US20110290896A1

US20110290896A1 - Controlling a heating/cooling system

Info

Publication number: US20110290896A1
Application number: US13/148,100
Authority: US
Inventors: Ulf Jonsson
Original assignee: Uponor Innovation AB
Current assignee: Uponor Innovation AB
Priority date: 2009-02-18
Filing date: 2010-02-16
Publication date: 2011-12-01
Also published as: EP2399077B1; FI20095147A; EP2399077A2; CA2752477C; WO2010095089A2; WO2010095089A3; CA2752477A1; FI121552B; FI20095147A0

Abstract

In a hydronic heating/cooling system, liquid is led along a main supply pipe (1) to a supply manifold (2) and distributed into heating loops (3). The heating loops (3) return to a return manifold (4). At least one of the manifolds (2, 4) has actuators (6) for controlling the flow in the heating loops (3). Actuators with fast operating times are used and valves of the actuators are controlled to close at different times in different heating loops (3).

Description

BACKGROUND OF THE INVENTION

The invention relates to a method for controlling a hydronic heating/cooling system in which liquid is led along a main supply pipe to a supply manifold and distributed in the manifold into heating loops, the heating loops returning to a return manifold, and at least one of the manifolds having actuators for controlling the flow in the heating loops.
The invention further relates to a hydronic heating/cooling system comprising a main supply pipe, a main return pipe, at least one supply manifold, at least one return manifold, heating loops from the supply manifold to the return manifold, and actuators for controlling the flow in the heating loops arranged to at the supply manifold and/or the return manifold.
Yet further the invention relates to a software product of a control system of a hydronic heating/cooling system in which liquid is led along a main pipe to a supply manifold and distributed in the manifold in to heating loops, the heating loops returning to a return manifold, and at least one of the manifolds having actuators for controlling the flow in the heating loops.
In hydronic heating systems the liquid acting as medium is typically led to a supply manifold, and the heating pipes forming the actual heating loop extend from the supply manifold and, having made a loop in the space to be heated, return to a return manifold. Valves controlling the liquid flow in the heating pipes are arranged to either the supply manifold or return manifold or both. The valves are actuator-operated and the operation of the actuators is controlled by a control system. Controlling the actuators is quite complex, and it is necessary to take into consideration in the control system several things related to temperature control, reliable operation of the system, and acoustic problems caused by the system, for instance. An example of a hydronic heating system is described in the document JP 2001004157.
The document JP 2001336809 discloses a floor heating system comprising a plurality of thermally operated valves. When the thermally operated valves are opened they are energized sequentially in order to minimize the electric inrush current.

BRIEF DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a novel solution for controlling a heating/cooling system.
The method of the invention is characterised by using actuators with fast operating times, and preventing the simultaneous closure of actuator valves in different heating loops.
The system of the invention is characterised in that the actuators have fast operating time and the system comprises means for preventing the simultaneous closure of actuator valves in different heating loops.
The software product of the invention is characterised in that the execution of the software product on a control unit of the control system is arranged to provide the following operations of detecting endings of the duty cycles and preventing the simultaneous closure of actuator valves in different heating loops.
The idea of the invention is that in a hydronic heating/cooling system liquid is led along a main supply pipe to a supply manifold and distributed into heating loops. The heating loops return to a return manifold. At least one of the manifolds has actuators for controlling the flow in the heating loops. Actuators with fast operating times are used and valves of the actuators are controlled to close at different times in different heating loops. Fast actuators provide an extremely versatile control function, and when the valves are controlled to close at different times, hydraulic impacts caused by valve closure cannot become disturbing in view of acoustic problems caused by the piping structure and hydraulic impact.

BRIEF DESCRIPTION OF THE FIGURES

Some embodiments of the invention are described in greater detail in the attached drawings in which

FIG. 1 is a schematic representation of a hydronic heating/cooling system,

FIG. 2 is a schematic representation of duty cycles of two actuators in different loops according to one embodiment,

FIG. 3 is a schematic representation of duty cycles of two actuators in different loops according to another embodiment, and

FIG. 4 is a flow chart describing an operation of a control system controlling a hydronic heating/cooling system.

