Air-conditioning system

Description of the invention

The invention relates to an air conditioning system.

Modern buildings tend to have large glazed surfaces and a wide range of required indoor temperatures, with both external and internal heat sources. Such a wide temperature range requires a zone temperature control system and a high degree of air purity in order to ensure adequate comfort also in the case of a high concentration of people and equipment. Internal heat sources contribute significantly to the overall balance of cooling and heating sources. The largest internal heat sources are electrical and electronic devices and high intensity lighting.

In large open spaces, where individual workstations or devices may require individual temperature control, locally controlled air conditioning is essential. Increasingly, people and devices are in the same room, which forces differences in heat delivery, both measured in watts per square meter and taking into account seasonal variations. Rooms with modern equipment, such as computer rooms or control rooms, typically require air conditioning also in winter, because the heat emitted by the devices located in them exceeds the natural heat losses of the rooms. Thus, there is a need for heating and air conditioning systems that can effectively control indoor conditions while being flexible enough to be adapted to different requirements in different parts of the building at different times of the year. Usually, independent air conditioning systems are used for different parts of the building, which excludes cooperation between them and intelligent control. It may be that there is no need for cooling and heating at the same time, both of which are provided independently with a significant energy input.

In addition, modern buildings are designed to provide far-reaching flexibility in the arrangement of interior space. As a result, the layout of the rooms and their purpose may change many times during the existence of the building. Consequently, the air conditioning system must also be easily adaptable to these changes.

The subject of the invention is an air-conditioning system in a building having: a hot water circuit; cold water circuit; a plurality of air conditioning terminals, each terminal having a fan forcing air into the space inside the building, a heating coil connected to the hot water circuit and / or a cooling coil connected to the cold water circuit; and at least one ambient temperature control system for controlling the heating power of the heating coils and the cooling power of the cooling coils. The system according to the invention is characterized in that it has a thermal energy management system with a heat pump that pumps thermal energy from the cold water circuit to the hot water circuit.

In one preferred embodiment of the air conditioning system according to the invention, the heat pump thermal energy management system additionally pumps thermal energy from the cold water circuit to the atmosphere and from the atmosphere to the hot water circuit, the thermal energy management system managing the heat energy so as to optimize energy consumption. .

In a further preferred embodiment of the air-conditioning system according to the invention, the optimization of the energy consumption is based on the minimization of the total energy consumption or the minimization of the total energy cost of the air-conditioning system.

In a further advantageous embodiment of the air-conditioning system according to the invention, the thermal energy management system additionally comprises an air / water heat exchanger which enables the transfer of heat energy from the cold water circuit to the atmosphere.

In another preferred embodiment, the air-conditioning system according to the invention additionally comprises a heat generator which generates heat energy and transfers it to the hot water circuit.

In yet another preferred embodiment, the air-conditioning system according to the invention additionally comprises a cooling energy store, the thermal energy management system extracting energy from this store for charging and transferring the heat energy from the cold water circuit to the cooling energy store.

In a further advantageous embodiment, the air-conditioning system according to the invention additionally comprises a thermal energy store, the thermal energy management system supplying energy to this store for charging and transferring the thermal energy from the thermal energy store to the hot water circuit.

PL 205 308 B1

In a further preferred embodiment of the air conditioning system according to the invention, the thermal energy management system monitors the cooling / thermal energy demand for each air conditioning terminal and varies the set point in the cold and hot water circuits depending on the cooling / thermal energy demand for the air conditioning terminals.

In a further advantageous embodiment of the air-conditioning system according to the invention, the thermal energy management system manages the thermal energy transfer taking into account the total heating / cooling requirement of the building, weather parameters outside the building and energy costs.

In another preferred embodiment of the air-conditioning system according to the invention, the cold water circuit and the hot water circuit have connections equipped with quick couplings arranged at regular intervals for connecting cooling coils and heating coils, respectively, by means of flexible conduits.

In yet another preferred embodiment of the air-conditioning system according to the invention, the air-conditioning terminals are placed in the process space under the floor or above the suspended ceiling, the fans of the air-conditioning terminals taking air from the air chamber under the floor.

In a further preferred embodiment of the air-conditioning system according to the invention, the air-conditioning terminal comprises: a modular casing mounted under the floor, the modular casing having an air outlet connected to an inlet ventilation grille arranged in the floor and an air inlet open to the air chamber; a fan, mounted in a modular housing, which draws air from the process space through the air inlet and blows it through the exhaust ventilation grille into the room above the floor; a heating coil connected to the hot water circuit and / or a cooling coil connected to the cold water circuit, the heating and cooling coil being mounted in a modular housing between the fan and the air outlet. In a more preferred embodiment, the air-conditioning terminal additionally comprises a filter element housed in a modular housing, the filter element being replaced by an inspection opening in the floor. In a particularly advantageous case, the air-conditioning terminal has a modular housing mounted under the floor, the modular housing having an air outlet connected to an exhaust ventilation grille open to a room located in the floor, and a mixing chamber with a return air duct and a fresh air duct; a fan mounted in a modular casing that draws air from the mixing chamber through the air inlet and blows it through the exhaust vent grille into an above-floor room; an expansion cooling system to cool and dry the air mounted in a modular housing, the cooling system having a water-cooled condenser connected to a cold water circuit; a heating spiral placed in the module housing and connected to the hot water circuit to heat the air after drying.

