Freq drives on new chiller but not old? Problems?

[CraziFuzzy]

I would rather have three way valves on all the loads than a VFD. It just seems to be more reliable.

This I certainly don't agree with. Pretty much any large pump will last a LOT longer with a VFD than without. VFD's not only match motor speed to system demand, but in doing so, they allow bearings and such to last much longer.

[Six]

This I certainly don't agree with. Pretty much any large pump will last a LOT longer with a VFD than without. VFD's not only match motor speed to system demand, but in doing so, they allow bearings and such to last much longer.

Meh....you have to take into account the reliability of the extra component compared to the reliability of a starter.

And I'm a huge fan of VFDs but they're on just about every motor now and they do fail.

One of my huge Munters blew the cover off of its supply air motor VFD over the weekend. I'll post pics.

Its critical in the operation of the Munters unit but not on a condenser water loop.

Plus the occasional OC or OV fault. If its not absolutely critical it's not worth installing.

Another example. I've got a 8 story office building with pneumatic receiver controllers and guide vanes on the AHUs actuated by large actuators with pilot positioners.

Simple but 14 out of the 16 receiver controllers and actuators are original to the building and they maintain static perfectly. ( provided the silly engineer doesn't monkey with them). But when he does I re calibrate and I'm done.

[jayguy]

Got an update today from the engineers. We do not have a common header, each chiller relies on its own dedicated set of pumPs. They are still wanting to put vfds on both pumps of the new chiller and on the compressor. Thoughts? Problems/issues? If they can, they are also going to put vfds on one of our existing 600 ton tranes. If not, the only chiller that will have vfds is the new one.

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.

individual pumps on each chiller is a good thing. Each chiller should be able to get what it needs. but does each chiller have its own tower or do you have a common condenser water sump? the condenser water temperature control is in question now.

[Nuclrchiller]

Got an update today from the engineers. We do not have a common header, each chiller relies on its own dedicated set of pumPs. They are still wanting to put vfds on both pumps of the new chiller and on the compressor. Thoughts? Problems/issues? If they can, they are also going to put vfds on one of our existing 600 ton tranes. If not, the only chiller that will have vfds is the new one.

Is this about the condenser water pumps? It's possible to have dedicated pumps and still have a common header. Why rely on someone else's word? Just look at it yourself. I realise that piping can look like spaghetti sometimes, so refer to drawings to help you trace it out.

[ZeroTolerance]

we have a return and supply condenser water pipe coming into the plant and a return and supply chilled water pipe coming into the plant .

All towers are piped into a common header at the tower. There are only two condenser water pipes in the riser going to the tower.

We have no de-coupler loop or 3-way valves currently

[jayguy]

we have a return and supply condenser water pipe coming into the plant and a return and supply chilled water pipe coming into the plant .

All towers are piped into a common header at the tower. There are only two condenser water pipes in the riser going to the tower.

We have no de-coupler loop or 3-way valves currently

when the new vfd chiller is installed, you will have sum splainin' to do Lucy!

good luck...man, are you going to need it!

I would love to be the contractor that gets called in after-the-fact. i absolutely love pissing off engineers who think that they can do anything. you will find that when it doesn't work, the engineers will tell you to call the chiller manufacturer to 'fix' the chillers that aren't working...the vfd chiller will run at nearly 60 hz all of the time or the non-vfd chillers will trip on low evap temp, motor overheating (which could also be oil overheating or bearing overheating), etc. the mechanical contractor will then charge you to pull the charge and weigh, replace the bearings, pull the motor for repair, etc and they won't have fixed anything...it will sound like it though.

sorry to have spoiled your day.

[CraziFuzzy]

when the new vfd chiller is installed, you will have sum splainin' to do Lucy!

good luck...man, are you going to need it!

I would love to be the contractor that gets called in after-the-fact. i absolutely love pissing off engineers who think that they can do anything. you will find that when it doesn't work, the engineers will tell you to call the chiller manufacturer to 'fix' the chillers that aren't working...the vfd chiller will run at nearly 60 hz all of the time or the non-vfd chillers will trip on low evap temp, motor overheating (which could also be oil overheating or bearing overheating), etc. the mechanical contractor will then charge you to pull the charge and weigh, replace the bearings, pull the motor for repair, etc and they won't have fixed anything...it will sound like it though.

sorry to have spoiled your day.

