GB2086088A - Boiler control - Google Patents

Abstract

In a central heating installation having a boiler 2 heated electrically or by a burner 3 and suppling water to radiators in one or more heating zones (under the control of motorised valves M1a etc.) and preferably also to a hot water storage cylinder, the boiler thermostat T4 is rendered ineffective when no heat is demanded by any of the zone thermostats T1a etc. or by a storage cylinder thermostat, to prevent undesired rapid cycling of the boiler. The arrangement shown uses a valve V supplying a burner 3 of the boiler 2. The valve V is controlled by a thermostat T4 located in boiler 2, and supplied via parallel relays RLP and RL2. RLP becomes conductive when any one of a plurality of pairs of on-off switches SW1a etc. and thermostats T1a etc associated with respective zones to be heated are closed, while RL2 will supply current to T4 when a thermostat in a domestic hot water cylinder is closed and will also open motorised valve 8 in a pipe 4, 7 from the boiler 2 to the cylinder. When RLP is closed and supplies current to thermostat T4, it also actuates a pump P to circulate water from boiler 2 through the central heating installation. When RLP and RL2 are both 'off', valve V is closed and burner 3 extinguished whatever the temperature of water in boiler 2. When either or both RLP and RL2 are 'on', valve V opens and closes, igniting or extinguishing burner 3 in response to the control of thermostat T4. <IMAGE>

Description

SPECIFICATION Area/district heating and boiler control: codified signal This invention relates to improvements in control of central heating systems, for effecting improved economy in energy consumption.

In known central heating systems wherein a plurality of heat transfer surfaces (radiators) are supplied with hot water from a single heating tank, it is usual for the radiators in each of several zones such as a room of a house or a whole floor of an office building, to be under the control of a thermostatic switch responsive to temperature in that zone, and for the heating tank to also be controlled by a thermostat. In each case this thermostatic control may be of the mini-max kind, whereby in the case of radiators, the supply of hot water is shut off when the zone temperature exceeds a certain value, and re-opened when the zone temperature falls below a second, somewhat lower value.On the other hand in the case of a central heating tank, the gas or oil supply to a burner or the electricity supply to an immersion coil is switched off when a first higher temperature is exceeded, and restarted when the water in the tank falls below a second lower temperature.

This known arrangement imparts a useful degree of flexibility as compared with prior "all-ornothing" systems where a complete installation or a part of it was switched off or on, often with reference to the calender rather than the thermometer. However, the situation can arise, in for example a warm spell, that all the zones are above the threshold temperature for opening the valves which will admit hot water to their radiators. However, the boiler is kept running even though it has no useful 'load,' and it keeps switching itself on and off as the water temperature 'hunts' between the thermostat settings.This is of course clearly wasteful, and an object of the invention is to ensure that the boiler will be energised only when there is useful work to be done, i.e. when radiators in one or more zones are receiving heated water, so that the boiler or water heating tank is not operational when there is no demand, but can be immediately reactivated when demand arises.

It is frequently the case, that the same heating tank is used for the heating of central heating water, and water for domestic use, or for ablutions and canteen use in an office building.

In accordance with the invention, there is provided for controlling a burner or heating element of a water heating tank in a central heating system, comprising one or more zone radiators or groups of radiators, a central water heating tank, pipes for circulating heating water from said tank to said radiators or groups of radiators, comprising thermostat means in each zone for operating associated valve means for allowing or preventing water from the heating tank access to the radiator or radiators in the respective zone, and means for rendering the burner or element inoperative when all the zones have their radiators in the "off" condition.

This control may be effected by connecting the heater tank thermostat, controlling a heater tank fuel valve, to mains via a valve control relay controlling a motorized valve in the heater water outlet pipe of the heater tank leading to the hot water storage cylinder and a first transformer, the secondary of which is connected to the hot water storage cylinder thermostat, whereby the motorized valve can be actuated to feed hot water as required from the heater tank to the cylinder.

The transformer is connected to mains via a central heating control clock.

The heater tank thermostat is also connected to the control clock via other relays controlling a central heating circulation pump, and zone motorized valves in the hot water outlet pipes of the heater tank leading to zones and the circulation pump switched on or off. When a zone on/off switch or a zone thermostat is in the "off" state, the zone relay operates to actuate the zone valve to a closed state, whereby hot water from the heating tank is denied access to the radiator or radiators in the respective zone. When a pair of zone on/off switches and zone thermostats are in the "on" state, the zone relay operates to actuate the zone valve to an open state which then actuates the circulation pump, whereby hot water from the heating tank is allowed access to the radiator or radiators in the respective zone.When the zone on/off switches or zone thermostats are in the "off" state, the zone relays operate to stop the circulation pump, water only circulates when there is demand, i.e. one or more of the zones has the heating switch "on" and thermostat is also "on" because the air temperature is below the threshold minimum value.

