It can be used to demonstrate all three processes of transferring heat. The solar cooling load (SCL) factor is used to estimate the rate at which solar heat energy radiates directly into the space, heats up the surfaces and furnishings, and is later released to the space as a sensible heat gain. With this assumption, the amount of heat transferred through the surface is a direct result of the temperature difference between the space and outdoors. The culture of Japan still enjoys bathing in a hot water bath as a relaxing and healing experience. If you continue browsing the site, you agree to the use of cookies on this website. When the value for the shading coefficient decreases, more of the sunâs rays are reflected by the outer surface of the glass. 6B shows the fan in an off stage; 6C shows the fan when it is started; 6D is a draw-through with condensation drains. See our User Agreement and Privacy Policy.  have adopted the code with some region-specific modifications.Â. He also advised that the condensate pipe was not draining any water. We were surprised and couldnât think about what could have gone wrong. We went to the site and found that drain pan and the air handling unit floor was flooded and the fan inside the air handler was wet. When the coil section door was opened, however, the water in the pan drained very quickly. Â, We had studied the design of the condensate trap. We inspected the trap to figure that the difference in elevation between the AHU drain pan outlet and the exiting end of the U trap (termed here âHâ) was zero. The sensible and latent loads from ventilation are calculated using the same equations as for infiltration: It is important to know where the fan heat gain occurs with respect to the cooling coil. Similar to heat transfer by conduction through an external wall, the space can therefore experience a time lag between the time that the sensible heat is originally generated and the time that it actually contributes to the space cooling load. judgment, sound engineering principles, and local practices instead of blindly following suggestions. When warm, moist air hits the indoor cooling coil, itâs forced to shed some of its moisture as it cools. Similar to CLTD, the SCL factor is used to account for the capacity of the space to absorb and store heat. Air conditioning can be used in both domestic and commercial environments. The proportions of sensible and latent heat must be known in order to determine the proper condition of the air being supplied to cool the space. as it relates to condensate disposal. Courtesy: EXP Global, Code requirement and enforcement within the U.S. varies from one location to another. In mechanical rooms, insulation will prevent any sweating, and prevent potential trip hazards. Provides features for copy-and-paste from displayed reports into other documents, and for saving reports as RTF-format documents. The process of comfort heating and air conditioning is simply a transfer of energy from one substance to another. A commercial–grade load calculation software to perform these calculations was used. Ventilation rate was calculated per Chapter 4 of 2015 International Mechanical Code. Assumptions are listed below. See results in the Table 2: Â, Building size = 10,000 square feet, Occupancy = 250 square feet/person, Miscellaneous load = 1 workstation/personÂ, The identical orientation of the building for all zonesÂ, U values for roof, walls, windows as per the 2013 edition of ASHRAE 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings.Â, Figures 4A, 4B and 4C: Example of problems due to incorrect design and installation of condensate piping. You can change your ad preferences anytime. The sum-of-peaks and block airflows for sizing the supply fan in these two cases can then be calculated as follows: Similar to the single-space example, the cooling coil in the HVAC system serving these two spaces must be capable of handling the space sensible and latent loads, plus any additional loads that only affect the coil. Heating, ventilation, and air conditioning (HVAC) is the technology of indoor and vehicular environmental comfort. This moisture, in the form of cold condensed water is removed from the building down the condensate drain. This leads to the accumulation of water in the drain pan and resulting flooding inside the AHU (see Figure 1). Â, Figure 1: Drain pan flooding example illustrates the situation discussed. 