GB2297832A

GB2297832A - Water heating system

Info

Publication number: GB2297832A
Application number: GB9602054A
Authority: GB
Inventors: Thomas Robison Carruthers
Original assignee: VENTANK PRODUCTS Ltd
Current assignee: VENTANK PRODUCTS Ltd
Priority date: 1995-02-08
Filing date: 1996-02-01
Publication date: 1996-08-14
Anticipated expiration: 2016-02-01
Also published as: NL1002281C2; NL1002281A1; GB2297832A8; GB9502396D0; GB2297832B; GB9602054D0

Abstract

A central heating and hot water system has a condensing type of gas-fired boiler 11 connected to supply hot water to radiators 12 and to a cylinder 13 for indirect heating of tap water stored in the cylinder 13. A system controller 40 is arranged to sense the temperature of the stored water in the cylinder 13 and, when the sensed temperature is below a first value, to cause the boiler 11 in its ON condition to deliver its full output to the cylinder 13 until such time as the sensed temperature equals said first value. Thereafter, the controller 40 is arranged to cause the boiler 11 to deliver its full output to the radiators 12 whilst thermostatically sensing the temperature of the water in the radiators 12. When the sensed temperature exceeds a second value, the controller 40 causes the boiler 11 to be held in its OFF condition whilst recirculating the radiator water around the radiators 12 in a circuit which bypasses the boiler 11. Said second value is selected so that the boiler 11 operates in its condensing mode when delivering to the radiators 12.

Description

WATER HEATING SYSTEM This invention relates to central heating and hot water systems primarily for domestic premises.

Modern central heating and hot water systems comprise a boiler which supplies heated water to a plurality of radiators for space heating and to a cylinder for indirect heating of tap water. Provision can be made in the system for accommodating thermal expansion of the heated water, for providing make-up water to replace losses due to leakage, and to pressurise the system. These provisions may be provided as described in European Patent Specification No. 260989 in order to dispense with high level storage cisterns or feed tanks and thereby render the system completely self contained. Alternatively these provisions can, of course, be provided by the traditional BS domestic central heating designed system.

In order to improve the efficiency of boilers for use in such systems there has recently been introduced to the market a gas-fired condensing type of boiler which is said to operate at an efficiency of at least 86% when operating in its condensing mode as against the efficiency of a conventional boiler at about 70%. The condensing boiler only operates in its condensing mode when the temperature of the water returned to the boiler is lower than the predetermined dewpoint temperature. The dewpoint at which condensate forms in the boiler is about 54OC.

It is an object of the present invention to provide a new and improved central heating and hot waster system which utilises a condensing type of gas-fired boiler.

According to the present invention there is provided a central heating and hot water system comprising a condensing type of gas-fired boiler which is connected to supply heated water to an arrangement of radiators for space heating and to a cylinder for indirect heating of tap water stored in the cylinder, the system comprising a controller for selectively turning the boiler ON and OFF, and wherein the improvement comprises a) thermostatically sensing the temperature of the stored water at a predetermined location in the cylinder and when the sensed temperature is below a first value causing the boiler in its ON condition to deliver its full output to the cylinder until such time as the sensed temperature equals said first value, thus giving priority to heating the stored hot water and thereafter b) causing the boiler to deliver its full output to the radiator arrangement, thermostatically sensing the temperature of the water in the radiator arrangement and when the sensed temperature exceeds a second value causing the boiler to be held in its OFF condition whilst recirculating the radiator water around the radiator arrangement in a circuit which by passes the boiler, said second value being selected so that the boiler operates in its condensing mode when delivering to the radiator arrangement.

The thermostatic sensing of the water temperature in the radiator arrangement may be at any suitable location in that arrangement. For example, in the flow line to the radiators or in the return line from the radiators.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 schematically illustrates a central heating and hot water system according to the present invention; and Fig. 2 is a control circuit schematic for the Fig. 1 system.

The system 10 shown in Fig. 1 comprises a boiler 11 which is of the gas-fired condensing type (for example as marketed by the Ideal Standard Company) and delivers its heated water output to an arrangement of radiators 12 and also to a cylinder 13 for indirect heating of tap water.

Cylinder 13 can be of the type described in European Patent Specification No. 260989 having a port 13A for receiving cold tap water via a pressure regulator 14 from a mains supply provided at 14A and delivering heated tap water from port 13B to tap 15 or alternatively by the traditional B.S.

domestic heating designed systems. Heating of the tap water is provided by a coil 16 inside cylinder 13 which is fed from the boiler 11 as will be explained. Cylinder 13 can be internally partitioned to provide an expansion chamber for the heated boiler water in the system and access to this is via port 13C. Cylinder 13 is of comparatively low volume such as 60 litres and can be highly insulated externally with about 80 mm thickness of foam insulation.

The pipework which interconnects the various components of the system 10 comprises boiler output pipe 20 which via T-junction 21 and pump 22 delivers to an electrically-controlled 2-way valve 23 so that the boiler output is fed to either the radiator arrangement via feeder 24, or the coil 16 via feeder 25. Return water from the radiator arrangement traverses pipe 26 which is exclusive to the radiator arrangement, and thereafter collects return water from the coil 16 at T-junction 27. The return water is then delivered to an electronically-controlled 2-way Tvalve 30 and depending upon the setting of valve 30 either the return flow is directed to boiler return pipe 32 or the return flow is recirculated to the pump 22 by pipe 33 which connects into T-junction 21.Additionally pipe 33 is connected into port 13C so that part of pipe 33 is dual purpose and, of course, at all times pipe 33 is water filled. For the purpose of facilitating initial balancing of the system return pipe 26 can be cross-connected to the input of 2-way valve 23 via valve 35. During normal operation of the system valve 35 is essentially fixed and merely provides a by-pass for both the radiator arrangement and the coil 16.

