The method of heat cost allocation, rated to the area of every flat in a. residential building is known. This method does not stimulate the saving of thermal energy and establishes an unfair relationship between tenants mostly in the case of unbalanced heating systems.

For the same purpose of heat cost allocation, a method based on the measurement, displaying and recording of some indices, which are strictly proportional to the heat emitted by every radiator in a building is known.

This method does not take into consideration the posi- tion of the rooms in the building and the additional heating given by the inlet and outlet pipes, as well.

Therefore, unfair differences between similar flats with different position in the building, are liable to appear, even if their thermal comfort level is similar.

A heat cost allocation method that takes into consid- eration the position of rooms in the building and the additional heating given by inlet and outlet pipes, ap-

plying some correction factors on the measurement re- sults is also known.

Although this method decreases the eventual inequities between tenants, it implies some sophisticated and spe- cialized evaluations meant to determine some approxi- mate and subjective factors.

For the purpose of the heat cost allocation, an instru- ment based on the evaporation principle is known, that contains an ampoule filled with a liquid in contact with the radiator surface and a graded scale on which indices depending on the emitted heat can be read.

The disadvantages of this type of instrument consist in the lower measurement accuracy, mostly in the case of lower temperature values of the heat conveying liquid, and in the low sensitivity that makes impossible the monthly interpretation of results.

For the same purpose, an electronic instrument is known, provided with one or two temperature sensors, a microprocessor and a display, which installed in a well-established location on the surface of a radiator indicates numerical values proportional to the heat supplied by the radiator.

The disadvantages of both types of instruments consist in the worsening of the measurement accuracy as a re- sult of the change of the installation position, of the flow rate variation and of the influence of additional

heating sources. Besides, the instruments that require sophisticated method for data processing are quite sen- sitive to the fraudulent manipulations of records and do not allow the automatic control of the heat consump- tion, depending on the required thermal comfort level.

EP 139 361 A2 shows a method in which a difference be- tween the internal room temperature and a predetermined temperature is integrated over a predetermined time pe- riod to give a measurement of degree-days.

The problem solved by this invention, is to provide simple and reliable method and instrument for allocat- ing the heat cost, depending on the thermal comfort level, chosen by every tenant, performing simultane- ously the automatic control of the heating.

The method, according to the invention, eliminates the inconveniences of the known methods because the heat cost related to a square meter in any particular flat and period is multiplied with a factor proportional to a consumption index that is determined by adding the consumption indices of all rooms in the flat. In its turn, the consumption index of a room is determined by the integration of the difference between the internal temperature and the average external temperature and by the multiplication of the result with a factor calcu- lated as the ratio between the percent by volume of the room and the average number of degree-days of the re- spective period and locality.

The invention uses a relation between an internal room temperature and an external temperature around the flat to calculate the room consumption index. This index is calculated for each room. The relation between the room consumption index and the sum of all room consumption indices of the flat, i. e. the flat consumption index, gives a reliable result according to which the heat costs can be allocated to each room. Another possibil- ity is that the index is calculated for each room and the sum of all room consumption indices gives the flat consumption index. The relation between the flat con- sumption index and the sum of all flat consumption in- dices gives a reliable result according to which the cost can be allocated to each flat in the building, that is, the heat cost for each flat is allocated ac- cording to the ratio between the flat consumption index and the building consumption index, which is the sum of all flat consumption indices.

Advantageously, prior to the integration the difference between the first and the second value is divided by a third value depending on a difference between a prede- termined temperature and the external temperature. This is a normalization of the temperature difference which takes into account a kind of comfort level. In other words, the result of the division gives an indication how far the actual comfort of a room is from the prede- termined reference temperature.

When statistical data are used for a second and/or the third value it is not necessary to measure these values

at each instant. In most cases statistical data are sufficient to give reliable information.

It is of advantage when a previously determined average external temperature is used as the second value. Usu- ally the average external temperature of a month is known. Although there are differences of the external temperature from year to year, the average external temperature of a month is reliable enough for heat cost allocation.

An easy way for heat cost allocation is the use of the number of degree-days as third value. Degree-days are statistical data indicating how cold the weather is in certain periods.

The integration is interrupted when the temperature of a heating medium, for example heating water, drops be- low a predetermined threshold value. This takes into account that no sufficient heating takes place when the heating medium is too cold, and therefore heating costs cannot be allocated.

