Chilled Water vs. DX

[Graybeard]

I recently posted a question in the Heat Transfer & thermo forum which might better be suited here. The question was related to which was better for a building HVAC system Chilled Water or DX. I would appreciate any response to the other forum.

 

[Goorah]

Graybeard:

I think you may be confusing "DX" and "chilled water" with what us HVAC call "unitary" vs. "built up" systems. This is because, a "chilled water" system ould be DX.

"DX" means "diect expansion" (thru a throttling valve). The other type of system is a "flooded evaporator".

Sorry if I've only confused you more. Take an HVAC guy out for lunch and maybe he'll explain more thoroughly.


I absolutely don't mean to be "condescending"... but, hey: I HATED organic chemistry. I could never visualize all those 3D molecules like you probably can!!!

Your question (to an HVAC guy) is like mine to you: How do you REALLY know that there's 2 H atoms and 1 O atom in a molecule of water? Hey: I read ALL ABOUT the electron microscope in the the last issue of "American Heritage of Invention and Technology" and I don't buy it! Dem guys probably just made what they wanted to appear on their "photos". You know?

Am I being "irreverant"?

Let's get some open discussion going on this board!

 

[Graybeard]

I was trying to be brief. When I said DX, I meant an air-refridg-air system. When I said CW, I meant an air-refridg-water-air system. In both cases, we will be using steam to provide heat in cold weather. I've asked a couple of our plant HVAC guys, one got upset that I asked, the other said he didn't know why, unless it was related to cooling down the 95F makeup air to 65F. He said DX systems don't like to operate on that high I difference. He said typical systems do 72 inlet 60 outlet.

I know a lot of ChE's that hated organic chem. too.

 

[ChasBean1]

Graybeard, chilled water cooling of air is typically preferable to DX as CHW provides better cooling control over varying loads, and performs much better at low cooling loads. In some cases it's not practical to have a chiller system to serve a single air handler or just a few air handlers, it's cheaper to buy a packaged DX unit and plop it on the roof.

I've also heard that CHW systems are better overall in operating cost, although I have no confirmation of that - maybe someone else out there who's dealt with this from a facilities side can clarify. DX technology is improving, however. At this point there are probably some DX systems that can rival CHW systems in finely-controlling cooling temp...

 

[YorkMech1]

Greybeard;
I fear your plant HVAC guys might have led you astray on the numbers..
"ALL" hospitals (example)"MUST" use 100% fresh(outside) air for the operating, recovery & delivery rooms.
Many of these use "D/X" units and are set-up to supply 55deg/f (52preferred)& 30-50%RH Supply air with Outside air temps ranging from 0deg.f to 105deg/f. & 25-100%RH
All use a "Pre-Heat" of whatever source, (electric,steam, hot water) to temper the colder air to say 55deg/f. Entering the "Cooling Coil". A Re-heat coil is also provided to maintain discharge Temps/RH under virtually all outside air conditions..
My point is that "Many" DX systems are set-up for Temperature drops of up to 65deg/f.
The last hospital operating room A/C I set-up was a "Brine" system(Glycol Anti-freeze) set to maintain 39deg/f discharge...The operating staff insisted on 50deg/f discharge air...
They got it...
Your question of which is better would depend on many things to give a specific answer....the main factor would be $$$$$$.
A chill water system "WITH" a decent sized storage tank is without equal....

 

[Goorah]

Graybeard:

Sounds like you plant HVAC guys don't know the answer to you potentially complex question (depends on the operations scale and criticality... did I just inventabalize a word????)... so they've blown you off!

I've got a better idea than my first one: When I said an "HVAC guy", I meant a trained , professional, degreed, experienced, industrial sales person. In my experience, Trane has the BEST.

Here's the better idea: Call your local Trane office, tell them whatyou want to do and THEY'll TAKE YOU OUT TO LUNCH!!

I worked for Trane for 26 years; but am now in private practice. Tell me your location and I might be able to give you a name.

 

[quark]

Graybeard!

If its for lunch i opt York rather.(oops i couldn't find any emoticons) As for your question when treating air with DX systems, there will be lot of problems of icing on the evaporator coils below 70 deg. F. If its used for centralised HVAC system the cost of installation could be high and leakages are to be taken care of. (Though i am not a professional working in HVAC company, I studied some because I am working in a pharma company) Efficiency of DX system is better in the sense you are reducing energy losses in the heat transfer, first from refrigerant to water and then water to air.

To be true Goorah is better option for you for his vast experience. I am just giving my views only so that you can discuss with the experts in the field.

Regards,

 

[Goorah]

Hey, Quark:

The smiley or sad icons or easy: just use the colon, minus sign and parentheses;and after you "submit post", the system puts the Icons in, like this :-(

Anyway, my experience is that York guys are wonderful relationship builders. Once they have awonderful relationship with you, they'll tell you "whatever" you want to hear ... even if it defies the laws of physics. Not only that: but it will have a super price; and all too sadly pressured facilitis peopl are apt to believe that ther IS such a thing as a free lunch (Tanstafal)

Trane on the other hand, while excellent at building relationships, also EDUCATES.. even if it might not give them a sale. This, I'm told, is because they WANT a LONG TERM trusting relationship and they know that if they aren't honest, it'll comeback to poison the relationship. Besides being degred engineers without exception and working on 100% commission (to motivate them) these men and women actually take a six moth course aside from their HVAC studies to simply study and understand relationships.

