nvq 3 prenstation help?

[airconadam]

hey fellas,just wondering if any one has got any good info on air cooled water chillers? I have got to do a presentation on them and how they work etc aswell as the water side with what controls it etc i have been on hundreds of website but they all seem to go into all the sizing of them and not just what iam after thanks alot

adam:D

[Toosh]

hey fellas,just wondering if any one has got any good info on air cooled water chillers? I have got to do a presentation on them and how they work etc aswell as the water side with what controls it etc i have been on hundreds of website but they all seem to go into all the sizing of them and not just what iam after thanks alot

adam:D

Hi Adam, go throughthis document there is a lot you can get from it

Norm

http://www.iit.edu/~ipro328f04/downloads/IOMALR-3.pdf

[Brian_UK]

Any of this info of use ?

http://home.howstuffworks.com/ac3.htm

[airconadam]

thanks fells will have a good look through now

adam

[Brian_UK]

Also Adam, when doing a Google on something try typing in the complete question that you have - it always surprises me with what it comes back with ;)

[airconadam]

thanks toosh and brian both good sites will be able to pull alot of info from them both much appreciated

adam

[Toosh]

You are very welcome good luck

Norm

[airconadam]

hey again fellas i want to know what is the main reason you use a flow switch on a chiller for?? if for example their was no water in the system would the valve close and if so why?

thanks alot

adam

[Brian_UK]

A water flow switch is an essential safety device to protect the evaporator from damage.

In the event of a loss of water flow it is possible for the evaporator to freeze up and burst the tubes because the compressor is still running and providing cooling.

In theory the compressor should be protected by the low water temperature sensor but depending on the location of it there is a chance that it will not see the lower freeze happening. Why? with no water flow the sensor does not see the temperature inside the evaporator.

[Grizzly]

A water flow switch is an essential safety device to protect the evaporator from damage.

In the event of a loss of water flow it is possible for the evaporator to freeze up and burst the tubes because the compressor is still running and providing cooling.

In theory the compressor should be protected by the low water temperature sensor but depending on the location of it there is a chance that it will not see the lower freeze happening. Why? with no water flow the sensor does not see the temperature inside the evaporator.

A very good point of Brian's there Airconadam.
But I must correct a slight grammatical error.
On a Shell and Tube evaporator the cooling medium flows through the tubes in the middle.
And the water or glycol flows across, through and around this tube bundle.
If this flow drops off sufficiently the remaining water will freeze around the tubes CRUSHING them not Bursting them.
That is why whenever a tube or tubes have been crushed the system can exhibit low pressure / undercharged / expansion valve issues!
So Brian is spot on with the reason for a flow switch but the tubes can be crushed not burst.
But that may well mean the same thing in Dorset?
Cheers Grizzly

[Brian_UK]

Thanks for the correction Grizzly, too busy typing to read what I wrote ;)

[airconadam]

ah rite thanks alot once again for your info my presentation is coming along good now hehe iam sure i will be posting a few more things as of yet

p.s does bms mean building manangement system??

thank you

adam

[airconadam]

also grizzly when you say as the flow drops sufficiently the remaining water will freeze,is this due to the outside temp being cold or just because the chiller is still cooling and the small amount of water in the tube will freeze??

adam

[Brian_UK]

Yep, BMS is correct.

[airconadam]

hey brian on maintenance would you check the flow switch? and if so how would you do it is it a simple case of stopping the water flow and seeing if it closes and faults??

thanks alot

adam

[Grizzly]

also grizzly when you say as the flow drops sufficiently the remaining water will freeze,is this due to the outside temp being cold or just because the chiller is still cooling and the small amount of water in the tube will freeze??

adam

To clarify.
The refrigerant is passed through the central tube bundle.
Which is covered over by the water / glycol being cooled.
Much the same as an element in a kettle is covered by the water being heated.
The temperature of the refrigerant within the tubes
Is decided by the chiller suction pressure at that given time.
If the flow rate across the evap tubes slows down
then the water/ glycol is cooled further than the normal running setup!
Therefore you when commissioning or indeed servicing a chiller, have to pay attention to the flow rate across the tube bundle.
Hence comments from time to time about Binder gauges re pressure drop across the tube bundle.
IE to fast a flow rate = poor cooling efficiency
Whereas too slow = means to little of the required amount being cooled.
Stopped or severely restricted flow means that the water around or the droplets sat upon the tubes.
Can and will freeze! If enough Ice crystals form around what is effectively a very thin walled copper tube (to give the heat transfer).
The tube will be crushed.
Therefore you could achieve very low water temps without reaching system LP or freeze stat (LWT Alarm) settings.
Simply by having a stuck or non-operational water flow switch.
Which is why it is so important to test them when carrying out maintenances!!!!
Please excuse my simplistic answer but I am not a trainer.
Just like many other an Engineer.
Grizzly
PS BMS = Building Maintenance System. A Computerised monitoring / control system which usually with chillers gives a remote run/ stop command signal to the chiller controls!