In a further advantageous embodiment, the air conditioning system according to the invention has a fresh air pre-treatment system that prepares fresh air and feeds it to the air chamber.

In a further advantageous embodiment of the air-conditioning system according to the invention, the energy supply system comprises: at least one refrigerant compressor; a water-cooled condenser for a coolant, the water-cooled condenser being connected to the hot water circuit and transmitting condensation energy to the hot water circuit; an evaporator for a refrigerant connected to the cold water circuit that receives evaporative energy from the cold water circuit; an air-cooled condenser for a refrigerant connected in parallel to the water-cooled condenser, the air-cooled condenser discharging excess condensation energy to the atmosphere; and a cooling coil connected in series with the evaporator in the cold water circuit. In a particularly advantageous case, the air-cooled condenser is a heat exchanger between the air and the coolant, and it also acts as an evaporator for the coolant by taking evaporative energy from the atmosphere.

The device according to the invention solves the problem of developing a flexible energy-saving air-conditioning system in a building where zone temperature control is required and where there is a simultaneous need for heating and cooling.

As indicated above, the air conditioning system according to the invention has a hot water circuit, a cold water circuit, and a plurality of air conditioning terminals. Each of the air conditioning terminals has a fan forcing air in the space inside the building, a heating coil connected to the water circuit

And / or a cooling coil connected to the cold water circuit. The ambient temperature control system allows you to control the heating power of the heating coils and the cooling power of the cooling coils. An essential aspect of the device according to the invention is that the air-conditioning system additionally has a thermal energy management system with an energy source, a heat pump, capable of transferring thermal energy from the cold water circuit to the hot water circuit. In a preferred embodiment, the thermal energy management system may additionally pump thermal energy: a) from the cold water circuit to the atmosphere, and b) from the atmosphere to the hot water circuit. The thermal energy management system manages the thermal energy in such a way that it maintains the set temperature in the hot water and cold water circuits and in such a way as to optimize energy consumption, whereby optimizing energy consumption may mean, for example, minimizing energy consumption or minimizing the cost of energy used by the air conditioning system.

To further optimize energy consumption, the system preferably includes a heat exchanger capable of transferring thermal energy from the cold water circuit to the atmosphere in a free cooling process.

To optimize the production of cooling energy, the system preferably has a cooling energy storage. The cooling energy storage allows either the storage of excess cooling energy or the production of cooling energy in reserve when the conditions for generating cooling energy are optimal, regardless of the instantaneous cooling energy demand.

In order to optimize the production of heating energy, the system preferably has a heating energy storage. The heating energy storage device enables the storage of excess heating energy or the production of heating energy in reserve, when the conditions for generating heating energy are optimal, regardless of the temporary heating energy demand.

To meet the peak cooling energy demand, the system preferably includes a heat generator that generates thermal energy and transfers it to the hot water circuit.

The energy consumption is further limited if the thermal energy management system can monitor the heating / cooling energy demand of each air conditioning terminal and the temperature deviation in the cold and hot water circuits as a function of the heating / cooling energy demand of the air conditioning terminals.

The thermal energy management system can advantageously manage the heat energy flow considering the building's total heating / cooling demand, outdoor weather performance and energy cost.

In order to ensure flexibility in the arrangement of the space inside the building, the cold water circuit and the hot water circuit preferably have connections equipped with quick couplings arranged at regular intervals for connecting cooling coils and heating coils respectively with flexible conduits.

The air-conditioning terminals are preferably located in a process space below the floor or above a false ceiling, with the fans of the air-conditioning terminals drawing air from the air chamber.

The air-conditioning terminal preferably has a modular housing mounted, for example, under the floor. The modular housing of the terminal has an air outlet connected to an inlet ventilation grille located in the floor and an air inlet open to the air chamber. The fan, mounted in a modular casing, draws air from the technological space through the air inlet and blows it through the exhaust ventilation grille into the room located above the floor. Additionally, the air conditioning terminal has a heating coil connected to the hot water circuit and / or a cooling coil connected to the cold water circuit. The heating and cooling coil are preferably mounted in a modular housing between the fan and the air outlet. The air-conditioning terminal can additionally have a filter element housed in a modular housing, whereby the filter element can be replaced through an inspection opening in the floor.

