Cooling tower bypass into the basin VS completely bypassing the tower 1

[BronYrAur]

Any thought on pros and cons of bypassing water into the tower basin (ie not up through the fill) versus completely bypassing the tower. I am specifically talking about a non-winter operation, so the tower fill would not be bypassing as a means of freeze protection. No concerns of freezing at all here.

The purpose of the bypass here would strictly be to warm up the condenser loop in the even that it is too cold during startup, etc. Why bypass into the basin? Why not just bypass between the supply and return lines inside the building?

Thoughts either way for a non-winter scenario?

 

[nuuvox000]

Maybe I'm missing something but why are you warming up the condenser loop? What's the danger of it being too cold?

 

[BronYrAur]

to keep it above min recommendation of the chiller manufacturer.

 

[HVAC-Novice]

Could modulate the return flow to chiller based on temperature to avoid too cold water. Should stay above minimum flow requirement. consult with chiller manufacturer on options.
This really only is an issue as chiller starts up. If you need to run the chiller at very low ambient temp, you are better off implementing some economizer anyway.

Without information on what temperatures we are talking about, this is a guessing game. What is "too cold"?

Believe it or not, chiller requirements, operating conditions, and climate data are important.

 

[BronYrAur]

Hvac-Novice

I appreciate your comments but I'm really only looking to get opinions on bypassing the cooling tower entirely or sending water into the basin. Usually water is sent to the basin in order to help with freeze protection when the tower is running year-round. This is not the case with my application. My tower will not be running year-round. I anticipate very little use of this bypass only in the event that condenser water temperature gets too low. It may in fact never happen. But I need to convince someone that is unnecessary to bypass to the tower Basin and that a bypass strictly from Supply to return will be adequate. The ashrae manuals show both ways. They do not recommend bypassing directly from Supply to return, but their reason for this is freeze protection at the tower basin. I have no concerns of freeze protection in this case. So I'm just looking for any other opinions on One Way versus the other.

 

[Rputvin]

We will bypass to the tank/sump in industrial cooling (non-HVAC) loops using cooling towers. We do this as a stage of over-cooling protection to prevent condensation in equipment when the tower is able to cool below dew point - dew point in the facility is not the same as outside at the tower. It's also a freeze protection method when we're running a secondary remote sump indoor.

Go to the basin to ensure you're mixing your water, otherwise the basin could be holding water at a lower temperature and you might see odd valve behavior when an un-mixed cold slug passes through when you come off bypass and sensors pick up the temperature drop.

Even with a 3-way valve on the heat exchanger for temperature control, another 3-way setup as an on/off valve at the tower allows you to keep the pumps running, but prevent additional cooling, and still keep all of your process sensor values updated.

 

[SAK9]

BronYrAur,

Where are you located? It looks like you are in a mild climate location. If you bypass the entire water flow away from the tower, the temperature rise on startup will be very quick and may trip the chiller on high pressure cutout. Based on the line-fill volume you can calculate how much time is required to get the water temp above the safe limit.

 

[BronYrAur]

This is in the Chicago area, so not a mild climate, but again this does not run in the winter. Minimum chiller Inlet condenser water temperature is 55°.

 

[SAK9]

I would go with a blending valve set to couple of degrees higher than 55F(a portion of water going through the tower fills and the balance bypassing the tower completely)

 

[mrev23]

What 'pros' are you claiming while trying "to convince someone that is unnecessary to bypass to the tower Basin?"

Two 'cons' to completely bypassing the basin:
1. Water treatment chemicals in the basin will not be refreshed while it is bypassed. Depleted chemicals will be less effective in combatting corrosion and the growth of Legionella.
2. The filter in the condenser water loop cannot clean the water in the basin while it is bypassed. The fan would be off, but pollen, cottonwood seeds, and other airborne debris might accumulate in the basin while it is bypassed. The filter isn't meant to accommodate a slug of debris when flow through the basin is restored.