To alleviate temperature fluctuations in living quarters and store excess heat for the night and the next few days, various types of warehouses are used in passive systems.. Heat accumulation by increasing temperature or latent heat takes place using traditional and improved building structure elements, Trombe walls and its modifications, as well as containers independent of the building structure. It is of a short-term nature.
In a direct system, the accumulation of thermal energy takes place thanks to the use of appropriate materials for the construction of underground and vertical partitions in the building.
These materials should have high specific heat and high volumetric density, and therefore a large mass. It is desirable, so that the partitions also have a high capacity to absorb solar radiation. Arrangement of thermal insulation and finishing materials (exterior cladding, Carpet) should not be an obstacle to sunlight and heat. The ability to absorb solar energy is characterized by the absorption coefficient α, which achieves the highest values for heavy materials, Porous, Dark.
List of materials used in the construction of houses and their coefficients of energy absorption of solar radiation
| Material, surface type | Absorption coefficient - α |
| Concrete destroyed | 0,54 — 0,65 |
| Sheet: | |
| — aluminium | 0,52 — 0,63 |
| — galvanized steel | 0,94 |
| Light lacquered wood | 0,60 |
| Eternit - Rough Plates | 0,42 — 0,65 |
| Oil paint: | |
| — brown | 0,65 |
| — matt black | 0,97 |
| — matt red | 0,52 |
| — dark ocher | 0,63 |
| Granite grey | 0,80 |
| Light glaze | 0,18 — 0,26 |
| Marble | 0,30 — 0,65 |
| Papa: | |
| — asphalt | 0,76 — 0,74 |
| — tar | 0,86 — 0,88 |
| Plaster: | |
| — light | 0,40 — 0,42 |
| — dark | 0,73 |
| Water | 0,94 — 0,97 |
| Interior of the rooms: | |
| — clear | 0,90 |
| — dark | 0,95 |
| Brick wall: | |
| — red | 0,56 — 0,75 |
| — silicate | 0,35 |
As can be seen from the table, building structure elements should be designed from heavy building materials, to increase thermal inertia, which absorbs changes in sunlight and outdoor temperature.
Thus, the efficiency of using passive solar space heating systems with a lightweight housing is small.
In order to improve the heat absorption by the elements of the building structure, heated air is directed to the hollow ceilings and walls. If the movement of air is carried out on the principle of convective movements, then we are dealing with a passive system. Most often, this movement must be supported by blowers or fans and then these are semi-active systems.. Most of the ceiling structures used in construction have hollow blocks or slabs (in Poland — Żerańskie plates, DZ, Akerman, Fert etc.), so it is easy to use them to circulate air inside the ceiling. Similarly, walls can be used, in which air ducts should be developed. Walls of similar construction were built already in ancient Rome (hypocaustic). In Aichwald (Germany) w 1984 r. built a house with a greenhouse and an air collector on the roof. Gable walls of thickness serve as a heat storage there 52 Cm, solved as hypocaustic walls with a total surface area 120 m2. The saving of fuel used to heat the building was 26%.
Scheme of air circulation in the greenhouse, collector and hypocaustic wall of a single-family house in Aichwald.