As indicated above, in another preferred embodiment, the air conditioning terminal has, for example, a modular housing mounted under the floor, for example, and has an air outlet connected to an air inlet grille located in the floor and a mixing chamber with a return air duct and a fresh air duct. A fan mounted in a modular housing draws air from the mixing chamber through the air inlet and blows it through the exhaust ventilation grille into the room above the floor. The air conditioning terminal may additionally include an expansion cooling system for cooling and dehumidifying the air. The expansion cooling system mounted in the modular housing may have a water-cooled condenser

It is connected to a cold water circuit, and a heating coil is housed in a modular housing and connected to a hot water circuit to heat the air after drying. The air-conditioning system can additionally be equipped with a fresh air pre-treatment system that initially prepares fresh air and feeds it to the air chamber.

Advantageously, the air-conditioning system according to the invention allows heat energy to be transported from the space to be cooled to the space to be heated and in the opposite direction, external energy sources being used only for energies exceeding the internal balance. Another advantage of using the air-conditioning system according to the invention is the integration of a heating and cooling system, which reduces energy consumption and space. Another advantage of the air-conditioning system according to the invention is the simplification and acceleration of installation and the reduction of its costs. A further advantage of the use of the air-conditioning system according to the invention is its high flexibility, so that it can be easily and cost-effectively adapted to changes in the interior layout of the building.

The subject matter of the invention is shown in exemplary embodiments in the attached drawing, in which fig. 1 shows a schematic view of an air-conditioning system according to the invention, fig. 2 shows a schematic cross-section of a first type of air-conditioning terminal, fig. 3 shows a schematic section of a second type of air-conditioning terminal, fig. 4. is a schematic diagram of the energy flow in the system, Fig. 5 is a schematic representation of a single power source module in Fig. 6. is a schematic diagram of different levels of control, Fig. 7 is a diagram of the temperature in the cold water circuit and the energy consumption versus heat loads in different operating modes, Fig. 8 is an hourly diagram of energy consumption in January, Fig. 9 is an hourly diagram of consumption in March, and Fig. 10 shows the hourly diagram of the water temperature.

Fig. 1 shows a schematic view of an air-conditioning system according to the invention. The system has a hot water circuit 10, a cold water circuit 12, a plurality of air conditioning terminals 14 (also referred to as "zone terminals"), and a heating / cooling generator 16 also referred to as an "energy source".

The hot water 10 and cold water 12 circuits are closed energy loops in the building 18. Depending on the specific needs, the different zones of the building 18 ', 18 ", 18" "require cooling and / or heating. The entire air-conditioning system works similarly to the electricity distribution system: hot and cold water circuits are distributed throughout the building 18 and, depending on individual needs, air-conditioning terminals 14 provide temperature and humidity control in various zones 18 ', 18 ", 18", while the energy source 16 maintains the energy level in the energy distribution circuits 10, 12 by interacting with all components of the system to optimize energy utilization. Preferably, all connections between the power distribution circuits 10, 12 and the air-conditioning terminals 14 are made with quick couplers and pre-insulated wires so as to ensure easy installation.

Various types of air conditioning terminals 14 allow for efficient air conditioning of the individual zones 18 ', 18 ", 18" "of the building. The air conditioning terminals 14 provide heating / cooling to the individual zones 181, 18 ", 18" "in which they are installed. Preferably they are designed to be mounted in a process space under the raised floor for maximum system flexibility and space saving.

Fig. 2 shows an air conditioning terminal 14 that can be used for heating and cooling. It has a modular housing 30 secured underneath the floor panel 32 in a raised floor system. The modular housing 30 includes an air outlet 34 connected to an inlet grille 36 in the floor panel 32, and an air inlet 38 open to a space below the floor 20. A fan 40 fitted in a modular housing 30 draws air in from the space 20 under the floor through the air inlet 38 and blows it through the outlet grille 36 in the floor panel 32 to the building zones 18 ', 18 ", 18" "above the space 20. Between the fan 40 and air outlet 34, a heating coil 42 and a cooling coil 44 are mounted in the modular housing 30. A filter element 46 is mounted between the air inlet 38 and the fan 40. Preferably, the filter element 46 is replaceable through an inspection opening 48 in the floor panel 32.

In technical zones such as the 18 ”zone, fresh air intake and dehumidification are generally not required. In such applications, the air conditioning terminals 14 are primarily used for cooling. As a consequence, A / C terminals should have a very high SHR [sensible heat ratio]. On the other hand, in zones such as the 18 "zone, where people are present, it may be additionally necessary to dry the air and supply fresh air.

Air. For this purpose, a separate device is used to provide humidity control in this zone. The dehumidification device can be installed under the floor. The dehumidification device may, for example, operate on the principle of direct expansion with air cooling and series connected evaporator and condenser scrolls. Thus, the temperature in the cold water circuit need not be limited by the temperature required to remove latent heat, which is a fraction of the total thermal load. If the latent heat loads are significant, excess heat must be dissipated to the outside. Where there is controlled room ventilation, the exhaust air stream can be used for this purpose.

