Patent Publication Number: US-2011048404-A1

Title: Heating system

Description:
This invention relates to a heating system, and in particular to a system suitable for use in supplying heat and hot water to a building in an environmentally efficient manner. 
     It is known to provide a heating system including a hot water storage tank or cylinder in which a heat exchange coil is provided to permit water within the cylinder to be heated by hot water or another fluid heated by a boiler, for example a gas or oil fired boiler. The output from the boiler may also be supplied to a space heating system, for example including a series of radiators, to provide heat to a building. 
     It is also known to provide, in the cylinder, an additional input coil connected, in use, to a solar water heater panel or other device whereby the water within the cylinder can be heated using solar energy. Depending upon the environmental conditions and upon the quantity of hot water required, the solar input may be sufficient, alone, to heat the water within the cylinder, or at least part thereof, to the desired temperature. Alternatively, the water may be heated using the solar energy driven circuit in combination with the output of the boiler. In such a mode of operation, the solar derived energy raises the base temperature of the water within the cylinder, thereby permitting a reduction in the energy requirement from the boiler to achieve a given water temperature and so permitting energy savings to be made. Under some conditions, the boiler output alone may be used to provide the hot water. 
     The cylinder may include a further coil to permit heat to be extracted from the hot water within cylinder for use by another heat demand, for example, to operate a space heating system, an underfloor heating system, a swimming pool, or other heat demands. 
     The control systems used in such heating systems are relatively complex. 
     It is an object of the invention to provide a heating system of this general type of simple and convenient form. In particular, the invention relates to a control system associated with the heating system to permit operation thereof in a simple, convenient and efficient manner. 
     According to the present invention there is provided a heating system comprising a hot water tank or cylinder having a first input coil whereby water within the cylinder can be heated using solar energy, a second input coil whereby water within the cylinder can be heated by a boiler, and a third, output coil whereby heat can be extracted from the water within the cylinder, the system further comprising a heat demand, and control means operable to determine whether the heat demand is supplied from the boiler, from the third coil. 
     Preferably, the control means comprises a mixer valve operable to control the supply of hot fluid from the boiler to the heat demand. The mixer valve preferably further controls the supply of cooled fluid from the heat demand back to an input thereof. The control means preferably comprises a control valve operable to control the supply of heated fluid from the third coil to the heat demand. Preferably, the control means additionally includes a control pump operable to return cooled fluid from the heat demand to the third coil. 
     A controller is preferably provided to control the operation of the components of the control means. The controller preferably receives temperature signals representative of the fluid temperature in parts of the system and uses the temperature signals in controlling the operation of the control means. The temperature signals are preferably derived from temperature sensors operable to sense the fluid temperature at the third coil and at the output from the mixer valve. Preferably, a differential temperature sensor is provided, the output of which is used to control the operation of the control pump and the control valve. 
     Preferably the heat demand comprises an underfloor heating system. However, this need not always be the case and the invention is also applicable to the operation of, for example, a series of radiators. Further, by appropriate design, the invention could be used in controlling the operation of two or more heat demands of different types. 
    
    
     
       The invention will further be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic representation of a heating system in accordance with one embodiment of the invention; 
         FIGS. 2 to 4  are views similar to  FIG. 1  illustrating alternative configurations; and 
         FIGS. 5 and 6  illustrate wiring schemes suitable for use in the heating systems of  FIGS. 1 to 4 . 
     
    
    
