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Peter_1
16-01-2004, 11:16 AM
Hi all,

I want your comments on a subject discussed this morning.

I had a meeting wit some engineers of a multi-discipline engineering company.
We have to made an offer for the cooling of 6 switch-cupboard rooms 'with heavy frequency inverters in it) with a total capacity of 250 kW.

In the papers we got, they described 2 Carrier chillers on a water regime of 6C/12C. Temperature of the rooms should be +/- 24C.

Because I don't like that much chillers because anyone can install them, even someone who never saw a chiller before in his life - in Belgium very often a plumber who only knows you if he has problems with it - i suggested that the running costs of a pack is cheaper. I had the wind complete in front of me from most of the engineers, mostly construction engineers who saw the basic principles of cooling/heating while studying.
For them cooling is just the same as heating, you have a waterflow and pumps, in the first case a burner, in the other a chiller. That's it.

I argued the following: We need +/- 45 kW/room. We did a selection for a AHU with a condition of 6/12.
So, for a condition of 6C leaving water, we need to evaporate at 0C.

Now, we install the same AHU but now with a direct expansion coil in it.
For the same capacity I need the cooling medium to cool down also to +/- 6C to 5C, so evaporating at 5C. I gain 5K, so that's a (big) advantage (the way I see it anyway) in COP.

Any comments or other ideas?

chemi-cool
16-01-2004, 02:47 PM
peter.

I have done somthing similar in big trasformers room.

On each cupboard I have used two ducted splits, one on each side pushing cold air from the top and return air from the bottom.

one unit out of the two is stand by.

maybe cost a little bit more but very reliable.

chemi

Brian_UK
16-01-2004, 10:45 PM
Originally posted by chemi-cool
........ pushing cold air from the top and return air from the bottom.

Chemi, I know it depends on the room layout etc but it would make more sense, surely, to put the cold air in at the bottom and take the hot from the top. Hot air naturally rises so why spend effort pushing it back down again ? :confused:

Andy
16-01-2004, 11:01 PM
Hi Peter:)
DX is ofcourse cheaper, but water is very flexible, and piped into coils that are compact for applications with little space.
Me I would go for DX and an AHU, but that would be a up hill struggle to sell as most people have a pre conceived idea that a chiller is what they need.
We are developing R744 secondary/ volitile systems for such applications, servers especially.
Regards. Andy.:)

chemi-cool
17-01-2004, 07:14 AM
hi Brian,

its true what you say but forced air change the rules.

olso it saves a lot of duct work and when electricians are working there, they (and most people) prefer the cool air coming from above and cooling the top of the body first and not cooling the b.....ls.

chemi

Peter_1
17-01-2004, 07:46 AM
This is a picture of an AHU we did in september last year: 2 packs of 350 kW (0C/40C) for an exhibition room.

Peter_1
17-01-2004, 07:47 AM
Another picture and we achieved our goals

Peter_1
17-01-2004, 08:00 AM
Originally posted by Brian_UK
Chemi, I know it depends on the room layout etc but it would make more sense, surely, to put the cold air in at the bottom and take the hot from the top. Hot air naturally rises so why spend effort pushing it back down again ? :confused:

I disagree with this: you always have to blow out the cool air as high as possible.

Cold air is the primary air. If you blow it along the ceiling then it will mix via the coanda effect with upcoming warmer air, the secondary air. This secondary air becomes a little bit hotter whereby it's more agreeable for the occupants. The cooling effect is not that high. This mix which is still colder then the surrounding air will descend automatically through is greater density.

If you do it otherwise, then you will encouter a lot of problems on the field of comfort .

This is in fact the whole meaning of ceiling grilles.
Trox has even special ceiling grilles with electrical motors build on the vanes so that you can adjust the vanes when you cool or when you heat with the same grilles.

We always try to install airco's with ducts so that you can't hear them (lower then 28 dBA) nor feel them. It's not always easy but we try.