When initial data including the number of degree-days, the average external temperature, the threshold value of the heating medium, and the distinct integration pe- riod are set into a memory of each room (instrument) the calculation of the room consumption index can be made very easily.

Each room is personalized by setting into the memory the percents by volume of respective room. This means, that. the initial data can be set to the memories in a similar manner for all rooms. The adaptation to a spe- cific room is made by determining the percentage by volume of the room within the volume of the whole flat.

The instrument, according to the invention, includes as a whole, a thermostatic valve, an internal temperature sensor, a temperature sensor of the heat conveying liq- uid and a microprocessor. The latter memorizes the of- ficial average values of the external temperature and of the number of degree-days for the respective local- ity and period and the percent by volume of the room.

The microprocessor calculates continuously the differ- ence between the measured internal temperature and the memorized average external temperature, integrates the result depending on the time, applies the multiplica- tion factor and displays the consumption index of the room for the given period. The internal temperature of the room is maintained at a preset level using the thermostatic valve while the temperature of the heat conveying liquid is taken into consideration only for starting or stopping the integration when a preset value is reached, as a result of the starting or stop- ping of the heating system.

The instrument is rather simple. It can be installed very quickly. Basically it needs a temperature sensor for room temperature only and some means to calculate the room consumption index on the basis of room tem-

perature and initial data. This consumption index can be displayed and/or stored in order to enable the heat cost allocation at the later stage.

If a second temperature sensor sensing the temperature of the heating medium is used the integration can be interrupted when said temperature decreases under a preset value. Such threshold value (i. e. the preset value) can be used to indicate a situation in which the room is not heated. In such a case no heat costs should be allocated to this room.

Advantageously the instrument can be placed within a thermostatic valve. In this case basically there is no additional room necessary. The temperature of the heat- ing medium can be sensed very easily since the housing (the metallic body) of the thermostatic valve has al- most the same temperature as the heating medium.

As an alternative the instrument can be installed out- side the thermostatic valve inside a box mounted on the heating pipe the temperature of which is measured. In this case it can be desirable that the second sensor is protected by a collar with which the instrument is mounted on the pipe.

By applying the present invention the heat consumption is decreased, the thermal comfort level is optimized, the heating demand is adapted to the offer and the eq- uity of heat cost allocation between tenants is in- creased.

Here there is an example of how this invention might be implemented relating to fig. 1... 4 as follows: fig. 1, the scheme of the stages needed for the ap- plication of the allocation method; fig. 2, the plan of a flat, with an example of the consumption index calculation; fig. 3, the top view of an allocation instrument, built inside a thermostatic valve; fig. 4, the lateral view of an allocation instru- ment, installed on the heating pipe.

The heat cost allocation method, according to the in- vention, is initiated by a first stage when some heat cost allocation instruments are installed in each heated room.

During the second stage, the official number of degree- days and average of external temperatures which charac- terizes the respective locality, along the heating pe- riod are set into the memory of the microprocessor of every instrument and the threshold temperature of the heat conveying liquid and the distinct integration pe- riods are programmed. The official definition of the number of degree-days is the integration of the differ- ence between a reference temperature, for example 20 degrees C, and the external temperature.

The third stage comprises the evaluation of the heated rooms volumes, the calculation of the percents by vol- ume of the rooms in the whole volume of the flat and the registration of these data on a registration flat card.

During the fourth stage the personalization of each in- strument is performed, by setting into its memory the percent by volume of the rooms and the application code, as well.

The fifth stage contains the automatic measurement, when beside the data preset into its memory the micro- processor continuously receives data on the internal temperature of the room as well as on the heat convey- ing liquid temperature. The microprocessor continuously calculates the difference between the internal tempera- ture and the average, monthly external temperature, in- tegrates that difference depending on the time, applies a multiplication factor calculated as the ratio between the percent by volume and the number of degree-days of the month and displays the result as the consumption index of the room for the respective month. The tem- perature of the heat conveying liquid is taken into consideration only for starting or stopping the inte- gration, when a preset threshold is reached.

In a sixth stage the consumption index of the flat is calculated by adding the consumption indices of all heated rooms and that particular consumption index is

correlated to the ones of the other flats, thus per- forming an equitable heat cost allocation between the tenants.