ON/OFF control of the boiler 11 and of the pump 22 is provided by a controller 40 operating under the influence of a time clock programmer 41 in association with a boiler thermostat (not shown) and a room thermostat (not shown).

However, additionally, temperature sensors 28 and 29 are provided in the system to deliver signals for operating valves 23 and 30 and for signalling to the controller 40 whether or not to hold the boiler 11 in the OFF condition.

The temperature sensor 28 is located in the radiator return pipe 26 prior to the Tee-junction 27 and therefore only senses the return water temperature from the spaceheating radiators 12 or alternatively on the radiator flow pipe 24 after control valve 23. Temperature sensor 29 is located in the cylinder 13 and therefore only senses the stored water temperature. The radiator temperature sensor 28 is set at or about 400C whereas the cylinder temperature sensor 29 is set at or about 700C for a boiler output temperature of 800C.

When the system starts from cold boiler 11 and pump 22 are energised by controller 40. Cylinder temperature sensor 29 controls valve 23 to deliver the entire boiler output to coil 16 and signals the controller 40 to hold the boiler 11 in its ON condition. Cylinder 13 can be comparatively low volume, of the order of 60 litres, and fitted with a fast recovery high performance coil 16 and externally very heavily lagged to prevent heat loss so that the temperature of the stored water in the cylinder 13 very rapidly rises, typically in about 10 or 15 minutes, to the set temperature of 700C. At this point temperature sensor 29 controls valve 23 to deliver the entire boiler output to the delivery pipe 24 for the radiators 12 and signals controller 40 enabling controller 40 to operate according to the sensed temperature of radiator temperature sensor 28.

If the sensed return water temperature is below the 400C setting of temperature sensor 28 valve 30 is controlled, by temperature sensor 28, to return the flow via pipe 32 to the boiler 11 with the boiler 11 in its ON condition. However, when the pre-set temperature is reached temperature sensor 28 controls valve 30 to recirculate the flow via pipe 33, thereby by-passing the boiler 11, and signals controller 40 accordingly so that boiler 11 can be de-energised to its OFF condition. Pump 22 of course continues to run. When the sensed temperature falls to say 40"C or thereabouts temperature sensor 28 again cuts in to reset valve 30 so that the return water is delivered to the boiler 11 which is reenergised by controller 40 because it has received the required signal from temperature sensor 28.This cycle of events continues until such time as there is a significant draw of tap water from tap 15 which causes the temperature sensed by cylinder temperature sensor 29 to fall to say below 700C. When this occurs valve 23 is reset by temperature sensor 29 to deliver the entire boiler output to the coil 16 with boiler 11 energised and in its ON condition and valve 30 delivering return flow to pipe 32.

If the boiler design requires a very small amount of water passing through it at all times this can be accommodated even with the boiler in the OFF condition by a controlled by-pass 43, incorporating a valve, similar in purpose to valve 35. This by-pass would be set so as not to interfere with the primary purpose of temperature sensor 28 and valve 30.

The preset temperature value for temperature sensor 28 can be manually adjustable and can be set in relation to the particular boiler 11 so that when return water is delivered to the boiler by the valve 30 the boiler is obliged to operate in its condensing mode.

The preset temperature value of the temperature sensor 28 is manually adjustable, typically in observation with a dial thermometer on the pipe line. The end user has the option two choose the operating return temperature of the system at any temperature below the dewpoint temperature of about 540C. In practice, the lower the return temperature the higher the efficiency of the condensing boiler but there is a compromise if adequate space heating from the radiator arrangement is to be achieved. A suitable compromise return temperature is about 400C for a boiler 11 which has a design delivery temperature of 800C. The 400C setting of temperature sensor 28 forces the boiler to deliver only at a comparatively low temperature of 600C. On the other hand it will be appreciated that when the hot water temperature sensor 29 is operational to control the system the boiler output is permitted to deliver at its design temperature of 800C.

By way of example Fig. 2 illustrates a control circuit schematic which is capable of controlling the performance of the system 10 to that previously described. The control circuit can be achieved by an electrical/mechanical means, or alternatively by means of printed circuit featuring a wholly electrical thermistor type of temperature sensor.

As has previously been stated temperature sensor 28 may be located in the flow line 24 to the radiator arrangement. In this case the preferred setting is 60"C which forces boiler 11 to deliver at 600C whilst the return temperature is in the region of 400C due to the temperature drop over the radiator arrangement.

Claims

1. A central heating and hot water system comprising a condensing type of gas-fired boiler which is connected to supply heated water to an arrangement of radiators for space heating and to a cylinder for indirect heating of tap water stored in the cylinder, the system comprising a controller for selectively turning the boiler ON and OFF, and wherein the improvement comprises a) thermostatically sensing the temperature of the stored water at a predetermined location in the cylinder and when the sensed temperature is below a first value causing the boiler in its ON condition to deliver its full output to the cylinder until such time as the sensed temperature equals said first value, thus giving - priority to heating the stored hot water and thereafter b) causing the boiler to deliver its full output to the radiator arrangement, thermostatically sensing the temperature of the water in the radiator arrangement and when the sensed temperature exceeds a second value causing the boiler to be held in its OFF condition whilst recirculating the radiator water around the radiator arrangement in a circuit which by passes the boiler, said second value being selected so that the boiler operates in its condensing mode when delivering to the radiator arrangement.

2. A system according to claim 1, wherein the thermostatic sensing of the water temperature in the radiator arrangement is made in the flow line to the radiators or in the return line from the radiators.

3. A system according to claim 1 or 2, wherein said first temperature value is about 700C and said second temperature value is about 40"C.

4. A central heating and hot water system substantially as hereinbefore described with reference to the accompanying drawings.