i.e. the expansion volume, is lost during every heating cycle. This reduces the energy efficiency of the system and increases the running costs. In some circumstances it could also be unsafe to discharge boiling water into a low pressure waste system.

Another known way of allowing for expansion is to incorporate a sealed expansion vessel between the non-return valve and the pressure tank. The sealed vessel contains a membrane which separates the water from an internal gas space within the vessel.

Over a period of time however, there is a tendency for the pressurised gas to leak through the membrane, which reduces the expansion capacity. Furthermore, high water temperatures in contact with the membrane will eventually cause it to perish.

Thirdly, bacterial growth can occur in the expansion vessel presenting a possible health hazard. Regular servicing is therefore essential to maintain the safety of the system, which is a major drawback.

Another solution which allows for internal expansion without significant heat loss is to trap a quantity of air in the pressure vessel above the water volume. When the water expands the internal air space is compressed allowing the expansion to take place. One drawback of this system is that the air space significantly reduces the volume of water which can be held in the pressure vessel. More importantly, since the trapped air is in direct contact with the water the volume of the air bubble may vary; an increase in the volume of traped air may result in air being released with the pressurised water causing a spray of scalding water, whereas a decrease in the air volume may result in dangerous overpressure within the system. Thirdly, the combination of water vapour and oxygen in the air space increases the risk of corrosion.

Another known solution is to construct the pressure vessel such that its wall can deform under pressure allowing the vessel to expand in a bellows-like manner with a rise in internal pressure.

However, this significantly increases the construction cost of the pressure vessel. There is also a risk that the deformations will introduce weaknesses into the wall of the vessel which may be prone to work hardening as the vessel expands and contracts.

Consequently the risk of failure of the pressure vessel is significantly increased.

The present invention seeks to provide a new and inventive point-of-use water heater which is energy efficient, inexpensive, easy to implement, and has a long working life.

SUMMARY OF THE INVENTION

The present invention proposes a point-of-use water heater which includes -a water tank having a water inlet and a water outlet; -a heating element, disposed within the water tank, regulated by a temperature control device; -a supply pipe for connection to an ambient water supply, the supply pipe being arranged to supply fresh water to the water inlet; and -a discharge valve (e.g. a tap or faucet) connected to the water outlet to control the flow of heated water through a discharge orifice; characterised by -an expansion vessel having first and second connections connected respectively to the supply pipe and the water inlet so that water flows through the expansion vessel before entering the water tank; and -a waste outlet connected to the expansion vessel via a pressure release valve to conduct water to waste in the event that the pressure in the expansion vessel exceeds a predetermined maximum figure.

The invention also provides a point-of-use water heater which includes an expansion vessel having a first connection disposed in a lower region of the expansion vessel and a second connection disposed in an upper region of the expansion vessel.

The invention also provides a point-of-use water heater which includes an expansion vessel having a waste outlet positioned at or adjacent to a supply pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. In the drawings: Figure 1 is a schematic diagram of a point-of use water heater in accordance with the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The drawing shows a point-of-use water heater of the kind which is installed in a kitchen cabinet adjacent to a sink to provide a source of boiling water on demand. A water tank 1 has a water inlet 2 and a water outlet 3, preferably both disposed at the top of the tank. A heating element 4, e.g. a suitably insulated electrical heating element, is disposed within the water tank 1, regulated by a temperature control device comprising a temperature sensor or thermostat 5 suitably positioned in the top wall of the tank. The water outlet 3 is arranged to supply heated water to a tap (faucet) T which comprises a manually operable discharge valve 6 controlling the flow of heated water through a discharge orifice 7.

A supply pipe 10 is connected to an ambient water supply such as a water main, usually via a filter (not shown) and a non-return valve 11, to supply fresh water to the water inlet 2 and thus replenish the water tank when hot water is discharged by the tap T. The fresh water from the supply pipe 10 flows through an expansion vessel 15 before entering the water tank 1. In a preferred embodiment the expansion vessel 15 is of elongate cylindrical shape with a vertical axis and has a first connection 16 positioned co-axially in a lower region of the expansion vessel, and second connection 17 positioned co-axially in an upper region of the expansion vessel, the second connection 17 being joined to the inlet 2 of the water tank via a short length of feed pipe 18.

