Three Pipe System

Description

THEORETICAL CONSIDERATIONS

In HVAC systems, heat transfer is achieved by building closed hydraulic networks, in which the heating medium—usually water—flows. The water flows through pumps or circulators, which lend water with energy that compensates for friction loss in the network. Network building methodologies are plenty. All networks are comprised of a central distribution pipe and a central return pipe. The water flows through the central pipe of distribution, supplies the terminal units through the local distribution risers and branches, enters the local return pipes and, finally, the central return pipe and ends at the point it started. Conventional network structures are demonstrated in FIGS. <1>, <2>, <3>, <4> and <5>.

To facilitate understanding, it is emphasized that in FIG. 1, object 1 is a circulator and object 2 is a two-way control valve. In FIG. 3, object 3 is a non-return valve and object 4 indicates the flow direction. The specific objects are depicted in all Figures according to the illustrated example.

In all networks, the initial distribution temperature is common for all terminal units. There are special cases, however, for which the temperature in the central distribution pipe is variable during water flow, and, therefore, in each terminal unit, temperature is decreased (heating) or increased (cooling) (FIG. 6). The specific structure is common, but not widely used.

Notably, the above applications, which are conventional structures in a number of versions, are comprised of 3-way or 4-way control valves, additional circulators apart from the basic ones, a pressure break bottle, and self regulating valves, which do not spoil the fundamental and original structure and network building methodology.

The structure demonstrated in FIG. <1> is the most common type and is widely used. A simple form of such a structure has got a central circulator for water flow, but in extended networks there can be more circulators for energy distribution.

The structure demonstrated in FIG. <2> has got one circulator for each terminal unit and after each circulator there is a non-return valve to cut off any undesirable reverse flow.

Frequently, structures like that in FIG. <2> include a central circulator (FIG. <3>, with or without a bypass pipe), whereas structures similar to those in FIG. <3> are often used as collectors of low pressure drop and provide for terminal unit hydraulic independence. Apart from the non-return valve above the circulators, it is likely that a 2-way on-off valve be used so that undesirable flow could be cut off. The structure demonstrated in FIG. <4> (also called Tichelmann structure), is similar to that in FIG. <1>, but the only difference is that each local branch is composed of equal sized pipes. The structure demonstrated in FIG. <5> is a Tichelmann structure with circulators per branch, whereas the structure in FIG. <6> is a special structure, which is not commonly used due to the fact that the distribution temperature in the local branches is variable. In the specific structure, the central distribution pipe is also used as a central return pipe.

In all structures discussed above, especially in the basic types, there are interference and interactive phenomena; in other words, adjusting or cutting off a branch can lead to flow variation and ΔP (pressure drop) in the rest of branches, which is different for different types of networks and depends on network sizing. Interactive phenomena in the branches are critical and bring about various problems related to network operation, heating or cooling failure per terminal unit, energy waste and, in general terms, network deterioration.

The specific problems can be partly eliminated by using self regulating valves, pressure break bottles and 3-way or 4-way valves, depending on the case.

REFERENCES

• 1. Recknagel Sprenger Schramek, Taschenbuch fuer Heizung und Klimatechnik 94/95
• 2. Robert Petitjean, Total Hydronic Balancing
• 3. H. Roos, Hydraulik der Wasserheizung. 2A
• 4. W. Burkhardt, Projektierung von Warmwasserheizungen
• 5. Trainings & Weiterbildungszentrum Wolfenbueteel e.V. (enev.tww.de)
• 6. Internetsite (hydronicpros.com) by John Siegenthaler
• 7. ASHRAE Handbook

THE PATENT

The structure suggested consists of a central distribution pipe which is split into two pipes and after that joined again in one pipe, so as to create a central closed loop where the local terminal units are connected.

In detail, the local terminal units are distributed through the one side of the split central distribution pipe and the water from each local branch returns to the other side of the split central pipe. The structure of the application suggested is depicted in FIG. <7>. The central distribution pipe <<A>> is split in two pipes, pipes <<B>> and <<C>>. In the specific pipes, water flow is also split. The two pipes, <<B>> and <<C>>, are joined again in one pipe, pipe <<D>>, and creates a closed loop. Water in pipes <<A>>, <<B>>, <<C>> and <<D>> flows in the same direction. The terminal unit branches are connected to the loop. Each local branch has a circulator to compensate for water distribution. During operation, when all terminal units are deactivated, water flow is split in branches <<B>> and <<C>> and does not enter any terminal unit branches. When one terminal unit is activated, water flow in branch “B” is increased by the rate of flow in the activated terminal unit and in branch “C” it is reduced by the same rate. At the point after the terminal unit, the opposite procedure takes place in the two branches, and consequently the water flow in branch “B” is reduced by the rate of flow in the activated terminal unit and in branch “C” it is increased at the same rate.

The more terminal units are activated, the more the quantity of water that enters branch <<B>> and the less that enters branch <<C>>.

On the contrary, at the end of the loop, water flow is increased in branch <<C>> and reduced in branch <<B>>.

Notably, water flow in the terminal unit loop requires the use of a central circulator, as demonstrated in FIG. <8>.

In case of reverse flow in deactivated terminal units, a non-return valve is recommended for each terminal unit, FIG. <9>.

In FIG. <10>, there is the structure of a simple application of the system. The Figure demonstrates the division of the central pipe, the terminal unit loop, the use of the one part of the loop for the local distribution pipes, and of the other part for the point where local return pipes end. FIGS. <11>, <12> and <13> demonstrate some other more complex applications of the three-pipe system.

In general terms, the system is characterized by symmetry, harmony and balance during operation. It is also particularly stable and hydraulically independent, and, compared with all existing similar systems, interference and interactive phenomena in the network, under similar conditions of operation, are significantly fewer and, in effect, negligible. This is an essential advantage in terms of operation, reliability and energy saving. The specific structure can be applied to any HVAC system, that is, in every hydraulic closed network of heat transfer, such as in home central heating units, district heating, and hotel or building air conditioning systems with water coolers.