Fig. 3 shows an air-conditioning terminal 14 'which can also be used for dehumidifying and supplying fresh air. Modular housing 50 includes an air outlet 52 connected to an inlet grille 54 in the floor panel 56 and a mixing chamber 58 with a return air duct 60 and a fresh air duct 62. A fan 64 mounted in a modular housing 50 draws in air from the mixing chamber 58 and blows it through the inlet grille 54 in the floor panel 56 to building zones 18], 18 ", 18" "above space 20. Additionally, the 14" air conditioning terminal has a cooling system. by expansion 66 to cool and dry the air. The cooling system, mounted in a modular housing, preferably consists of a drying evaporator coil 68 and a water cooled condenser (not shown) connected to the cold water circuit 12. A heating coil 68 is fitted behind the evaporator coil 68 and connected to the hot water circuit 10 to heat up dehumidified air. It is worth noting that in the 14 ”air conditioning terminal, the condensation heat is not lost, but is transferred to the hot water circuit 10 and used in zones 18], 18”, 18 ”'of the building which need to be heated.

Referring again to Fig. 1, the air-conditioning system may also have a fresh air pre-treatment system 78 (also called air freshening system 78) pre-preparing fresh air and feeding it to the process space.

The energy source 16 and the hot and cold water circuits 10, 12 are controlled by a thermal energy management system 80 which maintains the temperature in the circuits 10, 12 with minimal energy consumption under all operating conditions. The energy source 16 works by transferring heat between the hot and cold water circuits as a function of the heat demand of the air conditioning terminals 11. In this way, the temperature in the circuits 10, 12 is kept at a minimum energy consumption, since energy is only needed to make up for losses.

In order to minimize energy consumption, the system uses, for example, the following resources: (1) hot water circuit 10, (2) cold water circuit 12; (3) the surroundings of building 82; (4) a heat pump; (5) free cooling system; (6) one or more boiler 84 (if additional heating is required in winter).

If only air conditioning terminals are used for sensible cooling and if a separate system is used to control the humidity, it is possible to maintain a relatively high temperature in the cold water circuit 12 with a consequent increase in the coefficient of performance (COP) in cooling with the refrigerant compression cycle. , or it gives the possibility of greater use of free cooling.

We will now discuss the operation of the heat source with reference to Fig. 4. The heat pump located in the heat source 16 can pump the heat received from the cold water circuit 12 and the heat absorbed during the operation of the heat pump to the hot water circuit 10. After reaching the set temperature in the circuit hot water 10, excess heat is discharged to the outside (cold thermostat with infinite capacity 82 '). If cooling is required during the winter season (for example in 18 "technical rooms), the heat source 16 can use the outside air to cool the water freely in the cold water circuit 12. If during cooling the heat loads are lower than the maximum, the temperature can be increased in the cold water circuit 12 and hence increasing the COP without losing temperature control in the rooms.

The heat source 16 also maintains the temperature in the hot water circuit 10 using the heat pump. Thermal energy is obtained from the cold water circuit 12 or, if the cold water circuit has already reached the required temperature, from the environment (warm thermostat with infinite capacity 82 ”). If the heat generated by the heat pump is not sufficient to cover the thermal energy requirement of the building 18, it is possible to use a conventional boiler 84 to replenish the missing part of the energy.

The management system 80 can evaluate the temperature trends in the individual zones and process the collected data so as to determine the characteristic temperature and humidity trends and on

On this basis, determine the future operation of the energy source 16. Additionally, energy storage in the system can lead to a better use of thermal energy in the heating and cooling system, which obviously contributes to increasing the energy efficiency of the system. The temperatures in the circuits 10, 12 vary depending on the thermal loads in the various zones.

A preferred embodiment of the heat source is shown in Fig. 5. It preferably has a modular structure which facilitates its use in various situations. Each module has, for example, a cooling capacity of 150 kW. Up to sixteen such modules can be connected in parallel. Thus, the heat source 16 is very versatile and can be used for precise control under extremely different thermal loads. The base module is preferably equipped with four compressors 90. Due to the favorable indicators of noise level and efficiency, screw compressors are used. Preferably the refrigerant is HFC R407C in accordance with CEE 2037/2000 environmental standard. The condenser system 92 preferably has two heat exchangers connected in parallel: if heating is required (heat pumping or heat recovery) a water cooled condenser 92 '(plate heat exchanger type) is used. Otherwise, the condensation heat is discharged to the atmosphere via a 92 ”reversible scroll heat exchanger. The evaporator system consists of a water / refrigerant heat exchanger 94 which is used when the system is operating as a chiller together with said reversible scroll heat exchanger used in heat pump mode of operation. Each module is provided with water connections, pumps, expansion tank and free cooling spirals 96 through which the returning water pumped by the recirculation pump flows only when the outside air temperature is low enough to contribute to cooling. Preferably, the cold water circuit has a variable temperature set point. The flows in the building are controlled under the supervision of a central control system 80.

The air-conditioning system of the invention is particularly recommended for buildings where: (1) cooling loads are generally much greater than heating loads; (2) cooling operation is required all year round due to the magnitude of the internal heat loads and the quality of the building insulation.

