WO2001069341A2

WO2001069341A2 - A method of measuring and adjusting room temperature

Info

Publication number: WO2001069341A2
Application number: PCT/DK2001/000177
Authority: WO
Inventors: Søren HESSELDAHL
Original assignee: De-Vi A/S
Priority date: 2000-03-17
Filing date: 2001-03-15
Publication date: 2001-09-20
Also published as: WO2001069341A3; AU2001242307A1

Abstract

The invention relates to a method of measuring and adjusting room temperature by at least one temperature sensor which is present in a wall-mounted adjustment unit, wherein the adjustment unit contains means for adjusting the power dissipation in at least one heating element. The object of the invention is to provide a method of increasing the measurement accuracy of a room sensor which is arranged within the adjustment unit. This may be achieved if the adjustment unit also contains a calculating unit which, on the basis of a plurality of determined parameters and a plurality of measured parameters, uses a time-dependent model for the internal heating of the panel. This can ensure compensation of the error sources which would otherwise cause significant measurement errors each time the adjustment unit changes state.

Description

A method of measuring and adjusting room temperature

Description

The invention relates to a method of measuring and adjusting room temperature by at least one temperature sensor which is situated in a wall-mounted adjustment unit, wherein the adjustment unit contains means for adjusting power dissipation in at least one heating element, wherein the adjustment unit has means for setting a user- defined reference temperature, wherein the temperature adjustment is performed on the basis of a differential calculation between the measured room temperature and the reference temperature, wherein the internal temperature of the adjustment unit is determined by a further temperature sensor, and wherein at least one of the values which are included in the differential calculation is weighted in dependence on the interior of the adjustment unit .

An adjustment unit as described above is known from a non-published patent application PCT/DK99/00428 filed by the same applicant.

US 4 741 476 describes a digital electronic thermostat which performs adjustment of the measured ambient temperature in dependence on heating internally in the thermostat because of power dissipation inter alia in semiconductor switches. The measured ambient temperature is corrected by subtracting a constant multiplied by the difference between said temperature and a second temperature measured internally in the thermostat. The said constant is determined by measurement on a prototype thermostat, and various values of the constant are determined on the basis of various thermostat types. Within thermostats of the same type, the constant is determined at a fixed resistance value. The semiconductor switch of the thermostat is a triac, which is connected through a cable to a heating element or is connected to an air conditioning system. In this document, the terms room temperature and ambient temperature are synonymous .

In many situations, the selected form of correction of the measured ambient temperature is not sufficient to achieve a correct value of the room temperature, because only static compensation for the power dissipation within the thermostat takes place. There is no temporal correction for how long the power dissipation has taken place, and when the power dissipation ceases, and there is no compensation for the circumstance that the internal temperature only decreases in step with the heat conduction to the surroundings. A measurement error will occur each time the thermostat switches the load on or off. A meas- ure ent error may cause room temperature fluctuations each time the thermostat is to make an adjustment. The comfort of persons present in a room will hereby be adversely affected. Also, the consumption of energy may be increased without the comfort being improved. The tempo- ral behaviour of the switching operation is a priori not predictable, as it depends on the thermal characteristics of the particular room and its auxiliary heat sources and drains affecting the room temperature.

The object of the invention is to provide a method of increasing the measurement accuracy of a room sensor arranged in an adjustment unit, and with the sensor arranged in said unit to achieve approximately the same measurement accuracy as a temperature sensor arranged freely in the room, where the precise temperature determination reduces the actual consumption of energy while increasing the comfort of persons who are present in the room.

This can be achieved by a method like the one described in the opening portion, if the adjustment unit also contains a signal processing unit which, on the basis of a plurality of determined parameters and a plurality of measured parameters, uses a time-dependent model for the internal heating of the panel, wherein the internal heating of the adjustment unit is included in the correction of the measured ambient temperature.

This allows compensation for the error sources which would otherwise cause essential measurement errors each time the adjustment unit changes state. Using a corrected temperature measurement, the adjustment unit can avoid fluctuation of the room temperature. Fluctuations can oc- cur each time the adjustment unit is to change state and thus change its internal heat dissipation rate, and even a small change of its internal temperature may have a great influence on the comfort felt by persons in a room. Moreover, if the uncorrected measured ambient temperature is displayed on the adjustment unit, it may exhibit considerable deviation from the actual room temperature thus confusing the user of the adjustment unit.

