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Can a Chilled Water pump be sized (Flow & Head) on the Cumulative Water flowrates of HIgh Speed Coil (FCU & FAHU) Performance?
If it is designed for medium speed coil performance, will the pump capacity be enough?
In my project, duct design is made in high speed since fcu's are matching the calculated loads (Sensible & Air Flow) only in high speed. In this case, how to design the chilled water pipe sizing & pumps.
Add the total tonnage and arrive the flow rate by using delta T.
Arrive total head loss.
You can arrive power and flow requirement for the pump
In order to size chilled water pump, chilled water flow rate and pump head is required. Chilled water flow rate is calculated based on the cooling load requirement of each spcace. However, to caculate pump head, index run of the chilled water flow circuit is selected. Index run is the farthest path where pump faces high resistance to flow. Pump loss calculation included pipe friction losses, fitting losses (valves, tees, elbows etc), and terminal unit losses. The losses on supply and return pipes are added to get the total pump head.
Pump selection depends on the the total flow required for all the HVAC equipment & total pressure drop including heads required.
Q=mCPΔT shows that it is indepentent of speed. Therefore, the answer is yes and is that the pump can be sized for commulative water flow of high speed.
Total flow for the pump will be sum of flow of all the equipments connected.
Head depends on the piping sizing and layout , lengths,fittings etc...
first we have to select FCu/AHU based on the desired condition. then add the corresponding flow values to get the total flow
whatever maybe the speed,you will get a flow rate for each FCU.use it for other calculations.
pipe sizing can be done using software .(pipe sizer)
The medium speed is used as selection in FCUs because we dont want the unit to run always high speed since it may make loud sound and noise which needs to be reduced. Also not on slow speed so that the size of unit may be very big to achieve the load on small speed. So medium is an optimum selection to keep unit size and noise as balanced.
Q=M CP DELTA T is the equation here.
sizing the fan coil unit speed as high is not recommended since you might require more damping of the sound produced and also the supplier will never give you selection based on high speed fan they usually recommend medium speed .
If you still wanna size it based on high speed than use the equation to solve the problem for sizing also as what speed would you size the pipe generally we size pipe based on 1.5 to 2.5 meter per sec.
Now the what was the bypass factor you have considered also require to be checked generally in hap if you have calculated the by pass factor is 0.1 .
all together not recommended
Manufacturer's data usually gives you the equipment capacity based on medium fan speed. Using high fan speed means the same chilled water flow rate but increase in capacity. (Q=mCPΔT). There should be no issue calculating the total flow rates for both speeds. It will be the same. Issue will arise if there will be cooling loads added to the space in the future since your design capacity is already maxed out. You lose your flexibility.
Dear friend
normally the unit is selected with medium speed for both fan and coil. the load is selected in design as already peak with peak conditions of outside and inside load plus safety factor and all those parameters which we take in design.
If we select the unit with high speed of-course the size of unit may be decreased and its high speed may be equal to the medium speed of next bigger model of any FCU manufacturer (may be or may be not).
If we use high speed with FCU the fan will be run at high speed but water demand ofcourse will be higher than medium but we fixed that through a balancing valve. If we do not do so then the water demand will be very high which I think is not required in any case.
The medium speed is used as selection in FCUs because we dont want the unit to run always high speed since it may make loud sound and noise which needs to be reduced. Also not on slow speed so that the size of unit may be very big to achieve the load on small speed. So medium is an optimum selection to keep unit size and noise as balanced.
Hope this is clear
