Executive Summary
1.8–2.0 tonne fresh shelled coconut halves per batch · 1 batch/day · U-flow, three-stage profile
Project brief
A heat-pump dehumidifying hot room for drying shelled coconut halves to copra (~5.0% moisture, wet basis). The room serves one batch per day with comfortable turnaround, producing roughly 957 kg of copra per batch (~21 t/month at 22 working days). The design optimises for (a) energy efficiency, (b) product uniformity and quality (no case hardening), (c) ergonomic loading/unloading — every tray reachable from floor or a single 200 mm step.
Design rationale in three bullets
- U-flow air path with a single U-turn. Each air channel is a 2-channel serpentine with one U-turn at the door end. Compared to a cross-flow topology, U-flow reduces airflow per kg of moisture processed by ~1.8× and improves SMER from ~1.8 to 4.03 kg/kWh.
- Shelled kernel + three-stage drying profile. Removing the shell cuts the Page drying constant from ~0.10 to ~0.20 h⁻¹ (2.3× faster). A gentle 55°C first stage for the wet phase (0.9 h) prevents case hardening on the kernel surface; the 62°C finishing stage (5.2 h) completes drying to 5.0% MC in 19.7 h total.
- Circuit-modular capacity scaling. The width carries 2 trolleys abreast per channel — adding abreast trolleys (wider room) is the upgrade path: same air path, same 410 Pa fan duty, capacity scales with width. Lengthening the room is not used (it adds series passes and worsens uniformity).
Why this is the recommended configuration
All sixteen trolleys see an air path of identical length (8 passes, 410 Pa) — guaranteeing uniform drying. The heat pump recovers latent heat via the evaporator and reheats via the condenser, so SMER sits at the top of the band reported for industrial heat-pump dryers (2.5–4.0 kg/kWh). The whole batch fits inside a single 8 × 4 × 2.2 m insulated room — a standard bay.
Capacity scaling path
| Current target | 1,819 kg/batch · 16 trolleys · 1.11 batches/day · 21.1 t copra/month |
| +1 abreast per channel (wider room ~6 m) | +8 trolleys · ~+50% capacity · same air path, same 410 Pa |
| Tighter loading (11–12 kg/m²) | +10–20% capacity; case-hardening watch — mitigated by three-stage profile |
| Replicate rooms | Modular U-flow cells beyond ~3 t/batch — preferred over bigger rooms |