WO2010041011A2

WO2010041011A2 - A heating apparatus for a domestic central heating system

Info

Publication number: WO2010041011A2
Application number: PCT/GB2009/002400
Authority: WO
Inventors: Harald Massier
Original assignee: Next Generation Heating Limited
Priority date: 2008-10-08
Filing date: 2009-10-07
Publication date: 2010-04-15
Also published as: GB0818465D0; WO2010041011A3

Abstract

A heating apparatus for a domestic central heating system. The apparatus comprising a reservoir (15) for heat transfer fluid. A pump assembly (33) comprises a pump (33) and a pressure relief valve (35), wherein the pump is arranged, in use, to draw a heat transfer fluid from the reservoir and wherein the pressure relief valve is arranged, in use, to control the pressure on the outlet side of the pump assembly by diverting a first portion of the heat transfer fluid to the reservoir. A flow restriction (47) is located upstream of the pump assembly. The pressure relief valve is arranged, in use, to divert a second portion of the heat transfer fluid through the flow restriction to heat the second portion of heat transfer fluid, and to return the heated heat transfer fluid to the reservoir.

Description

A Heating Apparatus For A Domestic Central Heating System

The present invention relates to a heating apparatus for a domestic central hating system. The invention also relates to a method of heating a heat transfer fluid.

A large number of domestic residences employ central heating. It is common for domestic central heating systems to heat rooms by circulating hot water through a series of radiators arranged in a circuit . The water _for^_-such_systems is often heated by a gas or oil fired boiler. However, commonly domestic residences do not have a gas or oil supply. In such cases it is necessary to rely on other forms of heating such as electric heating.

Known types of electric heating apparatus include storage heaters, oil filled radiators and hot air blowers. Storage heaters are often selected as the preferred type of electric heating appliance since they are comparatively inexpensive to run when compared to oil filled radiators and hot air blowers, since they can be charged with heat during the night using cheap rate electricity. However, storage heaters have a number of drawbacks including a lack of flexibility and inability to heat a room sufficiently for the required period of time. In such cases it is necessary to boost the heat in the storage heater using peak rate electricity and this can make the running of storage heaters expensive .

Oil filled radiators and hot air blowers are not suitable as the sole source of domestic central heating since they are expensive to run and inefficient. They are therefore typically only used as top-up heaters.

An alternative system for providing electrically powered domestic central heating is disclosed in GB 2 035

541. In this system a reservoir of oil is heated by pumping the oil through an orifice so that the oil is heated by friction as it passes through the orifice. A heat exchanger, through which water circulates, is immersed in the. oil so that heat from the oil can be transferred—to - conventional radiators.

A pump, powered by an electric motor, is used to pump the oil through the orifice in GB 2 035 541. The extent of heating achieved as the oil passes through the orifice can be controlled by varying the dimensions of the orifice, such that a smaller orifice size creates more friction and therefore more heating.

The overall temperature of the oil reservoir is controlled by switching the motor on and off. A thermostat is immersed in the oil and is arranged to switch the motor off once the oil has reached a predetermined temperature. Once the oil has dropped below, a second, predetermined temperature, the thermostat sends a signal to turn the motor back on again.

When running, the pump of GB 2 035 541 operates at its maximum pressure. The power usage of the pump is therefore high. For example, a modern pump suitable for use in the system of GB 2 035 541 might have an operating pressure of 240 - 260 bar, requiring a power input of 7 - 7.5 kW. The motor to power such a pump would therefore need to supply power in the region of 12 kW. Such power requirements result in an expensive system to operate. In addition, because the motor and pump run at the maximum capacity when operating, their service life can be compromised.

According to a first aspect of the present invention there is provided a heating apparatus for a domestic central heating system comprising: a reservoir for heat transfer fluid; a pump assembly comprising a pump and a pressure- relief valve, wherein the pump is arranged, in use, to draw a heat transfer fluid from the reservoir and wherein the pressure relief valve is arranged, in use, to control the pressure on the outlet side of the pump assembly by diverting a first portion of the heat transfer fluid to the reservoir; and a flow restriction located upstream of the pump assembly; the pressure relief valve being arranged, in use, to divert a second portion of the heat transfer fluid through the flow restriction to heat the second portion of heat transfer fluid, and to return the heated heat transfer fluid to the reservoir.

Drawing off excess fluid and returning a first portion of the flow, whilst passing a second portion of the flow through the flow restriction, enhances the fluid movement within the reservoir. This helps to improve the heat distribution within the reservoir which, in turn, improves the speed and efficiency with which the heat transfer fluid is heated. Preferably the heat transfer fluid is a synthetic heat transfer fluid which may be engineered and selected to optimise the performance of the heating apparatus.

