FIELD OF THE INVENTION
The present invention relates generally to the field of integrated air-conditioning and atmospheric water generation systems. More particularly, the invention relates to a dual-function desiccant cycle system employing a rotary solid desiccant wheel, in which (i) an adsorption sector of the wheel produces a dehumidified airstream suitable for supply to a conditioned space, including without limitation a data centre server hall, a telecommunications exchange, a pharmaceutical cleanroom, a hospital critical-care ward, a commercial HVAC system, or an industrial process cabin; and (ii) a desorption sector of the same wheel, regenerated by waste heat recovered from the condenser loop of an associated chiller plant, produces a warm moisture-laden exhaust airstream from which fresh potable water is harvested by passive or active condensation. The invention further relates to a method of simultaneously dehumidifying conditioned space air and producing atmospheric fresh water using chiller waste heat as the sole driving energy for desiccant regeneration.
BACKGROUND OF THE INVENTION
A. The Dual Challenge of Data-Centre Cooling and Freshwater Scarcity In recent years, two seemingly unrelated but increasingly acute infrastructure challenges have converged upon the same geographies: (i) the exponentially growing energy demand of data centres and large HVAC installations, particularly driven by the proliferation of artificial intelligence workloads, and (ii) the chronic and worsening scarcity of potable water in most densely populated regions of the world. Global data centre electricity consumption exceeded 415 TWh in calendar year 2024, of which approximately 30% to 40% is attributable to cooling loads. A substantial proportion of this cooling energy is expended in the removal of latent heat — that is, in the dehumidification of incoming conditioned air — particularly in tropical, sub-tropical and coastal climates characteristic of South Asia, South-East Asia, the Middle East, coastal Africa, and Latin America, where ambient relative humidity routinely exceeds 70%. Concurrently, approximately three billion human beings presently reside in water-stressed regions, and a single hyperscale data centre typically consumes between three million and five million litres of water per day for evaporative cooling tower makeup.
The prior art has evolved two largely independent technological responses to these challenges. To address the cooling load, data-centre operators and HVAC designers have deployed progressively more efficient vapour compression chillers, evaporative cooling towers, immersion-cooling and liquid-cooled rack systems, and in some cases desiccant-assisted dehumidifiers to pre-treat supply air. To address freshwater scarcity, separate industrial installations have deployed reverse-osmosis desalination of seawater, atmospheric water generators employing refrigeration-based condensation, and desiccant-based atmospheric water harvesting systems driven by dedicated

heating sources such as natural gas burners, electric resistance heaters, solar thermal collectors, or thermoelectric modules.
No system known to the applicant, however, combines these two objectives into a single, energy- integrated architecture in which (a) the dehumidification of conditioned space air and (b) the generation of atmospheric fresh water are achieved simultaneously from a single rotary desiccant wheel, using, as the sole regeneration energy source, the low-grade waste heat that is otherwise rejected to ambient by the chiller condenser of the same conditioned-space cooling infrastructure.
B. Limitations of Existing Technologies (i) Conventional Vapour-Compression Dehumidification Conventional HVAC systems remove moisture from supply air by over-cooling the air through a refrigeration evaporator coil until condensation occurs on the coil surface, followed by reheat to restore the target supply temperature. This approach is thermodynamically inefficient —■- the energy expended in over-cooling and reheating is effectively wasted — and the condensate so produced is typically discharged to drain as waste water, notwithstanding that it is chemically pure and suitable for reuse after mild treatment.
(ii) Desiccant Dehumidification with Dedicated Regeneration Solid-desiccant dehumidification systems employing silica gel, lithium chloride, zeolite molecular sieves, or composite desiccant materials, arranged as rotating wheels or fixed beds, are known in the art. Such systems remove moisture from an airstream by adsorption onto the desiccant surface, and subsequently regenerate the desiccant by heating a second airstream to temperatures typically in the range of 65 °C to 140 °C to drive off the adsorbed moisture. The regeneration heat in prior art systems is supplied by dedicated energy sources — natural-gas burners, electric resistance heaters, district steam, solar thermal collectors, or biomass boilers — each of which imposes a significant additional energy cost and carbon footprint upon the dehumidification operation.
Further, in all such prior art systems, the moisture-laden regeneration exhaust is simply vented to atmosphere, wasting both the adsorbed moisture and the thermal energy contained in the exhaust
airstream.
(Hi) Atmospheric Water Generation as a Stand-alone System Stand-alone atmospheric water generators, whether of the refrigeration-condensation type or the desiccant-sorption-regeneration type, have been deployed independently of any cooling infrastructure. Such stand-alone systems must draw their full operating energy from a dedicated supply — grid electricity, solar photovoltaic, or combustion-based heat — and consequently suffer from high energy intensities per litre of water produced (typically in the range of 0.3 kWh/L to 1.2

