GB2474421A

GB2474421A - Thermostatically controlled mixing valve when connected with a high temperature source and a low temperature source

Info

Publication number: GB2474421A
Application number: GB0916535A
Authority: GB
Inventors: Nicholas Julian Jan Francis Macphail
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-09-21
Filing date: 2009-09-21
Publication date: 2011-04-20
Also published as: GB0916535D0

Abstract

The thermostatically controlled mixing valve 8 has a hot input port (H), cold input port (C) and an output port (M). The hot input port is connected with a high-temperature source 2 and the cold input port is connected with a low-temperature source 1. The output port may be connected with a low-temperature heating circuit, such as underfloor or imbedded-panel heating. The high-temperature source may be a boiler and the low-temperature source may be a ground or air-source heat pump in combination with a thermal store that may accept heat from alternative sources such as solar thermal. The mixing valve may be utilized in a heating installation further comprising a high-temperature heating load 6 such as a domestic hot water cylinder or a heating circuit comprising a plurality of radiators. The mixing valve gives preference to the low-temperature source when meeting heating loads required by the output, such that the high-temperature source is used only to meet any shortfall or breakdown of the low-temperature heating source. In an alternative arrangement (see figures 5-6), the low-temperature source may be a return line from underfloor heating and the output port may be connected to the return line of a heat pump.

Description

MEANS OF LINKING LOW TEMPERATURE HEAT PUMPS AND HIGH

TEMPERATURE BOILERS TO A HEATING SYSTEM

I, NICHOLAS JULIAN JAN FRANCIS MACPHAIL, a British subject of Mas des Sables, Grandes Rocques, Guernsey of the Channel Islands do hereby declare the invention for which we pray that a patent may be granted to me and the method by which it is to be performed to be particularly described in and by the following statement: -*..* * * S *5 * SS. * * * S... e * S S...

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S..... * S * S. * S S *S. *

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THIS INVENTION RELATES TO INTERLINKNG LOW TEMPERATURE HEAT

PUMPS AND HIGH TEMPERATURE BOILERS TO A HEATING SYSTEM

It has become common practice with gas and oil fired boilers to use a thermal store together with a plate heat exchanger as shown in patent No 2266762 to provide beating and mains fed domestic hot water. This arrangement has advantages over non storage arrangements, for example gas fired non storage combi boilers, in that a far greater short term flow rate of hot water to taps is achievable from a storage combi for a given instantaneous boiler load. Improvements permitting the better performance and control of electrically heated storage combi versions are disclosed in patent No 2423569 With the increasing importance of the use of "alternatives" to burning carbon-based fuels electricity, perhaps surprisingly given the comparative inefficiencies of its generation and distribution, becomes a sensible alternative to the remote or local burning of carbon-based fuels. These advantages stand out when electricity is used for heating and hot water supply with a thermal storage device, as the thermal store allows the input of heat energy to be suspended by the generating companies at times of peak demand while the thermal store's output to provide space heating and hot water can continue because of its large thermal mass. Because of its large thermal mass it also is able to utilise other intermittent input from "alternative" heat sources like, for example, "solar thermal".

The storage combi is attractive to the generating companies because most of the alternatives to burning carbon-based fuels (for example nuclear, wind, and tide flow) for generation cannot be switched on or off instantly to suit demand. Although remarkably useful to meet base loads, these "alternatives" means of generation have not been favoured by the generating companies as they cannot meet unexpected (or indeed expected) peak load demand.

Electric thermal storage devices, like electric thermal storage combis, that can have their loads remotely switched off by the generating companies' during times of peak load provide a good means of providing a flat base load while offering the option of peak load shedding needed by the generating companies to make best use of the "alternatives".

* Electric storage combis are thus more financially attractive to the generating companies and the generating companies offer special low charge rates to encourage their use.

These lower charge rates, in turn, make electricity more attractive than burning carbon-based fuels and will help with the reduction of carbon emissions required in the Kyoto agreements and make us less dependant on the, often less than helpful governments ** controlling, availability of gas and oil supplies. *

* Thermal storage combis, and like devices, will thus help to reduce the use of the finite * ** carbon-based fuels used in the supply of domestic heating and hot water to peak load :.: * needsonly. *S*

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It has been common practice to use direct firing of carbon-based fuels (commonly gas or oil) into storage combi boilers to provide heating and better hot water flow rates than are possible with non storage combis.

The use of gas or oil fired storage combis, while providing heating and good flow rate hot water for domestic premises have the disadvantage that they add to the use of carbon-based fuels, require a flue that adds to air quality problems, carry carbon monoxide production risks if not correctly installed or maintained and cannot benefit from the input of greener alternatives.

