Chilled water system

[tscna88]

I have a building that I am getting ready to troubleshoot some issues. I have a Chiller with one loop pump and 2 Air Handler s with 3-way control valves. The pump is a constant speed pump and the piping loop from the chiller to the pumps is relatively short (80-100 feet of 4" total). The supply side of the pump pushes the water through the AHU 3-way valves. Th chiller is outside on the ground level, I have one AHU on the ground floor and one AHU on the second floor. The pump is located on the second floor. I have several issue's I want to figure out to troubleshoot the system.

(1) I know the pressure drop through the chiller barrel is lower than what Trane recommends. They have butterfly valves on the inlet on outlet of the chiller, but when I try to modulate each one I see no significant rise in Barrel DP.

(2) I am going to check the flow against the design pump head to make sure that everything is ok within my pump curves

My questions from an engineering standpoint are:

(a) I know that when filling a system, the old school way I was taught was to check the measurement to the highest point, figure that static head and add 4 psi. Based on that theory, is that the best way to determine if I have enough water in my system.

(b) What would cause me to not maintain the DP through that barrel? Could it be low water, incorrect piping size, pump location.

I think this was s design build by a previous contractor and they did not engineer it correctly. I know that Trane chiller designers want to take the present value of flow through the barrel (assuming its within chiller min/max) and double that to figure if there is enough system capacity. So if I have 200 GPM through the barrel they want 400 gallons of system water capacity based on pipe size and length. But I cannot reach my minimum flow and I am not sure with the pump on the second floor what my static head should be at the ground level and is that the best way to determine water capacity.

Sorry to ramble and duplicate info/questions. me=confused

 

[Waramanga]

what are the butterflys in the barrel for and why are you interested in the dP? The dP would give you an indication of flow is that right? playing with the butterflys will reduce flow but not increase the dP in the tube itself. If the pump isnt passing enough water then the dP will be down. how are you measuring the pump flow?

 

[mfelzien]

The chiller is designed to be completely filled with cooling liquid. Gases are not suppose to be inside the exchanger. If you are getting a higher than expected DP that is a function of the exchanger design or scaling. If your exchanger DP is too high you may need to clean the exchanger you can do this or I know of some people that can help.

The reason you may have problems "modulating" the pressure you might be on the wrong side of the exchanger shell/tube side (depending upon which is the cooling side ).

I suspect you have everything worked out just fine.

Mike F.

 

[tscna88]

The chiller manufacturer uses a minimum and maximum flow thru the barrel to achieve proper heat transfer. The problem is I have almost no differential pressure thru the barrel. The butterfly valves are just for shut off purposes and not balancing types. Although the manufacturer recomends a balance valve on the leaving side of the barrel to increase or decrease flow. I am supposed to have a DP of 3-5 pounds and I have 1 psi. So I know its a fluid issue, the barrel tubes are clean and unplugged

 

[tscna88]

Oh, we measure the flow thru the barrel by checking the DP, converting to FT head an using a curve to tell what the flow is. I know by what flow's and math what my DP should be for min/max flow