5A is a general example of a blow-through AHU. The piping from the cooling coil to the condensate pump reservoir should be installed with minimum 1/8-inch slope to enable gravity flow. The condensate shall be collected into the reservoir. Once the water reaches a certain level in the reservoir, the float switch within the pump will turn it on, and water is pumped from the reservoir to a safe location. Â, Water leaks in applications such as data centers can be very costly. For example, if the supply ductwork is routed through an unconditioned space, such as a ceiling plenum or an attic, heat can be transferred from the air surrounding the duct to the supply air. Looks like youâve clipped this slide to already. Multiple-Space Analysis supply fan Room 101 Room 102 cooling coil 69. This helps ensure that if a backup occurs, the water properly trips the switch instead of overflowing out of the vent. Water-cooled condensers involve a heat rejection loop where condenser heat is dissipated to the environment via water. In our example, outdoor air for ventilation is the only additional load affecting the cooling coil. Heat generated by lights in the space is a significant contribution to the cooling load. The walls and roof that make up a buildingâs envelope have the capacity to store heat energy. This energy can be classified as either sensible or latent heat energy. The reason this was happening was the coil section was at negative pressure since this was a draw through AHU. Since the âHâ of the trap was zero, the suction pressure through the U trap inhibited the draining of any water. Now, determine the heat gain by solar radiation through the windows on the west-facing wall of our example space. He said the cooling coil drain pan inside the air handler was flooding. Assuming that the space in our example is of average construction and kept at a positive pressure relative to the outdoors, we estimate 0.3 air changes/hr of infiltration. Finally, that utilizes outside air ( free cooling ) and minimizes the runtime for the chilled water plant. Seminar presentation of HVAC cooling load calculation. Conduction through the roof, exterior walls, windows, skylights, ceiling, interior walls, and floor, as well as the solar radiation through the windows and skylights, all contribute only sensible heat to the space. When the fanÂ,  it would create a positive pressure (blow-,  fan) and pushes the water away from the pan. Recapping: PSI of water pressure at the base of any column of water of height H in feet = H x 0.434. The pan can have a water leak detection sensor installed at the lowest point.  resulting into proper draining of the system. Courtesy: EXP Global, Drains Based on the calculations performed in Period Two, the total load on the cooling coil is 99,195 Btu/hr (8.3 refrigeration tons) [28,978 W]. This particular table * includes CLTD factors for a west-facing wall similar to the type used in our example building. Determine the internal heat gain from people in our example space. This table shows the components of the space sensible load at both 8 a.m. and 4 p.m. (The cooling loads at 8 a.m. were calculated using the same methods introduced in Period Two.). A factor called the cooling load temperature difference (CLTD) is used to account for the added heat transfer due to the sun shining on exterior walls, roofs, and windows, and the capacity of the wall and roof to store heat. It can lead toÂ, Air locking in the pipe due to improper supports, Incorrectly supporting of condensate pipe will result into sagging of the pipe creating anÂ, . It came at the cost of $2,000, which included the cost to raise the AHU by 4 inches. The client was not happy about the change. There have been other cases where the AHU had to be raised, or condensate pumps had to be installed because the details were not thought out during design. The cost of these changes could be in the tens of thousands of dollars. Â, Ignoring coil condensate design makes engineers look incompetent. The CLTD is substituted for ïT in the equation to estimate heat transfer by conduction. Human or Thermal comfort refers to the range of temperature, humidity and air movement conditions that most people feel comfortable most of the time. Clipping is a handy way to collect important slides you want to go back to later. It is always a good practice to provide drain pipes with tees. Assuming that the air being recirculated from the space is the same condition as the space, we can determine the condition of the air entering the cooling coil. 5B shows a trap for a blow-through AHU with the fan off; 5C shows it with the fan started. Estimating the heat gain by conduction through a window is very similar to walls and roofs. Plate-type heat exchangers (a special kind of surface exchanger) are also possible, but appear to be more common in liquid-to-liquid heat transfer ⦠The relative humidity lies between 30%-60%. There can be a scenarioÂ,  are operating at different static pressure,  static pressure will result in drawing air through the drain line of another unit. q = air volume flow (cfm, cubic feet per minute) dw gr = humidity ratio difference (grains water/lb dry air) dw lb = humidity ratio difference (lb water/lb dry air) 1 grain = 0.000143 lb = 0.0648 g. Psychrometric chart; Example - Cooling Air, Latent Heat. The pan must be drained continuously to prevent overflowing and causing, , Chapter 1 Section 8: numerical calculation of moist air properties.