Patent Description:
Heating water can be done through a variety of means. Boilers are an energy conversion technology with Co-efficient of Performance ("COP") of always less than <NUM>. As fuel costs increase, the cost of heating increases proportionately.

Vapour compression heat pumps are a heat transfer technology with a COP of typically greater than <NUM>, which degrades with increasing compression ratio. The compression ratio, and therefore efficiency, is adversely affected by reducing source temperature, and by increasing water leaving temperature requirement. They are more efficient at lower compression ratios.

CHP ("combined heat and power", and otherwise known as "cogeneration" systems) have a COP of less than <NUM> and require a "spark gap" of a certain magnitude to realise cost-efficiency. As the spark gap narrows, the CHP becomes less cost efficient.

Trigeneration is a variant of cogeneration, in which the heat output of cogeneration is used to drive an absorption chilling system that delivers chilling as an output. One of the outputs of the cogeneration component is therefore consumed or part consumed to deliver the third output, via a chiller with a COP of less than <NUM>.

<CIT>), <CIT>), and <CIT>) describes systems in this field.

An objective of the invention is to improve efficiency in provision of hot water for environments such as a food processing factory, linen washing plant, hospital, hotel, pharma, or similar users of hot water.

The invention provides an energy system as set out in claim <NUM>, and other aspects are described in claims <NUM> to <NUM>. The invention also provides a method of operation of an energy system as set out in claim <NUM>, and other aspects of the method are set out in claims <NUM> to <NUM>.

We describe an energy system which supplies water at different temperature levels for various purposes. A major example of application of the system is a food processing plant with different load circuits each for a different purpose such as washing and process water. The system in some examples the system also supplies electrical power. It provides these supplies in a real time manner on-demand in a manner which minimises energy input and hence minimises CO<NUM> generated. The system is controlled by a digital controller linked as is known in the art for process automation. Links from the controller are either wired or wireless.

Referring to <FIG> an energy system <NUM> has a hot water tank <NUM> which holds water at a high temperature, say <NUM>, in some cases with a margin above to allow for small losses. The energy for this comes from a third stage, Stage <NUM>, which includes an exhaust heat exchanger <NUM> of a gas turbine <NUM>, the output of which also generates electrical energy for a heat pump <NUM> of a second stage, Stage <NUM>. The water from the high temperature tank <NUM> is fed on a high temperature line with a pump <NUM> to a set of supply circuits <NUM>. A first stage, Stage <NUM>, recovers waste heat from equipment to elevate temperature of a cold water supply for the heat pump of Stage <NUM>, thereby significantly improving efficiency of the heat pump <NUM>.

In more detail, the energy system <NUM> heats ambient temperature water to a high temperature, say <NUM>, in various stages with each stage contributing to a given temperature rise. Stage <NUM> comprises a heat recovery heat exchanger ("HX") <NUM> that heats ambient water for process use to say <NUM>, using freely available waste heat. This process stream is further heated in additional stages. This HX <NUM> may have a second function, to contribute an additional water stream at <NUM> to act as a source for Stage <NUM>, when Stage <NUM> comprises a water source heat pump <NUM>. The efficiency of Stage <NUM> is elevated because of receiving a warmer source than ambient. Once source heat is extracted from this water stream, it is recirculated to the heat recovery HX <NUM> for reheating. Stage <NUM> may also use as its source a chilling circuit, or cooling tower circuit, or other waste water source, or it may be an air source heat pump, or a refrigeration compressor. The process component flows onward to the heat sink, or condenser, of the heat pump <NUM> used as Stage <NUM> heating, to elevate the temperature of the process water stream to say, <NUM>, and is conveyed to a low temperature tank <NUM>. Some of this <NUM> water may be used directly in the process and the remainder is used as the low temperature component for blending in the supply circuits <NUM>.

A controlled output temperature from the heat pump <NUM> is preferably adjustable downwards to increase coefficient of performance ("COP") of the heat pump.

