MAKING MODERN LIVING POSSIBLE Planning Underfloor Heat DanFoss HeaTing SolUTions Handbook Handbook Planning Underfloor Heat Planning criteria Essential requirements for all calculations: Changes in building methods over the last few decades have brought about lower requirements • Detailed plan of building, construction of outer for heating homes, so that Danfoss underfloor walls, and size and type of windows. heating can meet respective heating requirements These data are essential for calculation of the for even physiologically acceptable surface tem- heating load in accordance with EN 12831. peratures. In some rooms, such as bathrooms, • Information on the type of flooring and its additional heating may be necessary, as areas thermal resistance Rλ,B , since the heat output is under bath and shower cannot be heated and dependent on the floor construction, particularly a higher temperature is required (24° C instead that over screed (in accordance with EN 1264 a of 20° C). In such rooms the underfloor heating 2 thermal resistance of Rλ,B = 0.1 m K/W Rλ,B for maintains the temperature in the floor while other living rooms is specified, in bathrooms Rλ,B = 0.0 heat comes from sources such as wall heating, m2 K/W. Other values up to a maximum of 0.15 heated towel rails, etc. 2 m K/W are to be separately agreed.) Rλ,B = 0.0 m2 K/W. • Building plans, building drawings and all room data have to be shown. After the calculations, the pipe layout and data are included in the building plan. • Danfoss forms for calculations. Standards for The following standards have to be observed when EN 13813 Screed Material and Floor Screeds underfloor heating planning and installing floor heating: Local building regulations. EN 1991 Action on structures Professional information on interface EN 1264 Underfloor Heating, Systems and co-ordination when planning heated Components underfloor constructions (ref: BVF). DIN 4109 Sound Insulation in the Building EN 1264 is crucial for the construction of under- Industry floor heating. With the inclusion of EN 13813 ‘Screed Material and Floor Screeds’ three Basic ISO EN 140-8 Measurement of sound insulation Danfoss constructions are possible. in buildings and building elements Estimated The output tables of Danfoss SpeedUp and Basic The required excess heat source temperature pre-calculations heating systems show output values for various determines the supply temperature which is room temperatures as well as the temperatures of described in more detail in the chapter ‘Calculating the central heating water in relation to different the supply Temperature’. The heat flow densities floor finishes. These tables give calculations of the are distributed evenly over the edge and comfort mean central heating water temperature with zones. The main central heating water tempera- which to run the underfloor heating in order to ture is determined by the type of installation (see achieve the desired output. output tables). 2 VGCTC202 © Danfoss 06/2009 Handbook Planning Underfloor Heat Standard heating load of When making calculations for Danfoss underfloor QN,f: Standard heating load of an underfloor an underfloor heated heating the standard heat load QN,f of the room is heated room [W] room essential. For underfloor heating in multi-storey QH: Heat output calculation buildings the heat gain of the shared floor can be included into the calculations if there are no If the heating system, such as an underfloor restrictions on the work. system, can raise the heat output by raising the The heat output QH is generally calculated from heat source temperature the extra allowance is is the standard heat load of an underfloor heated zero. Thus the calculated temperature output room QH,f plus an extra calculation allowance in equals the standard heat load of an underfloor accordance with EN 4701 Part 3. heated room. QH = (1 + x)* QN,f Thermal insulation to It is important to consider the thermal resistance The heat resistance Rλ.ins with a single insulation avoid downward heat of the insulation below the underfloor heating so layer is calculated as follows: loss that the heat of the underfloor heating radiates mainly upwards. S In accordance with EN 1264, Part 4 there are three ins Rλ,ins = different kinds of floor/storey constructions and λins various minimum heat resistances. with: Thermal Insulation R Ins, min Sins: effective insulation thickness [m] A above rooms with similar use 0.75 m2 K / W λins: thermal conductivity [W/m K] B above rooms with different use*, unheated rooms (e.g. 1.25 m2 K / W cellar) and on ground floor C above external air (-15°C) (e.g. 2.00 m2 K / W garages, passage ways) * e.g. rooms above commercially used premises Maximum surface In accordance with EN 1264 maximum surface temperature and room temperature of 9K (in temperature ΘFmax temperatures for phsysiological reasons are set comfort