An advantage of some thermal storage Combi boilers is that, in addition to being able to be powered by non carbon sourced electricity, their thermal store can be designed to be able to accept the, usually intermittent, input from alternative green heat sources like solar thermal, and/or act as a thermal buffer to reduce cycling or to buffer heat for the defrost cycle of air source heat pumps.

The utilisation of air or ground source heat pumps into heating systems has, despite their complication and need for care in the containment of their refrigerant, become important because of heat pump's ability to utilise the renewable low grade heat in the air or ground that has been largely heated by the sun and increase that low temperature unusable heat to a higher temperature usable heat by electrical or other motive means. Additionally the heat pump can produce a usable output heat energy that is as much as three or four times the input energy used to drive it. Its low grade heat input is obtained from the effectively infinite, renewable, ground or air source energy heated by the sun.

A further advantage with heat pumps is that they are ideally suitable for use with the increasingly favoured underfloor or imbedded panel heating systems. This is because "wet" underfloor heating systems commonly use a mean water temperature in their heating coils (about 45 to 50 degrees C) that is much lower than that used in, for example, radiator and domestic hot water cylinder heating coils (about 75 degrees C) and the coefficient of performance (sometimes referred to as the running efficiency) of heat pumps is higher the lower the differential between its input and output temperatures.

A disadvantage of the prior art of heat pumps is that their heat output is often smaller than the total required to heat a house without unacceptable large cost and physical size.

It would thus be advantageous to be able to supplement the heat pumps output with an . : additional heat source at times of peak load. Supplementing the heat pump's output by inputting the heat pump's output into a heating system having a high temperature boiler output has been regarded as impossible as it is not possible to input the low temperature output of heat pumps into high temperature out puts of boilers as "heat cannot run *.... uphill". Indeed if the low temperature output from a heat pump were just crudely linked into a high temperature circuit of a heating system the high temperature water that would * :: then circulate round the heat pump circuit causing its thermostatic controls to permanently shut it down making the high temperature heat source the sole heat source.

* This, of course, would cause the low running cost of the heat pump to be lost. *

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A further disadvantage of the prior art of heat pump is that their outputs have typically to be dedicated to low temperature underfloor circuits to benefit from their higher efficiency at lower output temperatures or their high efficiency has to be sacrificed to run them at the higher temperatures and lower coefficients of performance required to supply acceptable domestic hot water temperatures or to heat radiators. Attempts have been made to enable the interconnection of different heat sources to a heating system but the usually have heat sources of similar output temperatures and/or have utilised costly electronic sensors and electric proportional controlled valves to provide temperature mixing.

It is among the objects of the present invention to overcome or obviate the above disadvantages.

According to one form of the present invention there is provided at least two heat sources having different output temperatures configured to source heat input to at least one low temperature heating output circuit, typically an undertloor heating circuit, with the link point of at least one pair of heat sources having the higher input temperature source connecting to the hot port of and the low temperature heat source connected to the cold input port of an industry standard self contained thermostatically controlled mixing valve.

Said thermostatically controlled mixing valve having its thermostatically controlled output port forming the flow port to at least one said low temperature heating circuit.

Said thermostatically controlled mixing valve can have a small bleed in by pass from the low temperature supply to the cold port linking to the supply to the hot port to enable the correct function of the thermostatic mixing valve when the high temperature heat source is off. In this form the said thermostatically controlled mixing valve's out put port forms the flow to the said low temperature heating circuit. This arrangement gives priority to the low temperature, and normally cheaper to run and greener, heat source and only bleeds in heat proportionally from the higher temperature, and normally more expensive and less green, heat source, when the lower temperature heat source cannot meet the heating system requirement.

According to another form of the present invention the link point of at least one pair of heat systems having the higher temperature return connecting to the hot port of an industry standard self contained thermostatically controlled mixing valve and the low temperature return connected to the cold input port of the said thermostatically controlled * :. mixing valve with the said thermostatically controlled mixing valve's out put port forms the return to the said low temperature heat source. This arrangement also gives priority to *:* the low temperature, and normally cheaper to run and greener, heat source and only bleeds in heat proportionally from the higher temperature, and normally more expensive * . and less green, heat source, when the lower temperature heat source cannot meet the heating system requirement. S**S* * .

: * * Preferably at least one of the heat sources is a relatively low temperature output device * such as a heat pump preferably with thermal storage and preferably with the ability to * accept heat input from "alternative" sources such as solar thermal.

Conveniently at least one of the other heat sources is a relatively high temperature output device. Preferably an electric, gas or oil fired boiler preferably with thermal storage and preferably with the ability to accept heat input from "alternative" sources Advantageously at least one of the heating output circuits is an imbedded panel low temperature circuit such as an underfloor heating circuit.

Advantageously the said thermostatic mixing valve that is essential to the present invention may be incorporated in the factory assembled components of one or more than one of the heat sources.

