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