Patent Description:
Heat pump technology is well known, and its limitations are also well known. Temperature of water delivered, with acceptable efficiencies, is too low for many buildings, the typical requirements being in the region of <NUM> to <NUM>. To operate an air source heat pump (ASHP) in an existing building considerable refurbishment is often required, and there are inherent inefficiencies at low ambient temperature when most heating is required resulting in demand for extra electrical power from the grid. Commercial natural gas is typically about <NUM> times less expensive per kWh than electrical energy.

Documents in this field are <CIT>, <CIT>), <CIT>), and <CIT>).

The invention is directed towards achieving improved efficiency in water heating systems.

The invention provides a heating system as set out in claim <NUM> and the dependent claims <NUM> to <NUM>. It also provides a method of operation of such as system as set out in claim <NUM> and the dependent claims <NUM> to <NUM>.

Referring to <FIG> and <FIG> a heating system <NUM> comprises a main air flow conduit or "duct" <NUM> with an inlet <NUM> to take in ambient air from outside, and internal first and second secondary inlets <NUM> and <NUM> to take in hot air from within the system <NUM>, a variable speed drive (VSD) fan <NUM>, and an evaporator coil cooler <NUM> to extract energy from the combined air flow.

A turbine <NUM> is arranged to receive gas fuel and provide hot exhaust gas to a three-stage heat exchanger <NUM>, each stage of which can provide heated air or water at a desired temperature, progressively lower from the first stage to the third stage. The main conduit <NUM>, the fan <NUM>, and the outlet cooler <NUM> may be regarded as a fourth stage of heat exchange downstream of the heat exchanger's three stages. The turbine also provides electrical power to heat-pumps, in this case an air source heat pump ASHP <NUM> and a water source heat pump WSHP <NUM>. The heat pump <NUM> receives air at a temperature which is elevated above the outside ambient. Also, the ASHP <NUM>, using elevated-temperature inlet air, delivers elevated-temperature water to the WSHP <NUM>.

The first and second stages <NUM>(a) and <NUM>(b) of the heat exchanger <NUM> provide hot water as system outputs. The third stage <NUM>(c) provides hot water as a source to the WSHP <NUM> by extracting sensible and latent heat from the lower temperature exhaust gas.

For example, <FIG> gives indicative parameter values which are set out in the table below with notes on where they are, giving an understanding of operation of the system <NUM>.

The heat exchanger <NUM> is a three-stage heat exchanger with low pressure drop on the exhaust gas side, which provides heated process water from stage <NUM> (a) and <NUM> (b) at two temperature levels:.

The heat exchangers are comprised of a number of cassettes that are arranged both in series and in parallel to split the total water flows into two streams, thus reducing the flow through each stream, to manage port and channel pressure loss.

The heat exchanger <NUM> is shown in more detail in <FIG>. Flue gas from the turbine enters via a conduit <NUM>. The flue gas enters the first stage <NUM>(a) at for example <NUM>. The turbine flue gas is in the primary side of all three stages, the secondary side being water.

The turbine <NUM> receives gas fuel which with ambient air, is combusted to drive a turbine which in turn rotates a generator to generate electricity. The exhaust gas from the combustion exits after recuperation, at <NUM> and is progressively cooled to <NUM> in the three-stage water cooled heat exchanger system, HX <NUM>.

The heating system delivers high temperature heat with greater efficiency than a boiler, and, without additional fuel consumption, will deliver electrical power with no additional environmental costs. This is achieved through the use of ambient air as a heat energy source. The system supplies its own controlled energy source for the heat pumps regardless of outside ambient air temperature. It can supply a source temperature <NUM> above ambient on to the evaporator <NUM>.

In the example of <FIG> and <FIG> there are two heat pumps, the ASHP <NUM> supplies part of the working energy source for the WSHP <NUM>. A controller with digital data processors operates the heat pumps to maximise the combined overall efficiency by controlling the source temperature to each heat pump so that the combined heat pump cycle can deliver water at up to <NUM> from the WSHP 60as an additional output to process.

