Building on our I.C.E. Battery origin story, this post covers the engineering: how cold energy storage actually works, and how we monitor installations using the same HomeLab infrastructure that runs our other projects.
The Core Principle: You Can't Store Cold
The first thing to understand about the I.C.E. Battery is counter-intuitive: you cannot "store cold." Cold is just the absence of heat. What the system actually does is use electrical energy to remove large amounts of heat from a storage medium, creating a reservoir of low-temperature potential energy.
Think of it like pumping water uphill to store gravitational potential energy. We use electricity to "pump" heat out of the storage medium, dropping its temperature to -22°C (-7.6°F) or lower. That stored thermal potential can then absorb heat from surroundings on demand, providing sustained cooling.
Cold energy storage in its simplest form — a frozen storage medium at 0°C or lower within the I.C.E. Battery tank
The Three-Stage Process
Stage 1: Charging — The Big Chill
During charging, electrical energy powers efficient chillers that extract heat from the storage core. Water containing 25% ethylene or propylene glycol circulates through heat exchangers, progressively lowering the medium to -22°C or below.
Practical details:
- Timing: typically charges overnight when electricity rates are lowest and ambient temperatures are cooler
- Source flexibility: works with solar, wind, or grid electricity
- Duration: intensive charging during off-peak hours, then the primary energy input phase is done
Once charged, the battery holds its thermal potential for 24+ hours. The energy is "in the system" — no continuous power draw needed.
Stage 2: Storage — Maintaining the Cold
This is the hardest engineering problem, same as with our sand battery's heat storage but in reverse. Keeping -22°C inside while the outside is 35°C (typical Saigon conditions) requires serious insulation:
- Multi-layer vacuum-sealed panels with reflective barriers
- Elimination of thermal bridges — any conductive path from outside to core
- Phase change materials for additional thermal buffering at critical temperature ranges
- IoT sensors monitoring insulation performance in real time (this is where we catch degradation before it becomes efficiency loss)
Stage 3: Discharging — Passive Cooling
When cooling is needed, a heat transfer medium — air for space cooling, or liquid coolant for refrigeration — circulates through heat exchangers integrated with the cold storage core. The warmer medium transfers its heat to the cold storage material and comes out chilled.
The key advantage: this discharge process is passive. No compressor running, no high-power electricity draw. Just fan speeds and flow rates controlling how much cooling is delivered. The large thermal mass provides steady output — consistent cooling for 24+ hours per charge cycle.
Daytime cooling delivery — glycol solution circulates through ice storage tanks during peak hours
How We Monitor: The Distributed IoT Architecture
Our I.C.E. Battery installations use the same monitoring stack we run for everything at Alpha Bits. No fancy proprietary platform — just open-source tools on Raspberry Pis.
Node-RED handles the orchestration: collecting sensor data, running automation logic, triggering alerts, and managing charging schedules.
MQTT provides lightweight publish-subscribe messaging between sensors and the control system. Low bandwidth (critical for remote installations with spotty internet), guaranteed message delivery for control commands, and sub-second responsiveness.
ZeroTier connects everything across locations. Our Saigon headquarters, the Bien Hoa farm facility, and remote installation sites all sit on the same virtual network. Adding a new monitoring node means: install ZeroTier, join the network, done. No VPN configuration per site, no port forwarding.
Cloudflare Tunnel provides secure remote access to dashboards without exposing any ports. Zero-trust security with no inbound firewall rules.
What the Sensors Track
Each installation runs multiple sensor types:
Thermal: core temperature at multiple points throughout the storage medium, surface temperature (insulation performance), ambient conditions, and heat exchanger inlet/outlet differentials.
Energy: power consumption during charging, delivered cooling capacity, real-time coefficient of performance (COP), and flow rates for heat transfer medium circulation.
System health: vibration (early detection of mechanical issues), pressure (leak detection), and chemical composition of the heat transfer fluid.
The system processes over 10,000 data points daily per installation, all stored in InfluxDB and visualised through Grafana dashboards.
Performance
| Metric | Specification |
|---|---|
| Storage Temperature | -22°C (-7.6°F) or lower |
| Cooling Duration | 24+ hours per charge |
| Energy Cost Reduction | 40-60% (off-peak charging) |
| System Lifespan | 20+ years |
| Monitoring Data Points | 10,000+ per day per system |
| Remote Access Latency | <100ms via Cloudflare Tunnel |
The 40-60% cost reduction comes from a simple mechanism: charge when electricity is cheapest (overnight, or when solar is producing excess), deliver cooling when it's most expensive (afternoon peak demand). This peak-shaving also benefits utility companies — our systems can participate in demand response programmes.
The 20+ year lifespan reflects the fact that the storage medium itself doesn't degrade. Water-based thermal storage instead of chemical refrigerants means no ozone depletion risk and no global warming potential from the storage material.