Roof applications 2
Ice and snow melting on roofs
Ice and snow in gutters, down pipes, valleys and other roof constructions, often cause damage on buildings. Damage of this kind does not only apply to buildings but also people can be injured and property damaged by down‐falling snow or ice, when the dewatering system of the roof does not work satisfactorily. In some weathers, for example at midday thaw, tee stoppings are often formed in gutters and down pipes. This means that the melted snow and ice from the roof flood the gutters and icicles are formed. When these icicles fall down they can cause severe injury and damage both on people and material.
Pools remaining on the roof are often cause to leakage and damage due to moisture. By applying heating cables the gutters, box gutters, valleys, down pipes and other construction details of the roof, you eliminate the damage risk by frozen over dewatering systems. How do the de‐icing applications of Värmekabelteknik operate? These systems are based on heating cables and when the cables are voltage‐fed and warm the snow and the ice around will melt.
The cables can be applied in many a different way depending on the construction of the roof and the required functioning. How about the energy consumption? VÄRMEKABELTEKNIK has a large‐scale programme for control in order to optimize the energy consumption to a minimum. Air and roof sensors in combination with moisture sensors makes it possible to design a very efficient control, since the cables operate only when required.
Earth‐leakage‐circuit breaker All roof applications for 230V should, according to the safety regulations, be equipped with earth‐leakage‐ circuit breakers (30 mA). More information about this can be found on the pages D1400 and 1500.
Roof applications 3
The most frequently used cable types are TCPR, EL and BTL safe‐t
TCPR is a series conductor cable with return wire. The cable is custom‐made by us and is then provided with cold‐lead‐in cable connections at one end. The TCPR cable is a perfect low cost alternative with a good performance. This cable is used when you for sure know in beforehand what lengths are required. EL is a parallel resistive cable which gives a constant power/m. EL is available in two variants ‐ EL 20 (20W/m) and EL 30 (30W/m). This cable are most suitable chosen when you not in beforehand know the lengths which should be installed. At EL‐installations only one end is connected to junction box, the other is terminated waterproof with end termination kit EL. (E 89 892 10).
BTL SAFE‐T is a self‐limiting heating cable which delivers a varying power depending on the temperature of the cable and the character of the environment. Example: Temperature (°C)
Advantages with BTL SAFE‐T
• You can cut the exact length required. • It delivers the power that is required. • It is easy to design on the spot. • It is easy to apply. • It can be connected directly to a box. More details can be found in chapter H "Cabe data".
Roof applications 4
Dimensioning About power required in general
In gutters and pipes of normal dimensions (up to 5") the power required is calculated to 30W/m gutter/pipe. In box gutters and other wider valleys you have to apply the cable in several runs to obtain the power required. When calculating the power required for this type of applications the rule of thumb are 250 ‐ 300W/m². If a total melting and drying up is not necessary the cable can be applied in 4 runs in the middle of the gutter with a c/c‐distance of 30‐40mm. If the gutter is angular, one run is applied in each corner to avoid frost erosion. To keep bigger areas on roof applications free from snow and ice the power required is calculated to 30W/m².
How to choose type of cable Which type of application to choose (TCP or SAFE‐T) is often a question of economy. Whichever type you choose, with the correct dimensioning, you will obtain the power required. When choosing cable the following should be taken into consideration: If all gutters, pipes and other areas on the roof, where heating cable is to be applied, are measured, you can decide upon the lengths of the lengths and then it is easy to design a cost effective and well‐functioning application with TCPR‐cable. If you do not know the exact proportions of the application in advance, it is better to choose the SAFE‐T cable considering the total cost ‐ material and work. This cable type are sold by the metre together with a suitable number of cable connectors and termination kits to be cut and applied directly on the site.
Roof applications 5
Dimensioning roof applications with series conductor heating cable (TCPR)
You now know that the heating cable of 50m is required and that its total resistance should be in the interval 38.7 ‐ 48.4 Ω. This means that the Ω/m value of the heating cable should be between 0.77 ‐ 0.97 Ω. From the TCPR data sheet choose the cable resistance that is within the interval.
