GB2265453A - Balancing flow through the pipes of under-soil heating and method of installing the pipes - Google Patents

Abstract

Under-soil heating apparatus comprises a header flow pipe (2), a header return pipe (4), and a plurality of heating flow pipes (6) connected to the header flow pipe and a plurality of heating return pipes (8) connected to the header return pipe (4) running beneath a pitch. At each connection of a heating flow pipe (6) to the header flow pipe (2), and preferably also at each connection of a heating return pipe (8) to the header return pipe (4), there is a valve (16) for controlling the flow rate through each heating pipe (6, 8). The arrangement enables uniform heating of the whole playing surface of the pitch. The heating pipes (6, 8) are suitably buried in trenches (18, figure 3) at a depth, for example 350mm, deep enough to prevent damage to the pipes during normal ground maintenance. So that sufficient heat may permeate upwards to the surface (24), each buried pipe (6, 8) is covered with a layer of pea gravel (20) and a further layer of silica sand (22). <IMAGE>

Description

TITLE: Under-Soil Heating DESCRIPTION: Technical Field The invention relates to under-soil heating apparatus, particularly for preventing sports playing surfaces, such as football pitches, from becoming unplayable as a result of frost, and also relates to a method of installing under-soil heating apparatus in the ground.

Background Art There are a number of under-soil heating systems installed at football grounds in the United Kingdom. The systems are fed with hot water provided by a gas fired boiler. The water is heated by the boiler to a temperature of 82"C, which is hotter than required for thawing ground. The water is therefore cooled in a mixing chamber by adding cold water. The quantity of additional cold water is determined by the weather conditions. The system will usually operate with water at 25"C, but this could be varied between 20"C or 40"C depending upon the severity of the frost to which the pitch is being exposed and the time available for thawing.The water is pumped around the system by twin pumps, the second pump acting as a back-up in case the first pump fails, so as to avoid the possibility of water freezing in the pipes. The water is pumped to a header flow pipe which lays in the ground along one side or end of the pitch. Branching out from the header flow pipe are a number of heating flow pipes which run through the soil, under the pitch. It is the heat radiating from the heating flow pipes that primarily controls the temperature of the ground. Each heating flow pipe is connected at its extremity to a heating return pipe which conducts the heat expended water through the soil, back to a header return which is in the ground alongside the header flow pipe. The water is conveyed from the header return pipe to the boiler, where it is reheated.

A problem with the existing systems has been caused by the pressure drop that occurs along the length of the header flow pipe. The heating effect of the heating flow pipes is dependent upon the rate of water flow through the pipes. The pressure drop can result in insufficient flow of water through the heating pipes furthest from the supply. Without sufficient water flow the playing surface may not properly and fully thaw. The reduced heating effect will be particularly significant if the insufficient flow occurs through a region of ground which is more susceptible than other regions to freezing because, for instance, it lies in the shadow of a stand.

The result is that the ground suffers from what is termed "patching", that is, patches of unthawed turf.

A further problem with the existing systems has been caused by the depth at which the pipes are buried. It is conventionally thought that the pipes must be within the top 250mm of soil in order to avoid having excessively to heat the water to maintain the required temperature at the playing surface. However, pipes at less than 250mm depth interfere with ground maintenance, for example aeration, which involves inserting spikes into the playing surface down to where the pipes lay.

The Invention The invention provides under-soil heating apparatus comprising a header flow pipe, a header return pipe, a plurality of heating flow pipes connected to the header flow pipe, a plurality of heating return pipes connected to the header return pipe, and a valve at each connection of at least each heating flow pipe with the header flow pipe for controlling the rate of flow through each heating pipe.

The invention enables patching to be avoided by ensuring that the water flows at the same rate through each heating pipe, so that the resultant heating effect is uniform across the pitch and the whole playing surface can be raised to a reasonably uniform temperature.

The invention preferably has a valve at the connections of both the flow and return heating pipes with their respective header pipes.

The valve is preferably a balancing and setting valve with direct reading flow measurement. The required flow rate is set when the apparatus is being installed, before the pipes are buried.

The invention also provides a method of installing undersoil heating apparatus comprising excavating a trench, laying a heating pipe at the bottom of the trench, and filling the trench with a lowermost layer of gravel and an uppermost layer of sand.

The invention enables the heating pipes to be buried below the depth to which ground maintenance is carried out without having excessively to inerease the water temperature, because the conduction of heat by the gravel layer is better than if the heating pipe were covered by soil. Sufficient heat for thawing permeates upwards and dissipates through the sand layer to the surface.

The trench is preferably 350mm deep and 60mm wide.

The gravel is preferably pea gravel, with each gravel stone being less than 6mm in diameter.

The sand is preferably silica sand.

The trench also serves as a drainage channel water passing down through the layers in the trench to existing land drainage pipes situated further underground.

The Drawings Figure 1 is a schematic plan view of a section of an under-soil heating system under a football playing surface; Figure 2 is a plan view of sections of an under-soil heating system according to the invention, with a header flow pipe and a header return pipe connected to heating pipes; and Figure 3 is a partial end sectional view of an under-soil heating system according to the invention, installed in the ground.

