The most usual manner of measuring energy consumption in systems for carrying heat by means of air or a liquid, is to determine the temperature change of the heat-carrying medium as a result of the heat liberation, and the circulation rate of the heat-carrying medium, measured as mass per unit time. The supplied power is equal to this temperature difference multiplied by the circulation rate and the heat capacity of the heat-carrying medium.

This method is not particularly well suited if the heat-carrying medium in the heating system has a relatively large circulation rate (quantity per unit time) and a small temperature change. For instance in water-based floor heating installations, the complete floor area constitutes the heat-liberating surface, and the temperature difference between forward water and return water in such systems can often be less than one degree. The energy measurement is often used to determine what should be paid by the consumer for used heat, and this makes demands on accuracy in the calculation. Normally the quantity of energy should be determined with an uncertainty less than 5 %, to make the method suitable as a basis for payment. In such a case, and with a temperature difference of only one degree, the accuracy in the temperature reading must be better than 0.05 degree.

In practice this means a very costly sensor technology and strict measurement methodological requirements regarding positioning and organizing the temperature measurement.

Accurate volume flow rate measurements are relatively complicated also.

Such volume flow rate measurements become particularly demanding in installations where the heat supply is regulated through the volume flow rate, as in the case with room thermostats connected to thermo-valves on a distributor.

Another basic principle for regulating heat supply, is based on temperature control of the water by means of a shunt between forward and back lines. This makes even greater demands on a rapid and accurate recordation of the temperature difference. Besides, this method requires that the pump is placed between the shunt and a distributor to the floor heating installation, which is not a practical feature in joint installations.

Especially when a resource is common to many users, and it becomes a task to apportion the costs to be covered by single users in accordance with their consumption, measurement of energy becomes necessary. The lack of sufficiently accurate measurement methods and equipment that are at the same time economically justifiable, represents today a significant barrier against the use of low-tempered heat systems in such connections. This is unfortunate, since low- tempered heating systems are an important condition for effective utilization of energy-saving technologies (e. g. heat pumps) and renewable energy sources like solar energy and bio-energy.

From EP-A1-0 569 739 is previously known a system for a heating installation in which a circulation pump is switched in and out as a function of the deviation of the outside temperature from a preset temperature. Further, from EP- B1-0 150 671 there is previously known a method for regulating a heating installation, based i. a. on measurement of the temperature of the circulation medium in the return line of a consumer installation. The method is based on intermittent operation, alternatively variable speed of the circulation pump, controlled i. a. by the return temperature relative to a fixed or variable reference temperature. This method indicates also a method for determining supplied energy based on a circulation pump counter that measures the quantity of medium that has circulated in the consumer installation, and the temperature difference between supplied and returned circulation medium.

Regulation based on measurement of return temperature seems rather poorly suited for use in low-tempered heating systems. These systems are characterized by a large flow of liquid, and consequently return temperatures that are very close to the forward temperature of the circulation medium during the time of circulation. The return temperature measured during intermittent operation, further becomes a time-dependent function with intervals in which the return temperature is close to the forward temperature, and intervals having lower return temperatures. After a long-lasting circulation break (for instance 10 minutes or more), the return temperature will, after start of circulation, be quite close to the temperature of the construction (for instance the floor) where the heat liberators of the consumer installation are placed. Simply one reference temperature for controlling the circulation would hardly constitute a very adequate regulating principle for this type of application.

The energy measurement methods referred to, are based on measurement of circulation rate and temperature difference between supplied medium and return medium. As mentioned, this becomes complicated when the temperature difference becomes sufficiently small.

In other words, there exists a need of a method for supplying and measuring energy, that better than earlier is adapted to a situation with a low- tempered circulation medium, and where the consideration regarding a satisfactory regulating ability and satisfactory energy measurement does not have as a consequence that the temperature of the medium must be raised relative to the circulation medium temperature that is physically necessary to establish a desired temperature of comfort at the consumer's premises.