kWh/L). They do not exploit the thermal energy already being consumed and rejected by neighbouring HVAC or data-centre infrastructure. (iv) Waste Heat Recovery from Data Centres — Limited Deployment The waste heat rejected by data-centre chiller plants — typically low-grade thermal energy in the temperature range of 35 °C to 70 °C, delivered from the condenser loop of the chiller — has been the subject of intermittent prior-art interest, principally for use in district heating networks, swimming-pool heating, horticultural greenhouses, and low-temperature Organic Rankine Cycle (ORC) power generation. Such applications, however, typically require geographic co-location of a heat sink of similar scale, which is seldom available in the peri-urban or industrial-park settings where data centres are typically sited. The proposition of coupling this waste heat to the regeneration of a desiccant wheel so as to simultaneously yield atmospheric fresh water has not, to the knowledge of the applicant, been disclosed in any prior publication or granted patent.
C. Prior Art Considered The applicant has considered the following prior art documents, none of which, individually or in combination, discloses or suggests the invention claimed herein: United States Patent Application Publication No. US 2010/0058778 Al (Cook et al., 2010) discloses a thermoelectrically powered indirect evaporative cooling system incorporating desiccant dehumidification for residential and commercial cooling applications. The said prior art is silent on data-centre integration, or on the use of large scale chiller waste heat as the regeneration source, and on the harvesting of the regeneration exhaust for water production.
United States Patent No. US 5,373,704 (Hydes, 1994) discloses an air recirculation system employing a water heater as the heat source for desiccant regeneration, targeted at living-space air conditioning. The said disclosure does not contemplate the production of fresh water as a second output of the system, nor does it teach the recovery of waste heat from an external chiller plant.
United States Patent Application Publication No. US 2010/0192605 Al discloses the use of low- grade refrigeration waste heat to regenerate a desiccant wheel employed for humidity control in ice­rink applications. The system there disclosed is single-function (dehumidification only); the regeneration exhaust is discharged to the atmosphere, not harvested for water.
United States Patent Application Publication No. US 2020/0172411 Al discloses the use of data­centre waste heat for low-temperature saline-water desalination by vacuum evaporation. The said prior art requires a saline water source (seawater or brine), does not address atmospheric air dehumidification, and does not involve a solid desiccant wheel.

United States Patent Application Publication No. US 2015/0144562 Al discloses a system combining data-centre cooling with seawater reverse-osmosis desalination. The said prior art requires a saline water source and does not address atmospheric water harvesting from humid air.
The non-patent literature represented by Sun et al. (ScienceDirect, 2025) describes a desiccant- coated heat-exchanger (DCHE) regenerated by data-centre waste heat for the dehumidification of fresh air intended for workspace ventilation. The said prior art is expressly single-function: it describes the dehumidification outcome only, vents the regeneration exhaust to atmosphere, and does not contemplate dual-output operation including water harvesting.
D, Need for the Invention
There exists, accordingly, a long-felt and unmet need in the art for an integrated thermal-fluid system that simultaneously (a) reduces the latent cooling load of a data centre or HVAC installation by supply of dehumidified air; (b) harvests atmospheric fresh water as a usable co-product of the dehumidification operation; and (c) achieves the regeneration of the desiccant without the expenditure of any dedicated primary energy input, by instead employing the low-grade waste heat that is already being rejected by the chiller condenser loop of the same installation. The present invention seeks to meet this long-felt need.
OBJECTS OF THE INVENTION
The principal object of the present invention is to provide a dual-function desiccant cycle system that substantially obviates the disadvantages of the prior art enumerated hereinabove.
Another object of the invention is to provide a system in which a single rotary desiccant wheel simultaneously delivers (i) a dehumidified supply airstream to a conditioned space and (ii) a warm moisture-laden regeneration exhaust airstream from which atmospheric fresh water is harvested.
A further object is to provide a system in which the regeneration of the desiccant wheel is effected solely by waste heat recovered from the condenser loop of a chiller plant associated with the same conditioned space, thereby eliminating the need for any dedicated primary energy input for
regeneration.
Yet another object is to provide a closed-loop moisture-management architecture in which moisture adsorbed from the conditioned space supply air is not vented to atmosphere, but is instead systematically recovered and condensed into usable fresh water.
Another object is to provide a system that is flexibly deployable across a wide range of climatic conditions and facility scales, by providing for the selection of either passive condensation means (including radiative-cooling surfaces and dew-collection substrates) or active condensation means