With higher inlet water temperature, thermal output increases and net electrical output decreases. The heat pump capacities are selected so that the total power consumption, including pumps and other parasitic loads, do not exceed the power output of the turbine. The controller increases and decreases thermal and electrical outputs depending on ambient air temperature, and uses ambient air to increase output efficiency. It maintains efficiency at very low ambient (about -<NUM>) by not using mixing ambient air and by pre-heating ambient air to the turbine (Mode <NUM>).

The system generates electricity for its parasitic requirements on all operating modes, and the operating modes dictate surplus electrical output to process.

The system uses a three-compartment heat exchanger with three different temperature outputs, and it uses an air-to-air heat reclaim system which is temperature-controlled.

Flue gas exits the turbine (<NUM>, <NUM>/h) enters the HX <NUM>, and the gas is dispersed equally <NUM>/h per two heat exchangers streams in stage <NUM>(a).

Stage <NUM>(a), flue gas temperature is controlled by a temperature sensor Sensor <NUM> and a pump S-<NUM> by controlling the speed of the pump S-<NUM>, the flue temperature having a set point of <NUM>.

Flue gas exits stage <NUM>(a) at <NUM> and enters stage two <NUM>(b).

Stage <NUM>, flue gas temperature is controlled by a temperature sensor Sensor-<NUM> and a pump S-<NUM> by controlling the speed. Flue temperature set point <NUM>.

Flue gas second stage exit, <NUM> and enters stage three <NUM>(c).

Stage <NUM>(c), flue gas temperature is controlled in response to a temperature feed from a combined temperature and pressure sensor Sensor-<NUM> and a pump S-<NUM> is controlled by controlling the speed. Flue temperature set point is <NUM>. All of the pumps S-<NUM>, S-<NUM>, and S-<NUM> are VSD pumps.

Flue gas exits stage three <NUM>(c) at <NUM> and enters the air in the main conduit <NUM>, where it helps to increase the temperature in the main conduit to about <NUM>. Hence the ambient air inlet at <NUM> flows through the conduit <NUM> and its temperature is increased by the hot air at <NUM> in the duct <NUM> from the turbine electronics and the flow in the duct <NUM> from the HX third stage at <NUM>. This provides a flow to the evaporator <NUM>, the refrigerant coil of which is in closed circuit with the ASHP <NUM>, providing considerable energy to the ASHP while reducing the main conduit <NUM> air flow from <NUM> to <NUM>. The VSD (variable speed drive) fan <NUM> sucks air (from turbine electronics and ambient air) in the main conduit <NUM> and blows blended air over the evaporator <NUM>. Temperature of blended air is controlled by sensor S-<NUM>.

An anemometer and a temperature sensor Sensor-<NUM> calculate available energy in air flow leaving <NUM>(c), and this will modulate capacity of ASHP, WSHP and flow on pump S-<NUM>.

The speed of the pump P-<NUM> is modulated to ensure that the water temperature at the temperature Sensor-<NUM> inlet to the WSHP is <NUM> higher than water temperature at the temperature sensor Sensor-<NUM>.

If the temperature at the sensor Sensor-<NUM> ><NUM>, the system is disabled.

The sensor Sensor-<NUM> is a combined pressure and temperature sensor. The controller is programmed to monitor by way of a feed from Sensor-<NUM> the pressure in the flue gas heat exchanger <NUM>. It is maintained at approximately 15milliBar (mB) by control of the fan <NUM>, and the preferred pressure range for the heat exchanger <NUM> is 5mB to 20mB. If it rises above the level of 20mB the controller disables the overall system to prevent excessive fuel consumption. In one example, the fan <NUM> is varied if the Sensor-<NUM> sensed pressure in the heat exchanger is in the range of <NUM> to 20mB.

The setting of a modulating damper, that controls the amount of ambient air introduced, is-controlled by the output of a calculation involving the temperature sensor Sensor-<NUM>, anemometer and temperature sensor Sensor-<NUM> and heat pump output. The calculation is used to determine the optimum mix of ambient air and condensing of exhaust gas. The controller calculates which mix is best to increase the overall efficiency.

