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  1. mdonner

    Electrical Room Ventilation

    Heat load from each device is found in the device's data sheet. Positive pressure will keep dust away but will consume more energy. Filter type depends on the application requirements: MCC may be NEMA 1, 4, 14 etc, and may provide the required protection. For high loads such as VSD, it is best...
  2. mdonner

    How to limit variable speed drive power draw

    I implemented the idea described in iOmega's reply in several projects some years ago (VFD digital input to triger preset speed, and turn on the catching circuit. Rule of thumb for fans: Power ratio is the cube of speed ratio, flow ratio is the speed ratio, pressure ratio is the square of speed...
  3. mdonner

    increasing flow will decrease AHU capacity?

    To Macbeth I have to disagree with your theory. Lower DT means constant "capacity" with increased GPM across the coil. Actually you refer to constant prevailing "load" and not to increased potential "capacity". With DESIGN heat load and increased GPM (beyond design...
  4. mdonner

    increasing flow will decrease AHU capacity?

    Water coil Heat transfer coefficient increases with water flow. Heat transfer rate (water to air) is directly proportional to the product of water flow rate and water temp rise through water coil. This means the AHU water coil has a larger capacity with increased water flow rate.
  5. mdonner

    solenoid valve and controller

    Tip Check solenoid current and power factor agains controller data sheet corresponding values. If exceeded, use properly sized buffer relay.
  6. mdonner

    Tumble Dryer Exhaust Problem

    I use an household dryer with embedded air-air HX. The heated (secondary) air has no odor and has very low humidity. The primary humid hot air is cooled by the ambient secondary air, and the condensate water (from the primary hot humid air) is piped to the drain. The additional required power is...
  7. mdonner

    MULTIPLE MOTORS ON AC DRIVE PACKAGE

    You mentioned contant torque application. If motors are fan cooled, going under 50% frequency may cause motor overheat to burnout.
  8. mdonner

    Heat Rejected to room by VSD's

    Rule of thumb is 3-4% of VSD nominal rating.
  9. mdonner

    Can I use a 30 KBTU compressor/cond with a 42KBTU coil?

    The answer is no, and this is why: Increased coil area and increased airflow, assuming coil temp does not increase, means more Btu/hr absoarbed from the conditioned space. To handle this, the condensing unit will have to increase condensing temp, lowering compressor capacity, when actually...
  10. mdonner

    Continuous Regenerative braking of a downhill conveyor

    No difference. No duty cycle limitations. Check with Reliance Electric / Allen Bradley (under Rockwell Automation) local rep./dealer
  11. mdonner

    Continuous Regenerative braking of a downhill conveyor

    I failed to mention an important aspect: The regeneration system is connected to mains power lines to supply the network when regenerating. If mains supply disappears for any reason, you will have NO BRAKING!!! You will need powerfull emergency braking/holding drum to kick in on mains failure.
  12. mdonner

    Continuous Regenerative braking of a downhill conveyor

    I suggest using a VSD in conjunction with an embedded/external regenerative breaking system. This may not be the cheapest to install, but I believe will have the lowest overall price (design, install, maintain, control, operate). Such a unit works in a cement factory for several years now...
  13. mdonner

    Lab Pressure Control

    Temp control (not on/off I presume) is optimized at full airflow capacity, therefore it is recommended not to very it. This means negative pressure control via exhaust control. Door undercut or grille is acceptable if the infiltration air quality is not important. Use HEPA filters on exhaust if...
  14. mdonner

    Change the coil but not the condensor/compressor

    I want to add some observations, based on the assumptions the calculated heat load is 30,000 Btu/hr and the calculated airflow is 1450 cfm: Thumb rule figures: 400 cfm/Tr: yours is 1450/2.5=580 (+45%) 350-700 sq ft/TR: yours 3300/2.5=1250 (>+78%). 030 evaporator at 67F WB RA and 40F evaporator...
  15. mdonner

    Data Room Cooling - High Ceiling

    I suggest to use return air hoods over hot spots (equipment), with diffusers over the isles.
  16. mdonner

    Change the coil but not the condensor/compressor

    1. Are you sure 30,000 btu/hr is enough for 330 sq ft house? (it depends on design conditions which you do not specify). 2. Too large evaporator may increase superheat to a value that will dammage the compressor (too high discharge temp.) 3. With design conditions and the known capacity and...
  17. mdonner

    Operating Induction Motor at Reduced Speed

    1. Do not try it if your load is of the constant torque nature. Copper loses can not be handled without external cooling. 2. Motor should have thermal protection/detection to prevent burnout.
  18. mdonner

    Operating Induction Motor at Reduced Speed

    I started many water pump applications, with pump idling at 10% rated speed, and none had temp rise problem (100F environment). I believe the reason is the low power consumption at reduced voltage (v/Hz=constant), so the reduced cooling (1:10 squared = 1:100 cfm) has no impact. Your figures show...
  19. mdonner

    Air Compressor Burning Up!!

    Your tank is about 4 cubic feet volume. With 1 cfm diverted for consumption, 6 cfm is pumped into tank, and it will work about 40 minutes to pump 4 cu ft. Than it will rest no more than 4 minutes (obviously less than 4 minutes, to keep pressure). Increasing compressor size will never give you...
  20. mdonner

    automotive hvac!

    Try this site: http://www.delanet.com/~pparish/index.htm

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