Â, elevation. Where required, the signal can also be used to turn off the cooling equipment when water is detected. Â, When multiple units with pumped condensate are headered together, use inverted traps and pitch header in the direction of flow. Â, Search Products And Discover New Innovations In Your Industry, Sushil Kumar PE, CEM, LEED AP, MBA; Sagar Kanchi, EIT; EXP Global, Los Angeles.  directly state that the drain line must be insulated. When the sunâs rays strike an opaque surface, however, a certain amount of radiant heat energy is transferred to that surface, resulting in an increase in the surface temperature. See our Privacy Policy and User Agreement for details. Thanks to reader Gary A Sale for pointing out confusion in an earlier version of the text above. The average adult, seated and working, generates excess heat at the rate of approximately 450 Btu/hr [132 W]. In Period Two, we calculated the components of the space cooling load at 4 p.m. Room 102 is exactly the same as room 101, except that the exterior wall faces east instead of west. HVAC COOLING LOAD CALCULATIONS AND PRINCIPLES Sensible Heat Gain â is the energy added to the space by conduction, convection and/or radiation. Air conditioning (often referred to as AC, A/C, or air con) is the process of removing heat and moisture from the interior of an occupied space to improve the occupants' comfort. Courtesy: EXP Global, For blow-through units, the trap must be designed as shown in Figures 5B and 5C to avoid the problems associated with condensate traps. Ideally, it is recommended to have ½ inch of safety factor for any unaccounted increase in pressure. This also would take care of any increase in pressure drop due to dirty filters over the period. Courtesy: EXP Global, Table 1 gives an overview of how the amount of condensate collected varies in different climatic conditions. Â, There could be various scenarios where incorrectly installed trap and condensate piping can lead to issues. We would like to show you a description here but the site wonât allow us. The quantity of air required to offset the space sensible heat gain is determined using the following formula: The next step is to either assume the supply air dry-bulb temperature and calculate the supply airflow, or assume the supply airflow and calculate the supply air temperature. The vent opening should always rise above the trip level of the condensate overflow switch when it is in the primary drain line or pan or above the secondary/auxillary overflow port on the primary drain pan. When a drain line is PVC, the IMC dictates that it should be supported every 4,  when horizontal (while maintaining proper pitch) and every 10. Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. Using this U-factor, we will determine the heat gain, by conduction, through the eight west-facing windows. 6A is a general example of a draw-through fan. The cooling load for a space can be made up of many components, including: These load components contribute sensible and/or latent heat to the space. It should be noted that the data in this table are based on the following assumptions: Using CLTD instead of ïT, we will determine the heat gain, by conduction, through the west-facing wall and the roof. This helps ensure that if a backup occurs, water properly trips the switch instead of overflowing out of the vent. In most situations, ½,  or flexible elastomeric pipe insulation (min, Some municipalities do require drain inside the structure be insulated to prevent condensation.Â,  drain pipes with tees. It says that condensate must be disposed into an âapproved locationâ and that it should not dump on walkways, streets or alleys as to âcause a nuisance.â This leaves a lot of wiggle room for interpretation and much authority to the AHJ and design professionals to establish what is and what isnât an âapproved location.â Â, Figures 7A and 7B: Drain trap with tee for clean out for large AHU. The pan can have aÂ,  installed at the lowest point. Imperial units: The flow rate of chilled water into the evaporator is measured as 12,649ft3/h and the chilled water inlet temperature is 53.6*F the outlet temperature is 42.8*F. Now lets look at how to calculate the cooling capacity of a chiller in imperial units. In mechanical rooms, insulation will prevent any sweating, and prevent potential trip hazards. It is also based on similar assumptions as the CLTD tables for walls and roofs. If the supply fan in this example delivers a constant volume of air at all times, it must be sized by summing the peak sensible loads of both spacesâ137,040 Btu/hr [39,710 W]. In the IâP system of units, the unit for measuring the quantity of heat is the British Thermal Unit (Btu). Based on the table in Figure 36, people participating in moderately active office work generate 250 Btu/hr [75 W] sensible heat and 200 Btu/hr [55 W] latent heat. It cameÂ,  The client was not happy about the change.