The present invention aims at fulfilling this need, and therefore, in a first aspect of the invention there has been provided a method for measuring, controlling and recording a supplied quantity of energy when delivering energy to a consumer via a heat-carrying low-tempered circulation medium, using a circulation network for transporting the medium forward and back in a closed path between an energy supplier and the consumer, control being effected by regulating a duty factor in intermittent circulation of the medium to the consumer, as a function of measured variable parameters at the consumer's premises. The method of the invention is characterized in that an energy quantity to be delivered adapted to the consumer's needs during a subsequent period of time, is calculated on the basis of the measurement values of said parameters as well as a known medium inlet temperature to the consumer, and the result of the calculation is used for controlling intermittent operation as well as for the recording of supplied quantity of energy.

In a second aspect of the invention, there has been provided a means for measuring, controlling and recording supplied quantity of energy when delivering energy to a consumer via a heat-carrying low-tempered circulation medium, the means being attached to a circulation network for transporting the medium forward and back in a closed path between an energy supplier and the consumer, and comprising a regulating device operative to regulate a duty factor in intermittent circulation of the medium to the consumer's premises, as well as measuring devices for measuring variable parameters at the consumer's premises, which measuring devices are attached to a processor device included in the regulating device, for treatment of the parameters measured. The means of the invention is characterized in that the processor device is operative for calculating a quantity of energy to be delivered adapted to the consumer's needs during a subsequent period of time, on the basis of a known medium inlet temperature to the consumer's premises, and as a function of the measurement values of the parameters, the regulating device further being operative for regulating on the basis of the energy quantity calculation conducted for the subsequent period of time, and for recording the energy quantity supplied.

Particular and favorable embodiments of the invention appear from the attached dependent claims.

The present invention consists in utilizing the specific physical characteristics of low-tempered heating installations, to control energy liberation in a manner that enables accurate and substantially simpler measurement of energy, than previously known methods. Low-tempered heating installations are characterized in that large heating surfaces are heated. In practice, these surfaces exhibit a large heat capacity, so that supplied heat is first liberated to the heating surface, and thereafter from the heating surface to the object (the room) to be heated. The heat stored in this type of distribution systems, corresponds typically to heat consumption for duration of 1 to 10 hours. This means that if the heat is liberated continuously in a power-controlled system, or whether it is liberated in the form of energy pulses where the interval between pulses is substantially shorter than 1 hour, the secondary heat liberation from the heating surface to the object will not change noticeably.

In the present invention, heat liberation to the consumer premises is controlled by delivering heat in the form of energy pulses. In practice, this is organized in such a manner that sensors record the parameters that are important for calculating the energy needs, and in connection with heating of buildings, the outside temperature and the solar irradiation through windows are the most important parameters. The parameter values are read by a processor that calculates the need of heat delivered inside a time interval following thereafter, for instance 15 or 30 minutes. The temperature of the heat-carrying medium determines how much energy, in the form of heat, should be liberated per unit

time when the heat-carrying medium circulates at a constant rate through the heating system. Based on this information, the processor then calculates the necessary circulation time to liberate the correct amount of heat. The method presupposes that one has made measurements, when making an initial regulating of the installation, of the circulation rate, or possibly that the circulation rate is sufficiently large that the temperature difference between supplied liquid and return liquid is small (for instance a couple of degrees or less). The setting of the regulator can either be made from knowledge of heat liberation per unit area as a function of the temperature of the heat-carrying medium, or setting can be made successively on the basis of experiences regarding connection between liquid temperature and room temperature during operation of the plant.

In the following, the invention shall be illuminated in closer detail by discussing various aspects and embodiments thereof, and in this connection it is referred to the appended drawings, in which Fig. 1 shows a conventional control arrangement for water-borne floor heating, Fig. 2 shows a simple example of a control arrangement in accordance with the present invention, Fig. 3 shows experimental temperature variations in a floor heating installation in a wooden floor, with energy supply in pulses, Fig. 4 shows measurement results during a number of days for a housing in which the duty factor is regulated in accordance with the present invention, Fig. 5 shows, diagrammatically, the relation between energy consumption, as determined by circulation time, and directly measured consumption, represented as a function of water temperature, and Fig. 6 shows heat transfer from water piping to a room.

