ReplyIt shouldn't.
What kind of controls are staging the chillers?
The other chillers don't really run balls out unless you have load, that's what the IGV's do, control capacity.
Regular Guest
Our building is replacing an old Mcquay 800ton chiller with a trane 600 to accompany our two other trane cvhf570's and our trane 175ton. The big dog at corporate wants to put vfd drives on the new chiller. Our four trane cvhf pumps don't have vfd's. Will putting vfd's just on the new chiller cause surges in our other chillers that run balls to the wall?
Professional Member* / ARP Committee
It shouldn't.
What kind of controls are staging the chillers?
The other chillers don't really run balls out unless you have load, that's what the IGV's do, control capacity.
Professional Member*
Its raining VFDs !!
In general VFDs are a more efficient alternative to across the line starts but whether or not they actually modulate the frequency output depends on the application.
If you maintain a constant flow they're still ecficient because of their soft start capabillities.
Professional Member* / ARP Committee
I think he means on the compressor motor. In that case, the drive will ramp up and down with load, and parameters will be factory set, and perhaps field verified at time of start up. I believe Trane likes to modulate to maintain the chiller just below the surge boundary.Originally Posted by commtech77
As for water flow, there also real handy for setting max flow rate, much better then a tripple duty valve.
Professional Member*
He mentioned pumps in the first post.
Also would it be up to the big dog at corporate to install VFDs on a chiller compressor motor?
Professional Member
your biggest problem will be in properly controlling the condenser water temperature. with vfd driven chillers, you will gain efficiency by lowering the tower water which will slow the compressor down. with trane's newest model, the oil pump motor is doubleshafted and has a refrigerant pump on the other end. this allows for motor cooling at lower condenser water temperatures and/or higher evaporator water temperatures.
the problem comes in with your older chillers...do they have this type of oil/refriegerant pump? can they handle the lower condenser water temperatures? your BAS probably controls all of your towers to 1 set temperature...now there will have to be at least 2 temperatures...unless you have a common tower/sump system in which case you could be royally screwed. it is possible to have it work, however, i haven't seen a BAS person who can seem to understand how this all works and get it done.
"Right" is not the same as "Wise".
Don't step on my favorite part of the Constitution just to point out your favorite part.
Just because you can measure it, doesn't mean it is important. Just because you can't measure it, doesn't mean it isn't important.
Professional Member
VFD's on pumps is becoming a commonplace thing. It helps to prolong electrical and pump components by soft starting them, it also makes balancing easier, by setting your frequency reference, in lieu of choking back a triple duty on constant volume. By running at lower frequency, in lieu of sixty hertz, there are electrical efficiency gains as well.
With repsect to the chiller itself, pretty much the same dela. Instead of running at sixty hertz and maintaining capacity control with IGV's, you ramp the speed of the centrif, saving energy and more closely matching the load. The problem comes into play when you try to run the old plant at new conditions.
For example, trying to run cold condenser water on older chiller, in many cases, can cause issues. Also trying to do variable flow through am achine not designed for it can wreak havok on that machine. so yes, depending on your configuaration, it may be an issue, but there isnt nearly enough information provided to provide a strong argument.
Regular Guest
Ya, I will try and provide more info once I hear wind of it. As for right now, we are all gritting our teeth at the thought of VFD's on just the pumps of the new chiller and not the old ones. Combining 2007 technology with 2012 technology is going to be tricky.
I also don't feel our controls company is that up to date enough to make the programming work for the setup they are alotting.
I will try and provide more info when I receive
Professional Member*
Just so everyone's on the same page, are you talking about putting a vfd on the pump, or ordering a new chiller with a vfd on the compressor motor???
Regular Guest
As I understand it, they just want VFD's on the Condenser Water and Chilled Water Pumps.
Professional Member*
If you are going to run those pumps at 60hz then installing a VFD is going to be a waste of money.
Professional Member*
And a component that sometimea locks its self out in nuissance trips.
Regular Guest
If we were going to run the pumps at 60Hz why would they want VFD's on them? The whole point of VFD's is efficieny reason being they want to put the pumps on them. Sorry, your answer isn't making sense to me. Please elaborate.
Professional Member*
Is water flow going to be varied thru the chiller? If yes VFD's are going to payoff for you if not then they are going to be a pretty expensive starter that will never pay for itself. I just assume since you are adding equipment to an existing system the answer just may be no. But who knows. Sounds like a good sized plant thou.
Professional Member*
Sounds like hes saying soft start alone isnt justifucation enough to replace a starter with a VFD.
I happen to agree. Ive got a Carrier water cooled 50 ton with VFDs on the CWP and it runs at 60 HZ.
Its a headache when that VFD throws a OV or OC alarm and shuts down the chiller because the drive is glitchy.
Professional Member*
If the new chiller is being added to the same system that the existing chillers are on, then more info is needed. It sounds like the existing chill water system may be a primary/secondary arrangement. Variable chill water flow thru the chiller is usually used on a variable primary flow system. Not sure how the two will be combined. With the cooling tower water flow, variable flow usually involves different tower temperature controls compared to constant flow. If cooling towers are piped thru a common header between the towers and the chillers, again, not sure how that will be accomplished. It sounds as though your job is about to get more... interesting....Perhaps some of the other guys here have seen this done successfully. Good luck.
Regular Guest
Ya, Nucl its about to get very interesting haha.I think these engineers are even getting in over their heads.
All chillers currently are piped via a common header at the cooling tower then it runs down to the plant and branches to each chiller from there.
Regular Guest
Ok, mechanical engineers came back out again today. I stand corrected, they want to put a vfd on the compressor and not modulate the pumps. Pumps on new chiller will provide constant volume.
Professional Member*
Well, I think that will be better for you, as far as having a reliably running system goes. However, refer to Jayguy's post. The full energy saving potential of a vfd chiller probably won't be realized with your existing cooling tower arrangement. Perhaps the addition of head pressure controls on your existing chillers (i.e. individual condenser bypasses or throttling valves) will allow you to lower cooling tower temps to take advantage of all the energy savings potential of the new chiller. Personally, I'm more for rock solid reliability than I am for energy savings. Although a crashed chiller does consume very little power.....
Professional Member*
I was under the impression that variable compressor motors needed variable flow to maximize the efficiency of the chiller.
Posting Permissions