Condenser Water System Design

[NeoMeche]

Hi All,

I have to design an open loop central condenser water system for a 9 story building in New York City. There is an abandoned project that I am working from and already have selections for 2 cooling towers as well as two condenser water pumps operating in series.

The goal is to provide the system with capped and valves outlets at each floor for tenant use. I should also mention that the 3 stories of this building are retail (subcellar, cellar, ground) and floors 2-9 are class A office space.

The building currently uses packaged air cooled ac units within each tenant space but these are to be eliminated and all spaces will be served by the new central condenser water system. Specifying ac units, ductwork, etc is all outside our scope of work FYI.

I don't have a particular question in mind but I have never designed a condenser water system. I was hoping you guys could help me with design considerations and maybe point me in the direction of some helpful resources. My only experience with condenser water systems thus far in my career has been tapping into them for small tenant fitout jobs (eg. an office space).

Thanks.

 

[Ziggypump]

So, the air cooled ac condensers are being replaced by water cooled ac condensers? Or was the system to be more like a chilled beam system?

Should be a fairly simple hydronic cooling system. Pumps, cooling tower or chiller, air separator. . . Calculate your cooling loads, and size the condenser system accordingly. Obviously it's more difficult than this, but utilizing a sizing program should help.

 

[Drazen]

Yes, as you described it as condeser water system, only water - cooled units are to be expected, but that would be reversible heat pumps I beleive, such building could have thermal balance for large part of year, having commercial floors, for which it is not impossible that heat gains allways "overpower" heat losses.

If that is the case, the cleverest designer thing could be to select year-round water temperature in your system.

 

[mauricestoker]

It would be useful to describe the intended use for the open condenser loop. As Drazen states, a closed condenser loop with HX for the cooling tower, and possible second HX for supplemental heating (depending on climate). Water quality should be a consideration, as an open loop system could lead to fouling problems.

 

[KiwiMace]

You might want to consider closed circuit towers. Sediment and scale etc from open towers tends to build up and choke the smaller coils in the units described. Water quality is rarely well managed.

Glycol will likely be required. Check your NYC disposal regulations, as you may need containment.

You will need to coordinate with the airside specifier to get the CWS&R temperatures & flow reqmts.

Office buildings have server rooms. Check owners SLA for availability - you may also need to put the tower fans, (spray pumps), DCW pumps on 24hr and/or backup power with water storage as required.

Other things to consider: Pumps, basin heaters, controls, vfd's on fans and/or pumps, tower materials, weight/structural load, space reqmts, dunnage, access platforms, pipe routes/supports/penetrations, expansion, water treatment, distribution, pipe materials, crane or helo lifting, road closures, to use crimp joints or not...

Enjoy.

 

[NeoMeche]

Hi All,

Thanks for the tips thus far. The design is coming along well.

Some notes on the comments above.

-It is an open tower system. I have already specified all the equipment.
-There is no glycol in the system because it is open tower. All outdoor piping is to be double insulated and heat traced.
-I have sized all the piping and have coordinated the risers through each floor. I am provided capped outlets with shutoff valves at each floor off the condenser water supply are return risers for tenant use. I also have an express return from the pumps (subcellar) to the cooling towers (roof).
-I have already coordinated the towers with the structural engineer
-I am specifying VFD's on the cooling tower fans and pumps.
-Crane/lifting/road closures are all the landlords responsibility.

I have a few other question for the board.
What is the best type of pipe to use for condenser water?
Is insulation required for indoor condenser water piping?
What type of valves/strainers/etc. will I need in my supply loop (around the pumps i mean)?

 

[katmar]

Is the cold water from the cooling towers on the roof pumped or gravity drained to the users on the various floors? It sounds as though you are draining down through the condensers and then pumping back up from the sub-cellar.