As a general example of the method and means of the present invention, focus will in the following be placed on water as a heat-transporting medium, and on heating of floors in housings. However, the scope of the invention is not limited thereto, other types of circulation medium may be for instance oil-based liquids or water with a glycol additive, and"the consumer"mentioned in the claims represents an energy receiver or an area for receiving energy in general, for instance walls or ceilings in any type of building, or more generally, any type of heat exchanger installation working with small temperature differences.

A floor heating installation is a very slow or inert heating system. Power transfer rate through the floor is limited, and at the same time a lot of material is to be heated. The perceptible effect from changing the temperature or the flow rate of the floor water appears only after a long time (some hours). Therefore, the installation must be controlled automatically to achieve a good and stable temperature, and to provide minimum energy consumption at the same time. The energy consumption depends on the temperature level, and even differences of 2- 3 degrees, which are in themselves acceptable regarding comfort, may mean an energy consumption that is 15-20 % larger or smaller. Therefore, this represents a delicate challenge for the control automatics.

The use of room thermostats for controlling floor heating installations is a very ordinary solution, however a solution that is questionable subjectwise and regarding energy consumption. The reason is that the change in energy supply only takes place when the temperature in the room deviates from the desired level. Due to the previously mentioned inertia, such a correction on the basis of perceptible effect will come much too late, and it may therefore give rise to temperature fluctuations in the room, which fluctuations will often mean a substantially increased consumption of energy. In principle, the correct thing is therefore to control the installation on the basis of a future energy need.

Measurements conducted over an extended time in various housings, show that the need of heating is primarily determined by the outside temperature.

Particularly in spring and autumn, the solar irradiation through windows will also be of importance for the need of heating. Hence, these external factors will decide how much heat shall be supplied to maintain a constant and comfortable inside temperature. In modern housings with good insulation, the effect of a temperature change outside will arrive relatively long time after the temperature change itself.

This delay agrees rather well with the inertia in the floor heating installation.

Therefore, if the supply of heat is regulated in step with oscillations in the outside temperature, the two delays will compensate each other so as to make the inside temperature remain constant. Solar irradiation through windows has a more immediate effect on room temperature, but is relatively limited regarding power.

By placing a radiation sensor in such a manner that it records the radiation before the solar incidence is at a maximum, also this information can be obtained in time to compensate for the inertia of the floor heating installation.

The density of floor piping and the quality of possible heat distributors (in floors with a tier of beams) also have importance for the regulating and hence for the energy consumption in the plant. It is important that the floor maintains an even and relatively moderate temperature across the whole surface (preferably below 26 degrees), and that this temperature. is not essentially lower than the temperature in and around the floor piping (good thermo coupling). Then, such floors have a significant self-regulating effect, a temperature change of one or two degrees changing the energy liberation from the floor drastically. Note however that it is not only the air temperature in the room that determines the liberation of heat, but to an equally large degree the temperature of the other surfaces (walls and ceiling) in the room.

Fig. 1 and Fig. 2 show two control systems that are both based on adjusting heat supply on the basis of an expected future need of heating. The conventional solution, see Fig. 1, is to use a shunt valve 1, where the temperature of the water going into the floor is varied by mixing hot water from a tank 6 and somewhat cooler return water from the piping 7 in the floor heating system. The controller 2 determines the correct temperature by means of a temperature sensor 3 arranged outside, and is programmed to a certain functional interrelation between water temperature and outside temperature suitable for the building in question.

The shunt valve 1 is connected to a motor providing the desired mixing ratio between forward and return water at any time. This is recorded by means of a temperature sensor 4 on the pipe after valve 1: The circulation pump 5 operates on a continuous basis in this system.

Fig. 2 shows a simple example of an embodiment of the present invention.

