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ENGINEERING ADVANTAGE

ENERGY INSIGHTS

OPTIMISING HYDRONIC SYSTEMS

FOR ENERGY SAVINGS

Tom Pak

May 9th 2012


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Copyright

TAHydronicsSA.Allrightsreserved

.

World's energy consumption

2

40% of the world's energy

consumption is used in buildings*

50% of this is in HVAC systems alone*

(*) Sources: European Commission EPBD (point 6, pp1) &

US Department of Energys Buildings Energy Data Book


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Energy savings on HVAC in buildings

3

HVAC installation Use of new technologies System approach of

hydronic design

Shorter pay-back times

HVAC installation Use of new technologies System approach of

hydronic design

Shorter pay-back times

Building structure(insulation, double glazing, )

Best way to save energy Larger energy savings

Long pay-back times

Building structure(insulation, double glazing, )

Best way to save energy Larger energy savings

Long pay-back times

Human factor Avoid interferences with

the HVAC system

Educate tenants andmaintenance team

Never-ending task

Human factor Avoid interferences with

the HVAC system

Educate tenants andmaintenance team

Never-ending task

Building modifications require

adaptation or modernization of

the HVAC installation to take into

account new heat gains/losses

When modifying a HVAC

installation one must take into

account the capabilities of

people using the installation


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Energy savings via hydronic optimization

4

Optimising a building's HVAC

system can reduce its energy

consumption by 30% :

By avoiding the deterioration

of production unit

efficiencies,

By optimizing the energy

efficiency of the hydronic

distribution,

By guaranteeing a stable and

accurate room temperature.


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IMPROVING

PRODUCTION UNIT

EFFICIENCIES

12


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Coefficient of Performance (COP) isused to indicate chiller efficiency:

Heat transfer (and thus COP) is good when Log Mean Temperature Differencebetween water and refrigerant is kept high

Evaporator refrigerant temperature remains constant

Supply water temperature Tsis usually kept constant

Thus return water temperature Trmust be kept "high"

to keep LMTD high

Keeping a high Tr(thus a high T = T

s-T

r) provides higher COP at partial load

Chillers

24

Evaporator

Condenser

Chilled water

Tr Ts645.2

KK

=compressor

evaporator

P

PCOP

Refrigerant saturated

suction temp.

Tr

Ts


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TAHydronicsSA.Allrightsreserved.

Effect of a decrease of the return water temp. on COP

25

Example :

Chiller: 200 tons (703 kW)

Water condenser temperatures: 29,5/35C

Supply temperature of chilled water Ts

: 7C

A reduction of return temperature of chilled water can lead to a

15% drop of the COP

Return temp. chilled water Tr [C]

COP

5

4,6

4,4

4,24

4,2

4,4

4,6

4,8

5

5,2

10,5 11 11,5 12 12,5 13

15%


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6,0

8,0

10,0

12,0

14,0

16,0

18,0

20,0

22,0

24,0

26,0

0% 20% 40% 60% 80% 100%

Variable flow proportional control

26

Re

turntemp.Tr

2-way circuit (variable flow)

Flow through terminal unit

Temperature regime:

Ts/Tr/Ti = 7/12/24C

qp

STAD

H

C

Variable flow circuit

The T through a terminal unit increases

when the flow reduces.

Thus the return water temperature increases


All benefits for chiller COP.

Cooling


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Constant flow system proportional control

27

Returntemp.T

r

qs

qbSTAD-B C

H

STAD-P

qp


3-way diverting circuit (constant flow)

6,0

8,0

10,0

12,0

14,016,0

18,0

20,0

22,0

24,0

26,0

0% 20% 40% 60% 80% 100%

Variable flow circuit

Constant flow circuit

The T through a terminal unit increases


But the flow through the terminal unit is

reduced by bypassing an increasing fractionof the primary flow (at temperature Ts).

Thus the return water temperature decreases

when the flow reduces !!!Constant

flow

Variable

flow

Temperature regime:

Ts/Tr/Ti = 7/12/24C

Cooling


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shut

Variable flow system with 2-way on-off control

28

When some CV are closed:

there is less total flow and Dp in piping

and thus more available Dp everywhere in the system

open valves receive a flow that is higher than design flow

At partial load in the system,

if a valve is open: q >= qdesignopen

qd

openopen

open openopen

qd

qd

qd

qd

qd

shut

> 0 >

> >0


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On-off control Flow increase at partial load

Manually balanced variable flow on-off control system

100 identical units; Pump head 150 kPa; Terminal unit 20

kPa; On-off CV 5 kPa

Temperature regime:

Ts/Tr/Ti = 7/12/24C

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 20% 40% 60% 80% 100%

To

talsystemflow

System load

At 50% load, the total flow in system reaches 73% of the total design flow.

This is a 46% increase w.r.t. the required flow (50%) at 50% load.

Seasonal flow increase lead to an estimated increased pumping energy

consumption equal to +3% of total plant energy consumption

29

3%


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d.

0%

20%

40%

60%

80%

100%

120%

0% 20% 40% 60% 80% 100% 120% 140% 160%

On-off control Emission at partial load

At flow that is near design flow,

emitted power does not increase

much with the flow

Control signal switches on/off when

room temperature deviates much

beyond the thermostat differential

Flow

Emission

30

Roomt

Designset-point

24C

Time

At partial load in the system,if a valve is open:

k

TqP

=

(Troom - Tset-point) >=< q qdesign

P PdesignT Tdesign


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d.

