1Residential ETTV Criterion for Buildings in Singapore

13 July 2007

at Building and Construction Authority

by

S.K. Chou, Dept of Mechanical Engineering, NUS

Presentation Overview

Commercial building reference Residential air-con survey Building description and modelling Formulation of residential ETTV equation Relating Residential ETTV to cooling energy Residential ETTV cutoff value Approaches to reducing ETTV/RETV Tool for RETV calculation

2Commercial Building Reference

Parameters and Range

3.5 5.5COP0.5 0.8LTS10 20LIT (W/m)5 10OA (cfm)32% 90%WWR0.2 0.7SC0.2 4.21Uf(W/mK)0.5 2.5Uwall (W/mK)

3Distribution of Loads (MWh) in reference office building7%

1%

17%

1%

17%

30%

9%

15%

3%

Wall Win Solar Roof People Lights Equip Infiltration Others

Qenvelope ~ 25%

Office ETTV vs Energy

Cooling Energy vs ETTV

y = -0.001x2 + 14.801x + 2174.4R2 = 0.9909

2600

2650

2700

2750

2800

2850

2900

2950

3000

3050

3100

30 35 40 45 50 55 60ETTV

Coo

ling

Ener

gy (M

Wh)

4Residential Building ETTV

Air Conditioning Pattern Survey Results

0

2

4

6

8

10

12

14

16

18

20

Households

< 7pm 7pm 8pm 9pm 10pm 11pm 12am >12amTime

Week Day Turn On Time

50

2

4

6

8

10

12

14

Households

9amTime

Week Day Turn Off Time

0

2

4

6

8

10

12

14

Households

< 7pm 7pm 8pm 9pm 10pm 11pm 12am >12amTime

Week End Turn On Time

60

1

2

3

4

5

6

7

8

9

Households

9amTime

Week End Turn Off Time

Survey Summary From the survey, it can be seen that

most people turn on air conditioning between 9pm and 11pm for both weekdays and weekends

Air conditioning is turned off mostly between 6am and 8am.

This information is reflected in DOE2 coding

712 storeys4 x 144 m2

Building

Bedroom 1 and Bedroom 2Air-conditioned area

Opened when A/C is off to provide natural ventilation, closed when

A/C is on

Windows

A family of 4Number of occupants in an apartment2.0 to 3.0COP

24 oC Weekdays (Operation) 22:00-07:00Weekends (Operation) 22:00-08:00

Rest set point is 37 oC

Cooling setpoint

Split Unit, rated @ 22,000 BTU/hr for Bedroom 1 and 15,000 BTU/hr

for Bedroom 2

System type

HDB Building Description

Model of a point block

Bedroom 2

Bedroom 1

12m

12m

Common Corridor

8Model of a HDB slab block

Envelope Parameters and Ranges

0.45Wall Absorptance

20% to 51%WWR

0.2 0.9SC

2.2 6.2 Uf (W/m2 K)1.2 4.5Uw (W/m2 K)RangesParameters

9Private Residential Building Load Distribution

6%9%

23%62%

QwallQglassQsolarQothers

Includes loads due to: Infiltration Lighting People Miscellaneous

Equipment Roof

Uwall Value of 1.2 W/m2K

Uglass Value of 6.13 W/m2K

Average SC Value of 0.3

WWR = 51%

HDB Loads Distribution

21%

4%

16%59%

QwallQglassQsolarQothers

Includes loads due to: Infiltration Lighting People Miscellaneous

Equipment Roof

Uwall Value of 2.89 W/m2KUglass Value of 6.13 W/m2K

Average SC Value of 0.52WWR = 20%

10

Formulation of equivalent residential ETTV equation - considerations

Sensitivity and range

Effect of building shape or aspect ratio and orientation

Residential ETTV equation should relate to accurate estimation of cooling energy consumption like its commercial building counterpart

Residential ETTV equation coefficients

55.331.103.38660.434144.099216.3985

56.831.223.31352.35378.530337.4974

55.801.243.24567.66295.550332.2223

55.921.363.11406.30758.168421.6642

55.101.103.01408.379135.490266.0721

SFt (oC.)Tdeq(oC.)Qsol

(MWh)Qwin

(MWh)Qwall

(MWh)

Sample of simulation data

11

The residential ETTV equation is thus:

( ) ( ) ( )( )( )SCCFWWRUWWRUWWRETTV fwres 6.583.114.3 ++=

Point Block

Gr a ph of Cool i ng Ene r gy Vs ETTV

y = 9 . 4 7 5 5 x + 6 2 .2 9 6R 2 = 0 . 8 8 2 3

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30

ETTV r e s

12

Slab Block

Gr a ph of Cool i ng Ene r gy Vs ETTV

y = 6 . 4 9 0 7 x + 6 2 . 12R 2 = 0 . 9 8 3 3

0

50

100

150

200

250

300

0 5 10 15 20 25 30 35

E T T V r es

RETV (Residential Envelope Transmittance Value)

=

ETTVres (Residential ETTV)

13

Potential energy savings

About the mid point RETV range of 20 W/m2,

Slab block - A unit decrease in RETV results in 3.5% decrease in the annual cooling energy

Point block - A unit decrease in RETV results in 4% decrease in the annual cooling energy

Cutoff value of RETV

Based on results obtained, the following RETV cut-offs are recommended:

A cutoff at 25 W/m2 in the immediate and near term. From simulation, this value stands in the upper range of RETV of residential buildings. This is well within the capability of most public residentials as well as private ones which do not have high WWRs.

A cutoff of 20 W/m2 in a future phase/longer term. This can be achieved with continued application of modest WWR and improved design and material properties.

14

Approaches to reducing ETTV/RETV1. Glass shading coefficient2. Window-to-Wall ratio3. Wall absorptance4. Wall resistance5. U fenestration6. Wall cladding7. External shading devices8. Solar film

Tool for ETTV and Energy Calculation

Algorithm will be developed to estimate ETTV from multi-parametric changes(Sc, WWR, Alpha, Uwall, Uf)

Algorithm will be developed to estimate Cooling Energy from multi-parametric changes(COP, OA, LIT, LTS, Set-Pt Temp)

15

Tool for quick ETTV calculationBase Values New Values

Change in ETTV

Original ETTV

New ETTV

Tool for quick Energy calculation

Base Values New Values

Change in Ec

Original Ec

New Ec

16

THANK YOU