Cooling Tower Replacement

[MechWang]

Hello All, Newbie here, just want to get some expert advice, with regards to cooling tower replacement.
Do you just get the same specs of the cooling tower and replace it same for same? or you still calculate the heat load of the building to compare to existing?
second, when you change the cooling tower and condenser water pump, are you required also to replace VFD / controls or you can reuse what is there?
Third, for permit documents, do you add the rental cooling tower in the plans or just let the contractor figure it out? would really appreciate some advice. Thank you.

 

[EnergyProfessional]

The tower should be matched to the chiller plant. Probably good to verify if that actually was the case for the existing tower.

You can re-use what still works and has lot of expected life left if the size is correct.

I wouldn't just re-use specs, you are installing a new tower, not the 30 year old one. And any blind copying also copies any old errors.

For permit, ask the JHA what they require. From my point, you could be in Qatar, Sweden, or Brazil. they all will require different items. Probably depends on how long you need the temporary tower. Decades, years, days?

 

[MechWang]

Pardon my ignorance, i dont see a chiller, I see a Trane scwg model (2) 30 TON and (2) 35 TON. existing tower is Marley has 2550 gpm Condenser pump 2500 gpm, Yaskawa vfd. no existing drawings whatsover. I am here in Broward Florida. I just need some guidance on how to tackle so i dont duplicate the error/'s if there is any, so far i created an excel sheet to list all TOR of the apartments offices and common areas of the building.

 

[EnergyProfessional]

those might be chillers? If you don't know what they are, you should hire an HVAC engineer for the project.

 

[MechWang]

Yes they are chillers, I as i have said, i am really green with regards to hvac design, but im willing to learn, and not having any existing drawings make it more hard to learn the original design, and as previously mentioned, blind copying what was there is not really a good start to learn, that is why im trying to obtain valuable insights to further my knowledge

 

[moideen]

The wet bulb is important when you replace the cooling tower. In Dubai, the old cooling towers almost set the temp as 29 c. but, the climate is gradually changing, and nowadays’ the measured wet-bulb temp, on a peak reaching 31 or 32c. so, the new cooling tower selection I prefer as 31C. (when you increase the wet bulb, the approach will come down and may increase the size of the tower)
Second, comply with the selection with ASHRAE 90.1 energy standard. These times, even the “low” efficiency towers are significantly more efficient than the Standard 90.1 minimum of 38.2 gpm/hp (3.2
L/s·kW).
Check the existing clearance around the tower to prevent the recycling of moist air, follow manufacturer's recommendation


The problem with the world is that intelligent people are full of doubts, while stupid ones are full of confidence.
-Charles Bukowski-

 

[nuuvox000]

I would definitely do a quick review of the building and do some rules of thumb calculations to make sure that it's not way oversized or anything. I would also ask the building/maintenance manager if they have trouble keeping up with cooling in the summer months.

I always try to meet the latest energy code when I upgrade any system.

I would just put a note for the rental and show where it's going to connect into the system. I might include it in a schematic drawing.

 

[nuuvox000]

It sounds like you're tasked with finding a solution but for some reason don't have knowledgeable support. In that case, I would recommend getting with a cooling tower and chiller supplier and ask them to help you. In my experience, they're more than happy to take a look with you and sell you equipment. Usually in the commercial area, the sales people are trying to get it right so I typically don't have to worry about being taken advantage of and being sold something I don't need.

 

[IanVG]

Just finished my first cooling tower replacement job. I was also very green ( you got it! ), but I always had the help and guidance of more experienced engineers in my office, so that helped a lot.

Some things that came up with the cooling tower- re-evaluate the deisgn temp of the water is being used for. E.g. could be WSHP's (Water Source Heat Pumps), or AHU's or a variety of things. Depending on the system type, you may have different needs for the controls of the cooling tower system. My project included replacing a shell-and-tube heat exchanger. Where I work, we typically provide VFD (VSD's (Variable Frequency Drives or Variable Speed Drives)) with the cooling tower fan. Depending on the area you are in, you may get credit for the make-up water for the cooling tower-in that case you may need to get a city/county provided water meter for you to get those credits.

If you haven't already, create a P&ID (Process and Instrumentation Diagram) which will help you visualize what's happening where. A P&ID will also make it more convenient for you to see what kind of controls will be necessary where.

I also second the others' opinions on here that you should reach out to the cooling tower sales reps on helping you select a cooling tower. There can be a lot of variation in how you set them up and how they integrate into your systems (bypass or no bypass being one example).

Depending on who you are designing for, getting in touch with the people who maintain the system would be a good idea. I ending up getting some services from a structural engineer to design some custom railing for accessing the top of the cooling tower.

Some other points in no particular order of any kind that I think will help you:
[ul]
[li]Make sure to account for aesthetics as well. E.g. if the cooling tower is taller than before.[/li]
[li]Are there trees directly above the cooling tower? Consider that kind of debris.[/li]
[li]Make sure to consider any kind of NPSH (if applicable) requirement for your pumps.[/li]
[li]Consider what needs to be included in your BAS (Building Automation System) and what should be controlled by the device itself. Protip: Reps of both the equipment with built-in controls and control companies will each tell you that they can control the equipment most efficiently.[/li]
[li]If you can-reuse pipe! Save money.[/li]
[li]Obviously design to achieve project goals but also design for the people who will take care of the equipment. They will be stuck with both your successes and your failures. This means think about valve location and placement.[/li]
[/ul]

 

[MechWang]

Thank you all for the tips, the hvac suppliers are a mine of information, really help me a lot, I am getting the hang with the BMS system. I am a little lost with regards to implementing variable speed pumps for the cooling tower as I had the impression that too will have VFD's. so far, VFD is only for the fan. Any insight on Variable speed pump, is it worth doing it? The vendor said it would be costly to do and tedious, just want to get your thoughts

 

[nuuvox000]

I don't think I would ever do a VFD for the cooling tower pumps, just my two cents. So I've heard, you get scaling problems if your flow is too low. I have seen VFD's on the fans of the cooling towers.

 

[pierreick]

Hi,
Consider the document attached related to VFD.
Pierre

 

[oulearn]

consider looking at the past performance issues, especially during the peak season. I would discuss with the manufacturer application engineer; they are a great source to assist in design and selecting the right replacement equipment.
consider chilled and condenser water reset configuration. using VFD for condenser water pump with a minimum flow setpoint to avoid scaling and low flow conditions may save power.