Pump Head Calculation In high rise
Pump Head Calculation In high rise
(OP)
hi guys,
Could you please help in calculating head of closed loop system in high rise building.
I am quite confused, as in closed loop piping we dont consider head loss due to elevation(static lift) , i have seen some article on internet in which they have considered some hydro static pressure.
In closed loop system, we consider head loss through piping friction,fittings and equipment like chiller,AHU etc.
but in the article they have considered the static lift also.
Please guide me on this.
I am attaching the file please see pg 81 chapter-7
Could you please help in calculating head of closed loop system in high rise building.
I am quite confused, as in closed loop piping we dont consider head loss due to elevation(static lift) , i have seen some article on internet in which they have considered some hydro static pressure.
In closed loop system, we consider head loss through piping friction,fittings and equipment like chiller,AHU etc.
but in the article they have considered the static lift also.
Please guide me on this.
I am attaching the file please see pg 81 chapter-7





RE: Pump Head Calculation In high rise
in today's circumstances that is more issue of balancing than pump selection as most of pumps would be variable speed which can cover range from zero thermal lift to nominal design conditions lift.
the rule of thumb is to take 50% of calculated thermal lift as nominal condition.
however, if i ever have enough influence on concept design, i would always tend to separate high building into few height zones.
RE: Pump Head Calculation In high rise
In a closed system, once the pipe is full of water - the static pressure on the suction side of the pump is the same as the discharge, no matter where you put the pump because. So when pumping starts, the only thing the pump has to overcome is friction due to pipe, fittings, etc.
So that is what the pump is sized for.
RE: Pump Head Calculation In high rise
Drazon- If its closed loop system then why to consider building height in the head.
PEDARRIN2- Yup i agree with you, but they have shown the pressure at different level.
I m confused about the theory written in the document and the figure reflecting in the document.
RE: Pump Head Calculation In high rise
Static pressure at the bottom of a riser will always be greater than the static pressure at the top of a riser, so equipment that can only handle lower pressures should not be located on lower floors, unless some sort of pressure regulation is employed.
RE: Pump Head Calculation In high rise
what I know that, in close loop system we pipe is full of water and does not consider static lift.
in pump head calculation, we need to consider piping friction loss, fitting loss and loss in ahu, fcu and chiller for closed loop system.
correct me if I m wrong or not getting your point. I m jus beginner and will be thankfull to You if you guide me on this.
RE: Pump Head Calculation In high rise
If I use a pipe fitting or chiller that is only rated for 150 psig, I have to make sure that during no flow (static) and flow (dynamic) conditions - that fitting or chiller is not experiencing pressure exceeding its rating.
The article was talking about where to put the chiller.
From the article, "The decision about the level on which the refrigeration machines and the supporting chilled water and condenser water pumps are located in a building is a decision that can have a cost impact on the refrigeration equipment, the pumps, the piping, and the fittings and valves associated with the piping. The economic impact will be due to the change in the design working pressure to which the equipment, piping, fittings, and valves will be subjected by the system.... The working pressure on any equipment or the piping, valves, and fittings at any location in a building is the sum of the hydrostatic height of the water in the piping above the point being considered plus the dynamic pressure created by the pump at the point being analyzed. The hydrostatic and dynamic pressures are determined in feet of water. Their sum, when added together, is the total pressure or working pressure in feet at the referenced point. To determine the working pressure in PSIG, this total pressure in feet must be divided by 2.31. This is the conversion factor to convert pressure in feet of water to pressure in PSIG."
Using the example, the maximum pressure the chiller would see, if on the bottom floor, is approximately 900 ft (due to elevation) + 140 ft (due to pump shut off pressure, which is basically the TDH provided by the pump during operation and the shut off pressure of the pump) for a total static pressure of 1040 ft (450 psi) per Solution A. This would exceed the rated pressure of the described fitting/chiller.
If the chiller is on the top floor (Solution C), then the total pressure the chiller would see would be 65 psi. This would be within the pressure rating of the fitting/chiller. The pump is still contributing 140 ft to the pressure, but because of the difference in elevation, the static effect is much less.
In this case you would specify fittings/pipe with higher pressure ratings on the lower floors and decreasing ratings as you went up. You would locate the chiller at a level where the pressure does not exceed its maximum pressure.
I hope that helps.
