Patent Description:
Air handling units are used for heating and cooling fresh air for supply to HVAC system of buildings. They often employ heat pumps to improve their energy efficiency, with the heat pumps generally using R410a refrigerant, which has high global warming potential (GWP), with a GWP value of <NUM>. There is a drive to reduce the use of refrigerants with high GWP values, and to move towards refrigerants with lower GWP values. However, in general, refrigerants with low GWP values are flammable. A leak of flammable refrigerant represents a significant fire hazard.

Patent publication <CIT> describes a system for controlling the indoor climate in a building, at least comprising a first air duct for supply air, a second air duct for exhaust air, an exhaust-supply air heat exchanger or selective transfer of heat between supply air and exhaust air, a water system having a hot water circuit and a cold water circuit, a water-supply air heat exchanger at the first air duct and a water-exhaust air heat exchanger at the second air duct, both for selective connection to the hot water circuit or the cold water circuit, a heat pump for selective transfer of heat between the water circuits, wherein first fan devices circulate ventilation air to/from the building, wherein the system has a passage for admitting a partial flow of outdoor air upstream of the water-exhaust air heat exchanger, wherein second fan devices suck or blow the partial flow together with exiting circulated ventilation air, through the water-exhaust air heat exchanger, wherein the second fan devices provide a maximum air flow rate at least <NUM> times greater than the air flow rate from the first fan devices. Document <CIT> discloses a heat transfer device according to the preamble of claim <NUM>.

According to a first aspect of the invention, there is provided a heat transfer device as set out in accompanying claim <NUM>.

The heat transfer device is advantageous, as it means that the refrigerant in the vapour compression circuit is located remotely from the air handling unit, with the first heat transfer fluid used to carry fluid to or remove fluid from the supply air passing through the air supply passage of the air handling unit. The refrigerant in the vapour compression circuit may thus operate in isolation from the air supply passage such that there is no direct fluid path for refrigerant vapour to enter the air supply air passage in the event of leakage from the vapour-compression circuit. This means that the risk of refrigerant getting to an occupied area, such as a room to which the air handling unit supplies air, is reduced. This avoids contamination of the occupied area, and, in the case of a flammable low GWP refrigerant, significantly reduces the risk of fire.

In an example, the heat transfer device comprises a first inlet adapted to receive first heat transfer fluid returned from the air handling unit, the first inlet in fluid communication with the first outlet via the first heat exchanger to form a first circulation system. Recirculating the first heat transfer fluid is advantageous, as it means that first heat transfer fluid (and its thermal energy) can be reused.

According to the invention, heat transfer device comprises a first pump for pumping first heat transfer fluid to the air supply passage, the first pump controllable to control flow rate of first heat transfer fluid to the air supply passage. The first pump provides a straightforward means for supplying the first heat transfer fluid to the air supply passage, and the first pump being controllable allows the rate of heat exchange between the first heat transfer fluid and the supply air can be controlled, thereby allowing the temperature of the supply air supplied by the air handling unit to be controlled.

The vapour compression circuit comprises a second heat exchanger adapted to exchange heat with a second heat transfer fluid, the heat transfer device comprising a second outlet arranged to provide the second heat transfer fluid to a return-from-area passage of the air handling unit, so that the second heat transfer fluid exchanges heat with return air passing through the return-from-area passage. This allows thermal energy to be passed to or from the second heat transfer fluid in the vapour compression circuit, thereby increasing the efficiency of the vapour compression circuit.

In an example, the heat transfer device comprises a second inlet adapted to receive second heat transfer fluid returned from the air handling unit, the second inlet in fluid communication with the second outlet via the second heat exchanger to form a second circulation system. Recirculating the second heat transfer fluid is advantageous, as it means that second heat transfer fluid (and its thermal energy) can be reused.

According to the invention, heat transfer device comprises a second pump for pumping second heat transfer fluid to the return-from-area passage, the second pump controllable to control flow rate of second heat transfer fluid to the return-from-area passage. The second pump provides a straightforward means for supplying the second heat transfer fluid to the air supply passage, and the second pump being controllable means allows the rate of heat exchange between the second heat transfer fluid and the supply air can be controlled.

