GB1580451A - Combined central heating and indirect domestic water heating systems - Google Patents

Description

(54) COMBINED CENTRAL HEATING AND INDIRECT DOMESTIC WATER HEATING SYSTEMS (71) We, FLEMING FABRICATIONS LIMITED, a British Company, of 48 Elvan Street, Glasgow, Scotland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to combined central heating and indirect domestic water heating systems.

More specifically the invention provides for combined central heating and indirect domestic water heating systems which operate on what is termed a pumped primary system in which a relatively small quantity of water in a primary circuit is heated in a boiler and pumped through the primary circuit so as to provide a high water flow velocity through the boiler and primary circuit.

An indirect domestic water heating system is a system in which a boiler provides for heating water in a primary circuit or central heating radiators and a heat exchanger in the primary circuit provides for heating domestic water in a secondary circuit.

Central heating systems are invariably made of ferrous material and therefore are not suitable for direct communication with domestic water supply systems so that it is necessary to keep the central heating water in the primary circuit separate from the domestic hot water ìn the secondary circuit.

Recent design changes in the manufacture of central heating boilers and heat exchangers has necessitated the operation of a pump to work simultaneously with the operation of the boiler so as to bring about a high water flow velocity through the boiler and associated primary circuit which includes central heating radiators and a heat exchanger for heating domestic water in a secondary circuit the efficiency and performance of such boilers and heat exchangers being in proportion to the velocity of the primary water flow through them.

Tests have shown that such domestic water heat exchanger will exchange heat in the order of 40,000 BTU per hour from the water flow velocity of 4 gallons per minute at 1800F. This rate of heat exchange is so fast as to bring about a rapid "recovery" of domestic hot water which is normally contained in a well-insulated hot water cylinder.

A result of this high level of heat exchanger efficiency is to enable a water heating boiler, which would normally be regarded as of a too low a thermal output to serve both the needs of a domestic hot water heating supply and a measure of central heating by radiators to be utilized by diverting the load between these two requirements.

It is normal practice for water in the primary circuit for the central heating and heat exchanger to be supplied from a small primary feed or expansion tank independently supplied from the cold water mains as the water in the primary circuit is dirty from the effects of rust etc., and it is necessary to maintain a de-aerated round circuit of water within the primary circuit.

The secondary circuit for domestic hot water is usually supplied from cold water storage system and after being heated by the heat exchanger in a storage cylinder it is drawn-off for supply to domestic taps.

According to the invention a combined central heating and indirect domestic water heating system comprises a primary circuit and a secondary circuit, said primary circuit including a boiler for heating water in the primary circuit, a pump for circulating the heated primary water through at least one space heating radiator and a heat exchanger in said circuit, said secondary circuit comprising a vertically diposed storage cylinder for domestic hot water communicating at its lower end with a feed tank, the upper portion of said cylinder being adapted to form an air chamber when said system is in operation, said heat exchanger being located in said cylinder to heat water in the secondary circuit, an air vent to atmosphere extending into the upper portion of the cylinder so as to allow said air chamber to be formed, and a self-priming compensator device communicating with the primary circuit and with the secondary circuit, said compensator device being in the form of an expansion chamber and forming an air seal between the water in the primary circuit and the water in the secondary circuit during operation of the system, an auto air vent in said compensating device so located as to establish a minimum water level in the primary circuit, said compensator device communicating at one end with the primary circuit adjacent an inlet of the heat exchanger and at its other end with said upper portion of the cylinder.

Preferred embodiments of the invention are illustrated by way of example in the accompanying drawings in which: Fig. 1 is a schematic representation of a combined central heating and indirect domestic water heating system according to one embodiment of the invention; Fig. 2 is a representation of a modified portion of the system of Fig. 1; and Fig. 3 is an illustration of a preferred adaptor for the domestic water cylinder illustrated in Fig. 1.

According to one embodiment of the invention as illustrated in Fig. 1, of the drawings a combined central heating and indirect domestic water heating system consists of a primary circuit for heating and circulating primary water for central heating and for heating domestic water and a secondary circuit containing said domestic water to be heated.

