1) Research: working principle (what to understand first)

Core idea: Use a vapor-compression refrigeration loop (compressor → condenser → expansion

device → evaporator). Air passes over the evaporator (cold coil). When coil surface temp < air
dew point, moisture condenses. Condensate is captured, sterilized (UV-C/boil/filters), then
stored.

Key concepts the team should read up on

Psychrometrics: humidity ratio , dew point, enthalpy of moist air.

Refrigeration basics: COP/EER, superheat/subcooling, capillary vs. electronic expansion valve

(EXV).

Heat exchangers: fin density, face velocity, condensation on fins, anti-corrosion coatings.

Water hygiene: food-grade materials, UV-C dosage, carbon polishing, tank design to avoid
re-aerosolization.

Safety: electrical isolation, refrigerant handling, brazing, nitrogen purge, leak/pressure tests.

Quick reality check using Lagos-typical air (≈ 30 °C, 70 % RH):

Dew point ≈ 24 °C → so a coil at ~10–12 °C will condense well.

Each cubic meter of air processed at 30 °C/70 % RH yields ≈ 12–13 g of water if cooled to ~10
°C.

To collect 5 L/day, you must move ≈ 16.5 m³/h of air continuously and provide ≈ 255 W of
average cooling (≈ 6.1 kWh/day of cooling). With a small compressor COP of 2.5, electrical use
≈ 2.4–2.7 kWh/day + fans/pumps.

2) Design & sizing (step-by-step with equations)

2.1 Define your target

Pick one clearly:

Student build target: 5 L/day, 30 °C/70 % RH ambient, 24/7 operation, indoor use.
(You can scale with the same method.)

2.2 Psychrometric numbers (for your report)

Use (Magnus-Tetens approximations):

Humidity ratio:

Enthalpy (kJ/kg dry air):

With T1=30 °C, RH=0.70 → kg/kg_{dry}

Saturate at T2=10 °C →
Water condensed per kg dry air .
Enthalpy drop kJ/kg_{dry}.

Airflow needed:
Water per m³ air ≈ kg ≈ 12.6 mL.
For 5 L/day → m³/day → 16.5 m³/h (≈ 9.7 CFM).

Cooling capacity:
Total cooling/day kg_{dry}/day ≈ 6.1 kWh/day → average ~255 W cooling.

2.3 Component sizing

Compressor

Cooling capacity (evaporator): 300–450 W @ ~10 °C evap / ~45 °C condensing to give margin.

Options: R134a mini-compressor (easiest sourcing), or high-efficiency R600a/R290 (more

efficient, flammable → strict safety).

Evaporator (cold coil)

Face area to keep face velocity ~1.5–2.0 m/s at your airflow.

With only 16.5 m³/h, even a 120×120 mm coil works; but oversize for better condensation and
less frosting: suggest 200×200 mm, 3–4 rows, Al fins/Cu tubes, hydrophilic coating.

Target coil surface ≥ 1.5× the theoretical minimum for low fan noise.
Condenser (hot coil)

Size it larger than the evaporator (lower condensing temp → higher COP). Suggest 250×200
mm, 2–3 fans or one 120 mm EC fan.

Expansion device

Capillary tube: lower cost; tune length/ID experimentally for stable superheat at ~10–12 °C
evap.

Or EXV/TEV for better control if available.

Fans

Process air (across evaporator): ~20–30 m³/h EC blower to overcome filter + coil pressure drops
quietly.

Condenser fan: sized for 150–250 m³/h to keep condensing temperature ≲ 45 °C in warm
rooms.

Filtration & condensate path

G4 pre-filter (washable) + optional HEPA if you want drinking-grade polish upstream.

Drain pan with slope ≥ 2%, P-trap to block re-entrainment.

Tubing: silicone/PE, food-grade only.

Sterilization: in-line UV-C (with interlock), then activated carbon for taste.

Tank: HDPE or SS304, 10–15 L, sealed, float switch for auto-off.

Sensors & control

Inlet T/RH, coil surface temp, water level, optional TDS, UV fail sensor.

Control loops: maintain coil ~10–12 °C, defrost if coil < 2 °C for >5 min, stop on tank full/UV
fault.
Insulation & anti-condensation

All cold lines/coil casing: closed-cell insulation (e.g., 10 mm elastomeric).

Vapor barrier tape; drip-edge under coil.

3) CAD-style model (what to build)

I provided two clean diagrams you can drop into your report and use to guide CAD work:

System block diagram: shows air path, refrigerant loop, water path, sensors.

Enclosure front-view layout: compact unit 500 × 350 × 350 mm with component placement and
dimension marks.

You can CAD this exactly as shown in Fusion/SolidWorks/FreeCAD:

Sheet metal housing 1.0 mm galvanized steel or aluminum.

Coil mounting rails; removable front panel for filter service.

Drain pan welded/bent stainless or molded HDPE with a 10–15 mm OD outlet.

Partition hot/cold sides (condenser vs. evaporator) to prevent short-circuiting airflow.

4) Fabrication plan (hands-on steps)

A. Refrigeration circuit

1. Bend/braze copper: compressor → condenser → capillary/EXV → evaporator → suction

back.

2. Nitrogen purge during brazing.

3. Pressure test with dry nitrogen (e.g., 250–300 psi per component limits).
4. Vacuum to ≤ 500 microns, hold test.

5. Charge by weight (start 70–80 % of nominal), then tune by superheat/subcool.

B. Air & water side

1. Build sheet-metal enclosure and install partition baffles.

2. Mount evaporator with drain pan; set 2–3 ° tilt to drain. Add P-trap.

3. Install filter frame and EC blower.

4. Run food-grade tubing to UV-C module → carbon filter → sealed tank. Add float switch.

5. Add insulation and vapor barrier on all cold surfaces.

C. Controls

1. MCU (ESP32/Arduino) + SSR/relays for compressor & fans.

2. Inputs: T/RH, coil temp (NTC), water level, UV status, optional TDS.

3. Logic:

Start if RH > 40 % and tank not full.

Maintain coil ~10–12 °C via compressor duty or EXV.

Defrost if coil <2 °C for >5 min (stop compressor, run fan).

UV interlock: no dispense if UV fault.

D. Water safety

First 2 hours of condensate to waste (cleans system).

Sanitize tank & lines periodically (dilute hypochlorite, then flush).

Keep air intake away from kitchens/chemicals.

5) Performance & verification protocol

1. Ambient log: measure T/RH hourly.

2. Airflow: anemometer @ coil face; target 16–25 m³/h on evaporator path.

3. Power: plug power meter.

4. Yield: collect volume over 24 h; expect ~5 L/day at 30 °C/70 % RH after tuning.

5. Quality: TDS, UV status, taste/odor.

6. COP estimate: Cooling ≈ ; Electrical from meter → COP = Cooling/Electrical.

6) What to buy (starter BOM)

300–450 W mini-compressor (R134a or R600a), evaporator 200×200 mm, condenser 250×200

mm, capillary/EXV, EC blower (~20–30 m³/h), G4 filter (optional HEPA), UV-C in-line module,
carbon post-filter, 10–15 L HDPE/SS tank, sensors (T/RH, level, UV), controller + PSU,
insulation, gaskets.

Gracias