Best advice yet (if you have the time): Go out for two or more "Free" lunches with several vendors (Trane, CRR, York, McQ)... then about 2 weeks later and no further lunches, write down a technical summary of what you really learned from each.

Post Script: "Let the buyer beware."

 

[quark]

Goorah!

Thank you very much for the emoticons and for taking my message in right spirit. (Though I didn't really mean to offend anybody. It's by sheer fun i stated that). I do try your advice. (Don't hold you responsible eventhough if I don't learn anything technically:-()

Await your comments on technical suggestions I have mentioned in my previous message so that I can also refine my knowledge.

Regards,

 

[quark]

Goorah!

Thanks. It worked.

Regards,

 

[235zzzo]

Hello Guys

A few reflexions/thinkings about this subject: - CW versus DX systems, it sounds like an old question but keeping present, now-a-days!

To size and install a DX system, you don't need an engineer, even you don't need an experienced one, at all!
And if your aparthotel, or the hospital is big enough, you just have to multiply (to install many as you need!) that "brilliant", "shining" solution of yours and hope the architect/owner doesn't mind to see many boxes surrounding physically and noisy the building, in order "to entertain" the occupants way of life. Sorry for my irony.

If I'm right, for some technical and economical reasons, in a standard DX unit, the expansion temperature in the evaporator coil for standard equipment is trimmed, something in-between 43 and 46 ºF, which gives temperatures well bellow the Twb for typical humidity conditions.
That means those unities are working always as desumidifier device, even when it is NOT needed!
The temperature at the diffusion terminal devices is too low, you have thermal-chock. Therefore you must use a pre-heat or a after-heat system.
A DX unit is an on/of system not modulated system as your needs are, along the day and the season.

Regards to DX units, I wouldn't say that there are some situations, for which, no doubts, it is a reasonable solution, like in small and isolated spaces, but never applied in such scale as seen in offices buildings, hoteles, hospitals and so on... as we see everyday.

A question comes out: Is it possible to increase the evaporation temperature? What are the consequences in order to get a much more convenient (still cheap) DX unit? Shall these units turn bigger and expensive?
And what about the expansion valve, how to get a modulated effect to size the quantity of the evaporated gas ?? Electronic expansion valve. But then again, we have an expensive device....

Let's keep this discussion opened!
zzzo

 

[Goorah]

El ZoRRRo in Prtugal!! Welcome back!

I'm really enjoying this thread as we kick ideas around!

To answer ZZZ's question and respond to your VERY TRUE comments: That's why bypass VAV was developed!! And with the right supply diffusers, cold air "dumping" into the space is avoided due to the "coanda effect" and entrainment of the space air into the supply air. As the space temp drops,supply air is bypassed back to the return in what is called a "run-around loop". The unit's coil doen't freeze because the airflow over it too is constant ... but if total system airflow goes too low, the compressor can short-cycle.

Quark:

Don't fear to hurt my feelings: I have pretty thick skin!! The one and only "answer" to your request for technical suggestions that I tried to give was .... IT DEPENDS. What's your location; so I can maybe get someone to seriously assess your situation?... no obligation.

This would apply to unitary equipment (up to about 25 tons???) Buddha's advice 2,500 yrs ago (I'm Christian!): "After deep, careful observation/analysis; and it agrees with reason, is conducive to the common good: accept it and live up to it."

 

[235zzzo]

Dear Fellows:
Let me reply to Goorah: Pleasure to hear from you too!
To Goorah and everybody, I ask comments to this: A few years ago, when i was auditing an hvac installation i suggested in the report what you mentioned above, the "run-around loop" to a DX unit, to solve and balance its regime, because the compressor. Believe me, at that time i real dislike (hate!) those DX systems. That is NOT HVAC!! Today i'm trying "to accept it and live up to it", by Budha, as you noticed.
Now, suppose you have not a bypass VAV, but you just implement a cheap "run-around loop" as a common part of your air-duct installation with fixed air flow rates. Of course the total air flow to the space is lesser than the air flow rate through the unit. I have granted a more stable regime to your compressor, however in order to do that you had to size a DX unit some 25 ~ 35 % bigger than you need. (You saved money more than enough, because you don't have to pay the VAV bypass, nor its control device) I think you understand all the rest of this picture...
Regards to all
zzzo

 

[Goorah]

Zorro: You Portugise" are such deep thinkers!!! And I RESPECT that!! If not for PORTUGUISE... WHO would have discovered AMERICA? and WHO would have colonized JAPAN (Arrigato "in Japanese" = Obligato "in Portugese"!!!)