Â, There have been other cases where the AHU had to be raised, or condensate pumps,  and algae growth when not noticed early.Â, In engineering terms, condensation occurs when air hits a surfaceÂ, Latent heat is transferred by moisture inÂ, The higher relative humidity also means that the moisture content of the air is higher (expressed as the humidity ratio. Radiant heat is similar to light, in that it travels in a straight line and can be reflected from a bright surface. If the west-facing wall of our example space was completely shaded at all times, the conduction heat gain due to the wall would be 388 Btu/hr [133 W]. Because this resulting supply air temperature is different than the 55ºF [12.8ºC] that we assumed, we need to recalculate the supply airflow. Use Table 307.2.2 for condensate pipe sizing. Â, 2015 IMC dictates a 1% minimum pitch of the drain which is equal to 1/8 inch fall for every 12 feet of horizontal run. Wherever practical, it is safer to use ¼ inch of fall per foot to ensure proper drainage. Â, Drains can be made from many materials such as acrylonitrile butadiene styrene, chlorinated polyvinyl chloride, polyvinyl chloride, steel and copper. Latent Heat Gain â is the energy added to the space when moisture is added to the space by means of vapor emitted by the occupants, generated by a process or through air infiltration from outside or adjacent areas. Additionally, the economizers can pull in outside air to satisfy the demand for cooling from the local fan coil units. There are a number of methods available, such as hot-gas defrosting for direct expansion systems, water defrosting and electric defrosting. At Hour 17, the CLTD for a glass window is 13ºF [7ï°C]. Air movement, adequate fresh air, cleanliness of the air, noise levels in the space, adequate lighting, and proper furniture and work surfaces, are just a few of the other variables that contribute to making a space comfortable for its occupants. Search Products And Discover New Innovations In Your Industry!! When the fan starts, enough head to make sure water is not backed up into the system. This clinic, however, will focus only on the aspects of thermal comfort. Although often not applicable, a simplifying assumption when estimating the conduction heat gain through an exterior surface is to assume that the surface is completely shaded at all times. CxEnergy and the AABC Commissioning Group (ACG), By Sushil Kumar PE, CEM, LEED AP, MBA; Sagar Kanchi, EIT; EXP Global, Los Angeles, the condensate pumps and condensate pipes, requirements for condensate disposal perÂ, the cooling coil drain pan inside the air handlerÂ,  surprised and couldnât think about what could have gone wrong.Â, , the water in the pan drained very quickly.Â, the difference in elevation between the AHU drain pan outlet and the exiting end of the U trap (termed hereÂ, Once we fixed the trap, the problem went away. The Btu is defined as the quantity of heat energy required to raise the temperature of 1 lb of water 1°F. "Refrigeration" is sometimes added to ⦠Courtesy: EXP Global, Once we fixed the trap, the problem went away. Although the 1997 ASHRAE HandbookâFundamentals contains new, more advanced methods of estimating solar heat gain through glass, they are beyond the scope of this clinic. Solar heat energy is generated by the sun and radiated to earth. 7. The unit operating with greater static pressure will result in drawing air through the drain line of another unit. N*V Volume / 3600=0 .0213, Q sensible =0 ... as well as in view of the impossibility of a ferry crossing in winter due to the formation of ice cover on water bodies. This vent is after the trap and must remain open to be effective. Evaluating this during design can preventÂ, to avoid the problems associated with condensate traps.Â, of safety factor for any unaccounted increase in pressure.Â, increase in pressure drop due to dirty filters over the period. Sometimes combinations of these methods are employed, e.g., hot-gas defrosting followed by water spraying or hot-gas defrosting of coils with electric tray heating. 6. Programs a. DDC-PID Loop Control 8. It's obtained by dividing the sensible cooling load by the total cooling load. Donât dump condensate in places that couldÂ,  condensate drain inside diameter should not be smaller thanÂ,  and should not be smaller than the drain pan outlet diameter.Â,  is sufficient for up to 20 tons according to the IMC unless the drain outlet size is larger thanÂ,  minimum pitch of the drain which is equal to 1/8,  of fall per foot to ensure proper drainage.Â,  PVC is by far the most common.
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