(including refrigerant-based condenser coils, thermoelectric cooling elements, and chilled-water heat exchangers) in the water generation module.
A still further object is to provide a control system configured to dynamically modulate the rotational speed of the desiccant wheel, the ratio of the adsorption sector to the regeneration sector, the regeneration airflow rate, and the operation of the condensation means, so as to co-optimise the twin objectives of cooling energy reduction and water yield under varying ambient conditions and varying cooling demand.
A further object is to provide a system configurable as a modular, containerised unit for ease of deployment at existing data centres, HVAC installations, and industrial facilities, without major retrofitting of existing infrastructure.
Other objects and advantages of the invention will become apparent from the following detailed description, when read in conjunction with the accompanying drawings and claims.
SUMMARY OF THE INVENTION
In accordance with the foregoing objects, the present invention provides, in a first aspect, a dual­function desiccant cycle system comprising:
(a) a rotary desiccant wheel housing a solid desiccant material and partitioned, at any given instant, into at least an adsorption sector and a regeneration sector; (b) a first air circuit arranged to pass an atmospheric airstream through the adsorption sector of the said rotary desiccant wheel, whereby moisture contained in the said atmospheric airstream is adsorbed onto the said desiccant material to yield a dehumidified supply airstream, the said dehumidified supply airstream being directed to a conditioned space; (c) a waste heat recovery circuit thermally coupled to the condenser loop of a chiller plant associated with the said conditioned space, the said waste heat recovery circuit being configured to extract low-grade waste heat from the said condenser loop and to pre-heat a regeneration airstream to a temperature sufficient for desorption of moisture from the said desiccant material;
(d) a second air circuit arranged to pass the said pre-heated regeneration airstream through the regeneration sector of the said rotary desiccant wheel, whereby the said pre-heated regeneration airstream desorbs moisture from the said desiccant material, yielding a moisture-laden regeneration exhaust airstream; and (e) a water generation module disposed in fluid communication with the said regeneration exhaust airstream and configured to condense water vapour therefrom, producing atmospheric fresh water.
Significantly, the system is characterised in that the regeneration heat supplied to the second air circuit is derived substantially entirely from the waste heat of the chiller condenser loop of the conditioned space cooling infrastructure, such that the desiccant wheel imposes substantially no additional primary energy demand for regeneration, and the system constitutes an energy-integrated closed-loop moisture management architecture with dual useful outputs.
In a second aspect, the invention provides a method of simultaneously dehumidifying a conditioned space and generating atmospheric fresh water, the method comprising the steps of: (i) passing atmospheric air through an adsorption sector of a rotary desiccant wheel to produce a dehumidified supply airstream; (ii) directing the said dehumidified supply airstream to a conditioned space cooling system thereby to reduce the latent cooling load thereof; (iii) extracting waste heat from the condenser loop of a chiller plant associated with the said conditioned space; (iv) using the said extracted waste heat to pre-heat a regeneration airstream; (v) passing the said pre-heated regeneration airstream through a regeneration sector of the said rotary desiccant wheel to desorb moisture therefrom, thereby producing a moisture-laden regeneration exhaust airstream; and (vi) condensing water vapour from the said regeneration exhaust airstream to yield atmospheric fresh
water.
The invention further provides particular embodiments including: (i) passive condensation in the water generation module using radiative cooling surfaces; (ii) active condensation using refrigerant­based coils, thermoelectric elements, or chilled-water heat exchangers; (iii) control logic for co­optimisation of cooling performance and water yield; (iv) modular, containerised deployable configurations; and (v) integration with building management systems (BMS) and data-centre infrastructure management (DCIM) platforms.
BRIEF DESCRIPTION OF THE DRAWING
The accompanying drawing forms part of the present disclosure and is to be read in conjunction with the following Detailed Description.
FIG. 1 is a schematic process and instrumentation diagram of the dual-function desiccant cycle system in accordance with a preferred embodiment of the present invention, illustrating the airflow paths, the refrigerant circuits, the waste heat recovery circuit, and the principal reference numerals identifying the components described herein.

DETAILED DESCRIPTION OF THE INVENTION
The present invention will now be described, by way of non-limiting preferred embodiments, with reference to the accompanying FIG. 1. It is to be expressly understood that the embodiments described hereinbelow are illustrative only, and the invention may be practised in various other forms without departing from the scope of the claims appended hereto. Any reference to singular elements in the description and claims shall be read as including the plural, unless the context clearly indicates otherwise.

Overall System Architecture Referring to FIG. 1, there is shown a dual-function desiccant cycle system 10 in accordance with a preferred embodiment of the present invention. The system 10 comprises a rotary desiccant wheel 101 housing a solid desiccant material and configured to rotate about a central axis at a controlled angular velocity. At any given instant, the rotary desiccant wheel 101 is divided, by a pair of sealed stationary baffles (not separately numbered), into at least two angular sectors: an adsorption sector 101A and a regeneration sector 101B. The angular extent of the adsorption sector 101 A, expressed as a fraction of the full 360° rotation, may typically lie in the range of approximately 60% to approximately 80%, with the complementary fraction being assigned to the regeneration sector 101B. The specific sector-partition ratio is selected, in a manner described more fully hereinbelow, in accordance with the prevailing ambient conditions and the relative priority assigned, in the control logic, to cooling-energy reduction versus fresh-water yield.
An atmospheric air intake stream 100 is drawn, by means of a first blower (not separately numbered), through the adsorption sector 101A of the desiccant wheel 101. Within the adsorption sector 101 A, water vapour contained in the atmospheric air intake stream 100 is adsorbed onto the surface and into the pore structure of the desiccant material, giving rise to a dehumidified supply airstream 102 at the downstream face of the adsorption sector 101 A. The dehumidified supply airstream 102 is then conveyed, through appropriate ductwork and flow-control apparatus, to an air-handling unit 111 of a conditioned space 110, where it is used to provide dehumidified air to the said conditioned space.
Concurrently, a regeneration airstream inlet 104 supplies a second airstream to a regeneration airstream pre-heater coil 140. The regeneration airstream pre-heater coil 140 is thermally coupled, through a waste heat recovery heat exchanger 130, to the condenser loop 121 of a chiller plant 120 associated with the cooling of the conditioned space 110. Low-grade thermal energy, which would otherwise be rejected from the chiller condenser loop 121 to ambient through a cooling tower or air-cooled condenser, is thereby extracted and transferred to the regeneration airstream, raising the temperature of the said airstream to a level suitable for desorption. The pre-heated regeneration airstream is then passed, by means of a second blower (not separately numbered), through the regeneration sector 101B of the desiccant wheel 101. Within the regeneration sector 101B, the heat content of the pre-heated regeneration airstream supplies the enthalpy of desorption required to liberate moisture previously adsorbed onto the desiccant material, producing a warm, moisture­laden regeneration exhaust airstream 103 at the downstream face of the regeneration sector 101B.
The moisture-laden regeneration exhaust airstream 103 is directed, through further ductwork, to a water generation module 150, wherein the said airstream is brought into contact with, or passed over, a condensation surface 151 maintained at a temperature below the dew point of the said