In the figures, some embodiments of the invention are shown simplified for the sake of clarity. Similar parts are marked with the same reference numbers in the figures.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a hydronic heating/cooling system. In the system, liquid is led along a main supply pipe 1 to a supply manifold 2. The supply manifold 2 distributes the liquid to several heating loops 3. The heating loops 3 make the liquid to flow through the rooms or spaces to be heated or cooled. If the system is used for heating, the liquid can be warm water, for example. On the other hand, if the system is used for cooling, the liquid flowing in the pipes is cool liquid that cools the rooms or spaces.
The pipes forming the heating loops 3 return to a return manifold 4. From the return manifold 4, the liquid flows back again along a main return pipe 5.
Actuators 6 are arranged to the return manifold 4. The actuators 6 control the flow of the liquid in the loops 3.
A control unit 7 controls the operation of the actuators 6. The actuators 6 can also be arranged to the supply manifold 2. Further, there can be actuators both in the supply manifold 2 and in the return manifold 4. Either one of the manifolds 2 and 4 can further comprise balancing valves. The balancing valves can be manually operated, for example.
The system can also comprise a circulation pump 12 and a connection between the main supply pipe 1 and the main return pipe, the connection being provided with a mixing valve 13. A separate circulation pump 12 and/or a connection between the pipes 1 and 5 is, however, not always necessary.
A hydronic underfloor heating system distributes the needed heating to each room in the building by controlling the hot water flow through a heating loop in the floor. Normally, one loop per room is used but sometimes a large room is split into two or more loops. The controller will act on the information from the room thermostat and accordingly turn the water flow on or off in the floor loop.
The floor loop or heating loop piping is typically made of cross-linked polyethylene plastic pipes, for instance. These pipes can be used in different types of floor constructions, i.e., both concrete and wooden floors can be heated this way. It is essential that the insulation, under the pipes, in the floor construction is good to avoid the leakage of energy out downwards. The floor loop layout depends on the heat demand for each room.
In a concrete floor, typically 20-mm pipes are used, the pipes being usually attached to a re-enforcing net before the final concrete casting. The recommendation is that the top of the pipes should be 30 to 90 mm below the concrete surface and the pipe loops should be placed at a 300-mm center distance. Concrete conducts heat well, so this layout will lead to an even distribution of energy and give an even temperature on the floor surface. This building method using concrete and 20-mm pipes is an economical way of building a UFH (underfloor heating) system.
Due to the good thermal conduction in concrete, the loop can be fed with low supply temperature, normally below 35 degrees Celsius.
The step response is quite slow due to the large mass of the floor, normally between 8 to 16 h depending on the floor thickness.
In wooden floors there are some different construction techniques available and we can divide them into two main categories: floor loops inside the floor construction or on top of the floor construction. It is to be noted that all UFH wood construction techniques use aluminum plates to distribute the heat from the pipes. This compensates for the poor heat conduction in wood. Generally speaking, all “in floor” constructions use 20-mm pipes and the “on floor” technique uses 17-mm pipes that are mounted in pre-grooved floorboards. However, it is self-evident to a person skilled in the art that the diameter of the pipes can also be different and it is determined according to the need and/or requirements set by the system and/or environment.
Due to the poor thermal conduction in a wood floor, the loops need a higher supply temperature than a concrete floor, normally up to 40 degrees Celsius.
The step response is quicker than for concrete, normally between 4 to 6 h depending on the floor construction.
The previously mentioned systems are primarily installed when a house is built. In addition to these, there are UFH systems for after installation. This system focuses on a low building height and the ease of handling, and uses smaller pipe diameters, and the pipes are mounted in pre-grooved polystyrene floor panels. The supply temperature and step response are quite similar to those of wooden constructions.
The stroke cycle of the actuator 6 is preferably less than 120 seconds. The actuator 6 can be a conventional mechanical piston valve. The actuator can also be, for example, a solenoid valve. When using a solenoid valve the stroke time of the actuator can be very short. Thus, the stroke time or operating time of the actuator can be for example in the range of 0.1 to 120 seconds. Preferably actuators 6 with fast operating time are used. Thus, the operating time of the actuators 6 is preferably less than 10 seconds.
In the control system, the term “pulse width” refers to the on time of the flow, i.e., the duty cycle. A minimum pulse width is preferred in order to achieve efficient heating. However, the minimum pulse width is preferably determined such that during the duty cycle the longest loop is also filled with supply water. The minimum pulse width means that the time frame of control is quite short, which means high frequency. Preferably, the time frame is shorter than ⅓ of the response time of the floor in the room to be heated. The time frame may vary for example between 5 and 60 minutes. In order to achieve the feature that the duty cycles start at different moments in different loops, the length of the off-times between the duty cycles can be varied using a pattern or randomly. The variation must naturally be carried out within certain limits, such that the percentage of the duty cycles can be kept at a desired value. Another option is to vary the pulse width using a pattern or randomly in a corresponding manner. Yet another option is to use different time frames in different loops. For example, in one loop the time frame can be 29 minutes, in a second loop the time frame can be 30 minutes, and in third loop the time frame can be 31 minutes. Of course sometimes the duty cycles start simultaneously in different loops but using at least one of the above-mentioned systems, the duty cycles start at different moments in most cases. Thus, the object is to prevent the duty cycles in different loops from running synchronously.
