Electric heating – Heating devices – With power supply and voltage or current regulation or...
Patent
1997-10-14
1999-05-04
Paschall, Mark
Electric heating
Heating devices
With power supply and voltage or current regulation or...
219213, 219494, 219492, 1262712A, 246428, 237 80, 340581, H05B 102
Patent
active
059001780
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an installation for melting of snow or ice, especially on roofs, in roof downpipes and gutters, and around manholes in roadways and the like, comprising a heating means, a temperature sensor means and a control unit for connecting and disconnecting the heating means in dependence on sensed temperature.
BACKGROUND OF THE INVENTION
There are previously known different embodiments of control systems for the control of heating cables or the like for snow and ice melting at roof downpipes, in gutters and the like. In principle, two control systems are on the market today. One of these measures the air temperature and connects heating cables in an adjustable temperature interval, e.g. between -5 and +5.degree. C. The other system measures an air temperature and combines this with a water sensor in a gutter, and a heating cable is kept connected as long as the temperature is below the melting point at the same time as the water sensor registers moisture in the gutter.
The weakness of the first system is that it uses much current. The second system will be connected as long as one has minus degrees and snow. However, much dirt always gathers in gutters, something which may rapidly cause errors in the water sensor registration.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an installation which in an efficient manner prevents ice formation and thereby ensures a free water passage at the introductorily mentioned places, and which is very economic in operation, the power consumption being very low as compared to installations according to the prior art.
The above-mentioned objects are achieved with an installation of the introductorily stated type which, according to the invention, is characterized in that the temperature sensor means comprises a first temperature sensor for sensing the surface temperature at the place of snow or ice melting, and a second temperature sensor for sensing the air temperature at the topical place, and that a snow sensor is arranged on said surface, which sensor is connected by the control unit when the first temperature sensor at a rising temperature registers that the surface temperature rises above a chosen minus value, or when the second temperature sensor at a falling temperature registers that the air temperature falls below a chosen plus value, the control unit causing connection of the heating means if the snow sensor registers snow during a chosen time period, and further keeping the heating means connected at least until the second temperature sensor at a rising temperature registers that the air temperature rises above the chosen plus value, or at least until the first temperature sensor at a falling temperature registers that the surface temperature falls below the chosen minus value, but in both cases only on the condition that the snow sensor at intervals registers snow.
A principal feature of the installation according to the invention is that there are used two temperature sensors for controlling connection and disconnection of the heating means of the installation, usually a heating cable, namely a first sensor for sensing the surface temperature at the topical place, e.g. a roof surface, and a second sensor for sensing the air temperature at the place. As known, the temperature at a roof surface of a building will be more or less above the temperature of the ambient air because of the heat from the roof. The temperature difference between the surface temperature and the air temperature will never be constant, but will vary with the snow quantities on the roof and the moisture content in the snow. In addition, it will vary between different buildings, dependent on insulation and ventilation. In the installation according to the invention, both said temperatures are measured, so that the operation of the installation is made independent of variations in said temperature difference. One achieves thereby that the heating cable of the installation is only connected in the periods wherein there is a need for this, viz
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Stig Loden et al., "Fritt fran sno oc is med varmekabel," Elinstallatoren, vol. 57, No. 12, pp. 44-49, 1991.
Browning Clifford W.
Paschall Mark
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