This is a simplified system, in which the supply of heat to the floors is regulated through the operation of the pump 5 itself. In the same manner as for the shunt system, the need of heating is determined on the basis of the outside temperature, which temperature is measured by a temperature sensor 3, and possibly also on the basis of solar irradiation through windows. The calculated quantity of heat necessary for a specified period, for instance 15 minutes, is then supplied to the floor by limitation of the circulation time. The calculation of correct circulation time is based, in the same manner as for the shunt system, on the water temperature in question. Water temperature is measured by means of a sensor 4. A high water temperature will mean a short circulation time. From a

control view, the two control methods mentioned are equivalent, but the system in accordance with the invention has the advantage that the pump time is limited, so that the electricity consumption becomes less. This system is also substantially less costly regarding installation.

Since the system of the present invention represents a novel and unused control method, we shall in the following describe in closer detail the operation of the system, and the possibilities provided thereby for combining controlling and energy measurement for low-tempered heating systems: HEAT TRANSFER BY NON-CONTINUOUS WATER CIRCULATION A natural question regarding non-continuous heat supply to the floor, is if the floor temperature will thereby oscillate, and hence result in an unacceptable inside climate. In order to illuminate this question, we will take a close look at typical constructions. Floor heating is used both in concrete floors and in tiers of wooden beams. Especially regarding a concrete floor, but also in tiers of wooden beams, a significant mass is heated. The heat capacity of the concrete floor is typically 40 Wh/(m2K), and for the beam tier floor about 10 Wh/ (mK). Compared to the heat transfer through the floor surface, that will be 60 W/m2 at a maximum, this ability to store heat means a very constant temperature within the time intervals that are of interest. The effect of the temperature equalization is illustrated in Fig. 3, which is regarding an ordinary beam tier floor in which the floor piping is equipped with aluminum heat dispersers: In the upper part of the figure appears the forward and back water temperature, as a function of time. Therebelow appears the temperature progress for a heat dispersion plate, and lowest in the figure appear the temperatures of the floor surface and the inside air.

It appears how a varying temperature in the circulation water is equalized through the construction. The temperature variation that was at the start about 5 degrees in 15 minute periods, is reduced already in the heat dispersion plate to less than 2 degrees. The floor surface maintains a quite constant temperature, and the same goes for the room temperature. Thus, it is realized that a pulse period of 15 minutes will not give any measurable variation in temperature for the floor surface and the room. Hence, the floor as a source of heat is not influenced by whether the heat arrives in portions, or as a continuous delivery.

As previously mentioned, the need of heating in a housing depends primarily on the outside temperature, which thereby represents the most important control parameter in a low-temperature heating system. Hence, when one considers outside temperature variations that are measured, when calculating the pulse period for such a heating system, a stable comfort temperature shall be obtainable on a floor surface and in a room. Fig. 4 displays measurement results from a private house in Lrenskog, Norway, with floor heating as the sole source of heating. Heat is fetched from a heat store in which the temperature may vary.

The temperature of the heat store is also the temperature of the water going into the floor, as shown at the top of the figure. The outside temperature during the measurement period, appearing in the lower part of the drawing, varies from +6 °C to-20 °C. The inside temperature has been measured in two rooms having a beam tier floor and a concrete floor, as shown in the middle part of the figure.

The figure shows that the room temperature is maintained at a very stable level, even when there is more than 25 ° variation in the outside temperature, and with variation in the temperature of the supplied water. Due to a high standard of insulation and the perception of temperature in a case of radiation heat, the comfort temperature is somewhat below 20 °C, and the control provides for a very good temperature stability, combined with a low energy consumption.

MEASUREMENT OF ENERGY CONSUMPTION The energy consumption in low-tempered water-borne heating systems is often difficult to measure. The main reason is that in the conventional method, which is based on a determination of energy consumption by measuring liquid flow and temperature difference between forward and return water, the uncertainty becomes too large because the temperature difference is often only a fraction of a degree.