The relays are connected to the heating tank thermostat; irrespective of the temperature of water in the tank, when there is no demand from either the hot water utility supply or the central heating system, the fuel valve can be turned "off" even when the heating tank thermostat would otherwise switch in "on" in response to water temperature in the tank having fallen below the threshold value.

A preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings which is a block circuit diagram of a central heating control apparatus according to the invention.

Electrical energy (mains AC voltage) is applied to a programmed control clock 1 which determines generalised periods (such as working hours) when the heating system is "on" and may have a facility for switching the central heating circulation pump "off" thereby preventing water from circulating through the radiators. During the "on" period, voltage is applied to the primary of a transformer X1, and the primary of a transformer X2.

The secondary of transformer X1 has a lower stripped down voltage induced in it, and this is fed via a plurality of parallel zone on-off switches SW1 a, SW1 b et seq and zone thermostats Tla, Ti b et seq to the coils of relays Ri a, R1 b et seq operative to actuate a relay switch to open and close motor operated valves Mi a, Ml b et seq to actuate a relay switch RLP operative to switch a circulator pump P on and off.The pump P therefore is switched on when at least one of the pairs of switches SWla etseq and thermostats Tia etseq are activated together, and the associated motor valve M1a etseq has fully opened completing at least one circuit through the relay coils. The pump P then draws heating water through the pipe 5 from tank 2 and circulates it through pipe 6 to the zones concerned.

The motor operated valves Mi a et seq contain micro switches whereby the valves can only operate by electric power supplied via relays Ria et seq. These micro switches supply electrical power to relay RLP only when the valves are fully open. In the case where only one zone is involved, the motor operated valve can be omitted so that the circulation of hot water through the radiators is controlled via the circulating pump P.

The secondary of transformers X2 similarly supplies a reduced voltage via an on-off switch SW2 and a selector switch SW3 through thermostat T2 or T3, set for alternative temperatures to a coil of relay RL2 which controls a two way motorized valve 8. The alternative outputs of relay RL2 act to open or close the valve 8, which is connected by a pipe 4 to the heater tank 2, and a pipe 7 to a hot water storage and supply cylinder, wherein the thermostats T2, T3 are located and which supplies hot water for utility purposes e.g. canteen and washroom use.

The motorised valve 8 contains a microswitch which allows electrical power to traverse the motor only when the valve is fully open. The relay RLP and the motorized valve 8 are connected via a thermostat T4 in the heater tank 2 to energise a solenoid type full supply valve V, which when open admits fuel such as oil or gas to a burner 3 located to heat water in heater tank 2.

When there is any demand for heating in one or more of the zones served by switches SWla, b et seq and thermostats T1 a, b et seq, or from the utility hot water supply, potential will be applied to the thermostat T4, which will conduct whenever the temperature of water in the tank 2 falls below a preset threshold value, energize valve V, and allow fuel to the burner 3 which will then heat the water to the upper permitted temperature of the tank 2. The arrangement shown however only permits this if there is demand for the utility supply or any of the heating zones, (rooms or floors for example) and the burner 3 will remain inactive whenever there is no demand due to hot weather for example.

Claims (6)

1. Means for controlling a burner or heating element in a water heating tank in a central heating installation comprising one or more zones each comprising one or more radiators, a central water heating tank, pipes for cirulating heating water from said tank to said radiators, thermostat means in each zone for operating associated means for admitting water from the heating tank to the radiator or radiators in the respective zones, and means for rendering the burner or element inoperative when all the zones if their radiators in an "off" condition.

2. Means according to claim 1, wherein fuel or energy supply to the element or burner is controlled by a valve or switch which will be open or "on" when there is demand on any zone or other facility provided with heated water from the heating tank, and while a thermostat in the tank is conductive, and 'off' when there is no demand, irrespective of the state of the said tank thermostat.

3. Means according to claim 1 or 2, wherein each zone has an on-off switch and thermostat, all zones being connected in a circuit with motor operated valves located in the supply pipes from the water heating tank to the zones, said operated valves being connected to a relay coil controlling a relay operated switch in the power supply circuit of a water circulating pump, whereby when a zone thermostat is conductive a respective motor operated valve moves to an open position to permit transfer of water through pipes to a zone and the circulating pump is activated and when the thermostat means is non-conductive the valve will move to a closed position to prevent such transfer.

4. Means according to claim 3, wherein thermostat means in a utility hot water cylinder are connected in a circuit with a coil of a third relay, controlling alternative positions of a motor operated valve, located in a supply pipe from the water heating tank to the hot water cylinder, whereby when the thermostat means is conductive, the motor operated valve will move to an open position to permit transfer of water through the pipe, and when the thermostat means is non-conductive, the valve will move to a closed position to prevent such transfer.

5. Means according to claim 4 wherein the circuits are fed by the secondary windings of respective transformers, the primary windings of which are connected to mains via a pre programmed clock switch.

6. Means for controlling a burner or heating element in a water heating tank in a central heating installation substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.