The method uses a kind of thermal comfort level index "ITCL"which can be calculated according to equation (1) Te = external temperature Since in the equation (1), the value 20 is the refer- ence indoor temperature, the indices ITCL give us how far is the actual comfort of flats from the reference one. For having an image of relative comfort levels, the indices must be related to their average value.

In practice is very difficult to measure the external temperature for each room. Instead, could be used the average, external temperature (Tem) available for every locality, in national norms. Additionally, a second statistical data could be used: the number of degree- days (N1220). In the table 1 are given these data to- gether with the number of days (Z) in the heating pe- riod in Bucharest, as they result from the Romanian norm SR 4839: 1997. Month X XI XII I II III IV Tem (°C) 9, 2 5, 2 0, 2-2, 4-0,1 4, 8 9, 8 Z 23 30 31 31 28 31 21 N20 211, 6 458,8 613,8 694,4 562,8 471,2 205,8

Using these statistical data, we could calculate the thermal comfort level in two different formats. The first one (equation (1) ) has"instantaneous"style, meaning that in every moment the average value of the thermal comfort level is available.

The second format is a"cumulative"one. The value of the thermal comfort level is available at the end of the period, only and calculated according to equation (2): The number of degree-days is official data published for certain locations. However, if not available they can be measured according to the method described in EP 0 139 361 A2. The degree-days take into account the ef- fect of the weather, i. e. they are calculated from the outside air temperatures to give a single index number to indicate how cold it was in a given month, week, or other period.

The stages five and six use the equation (1) or (2).

These stages are repeated monthly. For each month of the heating period, the measurement results are stored in separate registers.

For instance, taking into consideration the case pre- sented in figure 2, of a flat in Bucharest, character- ized in the month of January by a number of degree-days of 658.4 and an average external temperature of-2. 4°C, the consumption indices of heated rooms, resulting from this method, taking into consideration the rooms areas and average internal temperatures noted on the figure, are the following: 26. 38- for the room a, 9. 71- for the room b, 6. 31- for the room c, 6. 03- for the room d, 7. 12- for the room e, 3. 18- for the room f and 4.65- for the room g. The consumption indices for the other months of the year are similarly calculated and sepa- rately memorized by the instruments. The consumption index of the flat in the given example is 63.38, re- sulting from the sum of consumption indices of the rooms. Irrespective of the flat size and position, the value of the consumption index characterizes the level of thermal comfort and the energetic behavior of its tenants, which could be considered as an economical be- havior, for values lower than 100, or a wasteful one for values higher than 100.

The instrument for heat cost allocation, in a first version according to the invention, comprises a bellows 1, placed inside a temperature control handle 2, a spring 3, assembled coaxially with a spindle 4, in full

contact with a valve cone 5, which are all the essen- tial components of a thermostatic valve installed on a radiator. Inside the thermostatic valve there is a tem- perature sensor 6 that measures the temperature of the heat conveying liquid in the flow pipe, while close to the bellows 1 is placed a second temperature sensor 7 that measures the temperature of the ambient air. The temperature measured with the sensor 7, the average values of the external temperature and of the number of degree-days, corresponding to the respective locality and period and the percent by volume of heated room are the input data of a microprocessor 8, which calculates the difference between the temperature measured with the sensor 7 and the average external temperature, in- tegrates the result depending on the time, applies a multiplication factor calculated as the ratio between the percent by volume and the number of degree-days and shows on a display 9 a consumption index of the room for the respective period.

When it is necessary to change the heat consumption, the bellows 1 is compressed or relaxed by rotating the control handle 2, making the valve cone 5 close or open and the internal temperature of the room is changed, which, measured with the sensor 7 and is taken into consideration by the microprocessor 8 for the calcula- tion of the consumption index. When the internal tem- perature of the room changes, for instance as a result of sun radiation, the content of the bellows 1 is ex- panded or compressed and, by means of the spindle 4, makes the valve cone 5 close or open. If, as a result

of the stopping of heating system, the temperature of the heat conveying liquid, measured with the sensor 6, goes down under a preset value, the integration is stopped and will be started only after the preset value is reached.

The instrument for heat cost allocation, in another version, according to the invention, is installed out- side the thermostatic valve, inside a box 10, mounted by means of a collar 11 on the heating pipe whose tem- perature is measured with a sensor 12 protected by the collar 11.

The method, according to the invention, applied with an appropriate instrument, might be also used in the case of ventilation and cooling cost allocation of the rooms that benefit of a centralized ventilation and cooling system.