Heating systems – Automatic control – Water
Patent
1992-01-15
1993-09-28
Bennett, Henry A.
Heating systems
Automatic control
Water
13762513, F24D 300
Patent
active
052480844
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an apparatus and a method for controlling the water flow rate from the boiler circuit to the heating circuit in hot water heating systems, particularly of low temperature type, with a four-way mixer and a control device controlling the position thereof which is so constructed that when the mixer is fully open it enables a variable amount of the returned water to be added into the heater supply. The invention further relates to a particular construction of four-way mixer for use in such an apparatus or such a method.
When using conventional mixers in low temperature heaters the maximum necessary supply temperature of 50.degree. C. is reached at a boiler temperature of 80.degree. C. at substantially less than half the mixer control travel. Too coarse a control characteristic was thus produced. Furthermore, it is a requirement of low temperature heaters, particularly floor heaters, that different volumes of water be transported into the pipe circuits of the boiler on one hand and the heater on the other hand. A calculated example of this is:
(A) typical temperatures in the boiler circuit are ##EQU1##
(B) typical temperatures in a floor heating circuit are ##EQU2##
The following water volume requirements are produced at an assumed heat requirement of 20,000 kcal: ##EQU3##
A conventional mixer is not capable of fulfilling these requirements. For this reason an appropriately dimensioned bypass connection has generally been provided between the heater supply and return. A constant amount of returned water was thus continuously fed to the supply independent of the position of the mixer with the advantage that the water volume in the heater circuit was thus increased and the angular control range of the mixer made use of.
The disadvantage of such control devices is that when the desired value changes the heating system reacts very sluggishly.
An apparatus and a method of the generic type are known from DE-C 3207427. The extent of the control range which is in practice available and the desired rapid control response, for instance with a thermal shift after the night-time reduction, are achieved by means of an adjustable bypass which is controlled in dependence on the mixer position and is substantially closed when the mixer path from the boiler supply to the heater supply is fully open. The adjustable bypass mixes an additional volume of returned water into the volume of hot water which flows through the multiway mixer. When the mixer is somewhat closed due to the supply temperature limitation, the volume of returned water fed through the bypass increases. The volume of boiler supply water flowing to the heater supply via the mixer path can thus remain substantially undiminished so that the mixer guarantees a sensitive control performance even in the upper control range. The association of a control bypass with a conventional multiway mixer and the provision of a control linkage therebetween was previously the only possibility for combining the desired control performance with small dead periods, relatively short transition phases and substantial useage of the mixer control range. The additional controlled bypass flap increases the manufacturing and maintenance expense, particularly since the wear in the two pathways via the mixer on the one hand and via the bypass on the other hand is not always uniform and homogeneous.
It is the object of the invention to optimise the desired control performance described above and to achieve it with substantially reduced constructional, maintenance and operational expense.
In order to solve this object the apparatus in accordance with the invention is characterised in that the four-way mixer is constructed as a cap mixer with a stationary profiled disc and a rotatable control cap, whereby the control cap is arranged with a sealing surface sliding on a preferably flat seating surface of the profiled disc; that the profiled disc is provided with at least three separate openings, of which a first is connected to the boiler supply, a second is connected to t
Bennett Henry A.
Tekmar Angewandte Elektronik GmbH
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