1、Dinesh Jaikumar is the Director - Projects at SunGreen Ventilation Systems Pvt ltd, Chennai, India. He has a Masters Degree in Industrial Engineering from the University of Texas, Arlington. HVAC solution with Evaporative Cooling System and Wind Driven Roof Ventilator Systems Dinesh Jaikumar ABSTRAC
2、T Wind driven roof ventilators (WRVs) and Evaporative Cooling Systems (ECS) have been in existence for quite some time and are highly energy efficient with considerable savings achieved in terms of operation and capital expenditure costs. This paper is about the use of evaporative cooling solutions
3、combined with wind driven ventilation in order to achieve energy efficient systems that provide the necessary comfort conditions inside the concerned industrial building space. INTRODUCTION Working comfort and reduction in pollution are two important parameters desirable for any industrial environme
4、nt, as they have direct impact on the workmen health, absenteeism of workmen, productivity etc. Energy efficient, sustainable solutions are the order of the day; considering the need to reduce the carbon footprints and costs, both in terms of initial capital as well as operating costs. Below are two
5、 case studies providing design details and result from the system installed at varied industries across India. Wind Driven Roof Ventilators (WRV) Wind driven roof ventilators are installed on the roof of a building with customized base plate adapters. They work on differential pressures / temperatur
6、es and wind energy and is noiseless while in operation. Strategic location of WRVs plays as an important role in achieving optimum results, particularly when working with in tandem with a forced fresh air system. The aptitude of the designer is an important factor for deciding on the locations. Key
7、factors including the geographical location of the building, the prevalent conditions, work environments, heat load locations, workmen locations, forced supply air in place are taken into account while deciding a WRV system. In most cases, the WRVs are concentrated at areas where high heat generatio
8、n and pollutants are present and 24-inch (610 mm) throat diameter WRVs are commonly used. Evaporative Cooling Systems (ECS) Evaporative Cooling systems are widely used around the world to provide comfort conditions at fraction of the cost of conventional air conditioning systems. The concept is not
9、new, ancient civilizations used adaptations of the same concept depending on specific applications, albeit not with as much efficiency as modern times. The evaporative cooling systems used in the below case studies use wet cellulose evaporative cooling pads through which hot dry air is forced where
10、the hot air picks up the moisture resulting in cold air. ECS could be used for both spot and zone cooling applications depending upon the workmen locations and conditions required inside the space to achieve efficient as well as economical solutions. AIR FLOW PATTERNS AND AIR BALANCING Airflow patte
11、rn and air balancing are two important factors considered while providing a general ventilation (GV) or an ECS to achieve the comfort condition. In a GV system proposed for an industry with WRVs, the locations of the WRVs are based on the conditions mentioned earlier. Fresh air is to cover most part
12、s of the building while shorter airflow path is considered for the heat generated from the machinery and other processes. Thereby restricting hot air to other parts of the building and ensuring better work environments at zero operating costs. While ECS is used in an industrial environment further i
13、mprove the work environment, air balancing plays a role in achieving efficiency since proper balancing is mandatory to achieve desired results. Quantified exhaust system is thus necessary and WRVs are used for the same, their installation is on the roof facilitates better exhaust since heat expands
14、and moves up. A strategic location of both these units complimenting each other is important. CASE STUDIES Two examples of varied Industrial environments where the above-mentioned systems have been incorporated have been provided below. Design considerations, details and end results have been quanti
15、fied. Garment / Apparel Manufacturing Company Problems A typical garment industry such as the company cited in this case consists of various processes including cutting, stitching, checking, ironing operations. The high workmen concentration, heat generation in a few processes contributed to discomf
16、ort, low morale / productivity. Sweating led to quality concerns on the end products. Geographic location and Site analysis The number of workmen working inside the space, the machinery involved, and the type of building they were working under was analyzed. The outdoor design data was checked for f
17、easibility ECS along with WRV. Project Detail: Garment Manufacturing Industry Location: Coimbatore, TamilNadu, India Latitude Deg.N: 11 Altitude Mtrs: 409 Table 1 Outdoor Design Data Temperatures Summer Deg F Monsoon Deg F Winter Deg F DB 98(310K) DB 82(301K) DB 65(291K) WB 76(298K) WB 75(297K) WB 5
