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Hi Drazen, Thanks a lot for your input, I agreed with your idea that the chiller will take over when the free cooling is not sufficient. One thing I like to point out too is that the article also mentioned that the free cooling heat exchanger can be used to precool the chilled water for the...

Hi Dave, It is in the ASHRAE Journal September Volume, article: Optimizing Design & Control of Chilled Water Plants Part 2: Condenser Water System Design I attachedd the snapshot. The water side economizer is piped in series with chiller evaporators.

Thanks Willard3, This is a integrated water side free cooling. So the heat exchanger is in seriers with the evaporaters and it is controlled by a bypass valve to determine if the chilled water is going to pass the heat exchanger or not.

Hi, Would add a water side economizer in a chiller plant cause low delta_T symptom for the chillers? The water side HX is in series with the chiller evaporators, therefore, i am a little worried about low delta_T symptom. Anyone has any experience before? Thanks a lot!

Thanks guys. To KiwiMace, You are right, but that is for the motor itself. I am considering slowing down the motor will also change the fan curve, so will need to redo the piping head loss calculation to make sure that the pump or fan is running at the speed that still go to the most critical...

Hi, I have a question about retrofitting the constant speed motor with VFD. The piping or duct system head loss design (pump or fan selection) is based on the full load pump or fan curve. When we do add VFD on the pump or fan motor, shouldn't we take a look of the pump or fan curve to make...

Thanks a lot , Dave! So it is fine to control both air and water flowrates. My concern is whether we would make the control strategy too complicated. We know four types of control methods in this kind of system: 1. change air flowrate 2. change air temperature 3. change water flowrate 4. change...

Hi guys, I am working on energy conservation project. This is a dual duct system, the supply fan and return fan motors are all equipped with VFD already. Is it necessary to install VFD on the hot water pumps and chilled water pumps? I do not think it is necessary since the air flow is adjusted...

Thanks guys! I understand it better now.

Hi, I was reading an HVAC tech sheet and confused by some sentenses in the sheet: The heating on this unit will be run off discharge air temperature with room temperature override. It will operate off discharge air temperature with room temperature override. I guess these two sentenses mean...

Thanks a lot for excellent suggestion!KiwiMace! One more question: For open loop cooling tower system, if it is not running 24/7, would you drain the water out of pipes in winter when the cooling tower is not running? or keep the pump running and just bypass the water?

The roof is about 25 foot height, have not designed the system, so the dimension of cooling tower is unknown. Thanks!

Hi, I have a question on choosing cooling tower or dry cooler. It is required that the cooling tower through the winter season. But it may have some freezing issues. I am thinking separate the sump and locate it indoor and put the cooling tower at the highest point of the building. So, when the...

Pressure relief valve release the builtup static pressure for safety. If you took a look of Bernoulli's equation, the pump discharge side has highest flow pressure, but not necessary highest static pressure. I agree with Compositepro, put it at somewhere the pressure is constant(low/no flow).

Thanks walkes! Right, delta T is going to vary with secondary load. A VFD chiller is the best option to solve this problem. So far, the delta T flutuation is acceptible in the design range.

Thanks a lot, KiwiMace!It is standard to put VFD on secondary pumps. I just find out that this does not solve low delta_T symptom, if the system is experiencing it. But, for this case, the chiller size is properly chosen. I believe that we will not suffer low delta_T symptom as far as we put...

Hi Guys, I am doing a energy conservation project and trying to add a VFD on the secondary and tertiary pumps in a primary/secondary chilled water system. But I am a little concerned about chiller low delta_T symptom when the cooling load is low in some cool days. Anyone has any experience on...