WO1989004442A1

WO1989004442A1 - Instantaneous hot water system

Info

Publication number: WO1989004442A1
Application number: PCT/AU1988/000425
Authority: WO
Inventors: Walter Iwanicki; Manohar Patil
Original assignee: South Australian Gas Company
Priority date: 1987-11-02
Filing date: 1988-11-02
Publication date: 1989-05-18

Abstract

An instantaneous gas hot water heater, the heater (1) being controlled by a controller (8) which senses the outlet water temperature (5), the water inlet temperature (4) and the water flow rate (6). The controller (8) is pre-set with the desired water temperature, and the controller (8) thus calculates the heat required and adjusts the gas flow rate accordingly via a gas modulating valve (14).

Description

INSTANTANEOUSHOTWATERSYSTEM

This invention relates to an instantaneous hot water system, more particularly to a gas hot water system.

BACKGROUND OF THE INVENTION.

In our earlier Patent No. 542652 there is disclosed an instantaneous gas hot water system incorporating a solar heating panel connected to a hot water storage cylinder, the outlet from the hot water storage cylinder passing through a heating tube assembly adapted to be heated by a gas burner. The outlet from the heating tube assembly is connected to a flow switch and a temperature sensing device, the flow switch being connected through an electrical control system to operate a control gas valve and a main gas valve to control the flow of gas to a pilot burner which is ignited on sensing the flow of hot water with the temperature sensing unit controlling the control valve to regulate the flow of gas to the main burner to maintain the water at the water outlet at a desired temperature.

Thus in this known system the gas rate to the heater is modulated by monitoring the outlet temperature from the gas heater, initially the outlet temperature is pre-selected, and the actual outlet temperature is then compared with a set temperature and the gas flow rate is then modulated accordingly to maintain constant the outlet water temperature.

While this system works fairly satisfactorily, in cases of extreme changes the heat inertia would not allow the set temperature to be achieved quickly and without overshooting the temperature limits.

It is an object of this invention to provide a means whereby a vast and precise control of outlet temperature is maintained even in extremely changing conditions. While our previous Patent refers to an instantaneous hot water system connected to a storage tank which in turn is connected to a solar panel, it is to be realized that the present invention is not to be limited thereto but could be connected directly to the water supply without being pre¬ heated by a solar heating system.

BRIEF STATEMENT OF THE INVENTION.

Thus there is provided according to the invention an instantaneous hot water system, the system comprising means to measure the water inlet temperature, means to measure the water outlet temperature, means to measure the water inlet flow rate, a microprocessor, the desired water outlet temperature being set in the microprocessor, the microprocessor thus calculating the heat required to raise the water to the desired set temperature on the basis of water inlet temperature and water inlet flow rate and regulating the gas input accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS.

In order to more fully understand the invention, reference will now be made to the accompanying drawing which illustrates one embodiment of the temperature controlled hot water system.

DESCRIPTION OF THE PREFERRED EMBODIMENT.

As shown in the accompanying drawing, the heater 1 has a water inlet 2 and a water outlet 3, there being a temperature sensing device 4 on the water inlet, and also means 5 for sensing the water outlet temperature. Also in the water inlet line 2 there is provided a flow meter 6, and the outputs of these three are then fed into the input ports 7 of a microprocessor 8. The microprocessor 8 has an output port 9 to control valve 10 in the pilot gas line 11 , a main flow switch 12 connected to output port 13, and a gas modulating valve 14 connected to output port 15 for supply of gas to burner 22. Also there is provided an output 16 to control the ignition of the pilot gas flame 17 by igniter 21 , and also a gas flame detector 18 feeding back into the microprocessor 8. A power supply 19 supplies electrical power to the microprocessor 8, and the ignition and flame detector unit 20.

Thus according to the present invention, the flow sensor 6 is installed in the inlet water pipeline to measure water flow rate. At the switching on instant the following two quantities are measured,

Tin - inlet water temperature °C.

m - water flow rate kg/sec.

and assuming the efficiency of the heater is 70 percent, the required gas input is quickly modulated to the calculated value according to the flow equation:

^1 heater ♦ Gas Input Energy = m.C_p • (Tset - Tout)

^ time

where C_p is the specific heat of the water.

Thus after a small period of time, the variation in the gas input is then recalculated by the microprocessor again using the above equation.

Thus as the desired output temperature (Tset) has been set into the computer, and again assuming the heater efficiency is 70 percent, and measuring the outlet water temperature (Tout), the amount of further adjustment to the gas input is calculated and the gas input is corrected accordingly.

The central microprocessor with the measuring and control systems continuously performs this task of correcting the gas input to achieve the constant outlet water temperature irrespective of variation in the input parameters (such as inlet water flow rate, inlet temperature, changing qualities of the heat exchanger with time etc.). If the inlet water temperature is very near to or above the pre-set outlet water temperature no gas will be used.

The system gives a very fast and precise control of the outlet temperature even in extremely changing conditions.

Also the central microprocessor can also be used for other purposes such as for failure diagnosis of the heater, the ignition system, the flow rate and the temperature of the inlet water, etc.

As noted above this system can be applied to gas hot water systems with the water inlet being directly connected to the main supply, or the water inlet can be connected to a storage tank which is heated by solar heating.

Thus according to the invention, as soon as the water begins to flow, the flow valve signal immediately initiates the turning on of the pilot gas line and the initiation of the ignition mechanism to light the pilot gas, and if this does not light, the detector output which is fed into the microprocessor inhibits the opening of the main gas valve and also the gas modulating valve.

If the pilot gas flame is detected, then the main gas valve opens, and also the gas modulating valve is modulated to the correct gas flow rate as determined by the above equation.

Thus it will be seen according to the invention that there is an instantaneous gas hot water system in which the system maintains the outlet water temperature at the desired rate.

Although one form of the invention has been described in some detail it is to be realized that the invention is not to be limited thereto but can include various modifications falling within the spirit and scope of the invention.

Claims

__ ^ instantaneous gas hot water system, the system comprising a gas heater having a gas burner and pilot flame, characterized by means to sense the water outlet temperature, means to sense the flow rate of the water, a microprocessor connected to said sensing means, means to set the desired water outlet temperature into the microprocessor, whereby the microprocessor calculates the heat required to raise the water to the desired set temperature on the basis of water inlet temperature and water flow rate and regulates the gas input to the burner accordingly.

2. An instantaneous gas hot water system as defined in claim 1 including means to sense the water inlet temperature, which means is connected to the microprocessor, whereby in operation when the inlet temperature is near the pre-set outlet temperature, the microprocessor does not operate the heater.

3. An instantaneous gas hot water system as defined in claim 1 wherein said microprocessor controls a pilot valve, a main gas valve to the burner, a gas modulating valve to the burner, an ignition unit and a gas flame detector.

4. An instantaneous gas hot water heater, said heater comprising a gas burner, a pilot flame, a pilot flame control valve, a main gas valve connected to the burner, a gas modulating valve connected to the burner, characterized by a water outlet temperature sensor, a water flow rate sensor, and a microprocessor controlling said water heater, said microprocessor calculating the amount of heat required to raise the temperature of the water to a pre-set temperature, and controlling the gas modulating valve accordingly.

5. An instantaneous gas hot water heater, as defined in claim 4 further characterized by the igniter and flame sensor controlled by said microprocessor, and a water inlet temperature sensor connected to said microprocessor, whereby said microprocessor actuates said igniter only when the pre-set temperature is higher than said inlet temperature.

6. An instantaneous gas hot water heater substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.