airstream. Consequently, a portion of the water vapour contained in the regeneration exhaust airstream 103 condenses upon the condensation surface 151 and is collected, under gravity, in a water collection reservoir 160. The collected water may thereafter be passed through a filtration and sterilisation stage 170 to yield fresh water of a quality suitable for cooling-tower makeup, fire­suppression supply, process water, or, upon appropriate treatment, potable use.
The rotation of the desiccant wheel 101, the flow rates in the first and second air circuits, the operation of the waste heat recovery heat exchanger 130, and the operation of the water generation module 150 are coordinated by a controller 180, which may comprise a programmable logic controller (PLC), an embedded microcontroller, or a module integrated with a building management system (BMS) or a data-centre infrastructure management (DCIM) platform of the conditioned space 110. The control architecture implemented in the controller 180 is described more fully
hereinbelow.
2, The Rotary Desiccant Wheel The rotary desiccant wheel 101 comprises a substrate and a desiccant material disposed upon or within the said substrate. In a preferred embodiment, the substrate comprises a honeycomb matrix fabricated from a corrugated fibrous medium — for example a silica-gel-impregnated glass-fibre paper, a ceramic-fibre paper, or a polymer-composite paper— wound into a cylindrical form having an axial depth typically in the range of approximately 100 mm to approximately 500 mm and a diameter typically in the range of approximately 300 mm to approximately 3,000 mm, in accordance with the volumetric airflow rate for which the system is designed.
The desiccant material deposited within or upon the substrate may be selected from the group consisting of silica gel, lithium chloride, calcium chloride, zeolite molecular sieve (including without limitation Types 3A, 4A, 5A, and 13X), activated alumina, metal-organic frameworks (MOFs), and composite polymer-inorganic desiccants. In a particularly preferred embodiment, the desiccant material comprises a composite of silica gel as the primary sorbent, stabilised by lithium chloride as a hygroscopic enhancer, dispersed within a porous ceramic matrix, so as to deliver a combination of (i) high moisture uptake at moderate relative humidity (characteristic of silica gel); (ii) enhanced uptake at low relative humidity (characteristic of lithium chloride); and (iii) low regeneration temperature requirements (characteristic of silica gel). The moisture uptake capacity of such a composite desiccant typically lies in the range of approximately 20% to approximately 45% by dry weight, at an inlet air relative humidity of 60% and an inlet air temperature of 30 °C.
The rotational speed of the desiccant wheel 101 is controlled by a variable-speed drive, typically a brushless direct-current (BLDC) motor or an inverter-driven induction motor, and typically operates in the range of approximately 8 revolutions per hour to approximately 30 revolutions per

hour. The optimum rotational speed is a function of the axial depth of the wheel, the relative humidity of the intake air, the temperature and flow rate of the regeneration airstream, and the desired ratio between dehumidification performance and water yield; the controller 180 implements a closed-loop optimisation, as more fully described hereinbelow.
The partition between the adsorption sector 101A and the regeneration sector 101B is effected by a pair of stationary sealing baffles, typically fabricated from graphite-impregnated PTFE or a similar low-friction, low-leakage sealing material, arranged such that the cross-flow leakage between the two sectors is limited to less than approximately 3% of the respective volumetric flow rates. In certain embodiments, the wheel 101 may be partitioned into more than two sectors, for example by the interposition of a purge sector between the adsorption and regeneration sectors, the said purge sector being traversed by a small fraction of the dehumidified supply airstream so as to cool the regenerated desiccant medium prior to its re-entry into the adsorption sector, thereby improving the overall thermal efficiency of the cycle.
14-M^y-2026/71750/202641061139/Form 2(Title Page)
3, The Waste Heat Recovery Circuit The waste heat recovery circuit comprises the waste heat recovery heat exchanger 130 and the regeneration airstream pre-heater coil 140, together with the necessary hydraulic piping, circulation pumps, expansion tanks, and control valves. The waste heat recovery heat exchanger 130 is thermally coupled to the chiller condenser loop 121 of the chiller plant 120. The chiller condenser loop 121 constitutes, in a typical installation, a water-cooled condenser loop delivering thermal energy at temperatures in the range of approximately 35 °C to approximately 55 °C at normal operating conditions, or an air-cooled condenser delivering thermal energy at refrigerant temperatures in the range of approximately 45 °C to approximately 80 °C. In certain embodiments, the chiller condenser loop 121 may be replaced or supplemented by a liquid-immersion-cooling loop of an immersion-cooled server rack, or by a direct-to-chip liquid cooling loop of a server rack, delivering thermal energy at temperatures in the range of approximately 45 °C to approximately 70
°C.
The working fluid of the waste heat recovery circuit may be selected from the group consisting of water, a water-glycol mixture, a heat-transfer oil, or a phase-change working fluid such as a hydrofluorocarbon, a hydrofluoroolefin, or a natural refrigerant. In a preferred embodiment, the working fluid is a water-glycol mixture, so as to permit operation at temperatures below 0 °C during optional winter-time storage-tank charging, and to resist biological fouling.
In a particularly advantageous embodiment, a thermal energy storage tank (not separately numbered) is interposed between the waste heat recovery heat exchanger 130 and the regeneration airstream pre-heater coil 140. The thermal energy storage tank stores thermal energy during periods

