Issue with CWP's

[mattinorange]

I just started at a new building and they handed me keys and my areas of responsibility. Of course my first stop in the main plant to see what I have. I have 2 marley cooling towers, with 2 aurora 60hp 1250 gpm condensed water pumps that basically transfer water to 2 Sonex heat exchangers. I looked at the triple duty valves and noticed that they are damn near closed (at 9 on a a scale of 1-10 and 10 being closed). So I checked the suction and discharge gauges and I am reading 0 at suction and 60 at the discharge. These are 8 inch iron pipe with Victaulic couplers. I was astonished at the suction pressure. I would like to see something in the positive pressure range and I believe these to be in vacuum. The cooling tower sump level is only about 50 feet away and about 2' above the suction of the pumps and the pump is rated for 100 feet of head.

I believe that these pumps should be on a lead/lag style operation and there is a Seimens Apogee system (haven't had access to the front end yet due to politics) and the original sequence of operations doesn't state the run status of the pumps for normal ops.

I also found out that the triple duty valves have either been replaced or rebuilt 3 times (once on one pump and twice on the other) in the past 5 years (building commission).

So any thoughts? I think I need to shut down one of the pumps and have it balanced again... or they have over sized the pumps for this application.

Thanks in advance.

Matt

[pecmsg]

Without seeing your set up its hard to tell. At my set up the cooling towers are at or below the top of the pumps by a few feet. The pumps run 8” vacuum. When I read 14 to 16” it time to clean the strainers.

Hope it helps

[screws]

Are the pumps in series or parallel? Pumps in prallel cause problems, series boost pressure.

[w8tn4rtmnt]

Need some more info! You say you have a sump and it is 2 feet above the suction of the pump. Is the top of the water level 2 feet above or the bottom of the tank 2 feet above? You need to measure how far above the suction inlet the sump tank waterline is, then multiply that by .433. 1 foot of water equals .433 psi. So if the waterline is 10 feet above the suction inlet, the pressure is 4.3 psi. This is assuming that the sump tank is open to the atmosphere. Then if the tank is 50 foot away you need to keep in mind that the line may have "some" pressure drop. How much pressure drop is going to be determined by whether or not the line is sized correctly. Shut the pumps off and see what the pressure is, that should tell you if you have enough water (head) in the tank. "IF" this is an open tank you probably have a strainer (If not 2) in that suction line somewhere. MAKE SURE IT'S CLEAN! Then check the system.

[mattinorange]

they are parallel. They are open to atmosphere on the suction side. there is grating on the suction diffuser at the cooling tower. The suction line is 8" and only about 1 1/2' about the suction centerline of the pump. The strainers according to past maint. logs were checked about 3 weeks ago and had nothing in the strainers.

Like I said, I just started last week and never saw a pump system so small with (2) 60 hp pumps rated for 1250 gpm each with 100ft head design and still have the triple duty valves at 90% closed and a 0 on the suction side. I calculated that each pump runs about 47 kwh and both pumps run 24/7. With southern california energy prices that a huge waste also. I assume I am having some cavitation due the vacuum in the suction side and I can hear it in one pump.

[klove]

What you don't say is the design GPM for the end use devices in the system (hx's, condensers, both?), if the pumps are in a manifolded (common inlet and outlet) or dedicated configuration (each pump dedicated to one device, but parallel as far as the overall system is concerned). Assuming that they are condenser water pumps (since you've labeled them as cwp's) as well as for HX's, the rated flow on your pumps - each - is good for 416 tons of cooling at 10 degrees TD on whatever it is cooling (3 GPM/ton = 10* TD). You're actually running at over 137 ft of head on the pump (60 psid x 2.317 = ft of head). That last calculation is made based on 0 psig at pump inlet because no vacuum reading was given. Regardless of that, you're still way over the rated head.

The question is "Why?". First things first - figure out if the ratings on the pump match the system design conditions. If not, why not? If they do, then it's time to start looking at why someone has induced that much head on the pump, knowing that the final delivery volume would be short. You need the pump curves and performance data to determine if you are in a detrimental condition at the pump suction due to lack of suction head. As has been stated, some pumps will run in a vacuum on the suction - but some won't (at least not very well). It may be good to get your pump rep out to look at the situation if it's something you're not very familiar with. Since you just took over, it could be that he already knows the issues - could have been a problem since startup and the problem has been band-aided to stop the pump cavitation. Which will cause drastically increased velocities thru the triple-duty valve, causing issues with it, as well.

A little info about yourself in your profile would go a long way, also.

[mattinorange]

Unfortunately the heat exchangers do not have a GPM rating and have not had a chance to contact the manufacturer. In fact I have never heard of this brand of heat exchanger. They are Sonex model 562-15230.

