STUDY THE ROLE OF CHILLED BEAMS IN IMPROVING COOLING EFFICIENCY OF BUILDINGS: LITERATURE REVIEW Saeed Reza Mohandes1, (Hossein Omrany2) Saeed Reza Mohandes1_ Master of Construction Management_Faculty of Civil Engineering _Universiti Technologi of Malaysia (UTM) _ [email protected]
Hossein omrany2 _ Master of Construction Management_Faculty of Civil Engineering _Universiti Technologi of Malaysia (UTM) _ [email protected]
Indoor environment has been considered as a key factor for residents comfort and their health and productivity. As such, to fulfill these requirements chilled beam can be useful for cooling, ventilating spaces and control the humidity of air. Chilled beams are of essence due to increasing energy saving leading to reduce electricity cost, improving the cooling efficiency of buildings in order to have comfortable working environment which result in boosting the resultant health and productivity. This paper is a literature review one which has comprised these issues from the past articles that have been done on this area from 1999 to 2010: The role of false ceiling about the passive chilled beams and how it should be to maximize efficient cooling, Air distribution through using chilled beams, Explanation of active and passive chilled beams, how they work and their advantages and disadvantages, The effect of a heat load location on flow velocity with a passive chilled beam. Chilled beams save a great deal of energy in terms of transferring cooling, ventilating of airflow, using higher chilled water temperature and eliminating the need for reheating the cooled air. To achieve the best result of efficient cooling of chilled beam in false ceiling, the return openings of false ceiling should be located in the perimeter of a room. Furthermore, the size of its area should be doubled compared to the beam. When it comes to the asymmetric workstation using chilled beams in office building, workstation shouldn’t be located in the downfall area in order not to cause local draught risk. Besides, asymmetric workstation causes circulation in a room which results in high air speed on at the floor. On the other hand, in the presentation of dummy, the plumes generated by the heat loads do not have impact on downward flow; however, it declines the downward flow velocity. Keywords: Active and passive chilled beams, Maximize efficient cooling, Air distribution, false ceiling, and Asymmetric workstation
1-INTRODUCTION It is generally believed that indoor environment is a key factor not solely for occupants’ comfort, but also for their healthy and productivity. Indoor air quality (IEO) includes several factors such as acoustics, thermal environment and air quality. Of these, thermal environment and air quality are the most significant two factors amongst the aforementioned one . As BOMA stated in 1999, respondents mostly consider these items as the most crucial relating to their productivity rate: comfortable temperature, IEQ, quality of maintenance work, building management’s responsiveness, building management’s ability to meet the tenants’ needs and finally acoustics. Additionally, mean air velocity, air temperature, relative humidity, vertical temperature gradient and mean radiant temperature have been contemplated for fulfilling good door environment. Also, the minimum air flow by the ventilation system is mentioned with the aim of assuring good air quality. Chilling beams are well-suited to be counted as a beneficial solution to enhance residents’ comfort within the buildings .
2-CHILLED BEAMS FUNCTION AND TYPES Chilled water pipes in modular units are used in chilled beams. On the contrary to the chilled beams, heat is transferred via convection instead of radiation. Owing to avoid condensation, chilled beams are well-suited in places with moderate internal humidity load. Generally, chilled beams are categorized into two types: active and passive [1-3]. 2-1-Active chilled beams Active chilled beams also known as induction diffusers which are more sophisticate than passive chilled beams. Turning to the figure 1, active chilled beams have a finned cooling coil. In addition, an integral air supply is designed to meet minimum outdoor air requirements. This supply air passes through nozzles comprising additional air flow thorough the cooling coil and release to the space. The location of an active chilled beam is at the ceiling. These types of chilled beams can also be used for heating; however, the problem is that heat remains under the ceiling .
Active chilled beam (adapted from )
2-2-Passive chilled beams As can be seen in the fig 2, passive chilled beams include a cooling coil with fins and perforated metal casing which is suspended from the ceiling. The air around chilled beams is cooled by the chilled water passing through the coil at temperatures usually from 13oC to 17oC . Thereafter; the aforementioned cooled air around the chilled beam down to the floor level. Cooing capacity of the passive chilled beam is around 60 w/m2. In contrast to an active chilled beam, a passive beam is solely connected to a chilled water system cooling the room by natural convection. One reason of using passive chilled beam is its silent cooling .
