Air Conditioning
Off-grid air conditioning unit research and recommendation for boondocking, including install options through the 80/20 window panel.
Research for the E350 shuttle-bus conversion: which AC to buy for off-grid boondocking, given the 48V house bank (3× ECO-WORTHY Cubix100, 14.4 kWh / ~11.5 kWh usable), 5 kW inverter, planned ~1,000–1,200W solar, and a shell bus with large windows and thin walls. Pair with Insulation & Frame — the two are one system.
The Core Finding
The most bank-efficient AC on the market cannot save a solar budget that’s 60% smaller than the load. The decision order is:
- Thermal envelope first (insulation + shade + window strategy) — halves or quarters the cooling load before any AC runs.
- AC type second — inverter-compressor, window/under-window class, 115V-via-inverter (or DC-native if quality proven).
- Power budget third — if AC becomes a mainstay (4+ hrs/day) AND no generator is carried, the solar target moves from ~1,000–1,200W to ~1,500–2,000W+. If the owned WEN DF1100T generator is carried (gen → ECO-WORTHY charger → bank → inverter), the bank is rebuilt in a 2–3 hr gen run and solar can stay ~600–800W — all-day AC stops being a solar-sizing problem (see power-supply.md §Generator-Assisted Power).
Solar gain is ~90% of a parked bus’s cooling load. Insulation halves it. Shade halves it again. The AC then only fights ~25% of the naive load — and that’s what makes off-grid cooling survivable. A 10,000 BTU non-inverter portable fighting an uninsulated shell burns bank Wh for almost nothing.
What the Bus Needs (hard requirements)
- Runs off the 48V bank when boondocking (DC-native or high-efficiency 115V through the 5 kW inverter)
- No permanent shell destruction — the large windows are the natural mount point; roof stays free for solar panels
- Removable for travel (shell is being built out around the living space; nothing should lock the bus into one AC)
- Weight within payload (est. 4,000–6,000 lb remaining — see Weight & Capacity, unweighed)
- Cooling-only is fine — heating is already propane per the power budget (microwave/coffee dropped for propane in power-supply.md)
Verified Options Matrix (research 2026-09)
| Unit | Class | BTU | Efficiency | Electrical | Real draw (est.) | Install on bus | Street cost | Verdict |
|---|---|---|---|---|---|---|---|---|
| Midea MAW12U1QWT — U-shaped inverter window AC | Window, R-32 | 12,000 | CEER 15.2 (Energy Star) | 115V only | ~0.45–0.6 kWh/cooling-hr (300–650W running; 592 kWh/yr certified) | Custom 80/20 window panel; no roof cut; removable | ~$509 (BBY, 3-yr warranty) | ⭐ Primary rec |
| Midea MAW08V1QWT — U-shaped 8K sibling | Window, R-32 | 8,000 | CEER 15.0 | 115V only | ~0.4–0.55 kWh/hr | Same panel approach | ~$359 | Budget/light-duty alt |
| EG4 12K Hybrid Mini-Split | Mini-split, R-32 | 12,000 | SEER2 22.5, EER2 12.6 | 115V (190–1,100W) or direct-PV DC 90–380V | 480–600W typical, ~900W max (real-world) | Indoor 42.5” wide + outdoor unit 70 lb + lineset; permanent | ~$1,150–1,700 | ⭐ Efficiency max; Phase-2 upgrade |
| Dometic RTX 2000 | 12V rooftop | 6,824 (2,000W) | n/a (COPs implied ~3) | 12V DC, ~10–58A (120–700W; 19A eco ≈ 230W) | Cool-only; 70.6 lb | 18.9”×15.3” roof hole + 12V rail (needs 60A-class 48→12 converter) | ~$2,400–2,650 | ⭐ Only if roof-mount + native 12V wanted; weak BTU for this bus |
| Generic 12V/24V/48V DC mini-splits (Velit, Skyeline, Nomadic S1/X3, budget 10–15K units) | DC split | 7.5–15K | Poor/unverified (claimed EER ~10; no Energy Star) | 12/24/48V DC native | 700–870W rated at spec → worse per-BTU than Midea | Outdoor condenser mount + lineset; brand/QC risk | $785–2,250+ | Caution — spec sheets weak, QC unproven |
| SereneLife SLPAC10 (already owned) | Portable, single-hose, R-32, non-inverter | 10,000 | SEER 10.5 | 120V only (1,150W rated) | 0.7–1.0 kWh/cooling-hr; negative-pressure single hose | Window kit; must seal hose to outside | Owned | Demote to shore-power-only backup |
The “48V mini-split” myth (check before buying)
The EG4 hybrid’s DC input is 90–380 VDC for a dedicated solar string — NOT a 48V battery input. On a 48V bank bus it runs the same way a 115V unit does: through the inverter (or direct-PV if you give it its own panels). Truly 48V-native ACs exist only in the budget DC-split segment (e.g., Velit 2000U claims 12/24/48V) with unverified efficiency and QC risk. Do not buy an AC expecting it to plug into the 48V bank directly. The bus’s inverter is the 120V path; everything else is a myth or a gamble.