PPS I hope you spell check you presentation first Adam.
Judging by the Heading!

[airconadam]

haha grizzly i know about the spelling in the heading but i was unable to change it;) thanks alot grizzly understand it alot better now dont worry about the simplistic answer thats what i need to understand it:D thanks again

adam

[Brian_UK]

The way I used to check a flow switch was firstly to lift the switch cover and examine the state of the cables and terminals. They are often corroded due to water ingress.

Check the voltage at the terminals, a poor contact will drop the voltage sometimes but also gives you warning of high voltages etc; 12vdc or 24vdc, or ac, aren't too much of a worry ;)

Then turn the chiller off, via a thermostat if possible - this keeps the control circuit active across the switch.

Now slowly close a flow valve and monitor the switch action. Hopefully it will fail to open circuit (assuming it is wired that way). Now try and restart the chiller; with basic controls it should refuse to start, with digital you should have a fault condition raised.

If the above works then now open the flow valve and monitor the switch action.

Things to watch out for when checking these things is finding the switch stuck/broken and the wiring changed at the switch to provide a continuous circuit; or possibly a link in the chiller control panel bypassing the switch.

Don't forget to turn the chiller back on after your checks or you'll have a call-back later in the day!

[Grizzly]

Don't forget to turn the chiller back on after your checks or you'll have a call-back later in the day!

I like that comment Brian!
Ever been there?
I know I have.

Adam check out the attached and yes you can use it.
Grizzly

[airconadam]

hehe cheers grizzly think i might put it in my presentation! another question sorry for all these simple questions but idont know them! can the flow switch be fitted on the flow or the return????

thanks alot

adam

[airconadam]

what are the baffles for in the shell is that just to smooth the flow of water or to even out the water????

adam

[Grizzly]

hehe cheers grizzly think i might put it in my presentation! another question sorry for all these simple questions but idont know them! can the flow switch be fitted on the flow or the return????

thanks alot

adam

Adam
I have only ever seen them in the flow ( water off the evap)
But I can't exactly remember the reason why?

If I remember correctly it's to do with the pressure drop across the evap and the corresponding drop in flow.
Maybe some of the other Guys can help out here?
Grizzly

[airconadam]

thanks grizzly iam sure someone eles will be along soon i hope!

thanks

adam

[Brian_UK]

I like that comment Brian!
Ever been there?
I know I have.
Grizzly:off topic: My normal trick this year seems to have been more CORGI stuff than AC. I finish the boilers and go help the electrician.

He turns off the power for his checks and then we wrap up and go.

Power off = gas safety valve shut = boiler pilot lights out = Oh F***


what are the baffles for in the shell is that just to smooth the flow of water or to even out the water????
adamBaffles are there to ensure that the water flows around all of the tubes etc.

No baffles means the water would travel directly from the inlet to the outlet.


If I remember correctly it's to do with the pressure drop across the evap and the corresponding drop in flow.
GrizzlyI think you're having a brain failure there Grizzly :D
I don't think that the water flow rate into the shell can be higher than that leaving the shell because of a pressure drop :eek:

[Grizzly]

I think you're having a brain failure there Grizzly :D
I don't think that the water flow rate into the shell can be higher than that leaving the shell because of a pressure drop :eek:
Brian.
You are correct I am struggling with this one?
For some reason I can't remember the answer.
I was hoping someone could answer for me?

:off topic:I am glad that I don't have to cover the Corgi side as well Brian!
It must be manic at this time of year?

Or is it a case of you find out as to who has been doing their maintenances?
Grizzly

[airconadam]

thanks once again fellas. The other part of our firm are all corgi gas lads with working on boilers etc and its manic on their side i have been helping them on some of the ripouts of thos big cast iron boilers. thanks alot

adam

[airconadam]

so any one know why the flow switch should be fitted on the flow or should it thanks alot

adam

[Brian_UK]

I can't say 100% but here is a article from ACR News which states that it should be in the flow from the evaporator.

http://www.acr-news.com/news/print.asp?id=645

One bit of logic for it being there is, I suppose, that if you open any bypass valves etc on the inlet side of the evaporator then the flow switch might still be satisfied when there isn't any flow through the machine.

[Grizzly]

I can't say 100% but here is a article from ACR News which states that it should be in the flow from the evaporator.

http://www.acr-news.com/news/print.asp?id=645

One bit of logic for it being there is, I suppose, that if you open any bypass valves etc on the inlet side of the evaporator then the flow switch might still be satisfied when there isn't any flow through the machine.


Basically that is about it Brian.
If the flow switch is fitted after the chiller ANY disruption to the flow is detected.
If fitted before the pipes between the switch and chiller could fail, burst or be broken. (Or as Brian suggests).
Leaving the chiller without a water supply but still running!
This is only a logical answer as there seems to be no hard and fast rule applied?
(Thanks to my friend and Colleague, Paul for the sound advise)
Grizzly