The time-dependent model may advantageously be imple- ented in an analogue signal-processing unit. The model may hereby be formed by an electronic circuit consisting of a plurality of analogue components whose values .are determined on the basis of constants in the time-dependent model. As a preferred embodiment, the time-dependent model may be implemented in a digital signal-processing unit. The constants of the time-dependent model may hereby be rep- resented as digital data, which may be stored in either fixed or programmable memory units. Thus, adjustment units may easily be adapted to different needs.

The time-dependent model may be based on the state of the adjustment means, their power dissipation, and their heat capacity. This can ensure that the time-varying power dissipation in electronic components controlling the dissipated power in a connected heating element, may take place without affecting the measured temperature. By in- corporating the heat capacity of the components, the heating of the components relative to time may be included in the determination of the actual ambient temperature .

The time-dependent model may also be based on the heat conduction of the adjustment unit to the surroundings and their heat capacity. Thus, the adjustment unit may be wall-mounted, without the temperature properties of the wall having any influence on the measured temperature.

The time-dependent model may simultaneously be based on the internal heat conduction of the adjustment unit and the internal heat capacity. Thus, the physical structure of the adjustment unit may be incorporated in the deter- mination of the actual ambient temperature.

Further, the time-dependent model may use time-dependent functions for the heat capacities of the components.- In this way, the time that elapses from heating at a point has started and until the heating influences the temperature sensor, may be included in the determination of the actual ambient temperature.

The power adjustment means of the adjustment unit, which actuates the energy flow to the heating element, may^' be formed by a relay, said adjustment unit having means for dissipating uniform power internally in the adjustment unit independently of the state of the relay. Thus, dif- ferences in internal power dissipation may be reduced, and a simpler time-dependent model for the heating of the adjustment unit may be used.

The power adjustment means of the adjustment unit may in- stead be formed by semiconductor components, e.g. a solid-state relay. If semiconductor components are controlled so that change of state takes place with a low voltage drop across the components, the internal power dissipation in the adjustment unit may be reduced.

Advantageously, the adjustment unit may use reference temperatures set at various temperature levels, said adjustment unit being programmed by the user for time- dependent automatic switching between temperature levels. The adjustment unit may hereby be used for night lowering of room temperature.

Power dissipation in at least one heating element may be adjusted in dependence on at least one measured floor temperature. The method may hereby be used for effective adjustment of floor heating with great comfort and with a smaller consumption of energy. The user-defined reference temperature may internally be weighted time-dependently in response to the floor temperature of the room. The temperature in the room may hereby be lowered without adversely affecting the comfort of persons who are present in the room.

The heating element may be a floor heating element in the form of heating wires arranged in a flooring. The method may thus be used in an adjustment unit, which contains the entire electrical control of electrical heating wires arranged beneath a floor surface.

The floor temperature may be determined by an infrared radiation detector which is arranged in the adjustment unit. The surface temperature of the floor may hereby be determined without using a temperature sensor in the floor.

A possible embodiment of the invention will be described below with reference to sketches, where

fig. 1 shows an adjustment unit arranged in a box for recessed mounting in a wall, where

fig. 2 shows a printed circuit board with a possible arrangement of a heating source and two temperature sensors, where

fig. 3 shows the printed circuit board shown in fig. 2, seen from the side, where

fig. 4 shows a first equivalent diagram for a heat current in an apparatus, where fig. 5 shows a reduced equivalent diagram relative to fig. 4.

fig. 6 shows a control theory block diagram of the deter- mination of the ambient temperature based on measured temperatures and the thermal characteristics of the adjustment unit. This model only regards the states at an actual point in time.

fig. 7 shows a reduced mathematical model relative to fig. 6, where

fig. 8 shows a further simplified model relative to fig. 7, where

fig. 9 shows temperature curves for an adjustment unit without compensation, where

fig. 10 shows curves for a statically compensated adjust- ent unit, and where

fig. 11 shows temperature curves for a time-dependently compensated'^' adjustment unit according to the invention.

Fig. 1 shows an adjustment unit 1 arranged in a box 2 recessed in a wall 3. The adjustment unit is shown here with a direct connection via cables 9 to an electrical heating element 10 arranged in a floor 11. Also shown in the floor is a ther o sensor 11, which is connected with the adjustment unit 1 via cables 12. The adjustment unit is to measure a room temperature 4 with a temperature sensor 7 arranged within the adjustment unit 1. Fig. 2 shows a printed circuit board 5 which may be arranged internally in the adjustment unit 1, said printed circuit board having thereon a heat source 6 in the form of components for power adjustment. A first temperature sensor 7 and a second temperature sensor 8 are also provided on the printed circuit board 5. If the power dissipation of the heat source 6 varies, the heat conduction through the printed circuit board will affect both temperature sensors 7 and 8.

