6th IASME/WSEAS International Conference on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT (HTE'08) Rhodes, Greece, August 20-22, 2008

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1 Rhodes, Greece, August -, 8 The implications of thermostatic valves and individual heat meters in DH systems from Romania RODICA FRUNZULICĂ, MIRELA ŢOROPOC,VARTIRES ANDREEA Technical University of Civil Building Engineering Faculty of Building Services Engineering 66, Pache Protopopescu Av., sect., Bucharest ROMANIA Abstract: - District heating systems are major suppliers of heat to Romania s urban population. The performance of a DH system consist in his ability in maintaining the optimal indoor temperature in the rooms and in furnishing the necessary quantity and temperature for the domestic hot water. Due to the lack of maintenance and operators of DH systems it is sometimes impossible to maintain adequate levels of service to residential consumers. The implementation of thermostatic valves for each radiator and individual heat meters was one of the good measures in the last years. The effect was positive but also negative when the hydraulic balance of the interior heating installation was hardly influenced. However, the structure and the behavior of the buildings, the type of radiators, the heterogeneity of the rooms and the individual intervention of each consumer are not very easy to predict in the calculus of the heat consumption for each apartment. The various correction factors needed to be taken into consideration are permanently in debate of the specialists and consumers. In the present article, some of these aspects are shown, some deficiencies of the calculus and some recommendations are made, in order to obtain a better behavior of the DH systems and the consumers comfort. Key-Words: - DH systems, individual heat meters, thermostatic valves, correct fee for the heat consumption Introduction Romania has an area of 38,39 km² and a population of million. It has the seventh largest population and the ninth largest territory in the EU. District heating systems are major suppliers of heat to Romania s urban population. Bucharest has the second most important and largest DH system in Europe Purcentage(% Solid fuel for stoves District Heating Gas for stoves Other types of central heating Fig.. The structure of heating system in Romania Approx. 68 of Romania s larger towns have district heating systems, most of which are supplied by CHP (combined heat and power plants (Fig..In some towns, district heating is provided by heat-only plants, owned by municipalities or by industrial enterprises. In Fig. the evolution from to 7 of the total number of apartments fed by DH Systems in Bucharest (the capital of Romania is represented. Year Number of the apartments Fig..The number of apartments fed by DH systems However, almost all the existing DH system in the country are technologically obsolete, the heat losses are high and the energy efficiency is low. Due to the lack of maintenance and operators of district heating systems it is impossible to maintain adequate levels of service to residential consumers. In buildings, the two main problems still are: the lack of heat meters and controls for each apartment, and poor insulation of the buildings. The performance of a DH system consist in his ability in maintaining the optimal indoor ISSN: ISBN:

2 Rhodes, Greece, August -, 8 temperature in the rooms and furnishing the necessary quantity and temperature for the domestic hot water. Some households have decided to disconnect from the DH systems due to the increasing price of fuel and consequently, of the supplied heat. Instead of the DH heat, they buy individual gas boilers for only one apartment. In the same time, the poor status of the entire heat distribution systems, together with the lack of measurement of individual heat consumption and lack of transparency in heat cost allocation by the heat distribution company conducted to an ambiguous situation. Households adopted a variety of strategies to reduce their heating costs, some of which had indirect negative consequences on their thermal comfort (and that of other apartments also not heating apartments even if it is needed, disconnecting some radiators (about 7 percent of the connected apartment partially disconnected and a half of them for financial reasons [9]. The implementation of thermostatic valves for each radiator was one of the good measures in the last years. The effect was positive but also negative when the hydraulic balance of the interior heating installation was hardly influenced [4]. In the blocks of flats (condominium the thermostatic valves are implemented together with individual heat meters (IHM for each radiator. Problem formulation At a global view, the measures mentioned before have reduced with 5-3% the total heat consumption. However, the interventions of thermostatic valves introduce some supplementary pressure losses and lead to a variable flow, depending on the free heat supply, or on the individual consumer s intervention. That is why, in certain heating installations and certain buildings (depending of the age of the building, their interventions are extremely efficient but in some other cases they introduce important hydraulic derangements. On the other side, the heat