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Surface heating
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Range of application.
A full list of the different ways to apply surface heating could be very long and probably never complete, as new ideas of applications are brought forward all the time. We will, in this brochure, present the most frequently used applications, and we hope that you will contact us if you cannot find the solution to your requirement of surface heating. We will help you to design yet another solution fitting your surface‐heating requirement. Applications:
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Outdoor surfaces that are dry and non‐slippery all year round, stairs, entrances, pavements, footbridges, garage drive ways, wheel chair ramps, loading platforms, goods reception bays etc.
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Dry and non‐slippery multi‐storey car parks and approach‐ramps.
•
Frost protection of the ground below cold‐store rooms.
•
Heating of the earth‐layer in greenhouses.
How does the Velox surface heating operate?
VELOX‐surface heating is an electrical heating system employing cables as the generating source. The cables are installed in the ground in such a way that the requisite power is obtained.
How about energy consumption?
The heat is generated directly into the resistance wire of the cable which gives a high efficiency and a small loss. The output of the cable is easy to control with different kinds of thermostats. VärmeKabelTeknik has a large‐scale programme control equipment for heating cables. In combining different kinds of sensors we can always design an application. The combination of a high efficiency and an effective control will guarantee an energy saving application. MORE INFORMATION ABOUT CONTROL CAN BE FOUND IN CHAPTER "K" CONTROL
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Surface heating 3
Existing cable types are TCPR and TCPH
The TCPR cable is an armoured series conductor cable with return wire. This cable is easy and quick to apply, as the termination end is not to be connected. The cable is custom‐made by us and is delivered with cold‐lead‐in cable as well as mounted termination end. The TCPH cable is a variant of the TCPR cable. It is a TCPR‐cable provided with an outer sheath of teflon which means that the cable can stand a high temperature when applied. You can apply the TCPH directly in the asphalt. MORE INFORMATION ABOUT THE CABLES CAN BE FOUND IN CHAPTER "H" DATA SHEET.
Power required The power required for a surface heating application is depending on the geographical position and local variations. Guiding principles: ‐ South Sweden: 200 ‐ 300 W/m2. ‐ Central Sweden: 250 ‐ 350 W/m2. ‐ North Sweden: 300 ‐ 400 W/m2. The local variations can for example be: the surface that is to be kept clear is exposed to strong winds, snow drifts in or you want a rapid heating up. Miscellaneous When designing a surface heating application it is very important to cooperate with the constructors in the building, ground and electric fields. Different factors like the bedding, the load on the surface and the coating etc are of great importance to the final result. VÄRMEKABELTEKNIK has a vast experience and a large knowledge of designing ground heating applications from car testing ramps in north to entrances in south. VÄRMEKABELTEKNIK can design and deliver complete applications according to the clients request.
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Dry and non‐slippery entrances
Hotels, shops, public establishments and other buildings where people pass in and out often have problems with wet and slippery floors when it is raining and snowing. The problems is often solved if you apply heating into the entrance areas, hall and landings and/or the stairs right outside the doors and thus the snow will melt away.
There are also other advantages with heated stairs and entrance areas/hall‐space‐landings:
• The risk of accidents, owing to slippery conditions because of snow and ice, are eliminated.
• You do not have to shovel snow, which are bot timewasting and very little interesting. When you do not have to shovel away snow and ice the surface coating will not get damaged.
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Surface heating 5
Projecting instructions.
The heating cables are applied in different ways in stairs and entrances depending on the method of construction.
• Stairs/areas which are casted in one operation • Stairs/areas which are ground with a steel device after the casting.
• Stairs/areas with a coating of stone or filling.
OUTPUT
Most often you choose a high output (300‐400 W/m²), in order to obtain quick melting off and drying of the entrance. This does not mean a higher energy cost as the operating time of the cable is short. CONTROL The control of the heating cable is often done manually in combination with a thermostat. The purpose of the thermostat is to switch off the heating cable when the temperature is high enough to keep the surface dry. With bigger applications it is better to switch the heating cables on via an automatic control that can sense the moisture and temperature to decide whether the application is to be switched on or not.
INSTALLATION When installing heating cables in stairs the cable should be applied in such a way that the output is evenly distributed amongst the treads of the stairs. The outmost run of cable in each tread of the seal must not be applied too deep down in the step as this can cause freezing in the rubber nosing. The sensor of the thermostat should be placed in such a way that it senses the temperature in the most exposed position of the stairs. A suitable depth of application is 30‐50mm below the surface.