According to the invention, the heat transfer device is arranged to operate in a heat pump mode, and, in the heat pump mode, the heat transfer device heats the first heat transfer fluid using the first heat exchanger so as to heat the supply air. In an example, in the heat pump mode, the heat transfer device draws heat from the second heat transfer fluid using the second heat exchanger.

According to the invention, the heat transfer device is arranged to operate in a refrigeration mode, and in the refrigeration mode, the heat transfer device cools the first heat transfer fluid using the first heat exchanger so as to cool the supply air. In an example, in the refrigeration mode, the heat transfer device heats the second heat transfer fluid using the second heat exchanger.

In an example, in the heat pump mode and in the refrigeration mode, the vapour compression circuit operates a Carnot cycle.

In an example, the vapour compression circuit comprises at least one compressor, the heat transfer device switchable between the heat pump mode and the refrigeration mode by switching polarity of the at least one compressor. This means that the same components can be used to provide the refrigeration and heat pump cycles, with switching between the cycles effected in a straightforward manner.

In an example, the vapour compression circuit comprises the refrigerant, the refrigerant having a GWP value less than or equal to <NUM>. In an example, the vapour compression circuit comprises the refrigerant, the refrigerant having a GWP value less than or equal to <NUM>. In an example, the refrigerant is R290. Such refrigerants are better for the environment, and the use of the remote heat transfer device reduces the risk of fire when they are used, as described above.

In an example, the first heat transfer fluid is a liquid, for example water. Water has a relatively high specific heat capacity and provides a safe fluid for carrying thermal energy to the air handling unit.

In an example, the heat transfer device comprises a second vapour-compression circuit, the second vapour-compression circuit comprising a third heat exchanger adapted to exchange heat between a refrigerant in the second vapour compression circuit and the first transfer fluid. Using two independent circuits reduces the amount of refrigerant required in each circuit to achieve the same total heating/cooling. This keeps the flammable charge below the maximum allowable limit for safe operation, which is typically <NUM>. The minimum operational capacity for a compressor is typically <NUM>%, so using two circuits gives a total unit minimum capacity of <NUM>%, which provides improved flexibility in heating and cooling fresh air, to achieve the required supply air temperature at moderate atmospheric temperature.

According to a second aspect of the invention, there is provided an air handling system as set out in accompanying claim <NUM>.

In an example, the air handling system comprises a return-from-area passage for receiving return air from the occupied area and supplying the return air to the atmosphere, wherein the return-from-area passage comprises a return heat exchanger in fluid communication with the second outlet of the remote heat transfer device to receive second heat transfer fluid from the remote heat transfer device, the return heat exchanger adapted to exchange heat between the second heat transfer fluid and the return air. This allows thermal energy to be passed to or from the second heat transfer fluid in the vapour compression circuit, thereby increasing the efficiency of the vapour compression circuit present in the remote heat transfer device.

In an example, the air handling system comprises a recovery wheel for exchanging heat between the return air and the supply air.

According to a third aspect of the invention, there is provided a method of air handling, the method as set out in accompanying claim <NUM>.

The method is advantageous, as it means that the refrigerant in the vapour compression circuit is located remotely from the air handling unit, with the first heat transfer fluid used to carry fluid to or remove fluid from the supply air passing through the air supply passage of the air handling unit. This means that the risk of refrigerant leaking into an occupied area, such as a room to which the air handling unit supplies air, is reduced. This avoids contamination of the occupied area, and, in the case of a flammable low GWP refrigerant, significantly reduces the risk of fire.

The method comprises the features of claim <NUM>, and in particular exchanging heat between the refrigerant in the vapour-compression circuit and a second heat transfer fluid; providing the second heat transfer fluid to a return-from-area passage, wherein the return-from-area passage receives return air from the room and supplies the return air to the atmosphere; and exchanging heat between the second heat transfer fluid and the return air. This allows thermal energy to be passed to or from the second heat transfer fluid in the vapour compression circuit, thereby increasing the efficiency of the vapour compression circuit present in the remote heat transfer device.

