GB2054911A - Improvements relating to electrical control circuits for water heating systems - Google Patents

Abstract

An electrical circuit determines which of two modes of heating a swimming pool is to be used, either a combustible fuel boiler or a heat pump. A thermostat (3) Fig. 1 is responsive to ambient temperature and controls a relay (4) to switch between the boiler at ambient temperatures below a predetermined value e.g. 50 DEG C and the heat pump at temperatures above that value. A circulation pump (9) is energised for both modes, and is also selectively operable by a manual switch (13) when there is no heating, such as when a time switch (1) closes down both boiler and heat pump. <IMAGE>

Description

SPECIFICATION Improvements relating to electrical control circuits.

This invention relates to electrical control circuits. It is primarily intended for use in conjunction with swimming pool heating systems.

Most swimming pools have some form of heating system, conventionaliy using a gas or oil fired boiler. However, these are becoming increasingly expensive to run, and a cheaper alternative, despite quite a high initial capital cost, is a heat pump. However, heat pumps cannot contribute anything worthwhile if the ambient temperature is less than about 500C. A compromise has therefore been proposed in which a heating system has both a heat pump and a boiler which can be selectively operated according to conditions. However, this requires care and vigilance on the part of the user in order to make the most efficient use of them, and especially he must guard against simultaneous operation of the boiler and heat pump, which could damage the latter.

It is also usual for such heating systems to be governed by a clock, so that the pool is not being heated unnecessarily at times when unlikely to be in use.

The object of the invention is therefore to provide an electrical control circuit for such a dual heating system which automatically changes over according to ambient conditions, while still being subject to the timing control.

According to the present invention there is provided a control circuit for a swimming pool with two modes of heating, one mode using combustible fuel heating means, such as an oil or gas fired boiler, and the other mode using a heat pump, the circuit comprising a time clock, first means for energising a water circulation pump, second means for energising the heat pump, third means for energising the combustible fuel heating means, a thermostat responsive to ambient temperature, relay controlled switches for connecting the first and third energising means in parallel for said one mode and the first and second means in parallel for said other mode, the state of the relay being dependent on the thermostat and the clock, and means for connecting said first energising means into circuit independently of the second and third means.

For a better understanding of the invention, one embodiment will now be described, by way of example, with reference to the accompanying drawings, in which the four figures are diagrams of an electrical control circuit with switches in various positions according to the mode of operation.

The circuit has a main time switch 1, a clock (not shown) governing this being capable of being set to turn the switch on or off for any desired intervals during a twenty-four hour period. A connection form the "on" terminal of this switch leads through a manual switch 2, which is the main on/off switch for heating, a thermostat 3, which responds to ambient temperature to break the circuit at temperatures of 500C and above, and a relay 4. The relay governs two ganged switches 5 and 6 whose common terminals are connected to the "on" terminal of the time switch 1. When the relay 4 is de-energised the switch 5 connects through contacts 7 and terminal 8 to a main pump contactor coil 9 while the switch 6 connects to a heat pump contactor coil 10, which is in parallel with the coil 9. The contacts 7 are the side contacts of the heat pump and are closed when it is operating.When the relay 4 is energised, the switch 5 couples directly to terminal 8 while the switch 6 transfers to the firing system of an oil or gas fired boiler 11 via a thermostat 12 which guards against over heating of the water in that boiler.

The "off" terminal of the time switch 1 has a connection to a switch 13 and thence to terminal 8.

Referring to Figure 1, the switches are shown in their "off" positions. The state of the thermostats 3 and 12 is immaterial; nothing is energised.

However, it may be desired to keep the water circulating through the filtration plant even though the clock may be off. This is simply achieved by closing the switch 13, which energises the coil 9 as may be seen from Figure 2. Nothing else is energised, for if the heat pump is not operating, the side contacts 7 will be open.

Assuming now that the main heating switch 2 is closed and that the clock turns the switch 1 on with the temperature less than 500 C. The contacts of thermostat 3 are closed and the relay 4 will be energised. The switches 5 and 6 will be in the Figure 3 position with the main pump contactor coil 9 energised directly through switch 5 and the boiler 11 through switch 6. If the boiler water exceeds a temperature sufficient to break the contacts of thermostat 12 the boiler will temporarily close down, but the main pump will continue to operate.

When the temperature climbs above LiOOC, the contacts of thermostat 3 will break, de-energising relay 4 and changing the switches 5 and 6 to the Figure 4 position. The heat pump will now operate and its side contacts 7 close, so that the main pump contactor coil 9 will continue to be energised.

It will be seen that the operation of the heat pump and the oil or gas boiler are mutually exclusive, but whichever is functioning the main pump will continue to work. Heating occurs only during periods set by the time switch and provided the switch 2 is closed, but water circulation can be achieved independently.

The circuit shown is a lower one. The coils 9 and 10 operate respective double-pole switches (not shown) in power circuits containing the main pump and heat pump respectively.

Preferably, they will have their own magnetic trip or other fuse arrangements.

A control panel (not shown) will have the manually operated switches 2 and 1 3 together with other switches for equipment commonly associated with swimming pools, such as lights and a fan for keeping a flexible cover inflated. The time clock controls will also be presented there.

Generally there will also be indicator lights on the panel to show which of the power, the main pump, the heat pump, or the gas or oil boiler is on.

More particularly small neon amber light indicators may be fitted to the control panel to show power out in the following positions: (a) the main pump out; (b) heat pump out; (c) mains power in; and (d) gas/oil boiler on.

To avoid possibilities of incorrect operation, the contents 7 are biassed mechanically into the "off" position.

Claims (9)

1. A control circuit for liquid in a container, such as a swimming pool, with two modes of heating, one mode using combustible fuel heating means, such as an oil or gas fired boiler, and the other mode using a heat pump, the circuit comprising a time clock, a thermostat responsive to ambient temperature, first means for energising the combustible fuel heating means for said one mode during a clock 'on' period and when ambient temperature is below a pre-determined level, second means for energising the heat pump for said other mode during a clock 'on' period and when ambient temperature is above said level, and third means for energising a liquid circulation pump activated for both modes and also being activatable independently of time or temperature.

2. A control circuit as claimed in claim 1, wherein a time clock controlled switch is in series with a relay controlled switch which is governed by the thermostat selectively to activate the first or second energising means.

3. A control circuit as claimed in claim 2, wherein the relay coil is in series with the time switch so that during a clock 'off' period or when the relay is otherwise de-energised the relay switch connects to the second energising means.

4. A control circuit as claimed in claim 3, wherein the thermostat is in series with the relay coil and its contacts break above said predetermined level to de-energise the relay.

5. A control circuit as claimed in claim 3 and 4, wherein a manual on/off switch is in series with the relay coil.

6. A control circuit as claimed in any one of claims 2 to 5, wherein a second relay controlled switch is ganged in parallel to the first relay switch to activate the third energising means during a clock 'on' period, the second relay switch connecting directly to the third energising means in said one mode and via side contacts of the heat pump during said second mode, and a manual switch, in circuit during a clock 'off' period, is operable to activate the third energising means during such period.

7. A control circuit as claimed in any preceding claim, wherein a further thermostat is provided and is responsive to the temperature of liquid heated by the combustible fuel heating means to de-energise such means, but not the circulation pump, when that temperature exceeds a predetermined level.

8. A control circuit substantially as hereinbefore described with reference to the accompanying drawings.

9. A swimming pool with combustible fuel heating means, a heat pump, and a control circuit as claimed in any preceding claim for determining the mode of heating.