Conveniently the said thermostatic mixing valve may be separate from the factory assembled components of the heat sources.

Advantageously the thermostatically controlled mixing valve has a by pass from the cold inlet to the hot inlet that is integral to the valve body.

Conveniently the thermostatically controlled mixing valve has a by pass from the cold inlet to the hot inlet that is external to the valve body.

Preferably the thermostatically controlled mixing valve is of the type having an integral mechanical thermostatic actuation that is commercially available.

Alternatively the thermostatically controlled mixing valve may be electrically actuated and have actuation by temperature sensors such as thermisters and its control may incorporate extra features such as weather compensation optimisation PDF control and so on.

The invention will now be described by example with reference to the following drawings in which Figure 1A. is a diagrammatic representation of a high temperature and low temperature heat source linking at a thermostatic mixing valve that forms the present invention and which supplies a low temperature heat system -typically a wet underfloor heating system. Figure lB is a diagrammatic representation of the heat sources shown in Figure 1A but supplying both high (typically radiators and domestic hot water loads) and . : low temperature heating load (typically a wet underfloor heating system). Figure 2 shows a diagrammatic representation of a typical electric thermal storage boiler of the type shown in patent No. 082266762 with a heat pump using the thermal store as a thermal buffer to reduce cycling and to aid defrosting said electric thermal storage boiler having a control system disclosed in patent application No 2423569 but without the control features that are the embodiment of the present invention to give a comparison to Figure * 2. which is the same as that shown in Figure 1 but incorporating the thermostatically * controlled mixing valve to link the high and low temperature sources in one configuration :.: * that forms the present invention. All the above figures show the thermostatic mixing valve configured for its use to regulate the flow of a low temperature heating circuit as might be used in and underfloor heating system. Figure 5. and Figure 6. show the thermostatic mixing valve of the present invention configured for its use in regulating the return temperature to the low temperature heat source. Both the above configurations effectively produce the same priority to the lower temperature heat source to supply the low temperature heating system and only bleed in input, from the higher temperature heat source, proportional to the low temperature heat source's inability to meet the low temperature heating system's load.

Referring firstly to figure 1A. there is shown a high temperature heat source I. such as a gas, oil or preferably electric boiler preferably with thermal storage that can accept alternative input, that has a flow pipe connecting between it and the hot input port H of thermostatic mixing valve 8. A low temperature heat source 2, typically a ground or air source heat pump, has a flow pipe connecting to the cold inlet port C of thermostatic mixing valve 8. The thermostatically regulated mixed water exits from port M of thermostatic mixing valve 8. to flow onwards to the low temperature heat load 3. Pumps 4 aid circulation and an automatic bypass valves maintains a set differential flow pressure between system flow and return. Because heat pumps can take advantage of the low grade heat produced by solar gain in the ground and ambient air they can typically produce 3 to 4 times their driving energy input as heat output. Their output is usable low temperature heat that is ideally matched to the temperature requirements of wet under floor or other imbedded panel heating systems. As the output from the heat pump 2 is likely to be more economical and produces less CO2 than the boiler 1. the heat pump is the primary heat source with heat only being sourced from the boiler in event of the heat pumps output being less than the heat load in coldest weather or in the event of heat pump breakdown or service or off-peak heat pump electrical supply shut down. Zener diode symbols represent automatic differential pressure regulating by-pass valves that are not essential to the present invention and are not numbered.

In operation thermostatic mixing valve 8 would have its output (mixed) temperature set slightly lower than the normal output (flow) temperature from the heat pump. This would ensure that the cold input port C of the thermostatic mixing valve 8 would remain open to the heat pump and closed to the heat input port H unless the mixed temperature portM drops below the set temperature. Should the output temperature of the mixing valve drop, as would happen if the heat pump could not meet the underfloor heat load the valve will open to the hot input port just sufficiently to permit heat input from the boiler 2 to maintain the thermostatically controlled output from Port M. Thus the cheaper and * : greener heat pump heat source is automatically given priority of use while the boiler is automatically and proportionally utilised if the heat pump output needs supplementing to *... meet the heating system 3 load or supplanting in the event of heat pump failure or during maintenance or heat pump off-peak electricity supply shut down. **.* * *

Figure lB shows the same heat input units as Figure IA but shows both high temperature * : : heat loads 6 (for example radiator and cylinder loads) being met by the boiler 2 output with the low temperature heat load 3 (for example under floor load) being met under .: " normal conditions by the heat pump 1. As in Figure 1A the under floor circuit load input * is supplemented proportionally or supplanted if the heat pump cannot meet the load S..

requirement.