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Dimensioning heating cables for stairs When calculating the cable resistance and length this is the best way:
6. The length of the heating cable can now easily be worked out by dividing Rt with R/m.
Example: 30.84 ÷ 0.45 = 69 m
7. Solution: 69 m heating cable (TCPR) 0.45 W/m.
1. The total surface of the stairs (the treads). 2. Power required (Pt). 3. The total resistance (Rt). 4. The shortest cable length possible (l). 5. The cable resistance (Ω/m) is decided upon. 6. The real length of the cable (l). 7. The solution. 8. Check calculation.
Check: The power of the cable per meter is check calculated according to Pt ÷ l
Example: 1.704 ÷ 69 = 24.7 W/m
Example: A flight of stairs with a half‐space landing of 1,8 x 1,5m 4 treads 1,8 x 0,3m, 4 risers 1,8 x 0,2m in central Sweden is to be applied with heating cables as an anti‐ skid device. 1. Begin to calculate the total surface where the heating cable is to be applied. Example: 2,7m2 + 4 x 0.54 m2 = 4,9 m2
PLEASE NOTE! When the stairs and suspended and the underneath also is exposed to the air temperature you must calculate with much higher powers (+ 50 %).
8. Check: P= U2 ÷ R Example: 230 2 ÷ (69 x 0.45) = 1.704 W.
Compare these two values to the required initial values and find out whether they are within the decided tolerances.
2. The required power Pt = P/m2 x surface Example: 4,9m2 x 350 W/m2 = 1.715 W 3. Calculate the total resistance of the cable in order to obtain a power of 1.715W when connected to 230V.
Formula: Ohms law for power P=U2 ÷ R gives R = U2 ÷ P Example: 2302 ÷ 1.715 = 30.84 Ω
4. The shortest length possible is obtained by dividing Pt with the max. permitted cable power. The power when applying in concrete is 25Ww/m.
Example: 1.715 ÷ 25 = 69 m
5. Calculating the resistance of the cable per meter (R/m). R/m = Rt ÷ l
Example: 30.84 ÷ 69 = 0,45 Ω Theoretically calculated value is the 69m cable with 0,45 Ω/m. We chose this value (0,45 Ω/m).
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Surface heating 7
Application design
If you want to apply the TCPR or the TCP cable you have to think of the difference in the application of these cables. When applying the TCP‐cable you have to remember that the two ends of the cable should be connected into the same control point and thus the cable must be applied backwards and forwards all through the stairs, which means two runs through the risers. In contrast to the TCP‐cable, the TCPR‐cable has a return wire and therefore this cable only ahs to be applied in one way, which means only one run through the risers.
The treads: 5 runs à 1,7 m = 8,5 m 8,5 m x 24.7 W/m = 210 W/tread
surface power 210 W ÷ 0,54 m2 = 388 W/m2. The half‐space landing:
TCPR: 24 runs à 1,7 m = 40,8 m
40,8 m x 24.7 W/m = 1007 W Surface power 1007 W ÷ 2,7 m2 = 373W/m2. runs à 1,7 m = 37,4 m
TCP: 22
37,4 m x 24.7 W/m = 924 W Surface power 924 W ÷ 2,7 m2= 342 W/m2
Calculating the number of cable runs in the treads and half‐space landings. The cable can not, for obvious reasons, be applied throughout the whole width of the stairs. Usually you can deduct 50mm at each edge Example: 1.800 ‐ 100 = 1.700 mm The available cable length is calculated according to: TCPR the total cable length ‐ the depth of the stairs. Example: 69 ‐ 2,7 = 66.3 m TCP the total cable length ‐ the depth of the stairs x 2 Example: 69 ‐ 5,4 = 63.6 m
The number of cable runs are calculated according to: The available cable length/the length of cable runs: Example: TCPR 66.3 ÷ 1,7 = 39 slag. TCP 63.6 ÷ 1,7 = 37.4 slag. distribution of cable runs in treads and half‐space landings respectively The principal idea is to distribute the heating cable in such a way that you get the same surface power in the whole stair. In certain cases it can be of advantage if the power is distributed unsymmetrically. Example: From the calculation of the total of the plane surface of the stair you know that the surface of the half‐space landing is 2.7m² and the total surface of the treads is 2.2m². We also know that the half‐space landing is beneath the roof and thus it is not exposed to the weather in an extreme way. In this case the best is to distribute the power in such a way that a higher surface power is obtained in the treads. The best is to apply 5 runs of cable in each tread and the rest in the half‐space landing. This will give the following surface powers in our example:
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Installation of the heating cables.