Energy measurements are important, particularly in large installations with several users attached to the same energy source or system, because the energy costs should be apportioned in accordance with the consumption of each respective user. The lack of acceptable measuring equipment has been a barrier to the use of low-tempered heating systems in such joint installations.

The present invention opens for a new manner of determining energy consumption.

The circulation time for the water determines the heat transfer, and it becomes at the same time a measure of the energy consumption. If several users are attached to the same system, and the installations are correctly adjusted, the circulation time will in each respective installation give a good measure of the relative energy consumption in each respective installation. Thereby, the total energy costs can be divided between the respective users of respective installations, in accordance with their individual consumption.

Fig. 5 shows preliminary results of energy measurement based on circulation time in a specified installation. The figure shows the ratio Q between energy supplied to the floor heating installation per day, as determined by measuring circulation time and such as recorded in the controller, and measured, supplied electrical energy (in a case where the system receives no other energy supply than electricity), plotted as a function of the temperature of the inlet water.

The two measurements give a satisfactory correspondence, i. e. it is realized that the ratio Q is close to 1. It appears from the figure that the absolute energy consumption may be determined with a precision of about 10-12 % in this manner.

The method and means in accordance with the invention are favorable regarding determining the relative energy consumption of several users attached to a common heating installation. In this case, the temperature of the heat- carrying medium supplied to each respective user, will be approximately the same.

Under the assumption that the distribution systems are technically almost the same, the liberated heat per unit time will be proportional to the area of the heating surface, i. e. the heated floor area in the case with water-borne floor heating. Hence, the energy characteristic of each respective distribution system may be determined by measuring the circulation rate for each respective consumer when the installation is adjusted initially. Since there is often a common circulation pump for the whole plant for such installations, the supply of heat- carrying medium to the respective consumer may be regulated by means of a motor-controlled or thermally controlled valve that is connected to the temperature controller/energy meter with each respective consumer. Consequently, the method makes it possible to apportion the total energy consumption in the installation

between the respective users in accordance with the relative consumption of energy.

The relative energy consumption can be determined in several ways: i) The present system is based on calculating the need of energy before delivering the energy, and thereafter delivering the energy in accordance with the calculated need. Thereby, the energy measurement, in its simplest form, may consist in summing the calculated quantities of energy and adding this in a register attached to the processor. ii) It is also possible to measure, in an independent manner, that the energy calculated to be supplied to the distribution system, is actually delivered. This is done by measuring the actual circulation time, and the temperature of the heat- carrying medium. There exists a functional interrelation between the energy quantity delivered during a period and the following parameters; the temperature of the heat carrier conveyed to the distribution system, the circulation time, the standstill time and the heat transfer coefficient. The last mentioned parameter is determined by the constructive design of the distribution system. If the dimensions of the piping conveying the heat-carrying medium are very small, the quantity of heat that is delivered at standstill will be negligible. The energy actually liberated will then become directly proportional to the circulation time and the temperature difference between the temperature of the inlet heat carrier and a temperature that is representative of the constructional design of the distribution system.

In practice, the dimensions of the pipes in the distribution system will be large enough that the heat liberated at standstill, represents a significant contribution to the total energy amount liberated. The heat liberated at standstill is functionally dependent on the number of standstill periods, the duration of the standstill period, the temperature of the heat carrier and the coefficient of heat transfer. iii) It is also possible to measure the temperature of the heat carrying medium when it returns after having delivered the heat in the distribution system. The temperature will change with time, and the temperature variation exhibits a characteristic progress that carries information regarding liberated quantity of heat. As soon as circulation starts, the temperature measured will be approximately equal to the temperature of the distribution system, if the medium

that passes the temperature sensor has stayed some time inside the distribution system due to a standstill. After a certain period of time, this medium has been driven out, and a temperature increase will be recorded, characterized by the quantity of heat liberated from the medium when it circulates through the distribution system. The temperature will approach asymptotically a limit value that is somewhat lower than the temperature of the heat-carrying medium before it is sent into the distribution system. This temperature change is recorded using only one temperature sensor, and hence, one is not dependent on a temperature difference determination measured by means of two sensors having limited absolute accuracy.

