GB2267337A

GB2267337A - Water heating system control

Info

Publication number: GB2267337A
Application number: GB9309484A
Authority: GB
Inventors: Thomas Robison Carruthers
Original assignee: VENTANK PRODUCTS Ltd
Current assignee: VENTANK PRODUCTS Ltd
Priority date: 1992-05-28
Filing date: 1993-05-07
Publication date: 1993-12-01
Anticipated expiration: 2013-05-07
Also published as: GB9309484D0; GB2267337B; GB9211294D0

Abstract

A central heating and hot water system (10) incorporates a condensing type of gas-fired boiler (11) connected to supply heated water to space heating radiators (12) and to an indirect cylinder (13) for heating tap water. A control device (40, 41) selectively turns the boiler (11) ON or OFF. A thermostat (28) senses the temperature of water to be returned to the boiler and controls a 2-way T-valve (30) to direct the return flow to the boiler (11) when the sensed temperature is below a preset value or to direct the return flow back to the radiators (12) and to the cylinder (13) when the sensed temperature is above the preset value. The control device (40, 41) holds the boiler in the OFF condition when the sensed temperature is above the preset value. <IMAGE>

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. This invention can, of course, relate to a 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 a predetermined temperature. The dewpoint at which condensate forms in the boiler is 550C.

It is an object of the present invention to provide a new and improved central heating and hot water 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 a plurality of radiators for space heating and to a cylinder for indirect heating of tap water, the system comprising a control device for selectively turning the boiler ON and OFF, and wherein the improvement comprises thermostatically sensing the temperature of the water to be returned to the boiler and recirculating that water around the system without return to the boiler when the sensed temperature exceeds a predetermined value, and operating the control device to hold the boiler in the OFF condition during such recirculation.

An embodiment of the present invention will now be described by way of example with reference to the accompanying schematic drawing.

The system 10 shown in the drawing 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 a plurality 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. 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 is internally partitioned to provide an expansion chamber for the heated boiler water in the system and access to this is via port 13C.

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 3-way valve 23 so that the boiler output is fed to either or both of the radiators 12 via feeder 24 and the coil 16 via feeder 25. Return water from the radiators 12 traverses pipe 26 which is now exclusive to the radiators, and also collects return water from the coil 16 at Tee-junction 27. The common flow of return water then has its temperature thermostatically sensed by thermostat 28 the output of which electrically controls a 2-way T-valve 30 and 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 pipe 26 can be cross-connected to the input of 3-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 radiators 12 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 41 in association with a boiler thermostat (not shown) and a room thermostat (not shown) in a manner which is conventional. However, thermostat 28 in addition to operating the 2-way T-valve 30 delivers a signal to the controller 40 and the arrangement is such that when valve 30 directs the return water into pipe 33 (thereby by-passing the boiler 11) the boiler 11 is held in the OFF condition.This is achieved by the thermostat 28 delivering a first signal when the sensed water temperature is less than a preset value (of anything between 400C and 700C) in which case valve 30 is electrically operated to permit water flow only from pipe 26 to pipe 32 and this first signal is delivered to the boiler 11 to enable the boiler to turn ON if required to do so by the controller 40 and time clock 41. When the sensed water temperature is greater than the present value thermostat 28 delivers a second signal to achieve the opposite result. Conveniently the second signal is provided by the absence of the first signal and the valve 30 is mechanically spring biassed to permit water flow only from pipe 26 to pipe 33 so that the return water by passes the boiler 11 which simultaneously is held in the OFF condition by the second signal.

In the second signal condition the flow of water to the boiler 11 ceases entirely, however if the boiler design requires only a very small amount of water passing through it at all times this can be accommodated 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 thermostat 28 and valve 30.

The preset temperature value for thermostat 28 is manually adjustable and is 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.

In the illustrated embodiment thermostat 28 and valve 30 are physically associated with the cylinder 13 to provide an integrated package but in a modification they could be physically separate and can be associated with boiler 11 with suitable adjustment of the pipework such that by pass pipe 33 is located near the boiler.

The preset temperature value of the thermostat 25 is manually adjustable, in observation with a dial thermometer 44 on the pipe line between the thermostat 28 and the two-way Tee-valve 30. The end user has the option to choose the operating return temperature of the system. In practice the lower the return temperature the higher the efficiency of the condensing boiler.

Claims

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 a plurality of radiators for space heating and to a cylinder for indirect heating of tap water, the system comprising a control device for selectively turning the boiler ON and OFF, and wherein the improvement comprises thermostatically sensing the temperature of the water to be returned to the boiler and recirculating that water around the system without return to the boiler when the sensed temperature exceeds a predetermined value, and operating the control device to hold the boiler in the OFF condition during such recirculation.

2. A system as claimed in claim 1, wherein the predetermined temperature is manually set and lies in the range 400C to 700C.

3. A system as claimed in claim 2, wherein the predetermined temperature is set at about 700C.

4. A system as claimed in any preceding claim, including a by-pass enabling a minimum return flow of water to the boiler when the sensed temperature exceeds the predetermined value.

5. A system as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawing.