1. Water piping design

2. Fundamentals of water circuits
Open circuits
Closed circuits ET P
Source
Load
Open circuit
In an open circuit, the water flows into a reservoir open to the atmosphere. Thermal tank, cooling tower and air washers are examples of reservoirs open to the atmosphere.
An expansion tank is not used in an open circuit.
Closed circuit
A closed circuit is a system with no more than one point of interface with a compressible gas or surface.
In a closed circuit, the water does not get in contact with the ambient air. However, an expansion tank is included in the circuit.
Heat
Source P
Thermal tank
Cooling tower …
Expansion tank

3. Comparison Open versus Closed
Open circuit
Closed circuit
Higher output of pump motor (higher actual head)
Proper water treatment is required (avoid corrosion)
Sufficient air purging
Requires a properly installed expansion tank.
In an open circuit, the required output of the pump motor will be higher due to the actual head (difference between the discharge and suction level).
Due to the contact between water and air in an open system, proper water treatment will be required to avoid corrosion inside the water piping.
On the other hand, closed circuits require sufficient air purging and a properly installed expansion tank.

4. Water piping systems.
Supply of water according to the needs of the user of the required places.
Head and friction losses should be minimal
Water velocity should be properly managed to avoid streaming noise, pipe vibration, pipe expansion, … .
Water quality management
Arrangements for easy service and maintenance.
While designing a water piping system, the following suggestions should be considered:
- Water must be supplied according to the needs of the user to the required places.
- Head and friction losses should be kept minimal.
- The water velocity should be properly managed to avoid water streaming noise, pipe vibration or pipe expansion or contraction due to temperature differences.
- Pay attention to the water management: impact of the water quality, corrosion prevention in open circuits, … .
- Provide enough arrangements for easy service and maintenance.

5. Water piping systems - classifications
Return water method
Water pipe number method
Flow control method
Based on the lay-out, water piping can be classified according to:
- the return water method
- the water pipe number method
- the flow control method

6. Water piping systems – Return water method
Direct return
Reverse return

7. Water piping systems – Direct return method
The piping length connected to the fan coil unit located closest to the heat source, is the shortest while the piping connected to the most remote fan coil unit is the longest. As a consequence, the head loss at each fan coil unit is different.
Water channelling will happen easily and will necessitate control mechanisms at each fan coil unit.
The direct return method is recommended when the units have different pressure drops or require balancing valves.
Recommended when the units have different pressure drops or require balancing valves.

8. Water piping systems – Reverse return method
Since the piping length of the return and supply is almost equal for all fan coil units in the system, the friction loss is almost the same resulting into a balanced water flow to each fan coil unit. Adversely, the piping length is longer. Since the water circuits are equal for each unit, the major advantage of the reverse return method is that it seldom requires balancing. Due to the more balanced flow, the test run and maintenance work becomes easier.
This method is recommended in the occasion that the units have the same pressure drop over them and for most closed piping applications. It is often the most economical design on new constructions.
Recommended when the units have the same pressure drops and for most closed piping systems.

9. Water piping systems – Piping number method
Single pipe method
Two-pipe method
Three-pipe method
Four-pipe method

10. Water piping systems – Single pipe method
Orifice
Chilled or Hot water
Disadvantage:
Advantage:
This piping lay-out is used in small scale hot water heating applications. The installation cost is low, but the flow control is difficult.
Flow control is difficult
Low installation cost
Used in small scale hot water heating applications

11. Water piping systems – Two pipe method
Chilled or Hot water
The two-pipe lay-out is very commonly used and consists out of one pipe to and one back from the fan coil unit. Both chilled or hot water can be supplied to the fan coil unit.
Most commonly used system.

12. Water piping systems – Three pipe method
In this method, there are two pipes for the supply water and one common pipe for the return water. When cooling and heating are required simultaneously, chilled or hot water is supplied in a separate pipe to the fan coil unit. A mixture of chilled and hot water returns through a single pipe to the heat and cooling source.