Figure 2 shows a heat pump 1 and electric thermal storage combi boiler 2 linked so that the lower portion of the thermal store is utilised so that its thermal mass reduces the cycling of the heat pump 1 that increases wear and shortens life. The thermal mass of the lower portion of the thermal store is also utilised to defrost the evaporator of the air source heat pump that is commonly necessary in extremely cold weather in areas of high humidity. Three port bypass valve shunts the heat in the store 2 and closes the path to the heat load while passing the heat from the store to the return and the heat pump for defrosting. When the heat pump defrost cycle is finished the thermal mass in the base of the heatstore enable the heating system load to be re-established without delay.

What cannot be achieved with this combination of heat pump and heatstore is the supply of heat from the heat pump into the heatstore. This is because "heat cannot flow up bill".

Indeed if the output of the heat pump were to be fed into the main body of the heatstore it would cool the heatstore due to the heatstore boiler running at a higher temperature (about 70° -800 C) compared to the mean temperature of the heat pump (35 °C to 55°C).

Further, due to the higher temperature of the store the heat pump would be shut off by its thermostats as soon as the system switched on, converting the heat pump into an interesting but little used decoration.

Referring now to Figure 3. there is shown the thermal storage combi boiler arrangement of Figure 2. showing the incorporation of the thermostatic mixing valve that is the embodiment of the present invention as out lined in Figures la and lb with similar numbered features. The function of the thermostatically controlled mixing valve 8. is the same as described previously in that it will open and remain open to port C. and be supplied with heat energy from the heat pump unless the output temperature from the output temperature port M. drops bellow its set temperature signifying insufficient heat input from the heat pump whereupon port C. will close and port H. will open proportionate to the temperature shortfall permitting the shortfall to be made up from heat input from the boiler 1.

Figure 4. shows a thermostatically controlled system is one form of the present invention as may be incorporated if the high temperature heat source or boiler 1. is likely to operate intermittently. To cause the thermostatically controlled mixing valve 8. to actuate initially and open to port C. and close to port H. to give priority of heat input to the * : thermostatically controlled mixing valve from the low temperature source, typically a heat pump 2. it is necessary for water of sufficient temperature to enter the valve for the *... sensor on the output to port M. to actuate. If the high temperature heat source or boiler 1.

is off for any reason and unable to source water of sufficient temperature to cause the * * thermostatically controlled mixing valve to actuate initially, the thermal by-pass loop shown in Figure 4. provides water from the low temperature heat source or heat pump 2.

*:: that is of sufficient temperature to produce the necessary initial actuation of the thermostatically controlled mixing valve. Although the thermal by-pass loop may be as L: shown in Figure 4. made as a loop physically separate from the thermostatically * controlled mixing valve it should be understood that the thermal by-pass loop may be **S * incorporated within the structure of the thermostatically controlled mixing valve.

Figure 5 and figure 6 are examples of a second form of the present invention, with similar component numberings as before, showing the thermostatic mixing valve located in, and having the output from the mixed output port M regulating the temperature of, the return to the low temperature heat source, typically a heat pump. In the same way as the thermostatic mixing valve's location in the flow to the heating system described above, the present invention in it second form also gives priority to the low temperature heat source, only bleeding in sufficient heat from the high temperature heat source to proportionally compensate for any shortfall in the output of the low temperature heat source in meeting the heating system load Although the thermostatically controlled mixing valve and any of its attendant components is shown in the figures as physically separate from the heat pump and boiler is should be understood that it may be incorporated in a pre assembled package and/or fitted to either heat source.

Although the high temperature and low temperature heat sources have been described as being boiler or heat pump respectively it should be understood that any suitable high and low temperature heat source may be substituted. * * * ** * **. * * I... * * ** * * * S. * S S *** S *..

Claims

CLAIMS1. Means of linking at least two heat sources having different output temperatures configured to source heat output to at least one low temperature heating circuit typically an underfloor heating circuit. The link point of the said at least two heat sources having the higher temperature heat source connecting to the hot input port and the low temperature heat source connecting to the cold input port of a thermostatically controlled mixing valve. Said thermostatically controlled mixing valve having its thermostatically controlled output port forming the flow port to the said at least one low temperature heating circuit. Said thermostatically controlled mixing valve may be located on the flow or alternatively on the return of the said low temperature heating circuit and when fitted on the flow can have a small bleed in bypass from the said low temperature heat source to the said hot input port to enable the correct function of the said thermostatically controlled mixing valve when the high temperature heat source is off This bypass is not required when the thermostatic mixing valve is located on the heating system return. These arrangements of the thermostatically controlled mixing valve give priority to the said low temperature and normally cheaper to run and greener heat source and only bleeds in heat proportionally from the said higher temperature, and normally more expensive and less green, heat source when the lower temperature heat source cannot Q meet the heating system requirements. a) (\J