The installation of the heating cable must be adjusted to the method of construction of the stair. To obtain quick and even melting of the stairs it is important that the cable is applied in an adequate depth (30‐50mm below the surface).
Single‐course casting:
The cable is lashed on to the armouring with a plastic coated lashing wire or electric tape. If the armouring is placed too deep down special fixing irons are to be mounted for the heating cable. This application work has to be supervised by a competent engineer. The cable should always be tested (megatested and ohm‐ measured) by a responsible electrician before the casting. You have to be very careful not to damage the cable at the casting.
Double‐course casting:
Special fixing strips for the heating cables are mounted on the group‐stone mortar. The heating cable is applied and is fixed to the strips with the plate tabs. This work has to be supervised by a competent engineer. The cable should always be tested (megatested and ohm‐ measured) by a responsible electrician before the floor concrete is applied. You have to be very careful not to damage the cable when applying the floor concrete.
Tiling:
Application according to the double‐course casting. Please pay attention to the fact that the thickness of tiles can make the cables go too far down below the surface. PLEASE NOTE! Do not forget to apply a plastic tube/pipe for possible thermostat sensors. The pipe should be plugged at the termination end not to let concrete or finishing mortar penetrate. Flexible tubing are often used for electrical wires.
Consultation. VÄRMEKABELTEKNIK has knowledge and experience in designing heating cable applications within a large range and we can assist you with design and delivery of complete solutions. We can also assist you in consulting assignments regarding heating cable applications.
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Surface heating 9
Non‐slippery walking areas during frost and snow
With heating cables installed pavements, footbridges and other ground surfaces can be kept free from ice and snow even during the cold period of the year. The cables can be applied in many a different way. The most common way is to apply the cable in a bed of sand, which is coated with cement plates, ground bricks or asphalt. You can also apply the heating cables on concrete, which is then covered with a surface coating of some kind. When the construction is made of concrete and is cast in one phase the heating cables are applied in the concrete by lashing them at the upper edge of the armouring. Miscellaneous Power required: depending on the geographical position of the application, the local climate and the required operation the required power varies between 250 ‐ 400 W/m2.
If you choose a high power the melting off will get a faster start. Y/D‐change‐over switch: if the application is dimensioned for 380V operating voltage you can obtain a lower basic power (1/3) in the Y‐position with a Y/D‐ change‐over switch. Limitations in power depending on the type of cable: Type of cable
Concrete (W/m)
Asphalt (W/m)
Sand (W/m)
TCPH
30
30
25
TCPR
25
—
20
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Application of heating cable in a bed of sand.
A very frequently used method of applying heating cable is in a bed of sand. This method of application is universal and the surface coating can consist of different materials like asphalt, concrete plates, paving stone or ground bricks. Types of cables to use: TCP or TCPR. Limitation of powers Max 20 Watt per meter cable. Application: The cable should be applied in a well‐compressed bed of sand with a depth of at least 50mm. The cable is then to be covered with sand, which is well stowed around the cables in order to obtain a good spreading of the heat. When working on this you have to be careful not to damage the cables. This layer of sand also has to be about 50mm thick. Installation of the heating cables:
The fastest and easiest method is to apply a steel fabric or a chicken net to which you lash the cable with a fitting c/c‐distance. When lashing a plastic coated lashing wire should always be used. Another method is to fix the fixing strips in the first layer of sand by means of boards. These boards must not be applied in such a way that the cable can come in contact with the boards as the heating cable must not get direct contact with combustible materials. You can for example apply boards outside the heated area and stretch fixing strips between them. The cables are then mounted on the fixing strips with a required c/c‐ distance.
Check: The application of the cable should always be supervised by a competent engineer. Before the cable is covered it should always be tested (megatested and ohm‐measured). Control: At moisture/temperature control special sensors are mounted in the surface. A protective pipe for the sensor wire is then to be applied all the way to the sensor. more information about control can be found in chapter "k" control.