Stage <NUM> receives the <NUM> water from the tank <NUM> and includes the turbine flue HX <NUM> which elevates the process flow to <NUM> and feeds a high temperature storage tank <NUM> arranged to deliver water on a high temperature (<NUM>) line <NUM> to the supply circuits <NUM>. The low temperature (LT) storage tank <NUM> may be arranged to deliver lower temperature (<NUM>) water on a LT line <NUM>, <NUM> to the supply circuits <NUM>. A number of the supply circuits <NUM> are each arranged to receive high temperature ("HT") water, receive LT water, and blend these flows to deliver a process water supply at a desired high, low or intermediate temperature (<NUM>) in an outlet line <NUM>(a), <NUM>, <NUM>.

A high temperature circuit <NUM> receives water directly from the HT line <NUM>, and the temperature may be diluted by the cooling effect of a return pump <NUM>, which will have a relatively small effect. The outlet temperature from flue HX <NUM> may be controlled and increased to compensate for this cooling effect to ensure that the required flow temperature is met. This control is achieved by feedback from a temperature sensor <NUM>, resulting in the controller controlling the turbine <NUM> accordingly as indicated by the interrupted line from <NUM> to <NUM>.

In each supply circuit where the required water temperature is lower than the HT supply temperature, the blending may for example be controlled by control of blending pumps <NUM>, <NUM> according to temperature of the process outlet (<NUM>, <NUM>).

The number and capacity of turbines selected determines the base heating capacity. For example, one turbine may heat <NUM>/s of water from <NUM> to <NUM>. This same flow rate is heated upstream, from <NUM> to <NUM> (Stage <NUM>), and <NUM> to <NUM> (Stage <NUM>), as described in more detail below, with the capacity of Stages <NUM> and <NUM> being increased in proportion with the increased capacity of Stage <NUM>. Other particular process factors may allow the proportional increase to be varied. The capacity of Stages <NUM> and <NUM> will also include the additional heating requirements of the <NUM> flow to blending and/or direct to process.

The water supply <NUM> is either direct from mains or a holding tank, and its temperature is typically about <NUM>. This cold supply water is delivered to the heat recovery HX <NUM> which recovers heat from various refrigeration and air conditioning systems in the plant in which the system <NUM> is installed. So, its primary energy input is waste heat. The Stage <NUM> HX <NUM> comprises a plate heat exchanger, or other heat exchanger appropriate to the waste heat stream, with pump and control valves.

As an example, the flow rate of supply water to the heat recovery HX <NUM> may be <NUM><NUM>/hr. The HX <NUM> is rated at 225kW, of which 75kW is pre-heat energy to the received water, raising its temperature to about <NUM>, and the remaining <NUM> kW is used to deliver source heat to the Stage <NUM> heat pump <NUM>.

In an example, water is heated from <NUM> to <NUM>, using low grade heat recovered in the HX <NUM> from the relevant industrial process, and this pre-heats additional water that is used as a source for the heat pump <NUM>. The heat pump may alternatively be an air source heat pump, or it may use cooling tower water from an external chiller system, or use the chilling duty itself, as source.

The output water of the heat recovery HX <NUM>, elevated to <NUM>, is fed to the heat pump <NUM>. This adds 188kW of energy to the water, bringing its temperature up to <NUM>, meaning that energy of <NUM> kW is delivered to the LT water tank <NUM>.

A scaling factor applied to the heat pump <NUM> allows additional <NUM> water to be produced for direct use in the process, and for blending with <NUM> to produce, for example, wash water at a desired intermediate temperature.

In this example there are three process supply circuits <NUM>, <NUM> and <NUM>, each of which receives an input from the high temperature tank <NUM> via the pump <NUM>. This pump is controlled according to pressure at its outlet to the blending circuits <NUM>. The system controller therefore controls the delivery flow rate of HT water in real time according to overall demand in the supply circuits <NUM>, which deliver water to the plant at the desired temperature and flow rates. Each circuit <NUM>, <NUM>, and <NUM> is for a particular process water system such as hand washing, plant washing, or meat treatment, and may be a ring main system with water constantly flowing in the circuit to ensure that temperature stagnation at periods of low use does not occur. Return pumps <NUM>, <NUM>, <NUM> are employed to effect this.