A Belgium manufacturer, explaining the coanda effect
http://grada.vandenbroele.be/pages/engels/leesmeer/april/coandaE.html

chemi-cool
17-01-2004, 08:37 AM
mornimg peter,

I was refering to cooling inside electric cupboards.

what is most important, is not maintain the incoming cool air at a temp which is always higher then DPT to avoid condensation insde. about 20C is safe.

looks like you had an oil leak on picture 0016.
which sony do you use?

have a restfull weekend, got to run to one of my clients, low presure triped on a chiller.

chemi

lin
17-01-2004, 09:32 AM
of course, DX system is cheaper at same capacity.
But most cases like that need very reliable system. with a dx ahu with 45kw at each room, if the refrigeration system fail(the most frequent failure source), it cann't keep the temp.
and with chiller system, the ahu in room is simple, thus less failure rate. and there always have multi-chillers, because the actual load in each room may not be as much as predicted, so even one chiller breakdown, there are a great chance that other chillers could still keep system work.

A attention to this type of application. beacause of high sensible load rate, normal dx ahu may lead to low humidity and lack of capacity(even the total capacity is enough). select dx ahu at evaporating temp above 10C would help. (for chilled water system, run water at 9C/14C), because there may have cooling demand at cold weather, head pressure control for dx system would be needed.

Gary
17-01-2004, 11:34 AM
The name of the game is heat transfer. We transfer heat from one point to the next to the next, until we finally transfer it to the outdoor air. A chiller adds one more link to the heat transfer chain, so (all else being equal) it must necessarily be less efficient than DX.

Peter_1
17-01-2004, 11:47 AM
Originally posted by chemi-cool
mornimg peter,

I was refering to cooling inside electric cupboards.

what is most important, is not maintain the incoming cool air at a temp which is always higher then DPT to avoid condensation insde. about 20C is safe.

looks like you had an oil leak on picture 0016.
which sony do you use?

have a restfull weekend, got to run to one of my clients, low presure triped on a chiller.

chemi

Haha, nice try Chemi. But it was I who spoiled with the oilreceiver and and it left a big spot in/on the concrete.

This is also an example/installation of a DX evaporator/rack combination. Evaporator is divided in 2 equal circuits for partial load possibility.

Mark
17-01-2004, 06:02 PM
hello peter:)
The attached jpgs ,is the pack made by pro-froid ?.Several of the packs im involved with are made by pro-froid .How do you find pro-froid packs? .We had one supplied(approx 600hp) that was incorrectly piped and the consequences were that the fatique from a compressor,caused a leak on the steel discharge pipe onto the header ,once they had came to site and rectified the fault by altering the pipe work and welding(at there expense) we havent had many problems.
regards mark
:)

Peter_1
17-01-2004, 08:46 PM
Indeed, theseare Profroid packs (or Carrier or ECR with other words) I visited the factor 5 years ago and I was impressed. they make +/- 3500 packs a year and many of them are for the Far East, South and North America.

They have a huge stock of compressors, it was overwhelming.

Never install evaporators or condensors of them Mark. Capacity in catalogues is way over-estimated (of course none of them is Eurovent certified) We had enormous troubles with some. Once calculated for a DT of 7K, and we turned out on 14 K.
We've got new evaporators (at no cost) and installed almost the double as calculated. Finally we got it right that way.

Had the same problem with the discharge header. It's always a steel welded header. Had also once a problem wit the suction header from which the different inlet suction tubes were not equaly welded inside. One compressor always lost his oil.
Another problem, the flexibels they use are with steel nuts. They never fit a small copper ring in it and we had several times leaks on it.

Problems is always if there are any problems, they are far away from us.

We alwayys have contact there with Baranowsky and the sales person for us is Bajolle.

Mark
17-01-2004, 09:00 PM
hi peter:)
The reason for the leak i was explaining was due to the fact they had installed a discharge pipe horizontal to the header from the compressor.

regards mark:)

Peter_1
17-01-2004, 09:48 PM
Originally posted by chemi-cool
mornimg peter,
looks like you had an oil leak on picture 0016.
which sony do you use?
chemi

Chemi,
It's a Sony DSC-5P, 3,2 megapixels, now 2 years (or is it 3) old and we took already +/-6000 pictures with it. Realy a good invention.
Just the flash is not powerfull enough in some occasions.
Payed a lot of money then compared to the prices now.