Energy saving System w/fan & pump

[mastertech]

I have an application in which a cooling tower cools the water that comes from the heat exchangers of a compressor.
I want to implement a energy-saving system, and I want to things: reduce flow when only one compressor is operating, and 2-variate the fan speed in the colling tower with the day/night temperature changes. I am having problems in this second part because I need to compare the outlet water temperature (in the tower) vs the wet bulb temperature of the air in order to develop an equation that relates the fan speed vs delta T. Does someone knows about wet bulb termomethers with PLC output and does someone has experienced similar applications?
thx.

 

[TD2K]

Why not just use the 'cold' water temperature leaving the cooling tower basin to drive your fan(s) speed directly? The cold water temperature will vary both as ambient temperature changes and its humidity (wet bulb temp) changes.

I suppose I don't understand what you are trying to acomplish with the correlation between wet and dry bulb you want to develop.

How are you adjusting the circulation rate, shutting off pumps, variable speed on the CW pumps, etc.

Your one comment lost me "Does someone knows about wet bulb termomethers with PLC output".

As far as the overall intent, I don't think I've heard of anyone getting quite this sophisticated. You might have some fans with variable pitch but others are just turned off and on as needed.

 

[svanels]

I do not think that it is that easy. It may work in a laboratory not in the real world, cooling towers are to remove big quantities of heat and are mission critical equipment working 24 hours a day, 7 days in a week, and a shutdown maybe once in 3 years.


1) First reducing the flow rate will alter the whole heat balance in your heat exchangers.

2) If the flow rate fals below a certain point, scale forming is increased, have you ever descaled tubes where the cooling water has been evaporated?

3) You have to adjust your chemical injection and monitoring.

4) You have to adjust your blowdown and make up.

5) A cooling system can bring a plant down.

In a normal system there are a lot of parameters which need constant attention and monitoring, and are covered by operational personnel, maintenance, laboratory and process specialists, what will be the impact of such system to the daily operation? Steven van Els
SAvanEls@cq-link.sr

 

[jonralph]

Just on the Wet bulb with PLC output. Your looking for a dewpoint meter/analyser, yes they are available.

 

[PacificSteve]

Your tower needs flows and pressure within a certain range. Decreasing the flow rate by, say 50%, would almost certainly put you outside this range. If you have multiple towers, you can do your motorized valve and weir tricks that will allow you to capture the pumping savings. But as others have cautioned, it would be good to have a handle on all the possible implications of system impact prior to making a hardware change. VFD is nice on pump, since you can always tell it to operate at 100% until you get other issues worked out.

If your blowdown is automated, maybe based on conductivity, and you calibrate the sensor monthly, you should be able to ovecome issues. Your chem feed will also need to react to actual system parameters, not just set amount in set time. These problems are surmountable.

I personally wouldn't get too complicated with the control system, since I have walked that road before. For the most part, the compressor HX system only sees the return water temp, so control to that. I suggest 2 speed fans instead of expense of VFD. Marley reps a good single tower or multitower fan speed controller. Works well.

If your intent is to save energy, make sure you know the impact of your changes on all downstream equipment, esp dryers.

I hope some of this is helpful. I could key in some specifics if I had more detail on your system configuration and geographic location, and energy cost.

Steve

 

[MortenA]

Did a quick check on google and come up with this:

http://www.optrace.com/

Best Regards

Morten