zones and bathrooms) or 15K (in edge as follows: zones). Limiting the surface temperature has Comfort zone: 29° C the effect of limiting the heat output of the Edge zone: 35° C underfloor heating. It is an important factor when Bathrooms: ti + 9° C = 33° C deciding whether to choose additional heating. However, with modern insulation the heat output Standard room temperatures of 20 or 24° C in underfloor heating is sufficient in 99 of 100 in bathrooms result in a difference in surface cases. Fluctuation in The position of the heating pipe can further case, average floor temperature is significantly lower temperature (W) influence the output. Depending on the position, than the maximum permitted temperature. varying surface temperatures can occur. Output is higher above the pipes than in between. The max 29°C difference between the maximum and minimum surface temperatures is called fluctuation (W). W W = θF max - θF min Larger distances between pipes cause larger fluctuation. Lower lying pipes slow down the heating system but the ‘long way’ to the surface distributes the temperature evenly, the fluctuation remains small. Since the maximum floor temperature must not be exceeded, larger fluctuation causes greater loss in output than a smaller fluctuation. In the first VGCTC202 © Danfoss 06/2009 3 Handbook Planning Underfloor Heat Characteristic base line The Characteristic base line shows the relation- Since the characteristic base line has idealised ship between the heat flow density and the physical parameters and is valid independent of surface temperature (surface temperature minus the system, no system, kept at the maximum room temperature) when the heated area is permitted surface temperature, can reach an evenly heated (fluctuation = 0). output of more than 100 W/m2 or 175 W/m2 in edge zones. W/m² Consequently the specific heat output q of the 200 floor surface depends on the difference between room and surface temperatures as well as the transferability. The latter is dependent on the 100 room data, including the needs to air the room and is described as heat transfer coefficient αges here 11.1 W/m2K. 50 Heat output q 30 q = αges (θF - θi) 20 θF = Floor temperature °C θ = Room temperature °C 10 i 1 2 5 20 K Mean surface temperature difference Example: At a room temperature of 20° C and a floor With a surface temperature of 9K above room temperature of 27° C a heat output of temperature an output of approx. 100W/m2 is 2 achieved, with an excess temperature of 15K a q = 11.1 W/m K * 7°K (27° C - 20° C) 2 heat output of approx. 175 W/m2. = 77.7 W/m would be achieved. Heat source temperature The mean heat source temperature is a firm with: component of many calculations. It is calculated ΔθH: Excess Heat Source Temperature from the mean value of the supply and return θi: Standard - Inside Temperature temperatures: θm: Heat Source Temperature θm = θi + ΔθH Installation types The heating system Danfoss Basic comprises two The SpeedUp and SpeedUp Eco heating systems different installation types in edge zones and has installation types for the edge and comfort three in comfort zone areas. zones. They differ in pipe distance. System Possible pipe distance in cm BasicRail 8.8 (mean) BasicRail 12 (mean) BasicRail 20 BasicRail 25 BasicRail 30 BasicGrip and BasicClip 10 BasicGrip and BasicClip 15 BasicGrip and BasicClip 20 BasicGrip and BasicClip 25 BasicGrip and BasicClip 30 SpeedUp and SpeedUp Eco 12.5 SpeedUp and SpeedUp Eco 25 4 VGCTC202 © Danfoss 06/2009 Handbook Planning Underfloor Heat Heat output curve The heat output and the fluctuation of the surface with: Limiting curve temperature are dependent on several factors: ΔθH = θV - θR • Floor surface temperature • Room temperature θV - θi In • Pipe distances θR - θi • Thickness and thermal conductivity of the load bearing panels • Lateral heat output with: • Thermal resistance of floor finish θV: Supply temperature • Composition of the layers θR: Return temperature θi: Standard-inside temperature In accordance with EN 1264 all factors combine into the following equation heat flow density q: When keeping to maximum permitted tempera- tures, the above factors will give, apart from fluctuation, limiting curves (calculated according q = K + Δθ to EN 1264, Part 2). The intersections indicate the H H heat flow limits and the limits to excess heat source temperatures. with: q: Heat output [W/m2] 2 KH: Equivalent heat transfer coefficient [W/m K] (official DIN check) ΔθH: Excess heat source temperature Calculated heat flow When doing the calculations for underfloor The data for the heat flow densities of the edge density heating, the calculated heat flow density is to be zones or comfort zones qR and qA can be calcu- worked out as follows in accordance with DIN EN lated from the output diagrams where the excess 1264, Part 3 : temperature of the heat source applies.