13. Water piping systems – Four pipe method
HOT COIL
Unit Thermostat
COLD COIL
Unit Thermostat
Return
Chilled
Water
Hot Water
Supply
To overcome the disadvantages of the three-pipe system, the chilled and hot water circuit are completely separated in the four-pipe system. Each circuit has its own independent supply and return water piping.
Return
Hot
Water
Chilled Water
Supply

14. Water piping systems – Flow control method
Constant flow method
Variable flow method
Constant flow method.
In the constant flow method, the water flow is constant and is not related to the load variation.
Variable flow method.
In the variable flow method, the water flow is in accordance with the changing heat loads in order to keep the room temperature constant. Applying this method will lead to energy saving.

15. Water piping design – friction losses
Darcy equation:
l ρ * v2
ΔP = f * * d
∆P = pressure loss
ρ = fluid density
f = friction factor (Pa / m)
l = pipe length (m)
v = fluid velocity (m/s)
d = internal pipe diameter (m)
The Darcy equation is the basis of all fluid flow equations and relates the pipe pressure drop required to overcome the fluid viscous friction forces:
∂P = ( ρ * f * l * v² ) / ( 2 * d )
Where: ρ = fluid density
F = friction factor (Pa / m)
l = pipe length (m)
v = fluid velocity (m/s)
d = internal pipe diameter (m)
Based on the Darcy equation, the pipe friction / flow tables are made (e.g. charts …).

16. Water piping design – friction losses
There is a friction loss when water is flowing through a pipe. The friction loss is depending on:
- the water velocity
- pipe diameter
- pipe length
- and the inferior surface roughness
Most air-conditioning systems are using steel pipe or cupper tubing in the piping system. The friction loss based on the Darcy-Weisbach formula, can be read from the chart … .

17. Water piping design – water velocity
The recommended water velocity is depending on:
Pipe diameter
Effects of corrosion
The higher the water velocity:
The higher the noise level
The higher the effects of erosion
Water velocity.
The recommended water velocity through the piping is depending on two conditions:
- The pipe diameter and
- The effects of erosion.
The table below lists the recommended velocity ranges for the different piping diameters. The higher the water velocity, the higher the noise level of the moving water and the entrained air and the erosion will be.
Table …: Recommended water velocity.
Diameter (mm) Velocity range (m/s)
> ~ 2.7
50~ ~ 2.1
around ~ 1.2
Pipe diameter (mm) Velocity range (m/s)
~2.7
50 ~ ~2.1
Around ~1.2

18. Water piping design – expansion tank
Purpose:
maintain the system pressure by allowing the water to expand when the water temperature increases.
Provide a method to add water to the system
To release air contained in the water system.
The purpose of the expansion tank is to maintain the system pressure by allowing the water to expand when the water temperature increases in order to prevent that the pipes would burst and it provides a method to add water to the system
An expansion tank is required in a closed system. In an open system, the reservoir acts as the expansion tank.
The expansion tank can be of the open or closed type.
An expansion tank is required in a closed system.
The expansion tank can be of the open or closed type.

19. Water piping design – expansion tank
Location: suction side of the pump, above the highest point in the system
Sizing:
Calculate the water volume in the piping (tables)
Calculate the water volume in the heat exchangers (engineering data books of the manufacturers)
Determine the specific volume both for the lowest and highest working temperature and calculate the difference.
Calculate the required volume of the expansion tank
The tank is located at the suction side of the pump, above the highest point in the system. At this location in the system, the tank provides atmospheric pressure equal to or higher than the pump suction, preventing air is leaking into the system.