For a better understanding of the invention reference is made, by way of example only, to accompanying <FIG>, which shows a schematic drawing of an air handling system <NUM>.

The air handling system <NUM> comprises an air handling unit <NUM>. The air handling unit <NUM> comprises an air supply passage <NUM> and a return-from-area passage <NUM>, each in fluid communication with an occupied area <NUM> (for example, a room) and the atmosphere <NUM> (i.e. outside the room). In the present example, the air supply passage <NUM> and the return-from-area passage <NUM> are in direct fluid communication with the occupied area <NUM> and the atmosphere <NUM>. However, it will be appreciated that in other examples, either or both of the air supply passage <NUM> and the return-from-area passage <NUM> is indirectly connected to either or both of the occupied area <NUM> and the atmosphere <NUM> using ducting (not shown). The occupied area <NUM> is isolated from the atmosphere <NUM>, aside from through the air handling unit <NUM>.

The air supply passage <NUM> and the return-from-area passage <NUM> are of approximately equal cross sectional areas. The air supply passage <NUM> comprises an air supply fan 21a, the air supply fan 21a operable to drive supply air along the air supply passage <NUM> from the atmosphere <NUM> towards the occupied area <NUM>. The return-from-area passage <NUM> comprises an air return fan 21b, the air return fan 21b operable to drive return air along the return-from-area passage <NUM> from the occupied area <NUM> towards the atmosphere <NUM>.

The air handling unit <NUM> comprises a supply heat exchanger <NUM> located in the air supply passage <NUM>. The supply heat exchanger <NUM> is operable to exchange heat between the supply air and a first heat transfer fluid, as described in more detail below. The air handling unit <NUM> comprises a return heat exchanger <NUM> located in the return-from-area passage <NUM>. The return heat exchanger is operable to exchange heat between the return air and a second heat transfer fluid, as described in more detail below. The first heat transfer fluid is water. The second heat transfer fluid is water.

The air handling unit <NUM> comprises a recovery wheel <NUM>, which is formed of a heat absorbent material. The recovery wheel <NUM> is positioned with its axis of rotation aligned with the air supply passage <NUM> and the return-from-area passage <NUM>, with a first half of the recovery wheel <NUM> in the air supply passage <NUM> and a second half of the recovery wheel in the return-from-area passage <NUM>.

The air handling system <NUM> comprises a remote heat transfer device <NUM>. The remote heat transfer device <NUM> comprises a vapour-compression circuit <NUM>. The vapour compression circuit <NUM> comprises a first heat exchanger <NUM>, a compressor <NUM>, a second heat exchanger <NUM> and a metering device <NUM>. The metering device <NUM> is an expansion valve <NUM>. The first heat exchanger <NUM> is connected to the compressor <NUM> and the expansion valve <NUM>. The second heat exchanger <NUM> is connected to the compressor <NUM> and the expansion valve <NUM>.

The first heat exchanger <NUM> is part of a first circulation system <NUM>, which comprises the supply heat exchanger <NUM> and a first pump <NUM>. The first heat exchanger <NUM> is operable to exchange heat between refrigerant in the vapour-compression circuit <NUM> and the first heat transfer fluid in the first circulation system <NUM>, as described in more detail below. The refrigerant is R290.

The remote heat transfer device <NUM> comprises a first outlet <NUM>, through which the first heat exchanger <NUM> is connected to the supply heat exchanger <NUM>, as part of the first circulation system <NUM>. The remote heat transfer device <NUM> comprises a first inlet <NUM>, through which the supply heat exchanger <NUM> is connected to the first pump <NUM>, as part of the first circulation system <NUM>. The first pump <NUM> is located in the remote heat transfer device <NUM>, and connects to the first heat exchanger <NUM>.

The second heat exchanger <NUM> is part of a second circulation system <NUM>, which comprises the return heat exchanger <NUM> and a second pump <NUM>. The second heat exchanger <NUM> is operable to exchange heat between refrigerant in the vapour-compression circuit <NUM> and the second heat transfer fluid in the second circulation system <NUM>, as described in more detail below.