     Referring to  FIG. 1  there is illustrated a heating system comprising a hot water cylinder  10  to which cold water can be supplied through an inlet  12 , and from which hot water can be drawn through an outlet  14 . Hot water from the cylinder  10  is supplied, in use, to the sinks, basins, baths and/or showers of a domestic building, and/or to dishwashers, washing machines, etc. 
     The cylinder  10  includes three heat exchanging coils  16 ,  18 ,  20 . Although three such coils are illustrated, it will be appreciated that a greater number of coils may be provided, if required or desired. The first coil  16  is an input coil and is connected to a solar panel  22  operable to heat the fluid passing along a solar circuit  24  including the panel  22  and the coil  16 . The fluid preferably comprises water, ideally incorporating an anti-freeze liquid, but it will be appreciated that this need not be the case and that other fluids could be used. In use, the fluid passing around the solar circuit  24  is heated in the panel  22 , heat from the fluid passing to the water within the cylinder  10  as the fluid passes through the coil  16 . The precise details of the solar panel  22  and the solar circuit  24  are not of importance to the invention and so will not be described in further detail. 
     The second coil  18  is, likewise, an input coil connected, through a control valve  26  to the output of a boiler unit  28 , for example in the form of a gas or oil fired boiler. The boiler unit  28  includes a pump  30  operable to supply hot fluid under pressure therefrom along or through a boiler circuit  32  to the second coil  18 , depending upon the operation of the control valve  26 . A space heating circuit  34  including a series of radiators  36  is connected to the boiler circuit  32  via a second control valve  38  such that, depending upon the position of the second control valve  38 , the operation of the boiler unit  28  and associated pump  30  can be used to supply heated fluid to the radiators  36 . It will be appreciated that the output from the boiler unit  28  can be supplied to either or both of the second coil  18  and the radiators  36 , depending upon the operation of the control valves  26 ,  38 . 
     It will be appreciated that the heating system described thus far is capable of heating the water within the hot water cylinder  10  either by using heat energy derived from the solar circuit  24  or by using heat energy derived from the boiler unit  28 , or a combination thereof. When the environmental conditions are such that sufficient hot water can be supplied at the desired temperature using just the solar circuit  24 , then the boiler unit  28  is either not used or is used to supply heat to the radiators  36 . Where the environmental conditions do not permit hot water to be provided from the solar circuit  24  alone, the boiler unit  28  may be used to boost the provision of hot water, and where the environment conditions are poor, the boiler unit  28  may used to provide the majority or all of the hot water requirement. 
     In addition to the features described hereinbefore, the heating system further includes an additional heat demand in the form of an underfloor heating circuit  40 . Although the additional heat demand described herein is in the form of an underfloor heating system, the invention is also applicable to other arrangements, for example arrangements in which the additional heat demand is a network of radiators, a swimming pool heating circuit, or the like. The underfloor heating system  40  is arranged to derive heat energy from either the water stored in the hot water cylinder  10  via the third coil  20  thereof or from the boiler unit  28 , a control means  42  being provided to control this. As illustrated in  FIG. 1 , the underfloor heating system  40  includes a feed line  44  and a return line  46 . The feed line  44  is connected to the third coil  20  via a line  48  incorporating a third control valve  50 , forming part of the control means  42 . The feed line  44  is also connected to the boiler circuit  32  via a mixing valve  52  forming another part of the control means  42 . The return line  46  is connected to the return side of the third coil  20  via a line  54  incorporating a control pump  56  forming another part of the control means  42 , and is also connected to the return side of the boiler circuit  32 . The return line  46  is further connected to the mixing valve  52  so that, depending upon the operation of the mixing valve  52 , a proportion of the relatively cool fluid returning from the underfloor heating system  40  along the return line  46  can be returned to the feed line  44  thereof. 
     The operation of the control means  42  comprising third control valve  50 , the control pump  56  and the mixing valve  52  is controlled by a control unit  58  dependent upon demand signals and temperature information derived from a series of temperatures sensors  60 ,  62 ,  64  operable to sense the temperature at, at least, the third coil  20  and the feed line  44  of the underfloor heating system  40 . The control unit  58  further controls the operation of the first and second control valves  26 ,  38  to determine whether or not the boiler unit  28  is used to heat the water within the cylinder  10  and the radiators  32 . In part, in order to achieve this, the control unit  58  uses signals representative of the water temperature within the cylinder  10  and room thermostats. In use, the operation of the system to provide hot water and to drive the radiator circuit is as described hereinbefore. When it is desired to operate the underfloor