Life-Cycle Analysis of Building Retrofits at the Urban Scale—A Case Study in United Arab Emirates
1.1. Context and Motivation
- Insulation of poorly insulated envelope components;
- Window improvement/replacement;
- Improvement of envelope air-tightness;
- Cool roof retrofit.
- Adjusting up thermostat set-point: When appropriate, increasing cooling temperature set-points can be considered.
- Retrofit of constant air volume systems: For commercial buildings, variable air volume (VAV) systems should be considered when the existing HVAC systems rely on constant volume fans.
- Installation of heat recovery systems: Heat exchangers can be installed to recover thermal energy from air handling unit (AHU) exhaust air streams.
- Retrofit of central cooling plants: New chillers tend to be more energy-efficient and easier to control and operate.
- Re-commissioning of the controls: Generally, the following re-commissioning measures can be envisaged:
- Operating the systems only when required for comfort, safety or health reasons (e.g., no ventilation during unoccupied periods);
- Eliminate overcooling to improve comfort and save energy;
- Reduce reheat in the AHU;
- Provide free cooling whenever possible (e.g., by heat recovery systems or economizer);
- Reduce or better regulate the amount of fresh air delivered by the AHU.
- Development and calibration of a detailed engineering model on the basis of the data provided by the Urban Planning Council for a typical building in the Emirate of Abu Dhabi ;
- Simulation-based analysis of the impact of candidate energy efficiency measures on the energy performance of the aforementioned typical building;
- Estimation of the potential CO2 emissions abatement resulting from the implementation of the candidate measures;
- Life Cycle Cost/Carbon assessment of the candidate measures;
- Extrapolation of the typical building to the whole Emirate and development of several Marginal Abatement Cost Curves (MACCs).
2.1. Defining a Business as Usual (BAU) Building
- Length, width and height: 40 m, 40 m, 52.5 m;
- Number of floors: 15 (top floor is plant room);
- Total floor area: 23,312 m2;
- Volume: 81,593 m3;
- Windows applied for all the 13 middle floors and one side of the ground floor: continuous horizontal glazing with an overall window to wall ratio of 70%;
- Infiltration rate: 0.3 ACH (air changes per hour);
- People density: 0.085 person/m2 (approx. 12 m2/person);
- Minimum fresh air: 10 L/s-person (liter per second per person);
- Equipment intensity: 15 W/m2, applied to all the non-common areas of the ground and middle floors;
- Lighting intensity: 10 W/m2;
- Chiller COP: 2.8 (constant);
- Heat recovery: sensible only, 65% effectiveness;
- Main occupancy period: 6 am–8 pm;
- Envelope U-values: 1.71 W/m2·K for the wall, 0.53 W/m2·K for the roof;
- Glazing characteristics: U-Value = 2.4 W/m2·K, SHGC (solar heat gain coefficient) = 0.36.
2.2. Energy Efficiency Retrofits
- Space cooling load corresponding to internal and external gains (sensible + latent);
- Load due to mechanical ventilation (or fresh air load).
- Enhancement of wall insulation;
- Enhancement of the glazing (replacement);
- Enhancement of chiller COP (replacement);
- Enhancement of envelope air-tightness;
- Increase of the cooling set-point temperature;
- Enhancement of roof insulation;
- Cool roof.
2.3. Estimation of the Costs
2.4. Derivation of the Marginal Abatement Cost Curve (MACC)
3. Energy Impact of Retrofits
3.1. BAU Energy Performance
|Office BAU||Chiller (kWh)||Pumps (kWh)||Fans (kWh)||Lights (kWh)||Equip (kWh)|
3.2. Implementation of Retrofits
3.2.1. Air Tightness
|Cooling||BAU||0.25 ACH||0.2 ACH||0.15 ACH||0.10 ACH|
|BAU||0.25 ACH||0.2 ACH||0.15 ACH||0.10 ACH|
|Annual Load (MWh)||4034||3979||3922||3867||3811|
3.2.2. Cooling Temperature Set-Point
|Annual Load (MWh)||4034||3704||3395||3103||2827|
3.2.3. Chiller COP
- GLZ1 (U = 1.47, SHGC = 0.3): Double-Pane, Low-Gain Low-E, Insulated Frame, Argon Fill;
- GLZ2 (U = 1.7, SHGC = 0.3): Double-Pane, Low-Gain Low-E, Insulated Frame, Air Fill.
3.2.5. Opaque Partition Insulation
|Insulation layer added||Final Wall U-value (W/m2·K)|
|R-5 XPS, thickness: 30 mm||0.705|
|R-10 XPS, thickness: 50 mm||0.444|
|R-15 XPS, thickness: 80 mm||0.324|
|Peak Load||BAU||R5 XPS||R10 XPS||R15 XPS|
|Annual Load||BAU||R5 XPS||R10 XPS||R15 XPS|
4. Life-Cycle Assessment
5. Results and Discussion
5.1. Price of Electricity: 0.04 $/kWh
5.2. Price of Electricity: 0.09 $/kWh
6. Conclusions and Future Work
- Estimation of energy savings in a typical Abu Dhabi building after applying different types of retrofits;
- Extrapolation to the entire building sector of the Emirate;
- Analysis of CO2 abatement potential;
- Life cycle analysis of retrofit cost and carbon abatement potential;
- Development of a MACC for assessing the impact of AC related demand-side measures in Abu Dhabi.
Conflicts of Interest
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Afshari, A.; Nikolopoulou, C.; Martin, M. Life-Cycle Analysis of Building Retrofits at the Urban Scale—A Case Study in United Arab Emirates. Sustainability 2014, 6, 453-473. https://doi.org/10.3390/su6010453
Afshari A, Nikolopoulou C, Martin M. Life-Cycle Analysis of Building Retrofits at the Urban Scale—A Case Study in United Arab Emirates. Sustainability. 2014; 6(1):453-473. https://doi.org/10.3390/su6010453Chicago/Turabian Style
Afshari, Afshin, Christina Nikolopoulou, and Miguel Martin. 2014. "Life-Cycle Analysis of Building Retrofits at the Urban Scale—A Case Study in United Arab Emirates" Sustainability 6, no. 1: 453-473. https://doi.org/10.3390/su6010453