The remote heat transfer device <NUM> comprises a second outlet <NUM>, through which the second heat exchanger <NUM> is connected to the return heat exchanger <NUM>, as part of the second circulation system <NUM>. The remote heat transfer device <NUM> comprises a second inlet <NUM>, through which the return heat exchanger <NUM> is connected to the second pump <NUM>, as part of the second circulation system <NUM>. The second pump <NUM> is located in the remote heat transfer device <NUM>, and connects to the second heat exchanger <NUM>.

The remote heat transfer device <NUM> is located remotely from the air handling unit <NUM> and the occupied area <NUM>, to reduce the risk of the refrigerant leaking into the air supply passage <NUM>, the return-from-area passage <NUM> or the occupied area <NUM>, and thereby reducing the risk of fire. Pipework is provided between the remote heat transfer device <NUM> and the air handling unit <NUM> to allow the first and second heat transfer fluids to flow in the first and second circulation systems <NUM>, <NUM> respectively. Otherwise, the remote heat transfer device <NUM> is sealed. The remote heat transfer device <NUM> and the air handling unit <NUM> are separate units.

In use, refrigerant flows around the vapour-compression circuit <NUM>, driven by the compressor <NUM>. The first pump <NUM> drives the first heat transfer fluid around the first circulation system <NUM>, so that the refrigerant exchanges heat with the first heat transfer fluid in the first heat exchanger <NUM>. The second pump <NUM> drives the second heat transfer fluid around the second circulation system <NUM>, so that the refrigerant exchanges heat with the second heat transfer fluid in the second heat exchanger <NUM>.

The supply fan 21a drives supply air along the air supply passage <NUM>, so that the air supply passage <NUM> receives the supply air from the atmosphere <NUM> and supplies the supply air from the supply passage <NUM> into the occupied area <NUM>. The first heat transfer fluid exchanges heat with the supply air in the supply air heat exchanger <NUM>. The first heat transfer fluid returns to the first heat exchanger <NUM> via the first pump <NUM>.

The return fan 21b drives return air along the return-from-area passage <NUM>, so that the return-from-area passage receives the return air from the occupied area and supplies the return air to the atmosphere <NUM>. The second heat transfer fluid exchanges heat with the return air in the return air heat exchanger <NUM>. The second heat transfer fluid returns to the second heat exchanger <NUM> via the second pump <NUM>.

The recovery wheel <NUM> exchanges heat between the return air and the supply air, by absorbing heat from a warmer of the return air and the supply air, and passing heat to a cooler of the return air and the supply air.

The remote heat transfer device <NUM> is arranged to operate in a heat pump and in a refrigeration mode, as described below. The vapour-compression circuit <NUM> is a reversible heat pump.

In the heat pump mode, the vapour-compression circuit <NUM> operates a Carnot cycle, with the first heat exchanger <NUM> operating as a condenser and the second heat exchanger <NUM> operating as an evaporator. The second heat transfer fluid draws heat from the return air in the return heat exchanger <NUM>. The refrigerant draws heat from the second heat transfer fluid in the second heat exchanger <NUM>. The refrigerant passes heat to the first heat transfer fluid in the first heat exchanger <NUM>. The first heat transfer fluid passes heat to the supply air in the supply heat exchanger <NUM>. This allows cool air from the atmosphere <NUM> to be heated in the supply passage <NUM> before it is supplied to the occupied area <NUM>.

In the refrigeration mode, the vapour-compression circuit <NUM> operates a Carnot cycle, with the second heat exchanger <NUM> operating as a condenser and the first heat exchanger <NUM> operating as an evaporator. The first heat transfer fluid draws heat from the supply air in the supply heat exchanger <NUM>. The refrigerant draws heat from the first heat transfer fluid in the first heat exchanger. The refrigerant passes heat to the second heat transfer fluid in the second heat exchanger <NUM>. The second heat transfer fluid passes heat to the return air in the return heat exchanger <NUM>. This allows warm air from the atmosphere <NUM> to be cooled in the supply passage <NUM> before it is supplied to the occupied area <NUM>.