Gutters and down pipes Example: A gutter and the down pipes are to be applied with heating cable according to the sketch below. The diameter in gutter and pipe is ∅ 100 mm. By following the projecting below step by step you can calculate how much cable will be needed and which resistance to choose.
In our example we therefore choose TCPR 0.82 Ω/m. 6. Check calculations: The total power of the cable: Formula Pt = U² ÷ Rt Rt = the cables W/m x length.
Method of calculation:
Example: 220² ÷ (50 x 0.82) = 1.180 W The power of the cable/m: Formula: Pm = Pt ÷ l Example: 1.180 ÷ 50 = 23.6 W/m
1. Power required watt per meter gutter/pipe is decided. 2. The total length of the gutter and the pipe is measured. 3. The length of the heating cable is decided (l). 4. The required power (Pt) is decided.
The solution: 50 m TCPR 0.82 Ω/m Total power: 1.180 W Power/m cable: 23.6 W Power/m gutter: 47.2 W
5. The suitable cable resistance is chosen (Ω/m). 6. Check calculations. 7. The solution. 1. Power required: For gutters and pipes up to a diameter of ∅ 125 mm 30 ‐ 50 W/m gutter 20 ‐ 25 W/m cable. (Pm) 2. Measure the total length of all gutters and down pipes.
If the down pipes are connected to a ground surface drainage the heating cable should be put down about 1m below the ground level.
If the down pipes are terminated with ejectors the length of the heating cable should be adjusted to come in touch with these. You generally calculate with the cable reaching about 100mm above the mouth of the down pipe.
Example: 5 + 15 + 4 + 1 = 25 meter.
3. Heating cable length (l) = Length gutter + pipe 4. The total powr(Pt): Pt = Pm x l
max 25 W/m x 50 = 1.250 W min 20 W/m x 50 = 1.000 W
5. The resistance of the cable (Rt):
Ohms law for power R = U² ÷ P Rt min 220² ÷ 1.250 = 38.7 Ω Rt max 220 ² ÷ 1.000 = 48.4 Ω
Roof applications 6
Standard lengths for gutters and down pipes
To make it easier to choose the right heating cable for gutters and down pipes VärmeKabelTeknik has produced some standard lengths with TCPR‐cable for 230 Volt. Please note! All roof applications with 230V supply voltage should be equipped with an earth‐leakage‐circuit breaker. Standard lengths TCPR‐roofs Part.no
Gutters/Pipes Cable length Length Ω/m Power (m) (m) (W/m) 8987210 12 24 4.00 21.0 8987211 17 34 1.90 22.0 8987212 24 48 1.00 21.0 8987213 30 60 0.65 21.0 8987214 40 80 0.36 21.0 8987215 50 100 0.25 19.5 Cold‐lead‐in cable 2 x 1 m TCP 1,5 mm² Accessories included: Distance clips. Caution labels (2 pcs)
Total Power (W) 500 750 1010 1250 1680 1940
Dimensioning roof applications with series conductor heating cables (TCPR) Valley Example: A valley 12m long and 350mm wide is to be applied with heating cable of type TCPR for drainage and frost protection. The valley has a roof well with an inside pipe in the middle.
Box gutters and wide valleys When installing heating cables in box gutters and valleys it is important that the power installed is so high that the heating cable really is able to melt all the snow that might surround it. At too low power there is a risk that a tunnel might be built up around the heating cable. This can result in the heating cable not being of any use although it is operating and consuming power. Furthermore the risk of ice‐formation and falling snow remains.
An example below shows how to apply heating cables in wide valleys and box gutters. This type of application does not produce a total melting away of the valleys, but it drains the gutter and protects against frost damage.
