Cooling ceiling
The cooling ceiling belongs to the group of surface heating / cooling systems. A cooling ceiling is a room ceiling whose temperature is brought and kept below the room air temperature. This is done through closed cycles of chilled water. Since the latter must not fall below a certain temperature (around 16 ° C to avoid the formation of condensation), ideally natural resources such as the soil or groundwater can be used for pre-cooling.
Working method
Cooling ceilings remove heat from the room.
Cooling ceilings or elements also work at cooling water temperatures below 16 ° C if an existing ventilation system as a central or decentralized device has pre-dehumidified the blown supply air or if the moisture load is dissipated through a window through shock ventilation. In contrast to heating, the water temperature cannot be set as low as desired when cooling, otherwise there is a risk of dew formation. This is because, depending on the temperature, the air can only absorb a certain amount of water vapor. The higher the air temperature, the more water vapor it can absorb. If the saturation limit is exceeded, the water vapor precipitates in the form of water. These relationships are shown in the so-called hx diagram. If z. B. a 25-degree air with a relative humidity of 58% is cooled to about 16 ° C, condensation occurs. In any case, a dew point monitor should adjust the flow temperature to the dew point temperature, i. H. raise this.
Basically, cooling ceilings can be divided into two groups: radiant ceilings and convection ceilings.
Radiant cooling ceilings
Radiant ceilings usually have a closed surface. The heat transfer takes place mainly through radiation (at least 60%). The space required is usually no greater than that for the construction of the ceiling without cooling. The advantage of the radiant ceiling is that it affects the room temperature. The perceived room temperature depends on the room air temperature and the temperature of the surrounding surfaces. Large differences between the perceived temperature and room temperature of 1.5 - 2 K are only achieved by cooling systems with a high proportion of radiation. This creates a comfortable room climate. A high proportion of radiation depends not only on the design of the cooling ceiling itself, but also on a large, cooled surface, whereby this surface must be in the radiation exchange with the people and objects emitting heat (visual contact). With radiant cooling ceilings, cooling capacities of up to 100 W / m² can be achieved.
Convection cooling ceilings
In the case of convection cooling ceilings, the convective part predominates (at least 60%) in the heat exchange. These suspended ceilings are open structures. This increases the convection and thus the cooling capacity. Cooling capacities of up to 220 W / m² are achieved.
comfort
The cooling ceiling has over conventional HVAC equipment advantages due to several factors: First, the cause lower input air which are now determined by the minimum air exchange and not by the cooling load to lower air speeds. Furthermore, the perceived room temperature corresponds roughly to the mean value of the mean room air temperature and the mean surface temperature of the surrounding area. A cooling ceiling is able to build up a largely uniform vertical temperature profile in the room. With cooling ceilings with a high proportion of radiation, the perceived room temperature is 1.5 - 2 K below the room air temperature, which has a positive effect on comfort. Last but not least, humans give off around 50% of their excess heat through radiation onto surrounding surfaces. Thus, a cooling ceiling system based on radiation cooling accommodates the physiological release of heat from humans.
Construction methods
Cooling ceiling as concrete core activation (TABS)
Concrete core activation or concrete core temperature control is a cost-effective method for cooling and heating buildings. It uses the ability of the ceilings and walls in the building to store thermal energy and thus to heat or cool rooms. Prefabricated pipe systems, so-called "pipe registers", are installed within the reinforcement layers in the concrete components (mostly ceilings, but also pillars or possibly walls). Water circulates in the pipes, which, depending on the temperature, absorbs heat from the ceiling (cooling effect) or releases it to the ceiling (heating). For the temperature control of the water in the circuit z. B. Use energy piles or geothermal probes in the ground. In cooling mode, the cooling energy can be drawn directly from the geothermal source for approx. 80% of the usage time. Since the performance of concrete core activation is reduced by suspended ceilings, there are special ceiling sails that work on the basis of concrete core activation and only generate a small loss of heating / cooling output. The advantages of such a sail are the improved optics and increased sound absorption.