The pressure relief valve preferably has a valve element which is biased to a closed position by a biasing means and the apparatus further comprises means to adjust the biasing force on the valve element. By setting the biasing force on the valve element the degree of opening is then determined^ by the pressure in the system allowing the pressure within the system to be regulated and this, in turn, controls the heat generated. Such a value is sometimes referred to as a pressure impedance valve.

The pressure relief valve is preferably designed to open during normal operating conditions. This is done to maintain a constant pressure during normal operation. This should be contrasted with valves in the prior art which are designed as a safety feature to relieve pressure if, for some reason, there is an abnormal pressure build-up.

In a preferred example the dimensions of the flow restriction are variable in order to provide another degree of controllability.

The heating apparatus preferably further comprises a hydraulic block, wherein the hydraulic block comprises a passage from an inlet of the hydraulic block to an outlet of the hydraulic block, wherein the flow restriction is located within the passage. The use of a hydraulic block is preferable as it provides flexibility in the design of the flow restriction and passage. Preferably the passage comprises a bend to further restrict the flow of heat transfer fluid. The bend is preferably a right angled bend to optimise the flow restriction created by the bend.

In a second aspect, the present invention provides a central heating system comprising the heating apparatus of the first aspect of the present invention and a heat exchanger, wherein the reservoir is insulated and the fluid i-s" returned from the flow restriction substantially without heat loss and wherein the heat exchanger is arranged, in use, to be in thermal communication with the heated heat transfer fluid in the reservoir so that heat from the heated heat transfer fluid passes from the heated heat transfer fluid to a fluid within the heat exchanger. A heat exchanger provides a convenient and efficient way to transfer heat from the heat transfer fluid to the radiators of a central heating system.

In a third aspect, the present invention provides a method of heating a heat transfer fluid comprising: drawing a heat transfer fluid from a reservoir; pumping a first proportion of the heat transfer fluid through a flow restriction to heat the heat transfer fluid; and returning a second proportion of the heat transfer fluid to the reservoir without passing it through the flow restriction.

An example of a heater according to the present invention will now be described with reference to the following Figures in which: Figure 1 shows a schematic drawing of a central heating apparatus comprising a heating apparatus according to the present invention;

Figure 2 shows a schematic detailed view of the hydraulic block of Figure 1; and

Figure 3 shows a schematic drawing of the pressure relief valve of Figure 1.

Figure 1 shows a -schematic view of a central heating apparatus 1 comprising a heater 10. The heater 10 comprises a tank 15 which contains approximately 60 litres of a synthetic heat transfer fluid 70. The heat transfer fluid 70 may be, for example, BP Transcal N or any suitable equivalent. The tank 15 is surrounded by insulating material 17.

The heater 10 further comprises a pump assembly 33. the pump assembly 33 comprises a high pressure gear pump 30 and a pressure relief valve 35 which is directly connected to the pump 30. The pressure relief valve 35 controls the pressure of the heat transfer fluid on the outlet side of the pump assembly 33 as will be described in greater detail below.

The pump 30 is driven by electric motor 50 which is in turn connected to a control circuit 60. The control circuit 60 receives a signal from a thermostat 62 located inside the tank 15 and immersed in the heat transfer fluid 70. The control circuit 60 controls the operation of the motor 50 depending on the temperature of the heat transfer fluid 70 as will be described in greater detail below. The heater 10 also comprises a hydraulic block 40. A flow passage 46 passes through the hydraulic block 40. The passage 46 is configured and arranged to restrict the flow of heat transfer fluid 70 through the passage 46 as will be described in greater detail below.

Hoses 31, 32, 39 and 49 are provided for transporting the heat transfer fluid 70 between the tank 70, the pump assembly 33 and the hydraulic block 40.

As well as the heater 10, the central heating apparatus 1 further comprises a heat exchanger 20. The heat exchanger 20 is immersed in the heat transfer fluid 70 inside the tank 15. In use, water is pumped through the heat exchanger by a central heating pump 22. The water then passes through a circuit of conventional domestic radiators (not shown) .

The operation of the heater will now be described.

Before the first use, or after servicing etc., the tank 15 is filled with heat transfer fluid 70. A float switch may be provided to prevent over filling of the tank 15. The heat transfer fluid 70 is then heated to approximately 85⁰C by pumping the heat transfer fluid 70 through the hydraulic block 40 before returning it to the tank 15.