The fundamental rule is, when applying TCPR‐cable in this type of gutters, that the cable is dimensioned to 20‐25W/m and that the c/c‐distance between the cables in the middle is 30‐ 50mm. The cable is applied according to the drawing with 4 runs of cable in the middle and with one run in each corner.
Roof applications 7
By following the projecting step by step you can calculate how much cable will be needed and which cable resistance to choose. Method of calculation: 1. The length of the heating cable is decided (l). 2. Required power per meter cable is decided (Pm). 3. Total power (min/max) is calculated. 4. The total resistance of the cable is calculated (Rt).
PLEASE REMEMBER! Problems with heating cables are never bigger than the distance to the nearest phone. Please phone VärmeKabelTeknik. We are ready to help you with design as well as deliveries of complete heating cable solutions.
5. Suitable cable resistance (Ω/m) is chosen. 6. Check calculations. 7. The solution. 1. Measure the entire length of the cable:
The valley: 6 x 12 m Roof well: 2 x 1 m Extra for the short sides: Total length of the cable: (l)
72 m 2 m 1 m 75 m
2. Required power per meter cable (Pm) 20 ‐ 25 Watt 3. Total power (Pt) = Pm x l max 25 W/m x 75 = 1875 W min 20 W/m x 75 = 1500 W 4. Calculation of cable resistance: (Rt)
Ohms law for power R = U² ÷ P Rt min 220² ÷ 1875 = 25.8 Ω
Rt max 220² ÷ 1500 = 32.3 Ω
5. You now know that a heating cable of 75m is required and that its total resistance should be in the interval 25.8 ‐ 32.3 Ω. This means that the W/m value of the heating cable should be between 0.34 ‐ 0.43Ω. From the TCPR data sheet choose the cable resistance that is within the interval.
In our example we therefore choose TCPR 0.36 Ω/m.
6. Check calculations: The total power of the cable: Formula: Pt = U² ÷ Rt Rt = the cable´s W/m x length.
Example: 220² ÷ (75 x 0.36) = 1793 W The power of the cable/m: Formula: Pm = Pt ÷ l Example 1793 ÷ 75 = 23.9 W/m
7. The solution: 75 m TCP 0.36 Ω/m Total power: 1793 W Power/m cable: 23.9 W
Roof applications 8
Melting off on eaves, porches and bigger roof surfaces (TCPR) There are often problems on roof constructions with a projecting eave. The snow melts on the roof due to a heat leakage and the water comes down to the base where it gets cool and freezes.
On porches there is often falling snow coming from roofs higher above and thus they get overloaded and the construction might give away.
Today the architects more often use glass cupolas on roofs when constructing new buildings in order to get brighter and nicer rooms. There is a heat leakage from the cupolas, which makes the snow melt and come down on the roof where it freezes and a bank of ice is formed around the cupola. These and other disruptions in the functioning and accident risks due to the construction of the roof can be avoided if heating cable applications are installed, which will keep the roofs clear from snow and ice.
Roof applications 9
Dimensioning roof applications with series conductor heating cable (TCPr) Projecting eave Example: An eave (6x1m), subject to falling snow, is to be applied with heating cable to melt the snow efficiently. By following the projecting below step by step you can calculate how much cable will be needed and which cable resistance to choose:
9. The c/c‐distance: Formula c/c = a x 100 ÷ l you will get the answer in cm if a is put in m² and l in meter. Example: 6 x 100 ÷ 75 = 8.0 cm. 10.The solution: 75 m TCP 0.36 Ω/m is applied with a c/c‐distance of 8 cm gives: Total power: 1793 W Power/m cable: 23.9 W Surface power: 299 W/m²
Method of calculation: 1. Power required Watt per m² is decided. 2. The surface of the eave is measured and calculated (a). 3. Required power is decided (Pt). 4. The max. resp. min length of the cable is decided (l). 5. The total resistance of the cable is calculated (Rt). 6. Suitable cable resistance is chosen (Ω/m). 7. The real length of the cable is calculated (l). 8. Check calculations. 9. The c/c‐distance is calculated. 10.The solution. 1. Power required: The requirement for efficient snow melting is: • 300 W/m² • 20 ‐ 25 W/m cable. (Pm) 2. Surface:
Example: 1 x 6 = 6 m²
3. Total power: Example: 6 x 300 = 1800 W. 4. Length of the heating cable max/min: max 1800 ÷ 20 = 90 m min 1800 ÷ 25 = 72 m 5. Cable resistance (Rt): Ohms law for power R = U² ÷ P Example: 220² ÷ 1800 = 26.9 Ω 6. Suitable cable resistance: Example: min 26.9 ÷ 90 = 0.30 Ω/m max 26.9 ÷ 72 = 0.37 Ω/m
From the cable data sheet choose the resistance value that is within the interval.