I'm having trouble understanding what the cause of all this supposed calamity would be. The only 'problem' I can foresee in this situation, would be that they wouldn't be able to fully realize the advantages of the VFD chiller, since they will not be able to run the tower water colder, because they would have to keep the older chillers from surging.

[Dallas Duster]

I'm having trouble understanding what the cause of all this supposed calamity would be. The only 'problem' I can foresee in this situation, would be that they wouldn't be able to fully realize the advantages of the VFD chiller, since they will not be able to run the tower water colder, because they would have to keep the older chillers from surging.

Unless they get some cold condenser water for the VFD chiller it's going to be worthless.

[Six]

I think hes assuming worst case senario.

IF they chose to run with lower tower water temp and ignore the original chillers.

So whats the point of addung a VFD Chiller on a common header if you cant take full advantage of it. In my experience arguing with the average engineer is like arguing with a turnip.


They wont take into consideration the real world consequences of their "perfect sollutions"

[jayguy]

I'm having trouble understanding what the cause of all this supposed calamity would be. The only 'problem' I can foresee in this situation, would be that they wouldn't be able to fully realize the advantages of the VFD chiller, since they will not be able to run the tower water colder, because they would have to keep the older chillers from surging.

Unless they get some cold condenser water for the VFD chiller it's going to be worthless.

exactly! and how much extra did they pay for this new fangled chiller?

could this work? sure...here's how.

1. tower water set to 'very cold' for the new vfd chiller...ONLY this chiller can run.

2. need more chillers now. have the BAS raise the condenser water temperature to 85F to start the old chillers...losing ground fast now because the new vfd chiller couldn't keep up to begin with...new vfd chiller is at 60 hz which costs more money to run (at 60 hz) than a non-vfd chiller.

3. old chillers are now online and we are running a condenser water temperature that is much higher than needed for a vfd chiller (why did we buy this chiller to begin with?)

4. load is satisfied (at some point) and now we can run only the vfd chiller and use colder tower water. set the tower water to a colder temperature.

5. ever see a BAS guy who could even understand this? how about an engineer? how about an engineer who could write this up properly so that a BAS guy could program this? how about a BAS guy that won't dick with it later trying to be a hero and save some money? i haven't heard of even a fairy tale of these people.

now, obviously, i have skipped some steps and i haven't given the exact temperatures and rate changes that are needed to make this work which are just as important if not more important. you will also need to take into account the age of the chillers, mechanical condition, the chillers controllers and how fast they can react, etc.

i hope everybody gets the point that just adding a drive to something is much more complicated than at first glance. vfd manufacturers will SELL you on how plug and play everything is but it just isn't so.

[R123]

Jay, what about installing 3 way condenser valves on the old chillers, running the tower cold, and partially bypassing the condenser water on the old chillers to maintain 85 degree water coming in.

[jayguy]

Jay, what about installing 3 way condenser valves on the old chillers, running the tower cold, and partially bypassing the condenser water on the old chillers to maintain 85 degree water coming in.

that would be some big-a** 3 way valves!

now we got the BAS techs trying to maintain a bypass valve for each chiller except the vfd chiller...this is getting even more complicated! let's throw in a hot dog vendor cart and Teddy Ruxpin for them to control too!

all of this because someone wants to put a drive on a chiller. if they left the drive off, it would be a very simple to operate, simple to maintain, simple to understand and low cost of ownership chiller plant.

i want you to know that if we were designing a chiller plant from the ground up...go with drives on MOST of it...you don't need it on everything if you know how to control it well. the problem here is they are throwing good money at something that most likely will not work the way they want and even if they do get it to work properly, it probably won't stay working that way due to the fact that engineers do not design any control strategies that account for a failed component like a tower temperature sensor or a 3-way valve or a particular pump that doesn't work. they only add chillers as 'back up' and that's it.

i don't care if they install it and it doesn't work. i care that the OP is going to be stuck in the middle and a whole bunch of people are going to make a lot of money off of his company and it may not make a difference and his boss is going to be pissed.

i guess that i shouldn't care so much. all of that money floating around will help the economy get off of the ground. i am tired of doing it by myself.

[CraziFuzzy]

that would be some big-a** 3 way valves!

True, but it is not really that uncommon. There are many reasons plants run 3-ways on the towers. Condenser heat recovery is the most common reason. Another is free cooling operation. The improved part-load efficiency of the newer chiller as the float, and using the non-vfd chillers for base-load running at optimal efficiency loading, would definitely pay for a little bit of large piping, and a 3-way valve on each of the non-variable chiller's condensers.