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Surface heating 11
Dimensioning heating cables for a pavement covered with ground bricks
Brick
Layer of Sand
Heating cables Bed of sand Ground
When calculating the cable resistance and length this is the best way: 1. The required power is decided. 2. Distribution into an appropriate number of cable runs. For each run you then calculate: 3. The total resistance (Rt). 4. The shortest cable length possible (l). 5. The cable resistance (Ω/m) is chosen. 6. The real length of the cable (l). 7. Check calculations. 8. The distance between the cable runs (c/c). 9. The solution. Example: A pavement outside a shop, 3 x 12m, is to be applied with heating cables to be kept dry and non‐ slippery all the year around. The cables are to be applied in a bed of sand and the covering of the pavement is of ground bricks.
This means shortest cable length of 1800 ÷ 20 = 90m. 5. The cable resistance per meter (R/m): R/m = Rt ÷ l Example: 29 ÷ 90 = 0.3
The theoretical value will thus be 90m heating cable 0.3Ω/m.
In the data sheets you will find that there is no cable with this resistance value. You then have to choose the closest lower value, as a higher value would mean too short a cable and too high a power per meter.
You then choose 0.25 Ω/m.
6. The real length of the cable: l = Rt ÷ R/m. Example: 29 ÷ 0.25 = 116 7. Check calculations: The total power Pt = U2 ÷ Rt
1. Required power: surface power x surface
2302 ÷ (116 x 0.25 ) = 1824 W. Power/m: P/m = Pt ÷ l. 1824 ÷ 116 = 15.7 W/m
In this example the surface power is decided to 300 W/m2, the surface is 36 m2.
This power per meter is somewhat low and a new calculation is made with a shorter cable.
The required power will thus be 300 x 36 = 10.8 kW.
2302 ÷ (100 x 0.25) = 2116 W. 2116 ÷ 100 = 21.16 W/m.
This is a better value but it certainly gives a higher surface power but a lower price, as the cables are shorter.
2. Distribution on number of cable runs: 10.8 kW distributed into 2 three‐phase groups gives: 10 800 / 6 = 1800 W. From the installation point of view this is a suitable distribution as it gives a possibility to design the application for 230V and to fuse with 10 A. 3. The total resistance per meter: Rt out of Ohms law for power R = U2 ÷ P Rt = 2302 ÷ 1800 Rt= 29 Ω 4. The shortest possible length: The best cable in this example is, because of the expense, the TCP cable. In the data sheets you will find that the max. power per meter at a application in a bed of sand is 20 W/m for the TCP.
8. c/c‐distance: c/c = surface x 100 ÷ l.
The answer is obtained in cm if you put the surface into m² and l into meter. 6 x 100 ÷ 100 = 6 cm
9. The solution: 6 cable runs each 100 m TCP 0.25 Ω/m are applied with a c/c‐distance of c/c 6 cm.
Total power: 6 x 1824 = 10.94 Kw Surface power: 10.94 36 = 303 W/m²..
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Control
The application can be controlled in different ways manually or with an automatic switching on according to different control conditions. VÄRMEKABELTEKNIK can present a number of different solutions on how to control heating cables. If you for example want an automatic switching on of the application at snow falls and when there is a risk of slippery conditions, the best to choose is the control cabinet type 21‐IC.
More information about the control cabinets from Värmekabelteknik with function designs and complements can be found in chapter K 'CONTROL'.
Application of heating cables in asphalt on concrete
One method to apply the heating cables is to apply the cable directly in asphalt on for example cover of concrete. This method can be used in applications for example in handicap ramps and footbridges. Type of cables: TCPH, a variant of the ordinary TCPR‐cable is pvoded with an outer sheath of teflon, which means that it can stand the high temperature in hot asphalt (140‐160°C). Limitations: Max 30 W/m cable Application: the cable is fixed on special fixing strips which are nailed on to the concrete surface (c/c 500mm). Control: The laying of the heating cable should be supervised by a competent engineer. The cables should be tested (megatested and ohm‐ measured) by a responsible electrician before the asphalt is applied. Covering: when the asphalt is applied by hand you have to be careful not to damage the cables with tools or other objects.
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Surface heating 13
Dimensioning heating cables for a foot‐bridge.