In this case 0.36 Ω/m.
The real length of the cable: Formula l = Rt ÷ Rm Example: 26.9 ÷ 0.36 = 75 m. 8. Check calculations: The total power of the cable: Formula: Pt = U² ÷ (Rm x l) Example: 220² ÷ (75 x 0.36) = 1793 W. Formula: Pm = Pt ÷ l
Example: 1793 ÷ 75 = 23.9 W/m.
Roof applications 10
Designing roof applications with parallel resistive cable (el)
EL is a parallel resistive cable zoned in 1 meter and available in two different effects, 20 resp. 30 W/m. (Cable data sheet under H). It is easy to design an application with this cable due to the cables constant power/m irrespective of length. EL‐ 30 gives for example 30W/m. You therefore do not need to know the exact length on gutters or pipes. This makes it possible to adapt the length of the cable on site. By not needing to use double‐folded cable and distance spacers, and that you can adapt the length of the cable on site, the installation often get easier and quicker which make the total cost lower.
Though you have to consider that all parallel resistant cables due to the power loss in the conduits have a maximized installation length. For EL‐20 it is 90m and for EL‐30, 70m.
To dimension a roof application with parallel resistive cable you need to think on following:
In gutters with normal sizes up to 5" you can lay a EL‐30, which often gives enough power to drain the gutter.
In down pipes it is normally enough with a EL‐20 cable which are hanged up with a hooker VELOX.
If the down pipes ends above the ground with an ejector the cable must not be that long that somebody can come in touch with it. The cable is suitably finished approximate 50mm above the down pipes opening.
Roof applications 11
Dimensioning roof applications with parallel resistive cable (el)
Box gutters and wide valleys In roof constructions with wide valleys or box gutters you often choose to apply the heating cable with four lengths in the middle to obtain a channel always free from ice. If the gutter is shaped in such a way that there is a chance of frost blasting for example in sharp edges a cable is applied in each corner. For applications of this type you can either choose the EL‐20 or the EL‐30. Which type you choose is depending on the climate and the construction of the roof.
Eaves, porches and bigger roof areas When designing with the EL‐cable the total power (Pt) is calculated according to the following: surface power x roof surface. Required surface power ≈ 300 W/m² The cable length will then be obtained by dividing the total power per meter (P/m) of the cable. Example:
Eave 8 m x 0.5 m Surface = 4.0 m² Power required: 300 x 4.0 = 1200 W Length of cable: EL‐20 1200+20 = 60m EL‐30 1200 + 30 = 40 m
For example 40m EL‐30 is applied according to the sketch to the right. The c/c‐distance is calculated according to this formula: c/c = h x b x 100 x 2 ÷ l h = the distance between the tension wires b = the length of the roof l = the length of the cable c/c = the distance between the cable holders. If you put all the measurements into m² the answer is obtained in cm. Example: 0.5 x 8 x 100 x 2 ÷ 40 = 20 cm. The result of the c/c‐distance calculation is approximate and some margin of error must be tolerated.