The percentage of the duty cycle means how long the on-state of the time frame is. In other words, if the time frame is 10 minutes and the percentage of the duty cycle is 10%, it means that the flow is on for 1 minute and off for 9 minutes, if the percentage is 50 the flow is on for 5 minutes and off for 5 minutes, and if the percentage of the duty cycle is 90, the flow is on for 9 minutes and off for 1 minute. If the time frame is short enough, control can be considered continuous if the system is slow enough, i.e., the response time of the floor is long.
This specification refers to hydronic under surface heating/cooling. In such a system, liquid is supplied to supply loops for cooling/heating. The liquid can be for example water or any other suitable liquid medium. The liquid may comprise glycol, for example. Under surface heating/cooling means that the supply loops are installed under the floor, for example. The supply loops can also be installed in any other suitable structure. The loops may be installed in the wall or ceiling, for example.
In an embodiment an on/off control is combined with pulse width modulation per room. The pulse width depends on the response in the room. At the startup the pulse width is preferably always 50%. The time frame for the pulse width can be 30 minutes, for example. It is important to prevent the different channels/loops from running synchronously. Adding a random value of −30 to +30 seconds to the time frame can prevent this. Another possibility is to have a slightly different time frame for each channel/loop. It is enough if the difference is 5 seconds, for example.
The maximum value for the pulse width is 25 minutes and the minimum value is 5 minutes. The resolution can be 1 minute, for example. Preferably, the pulse width modulation counter is reset by a change of a set point which prevents delays in the system.
A heating cycle is defined as the time between one heating request and the next heating request.
Maximum and minimum room temperatures are monitored and saved during a full heating cycle.
The pulse width is adjusted at timeout, at heat-up modes or after a heating cycle.
The master timeout for pulse width adjustment can be for example 300 minutes.
The control system comprises an appropriate means for performing the desired functions. For example, a channel block calculates the control signal based on the set point, the room temperature and the energy required. The energy is pulse width modulated and the energy requirement is calculated by measuring the characteristics of the room temperature over time.
One way to describe this is that it is a traditional on/off control with self-adjusting gain.
In an embodiment, the pulse width modulation output can be adjusted between 15 to 70% of the duty cycle. The start value is 50%. The maximum and minimum values during an on/off cycle are stored and evaluated and the duty cycle is adjusted if needed.
The pulse width modulation timer is restarted if the set point increases more than 1 degree, for example.
FIG. 2 shows a duty cycle 8 a of an actuator. At moment t₁the control unit 7 gives the actuator 6 a closing command. At moment t₂the actuator is fully closed. The stroke time or operating time is denoted in the figure with reference numeral 9.
FIG. 2 further shows another duty cycle 8 b of an actuator in another heating loop. In this case, too, the pulse width of the duty cycle 8 b is such that the duty cycle 8 b ends simultaneously with the duty cycle 8 a at moment t₁if no extra action is taken. This is denoted in FIG. 2 with reference numeral 10. However, the control unit 7 detects that in such a case two actuators 6 would close simultaneously. Therefore, the control unit 7 adds a delay 11 to the duty cycle 8 b. Because of the added delay 11, the duty cycle 8 b is made longer such that the actuator 6 starts to close at moment t₂and is fully closed at moment t₃. The length of the delay 11 is equal to or greater than the operating time 9 of the actuators. Thus, the simultaneous closure of the actuators in different heating loops is prevented.
FIG. 3 shows another case in which the second actuator operating according to the duty cycle 8 b is not going to close exactly simultaneously with the first actuator at moment t₁, but the second actuator is going to close at moment t₄. However, because the difference between the moments t₁and t₄is shorter than the operating time 9 of the actuators, the closing of the actuators would happen partly simultaneously or overlap. This would also cause acoustic problems and/or hydraulic impacts. Therefore, the control unit 7 adds the delay 11 to the second duty cycle 8 b, whereby in this case the simultaneous closure of the actuators is also prevented. Thus, the closure of the second actuator starts at moment t₃which is after the moment t₂when the first actuator is fully closed. In this case the length of the delay need not be as long as the operating time 9 but the delay 11 could be shortened by the time between the moments t₄and t₁. However, adjusting the delay 11 is not necessary, because typically the length of the delay 11 is much shorter than the length of the duty cycles 8 a, 8 b.
FIG. 4 is a flow chart according to the operation of the above-described control system. In block A the endings of the duty cycles are detected. In block B it is analysed whether two or more duty cycles end simultaneously. If the result of this analyzation is “no”, the loop returns the block A. However, if two or more duty cycles end simultaneously the procedure continues to block C. Block C comprises the step that the simultaneous ending of the duty cycles is prevented. Thus, in block C a delay is added to at least one duty cycle, for example.
The control unit 7 can comprise a software product whose execution on the control unit 7 is arranged to provide at least some of the above-described operations. The software product can be loaded onto the control unit 7 from a storage or memory medium, such as a memory stick, a memory disc, a hard disc, a network server, or the like, the execution of which software product in the processor of the control unit or the like produces operations described in this specification for controlling a hydronic heating/cooling system.
Preventing the simultaneous closure of the actuators limit pressure changes in the pipes. Limiting the pressure changes prevents noise problems. The difference between the closing commands given by the control unit 7 to the actuators 6 should thus be at least as long as the operating time 9 of the actuators. Preventing the simultaneous opening of the actuators also reduces pressure changes and thus prevents noise problems. Thus, applying the operation using delays described in connection with FIGS. 2 and 3 can also be applied to the starting moment of the duty cycles 8 a, 8 b.
In some cases the features described in this application can be used as such regardless of other features. The features described in this application may also be combined as necessary to form various combinations.
The drawings and the related description are only intended to illustrate the idea of the invention. The invention may vary in detail within the scope of the claims.

