water cooled

[tait71]

hi people, i have a small problem i have 6 cold rooms installed in the same building running with searl evaps and water cooled copland scrolls condensing units, the water is a chilled loop that feeds all the coldrooms the inlet temp is 25c which means on r134a i get head pressures of 200 to 300psi and out on hp, checked the condensers all clean no lime or scale good flow rate good heat transfer (water in 25 out 47c), i just think the water inlet temp is too high, what to you boys think, please help

cheers

[frank]

What do you call a chilled water "good flow rate"?

Whats the total condenser heat rejection?

[US Iceman]

...good flow rate ... (water in 25 out 47c)...

Sounds to me as if the flow rate is about one-half of what it should be.

[NoNickName]

Sounds to me as if the flow rate is about one-half of what it should be.

Even less. Unless flow valves are installed or inverter driven pumps.
Still, taking advantage of such cooling water, condensing temperature can be muuuuuuch lower and performance to kW muuuuuuch better.
tait, what about SH and SC?

[winfred.dela]

the water is a chilled loop that feeds all the coldrooms the inlet temp is 25c which means on r134a i get head pressures of 200 to 300psi and out on hp,

25 deg C - Is this the condenser water entering temp?

checked the condensers all clean no lime or scale good flow rate good heat transfer (water in 25 out 47c), i just think the water inlet temp is too high, what to you boys think, please help

delta T = 47C - 25C = 22 - This is too high.

You need to check the condenser water system, i.e. water Flow and air flow (cooling tower?)

[karelsdr]

I agree ,your flow rate is way too low.For 25 in you need 27 or so out.

[LRAC]

Hi tait71

The first thing to check would be the water inlet valve i am presuming its controlled off the H/P side of the system?

How did you measure the inlet water temperature i.e actual temp or pipe temp maybe water is sitting in the inlet side and warming up.

1 thing for sure the water temp is too high.

Regards
LRAC

[Samarjit Sen]

You should check the condenser water flow system ie measure the water inlet and out let temperature, flow of water and the pipe line along with the valves.

[old gas bottle]

think your right ,tooooooooooo warm comming in, where is the supply water comming from? can you ajust the incoming temperature,ie has it a remote cooling tower with ajustable fan settings ? it needs to be droped a good 5 deg,s

[tait71]

hi people many thanks for your replys, i spoke with a very wise man fron hubbard ref, he was saying the flow rate needs to be higher or/and the water inlet temp lower.
This system has a ref plant water cooled, the water stage is cooled by a second water heat recovery stage which heats the incoming hot water to the building then there is a final air cooled condenser on the roof also linked to a lennix waterchiller (not designed to run below 15c air temp) i have been told that my water stage should run bettween 25 to 35 c buy the on site engineers, me/we as a company didnt install this and looking at the coldrooms i have found blown fusable plugs and hp switches wound up may be a design failure? what do you think?

cheers again boys!

[US Iceman]

...looking at the coldrooms i have found blown fusable plugs and hp switches wound up ...

Well I'm not surprised. With that high of a temperature difference on the condenser water, it's a wonder the system operates at all.

It sounds like :

A) someone tried to get creative with energy recovery and shot themselves in the foot. (or maybe their customers foot )

B) The heat recovery is at the expense of everything else.

[old gas bottle]

sounds like one of those over complicated design miricles that are doomed from the start, so they have heat recovery to preheat the hot water,thats good, but on the same system it feeds the condensers yes ! then it needs to be cooled to make it work, i find it hard to see how it could save energy, i went to a big one last year where the cooling tower had been scraped and replaced with a chiller to cool the condenser water, there,s some funny ideas floating about.

[TSK]

Second stage chiller would not expect to see 22 dec rise from leaving water to returning water, if second stage is coping with load it is only doing so because the flow rate is so low. Pump definatly not moving enough, is there a strainer, often strainers are just too fine a mesh, found plenty full of thread seal compound & muck. Second stage chiller will have been designed to handle higher than normal chilled and condenser cooling water (its a heat machine) elevating the water temp to the point the heat is useful for rejection via quite large heat exchangers.
As for the first stage condensers, well any water cooled condenser had better be able to handle 25 deg C water on as you will not see lower than this in summer with a cooling tower.

[US Iceman]

...cooling tower had been scraped and replaced with a chiller to cool the condenser water,...

I have worked on something like this before. A chiller was used to cool what used to be the cooling tower water.

The tower water was for process cooling, so the chiller recovered all of the heat from the tower water and the energy added by the chiller was used for pre-heating another water stream.

The trick is not to use more energy than you save.

[winfred.dela]

sounds like one of those over complicated design miricles that are doomed from the start, . . .

old glas bottle hit it right . . .
"COMPLICATED DESIGN THAT IS DOOMED FROM THE START"

I again remember an old timer advise to us (new HVACR practitioners) in 1988:

K.I.S.S. - Keep It Simple Stupid

. . .

[US Iceman]

old glas bottle hit it right . . .
"COMPLICATED DESIGN THAT IS DOOMED FROM THE START"

Oh, I think he is exactly right on the point of the original problem posted in the thread. That system does NOT follow the K.I.S.S. principle at ALL.

And you are right Winfred, this principle should be the guiding light behind any design.

