Under floor heating Designing underfloor heating (UFH) system must always comply with the system suppliers instructions.

Underfloor heating advantages: No need for separate heat emitter visible on the walls Heat distribution is well suited to geothermal and solar thermal systems, because required circulating water temperature is low due to the large heat transfer surface area (increasing supply flow temperature drops the heat pump coefficient of performance) - The floor surface is pleasantly warm At vertical distribution of temperature due the underfloor heating is very close to the ideal temperature distribution of the thermal comfort point of view

Underfloor heating construction of a floor Underfloor heating problems: If the room have large and high window surfaces, the need for radiators or electrically heated glasses is possible to prevent from the draft If the heated floor area of ​​the room is small compared to the surface area of ​​ the building envelope or thermal insulation does not correspond to the current level of new construction, the floor surface temperature of the underfloor heating can limit the efficacy ie the heating capacity is not enough to cover the heat losses of the room - Heat output downwards form the floor to the space under Underfloor heating construction of a floor

Under floor heating capacity (heat output)     UFH heating capacity is determined by the temperature of the surface of the floor, which is bounded by a floor coating material and comfort factors. The surface temperature of the floor is not equable. It is high on the pipe, and the lowest between the pipes (Figure 2). Ts = the indoor air temperature, °C s = the radiation heat transfer coefficient, W/m2K k = the convection heat transfer coefficient, W/m2K Tp = the average floor surface temperature, °C λ = thermal conductivity W/mK b = installation depth, m L = spacing between the pipes, m  

The average floor surface temperature (and thus the heat output of the floor) may be increased by intensifying the pipe spacing (by reducing the distance between the pipes), or by increasing circulation supply water temperature in the heating circuit. The floor heat output (W/m2), also called the heat flux (heat output), is an average (1) q the heat output per the floor square meter, W/m2 s the radiation heat transfer coefficient, W/m2K k the convection heat transfer coefficient, W/m2K  total heat transfer coefficient (radiation and convection), W/m2K Tp the average floor surface temperature, °C Ts the indoor air temperature, °C

The floor surface radiation heat transfer coefficient is about 6 The floor surface radiation heat transfer coefficient is about 6 ... 7 W/m2K and for convection 4 ... 5 W/m2K. Total floor surface heat transfer coefficient is thus obtained about 10 ... 12 W/m2K.   By increasing the floor surface temperature by 1°C, rises the floor heating heat output about 10 W/m2. The floor surface temperature should not exceed 30 ° C. Recommended floor surface temperatures are: - Warehouses, garages Tp  23 ° C - Living rooms Tp  26 ... 27 ° C - Shower rooms (tiled floor) Tp  30 ° C - Workspaces, where people work while standing Tp  25 ° C

The indoor room temperature is normally in the winter at 21°C, then the maximum heat output capacity, which can be through the floor to a room of 60 ... 72 W/m2. If the room is high and the surface of the window is big, may the room heat losses are bigger than the underfloor heating can exceed the maximum output capacity. When a tiled floor and not standing constantly on the floor the surface temperature of the floor can be raised to 30°C (fringe areas below of large window surfaces), the heating capacity of the room can be brought through the floor 90 ... 108 W/m2 in the periphery. Floor heating supply water design temperature value is used 30 ... 45 ° C, depending on the floor construction. Design temperature difference between supply and return water is 5 ... 10 ° C. For a concrete or tiled floor, the supply flow temperature 30…35C is usually sufficient as designing temperature. When having wooden floor the supply flow temperature may be necessary to lift up to 40…45C, depending on the structure of the floor. When using under floor heating, foundation slab insulation thickness should be at least 150 mm.

With underfloor heating oxygen diffusion protection is needed with plastic pipe. Oxygen diffusion protection prevents oxygen entering into the heating water and prevents consequently corrosion. In UFH every room is own heating circuit (in the room it can be one or more tube circuits). Underfloor heating pipe spacing is 5 to 30 cm depending of the room heating demand. The size of the pipe to be used depended UFH system vendor. Underfloor heating pipe external diameters are 12 mm - 20 mm. Typically, underfloor heating pipes are installed in the room using spiral-piping or row-piping. Because the supply water temperature is about 5…10C higher than the return water temperature, the supply water pipe is always installed near by the outer wall.

Heat emitter vs. UFH Spiral piping Row-piping Integrated peripheral loop

Separate peripheral loop (Two circuit, but only one room thermostat) Spiral Row Hot supply water pipe installed next to the outer wall

The margin strip (Reunanauha) between the floor and the wall

Under floor heating, main parts - A heat source (boiler, capacitor, heat pump, district heating substation) - Feed piping (heat source and the manifolds) - Manifolds and manifold control valves and actuators - underfloor heating system (if necessary heat transfer plates or mounting plates) - A control system Manifold 2 A heat source Manifold 1

An example of the manifold and its accessories.

Apartment building hydronic under floor heating system.

The manifold can also be fitted on the wall or inside the wall Manifold box.

The room thermostat location

Underfloor heating pipes to the mounting plate attached to the concrete floor. Underfloor heating pipes mounted on the grooved chipboard heat transfer plates. Underfloor heating pipes attached to the mounting tray

actuator Cover cork Supply manifold Shut off valve Balancing valve Pass by pipe Return manifold

A pipe circuit (loop) is limited by the length of the pipe because of the pressure drop, which depends on the size of the tube and the heating power (needed flow). For example, Uponor's underfloor heating system manufacturer's recommended maximum permitted pipe lengths for different pipe dimensions are:   20 x 2 mm pipe Lmax = 100 m 17 x 2 mm pipe Lmax = 80 m 12 x 2 mm pipe Lmax = 55 m