energy insights singapore 2013-04

8/11/2019 Energy Insights Singapore 2013-04

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ENGINEERING ADVANTAGE

ENERGY INSIGHTSOPTIMISING HYDRONIC SYSTEMS

FOR ENERGY SAVINGS

Jean-Christophe Carette

Singapore, April 2013


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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 installationUse of new technologies

System approach ofhydronic design

Shorter pay-back times

Building structure(insulation, double glazing, )

Best way to save energyLarger energy savings

Long pay-back times

Human factorAvoid interferences with

the HVAC systemEducate tenants and

maintenance 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

peopleusing the installation


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Energy savings via hydronic optimization

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Optimising a building's HVAC

system can reduce its energy

consumption by 30% :

By avoiding the deterioration

of production unit

efficiencies,

By optimizing the energyefficiency of the hydronic

distribution,

By guaranteeing a stable and

accurate room temperature.


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IMPROVING

PRODUCTION UNIT

EFFICIENCIES

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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 Ts is usually kept constant

Thus return water temperature Trmust be kept "high"

to keep LMTD high

Keeping a high Tr (thus a high T = Tr-Ts) provides higher COP at partial load

Chillers

6

Evaporator

Condenser

Chilled water

Tr Ts645.2

compressor

evaporator

P

PCOP

Refrigerant saturated

suction temp.

Tr

Ts


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

7

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%



C


6,0

8,0

10,0

12,0

14,0

16,0

18,0

20,0

22,0

24,0

26,0

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Variable flow proportional control

8

Returntemp.Tr

2-way circuit (variable flow)

Flow through terminal unit

Temperature regime:

Ts/Tr/Ti = 6/12/23.5C

qp

STAD

H

C

Variable flow circuit

The DT through a terminal unit increases

when the flow reduces.

Thus the return water temperature increases

when the flow reduces.

All benefits for chiller COP.

Cooling


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On-off control Flow increase at partial load

Manually balanced variable flow on-offcontrol system

100 identical units; Pump head 200 kPa; Terminal unit 20kPa; On-off CV 5 kPa

Temperature regime:

Ts/Tr/Ti = 6/12/23.5C

Totalsystemflow

System load

At 50% load, the total flow in system reaches 77% of the total design flow.This is a 54% increase w.r.t. the required flow (50%) at 50% load.

Seasonal flow increase lead to an estimated increased pumping energy

consumption up to +4% of total plant energy consumption

10

4%



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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

Em

ission

11

Roomt

Design

set-point23.5C

Time

At partial load in the system,

if a valve is open:

k

TqP

D

(Troom - Tset-point) >0

energy insights singapore 2013-04

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