Is it necessary to control the pressure to each floor, or can the equipment cope with the pressure variation between the bottom and top of the building? You have to ensure that the top floor gets sufficient pressure, while the bottom floor is not over-pressurised.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[KiwiMace]

CW pipe is ideally done in hot dipped galv at larger diameters - standard spec for some places, but not as common in US where most opt for painted steel. Insulated only for freeze protection. For smaller diameter branch distribution, you will likely reduce to copper.

A basin strainer and typical Y-strainers should suffice as these are only catching the larger debris anyway. A cyclone filter (Pep, Carver) is good for clearing out smaller particles. This can be installed as a bypass on the CWS/R where there is some likelyhood of the basins being routinely cleaned, or swept from the basin with eductors where less likely.

 

[Ziggypump]

A cyclone filter is a good idea, but so is a non-chemical treatment system. You can try the following website to see about one of these systems. The treatment process uses electricity to zap organic materials in the systems until they die. The solids separator is needed to remove the dead particles that is similar to white powder when dry. This way you can save money on chemicals that would be evaporated away in the cooling tower.

 

[mauricestoker]

I haven't met a plant operator yet that had a dolfin installed that still has a dolfin installed.

 

[Ziggypump]

After how long? As far as I know, 2 years after operation, the one I had installed in the system is still in use. And this is a company that complained that the domestic cold water wasn't cold enough. And the dolphin system was their idea.

What is wrong with them?

 

[mauricestoker]

Having met with their sales engineers, I've been in informed that the dolfin is not suitable for karst geology areas. Maybe it works well for areas where the water quality is already good, but definitely not if you are pumping water from limestone.

My last chiller project had a dolfin-and rapidly packing bundle. Based on LMTD readings showing the dolfin was not working, we went to chemical treatment. That location had problems with routine high turbidity, which apparently the dolfin doesn't like.

As part of current chiller project, about 2280 TR, I've talked with plant operators in four surrounding states where dolfins were installed, and in every case where I asked, the dolfin was removed. My experience has been bad; yours would be the first time I've heard that a dolfin is kept in operation.

I think the dolfin has the same track recoord as magnets for water treatment. I know ASHRAE has endoresed two different phyiccal water treatment systems, but I still have not heard a plausible explanation of how the parrot worked, much less the dolfin.

 

[KiwiMace]

There have been so many reports of various kinds of non-chemical water treatment not working, that most engineers are very hesitant to specify them.

Usually it is the client pushing for these systems as it was in your case, which means a nice quiet replacement project, not broadly discussed and tagged onto the budget of another project. Ask your client if they are still happy with it.

 

[Ziggypump]

Like most clients, this one wanted a BMW while paying for a Honda. Nothing worked right, one heat pump wasn't operating correctly and it was our fault, until it was discovered that it was wired incorrectly. If there had been any issues, we would have been made aware. I'm no longer working for the company that designed the system, so I can't get back in touch with them.

 

[ChrisConley]

Nothing worked right, one heat pump wasn't operating correctly and it was our fault, until it was discovered that it was wired incorrectly

And why did it take you so long to find the problem?

I don't mind solving problems that everyone says is a design problem, but turns out to be a construction/maintenance item (actually I do), but the worst is still getting no credit when you do solve someone elses problem [/rant].

 

[Drazen]

Galvanized pipe or cast iron should be the choice.

As mentioned in previous post, you should decide on temperatures if you already did not (cast iron has some limitations on higher temperatures, but that should not be the issue in your case).

Moreover, I think you need some sort of chemical treatment in any case, and than you need to check with chemical compactibility.

I would recommend insulation in any case, as you are assumably working with low temperature differences and high flows, so any degree makes difference for water cooled heat pumps.

Thickness? Arbitrary decision would be needed. Use some of insulation calculation software, as one of Armstrong, and calculate according to per meter losses to see where diminishing returns come into play.

 

[coldmaster]

Consider winter operation and operation under low loads. A three way bypass valve below the roof level may help with this.

The main piping should be insulated throughout the building if CW used for free cooling in the winter.