Plastered cooling ceilings
Here, capillary tube mats made of plastic are inserted into the ceiling plaster and plastered over. This means that these ceilings do not differ from conventional plastered ceilings. Caution should be exercised when installing lamps as the capillaries can be damaged. In order to avoid this, careful planning of the intended ceiling fixtures in advance of the installation is strongly recommended. Plastic as a pipe material is very inexpensive and also durable. Experience from the use of plastic pipes in underfloor heating systems confirms these advantages.
Alternatively, thin-walled copper pipes are used. In addition to the excellent cooling and heating performance of up to 90 watts / m², these systems are easy to assemble. To do this, aluminum strips are mounted on the raw ceiling and the pipes are clipped in. These flat oval shaped tubes are available in heights of <10 mm. Since the pipes have high mechanical strength, they also serve as plaster bases.
Suspended cooling ceilings
Suspended cooling ceilings can be designed just like conventional suspended ceilings. They usually consist of a substructure and a top layer, such as B. cassettes, linear panels, panels, slats or ceiling sails. Copper or plastic pipes through which the cold water flows, transfer the cold to pressed-on heat conducting profiles, usually made of aluminum. Alternatively, capillary tube mats made of plastic can also be used very inexpensively. When using capillary tube mats, no heat conducting plates are used. However, the capillary tube mats should be glued on or at least applied with good thermal conductivity. The close installation distance between the individual capillary tubes of around 10 millimeters ensures good heat transfer and thus good cooling performance. Higher-density plasterboard (GK climate panels), graphite-modified plasterboard or coated metal surfaces form the end of the room.
A critical point for the functionality of the cooling ceiling is the connection of the heat conducting profiles with the selected ceiling soffit (plasterboard or metal). A permanently thermally conductive connection must be ensured here.
It should be noted that in the case of acoustically effective suspended perforated ceilings, heat conducting profiles cover part of the perforation and thus have an influence on the acoustic damping.
Closed cooling ceiling systems
Closed cooling ceilings are radiant ceilings and work mainly according to the radiation principle.
Seamless cooling ceilings
Seamless ceilings have a smooth underside with no visible support profiles or system-related joints. Individual ceiling elements are not recognizable. The surface is coated after the individual panels have been installed. Optionally, the panels can be made of various materials (e.g. plasterboard, clay building panels, metal, FMA)
Metal cooling ceilings
Metal cooling ceilings are suspended from the raw concrete ceiling. Copper or plastic pipes through which the cold water flows absorb the heat via pressed-on heat conducting profiles (mostly made of aluminum) or, if capillary tube mats are used, directly on the metal cassette. There are several plate types to choose from (e.g. linear plates, cassettes). These systems enable a high degree of revisionability and a variety of possible uses. Bandraster cooling ceilings can also be designed as longitudinally insulated cooling ceilings in order to minimize the transmission of sound from room to room. In this way, the ceiling void can be used for installations and any flexible partition wall position is possible.
Open cooling ceiling systems
Open cooling ceilings are among the convection ceilings and work mainly according to the convection principle.
Louvre cooling ceilings
In the case of lamellar cooling ceilings, individual lamella modules are suspended from the ceiling with variable center distances. The lamellas can consist of a sheet steel sheathed heat conducting profile or an aluminum lamella, which also represents the heat conducting profile. In addition, mineral wool inserts can be used if necessary to ensure greater sound absorption. Corresponding distances and suspension heights ensure convection or "air circulation". Different designs and variable center distances of the lamellas influence the appearance and cooling performance as well as the sound absorption. The space between the slats can be used to integrate lights, sprinklers or ventilation systems. These systems are suitable for airports and other buildings with strict fire protection regulations.
Chilled ceiling sails
With cooling ceiling sails, parts of the ceiling surface are suspended and designed as a cooling ceiling. This enables aesthetically pleasing solutions. Due to the higher convection, which is given by an active ceiling sail, these have a higher specific cooling capacity than closed cooling ceilings. The corresponding distances and suspension heights must be observed to ensure convection or "air circulation".