The pumps are manifolded also. All the pipe connections are Victaulic and until recently Victaulic only rated their standard connection for 5 in/HG. To upgrade the connection to withstand higher vacuum a metal sleeve is intalled withing the rubber gasket. These connections are original. So not only is it cavitating due to the vacuum in the suction side, but also possibly sucking air. I do believe someone knows there are issues and just not recognizing that damn near closing the triple duty valves is not the solution. I think that this system was designed to be on a lead/lag operation and not both pumps at 24/7. Then after that have the system balanced under the load of each pump operating independently.

I do not see a GPM designation for the Marley cooling towers. To further make my life tortured, the developer is being very difficult about getting as builts and I cannot trust any plans that I have for mechanical. For example, I have seen some plumbing plans and they state that for the sump pumps they require Myers 100 GPM x2 for each sump. While investigating why on pump is down, it is not a Myers! They are all Stancor. Even the controls are Stancor.

This building has already had boiler design and installation issues and since commision (5 years) has already replaced (not repaired) 3 to my knowledge.

I will update my profile if it helps. But a little history on me. I have worked in about 18 different buildings in the Orange county building as a building engineer. I have operated and maintained basic Cogen plants down to your basic carrier heat pump and all the equipment to support them. I am familiar with trane CVHE centrivac 500 ton chillers and smaller.

Before that I was in the Marine Corps. Did 4 years as a water purification and distribution technician. At the time of my discharge I was the NCOIC in charge of the utilities platoon for MWSS-372 at Camp Pendleton and was in charge of over $30 mil in equipment and 25 marines.

I also am very experienced in automotive A/C. Worked for over 4 years in the industry and still do free lance work for some of the A/C shops and custom builders in the Souther Ca area. Also have designed systems for Robby Gordons Baja 1000 team.

I dont carry any technical certifications from any prestigious schools... but it doesn't make me stupid. Just like to learn as I go.

[klove]

Never meant to imply stupidity - we all like to know with whom we're speaking, especially when going in-depth on a subject such as this. There's a "Refrigeration and Icemaking" section here where you can go and read the first threads' opening post by "market tech" - explains it much better than I can.

On the sump pumps - you probably have the "or equal" instead of the spec'ed.

About the CWP's: Do you know what the suction pressure is? Depending on the length of run from the cooling tower, there shouldn't be too much DP on the piping, assuming correct pipe sizing. Unless someone just threw this thing together off the cuff, you should be able to go to the equipment reps and get the design specs on everything that you have. Even if it was thrown together, they can give you basic flows, DP's and DT's for the HX's and cooling towers - mfr reps won't guess, they have to be given something hard to go on or it can come back on them. Sonex is a reputable HX - our Aurora pump rep handles those, also. Your problem is fixable (maybe with less trouble than at first glance), but you're going to have to know what it's supposed to do before you can make it do what it's supposed to do. Sometimes, getting that part, is the hard part....

[mattinorange]

Well I guess I am trying to circumvent all the politics. I am hired under an engineering services contract. Working with the propert manager is impossible. The past contractors are less than helpful and I do have to be careful to not step on any toes as the new guy and try not to make it sound like I am challenging the designers. But, seeing that the designers gave no reason for thier design (proper plans ... etc.). Just seems like I have more work to do by contacting Sonex and Marley for GPM rates for the equipment. Hell, I may just need to call out an independent contractor to survey what we have and submit thier findings.

I have the rest of the building on my shoulders besides the HVAC side. They have never even had an infrared inspection of any of the electrical and any time anything breaks, they just replace it no questions asked. Triple duty valve failed... so i guess we just get it replaced and ask no questions.

Anyone in So Cal need a building engineer? I may be looking for a new job soon.

Matt

[mattinorange]

I just calculated the NPSH and found it to be -4.56 but do not know the NPSHR. Wondering if I did it wrong... if anyone can help me it would be greatly appreciate it.

thanks.

Matt

[w8tn4rtmnt]

I'm just curious here, and please don't be offended at my questions as I am only trying to help. You are awfully concerned about how much suction pressure you have or do not have. With all due respect, you are chasing the wrong thing! You should be more concerned with TDH then plotting that on the pumps curve. That will tell you how many gpm's you are moving. Then it's up to you to determine if your GPM's are adequate. You say you're in a vacuum on the suction side, where is your guage hooked up at, is it downstream of the strainer (strainers)? Is it a compound guage, are you SURE you're in a vacuum. YOU are gonna have to pull apart all strainers and see if they are plugged. You are saying that you have -4.56 Net POSITIVE Suction Head. It's not positive suction head if it's negative! A negative would indicate you are operating under Suction LIFT conditons. That's concerning considering you stated that the sump was above the pumps. Again, how far above the suction of the pump is the waterline of the sump? That should tell you your NPSH.

