COOLING TOWER SELECTION WRONG 1

[moideen]

I have a cooling tower; capacity mentioned in submittal that 450 ton. Centrifugal chiller capacity is 450 ton. Very clear cooling tower is undersized. In the summer running two towers for one chiller. As per the same document, the condenser flow rate is 1350 gpm and range 10F. Then capacity will be 1350*500*10=562 ton. I don’t know what happened in design and selection time. I am planning to increase the capacity and improve the efficiency of chiller. Stiil I have a confusion, why the design eng selected 1350 gpm for 450-ton chiller

 

[DrRTU]

Cover the basics first with known data. 1. Hire a balance contractor to measure the condenser water flows. Inspect all strainers and pressure gauges first. Verify sump inlets and header nozzles. Run thru combination of pumps. The 6” is undersized for 1350 gpm - tower isolation vlv may not be fully open. 2. Work with SPX rep to inspect tower. Fan and fill must be correct. Verify rpm at fully HZ at drive. 3. At full chiller flow, utilize flow and temps at tower & chiller. Run thru chiller and tower flow combinations.

 

[lilliput1]

Consider also adding cooling tower discharge cowl to discharge exhaust above the wall enclosure to avoid recirculation of discharge to intake. Confirm also that the distance between the wall and cooling tower is at least equal to the height of the cooling tower fill.

 

[moideen]

i have a related question. not this tower. another tower brand MEZAN, it's fills are splash fills. is it possible to replace it with film. because film fill is very efficient compare to splash fills.

 

[LittleInch]

Start a new post - it gets very messy otherwise and add some more data, drawings, photos etc

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[moideen]

UPDATE
I checked actual water flow with a water flow meter, job done by a company whose main activities are water balancing in the chilled water system, found the flow rate is maximum 600 gpm through one pump. Design 1350 gpm!!!

 

[itsmoked]

ouch..


Keith Cress
kcress -

http://www.flaminsystems.com

 

[moideen]

When running two pumps, flow rate of each pump comes down to 300 gpm; I suspect the problem may be any restriction in suction side. still checking..................

 

[LittleInch]

I don't think the restriction will be on suction side as this is essentially at atmospheric pressure.

Sounds to me more like someone got theirs sums very wrong when working out the required differential head / pressure required or there is some sort of blockage / partly open valve somewhere in the system.

The obvious ones to check are:
Is the electrical supply what the motor needs ( Voltage, frequency etc)
Are the motors going the right way around?
Is there any VFD drive?
Is there a blocked filter somewhere?
Is the water level correct in the tower collection pond?

Back in your post of 29 Nov you said the pump trips on high discharge. High what? Pressure? temperature? Amps?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[moideen]

LITTLEINCH:The obvious ones to check are:
Is the electrical supply what the motor needs ( Voltage, frequency etc)-OK
Are the motors going the right way around?-WHAT YOU MEAN
Is there any VFD drive? NO
Is there a blocked filter somewhere? NEED TO BE RE-CHECKED, SUCTION SIDE FILTER AND FILTER BEFOR THE CONDENSER ALREADY CLEANED.[highlight #FCE94F][/highlight]
Is the water level correct in the tower collection pond? LEVEL OK

Back in your post of 29 Nov you said the pump trips on high discharge. High what? Pressure? temperature? Amps? HIGH DISCHARGE PRESSURE

 

[LittleInch]

If the motors are three phase supply, then depending on how you wire the motors will depend on which way around they spin.

There is usually an arrow on the motor or pump (or both) showing which way they should rotate. When you start and stop the pump you can normally see which way the motor rotates. It is an easy thing to check but a centrifugal pump will work in both directions, but be much less effective the wrong way round. It's not common but does happen.

The degree of lack of flow is a lot and the only other thing is whether someone has mistaken a requirement in metres head for a requirement in feet or some other sort of gross error if it's not a mechanical issue like a blockage or partially closed valve.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[moideen]

Little Inch: I will recheck the direction of the pump. you are correct that there is no possibility for any blockage. Because ampere is correct as per the motor nameplate.

 

[LittleInch]

You also need to start measuring pipe sizes and lengths and number of elbows etc to be able to calculate what the differential pressure needs to be at either 1350 or 2700 gpm and then compare it to your pump curves.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[moideen]

LittleInch :very true, i have no cad drawings to measure the length and count the number of fittings. Planned to take the measurement physically on site. Thank you

 

[moideen]

pump flow direction is correct, name plate kw is 18.5 and amps draws 30A.

 

[LittleInch]

Well then you need to work out if the original design was incorrect or the pump size incorrect for your 1350 gpm.

BTW it is very unlikely that two equal pumps in parallel will actually do 2700 when sized for 1350. The only way is if the pressure loss through the chillers is a large part of the pressure losses and the second one only comes on line when more flow is required.

You seem to have narrowed the issue down to water flow rate not being what was anticipated.

What are you planning to do next?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[moideen]

LittleInch: now i am trying to measur the actual head loss throughout the loop.

 

[Bos88]

HI Moideen,

Based on your 18.5 kW nameplate, the head should be around 60 feet for the pump (1350 GPM). Using 15 Feet for tower, 20 feet chiller, that gives you about 25 feet for the piping/valves.

 

[moideen]

LittleInch: i checked the chilled water drawings, cannot see any piping issues. 8,10 and 12 inch pipes is suitable as per the design flow. 8"@ 1350gpm head loss 2.8ft/100ft,10@2700 is 3.3ft/100 ft. please see the drawings attached

 

[Bos88]

The drawing shows the pumps to be rated for 1700 GPM. Typo?

 

[moideen]

Bos88 :but in shedule and chiller capacity, pump urve....shows 1350 gpm.