The primary circuit consists of a boiler 1 for heating the primary water, a heat exchanger 2 for heating domestic water in the secondary circuit, a pump 3 for circulating the primary water through the primary circut, at least one space heating radiator 4, a selector valve 5 for selectively distributing the primary water through the radiator or radiators and/or the heat exchanger and a self-priming compensator device 6 for keeping the primary water separate from the secondary water when the system is operating.

The secondary circuit consists of a domestic hot water cylinder 10 supplied from a feed tank 11 and having a draw-off 12 to domestic taps, and a vent 13 to atmosphere.

The heat exchanger 2 used in the system is ideally similar to that described in Patent Specification No. 1,253,025 and is located in the domestic hot water cylinder 10 having its output and input connected to the pumped flow and return circuit to the boiler through the selector valve 5.

Tests have shown that the efficiency of the heat exchanger is proportionate to the velocity of primary water flow therethrough.

It has been found that a heat exchanger can exchange heat in the order of 40,000 BTU per hour from a water flow velocity of 4 gallons per minute at 1800F to provide a rapid recovery of domestic hot water.

The selector valve 5 can be manually or automatically actuated to selectively divert primary water from the boiler 1 through the radiators 4 and/or through the heat exchanger 2 so that when the domestic water requires to be heated rapidly the selector valve 5 can be actuated to divert a major portion or all of the primary water through the heat exchanger 2 to provide a rapid recovery of domestic hot water or to close down the air space heating from radiators 4 during periods when not required. Under normal working conditions the selector valve 5 would be set to divert a major portion of primary water to the radiators 4 and a minor portion to the heat exchanger 2 to maintain hot domestic water.

The selector valve 5 may be automatically actuated and controlled by a cylinder thermostat (not shown) for the domestic hot water and/or by an air or radiator thermostat (not shown) to control air space heating. Actuation of the pump 3 is controlled by operation of the boiler 1.

The present system is a single feed system whereby the domestic water in the secondary circuit and the initial filling and topping up of the primary circuit is provided from a common feed tank 11. The primary water and the secondary water being constantly separated by an air seal after initial filling of the system.

The separation of the two circuits is achieved by the self-priming compensator device 6 in the primary circuit which acts as expansion means for primary water and provides an air chamber between the circuits.

The compensator device 6 is in the form of a vertically disposed chamber which may be cylindrical which communicates at its lower end 15 with the primary circuit to the boiler 1 and one end of the heat exchanger 2 and its upper end 16 communicates with the upper end 17 of the cylinder for domestic water. The compensator device is also provided with an auto air vent in the form of a valve 18 located adjacent the lower end of the chamber. The auto air vent 18 which can be manually and automatically actuated comprises a series of water absorbent diaphragms within the valve which swell up when wet to seal off the vent and when permitted to dry they contract to open the vent. The auto vent can be manually actuated for initial filling of the system.

An air release vent 19 is also provided at a high point above the selector valve 5 and pump 3 to vent the primary circuit during initial filling.

The cylinder 10 for domestic water in the secondary circuit is vertically disposed and has an inlet 20 adjacent its base for cold water from the feed tank 11. The upper end of the cylinder 10 communicates with the upper end of the compensator device 6 and the vent to atmosphere 13 extends through the top of the cylinder into the cylinder a predetermined distance so as to establish an air chamber in the upper end of the cylinder when the system is in operation, and a draw-off 12 for domestic hot water to taps is connected to the vent 13.

The vent to atmosphere and the connection to the compensator device may be coaxially arranged to enter the cylinder through an adaptor 21 (Fig. 3) fitted to the upper end of the cylinder, or alternatively enter the cylinder by separate ports.

In a modified embodiment of the invention as illustrated in Fig. 2 the feed tank 11a is integrally formed with or secured to the top of the cylinder 10a. Such combined tank and cylinder is particularly useful in conditions where space is restricted such as in low-rise buildings or a low ceiling. The feed tank located on top of the cylinder has a cold water feed outlet 25 adjacent the bottom of the tank which is connected to an inlet 26 adjacent the bottom of the cylinder 10a.

