Variable Primary chilled water system

[nawal127]

Hello there engineers!

I am working on a project which uses variable primary flow system. Our chiller is sized at 93.6 L/s. But according to the procurement of air handling units and some other equipments which uses chilled water, the total chilled water requirement is exceeding 93.6 and is close to 101 L/s. These equipment's are over-sized. My question a VPF system requires a minimum amount of water flowing through the chiller. So is 93.6 the minimum amount or maximum ? Like can I exceed 93.6 ?
My second question is, an air handling unit sized for 10 L/s requires 12 L/s so does the flow control valve be sized for 10 or 12 L/s as if I select 12, it may affect valve authority.

Thank you in advance

 

[willard3]

Contact the chiller mfg for min/max water flow.

 

[LittleInch]

At that level of excess flow, it is probable that you chiller will accept the excess flow. However the temperature of the water leaving at 110 l/sec will not be at the temperature you have specified.

it sounds to me like 93.6 is the rated flow based on a certain return temp, a certain ambient air temp and a certain outlet temp. Vendor will supply min flow as part of his data sheet.

I don't understand why a unit "sized for 10 L/s requires 12 L/s" This doesn't make sense. It either needs 12 l/sec or it doesn't.

Also you don't mention the pump in any of this. If that won't do 110l/sec with all your frictional resistance then it doesn't matter what anything else will do.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[nawal127]

yes, 93.6 L/s is the chilled water amount I'm talking about rated flow for certain entry water and leaving water temperature. So, 93.6 L/s is maximum and the minimum I can find from the vendor.
But I'm not clear on this part, 93.6 L/s gets distributed into various equipment's. For eg. an AHU which according to design requires 10 L/s but procured equipment can work upto 12 L/s (in this case the leaving air temperature will be lower). The motorized valve should be selected for 10 L/s or 12 L/s ? Selecting a bigger valve may affect valve authority. This is what I'm expecting.

 

[urgross]

The minimum flow for the chiller is based on chiller protection and has nothing to do with your connected load. Use of 10% diversity for a variable primary pumping operation is standard. For your pumping, it may be of use to consider where to put your dP's and whether to use distributed booster pumping.

The control valve would hopefully be a 2-way pressure independent control valve. Range can vary.

 

[LittleInch]

Ok, it sounds as if the chiller has no real control?

How does the chiller turn on and off when the cooling load is not flat out? This will feed into your minimum flow and you need to engage the vendor a bit more to explain your system requirements.

You might need a three way valve system to keep the flow up even if the AHU doesn't need it whereby return temperature will fall and hence the chiller needs some sort of control or cycling.

I don't understand your issue on the valve. Is this a flow control valve ( max flow is 10 l/s) or is it some sort of on/off valve?

sorry, I don't understand this statement "Selecting a bigger valve may affect valve authority" what authority?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.