Best Mode With reference to figure 1, an under-soil heating system illustrated generally at 1 has a header flow pipe 2 and a header return pipe 4, both situated underground, adjacent one side of a pitch whose outline is shown as 10. Heating flow pipes 6 are connected to the header flow pipe 2 at 600mm intervals. The heating flow pipes 6 branch perpendicularly out from the header pipe 2, through the soil under the pitch. Each heating flow pipe is connected at its extremity, that is underneath the side of the pitch 10 furthest from the header flow pipe 2, to an adjacent heating return pipe 8, so that there are pairs of flow and return heating pipes 6,8 under the length of the pitch. Each heating return pipe 8 is connected to the header return pipe 4, again at 600mm intervals.The water flows through the header pipes 2,4 at a rate of 150 1/minute, from the boiler (not shown) through the flow pipes 2,6 and back to the boiler through the return pipes 4,8, as shown by the arrows.

Figure 2 shows that each of the heating pipes 6,8 is connected to the respective header pipes 2,4 by a reducing T-connection 12, the heating pipes 6,8 being only 25mm in diameter as compared to the header flow pipe 2 with a 140mm diameter and the header return pipe 4 with a 110mum diameter. Between the constricted branch 14 of the connection 12 and the heating pipe 6,8 there is a balancing and setting valve 16 with direct reading flow measurement, of the type commercially available in the United Kingdom from Tacotherm Lamaco Ltd. and identified by their product code INLINE DN 20. Once the system has been installed, each valve 16 is adjusted so that water flows at the same rate (indicated by the scale on the valve, not shown) through each heating pipe pair 6,8.

Each pipe pair 6,8 consequently achieves the same heating effect across the whole of the pitch so that patching is avoided.

The arrangement of the heating pipes 6,8 is shown in figure 3. Each pipe 6,8 is situated at the base of a trench 18 which is excavated in the ground 26 to a depth of 350mm and a width of 60mm. The pipe 6,8 is covered in the trench with a layer 20 of pea gravel up to about 150mm from the playing surface 24. The trench is filled up to the surface 24 by a layer 22 of silica sand.

If the trench were filled with soil, the water passing through the heating pipes 6,8 would have to be relatively hot in order to ensure that a sufficient temperature was maintained at the surface 24 to avoid freezing and to compensate for the heat dissipation that would occur over the distances involved. Furthermore, the cone-like form in which the heat would radiate from adjacent pipes 6, 8 at such a depth would significantly overlap at the surface 24, and the effect would be to unnecessarily overheat the pitch in certain regions. By having a layer 20 of gravel, preferably pea gravel of less than 6mm diameter stones, heat is conducted rapidly upwards away from the pipes 6,8 because the gravel layer 20 is better able to conduct heat than soil, and so the layer 20 acts like a heat sink, conducting the heat closer to the surface a lot quicker than would otherwise be the case.

The heat dissipates from the layer 22 of sand in the cone-like pattern to the surface 24. The conduction capabilities of the gravel layer 20 mean that the pipes 6,8 do not have to be heated to the level they would if the pipes 6,8 were covered by soil, and because the heat dissipates predominantly from the sand layer 22, there is no significant overlapping at the surface 24 of heat radiating from adjacent pipes 6,8.

The trenches 18 also act as drainage channels and water passes down through the trenches 18 to standard drainage pipes further underground (not shown).

Claims (11)

1. Under-soil heating apparatus comprising a header flow pipe, a header return pipe, a plurality of heating flow pipes connected to the header flow pipe, a plurality of heating return pipes connected to the header return pipe, and a valve at each connection of at least each heating flow pipe with the header flow pipe for controlling the rate of flow through each heating pipe.

2. Under-soil heating apparatus according to claim 1 further comprising a valve at each connection of each heating return pipe with the header return pipe.

3. Under-soil heating apparatus according to claim 1 or claim 2 wherein each valve is a balancing and setting valve with direct reading flow measurement.

4. A method of installing under-soil heating apparatus, the method comprising excavating a trench, laying a heating pipe at the bottom of the trench, and filling the trench with a lowermost layer of gravel and an uppermost layer of sand.

5. A method of installing under-soil heating apparatus according to any of claims 1 to 3, the method comprising excavating a plurality of trenches, laying the heating flow pipes and heating return pipes at the bottoms of the trenches, and filling each trench with a lowermost layer of gravel and an uppermost layer of sand.

6. A method according to claim 4 or claim 5 in which the gravel comprises stones of less than 6mm in diameter.

7. A method according to any of claims 4 to 6 in which the sand is silica sand.

8. A method according to any of claims 4 to 7 in which the bottom of the or each trench is below the greatest depth at which ground maintenance work is normally effected.

9. A method according to any of claims 4 to 8 in which the bottom of the or each trench is at a depth of 350mm beneath the ground surface.

10. Under-soil heating apparatus substantially as described herein with reference to the drawings.

11. A method of installing under-soil heating apparatus, the method being substantially as described herein with reference to the drawings.