Preferably, the air conditioning system is controlled at three levels (see Fig. 6): (1) microclimate level 100: tracking temperature and humidity settings in each zone (local control); (2) installation level 102: maintaining the set temperatures in the water circuits; (3) system level 104: optimization of energy consumption and minimization of costs taking into account the interaction of the building with the installation using adaptive control and thermal load forecasting techniques.

A microclimate level of 100 includes control in each zone. The user sets the settings that the control module 106 maintains by means of the three-way valve of the cooling or heating coil.

The installation level 102 accounts for the operation of the heat source 16. It monitors the temperature in the cold water circuit 12, measures the deviation from the set value, and provides adequate cooling. Regarding the production of cold water, the heat source 16 also monitors the temperature outside the building to take into account the possible use of free cooling.

System level 104 includes energy optimization / cost optimization. The control of the system is based on the analysis of the operating conditions of the system and the boundary conditions using an algorithm that raises the set temperature in the cold water circuit 12 as high as possible in order to increase the overall energy efficiency. Measuring the temperature of the returning water in the hot water circuit 10 determines the heating demand and enables the operating conditions on the condenser side (water or air cooled) to be determined. The condensation temperature, in heat recovery operation, is determined by the energy requirement to produce water at a temperature sufficient to feed the heating coils. In the analyzed building type, the available heat is always sufficient to satisfy the heating needs. The system can also force certain actions to achieve maximum energy savings in the long run, for example: storing hot or cold water and controlling free cooling. Generally, it concerns the change of certain parameters in the control algorithm to force energy storage based on the analysis of the building's thermal parameters or the regulation of parameters and observation of the system's reaction.

At the microclimate level 100, the temperature in the various zones (having one or more air-conditioning terminals 14) is kept at a predetermined level by opening and closing the valves of the heating and cooling spirals. Humidity is controlled by independent air drying systems.

PL 205 308 B1

At the installation level, the heat source measures the temperature of the return water in the cold water circuit 12 and evaluates the cooling demand (to which the cooling load must still be added by the energy storage algorithm operating in the third control level). Partial opening of the three-way valves 110, 112 from the air-conditioning terminals (cf. Fig. 2) allows the temperature in the cold water circuit to be maximally increased in accordance with the estimated heat load.

On the basis of these data, the control algorithm at level 3 increases the set temperature of the supply water, taking into account the limitations resulting from the course of parameters in the air-conditioned space with a simultaneous maximum increase in energy efficiency. The algorithm evaluates heat loads in particular zones, taking into account the nominal capacity and tolerance of temperature setting in a given zone. The same algorithm also evaluates the possibility of using free cooling under given conditions. All these factors are correlated because increasing the set water temperature increases the energy saving efficiency. The algorithm also takes into account the value of the use of free cooling in relation to the demand of the hot water circuit by comparing the costs of cooling by compressing the refrigerant with the cost of heating with a boiler. Once the operating conditions related to the cooling load have been determined, the amount of heat that can be recovered is calculated. The hot water circuit demand is estimated and the level 3 control system evaluates the following options. If there is an immediate heat demand less than the available heat energy, heat recovery is used and the difference is discharged through an air-cooled condenser. Heat recovery adversely affects the condensation temperature. If there is an immediate demand for heat greater than the available heat energy, the system decides, based on a cost analysis mainly based on the PER (primary energy ratio) of the heat pump and boiler efficiency, how to generate the required additional heat. If the energy demand is not immediate, a certain amount of the thermal energy may be stored in the reservoir in the hot water circuit.

The third control level 104 evaluates the performance of the system over a long period of time compared to the previous period. Based on the results of such a comparison, the parameters of the control algorithm, such as set temperatures in the circuits, are modified and "fictitious" thermal loads are determined in order to make greater use of heat recovery when the actual loads are not in phase so as to obtain maximum efficiency.

The control on the third level also defines the operating parameters of the heat source (cold water temperature, division between water and air condensation, division between water and air evaporation).

Description of the simulation program

A computer program was used to simulate the entire air conditioning system. Within the main program, there are many subroutines, each of which describes one element of the system.

The following INPUT parameters are set: thermal and cooling loads, outside air temperature, required temperature in cold and hot water circuits. At the OUTPUT, the operating parameters of the cooling circuit (temperature and pressure at various points), heat flows, electrical parameters of the motor and coefficients of performance (COP) of the cooler and heat pump are provided.

The simulation program also takes into account the use of a heat exchanger for free cooling, if possible under the given operating conditions.

The simulation program places emphasis on saving energy through careful management. Optimization involves operating with the highest possible return water temperature in the cold water circuit and the lowest possible in the hot water circuit, while still being able to cope with heating and cooling loads. Meeting these conditions is not always easy in the presence of thermal loads with varying amplitudes and frequencies between zones. A few particularly disadvantaged terminals can impose a temperature level that will be too heavy a burden on the system. In this case, it is necessary to determine whether the fluid temperature in both circuits is to be determined on the basis of the average demand in the zones and not on the few terminals under particularly demanding conditions. The control system must take into account the presence of thermal inertia, and must be able to smooth the thermal load waveforms over time.