18、7(287K) RH % 37 RH % 72 RH % 60 Wind Speeds Summer Km/ Hr. Monsoon Km/ Hr. Winter Km / Hr. 15(9.3m/hr.) 10(6.2m/hr.) 10.5(6.53m/hr.) Table 2 - Design Data Outside Temperature /Design Temperature 98 F (310K) /82.4 F (301K) Building Size 360 ft. x 140 ft. x 18ft ht (110mx43m x 5.5m) Total Floor Area 5
19、0400 Sqft (4682 Sqm) Total Workmen 500 ppl Building Type Pre Engineered Steel Building - GI PUF Insulated sheets Design Feasibility ECS It was evident with the above data; ECS was suitable for comfort cooling in the given area. WRV Wind speeds suited WRV system along with the 24 hr. forced supply sy
20、stem from ECS. Design Basis A heat load calculation for the building was carried out to work on a comparative statement between the ECS/ WRV systems against a conventional Air Conditioning System. General formula, Heat Load (Q) =Area x U-factor x T. 1. Summary Total Heat Load (Includes machinery, Oc
21、cupant Loads, building loads etc.)Q (Total): 1620029.44 BTU (1709221781 J) Sensible Heat Gain: 1345029.44 BTU (1419081381 J) i.e. 135TR Table 3 - Evaporative Cooling System - Design Outside Temperature 98 F (310K)- DB / 76 F (298K) - WB System Cooling Efficiency 90% Cooling System - Outlet DB Temper
22、ature 77.1 F (298K) Total Air Volume required for achieving indoor design conditions = Indoor sensible heat gain (btu)/ 1.08x(density ratio (0.95) x (Indoor desired dry bulb - leaving dry bulb temp of cooler) = i.e. 247348 CFM (116735 L/s) Air Quantity / Unit of ECS: 10000 CFM (4719L/s) - Total Numb
23、er of Units 25 Nos Air Velocity at 8ft height through 360D Diffusers - 2583 Fpm (13.1m/s) / Fabric Duct - 500 Fpm (2.54m/s) Table 4 - Air Changes Achieved with the 100% fresh air Evaporative Cooling System Total Air Volume - L x B x Effective Height (10ft) 50400 cft (1427169L) Total Air Volume throu
24、gh Evaporative Cooling System 260000 CFM (122706L/s)/ 15600000 CFH Total Air Changes/ Hr. (ACPH) 31 Exhaust Air Quantity (Assumption - 90% of Supply Air Volume) 222613 CFM (10672L/s) Wind Driven Roof Ventilation - Model - 24“ Throat Dia - Exhaust Capacity / unit / Total Number of WRV 1500 CFM (708 L
25、/s) / 148 Nos Execution And Performance Analysis The roof mountable compact ECS systems were installed at zones where process was involved with high workmen concentration. The WRVs were installed at locations where the heat loads were higher, (ironing area) for shorter airflow path from the process.
26、 A schematic drawing (Figure 1) is provided below. The ECS was installed with drop down ducts with 360 Deg diffusers. The distance between them was based on the angle of flow. Varied velocities namely low velocity for cutting areas with fabric ducts (micro perforations) was chosen so that air flow d
27、oes not affect dimensional accuracy by causing disturbance to the fabric lay. Temperature sensors were placed at various zones where occupancy was high (Locations marked in the drawing) to take regular readings of the temperature. The temperatures achieved were within the acceptable range of operati
28、ve temperature and humidity as per section 5.2.1.1 of ASHRAE Standard 55-2004 for clothing insulation of 0.5clo. The airspeeds were high in majority of areas making the feels like temperature much lower. The efficiency of the WRVs was acceptable considering that the temperature / humidity readings a
29、t the higher heat load areas including the ironing zone was within the acceptable temperature limits. With continuous operation of ECS system the objects, structures inside the plant were cooled. The floor temperatures were reduced which also provided the required comfort Occupant survey was carried
30、 out in accordance with ASHRAE Standard 55-2004 at various ECS system operation levels and outdoor weather conditions to validate the system and a majority of over 95% were convinced with the comfort provided by the system Figure 1 (a) Section view A-A with the drop down ducts, diffusers with refere
31、nce to workmen height.(b) Top view showing the location of ECS along with the WRV. Energy and Cost Savings - Comparison The energy consumption of ECS system was measured in a periodic manner every 5 days over a year. The measured readings were normalized with the outdoor temperature at the given tim
32、e. Since the total air volume required for cooling was served with multiple individual units, during times when the outside temperature was already below the acceptable range of operating temperatures, the number of units /total air volume supplied was reduced only to meet the minimum fresh air requ
33、irement as per ASHRAE Standard 66.1-2007. The quantity of units / air volume was increased with increase in outdoor temperatures. All units/total air volume was used when the outside temperature was higher than the design requirement. Thus enabling higher savings than functioning in full load capaci