The circuit <NUM> has an outlet line <NUM>(a), a temperature sensor <NUM>, a return line <NUM> with a return pump. The temperature of the outlet line <NUM> is controlled as the output temperature of the Stage <NUM> heating system, being the turbine <NUM>, and the heat exchanger <NUM>.

The circuit <NUM> has an outlet <NUM>, return pump <NUM>, a temperature sensor <NUM>, and a blending pump <NUM> controlled according to temperature feedback from a temperature sensor <NUM>. The circuit <NUM> has an outlet <NUM>, a return pump <NUM>, a temperature sensor <NUM>, and a blending pump <NUM> controlled according to temperature feedback from the sensor <NUM>.

In this example the circuits <NUM>, <NUM>, and <NUM> provide water at <NUM>, <NUM>, and <NUM> respectively. However, these values may be varied by control of the pumps, <NUM>, <NUM>, and the outlet temperature of Stage <NUM>. Also, the components feeding the tank <NUM> are controlled according to the highest desired temperature from the supply circuits. In this case the highest level is <NUM>, and accordingly the HX <NUM> is controlled in real time to deliver water at the required elevated temperature so that the circuit <NUM> can maintain the water at a consistent level of <NUM> as measured by the sensor <NUM>. This is to overcome the slight cooling effect of the return flow <NUM>.

Returning to the energy flows, the turbine <NUM> exhaust flue provides <NUM> kW, which is added to the <NUM> water in order to deliver the <NUM> to the tank <NUM>. The turbine <NUM> receives 222kWg of energy from the gas, delivering <NUM> kW to the heat exchanger <NUM> and 65kW in electrical power to the heat pump <NUM>. In this example this electrical power is split into <NUM> kW to the heat pump and <NUM>. 5kW to the process.

Overall, the primary energy inputs are the gas supply to the turbine <NUM> and the waste heat into the heat recovery HX <NUM>. The system <NUM> captures low grade heat from the plant and uses this free energy to raise the temperature into the heat pump <NUM>, thereby reducing its compression ratio. This initially-heated water may also be used to provide water to a process which uses water at this relatively low temperature. Hence the tank <NUM> is filled in an inexpensive way and which contributes little carbon dioxide generation. This tank directly supplies the blending, process water, circuits <NUM> via variable speed drive (VSD) pumps <NUM> and <NUM>. This water may be used directly as in the circuit <NUM>, or as a blending input as for the circuit <NUM>. There is therefore optimum use of energy, with very little waste due to the real time control of the components to optimise the temperature in the tank <NUM> (according only to the maximum required at the circuit <NUM>.

The following is an example energy profile.

COP (Purchased (Imported) Energy Input / Useful Energy output) = <NUM>/<NUM> = <NUM>.

CO<NUM> savings may be calculated as follows:
Grid electricity replaced: (<NUM>. 5kWe/<NUM>) x <NUM> = <NUM> kW.

Boiler at <NUM>% nominal efficiency: <MAT> <MAT>.

There is a gas fuel input to the system <NUM> of 222kW, replacing a prime energy input of <NUM>. 8kW, yielding a saving of <NUM> kW of prime energy. Assuming a natural gas fuelled boiler, this equates to a saving of about <NUM>/hr CO<NUM>.

Overall, the system <NUM> has excellent energy efficiency due to the manner in which waste heat is utilized, being recovered to preheat process water and also to elevate temperature of a cold water supply to optimize efficiency of a heat pump, which in turn feeds the low temperature storage tank used by the supply circuits for blending, and to preheat the process flow to the Flue heat exchanger <NUM>.

The system may be operated using only the heat pump <NUM> to provide the high temperature water, bypassing the turbine <NUM> and using electricity from the grid to operate the heat pump. Such grid power is preferably from carbon-neutral sources such as wind power. This is shown in <FIG>. In this example the heat pump <NUM> provides a flow of water at <NUM> and the low temperature tank <NUM> is fed directly from the Stage <NUM> heat exchanger <NUM>, at about <NUM> in this example.