Recommendation
Buy now — Phase 1: Midea 12,000 BTU U-Shaped (MAW12U1QWT)
- ~2× the efficiency of the SereneLife per cooling hour (CEER 15.2 inverter vs SEER 10.5 non-inverter) — the single biggest lever after insulation
- No roof cut. The whole roof stays available for the 1,000–2,000W solar array — rooftop AC (Dometic RTX or 120V rooftops) competes with panel space
- U-shape design exists for exactly this mount: the window/panel closes over the unit — the U channel becomes the seal. In a bus window panel, that means the panel + U + polyiso filler = one sealed assembly (integrates directly with the 80/20 window frames in insulation-frame.md)
- Removable for driving/season — no dead weight or theft target left behind when traveling; an 80/20 insulated plug closes the window when the AC is out (that plug is also the permanent window-insulation insert)
- 31–51 dBA (low/high) — quiet in inverter cruise
- 57 lb, 21.9”W × 19.17”D × 13.46”H; opening min: 23” wide, 13.75” high — fits most large shuttle-bus windows, verify on your bus
- Power: 115V through the existing 5 kW inverter (AC is the inverter’s natural load; ~0.45–0.6 kWh per cooling-hour, +~10% inverter tax)
SereneLife SLPAC10: keep as shore-power-only unit (its natural home per power-supply.md) or sell after the Midea is proven in trip 1. Never plan off-grid cooling hours on it — single-hose negative pressure pulls hot air through the unsealed shell and it burns 0.7–1.0 kWh/hr doing it.
Phase 2 (only if cooling proves to be a mainstay load): EG4 12K mini-split
- ~30% more efficient than the Midea (SEER2 22.5) and adds heat-pump heating
- Costs more, indoor unit is 42.5” wide, outdoor unit 70 lb + lineset, permanent — a real build project on a shell
- Worth it when you’re running 6+ cooling hours daily against the bank; not worth it for situational cool-downs
Not recommended for this bus
- Dometic RTX 2000: 6,824 BTU is ~half what the bus needs on a hot day, cool-only, $2,400+, roof hole + 12V rail converter required. It’s a sleeper-cab cooler, not a 24-ft bus cooler.
- Budget DC splits: claims don’t match Energy Star numbers; a failed compressor at a BLM site with 2,000 mi of dirt roads between you and a warranty = learning experience you don’t want.
Sizing Math for This Bus
- Interior floor ~160–280 sq ft (verify), with very large window area and thin walls
- Mobile/envelope rule of thumb ~25–35 BTU/sq-ft for poor-envelope spaces → 6,000–9,800 BTU demand band before sun load
- Big glass in AZ/desert sun pushes the design point up — 12K gives modulation headroom (inverter unit down-cycles; an oversized 12K at part load draws about what an 8K does at full)
- Recommendation: 12K. 8K minimum for a well-insulated + shaded + covered-window bus; 12K if you plan to boondock in real heat with the windows open to view.
Power & Solar Implications (planning numbers — measure on the bus)
| Load | kWh/hr | 4 hrs/day | vs bank | |
|---|---|---|---|---|
| Midea 12K cooling | ~0.5 (0.45–0.6) | ~2.0–2.4 kWh | ~18–21% of usable bank | |
| SereneLife cooling (old plan) | 0.7–1.0 | 2.8–4.0 kWh | 24–35% of usable bank | |
| Fan-only (both classes) | 0.03–0.07 | negligible | air movement only |
- Daily totals: base loads (fridge ~0.4–0.7 + Starlink ~0.6–1.0 + laptop/lights/gear ~1.5–2.5) ≈ 3.5–4.85 kWh/day. Add 2–3 kWh AC → ~6–8 kWh/day with AC as a regular load.
- Solar reality check (RV/van sizing sources, 2026):
- ~4,000 Wh/day → ~1,350W array @ 5 peak-sun-hrs (with buffer); ~6,000 Wh → ~2,000W; ~8,000 Wh → ~2,650W
- The existing plan is 1,000–1,200W for the gear stack without AC. AC as a mainstay moves the array target to ~1,500–2,000W+ (no-gen case); with good insulation + shade + duty discipline you can live at the low end of that band.
- Generator case (2026-09): with the owned DF1100T (11 kW dual-fuel, bank-charger path), these array targets stop being the binding constraint — a 2–3 hr gen run rebuilds the bank and covers all-day AC. Solar then drops to ~600–800W (fuel-saver/quiet-hours backup). Full-day AC moves from “solar-impossible” to “gen-assisted trivial.”