consumptions are registered by the individual heat meters mounted on each radiator. Some apartments have disadvantageous emplacement either from the level or from the geographical orientation (N, V... Thermostatic valves The role of thermostatic valves is on one hand, to adjust the flow, by offering in this manner important economies depending on free heat and each financial consumer s availability, by maintaining constant the indoor temperature in every room. Free heat can have important influences on heat demand. Considering that real heat demand for the consumer is Q r and free heat (from internal sources, solar radiation, electrical equipments etc. could be quantify with b coefficient, it can be written: Q r = G c ( t = G c ( t b G c ( t (.. = G c ( b ( t t = ( b( t and δ ' k' S = δks( b (.. t ( ti k' = ( b( ti k (.3. + m = ti + ( b( t + ( b ( ti The final temperatures t a ;t a and T a can be calculated as: + m a = ti +,5( b( t + ( b ( ti (.4. + m ta = ti,5( b( t + ( b ( ti (.5. T a = a + u( a ta where G is the flow; c-thermal specific capacity; t, t supply and return temperatures in the secondary circuit; T a,, a, t a - the modified temperatures when free heat is taken into consideration. k global transmission coefficient in the radiators; t i - the indoor temperature ; b- percentage cof the heat demand covered by the free heat ; m- coefficient depending on the type of the radiators. The form of the heat supply curves t a and t a for the residential consumers shows that there are some situations when the regulation equipment (thermostatic valves notice the free heat, and they will try to correct the controlled processes and they will reduce the flow [9]. water temperature Comparison between the diagrams for the qualitative heat supply regulation in the hypothesis of taking into consideration of the "free heat " and the hypothesis of negleting it Outdoor temperature Fig.3. The heating supply diagram with or without free heat taken into consideration The thermostatic valves are settled in order to obtain the nominal flows. These sets are valid only if the differential pressure when determining these presets are effectively applied on the valves [8]. As a result of the consumers disconnections from the district heating systems it is very possible that the installations will function with a much reduced flow or, as a result of an important free heat. In this situation, the differential a ta t T Ta ISSN: ISBN:

3 Rhodes, Greece, August -, 8 pressure might grow very much. If this pressure grows over -3 Pa ( - 3 mm H O, the risk for vibrations and noise appears. The problem consists in establishing of these differential pressures for all the thermal powers of the radiators. Generally, the thermostatic valves are pre-settled considering a constant value for the differential pressure of kpa. This value is convenient considering the following 3 reasons and demands: a it is a value not to high to produce vibrations and noise and clogging of the valve will be avoid, b it is a value not to low to ensure in the same time a turbulent flow in the valves and to ensure the recommended valve authority (kv values recommended by the producers, c it is a value not to low in order to reduce the relative influence of pressure losses on real differential pressure applied on radiators. If thermostatic valves are introduced in the installations, more or less variable flow in the interior heating installations, and as consequences, also in the secondary circuits of the district heating systems, will be induced []. The variation degree is directly related with the number of the consumers with thermostatic valves and on the other hand with the value of the free heat. At the present, most of the substations from Romania district heating system are not equipped with variable speed pumps, in order to react promptly to new situations in heat interior installations functioning. At an individual regarding if a thermostatic valve react at a certain radiator, reducing the flow for example, that will influence all the nearby radiators. A communicating vessels principle phenomenon can be assimilated to this problem. If others radiators don t have regulations valves at a reducing of flow, the head pump will rise, so the flow will also grow for these radiators... Individual heat meters (IHM These equipments represent a system that can identify the heat consumption for each radiator. The registration depends directly on the radiator temperature, on the functioning time of the radiator and its characteristics. The IHM has temperature sensors, one for the radiator heat temperature and one for the indoor temperature. Other heat sources, (such as solar radiation, light sources, cooking machines etc. must not influence the measurements. The presence of such individual meters must be mandatory accompanied by the presence of thermostatic valves..3. The influence of the heat meter type on the heat consumption calculus The IHM integrate function of time the difference between the average temperature of the radiator surface and the indoor temperature. The IHM with only one sensor summarize the average temperature of the radiator in a certain period of time. In order to identify the emitted heat of the radiator, if the integrated temperature difference in certain period of time is