1. The supply water temperature and return water temperature of underfloor heating system should be determined by calculation, the supply water temperature should not exceed 60°C, civil buildings supply water temperature should be around 35℃ to 50℃, temperature difference should not exceed 10℃.
2. Average temperature of ground surface (℃)
| Area | Suitable range(℃) | Highest limit(℃) |
| People always stay area | 24-26 | 28 |
| People temporary stay area | 28-30 | 32 |
| People not stay area | 35-40 | 42 |
3. Thickness of insulation layer of polystyrene foam.
| Floor type | Insulation material thickness(mm) |
| Insulation layer on floor between floors | 20 |
| Thermal insulation on the floor adjacent to the soil or unheated rooms | 30 |
| Thermal insulation on the floor adjacent to outdoor air | 40 |
4. When calculating the heat load of a comprehensive ground underfloor heating system, the calculated indoor temperature should be 2°C lower than the calculated indoor temperature of the convective heating system, or 90% to 99% of the total heat load calculated by the convective heating system.
5. The heat load of the local floor underfloor heating system can be determined by multiplying the heat load calculated from the overall radiant heating of the entire room by the ratio of the area of the area to the area of the room and the additional coefficients specified in the following table.
| Ratio of heating area to total room area | 0.55 | 0.4 | 0.25 |
| Additional factor | 1.3 | 1.35 | 1.5 |
6. For rooms with a depth greater than 6m, it is advisable to take 6m away from the outer wall as the boundary zone to calculate the heat load and arrange the pipelines separately.
7. On the building ground where heating pipes are laid, the heat transfer loss of the ground should not be calculated.
8. The heat load calculation of the ground underfloor heating system does not need to consider the height addition.
9. The heat load calculation of the floor underfloor heating system with household heat metering should consider factors such as intermittent heating and heat transfer between households.
Check the table method to determine the floor heating pipe spacing:
The heat dissipation Qr and the downward heat transfer loss Qs per unit ground area of the PE-X tube (W/㎡)
The outer diameter of the tube is 20mm, the thickness of the filling layer is 50mm, the thickness of the polystyrene foam insulation layer is 20mm, and the temperature difference between the supply and return water is 10℃ (cement or ceramic floor, thermal resistance R=0.02(㎡.k/w))
| Average water temp | Indoor temp | Heating pipe spacing (mm) | |||||||||
| 300 | 250 | 200 | 150 | 100 | |||||||
| ℃ | ℃ | Qr | Qs | Qr | Qs | Qr | Qs | Qr | Qs | Qr | Qs |
| 35 | 16 | 84.7 | 23.8 | 92.5 | 24 | 100。5 | 24.6 | 108.9 | 24.8 | 116.6 | 24.8 |
| 18 | 76.4 | 21.7 | 83.3 | 22 | 90.4 | 22.6 | 97.9 | 22.7 | 104.7 | 22.7 | |
| 20 | 68 | 19.9 | 74 | 20.2 | 80.4 | 20.5 | 87.1 | 20.5 | 93.1 | 20.5 | |
| 40 | 16 | 108 | 29.7 | 118.1 | 29.8 | 128.7 | 30.5 | 139.6 | 30.8 | 149.7 | 30.8 |
| 18 | 99.5 | 27.4 | 108.7 | 27.9 | 118.4 | 28.5 | 128.4 | 28.7 | 137.6 | 28.7 | |
| 20 | 91 | 25.4 | 99.4 | 25.7 | 108.1 | 26.5 | 117.3 | 26.7 | 125.6 | 26.7 | |
| 45 | 16 | 131.8 | 35.5 | 144.4 | 35.5 | 157.5 | 36.5 | 171.2 | 36.8 | 183.9 | 36.8 |
| 18 | 123.3 | 33.2 | 134.8 | 33.9 | 17 | 34.5 | 159.8 | 34.8 | 171.6 | 34.8 | |
| 20 | 144.5 | 31.7 | 125.3 | 32 | 136.6 | 32.4 | 148.5 | 32.7 | 159.3 | 32.7 | |
The heat dissipation Qr and the downward heat transfer loss Qs per unit ground area of the PE-X tube (W/㎡).
The outer diameter of the tube is 20mm, the thickness of the filling layer is 50mm, the thickness of the polystyrene foam insulation layer is 20mm, and the temperature difference between the supply and return water is 10℃ (wood floor, thermal resistance R=0.1 (㎡.k/w))
| Average water temp | Indoor temp | Heating pipe spacing (mm) | |||||||||
| 300 | 250 | 200 | 150 | 100 | |||||||
| ℃ | ℃ | Qr | Qs | Qr | Qs | Qr | Qs | Qr | Qs | Qr | Qs |
| 35 | 16 | 64.2 | 24.4 | 66.0 | 24.6 | 69.6 | 25.0 | 73.1 | 25.5 | 76.2 | 26.1 |
| 18 | 56.3 | 22.3 | 59.6 | 22.5 | 62.8 | 22.9 | 65.9 | 23.3 | 68.7 | 23.9 | |
| 20 | 50.3 | 20.1 | 53.1 | 20.5 | 56.0 | 20.7 | 58.8 | 21.1 | 61.3 | 21.6 | |
| 40 | 16 | 79.1 | 30.2 | 83.7 | 20.7 | 88.4 | 31.2 | 92.8 | 31.9 | 96.9 | 32.5 |
| 18 | 72.9 | 28.3 | 77.2 | 28.6 | 81.5 | 31.2 | 92.8 | 31.9 | 96.9 | 32.5 | |
| 20 | 66.8 | 26.3 | 70.7 | 26.5 | 74.6 | 26.9 | 78.3 | 27.4 | 81.7 | 28.1 | |
| 45 | 16 | 96.0 | 36.4 | 101.8 | 36.9 | 107.5 | 37.5 | 112.9 | 38.2 | 117.9 | 39.1 |
| 18 | 89.8 | 34.1 | 95.1 | 34.8 | 100.5 | 35.3 | 105.6 | 36.0 | 110.2 | 36.8 | |
| 20 | 83.6 | 32.2 | 88.6 | 32.7 | 93.5 | 33.1 | 98.2 | 33.8 | 102.6 | 34.5 | |
Estimated heating design:
| Building type | Advised underfloor heating kw data | |
| No insulation measures | Insulation measures have been taken | |
| Residential | 58-64 | 40-45 |
| Comprehensive residential area | 60-68 | 45-55 |
| School, office | 60-68 | 50-70 |
| Hospitals, kindergartens | 65-80 | 55-70 |
| Hotel | 60-70 | 50-60 |
| Shop | 65-80 | 55-70 |
| Canteen | 115-140 | 100-130 |
| Theaters, exhibition halls | 95-115 | 80-105 |
| Auditorium | 115-165 | 100-150 |
Remarks:
1. In the plan design stage, in the absence of basic data, the heating load can be estimated based on the thermal index. When conditions permit, the load calculation should be carried out room by room and item by item.
2. The thermal index is used in a single room, and the error may be large.
3. The table is based on continuous heating, intermittent heating index = continuous heating index × 24/day heating hours.