When calculating the cable resistance and length this is the best way: 1. The required power is decided. 2. Distribution into an appropriate number of cable runs. 3. The best cable and voltage feed are decided. For each run you then calculate: 4. The total resistance (Rt). 5. The shortest cable length possible (l). 6. The cable resistance (Ω/m) is chosen. 7. The real length of the cable (l). 8. Check calculations. 9. The distance between the cable runs (c/c). 10. The solution. Example: It is difficult to keep a footbridge made out of concrete free from snow and ice. It has thus been decided to install heating cables and then apply asphalt on the surface. 1. Required power: The bridge is situated in southern parts of Sweden and the required power is actually 200‐250 W/m2 but as it is a suspended bridge and subject to cold weather even from below the required power must be adjusted upwards with ≈ 50%, which gives ≈ 350 W/m2. The surface power will then be ≈ 350 W/m2 The total power: The bridge is 9 x 3m2, the total required power will then be 27 x 350 = 9.450 W. 2. Distribution on runs: Seen from the installation point of view as well as from the power it is best to distribute the power on three runs each 3150W. Each run will then heat a surface of 9 m2 3. Voltage feed: If you calculate the operating power of the cable runs at a feed voltage of 380V, it will be possible to supply also with 230V via an Y/D‐ change‐over switch and thus a power of 1/3. This can be of advantage if you for example want a basic heating, which is always below an adjusted value. This means a much faster heating up when there is a change in the weather and at precipitations. 4. The total resistance of the cable (Rt): is obtained out of Ohms law for power P = U2÷ R shows that R = U2÷ P Example: 3802÷ 3.150 = 45.8 Ω 5. The shortest possible length of the cable (l). Example: 3150W/30W/m = 105 m 6. Required resistance per meter cable (R/m): R/m=Rt÷l Example: 45.8 Ω/105 m = 0,44 Ω/m
In the TCPH cable data sheet you will find that there is no cable with this resistance. You then have to choose the closest lower value, as a higher value would mean too short a cable and too high a power per meter cable. You then choose the 0.36Ω.
7. The real length of the cable: l = Rt÷ R/m
Example: 45.8 Ω/0,36 = 128 meter
Choice of cable: As the application of the cable will be directly in the asphalt layer the cable must resist the high temperature of the asphalt (140‐1600C). The TCPH is such a cable.
8. Check calculations ‐ total power Pt = U2 ÷ Rt Example: 3802 ÷ (0.36 x128) = 3.132 W ‐ power/m cable P/m = Pt ÷ 1 Example: 3.132 ÷ 128 = 24.5 W/m 9. c/c‐distance; c/c = surface x 100 ÷ 1 The answer is obtained in cm if you put the surface into m² and l into meter. Example: 9 x 100 ÷ 128 = 7 cm 10. The solution: 3 lengths of heating cable each 128m TCPH 0.36 Ω/m fare applied with a c/c‐distance of 7cm. Control: The application is best controlled by a 3‐position control with the power positions: 0, 1/3 or full power. ‐ 0:0‐ power: The cables are dead. Operating position at high temperatures over 0°C and dry pavement. ‐ 1/3: Ground heating: the cables are supplied with 230V and delivers 1/3 power. Operating position at low temperature when there is no urgent risk for slippery roads (thermally operated). ‐ 1/1: Full heating The cables are supplied with 380V and heating: delivers full power. Operating position when there is a risk of slippery roads (thermally operated and moisture controlled). The above control is only one of the many methods. VÄRMEKABELTEKNIK has one department working only with developing and constructing control cabinets. If a control cabinet in our standard range can not be used, we will design and produce a new cabinet which is adjusted to the application. More information about the control cabinets from Värmekabelteknik with function designs and complements can be found in chapter K 'CONTROL'.
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Non‐slippery driving areas during WINTERTIME. Having applied heating cables underneath the surface the garage driveways, ramps in multi‐storey car parks and other exposed driving areas can be kept free from snow and ice during the wintertime. The cables can be applied in many a different way:
• Bed of sand with a surface covering of for example concrete slabs or asphalt.
• On concrete which is then provided with a surface covering of asphalt. In concrete, when the construction is out of concrete and is cast in one step, the heating cables are applied in the concrete by lashing the cable in the upper part of the armouring.