It is also possible to measure the absolute energy consumption by first determining the interrelation between the temperature of the liquid in the distribution system and liberated power per unit area in the present installation design. Different constructions for low-tempered heat liberation have characteristic coefficients of surface conductance. These coefficients can be determined experimentally for construction types of interest.

In connection with the above mentioned energy measurement method for low-tempered heat installations, we shall now take a closer look at certain basic concepts and theoretical deductions of central importance regarding understanding the present invention: a) Low-tempered heating installations with energy delivery regulated in accordance with the invention In an ideal low-heating installation, the temperature of the water fed to the user premises, is as low as possible. From this follows that the volume flow should be as large as possible (larger than in conventional floor heating installations), and that the heat transfer from the heat-carrying water to the room is at a maximum.

These idealized requirements can be approximated by the requirements that the temperature difference for water in passing the consumer premises is equal to zero, and that the temperature in the floor stays at a stable level and is approximately the same as the constant room temperature. Under these assumptions, supplied power can be expressed as P=AUvG (Tv-TG) (1)

where A is the floor area, and UvG is the specific coefficient of heat transfer per unit area.

For this to result in a correct temperature in the room, the water temperature Tv must be controlled carefully from the instantaneous need of power. However, if the heat capacity of the water in the pipe is negligible, the energy supply can be regulated by means of the circulation time of the water. We introduce a running time parameter d (duty factor) that indicates the percentage of a time interval t during which the water circulates in the heating system. Thereby, supplied quantity of energy per time interval t can be controlled by varying d.

Correspondingly, liberated energy may be measured using the same parameter d and the temperature Tv of the water. po = q/t = d A UvG (Tv-TG) (2) These ideal requirements can hardly be realized in practice. There is a thermal resistance between the floor and the room that makes the floor temperature vary also. Further, the water in the pipe represents a heat capacity that is not negligible, and the same goes for the floor. Added together, these effects entail that the expression (2) must be modified, and we will now take a closer look at how the various effects influence the measurement of energy. b) Heat transfer from water to room The efficiency in conducting heat from the water in the pipe and further out into the room, is of importance to the operation. The situation is described in Fig.

6, and we will now take a closer look at how this influences the measurement of energy. In the figure, Tv, To and TR are water temperature, floor temperature and room temperature, respectively. The coefficients of surface conductance Uv and UGR are for heat transfer from water to floor, and from floor to room, respectively.

Pi and P2 are power flows, and C is the heat capacity of the floor.

The heat transfer from the water in the pipe to the floor, is described by means of the following differential equation, that can be solved exactly.

CG dTG/dt + (UVG + UGR) TG = UVG TV + UGR TR (3)

For our purposes, it is sufficient to discuss the various boundary conditions.

If the coefficient of heat transfer UGR between floor and room is substantially higher than the coefficient UvG, between pipe and floor, the floor temperature will be close to the room temperature, and the temperature difference between pipe and floor will vary in step with the water temperature. However ; if on the other hand the heat transfer between floor and room is poorer than between pipe and floor, the first mentioned will represent a barrier that causes the temperature difference between floor and pipe to stay relatively constant, even if the water temperature should vary.

The effect of a varying water temperature will depend on the heat capacity of the floor. A large heat capacity entails that the floor temperature equalizes fluctuations in the water temperature, and the temperature difference between water and floor will vary in step with the water temperature. c) The effect of periodical circulation The heat transfer in periodical circulation can be expressed as the sum of the heat quantity transferred during circulation time tod, designated qd, and the heat quantity transferred as a consequence of water standstill in the pipe, designated qs. q=qd+qs=todA UvG (Tv-TG) +qs (4) The first term corresponds to equation (2), with a multiplication by the running time tod. Two effects contribute to the second term. In periodical circulation, hot water will remain standing in the floor piping to liberate heat. Besides, during standstill the temperature will fall in the bulk of the floor with which the piping is interacting, since the floor liberates more heat than it receives from the pipe. The consequence is that when hot water starts circulating again in the pipe, the temperature of the bulk of the floor will for some time be lower than if the circulation had been going continuously.