RE: Pump Head Calculation In high rise
RE: Pump Head Calculation In high rise
RE: Pump Head Calculation In high rise
I agree the article is reflecting the effects of pressure on equipment according to the location of chiller and height of building. that's fine.
so, doesn't it effect the pump head calculation.?
1-if a building is 900 ft in height having close loop system, do we consider this 900 ft in pump head calculation? or we consider only head loss in piping and accessories?
2- does height of the building effect the static pressure of the equipment only?
it has nothing to do with pump head calculation?
RE: Pump Head Calculation In high rise
2 - yes.
RE: Pump Head Calculation In high rise
RE: Pump Head Calculation In high rise
yeah, agree.
but static pressure doesn't cancel. right.?
and we consider height to check the static pressure at the equipment.
RE: Pump Head Calculation In high rise
The static pressures at the suction and discharge of the pump in an open system are not equal, thus this pump has to be sized to compensate for this difference plus friction loss.
RE: Pump Head Calculation In high rise
you have to calculate it in high rise, with about 30 floors it can already be on level of 15% or more of friction losses.
RE: Pump Head Calculation In high rise
the fist one, we considered it for moving the fluid but the second one we considered it for determining the max. working pressure inflicted upon pipes, pump's parts (casing , mechanical seal ,....)and all the elements in network
example:
If we calculated dP=5bar required from pump to move the water with the required flow rate.
these 5bar may be from 1bar to 6bar
and may be from 15bar to 20bar
The 2 cases have the same dP (friction losses and fittings ,....) but not the same max. working pressure
RE: Pump Head Calculation In high rise
RE: Pump Head Calculation In high rise
Hatem2014- Hello, Thanks alot for your comment, I just need more explanation and clarifications about it, I have started getting your pint now.
I request you to please describe it briefly , i will be highly thankful to you, also please elaborate how to CALCULATE static pressure to check the pressure in pipe.
RE: Pump Head Calculation In high rise
RE: Pump Head Calculation In high rise
RE: Pump Head Calculation In high rise
Timothi
Yes, this confusion only occurs in the case of closed loop because regaining pressure during down flow as you said
RE: Pump Head Calculation In high rise
But with regard to velocity pressure is not our topic now to avoid more confusion
RE: Pump Head Calculation In high rise
HVACDomain,
Assume we have 150 meters tall building and the pumps installed in zero level
then, after finished installation we will fill the network by water
If we take the pressure gauge reading before running the pumps at zero level we will read about 15 bar . the pressure will be the same at discharge and suction line of pump and equal 15 bar.
This pressure is generated by the elevation without running pumps and without moving water means without pressure drop due to friction and fittings , .....
After running pumps we will obtain more than 15 bar pressure at discharge point of pump may be for example 20 bar
RE: Pump Head Calculation In high rise
PEDARRIN2,
You are right, so it is more economic to install equipments in high level as you can because you will need no strong equipments to bear high pressure
RE: Pump Head Calculation In high rise
Sharing knowledge is the best way to learn
RE: Pump Head Calculation In high rise
Question:
I have a closed chilled water system driven by a centrifugal pump.
The outlet of the pump is 1.5" horizontally and the pipe diameter is enlarged to 3" horizontally.
If I put a pressure gauge on 1.5" pipe and the other on the 3" pipe, what do I expect from the readings?
Theory 1:
The flow speed is higher at the 1.5" pipe, so the pressure should be lower at the 1.5" pipe.
Theory 2:
With friction loss ignored, the reading should be the same as the pump head is the same.
RE: Pump Head Calculation In high rise
1) It is not good practice here to hijack someone else's thread, even if closed for along time. Just start your own. Don't do it again.
2) Is this homework??
3) There will be a difference due to the velocity head, but most times this is negligible and makes no difference or is not seen by a pressure gauge unless very well calibrated together. A differential manometer might show you the difference, but it would be difficult to factor in the friction and the effect of the reducer accurately.
If the same pump fed both pipes and you swapped flow between them you might get somewhere, but this is pretty academic.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Pump Head Calculation In high rise
the static pressure depends on height and is important for selection of equipment, relief valves etc. so it doesn't "explode" at the highest pressure. You need to imagine the hydro-static pressure + the pump pressure at tha tlocation. Pump pressure at pump suction side is zero, at discharge the max what the pump can do (assume someone overrides the VFD).
Consider gravity of fluid. for water every 2.3 ft you increase by one psi. this will be less for lighter fluids, more for denser fluids.
google concept of "point of no pressure change" and buy this book