20. Water piping design – closed expansion tank
Water piping design – open expansion tank
Vt = 2 * Vs[(v2 / v1 -1) – 3 * α *Δt]
Water piping design – closed expansion tank
[(v2 / v1) -1] – 3 * α *Δt
Vt = Vs *
( Pa / P1 ) – (Pa / P2)
The closed expansion tank is used in small systems and work at atmospheric pressure. The tank is located at the suction side of the pump.
The capacity of a closed expansion tank is larger than an open expansion tank operating under the same conditions.
For the sizing of the expansion tank, one can also consult the engineering data from the manufacturer of the expansion tank.
Vt = volume of the expansion tank (m³)
Vs = volume of the water in the system (m³)
t1 = lower temperature (°C)
t2 = higher temperature (°C)
pa = atmospheric pressure (kPa)
p1 =pressure at lower temperature (kPa)
p2 = pressure at lower temperature (kPa)
v1 = specific volume at t1 (m³/kg)
v2 = specific volume at t2 (m³/kg)
α = linear coefficient of thermal exp.
= 11.7 * 10-6 m / (m*K) for steel
= 17.1 * 10-6 m / (m*K) for copper
Δt = (t2 – t1) (K)

21. Water piping design – pump types
Most frequently used pumps are the centrifugal pumps.
More and more variable flow (inverter) pumps are used which offer the following advantages over the constant flow pumps:
Application of load diversity to the design allows approximately 70 to 80% of the peak building load.
No margin required for balancing of the circuits, saving possibly 10% flow.
Cost saving in material and labour for the main and branch piping system
Reduction in commissioning time.
Centrifugal pumps are the most commonly pumps in chilled water (CW) and low pressure hot water circuits (LPHW).
With the current emphasis on energy efficiency in buildings, the variable flow (inverter) pump is more and more used in CW and LPHW systems.
Systems designed with a constant flow pump require the pump to be selected at 100% of the design duty. In designing for variable speed pumps, the following advantages are realized over the constant flow pump:
- The application of load diversity to the design, allows approximately 70% to 80% of the peak building load sizing of the pump.
- There is no margin needed for balancing of the circuits, saving possibly 10% of flow.
- Cost saving in material and labour for the main and branch pipe system.
- Reduction in commissioning time.

22. Water piping design – pump types
tongue (cut off plate)
impeller
inlet
Usually an electric motor powers the impeller (the rotating specially shaped "heart" of the pump) rotation. The impeller's rotation adds energy to the liquid after it enters the eye of the impeller.
rotation
spiral shaped water passage
pump body

23. Water piping design – pump performance
Pump performance can be given in terms of:
discharge capacity= required flow rate
head
shaft power
efficiency
The performance of pumps can be given in terms of:
- discharge capacity
- head
- shaft power
- Efficiency

24. Water piping design – pump performance
Pump performance can be given in terms of:
discharge capacity
head
= pressure produced by the pump 1 2 3 4 5 6 7 8 9 10 12
Capacity
Total head
The head is the pressure which is produced by the pump in metre of water column. The higher the discharge capacity of the pump, the lower the head will be (Fig. …).

25. Water piping design – pump performance
Pump performance can be given in terms of:
discharge capacity
head
shaft power
= required power of the pump is roughly proportional to the delivered capacity.
The required power of the pumps is roughly proportional to the delivered capacity.

26. Water piping design – pump performance
Pump performance can be given in terms of:
discharge capacity
head
shaft power
efficiency
= ratio between the delivered work and the shaft power.
The pump efficiency (%) is defined as the ratio between the delivered work and the shaft power.

27. Water piping design – pump performance chart
The pump performance chart is the summary of the head, efficiency and discharge capacity (Fig …).

28. Water piping design – pump selection
Where is the operating point?
What is the system resistance curve?
What design flow rate is required?
What is the pressure drop?
The selection of the pump starts with the collection of the projected information: where is the operating point located, what is the system’s resistance curve, what is the design flow rate and what is the pressure drop?