Water from the supply pipe 10 enters the expansion vessel 15 through the first connection 16.

A pressure release valve (PRV) 20 is also connected to the lower region of the expansion vessel 15 via the first connection 16. As is well known, the PRV may comprise a spring-loaded piston which normally holds the valve closed, but when the pressure at the connection 16 exceeds the spring pressure the piston moves to open the valve. (See inset schematic diagram.) The PRV is thus arranged to release water from the bottom of the expansion vessel 15 to a waste outlet 21 in the event that the pressure in the expansion vessel exceeds a predetermined set figure, optionally via a tundish to reduce the risk of back-contamination. The PRV may typically be set to open at about 6.5 BAR (95 psi).

After the water heater has been installed the tap I is opened to allow ambient water to enter the system from supply pipe 10, filling the tank 1 via the expansion vessel 15. Once filled, the heater 4 can be turned on. During heating, the PRV 20 allows the pressure in the system to reach its set pressure of about 95 psi.

Since the system is pressurised the water in the tank 1 can attain a temperature of about 110 degrees Celsius (i.e. above the boiling point at atmospheric pressure) controlled by the sensor 5. When the set pressure is reached the PRV 20 releases a small quantity of water into the waste outlet 21. The release rate is relatively slow so that the water only flows in a drip-wise manner. Therefore, as the temperature in the hot tank rises and the water expands, hot water flows back down the feed pipe 18 into the expansion vessel 15, but the capacity of the expansion vessel is sufficient to prevent the hot water from reaching the first connection 16 and entering the waste outlet 21 so that only ambient water is released.

Typically, a hot tank of about 3 litres may have an expansion vessel of about 150 ml.

The physical separation between the first and second connections 16 and 17 of the expansion vessel 15 is helps to ensure that the hot water entering the vessel 15 through the second connection 17 will not reach PPM at the first connection 16, but the fact that the second connection is higher than the first connection further ensures that only ambient water escapes. Hot water is less dense than ambient water so it tends to remain near the top of the vessel.

Placing the PRV at the second connection 16 will also ensure that ambient water is more likely to be discharged. As a result, the heated water will remain above a certain level L in the expansion vessel whereas the water below that level will always be ambient.

When the tap T is opened to dispense boiling water from the discharge orifice the system pressure will fall towards the supply pressure and the hot water at the top of the expansion vessel 15 re-enters the water tank 1 as ambient water enters the bottom of the vessel through the non-return valve 11. Less energy is therefore required to re-heat the water in the tank 1 to the full operating temperature with a shorter recovery time, and energy is not lost by releasing hot water to waste.

Since the expansion vessel 15 is regularly flushed by supply water whenever the tap T is opened there is little or no risk of bacterial growth in the expansion vessel.

Whilst the above description places emphasis on the areas which are believed to be new and addresses specific problems which have been identified, it is intended that the features disclosed herein may be used in any combination which is capable of providing a new and useful advance in the art.

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Claims

CLAIMS1. A point-of-use water heater which includes -a water tank having a water inlet and a water outlet; -a heating element, disposed within the water tank, regulated by a temperature control device; -a supply pipe for connection to an ambient water supply, the supply pipe being arranged to supply fresh water to the water inlet; and -a discharge valve (e.g. a tap or faucet) connected to the water outlet to control the flow of heated water through a discharge orifice; characterised by -an expansion vessel having first and second connections connected respectively to the supply pipe and the water inlet so that water flows through the expansion vessel before entering the water tank; and -a waste outlet connected to the expansion vessel via a pressure release valve to conduct water to waste in the event that the pressure in the expansion vessel exceeds a predetermined maximum figure.
2. A point-of-use water heater according to Claim 1 in which the first connection is disposed in a lower region of the expansion vessel and second connection is disposed in an upper region of the expansion vessel.

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3. A point-of-use water heater according to Claim 1 or 2 in which the waste outlet is positioned at or adjacent to the first connection.
4. A point-of-use water heater substantially as described with reference to the drawings.* * * * * * * *