GB2282890A

GB2282890A - Hot water indicator

Info

Publication number: GB2282890A
Application number: GB9321308A
Authority: GB
Inventors: John Edward Dike; Anthony Frank Brown
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-10-15
Filing date: 1993-10-15
Publication date: 1995-04-19
Anticipated expiration: 2013-10-15
Also published as: GB9321308D0; GB2282890B

Abstract

A hot water indicator has a meter M which indicates the amount of hot water present in a domestic or commercial hot water tank in terms of percentage of tank contents. The indicator can be set by the user to indicate 100% hot water by adjusting trimming resistor R1 at a time when the water has been fully heated. The indicator functions by measuring the amount of current flowing through temperature sensing thermistors T1, T2 and T3 which are situated at three points down the surface of the hot water tank. The indicator is housed in a small plastic box, is powered by a nine volt battery, and can be situated at any convenient point local or remote to the tank. <IMAGE>

Description

HOT WATER INDICATOR Hot water for use in the home or in commercial premises such as shops offices and restaurants is usually contained in a hot water tank.The water in the tank can be heated in various ways such as gas or electricity.

This invention offers the advantage of providing an indication of the amount of useable hot water in the tank and answers the following questions: -Is there sufficient hot water for a particular use such as washing-up or having a bath ? -Is it necessary to heat more water or can energy be conserved ? -Is the hot water heater functioning correctly and heating the water to the correct temperature ? -Is the insulation fitted to the tank efficient in keeping the water warm ? According to the present invention there is provided a system of temperature sensing comprising three parallelconnected thermistors attached to the hot water tank,a moving-coil electrical panel-meter to measure the electrical current flowing through the thermistors and thereby indicate the amount of hot water in the tank,a shunt variable resistor to adjust the meter reading and a nine-volt battery to drive the circuit.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which : Figure 1 shows the schematic drawing of the circuit with the temperature sensors attached to the surface of the hot water tank.

Figure 2 shows the effect on the temperature sensors and the meter of a full tank of hot water.

Figure 3 shows the effect of only two-thirds of a tank of hot water.

Figure 4 shows the effect of only one-third of a tank of hot water.

Figure 5 shows the effect of a tank filled with cold water at ambient temperature.

Referring to the drawing Figure 1 the hot water indicator comprises a nine-volt battery B connected in series with a push-button momentary-action switch S which in turn is connected to the 100 micro ampere F.S.D panel meter N.In parallel with the meter N is a 50 ohm trimming resistor R1 set to approximately 13 ohms.The meter N and the negative pole of the battery B are connected to a twin core cable C.All of the items M,S,R1 and B are housed in a small plastic box forming the remote indicator for the hot water indicator and mounted at a suitable location for the user.

The cable C is run from the remote indicator to the hotwater tank and connected to the three 10,000 ohm dise thermistors T11T21T3 which are connected in parallel.

These thermistors Tl,T2,and T3 are affixed to the surface of a tank fitted with a lagging jacket and between the lagging jacket and the tank itself.With a pre-lagged jacket the thermistors are inserted in three holes cut in the polystyrene lagging and pushed-in to touch the tank wall.The three thermistors T1,T2 and T3 aro positioned approximately at the top of each third of the tank when it is divided into three imaginary smaller tanks standing one on top the other.

Each thermistor has a resistance which varies over the approximate range of 20,000 ohms at 10 degrees celcius to 10000 ohms at 25 degrees to 2000 ohms at 60 degrees.

With the tank full of hot water at approximately 60 degrees Celcius conditions shown in Fig 2 apply.All three thermistors will have their temperature dependent resistance reduced to approximately 2000 ohms apiece giving a parallel value of 667 ohms.Trimming resistor R1 is adjusted to give a reading on meter N of 100 microamps which represents a full tank of hot water.