34、ty. The comparative Air conditioning costs were predicted based on the manufacturers average power consumption details provided. Table 5 - Energy Requirement Comparison Item Description ECS with WRV Conventional A/C Total Number of Units (Nos vs. TR) 26 Nos 135 TR (475KW) Power Consumption Power Con
35、sumption / Unit (KW) 1.15(1.5hp) 1.5(2.0hp) Total Power Consumption (KW) 29.9(40hp) 202.5(271hp) Water Consumption Avg Water consumption / Unit / Hour (Litres) 25(6.6g) NIL Total Water consumption / Hr. (in Litres) 650(172g) NIL Total Water consumption / Year (in Litres) 5694000(1504196g) NIL Energy
36、 Consumption Summary Energy Consumption / Month (KW) 21528(28870hp) 145800(195521hp) Energy Consumption / Annum (KW) 258336(346434hp) 1749600(2346252hp) Annual Energy Savings With ECS Conventional Air conditioning was prohibitive in costs. WRVs It was ideally suited due to the slow stratification wi
37、th displacement ventilation of hot air making it a safer option than powered exhaust pulling air at higher velocities, which could be a health hazard. Improved distribution and zero operation cost factors were also considered in the decision-making. System Design The production involved a lot of hea
38、t, which was also a process requirement, and thus cooling of the whole plant was never an option. Considering providing fresh cool air for the workmen to carry out the process comfortably as well also to dilute the space with surplus fresh air, 100% fresh air-spot cooling was decided upon. The exhau
39、st of air as mentioned in the earlier segment was designed to be carried out with WRV located at areas where the major heat and fumes where involved, the concentration of the units was planned in and around the building for slow dilution and displacement of air. Sensible Cooling Load (Q) - 1.085(i.e
40、. Specific heat x density of air) x Air Volume x T Heat Load (Q): 3645600 Btu (3846312154 J) i.e. 304 TR Table 9 - Evaporative Cooling System - Design Outside Temperature 110 F (316K) - DB / 75 F(297K) - WB System Cooling Efficiency 90% Leaving DB temperature from Cooling System 78.5 F (299K) The ab
41、ove conditions exceed the design requirement. Its also suitable for operations during colder months without the water module being used enabling more savings. Total Air Volume: 120000 CFM (5664 L/s) Spot Velocity: 3600 ft./min (18m/s). No of ECS Units: 12 Nos. Flow Direction: Back of the workmen, Pr
42、ovides comfort cooling, reduce effect of heat / fumes from process. Table 10 - Wind Driven Ventilator - Design Details Floor Area of Building / Height 86000 Sqft (7990 m2) / 35 ft. (11m) Total Air Volume / effective zone height for displacement 1290000 Cft (36533 m3) / 15ft(4.6m) Total Air Changes /
43、 Hour Considered 15 ACPH Total Air volume to be changed/ Hr.: Volume x No of ACPH - 19350000 CFH (9132183 L/m) WRV system: 24inch(610mm) Exhaust Capacity / unit: 102000 CFH (48138 L/m), Qty: 190 Nos. Execution And Performance Analysis The compact roof mountable ECS systems were installed on the roof
44、 along each line with GI circular insulated ducting with nozzles. The airflow direction from the nozzles was from the opposite direction of the heat radiation from the process. Considering higher air volumes per spot at lower temperatures from the nozzle outlet (78.5F(299K), the air temperature arou
45、nd the workmen was within the acceptable range of operative temperature and humidity as per section 5.2.1.1 of ASHRAE Standard 55-2004 for clothing insulation of 0.5clo. The higher outlet velocities thus reducing heat and fumes from the process also contributed to this air temperature. The WRV syste
46、ms were located above the formation process tanks considering the fumes generated. It was also installed along the process lines for continuous air changes from the required locations. This way the path of the fumes was shortened and removed from source and thus not displacing to other areas of the
47、space. Occupant survey was carried out in accordance with ASHRAE Standard 55-2004 at various outdoor weather conditions to validate the system and a majority of over 89% of the occupants was convinced with the comfort provided by the system. Absenteeism of workmen was reduced drastically which also
48、contributed to better productivity. . Figure 2 (a) Top view showing the location of ECS along with the WRV. (a) Section view A-A with the drop down and horizontal ducts, workmen locations with airflow directions. Savings in Energy and Costs The energy consumption of ECS system was measured in a peri
49、odic manner every 15 days over a period of 1 year. The measured readings were normalized with the outdoor temperature at the given time. The units were functioning in full quantity all through the year considering the application, however the water circulation mode was switched off during monsoons and winter, which enabled further savings. The comparative Air conditioning costs were predicted based on the manufacturers average power consumption detail considering that measuring was not an option since the air conditioning system was not commissioned and is only used f