known,, the value of the difference is multiplied by heat surface of the radiator, and by the global transmission coefficient, based on the relation: Qh = S k [kcal/h] (.6. where : S is the heat surface of the radiator [m ]; k- the global transmission coefficient [kcal/m Kh]; - the hourly difference between the average temperature of the radiator surface and the indoor temperature [K]. If the average temperature difference between the average temperature of the radiator surface and the indoor temperature is established during a day, then, the emitted heat of the radiator is calculated based on the relation: Qh = 4 S k [kcal/day] (.7. The relation can be written also as : Q = S k = 4 day t = [kcal/day] (.8. For a longer period of time ( n days that can be a week, a month or a year, the relation is: 4 = Q nday = S k... [ kcal/nday] (.9. = The IHM with one sensor register only the average temperature of the radiator, so in this case the emitted heat of the radiator in a certain time will be: 4 = Q nday= S k ( = t i [kcal/nday] (.. where - the hourly average temperature of the radiator; t i the average indoor temperature during the period of time analyzed. On the other hand, in the analyzed period, the average indoor temperature cannot be registered because it is different from a room to another or from an apartment to another. In the mean time, this temperature cannot be considered as the average indoor temperature from a reference room, knowing that there are differences between reference room and any other room. In that case, the average indoor temperature will be approximate as an average temperature comprised between 7 and 3 C. It is obvious why the IHM with sensors are preferred instead of those with only sensor, the errors in this case being of -5%. The IHM with only one sensor can be utilized in the case of a minimal temperature of the radiators higher than 55 C. This case is not specific for district heating systems where this temperature arrives to maximum 45 C. The existing IHM give a number of 6 ISSN: ISBN:

4 Rhodes, Greece, August -, 8 to 9 units during a month. This leads to an average temperature of about 4 C per unit, considering that the IHM show on their screen no dimensional units. Even that these IHM don t show the number of degrees-hour or degrees-days but a certain of the real value, these units expresses however the number of degrees-hour or degrees-days because this is the only way to establish the emitted heat by the radiators. The repartition of the heat costs per apartment it is not based on the units expressed by these IHM but based on computer soft that take into consideration the registrations of each IHM and certain correction coefficients. These coefficients refer to the thermal power of each radiator, to the thermal coupling at the temperature sensor and on the specific situation of the rooms with low conventional indoor temperatures. In reality, what IHM register is the degrees-hour or degrees-days corrected by a coefficient, and it represent a fraction of the real value. Even the denomination in romanian nomenclature as cost repartition equipment is incorrect. The most appropriate denomination is individual heat meters for average temperatures (IHMAT. In SR EN 834 it is precisely stipulate that the shown values by the IHM are transformed in an adequate form for the heat costs calculation through the evaluation factors such as: evaluation factor K Q for the thermal power of the radiator, evaluation factor Kc for the thermal coupling at the temperature sensor, evaluation factor K T for the rooms with lower indoor temperatures comparing with the reference indoor temperatures The evaluation factor K Q is the non dimensional number for the nominal thermal power of the radiator. This nominal thermal power is the thermal power of the radiator established in certain conditions that refer to: supply/ return temperature of the fluid 9 C, 7 C, the indoor temperature is C and the radiator is verified in a thermostatic room. The indoor temperature must be measured at,75 m under the floor at a distance of,5 m of the heat radiator surface. If the nominal heat power for a radiator was established in other temperature conditions than, this power must be corrected according to before mentioned conditions. The evaluation factor K c takes into consideration the thermal coupling between the temperature sensors and the temperature to be detected and measured, function of different type radiators surfaces. The evaluation factor K T for the rooms with lower indoor temperatures comparing with the reference indoor temperatures, takes into consideration the modifications of thermal power and temperature of the sensors in the cases of IHM with only one sensor temperature are utilized. The global evaluation factor K, represent the multiplication of the three individual evaluation factors: K = K K K (.. Q c T If the factor K Ţ (which is characteristic for special conditions and very rare cases and the factor K c is considered like a constant subunit value the global factor can be written as: K = c (.. K Q In the definition for the evaluation factor K given by SR. EN 834, the determination conditions for the radiator thermal power in the thermostatic room are recognized. In order to compare the thermal powers for different types of radiators, it