To switch between the two modes, reversed valve system is engaged to reverse the refrigerant flow direction in the vapour-compression circuit <NUM>.

In both the heat pump and the refrigeration mode, the first pump <NUM> is controllable to control flow rate of first heat transfer fluid to the air supply passage <NUM>, and the second pump <NUM> is controllable to control flow rate of second heat transfer fluid to the return-from-area passage <NUM>. The refrigerant operating pressure is controlled by controlling the flow rate of the first and second heat transfer fluids. This allows the evaporating pressure and the condensing pressure in the vapour-compression circuit to be maintained, allowing the efficiency of the heat pump/refrigerant to be increased. Additionally, the speed of the compressor can be varied to control the required flow rate and capacity of the vapour-compression circuit.

Some additional modifications/variations are described below.

In another example (not shown), the vapour compression circuit comprises a variable compressor and a fixed speed compressor operating in tandem. This is particularly suited to small capacity air handling systems. In another example (not shown), the vapour compression circuit comprises a pair of variable speed compressors operating independently. This reduces the quantity of refrigerant in each circuit for larger air handling systems.

In another example (not shown), the remote heat transfer device comprises a second vapour-compression circuit, the second vapour-compression circuit comprising a third heat exchanger adapted to exchange heat between a second refrigerant in the second vapour compression circuit and the first heat transfer fluid. Additionally, the second vapour-compression circuit comprises a fourth heat exchanger adapted to exchange heat between the second refrigerant and the second heat transfer fluid. While this example requires a remote heat transfer device of increased complexity, using two independent circuits reduces the amount of refrigerant required in each circuit to achieve the same total heating/cooling. This keeps the flammable charge below the maximum allowable limit for safe operation, which is typically <NUM>. The minimum operational capacity for a compressor is typically <NUM>%, so using two circuits gives a total unit minimum capacity of <NUM>%, which provides improved flexibility in heating and cooling fresh air, to achieve the required supply air temperature at moderate atmospheric temperature.

Claim 1:
A heat transfer device for use with a separate air handling unit (<NUM>), the heat transfer device configured for being located remotely from the separate air handling unit (<NUM>) and comprising
a vapour-compression circuit (<NUM>), the vapour-compression circuit comprising a first heat exchanger (<NUM>) adapted to exchange heat between a refrigerant in the vapour compression circuit (<NUM>) and a first heat transfer fluid;
a first outlet (<NUM>) arranged to provide the first heat transfer fluid to an air supply passage (<NUM>) of the air handling unit, so that the first heat transfer fluid exchanges heat with supply air passing through the air supply passage (<NUM>);
a first pump (<NUM>) for pumping first heat transfer fluid to the air supply passage (<NUM>), the first pump (<NUM>) controllable to control flow rate of first heat transfer fluid to the air supply passage (<NUM>);
a second outlet (<NUM>) arranged to provide a second heat transfer fluid to a return-from-area passage (<NUM>) of the air handling unit, so that the second heat transfer fluid exchanges heat with return air passing through the return-from-area passage (<NUM>),
and
a second pump (<NUM>) for pumping the second heat transfer fluid to the return-from-area passage (<NUM>), the second pump (<NUM>) controllable to control flow rate of second heat transfer fluid to the return-from-area passage (<NUM>);
wherein the vapour compression circuit (<NUM>) comprises a second heat exchanger (<NUM>) adapted to exchange heat with the second heat transfer fluid,
wherein the heat transfer device is arranged to operate in a heat pump mode, and, in the heat pump mode, the heat transfer device heats the first heat transfer fluid using the first heat exchanger (<NUM>) so as to heat the supply air,
wherein the heat transfer device is arranged to operate in a refrigeration mode, and in the refrigeration mode, the heat transfer device cools the first heat transfer fluid using the first heat exchanger (<NUM>) so as to cool the supply air,
characterized in that
the heat transfer device is configured to control an operating pressure of the refrigeran by controlling a flow rate of the first heat transfer fluid and a flow rate of the second heat transfer fluid.