Performance determination
According to DIN EN 14240, the performance must be determined in a standardized test room. For cooling ceilings with a smooth surface and cast or plastered pipe registers (homogeneous systems), a general calculation method based on the FAXEN algorithm, which can be used for all pipe dimensions and pipe spacings, can be used with very good results. The results have been verified on measured values and have also proven themselves in determining the performance of underfloor heating. For constructions with contact surfaces between the pipes and the ceiling slab (heterogeneous systems), special construction-related calculation methods have been developed. Since the simulation of the performance is significantly more cost-effective than the standard test, the simulation methods have gained great importance in component development. This means that only final standard tests in accordance with DIN EN 14240 are required. Determining the performance of cooling ceilings with a PCM component is very complicated, as a phase change takes place in the material during operation, which results in heat storage effects. The standard test procedure cannot be used for this, and experimental investigations are extremely time-consuming because of the different boundary conditions over time. For this reason, calculation algorithms for the thermal simulation of these components have been developed. The simulation models mentioned can be downloaded free of charge.
The individual test methods are important when comparing the individual cooling ceiling system performances. There are a wide variety of applications, such as B. a ceiling with an open joint of approx. 100 mm, in which case the ceiling cannot be regarded as a closed ceiling.
The "old" cooling performance test according to DIN 4715-1 was carried out at a standard temperature of 10 K. When comparing the two standards, however, it is often forgotten that a 10 K sub-temperature can lead to a dew point falling below. For example, at a desired room temperature of 26 ° C and a sub-temperature of 10 K, a flow temperature below 16 ° C is required, which in most cases is not feasible.
The new standard according to DIN EN 14240 takes this problem into account and is measured at an under temperature of 8 K, which is more true in reality.
However, you then have to convert from the "old" standard to the new standard using a special process so that the values can be compared correctly. Here errors can often occur consciously or unconsciously and so different systems cannot be compared correctly with one another.
Calculation of active heating / cooling area
The calculation of the active heating / cooling surface is decisive for determining the output. This power is always given in watts / m² active area. There are several ways to determine performance. Depending on the criterion, the following DIN standards are taken into account in the calculation:
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| Calculation according to DIN 4715 board length × board width |
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| Calculation according to DIN EN 14240 old heat conducting profile length × center distance × number of bars |
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| Calculation according to DIN EN 14240 new register length × center distance × number of bars |
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| Calculation according to DIN Certco register length × register width |
Sound absorption with cooling ceilings
Most cooling ceiling systems use inserts to improve sound absorption. These are mostly acoustic fleece or mineral wool that are integrated into the system. The fleece also serves as trickle protection for mineral wool inserts. For this purpose, the mineral wool is welded in PE foil. This is particularly important because the temperature difference between the ceiling void and the room creates an air circulation that whirls up the individual fibers of the mineral wool and transports them into the room.
Chilled ceiling hydraulics
A cooling field consists of one or more active cooling ceiling elements that are connected in series (e.g. by means of plastic hoses braided with stainless steel). This is a prerequisite for an even flow. The number of active cooling ceilings should be selected so that a certain pressure loss occurs. The pressure loss influences the specific heating or cooling capacity. From a critical flow velocity, the laminar flow becomes the turbulent flow. This is influenced by the size of the pipe cross-section. For an optimal heat absorption of the medium, a turbulent flow form is required, which is created by the certain pressure loss.
A control zone consists of one or more cooling fields that are connected in parallel to a distribution line. The control areas are predominantly chosen by room or by axis. The size of the control areas is limited by the control group. The entire cooling process is controlled with this control group.
Hydraulic components for cooling ceilings
The perfect functioning of a cooling ceiling also depends heavily on the hydraulic components. The two most important points include the connection technology of the individual pipes and the control group with which the entire heating / cooling process is controlled.
Connection and connecting hoses
Various types of hose are used in connection technology. The choice of hose type depends on the area of application and the load the hoses are subjected to. Frequently used are e.g. B. stainless steel braided plastic hoses, corrugated hoses or simple plastic hoses (oxygen diffusion tight according to DIN 4726)
Multifunction rule group
For each control zone, a control group is required for passage control, regulation, shut-off and filling / emptying. A great advantage of rule groups is that different temperatures can be generated independently of one another in different rooms, as each room has its own rule group. This room control function can be compared to that of floor heating.
Advantages of a cooling ceiling
Conventional air conditioning systems, which achieve the cooling of the rooms with a supply of cooled air, often cause an unpleasant draft. Not so with the cooling ceiling, which has a positive effect on comfort. In addition, the perceived room temperature is usually slightly below the room air temperature, which means a further increase in comfort and energy savings.