in which the cooling load of the conditioned space 110, and therefore the heat rejection from the chiller condenser loop 121, exceeds the instantaneous regeneration demand of the desiccant wheel 101, and discharges the stored energy during periods of high regeneration demand, thereby decoupling the temporal profile of heat availability from that of water production. The thermal energy storage tank may employ sensible-heat storage in water or oil, latent-heat storage using a phase-change material such as a eutectic salt hydrate, or a hybrid of the two.
The regeneration airstream pre-heater coil 140 comprises a finned-tube or plate heat-exchanger disposed in the path of the regeneration airstream inlet 104 and configured to raise the temperature of the regeneration airstream from ambient to a set-point temperature typically in the range of approximately 55 °C to approximately 85 °C, in dependence upon the desiccant material employed and the desired depth of desorption. Higher regeneration temperatures yield deeper desorption and correspondingly higher moisture uptake in the subsequent adsorption half-cycle, but require correspondingly higher temperatures at the chiller condenser loop 121; the control architecture implemented in the controller 180 balances these considerations as described hereinbelow.
4. The Water Generation Module The water generation module 150 comprises a condensation surface 151 maintained at a temperature below the dew point of the regeneration exhaust airstream 103 entering the said module, together with a condensate collection arrangement, a water collection reservoir 160, and optionally a filtration and sterilisation stage 170.
In a first sub-embodiment, the condensation surface 151 is cooled by passive means. Passive condensation means may include, without limitation: (i) a radiative-cooling surface oriented towards the night sky and configured to radiate thermal energy in the atmospheric transmission window (between approximately 8 pm and approximately 13 pm) to outer space, so as to cool the said surface below ambient dry-bulb temperature during clear-sky nocturnal periods; (ii) a dew­collection substrate having a micro- or nano-structured surface texture promoting dropwise condensation and gravitational drainage of condensed droplets; or (iii) an enthalpy-exchange surface in which the regeneration exhaust airstream 103 is placed into indirect thermal contact with an incoming stream of ambient air, so as to cool the regeneration exhaust while pre-heating the ambient air for use as the regeneration airstream inlet 104.
In a second sub-embodiment, the condensation surface 151 is cooled by active means. Active condensation means may include, without limitation: (i) a refrigerant-based condenser coil forming part of a dedicated vapour compression refrigeration circuit powered electrically; (ii) a thermoelectric (Peltier) cooling element disposed in thermal contact with the condensation surface; (iii) a chilled-water heat exchanger, wherein the chilled water is drawn from the chilled-water
supply loop of the same chiller plant 120, or from a separate dedicated chiller; or (iv) an indirect evaporative cooler in which an auxiliary water stream is evaporated to cool the condensation
surface.
In yet a further sub-embodiment, the water generation module 150 is configured to operate in either passive or active mode in dependence upon the ambient conditions, under the governance of the controller 180. Specifically, during nocturnal periods of clear sky and low ambient dry-bulb temperature, the controller 180 selects passive radiative cooling; during diurnal periods or periods of overcast sky, the controller 180 selects active cooling from the chilled-water loop of the chiller plant 120. This hybrid configuration extends the operating window of the water generation module 150 across the full diurnal cycle and across a wide range of climatic conditions.
Condensed water collected in the water collection reservoir 160 may optionally be passed through the filtration and sterilisation stage 170, which may comprise, in sequence, a particulate filter (typically of 5 pm or 1 pm nominal rating), an activated-carbon filter for removal of any volatile organic compounds, a reverse-osmosis membrane or ultrafiltration membrane for removal of dissolved solids and microbial contaminants, and an ultraviolet sterilisation lamp, so as to render the water suitable for potable use in accordance with the Indian Drinking Water Specification (IS 10500:2012) or the World Health Organization Drinking-Water Quality Guidelines.
5. The Control System
The controller 180 is operable to monitor a plurality of system state variables and to modulate a plurality of system actuators so as to co-optimise the twin objectives of (i) maximising the reduction in latent cooling energy at the air-handling unit 111 of the conditioned space 110, and (ii) maximising the quantity of fresh water produced at the water generation module 150.
The state variables monitored by the controller 180 include, without limitation: (a) the dry-bulb temperature and relative humidity of the atmospheric air intake stream 100; (b) the dry-bulb temperature and relative humidity of the dehumidified supply airstream 102; (c) the temperature and flow rate of the waste heat recovery circuit working fluid; (d) the temperature and flow rate of the regeneration airstream inlet 104 and the regeneration airstream entering the regeneration sector 10IB; (e) the temperature and relative humidity of the regeneration exhaust airstream 103 at the outlet of the regeneration sector 101B; (f) the temperature of the condensation surface 151 and the mass flow rate of collected condensate at the water collection reservoir 160; and (g) the electrical power draw of the chiller plant 120 and, where present, of the air-handling unit 111.
The actuators controlled by the controller 180 include, without limitation: (a) the rotational speed of the desiccant wheel 101 (via a variable-speed motor drive); (b) the angular position of the sealing baffles between the adsorption sector 101A and the regeneration sector 10IB (in embodiments