Heat transfer fluid 70 is taken from the coldest part of the tank 15. This is at the bottom of the tank 15 as heat rises. The heat transfer fluid 70 is transported via hose 31 to the inlet side of the pump 30. The pressure relief valve 35 comprises a control knob 37 which may be manually adjusted to set the pressure on the outlet side of the pump assembly 33. The outlet pressure selected is shown on manometer 38.

The pressure relief valve 35 diverts a portion of the heat transfer fluid 70 back to the tank 15 via hose 32. The proportion of heat transfer fluid 70 diverted back to the tank 15 determines the pressure on the outlet side of the pump assembly 33. A suitable pressure relief valve is the DBD 10 Dl B manufactured by Kracht GmbH, Gewerbestrasse 20, D-58791, Werdohl, Germany. A -schematic—drawing- of such a pressure relief valve is shown in Figure 3 and described below. Heat transfer fluid 70 enters the pressure relief valve 35 from the pump 30 via inlet 320 (below plane of page) , and exits via outlet 325 (above plane of page) . A passage 310 is in fluid communication with the inlet/outlet line for the connection of the manometer 38. A branch passage 330 is also in fluid communication with the inlet/outlet line. Flow through the branch passage 330 is controlled by a spring loaded poppet 335. The load on the poppet 335 is controlled by spring 340. The spring force of the spring 340 is adjustable by turning the control knob 37 to increase or decrease the spring pressure as desired. The poppet 335 opens to allow heat transfer fluid 70 to pass through branch passage 330 and out, back to the tank 15, via drain passage 315. The extent to which the poppet 335 opens depends on the spring pressure, and this in turn determines the outlet pressure of -the pump assembly 33 and hence the operating temperature. A user can therefore readily adjust the heat output of the apparatus to meet their needs .

The pressurized heat transfer fluid 70 leaving the high pressure side of the pump assembly 33 is transported via high pressure hose 39 to the inlet 42 of the hydraulic block 40. As shown in Figure 2, the flow passage 46 extends from an inlet 42 to an outlet 44. A set screw 45 is located in a threaded portion of the passage 46 upstream from the inlet 42 to create a flow restriction 47. In the example shown, the set screw 45 is solid such that the heat transfer fluid 70 may only flow around the sides of the set screw 45. In an alternative embodiment, the set screw may be hollow such that the heat transfer fluid 70 may also flow through the set screw 45^". The passage 46 in the vicinity of^" the set screw 45 is tapered such that by screwing the set screw 45 in and out the extent of the flow restriction 47 can be varied.

As the high pressure heat transfer fluid 70 passes through the flow restriction 47 it is heated by friction. The extent of heating achieved as the heat transfer fluid 70 passes the flow restriction 47 can be varied by varying the dimensions of the flow restriction 47 by screwing the set screw 45 in or out.

Once the heat transfer fluid 70 has passed the flow restriction 70 it flows towards the outlet 44 of the hydraulic block 40. The passage 46 moves through a 90° bend before reaching the outlet 44. This bend further restricts the flow of the heat transfer fluid 70 and further heats the ^"heat transfer fluid 70 before it exits the hydraulic block 40. On exiting the hydraulic block 40 the heated heat transfer fluid 70 is returned to the tank 15 via hose 49.

Once the heat transfer fluid 70 has reached its target temperature, in this case 85°C, the thermostat 62 sends a signal to the control circuit 60 which then turns off the motor 50 in order to turn off the pump 30. When the temperature of the heat transfer fluid 70 drops below a predetermined temperature, in this case 65°C, the thermostat 62 sends a signal to the control circuit 60 to turn the motor 50, and therefore the pump 30, back on again. This process repeats itself in order to maintain the temperature of the heat transfer fluid 70 between the chosen operation temperatures. When the heat transfer fluid 70 has reached a sufficient temperature, whether or not the pump 30 is running and the heat transfer fluid 70 is being heated, water is circulated through the heat exchanger 20 by pump 22. The water in the heat exchanger is heated by the hot heat transfer fluid and is then pumped through a circuit if domestic radiators where it loses its heat to the environment .