Miscellaneous Power required: Depending on the geographical position of the application and the construction of the building the power required could vary between 200 ‐ 400 Watt/m2. There are some things you have to think of when deciding the power required, for example how fast the melting off is going to start, to what extent the surface is exposed to falling snow and cold and if vast quantities of snow are coming down from the adjacent areas. In the previous chapters we have described the design and the installation of heating cables in beds of sand and in asphalt. What now remains is to describe how to apply heating cables on concrete.
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Surface heating 15
Application of heating cable in concrete.
Control:
The most often used method when applying heating cable in concrete is to apply the cable directly in the concrete.
At moisture/temperature control a special sensor has to be applied in the surface. A protective pipe for the sensor cable should then be applied up to the sensor.
Cable types to be used: TCPR.
More information about the control cabinets from Värmekabelteknik with function designs and complements can be found in chapter K ' CONTROL'.
Restrictions: max 25 Watt per meter cable. Installation: The cable is installed on the armouring according to the planned application design and is fixed temporarily. When the cable is applied and adjusted to cover the entire surface that is to be heated, the cable should be lashed to the armouring with a plastic coated lashing wire. Control: The installation of the cable has to be supervised by a competent engineer. Before the concrete is cast the cables have to be tested (megatested and ohm‐measured).
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Dimensioning heating cables for ramps in multi‐storey car parks Conditions: A multi‐storey car park in a city is planned. To solve the problems with snow‐clearance and slippery ways heating cables are going to be installed in the ramps.
Voltage feed: If you calculate the max. power at a voltage of 415V it will be possible to supply also with 230V via an Y/D‐change‐over switch and thus a power of 1/3. This can be of advantage if you for example want a basic heating which is always switched on when the temperature drops down below the adjusted value.
Calculated ‐ ramp in storey one 350 W/m2 Power required‐ ramp in storey two 250 W/m2 . The car park is built out of prefabricated concrete panels. The ramps are constructed of concrete panels 1.500 x 4.500mm (6.75m2). Six panels per ramp.
Construction: the heating cable is applied in the panels in the factory. The heating cables are connected to junction boxes which are cast inn the short sides of the panels. The power required of each panel is calculated. Heating cable calculations As the surface power of the concrete panels is not the same in ramp one and ramp two, two different calculations must be made. The method is the same and that is why we here only will explain the calculation of ramp one. When calculating the cable resistance and length this is the best way: 1. The required power is decided (Pt). 2. Distribution on the number of heating cable lengths. 3. The best cable and the voltage feed are decided. 4. The total resistance is calculated (Rt). 5. The shortest cable resistance possible is calculated(l). 6. The cable resistance is calculated and chosen (Ω/m). 7. The real length of the cable is calculated (l). 8. Check calculations. 9. The distance between the cable runs is calculated (c/c). 10. The solution 1. Required power: surface x required surface power Example: 6.75 x 350 = 2.365 W. 2. There is no reason for distributing this power into several cable lengths. It is sufficient with one length per concrete panel. 3. The best cable type is: The TCP is applied directly in the concrete (max 25 W/m cable)
This possibility is used in ramp one where it can be of advantage to have a certain maintenance heating when it gets very cold in order to get the melting of snow and ice to start quickly when there is a change in the weather and precipitation's. On the other hand this is not needed for ramp two, which is not subject to snowfalls in a direct way but only to what is brought in.
The heating cables for the panels in ramp one are calculated for 415/230V. The heating cables that are to be installed in the panels in ramp two are calculated for one voltage only.
4. The total resistance of the cable length (Rt): Ohms law for power R = U2 ÷ P Example: 3802 ÷ 2.365 = 61Ω 5. The shortest possible length of the cable length (l). l = Pt ÷ P/m Example: 2.365 W÷25 W/m = 95 m 6. Required resistance per meter cable (R/m):
R/m=Rt÷l
Example: 61 Ω ÷ 95 m = 0,64 Ω/m
In the TCP cable data sheet you will find that the nearest higher resistance value is 0.65 Ω/m and the closest lower value is 0.45 Ω/m.
We will here abandon the rule always to choose the lower value, as it, in this case, differs too much from the required value and the closest higher value is almost perfect.