0

2

4

6

8

10

12

14

0% 20% 40% 60% 80% 100%

Return water temp. degradation

Re

turntemp.T

r

System load

Temperature regime:

Ts/Tr/Ti = 7/12/24C

Below 50% of the load, which represents typically 70% of the cooling

season, the return water temperature is degraded by 1.5 to 2C.

This will result approximately in a 3 to 4% increase in seasonal chiller

energy consumption

Manually balanced variable flow on-off control system

100 identical units; Pump head 150 kPa; Terminal unit 20

kPa; On-off CV 5 kPa

31

3%


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d.

6,0

8,0

10,0

12,0

14,0

16,0

18,0

20,0

22,0

24,0

26,0

0% 20% 40% 60% 80% 100%

6,0

8,0

10,0

12,0

14,0

16,0

18,0

20,0

22,0

24,0

26,0

0% 20% 40% 60% 80% 100%

Return water temp. proportional vs on-off control

32

Returntemp.T

r

2-way proportional

3-way proportional

Temperature regime:

Ts/Tr/Ti = 7/12/24C

Cooling


Returntemp.T

r

System load

2-way on-off, MBV

3-way on-off, MBV

Proportional control On-off control


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d.

Case Study - Local University campus buildings

33

Renovation of 2 University buildings with a total of 9840 m2

Installed cooling capacity: Building 1 : 1452 tons refrig.

Building 2 : 1730 tons refrig.

Work performed during summer 2010

Results compared for Oct.-Nov. 2009 vs 2010

DP controllers paired with manual balancing valves installed


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Local University campus building 1 chiller saving

34

Variable secondary flow

with differential pressure

bypass

Dp controllers at on-off

control FCU groups and

PAU/AHUs

and re-balanced

Annualized 22%

chiller energy

savingCooling load [kW]

Powerinput[kW]

2009

2010

Chiller Power Input vs. Cooling Load

34

22%


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d.

Local University campus building 2 chiller saving

Variable flow primary-secondary system

Addition of Dp controllersat FCU groups zones and

pressure independent

control valves for

PAU/AHU and re-balanced

Annualized 16.5%

chiller energy

savingCooling load [kW]

Powerinpu

t[kW]

2009

2010

Chiller Power Input vs. Cooling Load

35

16%


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Case study - business hotel at Sheung Wan

> First LEED and BEAM Plus Platinum

certifications of new-built hotel

> 38 floors, 274 rooms

> Chiller capacity 667 kW x 2 nos

> Variable primary flow design

> Hydronic balancing design

> Chiller plant balancing> Dp control at each floor and

modulating terminals

> Balancing and control valve at FCUs


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Hydronic balancing in variable primary flow

Balanced chiller plant

1

Proper fail-safe bypass valve

sizing and characteristic

2

Balancing & control

valve for proportional

balancing

4

DP stabilization against large

Dp fluctuations in part load

3


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Computerized hydronic system design

TA Select 4

hydronic system calculation


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> Pipe sizing per BEC recommendations

> Balancing valve sizing and pre-settings for easy and efficient

commissioning

> Minimum control valve authority checks (suggest > 0.25) to ensure

indoor comfort with stable temperature control

> Correct Index circuit identification to help determining optimal VFD

sensor location and set-point

> Pump head optimization:

> Initial : 350 kPa

> Select 4 : 236 kPa (-33%)

> Final set : 250 kPa (-29%)


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> Bypass valve sizing calculation


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Tips for reliable and energy efficient VPF system

> Make use of computerized software for hydraulic design calculations

> Chiller plant must be balanced to avoid uneven distribution of flow

> Proper bypass valve sizing and select with good rangeabilty, linear

characteristic (or equal percentage characterisitic at 0.25 authority) valve> Use of high precision flow meter and local controller to monitor total return

flow as fail-safe measure against chiller minimum flow

> Use of DP controllers

> to stablize Dp fluctuations to avoid overflow and low dT problems

> to maintain good control valve authority necessary for stable temperature control

> as flow/DP/DT/energy measuring station for energy audit purpose

> Make system sustainable and adaptive to future changes

> Locate VSP sensor at index circuit and adjust set-point to the DP of the most

demanding stablized circuit potentially up to 40% pump energy saving

> Make use of computerized balancing method and instrument to produce

balancing report without manual record of measurements and verfications


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Conclusion

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Important energy savings can be achieved by taking care of: Maintaining cold/warm return water temperature

to condensing boilers/chillers (~15%),

Having an adequate pressurisation avoiding scaling/foulingin boilers/evaporators (~5-10%).

Minimising pumping costs requires having (up to 40% on 7-17% in cooling):

A good pressure maintenance to avoid corrosion leading to aging and fouling,

An optimized hydronic distribution design (Dp control),

A systematic methodology of balancing and commissioning.

Stable and accurate room t control gives (~5-20%) energy savings by:

Avoiding oversizing in on-off systems,

Using state-of-the-art thermostatic radiator valves,

Sizing of modulating control valves for good minimum authority.

The approach "He who can do more can do less" is to be avoided


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ed.

[email protected]

[email protected]

93

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