Condenser Water Relief

[Friction1]

Hi All,

I'm looking at a project involving the installation of a Variable Frequency Drive and Condenser Water Relief for an 800-ton Trane CVHF.

The basics are:
1. The VFD allows the compressor motor better start-up, shut-down, and part load operation (ie as low as 50% motor speed & therefore compressor speed).
2. The condenser water relief allows for the conderser water set temp to be lower (must be because compressor not working as hard).

My question is: What does the actual physical implementation of a condenser water relief entail? Is it only operational or is actual equipment installation necessary. What exact changes to process & equipment allows the condenser water temp to be set to a lower temperature?

Thanks, Friction

 

[KenRad]

Your post implies that the condenser water setpoint HAS to drop with the change in chiller load, but I don't see why. My thought is that you take cooler condenser water (within the limits of the chiller) whenever you can get it based on the improved chiller efficiency it can offer. Obviously, when the chiller is operating at a lower load, you will be able to achieve lower condenser temperatures easier.

The way I accomplish a variable condenser water setpoint is with a VFD on the cooling tower fan. Aside from the cost of the VFD (which is partially offset by the cost of the conventional motor starter which you no longer need), the only other equipment difference would be a tower fan motor that is rated "inverter duty."

If you're using DDC controls for the tower operation anyway, the only difference would be the reset schedule that would adjust your condenser water setpoint based on outside air conditions. This takes advantage of times when you can get cooler condenser water cheaply (ie, when the wet bulb temp is low), and will work regardless of what method of chiller capacity control you're using.

You might be able to use a VFD on your condenser water pumps, to save pump energy as the chiller load drops. I've never done this -- depending on the design of the tower, this could create some problems as you go below design values for flow. Maybe someone can comment on variable condenser flow.

---KenRad

 

[jherbert]

hi,

I agree with KenRad. I would take a very close look at the economics before proceeding. Keep the condenser water flowing, within chiller limited will lower the compressor load. I understand that some proponents want to drop condenser water from 3gpm/ton down to 2.2gpm/ton personally I am not persuaded.

cheers,
John