7. The real length of the cable length: l = Rt ÷ R/m
8. Check calculations: 94 m TCP 0.65; 6.75 m2 P = 3802 ÷ (94 x 0.65) = 2.363 W P/m = 2.363 ÷ 94 = 25.1 W/m P/m2 = 2.363 ÷ 6.75 = 350 W/m2
In this example it is shown that the power per meter is somewhat high. If you then increase the length by a little and make new calculations until you find the correct length.
New check calculation: 95 m TCP 0.65; 6.75 m2 P = 3802 ÷ (95 x 0.65) = 2.340 W P/m = 2.363 ÷ 95 = 24.6 W/m P/m2 = 2.363 ÷ 6.75 = 346 W/m2 c/c = 6.75 x 100 ÷ 95 = 7 cm.
Example: 61 Ω ÷ 0.65 = 94 meter
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Surface heating 17
Control:
Ramp one: is controlled by a 3 position control with the power positions 0, 1/3 or full power. ‐ 0: 0‐ power:
The cables are dead.
Operating position at high temperatures for example over 0°C and a dry driveway.
‐ 1/3: Ground heating:
The cables are supplied with 230V and delivers 1/3 power. Operating position at low temperatures when there is no urgent risk for slippery roads (thermally operated).
‐ 1/1: Full heating:
The cables are supplied with 380V and delivers full power. Operating position when there is a risk of slippery roads (thermally operated and moisture controlled).
The moisture/temperature sensor should be placed outside the entrance of the car park in order to sense the snow or other precipitation immediately. Control of ramp 2: This ramp is controlled by a separate moisture/temperature sensor applied in the plane‐ driving surface after ramp one. If the sensor is placed really close to the driving surface the shorter the delay time for the heating in ramp two will be. Control cabinet: The two controls are placed in a control cabinet where all the components required for a heating cable application are placed, like earth‐leakage‐ circuit‐breakers, fuses, contactors etc. The above control is only one of many methods. VÄRMEKABELTEKNIK has one department working only with developing and constructing control cabinets. We will design and produce a new cabinet which is adjusted to the application. More information about the control cabinets from Värmekabelteknik with function designs and complements can be found in chapter K 'CONTROL'.
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Soil heating in greenhouses
If heating cables are applied in greenhouses or hotbeds, the season of cultivation can be extended. With an earlier start of growing in the spring and a longer autumn many so‐called impossible plants can be cultivated and this despite the severe climate. Earth heating can be arranged in an easy way and without too much encroachment by applying heating cables below the bed of earth. The heating cables are then controlled to obtain the required earth temperature (6‐14°C). Miscellaneous
Application:
• A reinforcing netting is applied on the bed of sand
Power required: 60‐140 W/m2 Cable types to be used: TCP and TCPR Dimensioning: The power should not exceed 15W/m cable to prevent a drying up of the roots. Control: The heating cables are controlled by a thermostat and the sensor is placed in the bed of plants (temperature zone 0‐40°C). Application of heating cables in earth beds. The heating cables are applied in the sand below the bed of plants, which can be of a varying depth, usually 40‐50cm. A layer is applied on top of the cable to prevent the cable to get damaged at digging or at some other kind of earth cultivating. As digging protection a strong wire netting, tiles or something equivalent can be used.
as bedding for the cable.
• Reel out the cable on the netting and fasten it into position.
• Lash the cable on to the reinforcing netting with a plastic coated lashing wire.
• Check that the cable is working. (Megatesting and ohm measuring).
• Apply the upper bed of sand (5cm). • Apply the digging protection. Be careful not to damage the cable.
• Another check measuring could be made. • Apply the bed for plant growing.
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Dimensioning heating cables for soil heating in greenhouses When calculating the cable resistance and length this is the best way: 1. The required power is decided (Pt). 2. Distribution on a suitable number of cable lengths. 3. The best cable and voltage feed are decided. For each length the following is then decided: 4. The total resistance (Rt). 5. The shortest cable length possible (l). 6. The cable resistance (Ω/m) is chosen. 7. The real length of the cable (l). 8. Check calculations. 9 The distance between the cable runs (c/c). 10.The solution. Example: In a hothouse there are two cultivating areas 6 x 2m that are to be provided with heating cables for earth heating. 1. Required power: The surface x required surface power Example: 12 x 100 = 1.200 W. 2. Number of cable lengths: The relatively low total power of 1.200W you can without problem put on one cable length.