Roof applications 12
Designing roof applications with self‐limiting heating cable (BTL Safe‐T)
BTL SAFE‐T is a self‐limiting heating cable in which the output is depending on the temperature of the cable. At an ambient temperature of 0°C in ice/snow this heating cable delivers 36W/m. At the same temperature, but in air, it delivers 18W/m. The output of the cable goes towards 0 at a rising temperature (65°C). With these qualities this cable is a very good alternative when constructing roof applications.
• The BTL SAFE‐T cable has all the advantages a parallel resistive cable can have and in addition:
• The BTL SAFE‐T delivers power only when it is needed. (36 W/m in ice/snow).
• The BTL SAFE‐T can be cut in the exact length required (no zone‐length to think of).
• The BTL SAFE‐T‐applications are very easy to design
• The BTL SAFE‐T can be connected directly in a control point.
• The BTL SAFE‐T can be applied directly on a surface coating of roofing cardboard design basis for Velox SAFE‐T.
Roof applications 13
Dimensioning roof applications with safe‐t
Considering the max. permitted heating cable length ‐ please see data sheet chapter "H" ‐ the Velox Safe‐T can be connected in several different ways: 1. Add up the lengths of the gutters and pipes where heating cable is to be applied.
PLEASE NOTE! If the down pipes are connected to a ground surface drainage the heating cable must go down to a depth free from frosts to guarantee the outflow of water.
Add the length needed for the connection to the control point and 1 meter for each branching.
Example:.......................m BTL SAFE‐T
2. Put together the requirement of junction boxes. All connections and branchings are done in standard cabinets.
E 14 396 02 (2 pcs glands)
E 14 396 04 (3 pcs glands)
E 14 396 10 (4 pcs glands)
E1439602...….pcs E1439604.…..pcs E1439610...….pcs 3. Accessories:
Number of cable connectors and termination kits (1 per length of cable) Suspension hook (1 per down pipe)
....... cable connectors and term. kits ....... suspension hooks VELOX
4. Safety device: fuser, sizes of fuses
Max. cable lengths for Velox SAFE‐T when starting up in ice/water (0°C)
Dealy action fuses (characteristics G or K)
10 A 16 A 20 A
The voltage drop in the conductors gives a 10% power drop out at 57m cable.
37 meter 59 meter 74 meter
PLEASE NOTE! THE REGULATIONS REQUIRE EARTH‐ LEAKAGE‐CIRCUIT‐BREAKERS 30 MA.
Roof applications 14
Control of roof applications
In order to obtain a roof application that has a low energy consumption it is a must that the switching on and off is controlled in some way. This can be done in quite a few different ways. What method to choose is depending on the size of the application and how it can be supervised. Manual switching on/off The application is switched on when it is required. You should avoid this method as it often gives a high energy consumption.
Control with single thermostats
Sensitive to the air temperature The application is switched on when the temperature is below the adjusted value.
Control with double thermostats Sensitive to the air temperature The application is switched on when the temperature is within the adjusted difference. Example: +2..... ‐2°C
Roof applications 15
Control with roof surface‐ and air detecting sensors
Sensitive to the surface temperature of the roof and the air temperature The application is switched on when the temperature of the roof is so high that the snow melts at the same time as the air temperature is below 0°C and there is a risk of freezing in the gutters and pipes.
Control with lcd‐2, snow/rain‐ and temperature detecting sensor
Sensitive to moisture and temperature. The application is switched on at snow fall (supercooled rain) if the temperature conditions is performed and is switched on as long as moisture is left in the gutters. A complete control where the operating time of the application is minimized. This is the most economical way of controlling smaller installations.
VÄRMEKABELTEKNIK has a large range of control cabinets of all kinds of heating cable applications. If required, we also design and manufacture special control cabinets according to the clients request.
Roof applications 16
Telephone: +46‐301‐418 50 – Email: email@example.com – Homepage: www.vkts.se
Södra Hedensbyn 43
S‐430 64 HÄLLINGSJÖ
S‐931 91 SKELLEFTEÅ
Fax: +46‐301‐418 70
Fax: +46‐910‐881 33
Published on Mar 2, 2011