Planning Underfloor Heat

MAKING MODERN LIVING POSSIBLE

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).

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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

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Heat output curve The heat output and the fluctuation of the surface with: Limiting curve temperature are dependent on several factors: Δθ = θ - θ • Floor surface temperature H V R • 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 temperatures, 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. The approved threshold of the heat flow density Q (intersection of curves with limiting curve) must N,f not be exceeded. The approved density depends qdes = AF on the thermal resistance of the floor covering and the construction type. If one value of the calculated and distributed heat with: flow density (q /q ) is above the threshold heat q Calculated heat flow density [W/m2] R A des flow density, the threshold density rather than the Q Standard-heat load of an underfloor heated N,f heat flow density applies. The resulting decrease room [W] in excess heat source temperature also reduces A Floor area to be heated [m2] F the heat flow density of the other combination type of installation. The heat output achieved from underfloor If the standard heat load of a room heated with heating is underfloor heating is greater than the heat output of the underfloor heating, additional heating for

the shortfall should be considered. QN,f - QF. QF = q * AF

with:

qdes Calculated heat flow density

QN,f Standard-heat load of an underfloor heated room

AF Floor area to be heated

where q is evenly distributed over the edge zone (maximum 1 m wide) and the comfort zone:

AR AA q = * qR + * qA AF AF

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Calculation of excess The calculated supply temperature for a room In all other rooms which are operating on supply temperature with the highest calculated heat flow density is calculated flow temperatures the differential

assigned qmax (except bathrooms) and given a temperature is calculated as follows, as long as 2 thermal resistance for floor cover of Rλ,B = 0.10 m the relation:

K/W. Higher values for R λ,B have to be taken into account. Bathrooms will have R = 0.0 m2 K/W. λ,B σ j The differential temperature σ for the room to be < 0.5 Δθ calculated is defined as σ = 5 K. The installation H, j type is chosen so that q max fully achieves the threshold heat flow density indicated in the is: limiting curve. The maximum permitted excess Δθ : Excess heat source temperature of each room j flow temperature is H,j with: σ when ≤ 0.5: ΔθH σ j = 2 * [(ΔθV, des) – ΔθH,j ]

σ Δθ ≤ Δθ + with Δθ ≤ Δθ V, des H, des 2 H, des H, G otherwise:

otherwise: 4(ΔθV, des - ΔθH, j) σ = 3 * Δθ * 1+ -1 j H, j 3 * Δθ [√ H, j ] σ σ2 ΔθV, des = ΔθH, des + + 2 (12 ΔθH, des)

Calculation heat source For calculating the size of the circulating pump The sum of the downwards thermal conductivity temperature the mass flow rate is determined as Hm (flow rate and downwards thermal resistances is: of heating water in kg/s). It is independent of the total output (floor heating output, and heat losses to other rooms) as well as differential temperature. Ru = Rλ, ins + Rλ, floor + Rλ, render + Rα, floor

A * q R θ - θ m = F 1 + o + i u with R = 0.17 m2 K/W H σ * C R q * R α, floor W ( u u )

The mass flow rate Hm can also be expressed

when converted as the flow rate HV : with CW = 4190 J/kgK

m The partial heat transfer resistance of the floor V = H H ρ construction Ro (upwards) encompasses both the thermal conductivity and thermal resistance upwards: with ρ = 0.998 kg/dm3 1 S R = + R + u o α λ ,B λ u To determine the flow rate of a heating circuit the

flow rate of the room VH must be divided by the number of heating circuits: 1 with = 0.093 m2 K/W α V V = H HK Number of heating circuits

Pressure loss For the calculations and size of the circulating The pressure loss diagram (cf. pressure loss pump it is important to calculate pressure loss. In diagram for Danfoss composite pipe) shows, via

order to calculate pressure loss the total length of flow rate per heating circuit HKV , the pipe friction

the pipes IHK and supply and returns have to be resistance as pressure loss Δp per m. To calculate determined. Here it is important that the length the total loss of a heating circuit, this value has to of the supply and return pipes FEED is double the be multiplied by the length of the heating circuit. distance of room to manifold (supply and return). Depending on the laying type the following

values are relevant: ΔpHK = Δp * lHK

l = Pipe length of edge zone layout plan * A H R Individual heating circuits have different lengths + Pipe length of comfort zone layout plan * A A and differential temperatures and show different loss of pressure. Pressure compensation ensures that all heating circuits are supplied with The mean length of the heating circuit IHK is calculated thus: sufficient water. The flow adjustment is made on the return valve by determining the flow per minute (i.e. the volume flow [l/h] of the individual I heating circuits is divided by 60 [min.]). I = FEED + H HK Number of heating circuits ( ) The total water volume within an underfloor heating system is calculated by the length of all heating circuits I multiplied by a factor of 0.113 Here it must be mentioned that the area layout HK (l/m). and the number of heating circuits are determined by the type of screed, i.e. the heating circuits must be compatible with the screed sections.

Correlation between flow The smaller the differential temperature: Raising the differential temperature causes a rate, pressure loss and • the higher the volume flow reduction in flow rate. differential temperature: • the higher the flow speed of the medium and • the higher the pressure loss

Threshold values • The maximum supply temperature must not exceed 55° C for wet cement and calcium sulphate (CAF) screed • Heating circuits should not be longer than 100 m, 110 m maximum. • The optimum length is 120 m. • Pressure loss of 250 mbar must not be exceeded since the circulating pump, apart from maintaining the pressure head, has to cope with pressure losses in the heating circuits and in the whole system (in manifold, its valves, supply and return pipes, mixing valves, etc.). • The maximum supply must not exceed 50° C for gypsum plaster.

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