Examples of potential energy savings using the presented control philosophy will be given below. Several basic schemes for their practical implementation were also proposed.

The simulation program makes it possible to establish an equilibrium point between the various elements of the system. In simple terms, it determines the condensation and evaporation temperatures that lead to equalization

The refrigerant flows through the compressor, condenser and evaporator, using the setpoints of vapor superheat at the evaporator outlet (which is some function of the calibration of the thermostatic expansion valves) and the liquid subcooling at the condenser outlet (generally user-defined in the case of a liquid condenser or equal to zero when a liquid receiver is used). It is assumed that the expansion device, for example a thermostatic valve, does not affect the operation of the circuit, but it follows the equilibrium conditions of the three main components. The convergence of the system parameters to the equilibrium state is obtained by using the secant method to reduce to zero two errors defined as relative deviations between the two values ​​of the coolant flows and the third value of the flow.

An interpolation subroutine (REFPINT) based on the data generated by the REFPROP program from NIST is used to determine the coolant properties required by the calculation procedures of the simulation program. While all common refrigerants are included in the sub-program, this analysis only covers the zeotropic mixture R407C. In this case, the temperature change during the isobaric phase transition was taken as a linear enthalpy function.

As mentioned above, the air conditioning system is designed as a modular system with the possibility of multi-stage control. To ensure high control flexibility and increase energy efficiency, in the event of thermal loads that vary significantly in time and position, the system consists of n identical modules, each module having a number of compressors 90 working in parallel, plate condenser 92 ', plate evaporator 94 a ribbed scroll 92 "(which may function as a condenser or as an evaporator) and an air-cooled scroll 96 for free cooling. The capacity control does not take place at the level of a single compressor 90, which therefore operates under nominal conditions, but is multi-stage, with the individual modules being turned on and off depending on the load.

The program determines the number of working modules based on the heating / cooling demand at a given moment. If the load cannot be taken by the total number of modules, the program determines the number of modules n that are capable of taking the load and the number n-1 just below the load. The percentage of a module's running time that must be on and off is therefore determined by the capacity it must provide.

A single module includes a plurality of compressors 90, a dual condenser 922, 92 ", an expansion valve and a dual evaporator 922, 94. The hermetic screw type compressor assembly has a nominal cooling capacity of 150 kW. In the program, the set of compressors represents a subroutine in which the compressor's work curve is given. Evaporators are represented by two subroutines: one that corresponds to the water-coolant heat exchanger and the other that corresponds to the air-to-coolant heat exchanger. The first of these exchangers has brazed stainless steel plates and is described by performance curves. The second is in the form of a ribbed spiral, assuming perfect flows of both fluids in opposite directions. The model adopted for the simulation is analytical and is based on dividing the heat exchanger into a finite number of elements, each of which assumes constant fluid properties and a constant thermal conductivity coefficient. Depending on the average surface temperature, the element can be treated as dry (only sensible heat flow occurs when the dew point temperature exceeds the surface temperature) or wet (heat flow and phase change occur when the dew point temperature is below the surface temperature). In the latter case, the heat flow potentials are determined by the enthalpy of the moist air between air and metal and the temperature difference between the metal and the fluid inside. Differences in helix fin performance due to different heat transfer regimes for dry and wet fin must also be taken into account. As with the evaporators, two different condensers were used: one for water (plate) and one for air (ribbed spiral). For the former, the performance curves provided by the manufacturer were adopted, and for the latter, an analytical model simulating a ribbed spiral with opposite flows was used. The expansion valve is described by a simple expansion with constant enthalpy between the condenser outlet and the evaporator inlet.

Simulations

Fig. 7 shows the air conditioning system behavior during a series of tests with an outside temperature of 10 ° C. This assumption is not necessary, but is made to demonstrate the feasibility of the system. The graph shows the ratio of cooling demand and heat load to show the changes of various parameters as the cooling load changes from maximum to minimum value. The abscissa shows the temperatures of the supply and return water in zones and,

On the other side, the power consumed by the compressor. This energy is given in terms of primary energy (electricity) for easy comparison between a conventional system and a system with total or partial heat recovery for heating in the winter season. The power consumed (marked with P._ep) was calculated with reference to a conventional thermoelectric system with a total efficiency (including transmission losses) of 0.33. When the system is operating in the winter season, it is possible to use an additional boiler to satisfy the heating loads. In this case, the energy consumed by the boiler should be taken into account in the calculation of the total energy, assuming the boiler efficiency is 0.9.