Fig. 3 is a lateral view of the printed circuit board 5. Dashed boxes are shown between the components 6, 7 and 8, containing arrows that mark heat radiation, convection and direct heat conduction through the printed circuit board 5. Heat conduction and convection can be modelled by an analogue electrical circuit. Both mentioned mechanisms of heat transfer have a linear relationship between heat flow and temperature difference. Heat flow due to radiation does not exhibit this linear relationship, but in this context it is of negligible magnitude due to small differences in the temperature levels encountered in practice and the small spatial angle between the temperature sensors. Heat flow between the components 6, 7 and 8 then transforms into electrical currents, which run through electrical resistors between the actual ' components, where a difference in temperature is transformed into an electrical voltage.

Fig. 4 shows an equivalence diagram for the printed cir- cuit board shown in fig. 3. It is described here how the power from a heat source (Ps) flows from the source to the surroundings. This is called a physical model below where : Ps (source) is the heat source, its rate measured in watt .

51 is the temperature sensor No. 1.

52 is the temperature sensor No. 2. Tl is the temperature measured by sensor No. 1. T2 is the temperature measured by sensor No. 2. Ta is the ambient temperature, the very result of the temperature correction.

Rth s-p (source to printed circuit board) is the thermal resistance between the source and sensor No. 1 on the printed circuit board.

Rth sl-s2 is the thermal resistance between sensor No. 1 and sensor No. 2.

Rth p-a (printed circuit board to ambient) is the thermal resistance from the printed circuit board to the ambient.

Cp is the heat capacity of the printed circuit board.

Sensors No. 1 and No. 2 are provided on the same printed circuit board in a possible embodiment. It may thus, be assumed that Cp is the same for both temperature sensors.

A thermal circuit may be aggregated into a ^black box" model when only the temperature at its terminals shall be known. Based on what it is desired to get out of the model, viz. determination of Ta, the model in fig. 4 may be reduced to the model in fig. 5.

It is not necessary to know the temperature of the source Ps. It is represented by the temperature Tl measured at the point SI. Nor is it necessary to know the magnitude of Ps as we know the thermal resistance Rth sl-s2.

It is just necessary to know the time delay between Tl and T2. This time delay may be described by a real pole in a control model. Hereby, all the heat capacities that might occur may be gathered in a central capacity, C.

The control model of fig. 6 is evolved from experimental observations of the temporal variation of temperatures Tl, T2 and Ta with the state of Ps . The observations revealed, that three parameters would map the measured temperatures Tl and T2 onto the actual ambient temperature Ta: An offset 0, an amplification or gain G, and a time delay tau. These parameters are determined on a per prototype basis . Based on those three parameters and considerations of the thermal behaviour of the adjustment panel described above, the block diagram was formulated.

Using elementary control theory algebra on the Laplacian transformations of the time-dependent variables, the diagram is further reduced in figs. 7 and 8.

In fig. 7, the voltage dividers Rth sl-s2 and Rth p-a are gathered in a single resistor R. The gain of the voltage divider is now expressed by the gain G.

In fig. 8, the model is further simplified, where the filter H(s) becomes: R- + - 1 s + - 1 1 + sτ sC RC

Equation 1

where s is the Laplacian independent variable and the term RC is the above-mentioned time delay tau .

The mathematical expression of the ambient temperature in the complex s-plane may be derived as :

₍ _ T2(s)- Tl{s)x G x H{s)- 0

Equation 2

where the size of Offset 0 is found empirically.

The calculation of the ambient temperature in prior art represented by US patent 4,741,476 follows the rule

Tα(s) = T2(s) -K x (Tl(s) - T2(sj) - O

= (1+ K)x T2(s) -K x T\(s)- O

Equation 3

where the naming of the temperatures Tl and T2 reflects the nomenclature of the present document. It appears from eqn. 3 that the filter K is independent of time. In the steady state, i.e. assuming no change of the state of the room or adjustment unit, time will have elapsed to infinity corresponding to s approaching zero, and eqn.2 will reduce to eqn. 4

T2(0) -G xT\(0) -O

Ta(s) = l-σ

^■x E2(0) — x El(O) — xO

1-G 1-G 1-G

Equation 4

Comparing to eqn. 3 it appears, that the identities of the constants K and G as expressed in eqn. 5 below will make the variable terms of eqns. 2 and 3 identical in the steady state. Only the offset term will turn out with a different magnitude, which poses no practical problem, as the offset is determined on a per prototype basis as mentioned above. Thus the present invention stated by eqn. 2 may be seen as a generalization of eqn. 3.

