High Supply temp. For chilled water

[Tawfik135]

Hi for all
We have chilled water system primary / secondary ( variable speed) designed for delta t of 12 f , designed supply temp 6 c , now we are measuring the supply temp. And we are getting 7 some times 8 c . What is the effect of the high supply temp. On the condensation & relative humidity inside the building ??

 

[KiwiMace]

Where are you measuring the supply temp? If at the primary loop, then this is likely a problem with the chillers or controllers. If at the discharge of the secondary, you might be overflowing your secondary loop, causing reverse flow in your bypass decoupler, which gives you a mixed flow condition in the secondary supply. Your primary flow should be more or at worst, equal to the secondary flow.

Effects are reduced dehumidification, higher space RH, and potential for condensation. Also space temps may not be met. This depends on the rooms and loads, of course.

 

[ChasBean1]

Tawfik135,

It depends on the cooling coils’ capabilities: number of rows, fins per inch, etc. Most of the time systems can perform without concern with a CHW supply temperature of 8°C vs. 6°C. In fact, many institutions with several buildings served by a central plant have booster pump and deny valve assemblies that recirculate building chilled water so as not to return water to the plant too cold. Excess flow penalties are assessed with cold return chilled water (e.g., below 13°C). So the deny valve assembly forces recirculation within the building to make sure water is returned no less than 13°C. But in doing so, supply CHW to the building may reach 10°C. I believe in outdoor or return air dew point overrides for this type of setup. Rarely would you see them as part of the controls package.

Basically, yes, there is a concern about elevated building moisture if chilled water becomes too warm. And as Kiwi indicated, a secondary flow exceeding the primary flow could be a cause.