was introduced a reference factor. This value is denominated as thermal equivalent surface. In conformity with a romanian standard STAS this surface S echjv is a conventional value that characterize the thermal power of the radiator in the following conditions: - supply/ return temperature of the fluid 95 C/ 75 C, the indoor temperature is C (so, the average logarithmic difference temperature water-air is 66,5 C - the radiator is branched in the heating interior installation with the supply pipe up to the radiator and down for the return pipe - the radiator is mounted on the exterior wall, under the window. The thermal powers can be determined either in the thermostatic room that leads to lower thermal powers and transmission coefficient, or in real functioning conditions. The difference between the nominal power and real thermal power could arrive to 6 %. For real conditions, the air circulation it is more intense, so the value of transmission coefficient is higher. If the difference between the radiator temperature and the indoor temperature is higher, the thermal power of the radiator will be higher. If a heating interior installation is equipped with radiators characterized by thermal powers determined in the same manner for all of them, the evaluation coefficients can be arbitrary chosen. The mandatory request for these coefficients is that they must be proportional with radiators thermal powers. In time, in many apartments, the owners have made some changes on the type of the radiators or they have enlarged the heating surfaces. When radiators with thermal power determined in different conditions are utilized in the heating installations it is mandatory to consider the powers corresponding to the thermal equivalent surface. Even that EN SR834 stipulates that the evaluation factor K Q is the no dimensional value for the nominal thermal power of the radiators (in Watt, in reality this value express the real thermal power of the radiator. If the evaluation factors are fraction of the thermal power of the radiators, then they cannot be no dimensional but a number (in Watt. As an example, for a radiator type 64/4 with elements, instead of a power of 4 W, an evaluation factor of,675 is given (arbitrary chosen which is times smaller than the thermal power. In the bills emitted ISSN: ISBN:

5 Rhodes, Greece, August -, 8 by the firms responsible for the IHM the evaluation factors are multiplied with the registered values in time. It was mentioned before that IHM register in time the sum of the temperature difference between the radiator temperature and the indoor temperature, that is the number of degrees-hour measured in [Kh]. If, in conformity with SR EN 834, the evaluation factor represent the value corresponding to the nominal power (in Watt, than, the multiplication with the registered values should lead to measure unit [WKh], which is incorrect. The evaluation factor should reflect in fact the value ks in the relation Q = S k, with the measure units [W/K]. In this case the result between the IHM registrations and the value ks represents the energy consumption and is measured in [Wh] [7]. Of course, the evaluation factors can represent only a fraction from the real value. For example: to elements of 64/4 radiator might correspond an evaluation factor equal with,675. A calculus of the real value of ks leads to the result 7,754,8 =,87W / K. This value divided to 35 might become an evaluation factor of,65. The essential condition remains to have only one reference (the thermal equivalent surface and to establish correctly this surface, no matter what type of radiator, for all the radiators in a building. Another problem is the accuracy of the placement factor of the radiators. Many articles and studies related to this subject demonstrated that the heat demand by applying the romanian standard SR 97 leads to a 3% over dimensioned value, due to the non simultaneity factors appeared in calculus. The wind influence is hazardous and in certain area, is practical very reduced. The solar radiation is enough disputed by considering the supplementary orientation coefficients of -5% for south exposure, +5% for north and for east and west exposure. As we mentioned before, the IHM suppose also the presence of the thermostatic valves to each radiator [4]. This means a different approach for the wind or orientation influence. Once that the thermostatic valve was settled for a certain indoor temperature, any other factors that leads to heat surface increase over the real heat demand (corresponding to the settled indoor temperature are not registered by the IHM. If a strong solar radiation appears, the thermostatic valves will reduce the flow until the settled temperature is reached. If there is no wind, the supplementary heat surface could not lead to a higher temperature because of the thermostatic valve. The conclusion is that all the placement factors applied until now should be reconsidered. The inaccuracy of the heat consumptions for the apartments is relevant from the following example: for a building with 58 apartments where IHM where placed by a certain firm (F the placement coefficients accorded for different apartments are,65 to,6. In Figure 4 the thermal m power for the radiators from the kitchens of 8 apartments on an ordinary level. The