having an adjustable sector partition); (c) the rotational speed of the first and second blowers (to modulate air mass flow rates in the two circuits); (d) the flow rate and temperature set-point of the waste heat recovery circuit working fluid (via pump speed and diverting valves); (e) the operating mode of the water generation module 150 (passive, active, or hybrid); and (f) the operation of the filtration and sterilisation stage 170.
In a preferred embodiment, the controller 180 implements a multi-variable model-predictive control (MPC) algorithm, informed by an onboard thermodynamic model of the desiccant wheel 101 (for example a non-equilibrium one-dimensional sorption model parameterised from empirical performance data of the specific desiccant material employed), a chiller performance map of the chiller plant 120, and forecast input data pertaining to anticipated conditioned-space cooling demand and anticipated ambient conditions. The objective function of the said MPC algorithm may be expressed as a weighted sum of the form:
J=W i • (A Pcooling) + w? • (mwater)
where APcooling - represents the reduction in electrical power demand of the air-handling unit 111 attributable to the dehumidification provided by the system 10, m water - represents the mass flow rate of fresh water produced at the water generation module 150, and wi and W2 are weighting factors whose relative values may be set by the operator in accordance with operational priorities.
For example, in a facility located in a region of acute water scarcity, the operator may assign a higher weight to W2; in a facility subject to peak-demand electricity tariffs, the operator may assign a higher weight to wi. In either case, the controller 180 dynamically re-optimises the system operating setpoints in substantially real time.
It is expressly to be understood that the multi-variable optimisation performed by the controller 180 is implemented as control logic embedded in a physical hardware apparatus comprising one or more programmable processors, memory devices, input/output interfaces, sensors and actuators, and produces tangible, measurable, physical outputs in the form of modified wheel rotational speed, modified blower speeds, modified valve positions, modified operating modes, and ultimately modified quantities of dehumidified air, harvested water, and cooling energy. The control architecture accordingly constitutes an integral part of the physical thermal-fluid apparatus of the invention, and not a disembodied algorithm or computer program per se.
6. Modes of Operation
The system 10 is operable in any one of, or any combination of, the following principal modes, in dependence upon the prevailing operational priorities and ambient conditions: Mode A — Dehumidification-Priority Mode: The controller 180 sets the wheel rotational speed and the regeneration airstream temperature so as to maximise the depth of

dehumidification of the supply airstream 102, thereby maximising the reduction in latent cooling load at the air-handling unit 111. In this mode, water yield at the water generation module 150 is treated as a by-product.
Mode B — Water-Harvest-Priority Mode: The controller 180 sets the operating parameters so as to maximise the mass flow rate of condensed water at the water generation module 150, treating the dehumidification outcome as secondary. This mode may be selected during periods of low cooling demand at the conditioned space 110 (for example, during nocturnal low-IT-load periods at a data centre), when the chiller waste heat remains available but the dehumidification benefit is of lower economic value.
Mode C — Balanced / Co-Optimised Mode: The controller 180 implements the weighted multi-objective optimisation described in Section 5 above, balancing dehumidification benefit against water yield in accordance with operator-specified weights.
Mode D — Standby / Thermal-Storage-Charge Mode: The controller 180 diverts the waste­heat recovery fluid to the thermal energy storage tank and holds the desiccant wheel rotation, the regeneration airflow, and the water generation module substantially idle. This mode is selected when neither dehumidification nor water-harvest is presently required, but waste heat remains available for storage.
7. Alternative Embodiments (i) Data-Centre Integration In one preferred embodiment, the conditioned space 110 comprises a data-centre server hall, the air-handling unit 111 comprises a precision cooling unit (PCU) or a computer-room air handler (CRAH) of the said server hall, and the chiller plant 120 is the primary chiller plant serving the said server hall. In this embodiment, the system 10 is configured to integrate with the data-centre infrastructure management (DCIM) platform of the facility through a suitable communications protocol (for example, Modbus TCP, BACnet/IP, or a REST API over HTTPS), and the controller 180 receives, as inputs, the real-time IT load signals of the data centre, enabling predictive operation that anticipates cooling-demand ramps associated with workload scheduling. The system 10 in this embodiment may be deployed in a modular containerised form factor, typically of 6.1 m (20 ft) or 12.2 m (40 ft) ISO container dimensions, for ease of retrofit installation at existing data centres.
(ii) HVA C/ Commercial Building Integration In a further embodiment, the conditioned space 110 comprises a commercial building, a hospital critical-care ward, a pharmaceutical cleanroom, an airport terminal, or a shopping-mall HVAC supply plenum, and the chiller plant 120 is the main HVAC chiller of the said building. In this embodiment, the system 10 supplies dehumidified air to the existing HVAC air-handling units,