[mattinorange]

The guage is a 0-100 and about 4' before the strainer. The strainer is located immediately prior to the impeller housing. I can guarantee I am in vacuum... how much... not sure. I was told by a contractor it was about 5"hg. But this may allow air to be sucked in at the Victaulic. I am not so much concerned at this time because if my pump impellers are damaged due to cavitation then discharge presssure and GPM will soon be 0. After I confirm and satisfied with suction pressure then I can balance gpm and discharge pressure via the throttling valves. I have plenty of room to open those.

Does anyone agree that running 2 60hp 1250GPM pumps with 8" pipe and throttling valves near closed at about 90% is a problem and that possible running one at a time with proper balancing will solve this?

Ultimately I am not going to pay for stuff when it breaks... but i just can't let this go and accept "thats the way it has always run".

[w8tn4rtmnt]

Does anyone agree that running 2 60hp 1250GPM pumps with 8" pipe and throttling valves near closed at about 90% is a problem and that possible running one at a time with proper balancing will solve this?

No way I can guarantee it's a problem until it's plotted on a curve and proven. The pump curve is going to determine valve position. Suction pressure in itself means nothing. Suction pressure is only used to determine TDH. Suction pressure is only part of the equation, whether positive or negative (pressure). You're still way short on info here dude! Until you get more info you're still chasing your tail.

Let me put it this way, You need the following to determine the answer to your problems.

1) Accurate SP reading
2) Accurate DP reading
3) TDH
4) Actual impeller size
5) The proper pump curve
6) Motor HP
7) You need to be able to work between FT H2O and PSI

Until those 7 requirements are met I can't say you have a problem with anything. Regardless of the fact you may or may not be operating in a vacuum.

The only other thing is operating both pumps at once should not be hapening if they are truly in parallel. 2 pumps in parallel operating together are not moving more water.

[mattinorange]

I can get those and maybe even some pics monday. I can also show your the distance we are talking between the component.

Thanks.

And I totally understand the reason alcohol is consumed now.

[klove]

[QUOTE=w8tn4rtmnt;5893452
The only other thing is operating both pumps at once should not be hapening if they are truly in parallel. 2 pumps in parallel operating together are not moving more water.[/QUOTE]

That's a mighty large statement to make about a system when you have no knowledge of it's design criteria or intent. What exactly is this based on?

[w8tn4rtmnt]

Not really. I said if they are TRUELY parallel, both pumps are the same size, of equal hp, and equal impeller size. I don't think thats out of line. I'm basing it off of what he's told me. I have no clue what reality is. Regardless of what I said, he's got a long ways to go here. What I've done is help him get the information to guide him toward plotting his info on a pump curve and finding his actual pump GPM's. Once he has that ( as you yourself stated ) he needs to find out how many GPM'S he's supposed to be pumping into whatever object he's removing heat from. I figure that'll also tell us if he needs one or two pumps. Chances are, based on what he's stated, one's redundant. But again, I'm not there, so I can't be certain. I've told him we need more info to help. If I'm wrong in any way feel free to correct me. JMHO! Thanks!

[oldtimer2]

Matt, Have you calculated your tonnage of the wshp's? Are the hoa switches on the pumps starters in hand or auto? If in hand turn them to auto. see if one of the pumps goes off. If it does you may have lead lag or alt. seq. Also, if they were in hand and you put them in auto and one pump shut down. Wait a few mins. and shut the other one down and see if the other one comes on. This will give you a good idea of how your atc system is controlling. As stated plot your pumps and see where your at.

[mattinorange]

Here is what I have found.

D.P. 45 psi
Imp. Size. 9"
I also found that the Heat Exchangers are rated at 1250 gpm each and there are 2.
Pump curve chart available and indicates that the NPSH is 20 for 60hp
Here is the link for it.

http://www.aurorapump.com/pdf/340_360/Curves_340_360.pdf

I am still working on TDH and Suction Pressure. Have to get a gauge that measures vacuum I can adapt to 1/2" for suction pressure. I did pull the gauge and cracked the valve and it sucked some air so I closed it. And not sure where I can tap in a flow meter for GPM.

As far as the WSHP's... thats tricky. They are resident owned and I do not have access to them. We just supply condensed water. As far as the HOA switches, they are all in Auto and I have not had access to the Siemens Apogee system yet. The management has been less than helpful in that regard and apparently I need to have a Siemens guy out to show me. But the is a MEC controller that does control the pumps.

Keep in mind. My throttling valves are not controlled by the Apogee system. They are manual and at 90% closed.

Matt

[w8tn4rtmnt]

Matt,

Please don't take offense to this, but I think you may need the help of a mechanical contractor. I appreciate your willingness to jump in and go looking for problems, but I think you need more help than can be provided here. I don't personally believe that you can teach someone how to plot a pump on a curve in a forum. Based on what you've stated, I think you should maybe look for some help on a local level, such as a mechanical contractor. Sorry man, but I'm out.