29. Water piping design – pump selection
Total head pressure = actual head + friction losses
Actual Head
Total Head
Friction Loss
Resistance curve
Head loss
The actual head pressure is not related to the water flow rate. The friction loss however is directly proportional to the square of the water velocity.
Since the total head pressure is the sum of the actual head and the head loss (friction loss), the total head of the piping system will take the form of the curve in fig … .
Flow rate

30. Water piping design – pump selection
Total Head
System resistance curve
Total head
Operating
point
The pump is operated at the intersection between the head and the resistance curve. This intersection is called the pump operating point.
Capacity

31. System resistance curve
Water piping design – pump selection
Total Head
System resistance curve
Total head
Operating
point
When the gate valve is throttled, the resistance increases and the water flow rate decreases. In doing this, the operating point can be changed. The same phenomena, a decrease in water flow rate and an increase in the head loss, can be caused when rust and / or scale is deposited on the internal surface of the water piping system.
Capacity

32. Water piping design – pump selection example.
H = Ha + Hf + Ht + Hk
H = Total friction loss (m H2O)
Ha = Actual head (m H2O)
Hf = Friction loss in straight lines
Ht = Partial friction loss
Hk = Internal friction loss
Ha = 0 for a closed system
Hf can be obtained from the friction loss diagram
The pump selection can be done through calculation or by using the pump selection chart. In both cases, the head losses need to be calculated.
Pump Head calculation.
After the decision regarding the pipe size has been taken, the maximum friction loss (usually the longest pipe branch in the piping system) can be calculated:
H = Ha + Hf + Ht + Hk
Where: H = Total friction loss (mH2O)
Ha = Actual head (mH2O)
Hf = Friction loss in straight lines (mH2O)
Ht = Partial friction loss (mH2O)
Hk = Internal friction loss (mH2O)
Actual head.
The actual head (Ha), is the difference between the discharge and suction level.
In a closed circuit, the actual head is zero; the discharge side equals the suction side (fig …). Even though an expansion tank is installed at the top of the circuit, the head from the expansion tank to the circuit is cancelled.
Friction loss in straight line.
The head loss of the piping can be obtained from the friction loss diagram.
Partial friction loss.
The partial head loss is caused by the friction loss of fittings in the pipe such as valves, elbows, strainers, … .
The partial head loss of those fittings is calculated as:
Equivalent length * Basic friction loss
The equivalent length can be obtained from table … and the basic friction loss from the friction loss diagram.
Internal friction loss.
The internal friction loss can be obtained from the technical data of the manufacturer. For example, the evaporator and / or condenser pressure drop is mentioned in the Daikin engineering data book.
Determine the equivalent length of the valves, strainers, …
Can be obtained from the manuf. tech. data.

33. Water piping design – pump selection example.
Given information:
WFR = 190 l/min
friction loss at the foot gate = friction loss of the check valve
water temperature: 30 °C
Gate valve
6 m
Check valve
1 m
10 m
2 m
7 m
4 m
2 m
Foot valve

34. Water piping design – pump selection example.
The water velocity at the suction side
Pipe diameter (mm) Velocity range (m/s)
Main lines of pump discharge 2.4~3.6
Main lines of pump section 1.2~2.1
Based on the WFR of 190 l/min and the limits of the water velocity, we have to select a 2B steel pipe.
The intersection between the WFR and the 2B pipe gives us the following data:
water velocity: 1.4 m/s
friction loss: mmH2O / m

35. Water piping design – pump selection example.
Actual head: suction: 4 m
discharge: 15 m m H2O
Friction losses in straight line
suction: = 7m * mH2O = m H2O
discharge: = 25m * mH2O = m H2O
Partial friction loss Equivalent length Qty
90° elbow 1.6 mH20 * = * mH2O= mH2O
Check valve 4.1 mH2O * = 4.10 * mH2O= mH2O
Foot valve 4.1 mH2O * = 4.10 * mH2O= mH2O
Sluice valve 0.37 mH2O * = 0.37 * mH2O= mH2O
Overall head loss: mH2O
Safety factor
H = 24 mH2O

36. Water piping design – pump selection example.
Pump selection (chart method)

37. Thank you for your attention