It has been found in practice that the pump need only run for 7 minutes an hour in order to maintain the heat transfer fluid 70 at a sufficient temperature to heat the water for the radiators. The tank 15 is well insulated by the insulating material 17 and this helps to maintain the temperature of the heat transfer fluid 70. Thus, for much of the time the central heating apparatus 1 is acting as a heat pump, moving heat from the heat transfer fluid 70 to the environment to be heated. The only power requirement for the central heating system are thus the power required to run the pump 30 for 7 minutes an hour and the power required to run the central heating system pump 22. The central heating apparatus 1 is thus very efficient. In the example heater 10 described above, a high pressure gear pump 30 with a maximum operating pressure of 260 bar is used. Typically the output pressure of the pump is throttled down by the pressure relief valve 35 so that the outlet pressure on the high pressure side of the pump assembly 33 is approximately 100 bar. The power required to run the pump 30 at this reduced pressure is approximately 4.08 kW as compared to 10.45 kW required to run the pump 30 at its maximum pressure. It can therefore be seen that the ability to reduce ^"the outlet pressure of the pump assembly 33 considerably reduces the operating costs. Because the pump assembly 33 is run for the majority of the time below its maximum operating pressure, the service life of the pump is increased. In addition, because it is possible to adjust the outlet pressure of the pump assembly 33, the extent of heating of the heat transfer fluid 70 can be more readily controlled than in the prior art system. The extent of heating can also be controlled by adjusting the size of the flow restriction 47. However, it has been found in practice that it is more efficient to control the extent of heating by adjusting the operating pressure of the pump assembly 33 by means of the pressure relief valve 35.

In alternative embodiments of the heater (not shown) the flow restriction 47 may be a fixed dimension flow restriction. In addition, as an alternative to the set screw 45, the flow restriction 47 could be provided by a fixed or variable dimension orifice.

The flow restriction 47 may be located at any position within the passage 46 of the hydraulic block 40. In addition, the passage 46 of the hydraulic block 40 may be straight rather than bent. Alternatively, the passage 46 may comprise additional bends of varying geometries. For example, the passage may comprise a radiused bend, or the bend, or bends, may pass through greater or less than 90°. In a yet further alternative, the hydraulic block may be replaced by a section of high pressure hose containing a flow restriction.

As an alternative to water, air, or any other suitable fluid may be passed through the heat exchanger 20 in order to move heat from the heat transfer fluid 70 and pass it to the environment to be heated.

It will be understood that the operational parameters (temperatures, power ratings, pressure ratings) etc. described above are examples only and that other operating parameters could be used. In addition, it will be understood that the gear pump 30 described above may be substituted for any other suitable pump.

Claims

Claims :

1. A heating apparatus for a domestic central heating system comprising:

5 a reservoir for heat transfer fluid; a pump assembly comprising a pump and a pressure relief valve, wherein the pump is arranged, in use, to draw a heat transfer fluid from the reservoir and wherein the pressure relief valve is arranged, in use, to control the

_JL0 pressure on the outlet side of the pump assembly by diverting a first portion of the heat transfer fluid to the reservoir; and a flow restriction located upstream of the pump assembly;

15 the pressure relief valve being arranged, in use, to divert a second portion of the heat transfer fluid through the flow restriction to heat the second portion of heat transfer fluid, and to return the heated heat transfer fluid to the reservoir. 20

2. A heating apparatus as claimed in claim 1 wherein the heat transfer fluid is a synthetic heat transfer fluid.

3. A heating apparatus as claimed in claim 1 or 2 wherein 25 the pressure relief valve has a valve element which is biased to a closed position by a biasing means and the apparatus further comprises means to adjust the biasing force on the valve element .

30 4. A heating apparatus as claimed in any preceding claim, wherein the valve is arranged to open during normal operating conditions.

5. A heating apparatus as claimed in any preceding claim wherein the dimensions of the flow restriction are variable.

6. A heating apparatus as claimed in any preceding claim further comprising a hydraulic block, wherein the hydraulic block comprises a passage from an inlet of the hydraulic block to an outlet of the hydraulic block, wherein the flow restriction is located within the passage.

1... -A÷heat±ng:^~ apparatus as claimed in- claim 6, wherein the passage comprises a bend.

8. A heating apparatus as claimed in claim 7, wherein the bend is a right angled bend.

9. A central heating system comprising the heating apparatus of any one of claims 1 to 8 and a heat exchanger, wherein the reservoir is insulated and the fluid is returned from the flow restriction substantially without heat loss and wherein the heat exchanger is arranged, in use, to be in thermal communication with the heated heat transfer fluid in the reservoir so that heat from the heated heat transfer fluid passes from the heated heat transfer fluid to a fluid within the heat exchanger.

10. A method of heating a heat transfer fluid comprising: drawing a heat transfer fluid from a reservoir; pumping a first portion of the heat transfer fluid through a flow restriction to heat the heat transfer fluid; and returning a second portion of the heat transfer fluid to the reservoir without passing it through the flow restriction.

11. A method according to claim 10, further comprising controlling the amount of fluid in the second portion using a pressure relief valve.

12. A method according to claim 11, further comprising adjusting—the_^-bias±ng- force on the pressure relief valve to adjust the pressure in the system and hence the heat generated.

13. A method according to claim 11 or claim 12, further comprising opening the pressure relief valve during normal operating conditions.