[mattinorange]

Well I would like to thanks everyone for understanding my situation and asking me more questions that help me side track from my original problem... Cavitation. I ended up running one pump at a time and opening my throttling valves back up to about 80 percent. No more noise in the impeller housing and suction pressure is about 22 psi.

Yeah I guess it was too much for me to handle and I will just go back to my rolodex to run my stuff.

[klove]

Well I would like to thanks everyone for understanding my situation and asking me more questions that help me side track from my original problem... Cavitation. I ended up running one pump at a time and opening my throttling valves back up to about 80 percent. No more noise in the impeller housing and suction pressure is about 22 psi.

Yeah I guess it was too much for me to handle and I will just go back to my rolodex to run my stuff.

If you were able to fix the problem with no assistance, why'd you ask for help in the first place? Responses like this are the reason that people like me want to know who they're talking to before offering any suggestions, and you would do well to remember that the responses are 90% of the time just that -suggestions. We're not on site with you, and you're asking for opinions from literally hundreds of different people about a problem that has no bearing on their well-being. They're simply trying to help. Why? Because you asked. You want to get a holier than thou attitude and make smart remarks, go do it somewhere else.... :payattention:

And by the way, if the vertical rise is only about 2 feet or so from pump inlet to water level in the tower basin (I believe that's close to what you said), you better go back and look at your pump suction pressure again. If you have 22 psig at inlet, that's some of the heaviest water I've ever heard about. Maybe that was the problem all along - the water in Orange Co., Ca. is heavier than elsewhere in the world...................

[mattinorange]

Maybe I came across wrong. There was no sarcasm. It was meant to be humble. I called out a pump specialist and he gave me his suggestions. Note I never mentioned the cavitation until my last post. Apparently that was my issue also.

The only sarcasm that was implied was at my expense. Maybe seeing the situation helped him more than it has in this forum.

As far as the water being heavier in So cal... not sure it was needed, but the fact remains that I have 22 psi on my suction gauge. I am just glad that my unrecognized cavitation is gone and that I wont be replacing a pump impeller soon.

Matt

[w8tn4rtmnt]

I was afraid this would happen. Look man, I was trying to help! Unfortunately there comes a point in this whole thing where I can do nothing more. The questions I asked are questions directly relative to what you were telling me. I can only steer so much. Understanding how hydronics really work is something that is learned in time. With hydronics, you could do some damage really fast or get yourself into a pickle before you know it, trust me, I've seen it happen. The next thing is that if I tell someone something that gets misinterpreted, then they come on here headhunting. I'm not gonna overextend myself, I'm just looking for people with a common interest and an opportunity to learn a few things in the process. One thing I'd suggest is going to the Bell and Gossett website. On there you will find a little piece of literature that is pretty helpful for people learning hydronics (but it's just a start). It's called "How hydronics really work". Trust me this is not sarcasm or a joke, but a serious piece of literature, and an interesting one at that! Best of luck man!

[davo]

After reveiwing his first post, I'll bet his triple duty valve had to be installed improperly on the suction inlet side.
I was thinking that it is next to impossible to cavitate a pump when it is throttled down 90%. I never thought until now he could have been throttling the pump inlet.
If he turned off one pump, opened the valve, and the suction went up, this would be the only explanation. If the valve was on the discharge outlet, the suction would have went down.

Ditto on the B&G website. I have the old volumes from my brother back in the early '70s. Pumps still work the same!

[Pneuma]

heat exchangers are built to order according to a design spec. Find the number for the company and call them with the serial number and you will get all the specs, gpm, temp splits on both sides of the exhanger. The gpm on the open loop side is exactly what your pump needs to put out, you can set that with the pump curve and your pressure delta acorss the pump housing.

[mattinorange]

Okay... lets get this straight. You guys couldn't help me... and that is okay. I am fine with it, seriously. I made a joke about myself and needing a rolodex to do my job (joke at my expense) and now everyone is butthurt?

You guys were leading me in the right direction for the information I gave you. The guy I called out just had the advantage because he could see the layout and everything working together.

As far as the outcome of this... I may end up subpoena'd in the lawsuit to the developer that installed pumps way too big for the application. I have 2 different contractors preparing more or less identical reports stating that the cooling tower elevation is too low in relation to oversized pumps. They are also questioning the heat exchangers. This is going to be a nightmare. I also found that they have replaced the triple duty valves 3 times in the past 2 years. And another company tried to stop the installation of oversized pumps and even gave an option for drives due to the excess energy waste and size of the pumps. This is going to be a legal and political nightmare and my name is all over it now. I am going in a different industry after this one.

But I do thank you for your input and your time. no offense should be taken.

Matt