C K K ≡ equivalent to G ≡ ^•

1-G l + K

Equation 5

Fig. 9 shows temperature curves 21, 22 and 23 for an adjustment unit without compensation, where the curve 21 shows power dissipation rate within the adjustment unit. The curve 22 shows an ambient temperature, which is constant here. The curve 23 shows the measured ambient tern- perature when a temperature sensor, say T2, is affected by the internal power dissipation. Thus, a significant measurement error may occur.

Fig. 10 shows curves for a statically compensated adjustment unit like the one described in the preamble, where a curve 31 shows power dissipation rate within the adjustment unit. The curve 32 shows an ambient temperature, which is constant here. The curve 33 shows the resulting ambient temperature if static compensation takes place each time the internal power dissipation changes. The curve 34 shows the measured temperature T2, while the curve 35 shows the measured temperature Tl .

Fig. 11 shows temperature curves for a time-dependently compensated adjustment unit according to the invention, where a curve 41 shows power dissipation rate within the adjustment unit. The curve 42 shows an ambient temperature which is constant here. The curve 43 shows the resulting ambient temperature if time-dependent compensation according to the present invention takes place each time the internal power dissipation changes. The curve 44 shows the measured temperature T2, while the curve 45 shows the measured temperature Tl.

It appears from fig. 12 that the curves 42 and 43 coincide, which means that the calculated ambient temperature coincides with the real ambient temperature.

Claims

Patent Claims

1. A method of determining room temperature by measuring and adjusting temperatures of at least one temperature sensor which is present in a wall-mounted adjustment unit, wherein the adjustment unit contains means for adjusting power dissipation in at least one heating element, wherein the adjustment unit has means for setting a user-defined reference temperature, wherein the tempera- ture adjustment takes place on the basis of a differential calculation between the measured room temperature and the reference temperature, wherein the internal temperature of the adjustment unit is determined by a further temperature sensor, and wherein at least one of the values which are included in the differential calculation is weighted in dependence on the internal temperature of the adjustment unit, characterized in that the adjustment unit contains a signal processing unit which, on the basis of a plurality of determined parameters and a plural- ity of measured parameters, uses a time-dependent model for the internal heating of the panel, wherein the internal heating of the adjustment unit is included as a parameter for the instantaneous correction of the measured temperature .

2. A method according to claim 1, characterized in that the time-dependent model is implemented in an analogue signal processing unit.

3. A method according to claim 1, characterized in that the time-dependent model is implemented in a digital signal processing unit.

4. A method according to one of claims 1-3, characterized in that the time-dependent model is based on the state of the adjustment means, their power dissipation and the heat capacity of the adjustment means.

5. A method according to one of claims 1-4, characterized in that the time-dependent model is based on the heat conduction of the adjustment unit to the surroundings and the heat capacity of the surroundings.

6. A method according to one of claims 1-5, characterized in that the time-dependent model is based on the internal heat conduction of the adjustment unit and the internal heat capacity.

7. A method according to one of claims 1-6, characterized in that the time-dependent model uses time-dependent functions for the correction of the heat capacities of the temperature sensors.

8. A method according to one of claims 1-7, characterized in that the power adjustment means of the adjustment unit are formed by a relay, said adjustment unit having means for dissipating uniform power internally in the adjustment unit independently of the state of the relay.

9. A method according to one of claims 1-8, characterized in that the power adjustment means of the adjustment unit are formed by semiconductor components.

10. A method according to one of claims 1-9, characterized in that the user-defined reference temperature of the adjustment unit is set at various temperature levels, said adjustment unit being programmed by the user for time-dependent automatic switching between temperature levels .

11. A method according to one of claims 1-10, character- ized in that power dissipation in at least one heating element is adjusted in dependence of at least one measured floor temperature.

12. A method according to one of claims 1-11, character- ized in that the user-defined reference temperature is weighted internally in time-dependence on the floor temperature of the room.

13. A method according to one of claims 1-12, character- ized in that the heating element is a floor heating element in the form of heating wires arranged in a flooring.

14. A method according to one of claims 1-13, characterized in that the floor temperature is determined by an infrared radiation detector which is arranged in the adjustment unit.