DIY Proposal 02 — HVAC (Ventura Malta, Hyundai split AC) — LOCKED

Status: subsystem 2 locked, 2026-04-11. User picked Option A — Full Ventura Hyundai with Tuya WiFi at -20% off list. Sourcing pivoted from AliExpress Midea (which doesn't exist on AE PL) to Ventura Malta local supplier with installer-included pricing.

Replaces: vendor_teardown/06_hvac_cooling.md — Green Jungle bills € 17 330 for 2× UCHA60-TDC ducted (15 kW) + 3× UCHA24-TDC + 4× cheap splits, half the actual cooling demand and zero redundancy.

This remains the single line where DIY delivers the biggest technical win on top of a price win. The vendor's flowering HVAC is under-sized AND a single point of failure. Ventura Hyundai approach is correctly sized, N+2 redundant, locally serviced, and €6 770 cheaper.

The heat load the vendor is trying to solve

(Note: with the user's solar power coming online, electricity OPEX is decoupled, but the heat output of the lights still has to be moved out of the room — solar doesn't change the cooling-load math.)

Sizing — 6 × 18 000 BTU per flowering room (N+2 redundant)

Derating stack on consumer wall splits

• Nameplate cooling capacity (at 35 °C / 27 °C rating)
• × 0.80 for Sensible Heat Ratio (consumer SHR ~0.75 wastes ~20 % on latent the dehu already removed)
• × 0.80 for 38 °C Malta peak ambient
• Effective ≈ 0.64 × nameplate

Per-room target

• Demand: ~20 kW sensible
• → Required nameplate: ~31 kW
• 6 × Hyundai 18 000 BTU (5.27 kW nameplate each) = 31.6 kW nameplate → ~20.2 kW effective at peak ✓
• N+2 redundancy: any 2 of 6 units can fail simultaneously, the room still gets ~13.5 kW effective — survival mode for 48 h until a €564 swap

This is NOT 4 units (the original DIY intuition) — that delivers ~13 kW effective, room runs at 30–32 °C canopy in summer, crop damage. 6 units is the right count.

Locked SKU — Hyundai 18 000 BTU DC Inverter from Ventura Malta

Why Hyundai (not AVG, not Midea)

Hyundai wins on price, single-vendor, Maltese installer, and is functionally identical to AVG. The HA integration tradeoff (Tuya vs midea-ac-lan) is the one real downside — accepted under Option A.

Tuya / LocalTuya HA story (the honest tradeoff)

LocalTuya is the weakest of the locally-controllable HA integrations. Risks:

• Firmware updates can break the local API binding → unit goes "offline" in HA until re-paired
• Cloud-key extraction required at setup (one-time pain, often via the tuya-cli tool or by sniffing during pairing)
• Some Tuya devices need a periodic cloud touch to stay alive — this is firmware-dependent and not documented per model

Mitigations baked into the build:

1. Disable automatic firmware updates on every unit at install time — pin to known-working firmware
2. Local fallback control via IR blaster (optional, +€270) — ESPHome IR transmitter per unit means HA can still control the AC even if Tuya breaks
3. Spare unit on hand — if a unit truly bricks itself via FW update, swap takes 3 hours
4. Sonoff SNZB-02P sensors as ground truth — HA reads room temp from independent sensors, never from the AC's onboard sensor, so VPD control loops aren't dependent on Tuya at all

Locked HVAC BOM (Ventura Malta -20%)

Comparison vs vendor and original DIY

The Ventura Hyundai approach saves €6 670 vs vendor AND €5 140 vs my original Midea plan, while delivering:

• ✅ Sized for the actual 20 kW load (vendor is 50 % under)
• ✅ N+2 redundancy (vendor has 1 unit per flower room, zero redundancy)
• ✅ Single-vendor + single-installer + Maltese F-gas certified
• ✅ Installation INCLUDED in unit price
• ✅ 4m copper line set included per unit
• ✅ Maltese warranty (no cross-border RMA headache)
• ✅ Spare units immediately swappable in 3 hours
• ✅ HA-controllable via Tuya WiFi smart kit (€20/unit)
• ⚠️ LocalTuya HA integration is the weakest of the local options — mitigated by sensor independence and FW pinning

Layout rules per flowering room

• 6 units mounted on walls not directly above canopy (condensate drip onto plants is the top failure mode)
• 3 per side, staggered along the two long (5.3 m) walls
• Each unit has a dedicated condensate pump feeding a common drain header
• Sonoff SNZB-03 leak sensor under each AC unit → HA alert → Telegram (in automation BOM)
• Spiral-wound drain hoses with heat trace (prevents algae plug + winter freeze)
• Insulation wraps on all refrigerant lines inside the rooms (high RH condenses on uninsulated lines → drip onto canopy)

Consumer-duty derating (still applies — these are residential units)

Hyundai consumer splits are designed for ~2 000–3 000 hours/year. Grow rooms run them ~8 000 h/year. Expected life: 3–5 years, not 10. Mitigations:

• 2 spare units on site at all times (already in BOM, €1 128)
• Preventive coil cleaning every 6 months (flowering room dust + salts) — Maltese installer can do this on a service contract
• Refrigerant top-up every 2 years (consumer split fittings leak slowly) — same installer
• Full replacement budget for the 12 flowering room units around year 4 (12 × €564 = €6 770 over 5 years, factored into 5-yr TCO)

Optional add-on: HA load rotation pattern

Commercial grow operators on Home Assistant forums use a rotation schedule to extend equipment life:

• Pair units: (1,2), (3,4), (5,6) per flowering room
• HA rotates which pair is "primary" every 2 h
• All 6 activate when room temp > setpoint + 0.5 °C
• Tracks runtime hours in HA statistics for predictive replacement

Cost: zero additional hardware. Saving: potentially 2× equipment life, i.e., 6–8 years instead of 3–5. Implemented in subsystem 3 automation YAML.

Procurement — single click

This is the simplest subsystem to procure: add 18 units to Ventura Malta cart, apply your 20 % discount, schedule installation. No bulk-quote chat needed, no AliExpress messages, no PL→Malta freight.

1. Login to shop.venturamalta.com
2. Add to cart:
   • 12 × Hyundai 18 000 BTU DC Inverter
   • 6 × Hyundai 12 000 BTU DC Inverter
   • 18 × Wi-Fi Smart Kit
   • 2 × Hyundai 18 000 BTU spare units
3. Apply -20 % discount code at checkout
4. Schedule installation dates per room (probably staged across 2–3 weeks of build)
5. Ventura installer handles F-gas refrigerant + 4m copper + commissioning per unit

Confirmations needed before order

1. Verify the -20 % discount applies to all units (ask Ventura sales — confirm at checkout, not assume)
2. Confirm Hyundai 18 000 BTU model number (e.g. HRH-S18INV, HC-AS18CRP — depends on Ventura's current stock)
3. Confirm Tuya WiFi kit is compatible with the specific Hyundai model (the kit is generic AVG/Hyundai per the Ventura listing — verify pre-order)
4. Confirm installation lead time — can they install all 18 within 2–3 weeks?
5. Confirm warranty term and how repairs work in year 4 when units start dying