How Low Can You Go? Chilled Water Economizer

[ME27272727]

My experience with chilled water economizer has been with inducted-draft counter-flow open towers in hospitals where we are able to reset the chilled water temperature upwards towards 50°F to get the approach needed to run free cooling with a 42°F min condenser water temp. The big name tower manufacturer's seem to recommend 40-42F as a minimum tower leaving water temp in order to prevent icing up the towers.

I'm currently analyzing a free cooling opportunity for a process chilled water application where 40F CHWS temp is required year round. Has anyone had success running towers down to perhaps 36F? There is big potential for savings, but the lower CHWS temp is hamstringing me.

 

[lukaiENG]

how big can you make the economizer heat exchanger? having a 4 degF approach across the heat exchanger seems excessive.
I would recommend you get yourself a larger heat exchanger and get a 1 degF approach therefore your tower water temperature (39degF) is closer to the manufacturers recommendations.

 

[BronYrAur]

I had a similar situation that needed 39 deg F year-round. We had to get down to 34 deg leaving the tower in order to get the 39 we needed on the other side of the heat exchangers. The tower kept freezing up. We attempted to send water only to the basin and not over the top, but that did not cool the water enough. Once we went over the top of the tower, we would freeze in certain conditions. The return water temp of course played a role as well. We did not have a good delta-T of the water being used, so our return was only 6 or 7 deg above supply.

So a heat exchanger with a closer approach would certainly help. In my case, the 39 deg we "needed" wasn't actually needed at all. There were politics at work forcing it. Still trying to introduce some common sense so that I can reset the temperature next winter and not have to get such cold water out of the tower.

So we did go below the 40-42 recommended by the tower manufacturer, but 34 deg proved to be too low in our case.