The water blending increases overall operating system efficiency by recovering energy from the heat pump and advantageous use of waste heat. This is achieved by supplying the lowest temperature water, about <NUM>, to recover the condensing and subcooling energy from the heat pump to maximize its COP. The higher the supply temperature process water to be heated by the heat pump the lower the COP, as less subcooling can be recovered.

Heat recovery is used as a heat source for the heat pump <NUM> and the low temperature tank <NUM>. For the heat pump <NUM> there is <NUM> in and <NUM> out which by-passes the tank <NUM> and fills the high temperature tank <NUM> with a piping configuration. This low-grade waste heat which can be <NUM> or more is injected to the blending circuits <NUM> and <NUM> by the blending system pumps <NUM> and <NUM> controlled by TT-<NUM> and TT-<NUM>. The pump <NUM> operates at a reduced speed controlled by PT <NUM>, and less energy will be required from the tank <NUM>. When operating in this mode maximum kW energy and efficiency is delivered from the heat pump <NUM> and the waste heat HX <NUM>. The blending can utilise waste heat at temperature above <NUM> which would in other prior systems be dumped to atmosphere.

Operating in this mode the invention overall COP is increased, and there is no burning of fossil fuels if the grip-provided power is by wind source.

It will be appreciated that the system delivers reliable temperature and flow to process with a variable flow demand, whilst maintaining the required temperatures. Also, it avoids the need for delivery-side heat exchangers and therefore avoids potential for fouling.

Also, it will be appreciated that the reduced temperature from the heat pump, being the temperature on to the turbine heat exchanger <NUM>, allows additional heat to be extracted from the flue gas flow from the turbine, thus increasing the efficiency of Stage <NUM>.

Advantageously, the system <NUM> is arranged so that the quality, or temperature, of the heat source is matched to the temperature requirement to optimise the efficiency of each stage.

Claim 1:
An energy system comprising:
a high temperature line (<NUM>), a high temperature water heater (<NUM>,<NUM>) and a high temperature storage tank (<NUM>) arranged to deliver hot water on the high temperature line (<NUM>),
a a low temperature line (<NUM>,<NUM>), a heat pump (<NUM>) and a low temperature storage tank (<NUM>) arranged to deliver lower temperature water on the low temperature line (<NUM>, <NUM>), a plurality of hot water supply circuits (<NUM>) each comprising a corresponding outlet line (21a,<NUM>,<NUM>) and each arranged to
receive high temperature water from the high temperature line (<NUM>),
receive low temperature water from the low temperature line (<NUM>, <NUM>), and deliver a process water supply at a desired high, low, or intermediate temperature in said corresponding outlet line (<NUM>(a), <NUM>, <NUM>), in which a supply circuit (<NUM>, <NUM>) delivering water at an intermediate temperature is arranged to blend the high temperature and low temperature flows; and
a controller configured to control the system, wherein the controller is configured to control the water heater (<NUM>,<NUM>) and the blending in real time,
characterized in that:
the system comprises a pump in the high temperature line (<NUM>) for delivering high
temperature water to the supply circuits (<NUM>), and the controller is configured to control said pump according to sensed pressure between said pump and the supply circuits (<NUM>),
at least one supply circuit of said supply circuits (<NUM>, <NUM>) comprises a low temperature line pump in said low temperature line (<NUM>, <NUM>), and the controller is configured to control said low temperature line pump according to sensed temperature in the supply circuit outlet line (<NUM>, <NUM>) to achieve a desired level of blending, and the controller is configured to control the low temperature line pump to dynamically control blending of water from the high temperature line (<NUM>), the low temperature line (<NUM>,<NUM>) and a return line (<NUM>) to provide process water,
the high temperature water heater comprises a gas turbine (<NUM>) and a flue gas heat exchanger (<NUM>), said heat exchanger being arranged to heat water for delivery to the high temperature storage tank (<NUM>),
the turbine (<NUM>) is arranged to provide electrical energy for the heat pump (<NUM>), either directly or indirectly, with surplus generated electricity being provided for a process.