7. The real length of the cable length (l):
l = Rt ÷ R/m Example: 44.08 ÷ 0.45 = 98 meter.
8. Check calculations: 98 m TCP 0.45; 12 m2 P = 2302 ÷ (98 x 0.45) = 1.200 W P/m = 1.200 ÷ 98 = 13.33 W/m P/m2 = 1.200 ÷ 12 = 100 W/m2 9. c/c‐distance (c/c): c/c = surface x 100 ÷ l
You will obtain the answer in cm if you put the surface in m² and l in meter.
Example: 12 x 100 ÷ 98 = 13 cm.
10. The solution: A heating cable length of 98 m TCP 0.45 Ω/m is applied with a c/c‐distance of 13 cm. Control. The heating cable can be controlled by a simple thermostat with a breaking capacity of 10 Ampere. Example:
Capillary tube thermostat F2000 Part.no: 85 800 54
Larger applications should better be controlled by control cabinets from VÄRMEKABELTEKNIK. We have a great deal of experience of application as well as deliveries of complete applications. MORE INFORMATION ABOUT CONTROL CABINETS CAN BE FOUND IN CHAPTER K "CONTROL"'
3. Type of cable: TCP or TCPR are two types of cables that you can choose between. Because of the expense the TCP is the cable that is most often chosen.
Voltage feed: There is no reason to choose a higher voltage than 230V.
4. The total resistance of the cable length: (Rt) is obtained out of Ohms law for power P = U2 ÷ R gives R = U2 ÷ P Example: 2302 ÷ 1.200 = 44.08 Ω. 5. The shortest possible length of the cable length (l): l = Pt ÷ P/m Example: 1.200 W ÷ 15 W/m = 80 m. 6. Required resistance per meter cable (R/m):
R/m = Rt ÷ l Example: 44.08 Ω ÷ 80 m = 0.55 Ω/m
In the cable data sheet you will find that the closest lower value is 0.45 Ω/m. You thus choose a cable with this resistance and then calculate what length is needed.
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Frost protection of the surface below cold storage rooms It is important to protect the ground from frost below cold‐storage rooms and other construction areas where low temperatures are frequent. You have to prevent the cold from permeating through the ground and give a deep‐going ground frost which can cause dislocations and cracks in the foundation. An easy and reliable way to protect from frost is to apply heating cables in the foundation and then control the heating cables in such a way that the temperature never will get lower than 0°C. As the insulating layers between the freeze space and the foundation are extremely thick a very little feed of power is needed in order to settle this.
Control Except for the operating thermostat of the application an alarm thermostat should be installed. The alarm thermostat is adjusted in such a way that an alarm is given if the temperature falls below the adjustment of the operating thermostat. The alarm thermostat is fused with its own fuse in the central unit. VÄRMEKABELTEKNIK has experience and know‐how about heating cable applications for cold‐storage rooms. We design and delivers complete applications according to requirement.
Miscellaneous Power required: 20 W/m2 Types of cables to use: TCPR. Dimensioning: The power per meter cable ought to be within 5‐7 W/m. The distance between the cable runs max. 30cm. Regarding the dimensioning and the application of the heating cable we refer to a fitting method described in the earlier chapters: -
Application of heating cables in concrete.
-
Application of heating cables in bed of sand.
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Control of applications for ground heating
To obtain an energy saving application for ground heating the switch on and switch off must be controlled in a rational way. This can be done in many a different ways and what you choose is depending on the size of the application and how it can be supervised. ‐ Manual switch on/off. You switch on the application when it is necessary. ‐ Control by single thermostat. The application is switched on when the temperature is below the adjusted value.
‐ Control by double thermostat. The application is switched on when the temperature is within the adjusted value. ‐ Control by temperature‐ and moisture sensitive sensors. This is a full‐scale control where the operating time of the application is switched on only when the temperature condition is wet and when there is moisture on the ground. ‐ Control cabinets. VÄRMEKABELTEKNIK has a full‐scale programme of control cabinets for control of all kinds of heating cable applications.
We also design and manufacture control cabinets with functions according to your requirements. More information about thermostats, control cabinets and other components for control can be found in chapter K 'CONTROL'.
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Telephone: +46‐301‐418 50 – Email: info@vkts.se – Homepage: www.vkts.se
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