The assumed interior air temperature is 24 ° C. The water temperature was calculated according to two different control schemes. In the first one, the system is step-controlled and supplies cold water to the cold water circuit at a temperature of 7 ° C. At partial loads, control of the heat capacity in the individual zones is achieved by controlling the cold fluid flow in the terminal heat exchangers. This type of control will be called constant temperature control. The second scheme allows the temperature of the cold water supplied to the zones to be raised above the traditional 7 ° C level when the cooling load is less than nominal. The control scheme assumes that this temperature rise will reach a maximum value at which it will still be sufficient to take over the cooling load while the heat exchangers operate efficiently. As a result, the COP increases in part load operation as the evaporation pressure increases with increasing cold water temperature. This type of control will be called a variable temperature control.

The graph clearly shows the advantage of variable temperature control when the system is operated at part load. As cooling demand decreases, the temperature of the water supplied to the zones increases, and with it the evaporating temperature, until, at zero load, it is equal to the air temperature. In the constant temperature control mode, the supply water temperature is constantly 7 ° C regardless of the load drop.

The increase in COP associated with the increase in the evaporation temperature consequently reduces the energy consumed during the day. In Fig. 7, it can be seen that when operating with a constant temperature, it varies linearly with the heat capacity, while it decreases when operating with a variable temperature. The maximum energy saving is 50% of the heat load as the amount of energy consumed is the same at 100% and 0% load.

In Fig. 7, an energy consumption curve is shown considering the possibility of working with free cooling. This can happen when the outside air temperature is low enough to be a free cooling source to replace mechanical cooling. It is obvious that free cooling is much easier to use when operating with variable than with constant temperature. This is because a significant increase in the water return temperature from the cold water circuit at part load means a much greater heat transfer in the free cooling spiral.

The start of free cooling is shown in the graph as a rapid decrease in energy consumption that reaches zero at partial loads less than 40%. It should be emphasized that the waveforms in Fig. 7 are shown as solid lines although the system is stepwise as they are based on average values ​​for the full cycle of the system. It is also essential that the system can operate in both constant and variable temperature control, in combination with free cooling where possible, using the heat of condensation whenever there is a simultaneous heating and cooling demand. This can happen in winter and in transitional seasons. To account for this effect, two additional modes of operation have been developed. Both of them take into account the condensation heat recovery and the possibility of changing the inlet water temperature. The first control mode assumes that the system module is working with two condensers 92, 92 'connected in parallel. In the plate condenser 92 ', the heat is recovered so as to balance the heat load by using 45 ° C water in the terminals, while in the 92' scroll condenser the excess heat of condensation is dissipated. In the event that the module is unable to meet the heat demand, it uses a plate condenser 92 'with full recovery, and the additional module starts working with partial recovery. This possibility never exists in the load profiles shown in the examples. This mode of operation will hereinafter be referred to as "continuous recovery".

In the second heat recovery mode, the module or modules are always operating at full power with heat recovery, that is to say they make maximum use of the heat of condensation in the plate heat exchanger 92 'even if the recovered heat is less than the heat of condensation. This recovery method means that the module works intermittently. In the simulations, it was assumed that due to a sufficiently high thermal inertia of the system, temperature changes caused by them are negligible. When the module does not need to deliver

It operates normally with an air-cooled condenser. This mode of operation will hereinafter be referred to as "periodic recovery". It is clear that this method allows greater energy savings compared to continuous recovery because no energy is lost due to increasing the condensation temperature in the air cooled condenser to that in the water cooled condenser.

The results of research on the system in various operating modes described above in relation to the loads typical for technological buildings are presented in the following.

To complete the analysis, it was necessary to study the behavior of the system at different times of the year. The characteristic load profiles are shown in Table 1.

Table 1. Load profiles

<td></td><td colspan="2">January</td><td colspan="2">March</td><td colspan="2">July</td>

<td>Time (hour)</td><td>P1 [kWh]</td><td>P2 [kWh]</td><td>P1 [kWh]</td><td>P2 [kWh]</td><td>P1 [kWh]</td><td>P2 [kWh]</td>

<td> 1:00-2:00</td><td> 375,0</td><td> 0,0</td><td> 375,0</td><td> 0,0</td><td> 375,0</td><td> 0,0</td>

<td> 3:00-4:00</td><td> 487,5</td><td> 0,0</td><td> 487,5</td><td> 0,0</td><td> 487,5</td><td> 0,0</td>

<td> 5:00-6:00</td><td> 562,5</td><td> 0,0</td><td> 562,5</td><td> 0,0</td><td> 562,5</td><td> 0,0</td>

<td> 7:00-8:00</td><td> 637,5</td><td> 0,0</td><td> 637,5</td><td> 0,0</td><td> 637,5</td><td> 0,0</td>

<td> 9:00-16:00</td><td> 675,0</td><td> 75,0</td><td> 712,5</td><td> 37,5</td><td> 750,0</td><td> 0,0</td>

<td> 17:00-18:00</td><td> 637,5</td><td> 0,0</td><td> 637,5</td><td> 0,0</td><td> 637,5</td><td> 0,0</td>

