|
| Article - 2 >>
Efficient system |
| DUEX® is leading AHU manufacturer with installations at Wockhardt, Dabur, Nicholas Piramal, Film division, Infragro, Lipap, Cipla to name few. Single/double skin, sisw/didw Nicotra. Krugger/ Pullman blower, GI/SS construction, DQ/OQ/IQ/PQ with validation all under single roof. No two AHUs are same though technically specs are similar because lot depends on site condition, ducting, terminals, dampers, area class, process. That is why to have proper validation and end results detailed site survey, AHU details, duct autocad design and drawing, site supervision is must. Its like growing a child |
| |
| 1) Variable-air-flow: |
- Change air-flow as per requirement (CO2) and total pressure (static + velocity)
- DTp= DSp+DVp= DSp+((vin/4005) 2 -(vout/4005) 2 )
- Vin and vout is in ft/min
- V can be calculated from air flow (CFM) and area (ft 2 )
- Dual maximum strategy has maximum airflow set point in addition to minimum air flow set point and cooling maximum airflow set point.
- Set ventilation requirement to 0.15 CFM/ft 2 . This is in compliance with Title 24 ventilation requirement.
- In the early morning, for example, when the building does not require much cooling, the main fans will run more slowly, reducing the total air-flow through the system. However, even at this time, a VAV terminal box supplying a room with many occupants can fully open its damper, providing needed cooling. As classrooms begin to fill up during the day and the sun rises, generally heating the building, the total air-flow will increase as necessary. If some rooms remain unoccupied throughout a particular day however, the VAV terminal boxes for those rooms will remain closed.
- Each VAV terminal unit has a motorized damper, which opens and closes, on command from the main control system, to allow more or less air flow.
- If the amount of fresh air in the main air supply is sufficient to meet the indoor air quality requirements, but the air flow past the cooling coil is too little to cool the room, the internal fan in the VAV unit pulls in additional air from the room to increase the air flow past the coil
- The wall-mounted thermostat determines how much the supply air valve should open in order to maintain the room temperature
- The pre-programmed Direct Digital Control (DDC) system operates the equipment differently during occupied and unoccupied periods. This is another energy-saving strategy, which allows the air conditioning equipment to "rest" during periods when the building is unoccupied.
- Many sensors installed in the air handler give the DDC system the information it needs to control the fans, dampers, etc
|
| |
| 2) Duct design: |
|
- Ducts are run as straight as possible to reduce possible pressure drop
- Standard length straight ducts are used
- Avoid turns and bends
- Use flat oval duct if round ducts are not space fit
- Use spiral round duct for long run
- Use radius elbows than square ones
- Taps in low-pressure mains will have pressure drop no matter how they are designed. Use 90 deg spin in taps for round ducts and 45 deg taps for rectangular ducts
- Two consecutive elbow turns will have 50% more pressure drop than with elbows separated with long straight
- Generally pressure drop is 0.25-.3 WC, gradually reduce to 0.1-0.15 WC
- Reduce velocity from 4-6 m/s to 2.5 m/s at zonal level
- Fan should discharge into duct system that is as straight as 10 duct size at delivery Do not use liner much to reduce sound
|
| |
| 3) Cooling: |
- Water has more thermal density than air
- Air needs 400 CFM per Ton whereas water need only 0.13-0.33 CFM per Ton
- Package cooling has efficiency of 1.1-1.4 kW/Ton whereas Water chiller has efficiency of 0.8-1.0 kW/Ton
- Life 20 years
- Title 24 Version 2001 has efficiency requirement of 0.58 kW /Ton
- Maintain set-point at higher temperature that can still satisfy requirement of warmer zones
- Design coil for 2-2.5 m/s velocity with larger coil size, this reduces fan pressure design
- Use VFD
- Use chiller temp 15 deg C than 26 Deg C to improve coil efficiency by 20-40% (1-2 % efficiency increase at 1 Deg C fall in temp for coil; Optimize between chiller and coil
- Use low capacity pumps
- Use 4 f/s (1.3 m/s) fluid velocity. Friction increase in square with rise in fluid pressure
- For temp difference of 6 deg C- 0.4 CFM/Ton fluid is to be circulated than 0.2 CFM/Ton for 12 Deg C difference Pump HP varies in cubic with fluid flow, so reduce flow
|
| |
| 4) Fan: |
- Use airfoil fan when it comes to selection between air foil and plenum fans
- Title 24 requires VFD- Variable speed drives for 25HP motor and above. New 2005 version require the same for 10 HP motor and above
- Use demand based Static Pressure (SP) sensors at far distance
- Do not operate two parallel fans which put them into unstable region
- Avoid using pre-filters- They generally pass all dust an of really no se, only cause pressure drop.
- Specify final filters with dust spot efficiency 80-85 (MERV 12), Max drop at 2.5 m/s is 0.6 WC allowed
- Use extended surface filters, they are costly but have more life and less pressure drop and do not clog fast
|
| |
| Continue >> |
| |
|
| Download Features / Print the Features |
 |
 |
|
| Read More >> |
|
| |
| |
| |
|
|