The vent to atmosphere 1 3a from the upper end of the cylinder extends into the cylinder a predetermined distance so as to provide for an air chamber 27 in the upper portion of the cylinder. The vent 13a is connected at its other end to the upper end of the tank as at 28 or extends over the tank.

The draw-off 12a for domestic hot water is located in the side of the cylinder as at 29 below the level of the end 30 of the vent to atmosphere 13a.

In both embodiments the volume of water in the primary circuit will change due to heating and cooling. The approximate change in volume of water can be in the order of 2 or 3% due to rise and fall in temperature from cold to hot so that the volume of the compensator device 6 must be sufficient to accommodate this change and at the same time maintain an air pocket in the chamber above the water level in the compensator device.

The systems are particularly suitable for operation with a low water content primary circuit using a high head pump, as in the case of micro bore tubing for central heating systems, as the compensator device will contain the head of a high head pump.

The pump head required is determined by the frictional resistance of the primary circuit and the frictional resistance charac tcristics of the primary circuit will change by actuation of the selector valve 5 while the pump and will remain constant. When the pump head is greater than the frictional resistance of the primary circuit the column of water in the compensator device 6, which acts as a primary vent, will rise. It is therefore necessary for the volume of the compensator device to be sufficient to contain this change in characteristics and still maintain an air pocket in the chamber within the compensator device.

The use of micro-bars tubing e.g. 8mm.

in central heating systems requires a pump head which may be in the order of 12 feet or more.

In the operation of the systems the primary circuit will initially be filled by manually opening the auto air vent 18 in the compensator device 6 to allow air to escape and opening the vent 19 above the selector valve and pump. The feed tank 11 or 1 lea will first fill the secondary circuit including the cylinder and secondary water will rise to the communicating pipe 31 between the cylinder 11 or 1 1a and the compensator device 6 and secondary water will flow into the primary circuit until it is filled to the level of the auto air vent 18 when water will emerge from the vent to seal it. The primary circuit is then fully charged with water in the cold start position.

When the boiler 1 is lit the pump 3 is simultaneously actuated, the primary water will be heated and pass through the heat exchanger 12 at high velocity. As there is a considerable amount of air normally dissolved in the secondary water, the act of heating this water by the heat exchanger will cause this dissolved air to be released and this will rise to form an air chamber in the top portion 27 of the cylinder 10 or 10a which communicates with the air chamber in the compensator device 6, until the air collecting chamber in the cylinder is filled with air.

When the air chamber 27 in the cylinder 10 or 10a is filled with air any surplus air emitted from the secondary water will escape through the vent 13 or 13a to atmosphere.

Domestic hot water may be drawn-off through the household taps and the water level in the cylinder will be maintained from the supply of cold water in the feed tank.

The level of the primary water in the compensator device 6 at cold start is established by the location of the auto air vent 18 which is adjacent the bottom of the device.

When the primary water heats and expands in volume the water level in the compensator device will rise. Dissolved air in the water will also initially be released into the air chamber in the compensator device.

The physical dimensions of the com pensator device are determined by the volume of water in the primary circuit allowing for expansion, sufficient volume to cointain any surplus pump head caused by actuation of the selector valve and maintaining an air chamber in the compensator device above the water level.

If for any reason e.g. there is a loss of primary water volume by evaporation or leakage within the primary circuit, the water level in the compensator device falls below the auto air vent level, this will cause the auto air vent to actuate, as it will become dry, and release air which in turn will cause water from the secondary domestic circuit to spill over into the primary circuit to replenish the primary volume to the level of the auto air vent when it will again close.

The combined cylinder and tank construction described in the alternative embodiment will operate similarly. This construction has a very low static head. Because the frictional resistance of the gravity fed cold water supply from the storage tank is greater than the resistance of the standing column of water in the vent to atmosphere, the standing column may collapse thus air will be drawn from the atmosphere into the upper air chamber in the cylinder to additionally maintain the air seal.