heating system  40 , the control unit  58  switches on the pump  40   a  of the underfloor heating system  40 . If the temperature at the third coil  20  as detected by the sensor  60  is higher than that at the feed line  44  of the underfloor heating system  40  as sensed by the sensor  62 , then the third control valve  50  is opened and the control pump  56  is switched on with the result that heat extracted from the water within the hot water cylinder  10  is used to heat the underfloor heating system  40 . The temperature at the feed line  44  of the underfloor heating system  40  is monitored by sensor  64  and, if it is at a predetermined target level, then the underfloor heating system  40  is driven using just the heat energy extracted from the hot water cylinder  10 . If the measured temperature is lower than the target temperature, then the boiler unit  28  is switched on and the mixing valve  52  is opened so as to temporarily supplement the heat derived from the cylinder  10  with additional heat from the boiler unit  28 . The degree by which the mixing valve  52  is opened is controlled to ensure that the desired target temperature is maintained. The opening of the mixing valve  52  in this manner results in the temperature at the feed line  44  of the underfloor heating system  40  exceeding that at the third coil  20 , and hence in the third control valve  50  being closed and the control pump  56  being switched off. Heat energy will then be derived just from the boiler circuit. If the temperature sensed by the sensor  64  is higher than the desired temperature, then the boiler unit  28  is switched off and the mixing valve  52  is controlled to return a proportion of the relatively cooler fluid from the return line  46  to the feed line  44 , thereby ensuring that the feed line temperature is maintained at approximately the desired target temperature. The target temperature at the feed line  44  to the underfloor system  40  is determined by the control unit  58  and is related to the temperature in the area being heated using the underfloor heating system  40 . As the temperature rises, the target temperature at the feed line  44  to the underfloor heating system reduces. When a point is reached where the target temperature, and hence the feed line temperature as achieved by the operation of the mixing valve  52 , is lower than the temperature at the third coil  20 , the third control valve  50  is opened and the control pump  56  operated with the result that the underfloor heating system  40  derives its heat energy just from the hot water within the cylinder  10  rather than directly from the boiler unit circuit. 
     If a point is reached at which the temperature at the third coil  20  exceeds the target temperature, the room controls will ensure that overheating of the room does not occur, for example by switching off the underfloor heating system  40 . 
     It will be appreciated that, in use, where the temperature in an area heated using the underfloor heating system  40  needs to be raised by a relatively large amount, then the majority of the heat energy required to achieve the heating will be derived from the boiler unit circuit. However, once the area is at substantially its desired temperature, maintenance of that temperature can often be achieved to a large extent using the heat energy derived from the hot water within the cylinder. Consequently, significant energy savings can be made. 
     It will be appreciated that, whilst the boiler unit is operating, any excess heat can be used to heat the water within the hot water cylinder, thus the heat energy can be stored for subsequent use. Appropriate lagging or insulating of the cylinder  10  is provided in order to minimise heat loss from the cylinder, thereby maximising the efficiency of the heating system. It is envisaged that, for operation of the underfloor heating system, the boiler unit will be switched on when the mixing valve opens beyond a 20% open position, and switches off when the mixing valve is moved to less than a 10% open position. However, other operating schemes could be used. 
     It will be appreciated that, in determining whether or not to open the third control valve and operate the control pump all that it required is information representative of whether the temperature at the coil exceeds that at the inlet to the underfloor heating system. The absolute temperatures at these locations are not required. Consequently, it is envisaged that the sensors  58 ,  60  will form part of a differential thermostat operable to sense the temperature difference between these locations, rather than sensing the absolute temperature at these locations. 
       FIG. 2  illustrates an arrangement similar to  FIG. 1  but in which the radiator circuit is omitted. 
       FIG. 3  illustrates and arrangement similar to  FIG. 1  but in which the third coil  20  is used to extract heat from the water within the cylinder for use by either the radiator circuit or the underfloor heating system, in either case the boiler unit being able to supply heat in the event that insufficient heat energy can be derived from the cylinder to meet the demand. 
       FIG. 4  illustrates an arrangement similar to that of  FIG. 2  but in which an alternative, four-port mixing valve  52  is used instead of the version shown, diagrammatically in  FIGS. 1 and 2 . 
       FIGS. 5 and 6  illustrate wiring diagrams or schemes suitable for use in controlling the operation of the heating systems of  FIGS. 1 to 4 . 
     A number of modifications and alterations may be made to the arrangement described hereinbefore without departing from the scope of the invention.