The two above mentioned energy contributions to qs can be calculated theoretically. The simplest case is when the heat capacity of the floor is sufficiently large that the changes in the temperature of the bulk of the floor can be neglected.

Then, liberated power from the water during a standstill becomes

PA =-Cv dTv/dt = UVG (Tv-TG) (5) Putting Tv-TG = T and assuming To = constant, then dTv = dT.

PA =-CV dT/dt = UvoT having the solution PA = UVG (TV-TG) exp [- (UvG/Cv) t] (6) Looking at a period of duration to and a duty factor (relative running time) of value d, the time period during which heat liberation takes place under a standstill, becomes equal to to (1-d). This is inserted in expression (6), and we find (1-d) to qs fUvG (Tv-TG) exp [- (UvG/Cv) t] dt 0<BR> Cv (Tv-TG) [1-exp [- (UvG/Cv) (1-d) to]] (7) If the heat capacity of the floor is such as to make the temperature of the bulk of the floor fall significantly during the period of standstill, this will increase the quantity of heat liberated by the water in the pipe during standstill, as well as lead to a larger liberation of heat when circulation starts after standstill.

To a first order the correction from this, in relation to the expression in equation (7) have the form 2ATGCG, where ATG is the temperature drop in the floor during the standstill period, and CG is the effective heat capacity of the floor. The consequence of this is that effect of reducing the running time, will vary with the floor construction.

Table 1: Heat capacity and coefficient of heat transfer per. m2 for ordinary floor heating installations, mv is water quantity per. m2 Pipe diameter c-c spacing mv Cv Uvo<BR> (mm) (cm) (kg/m2) (Wh/mZdeg) (W/mdeg) 17 25 0.53 0.62 18.8 20 25 0.80 0.93 22.6 20 30 0.66 0.78 18.8 In practice, the quantities UvG and CG will be determined by the design of the installation, and they must be determined experimentally. However, the mathematical form is described correctly, and this mathematical form is decisive as regards conducting relative energy measurements.

Table 2 shows results for qd and qs respectively, with values calculated in table 1. The table is valid for floors with a relatively high heat capacity, so that equation (7) is a good approximation.

It appears from table 2 that the effect of periodical operation is an enhanced liberation of heat, which becomes of relatively great importance for low duty factors. The heat liberation at minimum running time (d < 5 %) is often 15-20 % of the heat liberation in continuous operation. On account of the temperature control as well as the energy measurement, this effect must be compensated for.

The chosen compensation is that the period time increases when the relative running time becomes less than 10 or 20 %.

Table 2: liberated energy per period to in (Tv-TG) units, as a function of duty factor d. to = 15 minutes.

UVG CV2 d qd qs q<BR> (W/m deg) (Wh/m deg) (%) (relative units<BR> 18. 8 0. 62 0 0 0. 62 0. 62 20 0. 94 0.62 1.56 40 1.88 0.61 2.49 60 2.82 0.60 3.42 80 3.76 0.49 4.25 100 4.70 0 4.70 18.8 0.78 0 0 0.78 0.78 20 0.94 0.77 1.71 40 1.88 0.76 2.64 60 2. 82 0.71 3.53 80 3.76 0.55 4.31 100 4.70 0 4.70

d) Adapted function for energy measurement The analysis in the previous sections shows that equation (2) must be modified in order to provide a reliable picture of energy transfer in floor heating installations.

