Icing up of the evaporator
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Welcome to the PROBLEM PAGE. We find many people request assistance in the practical aspects of the industry. In response we will investigate the problem and endeavour to present the best possible solution. Thank you for all your questions sent in. Send your problems (and sometimes your creative solutions) to [email protected] with problem page in the subject line. You may include pictures. George Haskins sent in this interesting modification and writes: I found the following interesting scenario at a computer company, the combined air flow from the fans was not sufficient and caused icing up of the evaporator. The computer technician then partially blocked the condenser to remedy the problem. George, thanks for the pictures and the smile, yes we get to see many interesting fixes. One wonders at the combined cost of the fans and time spent. I performed a rough calculation and came up with the following: 2 x power supplies and 30 x fans @ R195.00 each and 3 hours labour at computer technician rates R 600.00 Total cost for solution R 6450, 00. More than a new, installed unit! Let’s not even mention the aesthetic appeal. Werner Mans asks: We have air handling units that either break their V belts or the bearings don’t seem to last as long as I would expect them to. When I discussed this in the workshop the result was a heated debate. This leads to my question, what is the correct way to align and tension a V belt? Thanks for the question Werner. Air conditioning is a diverse trade and this represents a mechanical area that is often overlooked. Maximum belt life is dependent on true alignment and correct tension. I will cover alignment first. Misalignment of belt drives results from shafts being out of angular or parallel alignment, or from pulley grooves being out of axial alignment. Types of misalignment are: Shafts not parallel Shafts misaligned Pulleys misaligned Correct alignment When aligning a “V” belt drive, bear in mind that the prime mover is adjusted to correct the alignment. • Tie a length of gut onto the shaft of the driven pulley. (You can use a straight edge if space allows) • Pull the gut across the face of the driven pulley and across the face of the prime movers pulley, keeping the gut taut at all times. • Look at the four points A, B, C and D as indicated in figure to see if the gut is resting on all of them. If they are, this will determine that the alignment is true. Experiencing problems of a technical nature, drop us a line at [email protected] with problem page in the subject line. Problem Page By Grant Laidlaw
description
I found the following interesting scenario at a computer company, the combined air flow from the fans was not sufficient and caused icing up of the evaporator.The computer technician then partially blocked the condenser to remedy the problem.
Transcript of Icing up of the evaporator
Welcome to the PROBLEM PAGE.
We find many people request assistance in the practical aspects of the industry. In response we will investigate the problem and endeavour to present the best possible solution.Thank you for all your questions sent in. Send your problems (and sometimes your creative solutions) to [email protected] with problem page in the subject line. You may include pictures.
George Haskins sent in this interesting modification and writes: I found the following interesting scenario at a computer company, the combined air flow from the fans was not sufficient and caused icing up of the evaporator.The computer technician then partially blocked the condenser to remedy the problem.
George, thanks for the pictures and the smile, yes we get to see many interesting fixes. One wonders at the combined cost of the fans and time spent. I performed a rough calculation and came up with the following: 2 x power supplies and 30 x fans @ R195.00 each and 3 hours labour at computer technician rates R 600.00Total cost for solution R 6450, 00. More than a new, installed unit! Let’s not even mention the aesthetic appeal.
Werner Mans asks:We have air handling units that either break their V belts or the bearings don’t seem to last as long as I would expect them to. When I discussed this in the workshop the result was a heated debate. This leads to my question, what is the correct way to align and tension a V belt?
Thanks for the question Werner. Air conditioning is a diverse trade and this represents a mechanical area that is often overlooked.Maximum belt life is dependent on true alignment and correct tension. I will cover alignment first. Misalignment of belt drives results from shafts being out of angular or parallel alignment, or from pulley grooves being out of axial alignment. Types of misalignment are:
Shafts not parallel Shafts misaligned
Pulleys misaligned Correct alignment
When aligning a “V” belt drive, bear in mind that the prime mover is adjusted to correct the alignment.• Tie a length of gut onto the shaft of the driven pulley.
(You can use a straight edge if space allows)• Pull the gut across the face of the driven pulley and
across the face of the prime movers pulley, keeping the gut taut at all times.
• Look at the four points A, B, C and D as indicated in figure to see if the gut is resting on all of them. If they are, this will determine that the alignment is true.
Experiencing problems of a technical nature, drop us a line at [email protected] with problem page in the subject line.
Problem PageBy Grant Laidlaw
The correct tensioning of “V” belts is of the utmost importance for the following reasons:If the “V” belt tension is too low, the belt is likely to slip, resulting in abnormal belt wear.If the “V” belt tension is too high, the belt life will be drastically reduced due to abnormal stretching and wear. Damage to the components of the drive, e.g. bearings, can fail prematurely due to the abnormal loads created by over-tensioning.
Also consider the following:Before tensioning ensure that the slack on all the belts is on the same side of the pulleys. If the belts are tensioned with slack portions in different positions, excessive strain will be imposed on the belts when they attempt to settle in a common position on the pulleys.
During the first 48 hours of operation, the belt tension should be checked and the belts re-tensioned.With multiple belt drives, each belt must absorb and equal proportion of the total load and must therefore be equally tensioned.
Multiple belts must be purchased in matched sets.This is due to the fact that although the belt specifications may be the same, slight differences occur between different production runs. In my experience unmatched sets can make it impossible to correctly tension the set of V belts as one or more belts will always be to under or over tensioned.
A general method that can be used when forced to do so, is to grasp one of the “V” belts between the finger and thumb midway along its span. If by using some effort it can be twisted between a ¼ and ½ twist, the tension should be sufficient for average requirements.Try to use the more accurate method where possible and especially when dealing with any high speed or specialised drives.
The most and accurate method of tensioning “V” belts recommended by all manufacturers, is the Belt Tension Indicator. This is a gauge which indicates the force required to deflect a belt 16mm per metre of the span (Centre distance) of the belt.
Tension the belts as follows:-• Measure the span of the drive.• Multiply the span length in metres by 16 to obtain the
belt deflection distance in millimetres.• Position the lower marking ring at the deflection
distance required in millimetres on the lower scale.• Position the upper marker ring against the bottom
edge of the top tube.• Position the belt tension indicator on top of the belt in
the centre of the span.
• Apply a force at right angles to the belt, deflecting the belt to the point at which the lower marker ring is level
with the top of the adjacent belt on multi-belt drives, see figure.
NOTE: For single belt drives a straight edge must be placed across two pulleys to act as a reference point for measuring the amount of deflection.
• Read off the force value indicated by the top edge of the upper marker ring.
• Compare the reading to the force value for the belt designations (Size) given on the table applicable to the make of Belt Tension Indicator being used. The belt should initially be tensioned to the higher value given in the table, to allow for the running in of the belt. If the force value measured falls within the values given on the table, the drive tensioning will be satisfactory. An example of a table is shown.
BELTDESIGNATION
FORCE REQUIREDTO DEFLECT BELT
Newton (N) Kilogram-force (kgf)
FORCE REQUIREDTO DEFLECT BELT
Newton (N) Kilogram-force (kgf)
10 4 - 5 0.4 - 0.513 10 - 15 1.0 - 1.517 20 - 3- 2.0 - 3.022 40 - 60 4.0 - 6.-32 70 - 110 7.0 - 11.0
• Loosen and adjust the prime mover to obtain the correct belt tension.
• Secure the prime mover and recheck the alignment and the belt tension as described.
• Repeat the exercise until the alignment and belt tension is correct.
Werner, I hope that this will help you set up your air handling units and create some clarity.
REFERENCES: Fenner SA
Greetings to all and thanks for writing in, looking forward to all your questions – Grant Laidlaw