Claims

1. A method for controlling a hydronic heating/cooling system in which liquid is led along a main supply pipe to a supply manifold and distributed in the manifold into heating loops, the heating loops returning to a return manifold, and at least one of the manifolds having actuators for controlling the flow in the heating loops, the method comprising using actuators with fast operating times, and preventing the simultaneous closure of actuator valves in different heating loops.

2. A method according to claim 1, wherein the endings of duty cycles are detected and, if two or more duty cycles end substantially simultaneously, a delay is added to at least one duty cycle.

3. A method according to claim 2, wherein the duty cycles are defined to end substantially simultaneously if the difference between the ends of the duty cycles is shorter than an operation time of the actuators.

4. A method according to claim 2, wherein the length of the delay is equal to or longer than the operation time of the actuators.

5. A method according to claim 1, wherein the actuators control the flow in the heating loops on and off such that during a duty cycle the flow is high and between the duty cycles the flow is off.

6. A method according to claim 1, wherein the duty cycles in different heating loops overlap partly.

7. A hydronic heating/cooling system comprising a main supply pipe, a main return pipe, at least one supply manifold, at least one return manifold, heating loops from the supply manifold to the return manifold, and actuators for controlling the flow in the heating loops arranged to at the supply manifold and/or the return manifold, the actuators having fast operating time and means for preventing the simultaneous closure of actuator valves in different heating loops.

8. A system according to claim 7, comprising the system comprises means for detecting the endings of duty cycles and means for adding a delay to at least one duty cycle if two or more duty cycles end substantially simultaneously.

9. A system according to claim 7, wherein the actuators are arranged to control the flow in the heating loops on and off such that during the duty cycle the flow is high and between the duty cycles the flow is off.

10. A non-transitory computer-readable medium having encoded thereon software for controlling a hydronic heating/cooling system in which liquid is led along a main pipe to a supply manifold and distributed in the manifold in to heating loops, the heating loops returning to a return manifold, and at least one of the manifolds having actuators for controlling the flow in the heating loops, wherein the software comprises instructions that, when executed by a control unit, cause a control to detect endings of the duty cycles and prevent the simultaneous closure of actuator valves in different heating loops.