apartments no.,4,5,8 have west orientation, the others are placed on east side. If we compared the apartments to 4, the thermal power of the radiators on east orientation are higher with 5 % comparing with the ones placed on west side. Between the apartments 5 to 8 the thermal power of the radiators on east orientation are higher with 8,5% comparing with the ones placed on west side and with 45% comparing to and Fig.4. Heat consumption for the kitchens from 8 apartments In Figure 5 the variation of the placement factors values appreciated by the firm (F are given and also the correct factors that should be considered. The purcentage values [%] Thermal power [W],,8,6,4, 8 6 4,95 Fig.5. The variation of the placement factors values appreciated by the firm (F and the correct ones The situation is extremely seriously at kitchens from the apartments 6 and 7 where the placement coefficients are higher with 3% and for the rooms 5 and 8 only with 3%. The same anomaly appears also for the placement of the apartments on the last floor and on the ground-floor ,8 The number of the apartment Corfficients offered by the firm (F firm,8,95,95,9 Correct coefficients,69,69 768,95, Number of the apartment ISSN: ISBN:

6 Rhodes, Greece, August -, 8 3 Problem solution If the evaluation factors for the heat surfaces, depending on the type radiator, give differences beginning with, to 4,8%, the evaluation factor depending on the placement of the apartment give differences from 8 to %. We must consider correct the fact that any apartment placed on disadvantageous position (such as superior level, inferior level, on the corner with the higher heat losses, insure in fact the insulation for the whole building. Thus, it is not normal to affect all the heat losses and be paid only by these apartments, but maybe only 5%, or be supported by all the apartments in the building. Another particular situation appears for the apartments where the thermostatic valves are settled on anti freeze position. This position corresponds to an indoor temperature of 6 C. It is very attractive to consider that these equipments lead to important energy economy. In the periods of time when the householders are not home or they are in vacation it is a good opportunity to make economies. For this situation, during this time, the households don t pay at all (or maybe only for the common parts. In reality, the apartments near by will register higher consumptions because of the heat losses through transmission. In Fig. 6 it is shown the variation one horizontal direction (the same floor if one room (number 3 is disbranched from the district heating installation.. Indoor temperature (grd. Celsius Room Fig.6 The variation of indoor temperature around an apartment disbranched from the heat installation Another negative influence of the thermostatic valves totally closed is on the temperature on the interior walls that can reach rouse temperature so that can leads to humidity, dampness, mildew on the walls and discomfort. 4 Conclusion From all the things we have mentioned before we conclude that it is wrong to apply placement factors arbitrary chosen or less theoretically based, because the errors could lead to a higher bill with 35%.If the households utilize radiators with thermal power established in different conditions comparing with those determined in the thermostatic room it is necessary to make calculus considering the thermal power corresponding to the thermal equivalent heat surface. Beside the less accuracy elements and incorrect from the calculus soft utilized by certain firms, some other factors conduct to some errors: - the wrong calculus for the apartments without IHM and thermostatic valves ; - the wrong calculus for the oversized radiators or for the apartments or modified by the households ; - the wrong calculus for the apartments or rooms where thermostatic valves are closed ; - the lack of the balance valves in the buildings with thermostatic valves and IHM. References: []Quinton, Jacques - Le debit variable. Application aux reseaux de chaleur ; Revue Chauffage,Ventilation,Conditionnement nr. 5/995. [] R.Dehausse- Enérgetique des bâtiments, vol 3, PYC Editions, 989. [3]J.Besse, F.Candas, P.Delpech, E.Denieuil, -Réglage des distributions de chauffage, Les Editions Parisiennes, 998, 8 p. [4] Frunzulica, R. Damian A - Energy consumptions analysis in a rehabilitated small-scale substation from a district heating system-3rd IASME / WSEAS International Conference on Energy,Environment, ecosystems and sustainable devolopment 4-6 july 7-Agios Nikolaos, Crete Island, Greece. [5] Kopp W; - Regelung des Heizwasserdurchatzes in Gebaudeheizungsanlagen bei Fernwarmeversergung Heizung, Luftung Klimatechnik, Haustechnik RFG - nr./97- pag [6] Davy de Virville- Regulation de temperature pour la production de l eau chaude sanitaire instantanee ou semi-instantanee - Revue Chaud,Froid,Plomberie nr.553-decembre 993. [7] Liviu Dumitrescu The individual heat meters are not instruments to measure heat consumption Revue Instalatorul no.,3,4,5/5 [8]Viktor Pyrkov - Hydronic Balance [9]Frunzulica R, others -Improvement of heat use în order to obtain occupant s comfort under optimal economical conditions, Research project no. 46/4, Technical University of Civil Engineering Bucharest, Final report 6. ISSN: ISBN: