Hydronic Balancing Chris Wolak
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Hydronic BalancingChris Wolak
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Outline
• Introduction
• Static Balancing
• Dynamic Balancing
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Two Reasons for Balancing
• Manual balancing
• On-off Control
• Single Speed Pump
• Pressure Independent balancing
• Modulating Control
• Variable Speed Pump
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Why Balance?• Without balancing, the circuits
closest to the pump would overflow and those further away underflow
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ASHRE 90.1-2010
6.7.2.3.3 Hydronic System Balancing. Hydronic systems shall be proportionally balanced in a manner to first minimize throttling loss; then the pump impeller shall be trimmed or pump speed shall be adjusted to meet design flow conditions
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Terminal 4
Terminal 3
Terminal 2
Terminal 1
5’
5’
5’
5’
5’
5’
5’
5’
5’
5’
5’
5’
5’
50’
40’
30’
20’
40’ 7gpm
30’ 13gpm
20’ 17gpm
50’ 3gpm
0’
10’
20’
30’
50’ 10gpm
50’ 10gpm
50’ 10gpm
50’ 10gpm
Simplified Building Schematic
Each leg has 5’ of resistance.
By adding manual balancing valves,
Different resistances cause different flows
we can equal out all the resistances and therefore all the flows
Static Balancing
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Manual Balancing Valves
• Three Functions:
– Throttling
– Flow Measurement
– Shutoff
ASHRAE Handbook 2013 Systems & Equipment, Chapter 47. Valves
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What is Cv?
𝐶𝑣 = 𝐹𝑆𝐺
∆𝑃𝐶𝑣 = 𝐹
1
∆𝑃
11 psi
10 psi
5gpm
Cv?
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2gpm
2gpm
2gpm
2gpm
2gpm
2gpm
2gpm
2gpm
2gpm
2gpm
2gpm
2gpm
Proportional Balancing
• Balance each section within itself
• Use partner valve to balance sections together 8gpm 8gpm 8gpm
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5’
5’
5’
5’
5’
5’
5’
5’
5’
5’
5’
5’
5’
50’ 17gpm
Two-Pipe
40’ 13gpm
30’ 7gpm
20’ 3gpm
5’
5’
5’
5’
5’
5’
5’
5’
5’
5’
5’
5’
20’
Reverse-Return
50’ 10gpm
50’ 10gpm
50’ 10gpm
50’ 10gpm
Reverse-Return
• Theoretically, reverse-return piping can self balance
• Each terminal has to have the exact same piping
• Hoses, strainers, dirty coils will effect balancing
• No way to verify flows• Adds extra piping
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Two Reasons for Balancing
• Manual balancing
• On-off Control
• Single Speed Pump
• Pressure Independent balancing
• Modulating Control
• Variable Speed Pump
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Terminal 4
Terminal 3
Terminal 2
Terminal 150’
40’
30’
20’
40’ 7gpm
30’ 13gpm
20’ 17gpm
50’ 3gpm
50’ 10gpm
50’ 10gpm
50’ 10gpm
50’ 10gpm
50’ 13gpm
50’ 13gpm
50’ 13gpm
Terminal 1
Terminal 2
Terminal 3
Terminal 4
10gpm
10gpm
10gpm
10gpm
Terminals are set to 10gpm with static valves. When all control valves are open, system is comfortable & efficient
When one control valve closes down, the other terminals overflow, wasting energy
As other terminals try to modulate, overflow situation intensifies, increasing energy costs
As more portions of the building close, the situation gets worse
0gpm
13gpm
13gpm
13gpm8gpm
15gpm
15gpm
0gpm
17gpm
11gpm
Static Balancing
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What is Overflow?
• Buildings are balanced to the full load
• As circuits of a building shut down, others will see excess flow
• Coils will still produce sufficient heat but will use more energy then is needed
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Why Prevent Overflow
• Pump Energy
• Noise / Pipe Erosion
• Boiler / Chiller Efficiency
• Control Valve Authority
• ASHRAE 90.1
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Variable Speed Pumps• Variable flow systems
reduce pumping costs at partial load
• Need to maximize pumping energy savings while keeping a 100% operational cooling/heating system
Constant Speed Pump
Variable Speed Pump
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Overflow Effects on System• Overflow causes water velocity
that is higher than expected per design flow
• Higher water velocity leads to erosion in elbows & heat exchangers
• Control valves work with very short open/close cycles– Limits actuator life
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0%
20%
40%
60%
80%
100%
0% 100%80%60%40%20% 200%180%160%140%120%
120%
220% 240%
Hea
t
Flow
Overflow Effects on Coils
• 250% flow = 120% heat
• Coils are designed to flow a certain amount
• Over 100% flow, the efficiency of the coil reduces
• 150% flow = 110% heat
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Differential Temperature (∆T)
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140°160°170°
180°
10gpm15gpm20gpm
Overflow = Low ΔT
Design:10GPM, 40°ΔT
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ASHRE 90.1-2010
6.4.2.2 Pump Head. Pump differential pressure (head) for the purpose of sizing pumps shall be determined in accordance with generally accepted engineering standards and handbooks acceptable to the adopting authority. The pressure drop through each device and pipe segment in the critical circuit at design conditions shall be calculated
6.5.4.2 Hydronic Variable Flow Systems. HVAC pumping systems having a total pump system power exceeding 10hp that includes control valves designed to modulate or step open and close as a function of load shall be designed for variable fluid flow and shall be capable of reducing pump flow rates to 50% or less of the design flow rate…The control or devices shall be controlled as a function of desired flow or to maintain a minimum required differential pressure. Differential pressure shall be measured at or near the most remote heat exchanger or the heat exchanger requiring the greatest differential pressure
6.7.2.3.3 Hydronic System Balancing. Hydronic systems shall be proportionally balanced in a manner to first minimize throttling loss; then the pump impeller shall be trimmed or pump speed shall be adjusted to meet design flow conditions
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EQM Control Valve
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Pressure Independent Control Valve
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Terminal 4
Terminal 3
Terminal 2
Terminal 150’
40’
30’
20’
40’ 7gpm
30’ 13gpm
20’ 17gpm
50’ 3gpm
50’ 10gpm
50’ 10gpm
50’ 10gpm
50’ 10gpm
50’ 13gpm
50’ 13gpm
50’ 13gpm
Terminal 1
Terminal 2
Terminal 3
Terminal 4
10gpm
10gpm
10gpm
10gpm
Terminals are set to 10gpm with static valves. When all control valves are open, system is comfortable & efficient
When one control valve closes down, the other terminals overflow, wasting energy
As other terminals try to modulate, overflow situation intensifies, increasing energy costs
As more portions of the building close, the situation gets worse
Pressure independent systems maintain a constant flow rate and proper control valve authority
When one control valve closes, desired control is maintained
When other valves modulate, desired flow is achieved through high control valve authority
0gpm
13gpm
13gpm
13gpm8gpm
15gpm
15gpm
0gpm
17gpm
11gpm5gpm
Current Balancing StrategiesLow Control Valve Authority
Differential Pressure ControlHigh Control Valve Authority
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Modulating Control
Time
Ro
om
Tem
p
72°
76°
68°
6:00am
On-off Control
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Control Valve Authority with an ABV
Required Flow Actual Flow
10gpm 10gpm7.5gpm5gpm2.5gpm 5gpm
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Differential Pressure Controller
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P2
(DP Stabilization)
STAD (Flow measuring)
P3
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Dp Controller Placement
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STAP Placement
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140°160°170°
180°
10gpm15gpm20gpm
Low ΔT
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Pressure Independent Options
Dp Controller
Standard Control Valve
Manual Balancing Valve
Pressure Independent Control Valve
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Review Questions
• Which organization requires systems to be proportionally balanced?• What type of balancing is more energy efficient?
• No balancing• Static balancing• Dynamic balancing
• What causes low ΔT?• Why are modulating control valves used?
• Energy efficiency• Better room temperature control• Lower cost
• What does EQM stand for?