In overall terms energy enters the system <NUM> as fuel to the turbine <NUM> and as ambient air into the inlet <NUM>. The turbine is run with a lean mix, in one example <NUM>:<NUM> gas:air ratio. Energy is captured from the turbine control electronics and residual flue gas increase the energy in the air flowing through the main conduit <NUM>, from the ambient inlet of <NUM> to <NUM> an entry to the evaporator <NUM>. Energy from the evaporator <NUM> coil water energy from the HX third stage boost the inputs to the ASHP and WSHP, greatly increasing their efficiencies. There are three hot water outputs, <NUM> from the first stage of the HX, <NUM> form the second stage, and about <NUM> to <NUM> from the WSHP <NUM>. For example, the WSHP <NUM> receives in one example inlet water at greater than <NUM> rather than about <NUM> which is typical.

<FIG> illustrate various modes of operation, set out in detail below. In these examples and in the drawings all flows are per hour. Also, Stage <NUM> is provided by the main conduit <NUM>, the fan <NUM>, and the cooler <NUM>.

The system recovers latent heat energy through the condensation of the water vapour in the exhaust gas, without creating excessive back pressure on the turbine, while recovering energy to do useful work. It avoids the problem of a large surface being required to extract latent energy with one heat exchanger as it will cause back pressure on turbine and reduce electrical output, by reducing the volume flow through the heat exchanger. This is achieved by a number (in this example <NUM>) of flue gas heat exchangers in parallel which divides the flow and halves the pressure drop.

Also, the system <NUM> achieves recovery of low temperature energy and delivery of high temperature energy by split heat recovery in multiple separate compartments and each compartment with its own delivered temperature set point with no temperature cross contamination.

Moreover, the system condenses flue gas, despite the fact that in general, condensing will not occur at exhaust gas temperatures greater than <NUM>. This is primarily due to the use of a water source heat pump to cool the flue and extract the latent energy and use this energy to increase the efficiency of the WSHP. The temperature of the source to the WSHP can be controlled to allow the delivery of higher temperature water from the WSHP, whilst maintaining efficiency.

For example, with an exhaust gas flow of <NUM>/h, with temperature in at <NUM>, temperature out at <NUM> (<NUM>): <MAT> <MAT>.

The system moreover recovers residual waste heat from the flue gas, waste heat from the electronic circuits and ambient air, and elevates the blended air above the ambient air temperature. This temperature will increase efficiency on to evaporator coil <NUM> which increases the efficiency of the ASHP, in a controlled manner.

ASHP efficiency is maximized by recovery of free energy from the environment and latent heat, as set out in the following example:.

Claim 1:
A heating system (<NUM>) comprising:
an electronic controller,
a turbine (<NUM>) for burning a fuel to provide flue gas and electrical energy,
a flue gas heat exchanger (<NUM>) for receiving the flue gas and using the flue gas to heat water,
a main conduit (<NUM>) for receiving inlet air (<NUM>) and gases from secondary inlets (<NUM>, <NUM>) from within the system to elevate the temperature in the main conduit (<NUM>) above ambient,
an air heat exchanger (<NUM>) for recovering heat from the air flow of the main conduit, and an air source heat pump ASHP (<NUM>) to receive energy from the air heat exchanger (<NUM>),
wherein the air heat exchanger comprises a cooler (<NUM>) arranged to cool air from the main conduit (<NUM>) for venting to atmosphere,
characterized in that
the cooler (<NUM>) comprises an evaporator coil cooler and it shares an evaporator coil with the ASHP (<NUM>) to transfer energy to said ASHP,
the system further comprises a water source heat pump WSHP (<NUM>) to receive a water feed at an elevated temperature from the ASHP (<NUM>), in which at least one stage (<NUM>(a), <NUM>(b)) of the flue gas heat exchanger and the WSHP are configured to provide process hot water,
and wherein recovered energy from the flue gas heat exchanger (<NUM>(c)) is provided to the WSHP (<NUM>),
wherein the cooler and the ASHP are in an evaporator circuit, whereby the cooler (<NUM>) delivers energy to the ASHP (<NUM>), the ASHP receives elevated-temperature water from the flue gas heat exchanger (<NUM>(c)) and delivers elevated temperature water to the WSHP (<NUM>), and the flue gas heat exchanger (<NUM>) delivers elevated-temperature water to the WSHP.