A representation that is appropriate for various types of flow constructions, is obtained by starting with temperatures that can be measured or are relatively constant, namely the water temperature Tv of the forward water in the circulation installation and the room temperature TR. During stationary conditions, i. e. a constant temperature over time and continuous circulation, the transfer of power can be expressed by Ps = UvR (Tv-TR) (8) The transmission coefficient UVR has a known value for various floor constructions. For floor piping in concrete floors with ceramic tiles, the heat transmission coefficient UVR is in range 6-9 W/m2 deg. For wooden floors, where the floor piping must be equipped with heat dispersion plates in aluminum, UVR is in the range 2-3 W/m2 deg, dependant on the thickness and the nature of the floor coating.

Power transfer when using periodical circulation, can be expressed as P = a (d) Ps' (9) Here, a (d) is an attenuation factor expressing the degree of reduction of the heat transfer, as a consequence of limited running time tod.

Good temperature control entails that the running time tod is varied with water temperature Tv in such a manner that the power transfer becomes independent of the water temperature, when the external variables determining the need for heating, are constant. On the basis of a desired temperature level, the user determines the relation between duty factor d and water temperature.

Mathematically, this relation can be expressed as an exponential function d (Tv) = exp [-K (Tvo) (Tv-Tvo)] (10)

in which Tvo is chosen on the basis of a desired room temperature. An empirical expression for K (Tvo) that provides good flexibility regarding adaptation of various floor constructions, is K (Tvo) = a-b (Tvo-25), a and b being coefficients that can be chosen. a is chosen between 0 and 1, and b is chosen between 0 and 0.1.

The energy measurement takes as a starting point that the attenuation factor a (d) absorbs the various mechanisms resulting in reduced power transfer when running time is reduced. In practice, a (d) is determined on the basis of measurements for various types of floor. Such-measurements have shown that a (d) can be expressed as an approximately linear function of d, as long as the period length to is constant. This functional relation can then be used to totalize the energy consumption q for every period to during which the system is operating. q = A K (Tv-TR) a (d) to (11) where A is the floor area, TRis room temperature and K is a parameter determined by the coefficient of heat transmission for the complete floor construction. The parameter K is of importance if the method shall be used for absolute energy measurements.

Finally, decisive features and advantages of the present invention shall be summarized: When using the invention, a need of energy or heat in a given time period that can be chosen, is calculated on the basis of measurable parameters, and care is taken that the correct quantity of energy is delivered to the user's premises by controlling circulation time or quantity, using intermittent admission, for the heat-carrying medium in accordance with the temperature held by the medium.

The calculated quantity of energy that is necessary per time period chosen, is totalized in a register. If several users are attached to one joint heating system, the relative energy consumption of each respective user can be calculated easily.

Moreover, the energy consumption can be determined by measuring the actual circulation time, the standstill time and the temperature of the supplied heat carrier. Since the circulation is often provided by a central pump, the circulation at each respective user's premises can be regulated by having the controller influence a motor-controlled or thermally controlled valve that is either open or

closed. The temperature of the heat-carrying medium is the same at delivery to each respective user. The circulation time at each respective user's premises, energy liberated at standstill, and the area of the heating surface (heated floor area) will then provide information regarding the relative consumption of each respective user. This information can be used to share the total energy cost in accordance with the actual consumption of each respective user.

If the heat liberation for the construction of interest to the distribution system is calibrated, the last mentioned method can also be used for an absolute determination of the delivered energy quantity.

The method can also be used to measure the temperature variation of the heat-carrying medium when it returns from the distribution system, and on the basis of circulation time and temperature variation within the time period that indicates the duration of each single energy pulse, the delivered amount of energy can be determined.

If the circulation rates in the distribution system of the respective apartments are different, or vary over time, the measurement above can be supplemented by installing a liquid flow rate meter in the distribution system.

Circulated quantity and corresponding liquid temperature provide further information regarding the energy consumption.

If the heat requirements in the various parts of the building or installation is different, or depends in different manners on the external parameters (for example in that one part of a building is facing south and has a large solar incidence through the windows), the installation can be divided into different zones to be controlled in different manners, independent of each other. The energy consumption is then recorded for each respective zone, and totalized.

The register (registers) showing the energy consumption, can be read externally by having each unit (for instance apartment) connected to a readout network (data bus).