- Full-day AC off solar alone is the “fast-recharge + big bank” regime — beyond a 24-ft bus roof unless panels are pushed to the limit. Bank-hours-limited cooling is the design reality: cool-down bursts (1–4 hrs) from the bank; all-day cooling on shore/gen (the gen makes all-day cooling real).
- Inverter interaction: the Midea is 115V → inverter path. Inverter idle tax matters only when inverter is on for the AC alone — run AC bursts concurrently with other inverter loads, or accept the tax during those hours. 5 kW inverter has ample headroom (AC max ~800W w/ soft-start inverter; no hard start surge like non-inverter units).
Install Plan (80/20 Window Panel)
- Pick the AC window — a side window near the living/sleeping centroid; measure its opening (need ≥23”W × ≥13.75”H for the 12K U-shape). Front windshield area is NOT a mount candidate.
- Build the panel from 80/20 (per insulation-frame.md): frame sized to the window opening, U-shaped AC seated in it so the window channel closes over the top sash rail of the unit (that’s the U design’s seal).
- Fill the surround with foil-faced polyiso inserts + foil tape — the panel is the thermal plug; this is the same insert you’ll use to close the window when the AC is removed for travel.
- Mount: panel anchored to bus rib/window surround (1/4-20 through 80/20 T-nuts); external support bracket + safety strap required — a dropped window AC is a road hazard and insurance claim. Tilt the unit ~1–2° outward (or drain pan + hose) so condensate exits; don’t trap water inside the U channel.
- Dedicated 120V circuit at the AC location from the 5 kW inverter (reuse the wiring plan discipline from power-supply.md — dedicated branch beats a stretched extension).
- Security at camp: the U-shape can be secured to the panel (lock bracket or pin) — it’s very removable, which is a feature for travel and a liability at camp.
Measurement Plan (trip 1 — same discipline as fridge/Starlink)
Bring actual numbers back to this file + power-supply.md:
- Kill-A-Watt (or inverter output meter) logging: fan-only, cooling in a hot unshaded bus, cooling in a shaded/insulated bus, dehumidify — with ambient temp + duty cycle
- Update planning numbers: kWh/cooling-hr, kWh/day, solar recharge days, and the AC row in the power spreadsheet
- Until measured: ~0.5 kWh/hr is the planning number
Verified Specs (sources, 2026-09)
- Midea MAW12U1QWT: 12,000 BTU DOE, CEER 15.2, R-32, 115V, 56.9 lb, 21.9×19.17×13.46 in, 592.1 kWh/yr (Energy Star), opening 23–36”W × ≥13.75”H, 31–51 dBA, variable-speed compressor, 3-yr warranty (2026 store listing). ~$509 Best Buy street.
- Midea MAW08V1QWT: 8,000 BTU, CEER 15.0, R-32, 400 kWh/yr, 53 lb, opening min 24”W × 14”H, 32–42 dBA, ~$359.
- EG4 12K Hybrid: SEER2 22.5 / EER2 12.6, R-32, 115V 190–1,100W (rated cooling 950W), DC input 90–380 VDC ≤1,100W PV (solar string, NOT battery), indoor 42.5×9.33×12.99 in / 33 lb, outdoor 31.57×12.72×22.2 in / 70.5 lb, quick-connect lineset. Real-world draw 480–600W typical / ~900W max (DIY-solar forum field report).
- Dometic RTX 2000: 2,000W / 6,824 BTU cooling, 12V, ~10–58A (Eco 19A ≈ 230W @12V; Turbo toward 700W), 70.6 lb, roof opening 18.9×15.3 in, cool-only, ~$2,400–2,650.
- [VERIFY] on the actual bus: window count + opening sizes, rib spacing (16” OC expected on E350 shuttle), roof hatch/vent state (matters only if a rooftop unit is ever considered), interior floor plan sq ft, and final AC window choice.
Pitfalls
- Buying more BTU than the bank — AC that cools fast but drains the bank is the wrong trade. Inverter + envelope > raw BTU.
- Single-hose portable negative pressure — the SereneLife pulls makeup air through unsealed shell gaps. Never the off-grid baseline.
- Roof AC stealing solar space — rooftop units and the 1,000–2,000W array compete for the same roof. Window-mount AC avoids the conflict outright.
- “48V AC” bait — hybrid mini-split DC ports are direct-solar, not 48V battery. Verify voltage paths before purchase.
- Unsupported window AC — no external bracket + safety strap = dropped unit on the road. Non-negotiable.
- Condensate inside the U channel — window units assume a horizontal sash; a vertical bus panel mount must tilt outward or drain.
- All-day AC on 1,000W solar — the arithmetic doesn’t close (~6–8 kWh/day demand vs ~4–5 kWh/day harvest). Size the array with AC in the budget, plan cool-down-burst usage, or carry the DF1100T gen (bank-charger path — a gen-run closes the gap and makes all-day AC real; solar stays ~600–800W).