<td> 19:00-20:00</td><td> 562,5</td><td> 0,0</td><td> 562,5</td><td> 0,0</td><td> 562,5</td><td> 0,0</td>

<td> 21:00-22:00</td><td> 487,5</td><td> 0,0</td><td> 487,5</td><td> 0,0</td><td> 487,5</td><td> 0,0</td>

<td> 23:00-24:00</td><td> 375,0</td><td> 0,0</td><td> 375,0</td><td> 0,0</td><td> 375,0</td><td> 0,0</td>

They differ only in the thermal loads of the offices, which are assumed to be constant during a normal working day and equal to zero during the rest of the day. Loads can be cooling or heating depending on the season. In July, there is only a need for cooling, both in technological and office rooms. January and March show a reduction in cooling in offices that require heating later. To analyze the operating mode during the different months, the temperature and humidity in the Padua region were taken into account during a typical day [x].

Simulation results

January

Figure 8 shows an hourly diagram of energy consumption for the four modes of operation described above. Moving from a fixed to a variable setpoint temperature allows energy savings of up to 50%. As shown earlier, this is possible thanks to the possibility of using warmer water for the zones, which significantly increases the temperature difference between the mini and the outside air temperature and thus increases the amount of heat that can be exchanged in the free cooling spiral. The heat recovery mode further reduces energy consumption. In particular, it is worth noting that in the variable temperature operating mode, continuous recovery only slightly improves the efficiency. This can be explained by considering the low heating requirement compared to cooling, since the energy gain during heat recovery is partially offset by the efficiency losses due to the higher condensation pressure at which the system has to operate to heat hot water to 45 ° C. This energy loss is minimized in the case of batch recovery as the system uses the condenser heat more efficiently and as a result the efficiency of the system is significantly higher. For an immediate comparison of the energy efficiency under the different control modes, Table 2 shows the energy consumption in each of the three months considered. It can be seen that by not using heat from the condenser, in the variable temperature mode, savings in electricity consumption of 50.7% are achieved, which translates into economic savings of the same order. In heat recovery modes, energy savings refer to different types of energy (electricity and heat) which, although they can be compared thanks to the primary energy concept, cannot be unequivocally translated into economic savings.

PL 205 308 B1

March

Similar to January, Fig. 9 shows the hourly diagram of energy consumption for the four modes of operation described above. In this case, it can be seen that the savings in switching from constant temperature to floating temperature operation are lower than in January as the possibility of using free cooling is reduced due to the higher outside air temperature. Regarding heat recovery operation, it is evident that continuous recovery degrades the efficiency for several hours during the day compared to other operating modes. In this case, the heating demand is lower than during the winter months, so that the gain from heat recovery does not compensate for the loss in efficiency caused by the increase in condensation pressure. In the batch recovery mode, this decrease does not take place since, as explained above, the heat of condensation is used with maximum efficiency.

July

The analysis of the hourly waveforms of energy consumption in the constant temperature and variable temperature mode shows that the energy savings are greater, the more the conditions deviate from those with the maximum load applied during the morning and afternoon hours, that is - the greater the operation with partial load , the greater the savings.

This is explained by the graphs of the inlet water temperature in the two modes of operation shown in Fig. 10, where it can be seen that when operating with a variable temperature, the water temperature rises as the load decreases. Table 2 shows the daily energy consumption. The percentage of energy savings is not particularly high because the behavior of the system is the same in both operating modes during the maximum load hours. However, it is worth paying attention to the absolute absolute energy savings.

Table 2.

Daily energy consumption in different seasons of the year [kWh / day]

<td></td><td>absorbed energy</td><td>difference compared to constant temperature operating mode</td><td>percentage difference</td>

<td></td><td>[kWh / day]</td><td>[kWh / day]</td><td> [%]</td>

<td colspan="4">January</td>

<td>constant temperature mode</td><td> 2794</td><td></td><td></td>

<td>variable mode</td><td> 1378</td><td> -1414</td><td> -50,7</td>

<td>temperature</td><td></td><td></td><td></td>

<td>variable temperature mode and continuous recovery</td><td> 1220</td><td> -1572</td><td> -56,3</td>

<td>variable temperature mode and periodic recovery</td><td> 964</td><td> -1828</td><td> -65,5</td>

<td colspan="4">March</td>

<td>constant temperature mode</td><td> 7623</td><td></td><td></td>

<td>variable temperature mode</td><td> 4628</td><td> -2996</td><td> -39,3</td>

<td>variable temperature mode and continuous recovery</td><td> 5118</td><td> -2505</td><td> -32,9</td>

<td>variable temperature mode and periodic recovery</td><td> 4364</td><td> -3260</td><td> -42,8</td>

<td colspan="4">July</td>

<td>constant temperature mode</td><td> 10660</td><td></td><td></td>

<td>variable temperature mode</td><td> 10136</td><td> -524</td><td> -4,9</td>

Note that in January and March, the outdoor air temperature allows the free cooling function to be used for several hours a day depending on the control strategy.

PL 205 308 B1