proportional balancing cpd

Andy Lucas Technical Development Manager CRANE BS&U

CRANE BS&U supporting the Building Services

Industry

Crane Co founded in 1855 by Richard Teller Crane who made the following resolution -

“I am resolved to conduct my business in the strictest honesty and fairness; to avoid all deception and trickery; to deal fairly with both customers and competitors; to be liberal and just towards employees; and to put my whole mind upon the business”

Crane Limited founded in Ipswich in 1919

Crane Building Services & Utilities created 2009

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CIBSE approved CPD

PROPORTIONAL BALANCING


To give an overview of Proportional Balancing within the commission process

This process applies to both constant & variable flow heating and chilled water systems

Title

Objective

Commissioning

Definition:

The advancement of an installation from the state of static completion to full working order to specified requirements.

CIBSE Commissioning Code W

Why commission?

Requirement L1 of Part L of the Building Regulations in England and Wales requires that “reasonable provision shall be made for the conservation of fuel and power in buildings by

providing and commissioning energy efficient fixed building services with effective controls”

Commissioning

Commissioning

Why Balance?

Waters lazy – will take shortest route!

• nearest terminal hottest

• furthest terminal coldest

Balancing forces design flow rates to all areas

Commissioning

Preparation for Commissioning

• Installed in accordance with specification

• successfully pressure tested

• flushed & cleaned

• filled, treated & vented

• safe & ready to set to work

• all valves fully open

Installation must be

Commissioning

Pump shut-off (closed) head test

Pre

ssur

e

Flow Rate

closed head from manufacturer

• measure closed head

• check against pump curve

• draw parallel curve

• pressure at full flow – check against graph

• if flow and pressure co-inside with graph – pump performance OK

pump curvecorrected pump curve

measured closed head

Commissioning

Preliminary flow rate check

• measure flow - all valves open

• if less than 100% - will result in final balance being less than 100%

variable flow systems may have ‘diversity’ designed in

• set to 110% pump design flow rate

Commissioning

Full system scan

• measure all flow rates

• highlights problems

Proportional Balancing

What is it?

The systematic process of bringing the fluid flow rates throughout a distribution system into balance with one another, in their correct proportions and within

tolerances specified by the designer.

CIBSE Commissioning Code W


• fixed speed pumps – no energy saving for part load

• constant volume of water is pumped around the system

• 3 or 4 port control valve diverts water through by-pass

• commissioned by proportional balancing or by the use of constant flow regulators – ABV (Automatic Balancing Valves)

Constant volume flow systems


• variable speed pumps – energy saving for part load

• variable volume of water to match demand

• 2 port control valve

• commissioned by combination of;

proportional balancing

DPCV – Differential Pressure Control Valves

PICV – Pressure Independent Combination Valve

Variable volume flow systems


Terms

• %DFR – Percentage Design Flow Rate

• Least Favoured/Index Circuit

• Reference Circuit

%DFR – Percentage Design Flow Rate


measured flow

design flow%DFR = x 100

eg

%DFR = 0.07kg/s

0.10kg/sx 100 = 70%

Terms

Least favoured & index circuit are same

the least favoured/index circuit is the circuit, when system is unbalanced, having the highest pressure drop relative to all other circuits – ie lowest %DFR


A ? B ? C ?

Terms - Least Favoured & Index circuit


The reference circuit is the circuit, when system is unbalanced, that all other circuits will be balanced against

For proportional balancing, the furthest circuit or terminal unit must be the reference.

If this is not the same as the least favoured, it must be made into the least favoured by adding resistance, ie closing double regulating valve

A ? B ? C ?

Reference

add resistance

Terms - Reference circuit


HighLow

Regulate

orifice

Δp

Signal - Δp (differential pressure) is measured

water

Net system pressure loss

Flow measurement valve


To allow us to measure Δp generally we use 1 of 2 instruments

• U tube manometer fluorocarbon 0 - 4.6kPa mercury 0 - 65kPa

• electronic equipment up to 250kPa


Δp measurement – U tube manometer

0

• zero Δp (differential pressure)

• measure Δp – ‘signal’

• equate to flow rate

Q = Kvs Δp

from graph

Δp

high low

0 1 2 3 4 5

Δp

Flow rate

1

2

36Kvs


Δp measurement - electronic

Electronic flow measurement meters are pre-programmed with valve data, therefore, directly display

• differential pressure

• flow rate

• %DFR


Procedure follows 4 stages

1. Measure (scan) each unregulated terminal to establish ‘least favoured’ & ‘reference’

2. Proportional Balance

3. Regulate flow

4. Complete test sheet

Proportional balancing

Measure each terminal


STAGE 1 Measure each terminal

Design (kg/s)

Actual (kg/s)

%DFR

0.10 0.10 0.10 0.10

0.16 0.13 0.10 0.04

160% 130% 100% 40%

Identify least favoured/index

0.160 0.13 0.04 0.10

160% 130% 40% 100%

least favoured/index

Adjust to 110%DFR

Proportional balancing

Measure each terminal


Make furthest equal to least favoured

Always remains index

made least favoured by regulating, ie adding resistance

0.04

40%40%

• add resistance to make furthest (the reference)

equal to least favoured

• if total flow rate drops bring back to 110% if furthest is reference/index then

regulating valve always fully open%DFR


STAGE 2 Proportional Balance

Design (kg/s)

Actual (kg/s)

%DFR

0.10 0.10 0.10 0.10

reference

0.09

90%

0.091

91%

0.092

92%

0.092

92%

0.091

91%

0.092

92%

0.092

92%

Each terminal is Proportionally Balanced against each other working towards pump


STAGE 3 Regulate flow

Design (kg/s)

Actual (kg/s)

%DFR

0.10 0.10 0.10 0.10

0.92 0.92 0.92 0.92

92% 92% 92% 92%

0.10 0.10 0.10 0.10

100% 100% 100% 100%

Adjust circuit commissioning valve to obtain 100%


Larger circuit• 2 floors

• each with commissioning valve

• divided into 2 sub-circuits


• sub-circuit divided into 4 terminal branches



• proportional balance each sub-circuit to reference, ie same %DFR

• sub-circuits can be balanced in any order

• proportionally balance each sub-circuit to reference sub-circuit,

ie same %DFR

Looking at each floorreference


Having proportionally balanced the floor sub-circuits

• Proportionally Balance floors to reference floor, ie same %DFR

• Regulate flow to 100% at pump

constant flow – by regulation

variable flow – by pump speed


Sample from BSRIA Commissioning Water Systems applications guide

valve datadesign data

initial scan measured results

L001 D931 15 lower 0.110 2.2 3.24 4.4 0.128 116 3.28 0.111 101 3.2

%DFR


Steps to Proportional Balancing

scan - %DFR

identify index

same as reference?add resistance

proportional balance

regulate flow

no

yes

complete test sheet

Variable flow CPD

• understanding variable flow systems

• commissioning variable flow systems

proportional balancing

adjusting DPCV

setting PICV

proportional balancing cpd

Documents

cibse commissioning

crane bsamp

proportional

proportional

add resistance

commissioning

valve data

favoured amp