reducing their latent load, while the water generation module 150 supplies fresh water that may be used for cooling-tower makeup, irrigation of landscaping, or (upon treatment) for potable use.
(iii) Liquid-Cooled Server Rack Integration In yet another embodiment, the chiller condenser loop 121 is replaced by, or supplemented with, the return loop of a direct-to-chip liquid cooling system or an immersion-cooling system serving high-density server racks. Such liquid-cooling systems typically operate with return-fluid temperatures in the range of approximately 45 °C to approximately 65 °C, which is particularly favourable for desiccant regeneration and enables higher wheel-scale water yields per unit IT load.
(iv) Solar-Assisted Configuration In an embodiment suitable for installations having additional available rooftop area, the waste heat recovery circuit may be supplemented with a solar-thermal collector array, so as to boost the regeneration airstream temperature during periods of high solar insolation or to extend the operation into periods when the chiller waste heat alone is insufficient (for example, during partial-load operation of the chiller plant 120). (v) Cascaded Multi-Wheel Configuration In a further embodiment, two or more rotary desiccant wheels may be arranged in series or in parallel, with successive stages operating at progressively lower regeneration temperatures, so as to achieve deeper dehumidification of the supply airstream and higher overall water recovery. Such cascaded configurations are particularly advantageous for applications demanding a supply-air dew point below approximately 5 °C. 8. Representative Performance Data In non-limiting representative embodiments of the invention, it has been estimated — subject to verification in pilot-scale trials — that a 1 MW-class data-centre installation employing the system 10 in accordance with the preferred embodiment hereinabove described may deliver the following performance improvements compared with a conventional installation in which chiller waste heat is rejected to ambient and no desiccant-based dehumidification is employed: (a) a reduction in the latent cooling load of the data-centre air-handling unit of the order of approximately 20% to approximately 35%, corresponding to an improvement in overall Power Usage Effectiveness (PUE) of approximately 0.05 to 0.15 units; (b) a fresh-water yield, from the water generation module, of the order of approximately 500 litres per day per megawatt of IT load, in dependence upon ambient humidity conditions and the selected operating mode;

(c) a net primary energy demand for desiccant regeneration of approximately zero, inasmuch as the regeneration heat is drawn entirely from waste heat that would otherwise be rejected to ambient.
The foregoing performance figures are provided by way of illustration and are not intended to limit the scope of the claims appended hereto. Actual performance in any particular installation will depend upon site-specific factors including climate, IT load profile, chiller efficiency, and the specific desiccant material and operating parameters selected

A dual-function desiccant cycle system (10) for simultaneous dehumidification of conditioned space air and generation of atmospheric fresh water, the said system
comprising:
(a) a rotary desiccant wheel (101) housing a solid desiccant material and partitioned at any given instant into at least an adsorption sector (101 A) and a regeneration sector (10IB); (b) a first air circuit arranged to pass an atmospheric airstream (100) through the said adsorption sector (101 A) of the said rotary desiccant wheel (101), whereby moisture contained in the said atmospheric airstream (100) is adsorbed onto the said desiccant material to yield a dehumidified supply airstream (102), the said dehumidified supply airstream (102) being directed to a conditioned space (110);
(c) a waste heat recovery circuit thermally coupled to a chiller condenser loop (121) of a chiller plant (120) associated with the said conditioned space (110), the said waste heat recovery circuit comprising a waste heat recovery heat exchanger (130) and a regeneration airstream pre-heater coil (140) and being configured to extract waste heat from the said chiller condenser loop (121) and to pre-heat a regeneration airstream to a temperature sufficient for desorption of moisture from the said desiccant material; (d) a second air circuit arranged to pass the said pre-heated regeneration airstream through the said regeneration sector (10IB) of the said rotary desiccant wheel (101), whereby moisture is desorbed from the said desiccant material to yield a moisture-laden regeneration
exhaust airstream (103); and. (e) a water generation module (150) disposed in fluid communication with the said moisture-laden regeneration exhaust airstream (103) and configured to condense water vapour therefrom to yield atmospheric fresh water;
characterised in that the regeneration heat supplied to the said second air circuit is derived substantially entirely from the waste heat of the said chiller condenser loop (121), such that the said rotary desiccant wheel (101) imposes substantially no additional primary energy
demand for regeneration.

The dual-function desiccant cycle system as claimed in claim 1, wherein the said solid desiccant material comprises at least one member selected from the group consisting of silica gel, lithium chloride, calcium chloride, zeolite molecular sieve, activated alumina, metal-organic framework (MOF), and composite polymer-inorganic desiccants, and preferably comprises a composite of silica gel stabilised by lithium chloride dispersed in a
porous ceramic or fibrous matrix.
3. The dual-function desiccant cycle system as claimed in claim 1, wherein the said water generation module (150) comprises passive condensation means selected from the group consisting of a radiative-cooling surface oriented towards the sky, a dew-collection substrate having a micro- or nano-structured surface texture, and an enthalpy-exchange surface in indirect thermal contact with an ambient air stream.
4. The dual-function desiccant cycle system as claimed in claim 1, wherein the said water generation module (150) comprises active condensation means selected from the group consisting of a refrigerant-based condenser coil, a thermoelectric cooling element, a chilled-water heat exchanger coupled to the chilled-water supply loop of the said chiller plant (120), and an indirect evaporative cooler.
5. The dual-function desiccant cycle system as claimed in claim 1, wherein the said water generation module (150) is configured to operate selectively in either a passive condensation mode or an active condensation mode, under the governance of a controller (180), in dependence upon prevailing ambient conditions.
6. The dual-function desiccant cycle system as claimed in claim 1, further comprising a thermal energy storage tank interposed between the said waste heat recovery heat exchanger (130) and the said regeneration airstream pre-heater coil (140), the said thermal energy storage tank being configured to store waste heat during periods of high chiller heat rejection and to discharge the stored heat during periods of peak regeneration demand, thereby decoupling the temporal profiles of heat availability and water production.
7. The dual-function desiccant cycle system as claimed in claim 1, wherein the said waste heat recovery circuit is configured to extract waste heat at a temperature in the range of approximately 35 °C to approximately 85 °C from the said chiller condenser loop (121), and the said regeneration airstream pre-heater coil (140) is configured to raise the temperature of the regeneration airstream to a set-point value in the range of approximately
55 °C.
8. The dual-function desiccant cycle system as claimed in claim 1, wherein the said conditioned space (110) is selected from the group consisting of a data-centre server hall, a telecommunications exchange, a hospital critical-care ward, a pharmaceutical cleanroom, a commercial building HVAC supply plenum, an airport terminal, and an industrial process
cabin.
9. The dual-function desiccant cycle system as claimed in claim 8, wherein the said conditioned space (110) comprises a data-centre server hall and the said chiller condenser loop (121) includes or is supplemented by a return loop of a direct-to-chip liquid cooling system or an immersion-cooling system serving one or more server racks within the said data-centre
server hall.
10. The dual-function desiccant cycle system as claimed in claim 1, further comprising a controller (180) configured to receive input signals representative of at least the diy-bulb

