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Energy·designed

Thermal Storage

Why it matters

The cheapest battery in any building is a tank of hot water. Storing a kilowatt-hour as heat costs a fraction of storing it as electrons. Heat stores without degradation. A village welder can repair the technology. That matters because heat is most buildings' single biggest energy demand, and heat demand is stubbornly out of phase with solar supply: the sun delivers at noon, the cold bites at night. A buffer tank lets the heat pump run when electricity is abundant and the house stay warm when it is scarce. Midday surplus becomes evening comfort with no lithium involved. In a blackout-prone country, a full 1000-litre tank is hours of guaranteed warmth that no grid failure can take away.

Role in 001's holistic picture

The buffer tank sits at the junction of the energy organism: the heat pump and any backup source charge it, the warm surfaces draw from it, Energy Management decides when charging happens — ideally, when the array is producing. Every kilowatt-hour the buffer holds frees the same capacity in the battery. It is also the component that lets multiple heat sources coexist without fighting. And the principle is older than plumbing: in passive solar design, the building's own sunlit mass is the tank, charged by the sun directly.

Details. Notable examples

A thermal store is a well-insulated water tank between heat sources and heat consumers. At its best it is stratified, exploiting the physics of hot water floating on cold. Stratification turns one tank into several: different sources feed different heights, different consumers draw from different heights, and temperatures coexist in layers instead of blending into lukewarm mediocrity. Sizing follows the job: a daily buffer smooths a heat pump's cycles, a larger store rides through a cloudy day. Seasonal storage exists but demands volumes and losses that rarely pay at building scale. The store can be dry too. A Trombe wall is a sun-facing massive wall behind glass. It is thermal storage with no tank, no pump and no controls, charging by day and releasing into the room through the evening. At Zion National Park's visitor centre, the US energy laboratory NREL measured the Trombe wall supplying about 20 percent of a full season's heating. A fifth of a public building's warmth came from a wall that faces the right way.

How 001 engages with it

The Unity Hub design contains our best stratification story, published in the heating article: one tank, two sources, two buildings. The heat pump feeds the middle of the tank at around 30 °C — exactly what the low-energy Unity Hub's floor heating wants. The wood boiler feeds the top at 60–65 °C — exactly what the neighbouring heritage hostel's radiators need, since its thin hutsul envelope demands fast, hot heat. Unity Hub draws from the middle, the hostel from the top, and both sources serve both buildings through one stratified vessel without conflict. The Hlibivka design went further on paper, sketching a supplementary source: a 5–10 m³ heat store charged by surplus solar.

Maturity: designed. The stratified two-source architecture is part of the accepted Unity Hub concept; its measured story arrives when the system runs.

Further reading