I plan on using 7.5 gpm RO effluent for CT makeup. The water is softened and then put through an RO; I am having the water tested this week. Does anyone have any ideas on designing a small (250 gallon) tank with a level sensor that would communicate with a VFD to slow/speed up the pump as the level sinks/rises in the tank?
Is there an off the shelf solution?

Ed Brady
edbrady1@verizon.net

Thanks, but if the effluent is better quality than the city water, seems to be a good measure?

Will the cooling tower actually require 7.5 gpm on a consistent basis?

Does the RO system produce a constant 7.5 gpm?

How did you come up with needing 250 gallons of storage?

Is the RO unit near the cooling tower?  If so, you could get by with a simple float valve, just like in a toilet tank.  Or, just have the tank above the makeup tank level for the cooling tower, fed by the RO tank, as long as the tank water level is above the cooling tower makeup tank water level.

Jeff;
Thanks for the reply.
Yes, the flow is a constant 7.5 gpm.
On Sunday during CIP, the effluent will hit 150 F so I can't use water on that day. Seems like I need a temp probe to shut the pump down.

Also will need a float to shut the pump off because the 7.5 will exceed the demand during the winter months. Looks like I need a PLC and a VFD? Multiple variables plus a level sensor in the tank.

The 250 gallon tank is not a definite, I was just using is for illustrative purposes. I need some kind of storage (kind of like a lift station) to control the pump speed by using a level sensor. At least that is what I am coming up with.

EJB

Bubbler systems or level sensors can put out a ma signal which can control a VFD.

See: http://www.google.com/webhp?sourceid=toolbar-instant&hl=en&ion=1&qscrl=1&nord=1&rlz=1T4ADFA_enUS356US357#hl=en&xhr=t&q=level+controls&cp=14&pf=p&sclient=psy-ab&qscrl=1&nord=1&rlz=1T4ADFA_enUS356US357&site=webhp&source=hp&aq=0&aqi=g1g-j3&aql=&oq=level+controls&pbx=1&bav=on.2,or.r_gc.r_pw.,cf.osb&fp=9bebf545d76b293f&ion=1&biw=1024&bih=510

How can the RO be less expensive than city water when the RO feed is City water that has all the other expenses added to it and is only 80-90% recoverable in addition to possible residual disposal. The second Law of Thermodynamics confirms that there is no free lunch.
You need to carefully analyse your proposal before execution. City water costs vs RO water costs. Consider the evaporation rates and cycles of concentration. It seems to me that once you reach a blowdown concentration with RO water, you'll have comparable blowdown rates with City water and the evaporation rates will be comparable. I suggest that you consult a cooling tower manufacturer.

grrun