Taizhou MECO Refrigeration Equipment Co.,Ltd

Sales & Support
Request A Quote - Email
Select Language
English
Russian
Spanish
Home
Products
About Us
Factory Tour
Quality Control
Contact Us
Request A Quote
Home News

Head for DCP chilled water primary/secondary pumps.?

Certification
Good quality Car UVC Air purifier for sales
Good quality Car UVC Air purifier for sales
Excellent product produced by Meco,all purchased items worked very good, tks.

—— Saliman

For your K series fan coil units, we liked it very much, the design is beautiful, only problem is prices for big sized models, anyway, i like it.

—— Roman-Silva

I'm Online Chat Now
Company News
Head for DCP chilled water primary/secondary pumps.?
Head for DCP chilled water primary/secondary pumps.?

Q:I'm doing a DCP project which is at its concept design stage.In order to estimate the chilled water pump size and ratings roughly, could anybody give me some tips on the average/normal chilled water pump heads for a typical 10000 TR DCP. The length of the longest loop could be around 600 m single run.

 

A:Before we can discuss pump head, we must understand the difference between an open hydronic system and a closed hydronic system. It is important to know whether the pump serves an open or a closed system, because the pump head calculation depends on the type of system that the pump serves. 


In a closed system, the fluid is not exposed to a break in the piping system that interrupts forced flow at any point. In an open system, it is. In a closed system, the fluid travels through a continuous closed piping system that starts and ends in the same place--- there is no break in the piping loop. The vast majority of hydronic piping systems are closed. The most common open system is the cooling tower portion of a chilled water system, as depicted below. A break in the piping system occurs where the water exits the spray nozzles, and is exposed to air in the fill section of the tower. The water collects in the cooling tower sump before being pumped around the loop again. Note that the chilled water side of this diagram (the right side) is closed. Because it is closed, an expansion tank absorbs any thermal expansion of the fluid. Open systems don’t require expansion tanks, as the fluid is naturally free to undergo thermal expansion. 

What is Pump Head? 

Units of Measure: In the U.S. system, head is measured either in PSI or in "feet of head" (usually abbreviated to "feet"). 

Pump Head is the total resistance that a pump must overcome. It consists of the following components: 

Static Head: Static head represents the net change in height, in feet, that the pump must overcome. It applies only in open systems. Note that in a closed loop system, the static head is zero because the fluid on one side of the system pushes the fluid up the other side of the system, so the pump does not need to overcome any elevation. 

Friction Head: This is also called pressure drop. When fluid flows through any system component, friction results. This causes a loss in pressure. Components causing friction include boilers, chillers, piping, heat exchangers, coils, valves, and fittings. The pump must overcome this friction. Friction head is usually expressed in units called "feet of head." A foot of friction head is equal to lifting the fluid one foot of static height. 

Pressure Head: When liquid is pumped from a vessel at one pressure to a vessel at another pressure, pressure head exists. Common applications include condensate pumps and boiler feed pumps. Condensate pumps often deliver water from an atmospheric receiver to a deaerator operating at 5 PSIG, meaning that in addition to the other heads, the pump must overcome a pressure head of 5 PSIG. One PSIG equals 2.31 feet, so the differential head in this application is 5 X 2.31 = 11.6.’ Pressure head is a consideration only in some open systems. 

Velocity Head: Accelerating water from a standstill or low velocity at the starting point to a higher velocity at an ending point requires energy. In closed systems the starting point is the same as the ending point. Therefore the beginning velocity equals the final velocity, so velocity head is not a consideration. In an open system, the velocity head is theoretically a consideration, but the pipeline velocities used in hydronics are so low that this head is negligible, and is ignored. (Note that the velocity head is defined by the formula V2/2g where V is the fluid velocity in feet per second and g is the gravitational constant 32 feet/second 2. Therefore at typical velocities of 2-6 fps, the velocity head is a fraction of a foot. Since head loss calculations are really estimates, this small figure becomes insignificant). 

So, for hydronic applications, we can say that: 

For closed systems: Pump head = the sum of all friction pressure drops 

Where: 

Friction pressure drop = piping pressure drop + terminal unit pressure drop + source unit pressure drop* + valve pressure drop + accessories pressure drop. 

For open systems: Pump head = the sum of all friction losses plus the static lift of the fluid plus the pressure head. 

* The "source unit" is defined as the boiler, chiller, or heat exchanger, which creates the hot or chilled water. 

Steps in Calculating the Pump Head 
Basically, we need to plug values into the proper formula above. 

Step 1: Lay out the piping system using logical routing as determined by the building requirements. Note each terminal unit and its GPM. 

Step 2: Select pipe sizes for each segment, based on proper velocity and pressure drop. 
The graphs below are from the ASHRAE Fundamentals Book. Recommended velocities are: 

Pipe Sizes of 2" and Under: 2 fps minimum to 4 fps maximum 

Pipe Sizes of over 2": .75 ft. of P/100 equivalent feet minimum to 4 ft. of P/100 equivalent feet maximum 

Where P is the head loss (also called friction loss or pressure drop). 

The recommended ranges ensure that the piping system will be quiet, consume reasonable pump horsepower, and be reasonably economical to install. Note that the minimum velocities are recommended based on the fact that lower velocities will allow air to collect at high points, with the possible result of air binding. 

Once the layout and pipe size for each section has been determined follow these steps: 

Step 3: Determine Friction Due to Source, Terminal and Accessory Equipment Including: 

Source and terminal Equipment: Consult manufacturer’s catalogs or computer selections. 

Accessory items include filters, strainers, check valves or multi purpose valves that could have a significant pressure drop that would not be covered under the equivalent feet of piping rule of thumb. 

To determine valve D P refer to curves or Cv ratings. A Cv is defined as the flow at which the valve will have a resistance of 1 PSIG (2.31 feet). Since the pressure drop is proportional to the square of the flow rate, use the following formula to calculate the pressure drop through the valve for any flow rate: 

PD In Feet = (Flow Rate/ Rated Cv)2 X 2.31 

Example: A valve has a Cv of 10. Flow through the valve is 21 GPM. What is the valve D P in feet of head? 

PD in Feet = (21/10)2 X 2.31= 10.2’ 

Special Consideration: Pressure Drops In PSI and Converting PSI to Head 
Sometimes pressure drops will be given in PSI units instead of feet of head. To convert PSI units to feet of head: 

PD in feet = PD in PSI X 2.31

Source:

 
 
For Fan coil units, our range include below catagories:
 
 
Contact Us for more info:
Mr.John Ding/Sales Manager
--------------------------------------------------
MECO,the Expert of FAN COIL UNIT
Taizhou MECO Refrigeration Equipment Co.,Ltd
Tel: +86 574 88152763            
Skype: John Ding
Johnding574@gmail.com
sales02@china-fancoil.com

 

Pub Time : 2014-08-06 10:07:08 >> News list
Contact Details
Taizhou MECO Refrigeration Equipment Co.,Ltd

Contact Person: Mr. Sam

Send your inquiry directly to us (0 / 3000)