Fig 3 shows the condition when approximately one third of the hot water has been drawn-off and the lower third of the tank contains water at ambient temperature.In this case the resistance of thermistor T3 has risen to 10,000 ohms and the combined parallel resistance is 909 ohms.This gives a meter reading of 73 micro-amps.If the water in the lower third of the tank was much cooler than ambient-which is normally the case with water drawn from a loft mounted tank or mains supply the resistance of T3 would be in excess of 20000 ohms,the parallel resistance would approach 1000 ohms and the meter reading would approach 67 micro-amps.This would be equivalent to two thirds or 67% of a tank of hot water.

Similarly the condition in Fig 4 shows the tank with only one third filled with hot water and two-thirds at ambient temperature and a combined thermistor resistance of 1430 ohms giving a meter reading of 47 micro-amps.This drops to 33 micro-amps or 33% hot water if the lower two thirds of the tank contain water at a temperature much lower than ambient and the resistance of thermistors T2 and T3 are forced to a much higher figure than 10000 ohms.

Similarly the condition in Fig 5 shows a tank full of cold water at ambient temperature.The combined thermistor resistance is 3333 ohms giving a meter reading of 20% hot water or less for water temperatures below ambient.

The hot water indicator can thus be used to give a remote indication of the amount of useful hot water in the tank.

Claims

CLAIMS 1. A hot water indicator comprising an indicator to indicate the amount of hot water present in the hot water tank and connected to the temperature sensors positioned at a plurality points down the vertical surface of the tank which monitor the temperature of the water in the bottom, middle and top thirds of the tank. 2 A hot water indicator as claimed in claim 1 where the circuit is powered by a 9 volt battery and controlled by a push-button switch. 3. A hot water indicator as claimed in claims 1 and 2 where the indicator is a 100 micro-ampere full scale deflection movingcoil meter shunted by a trimming resistor with a maximum resistance of 50 ohms. 4. A hot water indicator as claimed in claims 1,2 and 3 where the temperature sensors are made from disc type thermistors of nominal value 10000 ohms at 25 degrees celcius which are attached to the vertical surface of the tank underneath the lagging jacket or in the case of a pre-lagged jacket they are inserted into three holes cut into the foam so that they touch the tank wall. 5. A hot water indicator as claimed in claims 1,2,3 and 4 where the three thermistors are connected in parallel so that they represent the temperature of each section of the tank and so that the total current passed to the meter represents the total hot water in the tank. Amendments to the claims have been filed as follows

1. A system for indicating the amount of hot water in a hot water tank, said system comprising an indicator and a plurality of temperature sensors located in engagement with the tank at a corresponding plurality of positions spaced vertically of the tank, said sensors being connected in parallel in a circuit containing the indicator with the arrangement such that the reading displayed by the indicator gives an indication of the amount of hot water in the tank.

2. A system as claimed in Claim 1, in which the indicator is a moving coil meter.

3. A system as claimed in Claim 2, in which a variable resistor is connected in parallel with the meter.

4. A system as claimed in Claim 1, in which the temperature sensors are thermistors.

5. A system as claimed in Claim 4, in which there are three thermistors.

6. A system as claimed in Claim 5 in which the thermistors are disc-type thermistors of nominal value 10,000 ohms at 250C.

7. A system as claimed in Claim 1, in which the circuit is powered by a 9-volt battery and is controlled by a pushbutton switch.

8. A system as claimed in Claim 1 and substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

9. A hot water tank fitted with an indicating system as claimed in any one of the preceding claims.

10. A hot water tank as claimed in Claim 9, which tank is fitted with a lagging jacket, and in which the temperature sensors are attached to the vertical surface of the tank beneath the lagging jacket.

11. A hot water tank as claimed in Claim 9, which tank is fitted with foamed lagging, and in which the temperature sensors are inserted in holes cut in the foam so that they touch the surface of the tank.

12. A method of providing an indication of the amount of hot water in a hot water tank, said method comprising the use of a system as claimed in any one of Claims 1 to 8.