Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
  • F24D3/00—Hot-water central heating systems
  • F24D3/08—Hot-water central heating systems in combination with systems for domestic hot-water supply
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
  • F24D11/00—Central heating systems using heat accumulated in storage masses
  • F24D11/02—Central heating systems using heat accumulated in storage masses using heat pumps
  • F24D11/0214—Central heating systems using heat accumulated in storage masses using heat pumps water heating system

Definitions

• the present invention relates to heat pumps and in particular to heat pump installations for the supply of heat over different temperature ranges.
• heat pump make use of a working fluid to extract heat from a first environment at a first low temperature and to supply the heat to a second environment at a higher temperature.
• the working fluid may be pumped around a cycle comprising a number of stages: Firstly, in liquid form, the cold fluid is passed through a first heat exchanger where it absorbs heat from the first environment by evaporation to form a vapour; Secondly, the vapour passes through a compressor where it is compressed until it is supersaturated; Thirdly, the vapour is passed through a second heat exchanger or condenser, where it condenses. The latent heat of condensation is transferred to the second environment.
• the condensed working fluid returns to the first heat exchanger through an orifice or expansion valve, returning its pressure to the starting value
• the principle of operation of a heat pump is thus substantially similar to that of a refrigerator or air conditioning unit and in the past similar working fluids have been used, in particular Freon.
• the main advantage of heat pumps over conventional heating systems is the coefficient of performance or CoP.
• the energy input to drive the compressor and circulate the fluid is substantially less than the total heat delivered to the second environment.
• the energy removed from the first low temperature environment is effectively concentrated and supplied to the second high temperature envkonment. Since the first environment is usually external ambient air or water, this heat is supplied "free-of-charge".
• the total heat supplied to the second environment may then be considered as a factor of the energy input to power the pump, this ratio is known as the CoP.
• heat pumps usually use either external ambient air or ground water.
• the working fluid may circulate through a heat exchanger in direct heat exchanging relation with the air or water.
• an intermediate fluid such as water may be used to bring the heat from outside or underground, to the heat pump.
• the second environment may be provided by e.g. a circulation of air within a building or by a further liquid such as water within a domestic hot water or heating system.
• a heat pump installation may be designated as air/air, air/water, water/air or water/water.
• other alternatives exist using other media although these are not at present common in conventional systems.
• heat pumps have been limited by their low temperature operation. Early heat pumps were unable to operate effectively when the external temperature dropped much below 0°C. This made them unsuitable as a source of primary heating in colder climates in particular, since the requirement for heating increases as the external temperature falls. They were thus often combined with existing systems e.g. as an energy saving alternative for spring and autumn, but could not replace such existing systems.
• desuperheaters are used in combination with a condenser.
• a desuperheater extracts a first f action of the heat from the working fluid without allowing it to fully condense.
• Such desuperheaters allow a high temperature of the product fluid to be achieved but cannot extract a large quantity of the total available heat.
• Typical desuperheaters may remove only about 15% of the heat from the working fluid. The remaining 85% available heat is removed at a lower temperature in the condenser.
• the relatively high temperature achieved in the first heat exchanger may be close to the maximum temperature achievable from the working fluid for a given pressure e.g. about 40 bar for most common compressors. Preferably, it should be greater than 80% of the maximum temperature achievable. In the case of R-410A at 40 bar, the first temperature may be greater than 60 C, preferably greater than 70 C and more preferably greater than 80 C.
• the first heat exchanger is a counter flow small bore heat exchanger.
• a preferred embodiment comprises a pair of small bore tubes joined together in heat conducting relation over substantially their entire length.
• the tubes may have an internal diameter of between 4mm and 8mm, preferably around 6mm.
• the tubes may be wound as a coil such that the working fluid runs downwards in a spiral. In this way, the condensed working fluid may flow under gravity through the coil.
• the heat exchangers are arranged in parallel and a valve arrangement is provided for switching the flow of working fluid to flow either through the first heat exchanger or through the second heat exchanger.
• a pulse-modulating valve may also be provided at an outlet of each of the first and second heat exchangers for closing the respective outlet when flow through the respective heat exchanger is not required. Operation of these valves may be controlled by the control unit.
• the heat exchangers may be arranged in series and the first heat exchanger may be located above the second heat exchanger such that the condensed working fluid may then flow under gravity through the second heat exchanger.
• the second heat exchanger is distinct in design from the first heat exchanger to allow a relatively higher flow rate of the second product fluid with respect to the first product fluid.
• the design of the second heat exchanger may allow a flow of second product fluid that is more than five times the flow rate of the first product fluid and preferably as much as ten times the flow rate.