[tait71]

another day another cold room off the loop out on h.p after looking into it a bit more i think the water flow is low, ihave 1.8 bar off the water pump and only 0.8 bar back, im thinking there is a blockage somewhere, the on site engineer was at a training course today so no progress made will try to get a flow meter on the condenser water supply later this week and i will report back!


cheers again

[US Iceman]

...i think the water flow is low.

That's what we have been saying.

You need to find what controls/regulates the water flow and try to increase it. I think you have a real mess on your hands. If this system is tied into other systems for heat recovery, anything you do to this system will affect the others.

[Peter_1]

Air in the system? Are all the water lines sloped and at the highest point a dveice to remove the air automatically?

[winfred.dela]

And you are right Winfred, this principle should be the guiding light behind any design.

The old timer who told us the KISS principle is an American from Trane. Since the day i heard it, my notebooks will always have a big note: K.I.S.S. - to remind me to simplify.

Sometimes, we wanted to do something that is Faddish. New concepts and products that were in new publications or journals and considered new trend are being applied to our design so that it can be called state of the art.

To remind me not to follow a design fad, i always have a K.I.S.S. note.

. . .

[US Iceman]

In some areas state of the art is an attempt by someone to reinvent the wheel. Even on very complicated system designs, it is worthwhile as you mentioned to look for ways to simplify the design to the minimum requirements.

The more complex a system is the harder it is for someone to work on it too. That gets people hurt.

[TSK]

You say you have 1 bar PD and you think you have a blockage, 1 bar pd sounds reasonable for a well designed system, trouble is I belive yours is not!
Start with your pump, get the details off the makers plate and ask them for the pump curve, you can read off the curve at 1 bar pd the flow rate (if it is mid range you can trust the reading, if it is at the top of the curve beware. I was once told we had the correct flow because the pump PD was high, whilst the pump supplier was at lunch I shut the outlet valve and the pd did not change, the pump had simply reached its maximum and that was that, later the pump was changed for a much bigger one!

[winfred.dela]

. . . i have a small problem i have 6 cold rooms installed in the same building running with searl evaps and water cooled copland scrolls condensing units,
. . . the water is a chilled loop that feeds all the coldrooms the inlet temp is 25c . . .,
checked the condensers all clean no lime or scale good flow rate good heat transfer (water in 25 out 47c)
. . . This system has a ref plant water cooled, the water stage is cooled by a second water heat recovery stage which heats the incoming hot water to the building
. . . then there is a final air cooled condenser on the roof also linked to a lennix waterchiller (not designed to run below 15c air temp) i have been told that my water stage should run bettween 25 to 35 c
. . . i think the water flow is low, ihave 1.8 bar off the water pump and only 0.8 bar back,

Per above posts, the following are some of the system components:
- 6 cold rooms with searle evaporators
- water cooled copeland scrolls condensing units
- lennix waterchiller (not designed to run below 15c air temp)
- air cooled condenser on the roof also linked to a lennix waterchiller
- water pump, 1.8 bar off, 0.8 bar back

You could have a multiple problems with the ff:
- Water pump
- Water cooled condenser
- Air cooled condenser
- Water chiller

To be able to analyze your problem, a good engineer needs a complete schematic diagram with each component's actual air/water flow rates, temperatures, etc. The actual data needs to be compared with the design parameters (if there are?) and equipment performance data.

Since we are trying to figure out your system, could you make a schematic diagram indicating the above components with component quantities and brands (if still possible). Usually, in this kind of problems, the system had been modified without any data gathering, so i believe you have to make your own to be able to analyze it.

I have been trying to draw a schematic diagram of your system but i have a lot of unknown data. Am just trying to complete the picture. I hope you will provide. I remember one of my college instructor keeps on reminding us:

"IF YOU CAN'T DRAW A PICTURE OF IT, YOU DON'T UNDERSTAND IT."

So here i am. . . asking some data to be able to draw the picture.

. . .

[TSK]

Well said, winfred.dela, it's frustrating reading of a problem and only having a small percentage of what we would go check on, two things spring to mind, both of which I was told by old sages; the first thing you think is wrong with the system "is not what's wrong with the system usually" & if you can't sort it out whilst looking at it, go get a cup of tea and draw the system marking on all the pressures & temperatures, by the time you have done this you don't need to ask any more questions. Mostly this worked for me but i have to say if the concept is new to you you don't have much chance because in our game there are a few who create some strange systems, some are very clever & some not so.

[setrad7791]

Sounds like a major problem with the design... if you want to cure your inlet water problems why not install a chiller uit to de superheat the water before entry into the condensor. Easy fix!

[wkd]

If your water inlet temp is 25c this should be fine but 47 c out is way too high this points to low water flow.Normal water cooled condenser design will be with a delta T of 5-7 K on the water side.You should also get about the same difference between condensing temp and oulet water temp.

[Josip]

Hi, Setrad 7791

Sounds like a major problem with the design... if you want to cure your inlet water problems why not install a chiller uit to de superheat the water before entry into the condensor. Easy fix!

Who is going to pay that


Best regards, Josip

[tait71]

hi got to the bottom of this one we found that a water diverting valve on the chiller/ air cooled leg was installed the wrong way round since day 1, so starving 1 of the 1st stage water cooled legs to my fridge condensers.

Thanks for the help boys, we need to stick together!