temperature and relative humidity of the said atmospheric airstream (100), the dry-bulb temperature and relative humidity of the said dehumidified supply airstream (102), the temperature of the said waste heat recovery circuit, and the mass flow rate of condensate at the said water generation module (150), and to modulate, in response to the said input signals, at least the rotational speed of the said rotary desiccant wheel (101), the flow rate and temperature of the said pre-heated regeneration airstream, and the operation of the said water generation module (150), so as to co-optimise a weighted objective function combining cooling energy reduction and fresh water yield.
11. The dual-function desiccant cycle system as claimed in claim 10, wherein the said controller (180) implements a model-predictive control algorithm parameterised by a thermodynamic model of the said rotary desiccant wheel (101) and a performance map of the said chiller plant (120), the objective function of the said algorithm being a weighted sum of a reduction in electrical power demand of an air-handling unit (111) of the said conditioned space (110) and a mass flow rate of fresh water produced at the said water generation module (150). 12. The dual-function desiccant cycle system as claimed in claim 1, provided in a modular containerised configuration in which the said rotary desiccant wheel (101), the said waste heat recovery heat exchanger (130), the said regeneration airstream pre-heater coil (140), the said water generation module (150), and the said water collection reservoir (160) are housed within a single deployable enclosure compatible with standard ISO shipping­container dimensions, so as to facilitate retrofit installation at an existing facility.
13. The dual-function desiccant cycle system as claimed in claim 1, further comprising a filtration and sterilisation stage (170) disposed downstream of a water collection reservoir (160) receiving condensate from the said water generation module (150), the said filtration and sterilisation stage (170) comprising, in sequence, a particulate filter, an activated- carbon filter, a membrane filter selected from reverse-osmosis and ultrafiltration

membranes, and an ultraviolet sterilisation lamp, so as to render the collected water compliant with Indian Drinking Water Specification IS 10500:2012.
14. The dual-function desiccant cycle system as claimed in claim 1, wherein the said rotary desiccant wheel (101) is partitioned, in addition to the said adsorption sector (101 A) and the said regeneration sector (10IB), into a purge sector disposed angularly between the said regeneration sector (10IB) and the said adsorption sector (101 A), the said purge sector being traversed by a fraction of the said dehumidified supply airstream (102) so as to cool the desiccant material prior to its re-entry into the said adsorption sector (101A). 15. A method of simultaneously dehumidifying a conditioned space (110) and generating atmospheric fresh water, the said method comprising the steps of:
(i) passing atmospheric air (100) through an adsorption sector (101 A) of a rotary desiccant wheel (101) to produce a dehumidified supply airstream (102);
(ii) directing the said dehumidified supply airstream (102) to an air-handling unit (111) of a conditioned space (110) to reduce the latent cooling load thereof; (iii) extracting waste heat from a chiller condenser loop (121) of a chiller plant (120) associated with the said conditioned space (110);
(iv) using the said extracted waste heat to pre-heat a regeneration airstream; (v) passing the said pre-heated regeneration airstream through a regeneration sector (10IB) of the said rotary desiccant wheel (101) to desorb moisture therefrom, thereby producing a moisture-laden regeneration exhaust airstream (103); and
(vi) condensing water vapour from the said moisture-laden regeneration exhaust airstream
(103) to yield atmospheric fresh water;
characterised in that the said waste heat extracted from the said chiller condenser loop (121) constitutes substantially the sole energy input for the said regeneration of the rotary
desiccant wheel (101).

The method as claimed in claim 15, further comprising the step of dynamically modulating at least the rotational speed of the said rotary desiccant wheel (101), the flow rate of the said pre-heated regeneration airstream, and the operation of the said condensing step, by means of a controller (180) operable to co-optimise a weighted objective function combining reduction in electrical power demand of the said air-handling unit (111) and mass flow rate of fresh water produced in the said condensing step.
17. The method as claimed in claim 15, wherein the said condensing step comprises at least one of: (i) passive condensation by radiative cooling, dew collection, or enthalpy exchange with an ambient air stream; and (ii) active condensation by refrigerant-based cooling, thermoelectric cooling, or chilled-water heat exchange.