• a preferred form of the second heat exchanger is a plate type heat exchanger in which water is the product fluid. The water may then be provided either via a buffer storage tank or directly to an underfloor heating system.
• the second heat exchanger may be a convector type heat exchanger provided with fins and the second product fluid may be air e.g. for domestic warm air heating.
• the second product fluid when the flow of first product fluid through the first heat exchanger is stopped, a relatively higher flow of the second product fluid can flow through the second heat exchanger.
• the second product fluid will then be heated to a relatively lower temperature than the first product fluid.
• relatively low may be understood to be a temperature that is substantially lower than the effective maximum temperature that could be achieved from the chosen refrigerant for a given pressure.
• the second product fluid is heated to a second temperature lower than 50° C.
• the second temperature will be between about 25° C and 45° C.
• a method of operating such a heat pump installation by circulating a first product fluid through the first heat exchanger at a first volumetric flow rate to heat the first product fluid to a first temperature; and circulating the second product fluid at a second volumetric flow rate to heat the second product fluid to the second temperature.
• the first and second product fluids may both circulate simultaneously.
• the first and second product fluids may circulate alternately such that when the first product fluid flows, the second product fluid is stopped and vice versa.
• the installation when used to supply both domestic hot water and ambient (interior) heating, the installation is controlled to normally provide both supplies under thermostatic control with the hot water overriding the heating when both supplies are required simultaneously.
• Figure 1 is a schematic view of a heat pump installation according to the present invention
• Figure 2 is a schematic view of a coil heat exchanger
• Figure 3 is an exploded view of a plate heat exchanger
• Figure 4 is an exemplary control module for use in the installation.
• FIG. 1 shows a heat pump installation 1 comprising an outdoor unit 2 for mounting on the exterior of a building, an indoor unit 4, a hot water system 6 and a heating system 8. While reference is hereby made to individual elements and systems, it will be understood that these elements and systems are at least partially integrated with one another.
• the outdoor unit 2 contains an evaporator 10 and may be a standard split heat exchanger/ air- conditioning unit suitable for use outdoors. Exemplary devices for use as an outdoor unit 2 are the Dai Sei Kai, digital inverter and super digital inverter outdoor units available from Toshiba Corporation.
• the outdoor unit 2 also includes a number of other standard components such as compressor 3, electronically controlled pulse modulating expansion valve 5, control circuitry (not shown) etc.
• evaporator 10 is preferably a standard convoluted tube provided with fins, through which the refrigerant may flow and over which air may be directed.
• a fan 11 is included in the outdoor unit 10 to effect forced convection of air over the evaporator 10.
• the indoor unit 4 comprises a first condenser 12 and a second condenser 14.
• the first and second condensers 12, 14 are effectively heat exchangers through which the refrigerant may flow in thermal contact with a product fluid. They are in the present case referred to as condensers to indicate that they are each designed to allow complete condensation of the refrigerant. Further constructional details of the first and second condensers 12, 14 will be provided below.
• a refrigerant circuit 16 connects the evaporator 10 with the first condenser 12 and the second condenser 14 in series.
• the refrigerant circuit 16 contains a quantity of a commercially available refrigerant or heat exchange medium such as R-410A, which operates as the working fluid.
• Temperature sensors 20 are provided at various locations throughout the system.
• low-pressure refrigerant in the circuit 16 absorbs heat from the outside air as it flows through the evaporator 10.
• the heat causes the refrigerant to evaporate.
• the evaporated refrigerant is then compressed by a compressor (not shown) to a pressure of up to about 40 bar and directed to the indoor unit 4.
• a compressor not shown
• the high-pressure refrigerant enters the first condenser 12 where it flows downwards in close heat exchanging contact with water from the hot water system 6.
• Operation of the hot water pump 22 causes the water in the hot water system 6 to also flow through the first condenser 12 in counter flow to the refrigerant.
• the water exiting from the condenser 14 is supplied to the head of the buffer tank 26. Warm water from the head of the buffer tank 26 is also drawn off and supplied to the underfloor circuit 28 at a temperature of between 25° C and 45° C. Because of the nature of underfloor heating, the water must circulate at a flow sufficient to prevent excessive cooling thereof which could lead to local cold spots. The water leaving the underfloor circuit returns via the heating pump 34 to the condenser 14 at a temperature of between 20° C and 40° C.
• Individual room temperature control may be provided by the control module or by separate local (room) thermostats.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Water Supply & Treatment (AREA)
• Steam Or Hot-Water Central Heating Systems (AREA)
• Heat-Pump Type And Storage Water Heaters (AREA)

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• 2005
  • 2005-05-18 EP EP05741046A patent/EP1766295A1/de not_active Withdrawn
  • 2005-05-18 WO PCT/IB2005/001348 patent/WO2005114056A1/en active Application Filing

Non-Patent Citations (1)

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