Passive chilled beam (adapted from )
2-2-1-False ceiling impact on the passive chilled beams’ cooling capacity The passive chilled beams have been commonly installed above a false ceiling letting the air flow through an opening of perforated sheet metal or a grating which brings about more pleasant appearances for the residents in terms of architectural point of view. On the other hand, the main downside of installing chilled beams above a false ceiling is the cooling capacity of them. Due to the subdivisions of the room into two compartments, their cooling capacity might be decreased. When the return air flows from the lower to the upper compartment through the openings for substituting the airflow generated by the chilled beams, it meets resistance . When opening area for the return air is around twice the area of the beam, maximum cooling efficiency is obtained. An opening area is smaller than the area of the beam chokes the flow. If an opening area would be larger than the beam area, its cooling efficiency is larger in comparison with no false ceiling. In other words, the cooling efficiency of the false ceiling covered the whole room, no false ceiling at all and the presence of false ceiling which its area of the return openings is twice the area of the beam and located at the perimeter of the room are 45%,61% and 80%, respectively. With the presence of false ceiling, the air is forced to flow through the openings especially if they are located at the perimeter of the room causing to flow across the whole room. In fact, the main role of presenting a false ceiling is to prevent a radiation from the warm floor in order not to reach the ceiling .
2-2-2-Impact of the presence of a dummy on the cooling efficiency of a passive chilled beam The location of a passive chilled beam needs to be considered in the design phase; however, basic principal is to avoid installation over the working places. The geometry of a dummy is more important rather than its plume. Contrary to popular beliefs, in the presence of a dummy, the downward flow from the beam is not affected by the plumes from the heat loads due to its weakness even if cooling powers would be low. In both the presence and absence of the dummy cooling power is 200-500 w (93-225 w/m). Only if an extra load is added or the load is shifted, an upward plume is built up. When it comes to air velocity under the beams, there would be a fluctuation in the presence of a dummy. Air velocities in the absence and presence of a dummy are 0.23-0.33 m/s and 0.10-0.15 m/s, respectively .
2-2-3-The effect of asymmetric workstation using chilled beam on air distribution in office An efficient office space is crucial for the workers to spend most of their time daily and having better productivity. As a result, further consideration need to be taken into account in terms of designing workstation. Therefore, drought risk should not be overlooked in order to meet worker’s needs. Drought risk is obtained due to the following reasons: a) If the workstation is located in the downfall area due to downfall of colliding inlet jets causing local maxima of air speed. b) If the workstation is asymmetric with layout of chilled beams, large scale circulation is provided causing more constant high air speeds on at the floor level .
CONDITIONING (HVAC) In designing the HVAC system for buildings, further consideration need to be taken into account in order to hinder condensation of moisture on the chilled water supply pipes and cooling coils. To achieve this goal, the dew point of the indoor air should be lower than the chilled water temperature. Basically, ventilation outdoor air (OA) and infiltration are identified as the main sources of humidity. As a result, dedicated outdoor air system (DOAS) and tight building envelopes are required in most climates. The OA humidity loads are handled by the DOAS before releasing to the space [1, 2, and 6]. 4-AESTHETICS’ POINT OF VIEW Since 50% or less of the ceiling is covered by chilled beams and the buildings services can be seen by occupants, architects and end users might not like the aesthetics of them . To overcome this problem, integrated service beams have been used such as lighting, cabling for powers, smoke detectors and so forth. Moreover, in order to decrease the visibility of the ceiling and in-ceiling services, they are painted in black .
5-ADVANTAGES OF USING CHILLED BEAMS Employing chilled beams whether active or passive has numerous upsides as follows: a) b) c) d) e) f)
Delivering sensible cooling directly to spaces  Reducing ventilation fan energy consumption  Reducing the quantity of OA to be conditioned  Being more efficient compare to conventional system (15 to 20%) [3,6] Eliminating the necessity for energy-consuming reheat of the cooled air [3,5] Reducing per-story buildings height by 0.1 to 0.4m 
6-DISADVANTAGEOUS In spite of several advantageous of using chilled beams, there would be few drawbacks that have been mentioned on the followings: a) Being more expensive than VAV systems (Variable Air Volume) costing around $80/m2 b) Enhancing the total cost of the HVAC due to limitation heating capacities of chilled beams  7-CONCLUSION .Chilled beams save a great deal of energy in terms of transferring cooling, ventilating of
airflow, using higher chilled water temperature and eliminating the need for reheating the cooled air. To achieve the best result of efficient cooling of chilled beam in false ceiling, the return openings of false ceiling should be located in the perimeter of a room. Furthermore, the size of its area should be doubled compared to the beam. When it comes to the asymmetric workstation using chilled beams in office building, workstation shouldn’t be located in the downfall area in order not to cause local draught risk. Besides, asymmetric workstation causes circulation in a room which results in high air speed on at the floor. On the other hand, in the presentation of dummy, the plumes generated by the heat loads do not have impact on downward flow; however, it declines the downward flow velocity.
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