WHAT WE CLAIM IS: 1. A combined central heating and indirect domestic water heating system comprising a primary circuit and a secondary circuit, said primary circuit including a boiler for heating water in the primary circuit, a pump for circulating the heated primary water through at least one space heating radiator and a heat exchanger in said circuit, said secondary circuit comprising a vertically disposed storage cylinder for domestic hot water communicating at its lower end with a feed tank, the upper portion of said cylinder being adapted to form an air chamber when said system is in operation, said heat exchanger being located in said cylinder to heat water in the secondary circuit, an air vent to atmosphere extending into the upper portion of the cylinder so as to allow said air chamber to be formed, and a self-priming compensator device communicating with the primary circuit and with the secondary circuit, said compensator device being in the form of an expansion chamber and forming an air seal between the water in the primary circuit and the water in the secondary circuit during operation of the system, an auto air vent in said compensator device so located as to establish a minimum water level in the primary circuit, said compensator device communicating at one end with the primary circuit adjacent an inlet of the heat exchanger and at its other end with said upper portion of the cylinder.

2. A system as claimed in claim 1 in which the feed tank is integrally formed with the storage cylinder.

3. A system as claimed in claim 1 in which the vent to atmosphere and the connection between the cylinder and compensating device are co-axially arranged to enter the cylinder through an adaptor fitted to the upper end of the cylinder.

4. A system as claimed in any of the preceding claims in which the compensator device comprises an expansion chamber which communicates at one end with the upper end of the storage cylinder and at the other end with the primary circuit adjacent one end of heat exchanger and the auto air vent is located adjacent the end of the chamber communicating with the primary circuit.

5. A combined central heating and indirect domestic water heating system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. pensator device are determined by the volume of water in the primary circuit allowing for expansion, sufficient volume to cointain any surplus pump head caused by actuation of the selector valve and maintaining an air chamber in the compensator device above the water level. If for any reason e.g. there is a loss of primary water volume by evaporation or leakage within the primary circuit, the water level in the compensator device falls below the auto air vent level, this will cause the auto air vent to actuate, as it will become dry, and release air which in turn will cause water from the secondary domestic circuit to spill over into the primary circuit to replenish the primary volume to the level of the auto air vent when it will again close. The combined cylinder and tank construction described in the alternative embodiment will operate similarly. This construction has a very low static head. Because the frictional resistance of the gravity fed cold water supply from the storage tank is greater than the resistance of the standing column of water in the vent to atmosphere, the standing column may collapse thus air will be drawn from the atmosphere into the upper air chamber in the cylinder to additionally maintain the air seal. WHAT WE CLAIM IS:

1. A combined central heating and indirect domestic water heating system comprising a primary circuit and a secondary circuit, said primary circuit including a boiler for heating water in the primary circuit, a pump for circulating the heated primary water through at least one space heating radiator and a heat exchanger in said circuit, said secondary circuit comprising a vertically disposed storage cylinder for domestic hot water communicating at its lower end with a feed tank, the upper portion of said cylinder being adapted to form an air chamber when said system is in operation, said heat exchanger being located in said cylinder to heat water in the secondary circuit, an air vent to atmosphere extending into the upper portion of the cylinder so as to allow said air chamber to be formed, and a self-priming compensator device communicating with the primary circuit and with the secondary circuit, said compensator device being in the form of an expansion chamber and forming an air seal between the water in the primary circuit and the water in the secondary circuit during operation of the system, an auto air vent in said compensator device so located as to establish a minimum water level in the primary circuit, said compensator device communicating at one end with the primary circuit adjacent an inlet of the heat exchanger and at its other end with said upper portion of the cylinder.

2. A system as claimed in claim 1 in which the feed tank is integrally formed with the storage cylinder.

3. A system as claimed in claim 1 in which the vent to atmosphere and the connection between the cylinder and compensating device are co-axially arranged to enter the cylinder through an adaptor fitted to the upper end of the cylinder.

4. A system as claimed in any of the preceding claims in which the compensator device comprises an expansion chamber which communicates at one end with the upper end of the storage cylinder and at the other end with the primary circuit adjacent one end of heat exchanger and the auto air vent is located adjacent the end of the chamber communicating with the primary circuit.

5. A combined central heating and indirect domestic water heating system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.