KTM Krankenhaus Technik + Management 3/2016
Comfortable air conditioning
Special fan-coil units for hospital air conditioning offer interesting energetic and hygienic aspects
In buildings in which a high degree of hygiene is also required apart from climate comfort, planners and facility managers now rely on energy-saving technology in building climate control. But since patients are often only lightly dressed in such environments, the energetic savings generated by lowered operating points must not be detrimental to the air-conditioned comfort. A thrifty, hygienic and nonetheless comfortable air conditioning in the medical and nursing area is provided by installing fan-coil units for recessed mounting in ceilings – so-called cassette devices.
The cassette fan-coil unit HyCassette Geko with controllable Swirl outlet is also suitable for use in hospitals.
The room climate control in the medical and nursing area must satisfy high expectations:
On the one hand, the patients should feel comfortable, on the other hand facilities managers are obliged to save costs and thus energy. At the same time, the hygiene requirements are high; in sensitive areas of application, statutory requirements must be met (DIN 1946 T 4 and VDI 6022). Therefore, the materials used in room air conditioners may not be microbiologically metabolizable and must simultaneously be resistant to disinfectants. The requirements apply not only to surfaces visible from the room, but also the internal components of a fan-coil unit that come into contact with the supply and return air of a room or with condensate.
Relevant components are primarily casing, fan impeller, filter as well as inlet and outlet cover plate and condensate pan. In the design of 'corners', large radiuses, rounded forms and concave shapes are preferable in order to provide dirt with the least possible chance of adhering to the surface as well as to facilitate easy cleaning and disinfection. Standing water is a possible natural habitat for microorganisms and must be avoided. Therefore the condensate pan of a hygienically designed cassette device has a continuous slope.
Economical EC fans
The loads in a room can change rapidly depending on the solar radiation and the number of persons. In examination rooms or laboratories, aside from the people present, medical devices also contribute to a dynamic load profile. The user's desire for more energy efficiency as well as the Ecodesign Directive (ErP2015, Energy Related Products Directive) have both influenced many manufacturers to offer their room air conditioners with an option of infinitely variable EC fans instead of conventional, three-speed AC fans.
Thanks to the EC fans, the air flow rate – and hence the thermal performance – can be exactly adapted to the respective cooling requests in automatic mode. The resulting savings in the predominately employed part-load mode are particularly effective, since it is not necessary to switch between different fan speeds. Due both to the lower losses as well as the variable method of working, the electric power consumption can be reduced by approx. 50 percent. Simultaneously, there is less operating noise of the fan-coil unit.
Problem: air drafts
However, the use of EC technology and the then possible variable, often low fan speeds poses new challenges as well: a predetermined, static shape of the air outlet leads to different air volume flows at different air throws (= maximum attained penetration of the room with the temperature-controlled air). In turn, this has an impact on the homogeneity of the room air temperature and the air velocity, which are both criteria for climate comfort.
In order to achieve low-draft air conditioning and a uniform temperature distribution in the room under different load conditions, one should also be able to vary the outlet profile with the air volume.
Conventional cassette fan-coil units for installation in a ceiling generally have a square shape with four outlets positioned at right angles to each other (4-way fan-coil unit). Since in this case the air is primarily blown out in four directions, this arrangement results in so-called shade zones in the room, in which the units practically cause no direct air flow at all. In addition, the outlets can often only be adjusted by hand, in order to adapt the discharge angle to the air flow rate and the room geometry. In such devices, for practical reasons the position of the outlet cover is adapted to the most frequently used fan speed for cooling.
With respect to climate comfort, this is a system-related weakness:
If the rotational speed of the fans varies with a fixed setting of the outlet cover, the air velocity and the air throw change. The temperature distribution in the room is usually unfavorable at low fan speeds. With diminishing rotational speed, multiple 'cold-air lakes' and/or non-air-conditioned shade zones develop. At the worst, the cold inlet air in the area of the ceiling unit sinks so rapidly that an effective room penetration is no longer possible.
The result are drafts, which especially lightly-clad patients find very unpleasant.
Optimized room air flow with patented outlet
To satisfy the requirements for comfort, new concepts were developed for the patented Swirl outlet of the HyCassette Geko with regard to design and technology, claims DencoHappel: The optimized room air current allows for low-draft operation and a uniform temperature distribution. Due to the round shape of the outlet, a uniform room penetration is achieved and shade zones are avoided. The applied air volume is blown out in a not so concentrated form as by the 4-way technology. This effect already reduces the risk of drafts.
The round outlet consists of paired outlet nozzles, which are distributed with alternating integrated interstices throughout. The air does not flow exactly radially from the device, but rather with a twirling movement. These two characteristics create an induction effect when the air is blown into the room: the temperature-controlled air mixes with the room air at the outlet cover, so that the resulting flow-air temperature is already somewhat adapted to the room temperature. The density difference between the flow air and room air is thus less, which is why the flow air tends to sink less. This minimizes not only the risk of drafts, but also favors the Coanda effect. This can be noticed by a larger air throw and a better air flushing through the room.
The most important constructive characteristic of the Swirl outlet is its automatic adjustability. To achieve a sufficient air throw even at slight air volume flows, the outlet diameter is always adapted to the air volume. This way the air throw can be kept constant over a wide load range. Apart from the cross-section of the outlet, the discharge angle to the ceiling was repositioned in order to optimize the air-delivery direction and hence also the room ventilation, depending on the cooling or heating operation. The integrated control system automatically adapts the air discharge speed and direction to the operating state.
Cleaning work easy to execute
Summary of the manufacturer:
The Swirl outlet of the HyCassette Geko ensures a low-draft mixing of air at simultaneously high cooling capacity; temperature nests in the room corners (shade zones) are likewise avoided, as are high air velocities or large temperature differences in the occupied zone. These measures increase the indoor air comfort. In combination with EC fans, the patented Swirl system thus meets particularly high requirements with respect to thermal climate comfort, noise and efficiency in all the used load ranges. The use of smooth, closed porous surfaces in the interior of the unit and round geometries that avoid dirt adhesion allows for easy regular cleaning and disinfection of the air-contact surfaces and provides a hygienic operation. Based on the simple accessibility and optimized screw connections, it is easy to execute cleaning work. Its features recommend the HyCassette Geko with Swirl outlet for use in medical practices, hospitals, homes for senior citizens and other facilities that have particularly high demands for indoor air comfort and hygiene. The fan-coil unit is available in different models with cooling capacities up to 4.5 kW and heating output up to 8.6 kW.
Julian Appelhoff, Stefan Kuhlich
Thanks to the Swirl outlet, the room develops a uniform temperature also at low fan speeds.
The radial-tangential outlet avoids shade zones. A circular swirl flow with induction effect ensures a rapid reduction of the temperature difference between inlet air and room air.
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