I am NOT making FUN!! I really BELIEVE that you guys TRULY HAVE it TOGETHER!! Must be you independence due to the Pyranees Mountains... or maybe your fine wine ... and "corks!... Lo SIENTO!! I just COULD NOT RESIST!! I mean no harm... For some reason YOU GUYS ARE truly JUST Intellectuals and are responsible (although few know it) for western advance!! I know: I've worked with a few of "YOUR type)!!! Zorro: Do you know Orlando Marinho? He and I love to have philosphical-engineering debates. That is how we GROW our minds... by testing them!

ANYWAY, you ask a good question. AND THE ANSWER is (politically speaking)................. It DEPENDS!!

WHAT ARE YOU TRYING TO ACCOMPLISH???????



If you want to save OPERATING COST, then YES... that over-sized system is right!!!!!

But if you want to limit FIRST COST, "YOU" (who is "you???) is TOTALLY WRONG!!!!!!!

You SEE???? ... IT DEPENDS.... WHO are "you"? .... WHERE YOU are? (Italy, Spain, USA???)... what are your ENERGY prices (operating costs) utility, cogen or mix???? WHAT are you trying to accomplish??? (human safety or comfort or macine proper function???)... IT DEPENDS and ONLY WE acn decide!!! We need to consider ALL OF THESE!!!!


And then make the "best guess" we can. (????!!!!???)
Oh "you guys". Next time I'm in Portugal or you're in USA; let's look each other up!! My wife and I are ALWAYS looking for reasons to burn up our expense account in "professional development"!!

Keep an open mind and have FUN!!!

I'm starting to LIKE this website. ... Since I got "downsized" out of corporate life, I am finding HERE that the IS LIFE after the corporation!!

Take care and KNOW that this is in good spirit!!! Buddha's advice 2,500 yrs ago (I'm Christian!!???!!): "After deep, careful observation/analysis; and it agrees with reason, is conducive to the common good: accept it and live up to it."

 

[Goorah]

ZORRO:

PS to my last post: with the proper slot diffusers proper supply velocity for mixing will be obtained.

Hey: this is BORING... go discover some life in another galaxy.

But remember that my wife and I are looking for an excuse to go out to eat lobster and steak (Steke!!)... Yummmmm.

If you "traveler/vagabonds" ever "land in USA our number is (608) 786-3956. I speak "desent "Portenol". The wife?? She speaks only "American".. and is "amazed" that I can speak "Portenol" (what's that??) I guess only you would know!!

But my formewr boss ... a Colombian ... is FLUENT in NO LESS than FIVE (5) languages!!! Granted four of them are the "romantic" ones... BUT guess what??? He ALSo is FLUENT in MANDARIN!!!!!!!

MAN (HOMBRE!!!!!!!) I RESPECT that guy!!! ... And even though he is "Colombian" by ancestry he is "Portuguese", ZORRO!!!!!

Are we liking this forum yet??? Buddha's advice 2,500 yrs ago (I'm Christian!!???!!): "After deep, careful observation/analysis; and it agrees with reason, is conducive to the common good: accept it and live up to it."

 

[quark]

Goorah!

Corporate downsizing is a brilliant word (Excuse me for going out of way in this page. But could not resist myself)for I always think energy conservation should be a virtue rather than a compulsive force. With only 7 years experience as a mechanical engineer I too feel downsized. When imposed upon I found that energy is conserved quite paradoxically. (Everything is possible on paper and nobody bothers a counter check for the manager always thinks that he can understand any darn thing) :-(

One way of maintaining low energy bill(?) and to cater to all load condition for some rooms we installed DX units with hot gas bypass system. But compressor draws same power in all load conditions. (energy saving seems to be from reducing the losses in conversion)

I anticipate your association as you have good experience and request your mail id.

PS: I no way relate to Christopher Columbus

Regards,

 

[Goorah]

QUARK:

Are THEY QUARKY??!!??

HGP to save energy is like standing on the on the brakes and accelerator at the same time!!!

HGP is a capacity limiter... or a frost preventer! But don't "rock the boat" you young buck you.... or watch out... someone who is probably plder and "wiser" than you made that smart decision, right?

What is the specific problem?

Have a good day!

Buddha's advice 2,500 yrs ago (I'm Christian!!???!!): "After deep, careful observation/analysis; and it agrees with reason, is conducive to the common good: accept it and live up to it."

 

[235zzzo]

Hello Guys!

Enjoyble to read you, GOORAH!!

I´ll tell one thing: i'm very critical about the portuguese history, like something in my childhood, someone force you to buy it. I never did! But that is another "story".
Well, you are right, one of these days we have to meet, some place, somewhere, just say when and which galaxy!
Yes indeed, this crazy word is becoming too small and I don't have those 20e6 dollars to take a walk on the "dark side of the moon" and surroundings.....

Technically speaking, I have the feeling that the present subject is becoming exausted, or not?
Anyway, this has been a very nice and rather interesting, t some technical matters give place and the opportunity to us to talk about ours lifes and experiences.... That's this stands for!

I'll take the liberty to use your email in order to go deeper in certains subjects beyond this forum, if you agreed. Mine is raposso@net.sapo.pt
Regards.
zzzo