Energy Performance Indicators in the Swedish Building Procurement Process
Abstract
:1. Introduction
2. Method
2.1. Delphi Methodology
Application of the Delphi Methodology in this Study
- I1.
- the envelope air leakage @ 50 Pa (L/sm2);
- I2.
- U-values for different building parts (W/m2K);
- I3.
- the average U-value of the building envelope (W/m2K);
- I4.
- the specific heat loss through heat transfer, ventilation, and air leakage at the winter outdoor design temperature as defined by the Swedish Centre for Zero-energy [45] (henceforth SHLWDT) (W/m2K);
- I5.
- the heat loss coefficient including heat loss through ventilation, air leakage, and heat transfer towards the outdoor air, but not towards the ground (henceforth L) (kWh/°C);
- I6.
- the specific net energy need for space heating, domestic hot water, and facility appliances per heated floor area (not including any energy production conversion losses or heat losses within the house premise) (kWh/m2); and
- I7.
- the specific purchased energy for space heating, domestic hot water, and facility appliances supplied to the building’s technical installations for building services and energy system, per heated floor area (not including “free” energy such as solar or geothermal) [22] [kWh/m2].
2.2. Case Study Methodology
2.2.1 Reference Scenario
2.2.2 Parameter Variations
3. Results
3.1. Results from the Delphi Study
“(the cost) matters less, within reasonable limits”
“(the timeframe) matters less, but it may be difficult to enforce requirements (on building energy performance) if the verification process takes too long.”
“(You should) agree upon a calculation (procedure) in the procurement process and measure air tightness, heat exchanger function, and room air temperatures.”
“(You should verify building energy performance) in the design phase to show the theoretical level; (then) follow up in the finished building (at the final inspection) to ensure this level.”
“(You may use) a mix of both (evaluations in the design phase and operational phase) as long as you do not measure things we cannot influence (e.g., user behavior).”
“The building envelope may be verified in the final inspection, but the (technical) installations should be adapted to the function of the building and its residents.”
“…. (the specific purchased energy) says nothing about the performance of the building envelope, you can e.g., compensate for a bad envelope by putting solar panels on the roof.”
“Although you have to measure the energy use since there is an interest (from the client) to know the cost for heating the building, the energy performance (of the building) is of course something else.”
“… (the specific purchased energy) is difficult to verify. It is difficult to determine if any deviations depend on the building or on the users.”
“The stricter the requirements get the higher percentage of the energy consumption will be influenced by user behavior and operation. This leads to a need (for the construction companies) to keep very good track of the energy consumption in order to avoid disputes.”
”The building envelope should stand for 100 years, the installations are exchanged more often. It should therefore be more important to measure parameters connected to the building envelope.”
”…the contractor has more control over the installations than over the operation and user behavior.”
3.2. Results from the Case Study
4. Discussion
Future Research
5. Conclusions
Acknowledgments
Author Contributions
Conflicts of Interest
References
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External Conditions | Building Envelope | Technical Installations | Building Operation | User Behavior |
---|---|---|---|---|
P1. Climate [24] | P2. Form factor (envelope area/volume) [46] P3. Window to floor area ratio [46] P4. Average U-value [47,48] P5. Envelope air leakage @ 50 Pa [47] | P6. Heating system a P7. Ventilation heat recovery efficiency [49] P8. Specific fan power [49] | P9. Indoor temperature [48] P10. Ventilation rate [21,48] P11. Supply to exhaust air rate ratio [50] | P12. Energy use for household appliances [21] P13. Energy use for domestic hot water [51] P14. Number of occupants [21] P15. Airing (by opening windows) [51] |
Parameter | Value | Source/Comment |
---|---|---|
External conditions | ||
Climate data | Umeå1961–1990 | Average values 1961–1990 [69]. Yearly average temperature 4.00 °C. |
Wind profile | Suburban | [70] |
Building envelope | ||
Envelope area | 1847 m2 | From blueprints. |
Heated floor area | 1495 m2 | Heated above 10 °C. From blueprints. |
Volume | 3952 m3 | From blueprints. |
Form factor | 0.47 | Envelope area to volume ratio. |
Window to floor area ratio | 16.3% | From blueprints. |
Average U-value | 0.307 W/m2K | External walls 0.127 W/m2K. Roof 0.0810 W/m2K. Foundation 0.238 W/m2K. Windows 1.20 W/m2K. From blueprints. Thermal bridges assumed to 72.4 W/K, representing typical values [70]. |
Envelope air leakage at 50 Pa | 0.6 L/smenv2 | Highest allowed for buildings with less than 100 m2 floor area, with a window area smaller than 20% of the heated floor area and with no space cooling according to BBR [22]. |
Technical installations | ||
Heating system | District heating | For space heating and domestic hot water. From tender documents. Assumed to have 100% efficiency, since the heat not transferred to the buildings heating system returns to the district heating system. Heat losses from the internal heating system assumed to 4% of the delivered space heating energy, 50% contributing to space heating, representing typical values [70]. |
Ventilation system | A supply- and exhaust system with heat recovery. A rotary heat exchanger with 80% temperature efficiency. | From tender documents. Supply air duct heat loss assumed to be 1.16 W/m2 at a 7 °C temperature difference between duct and zone, 50% contributing to space heating, representing typical values [70]. |
Specific fan power | 2 kW/(m3/s) | Requirement for heat recovery ventilation systems (HRV) in BBR [22] Ventilation fan efficiency assumed to 60%, representing typical values [71]. |
Elevator | Gearless traction elevator | From tender documents. Using 50 kWh per apartment and year [72]. |
Lighting in common areas | 11 fluorescent lamps, each emitting 25 W 16 h/day | Assumption. |
Building operation | ||
Indoor temperature | 22 °C | [22] Used as supply air temperature set-point for the ventilation heat exchanger, to allow for maximum heat recovery. |
Ventilation rate | 0.35 L/sm2 | [22] |
Supply to exhaust air rate ratio | 1 | Supply air rate = exhaust air rate. Assumption. |
User behavior | ||
Energy for household appliances | 3.42 W/m2 | 70% becomes internal heat gains [23]. |
Energy for domestic hot water | 25 kWh/m2 year | 20% becomes internal heat gains [23]. |
Number of occupants | 40 | Emitting 80 W each 14 h/day [23]. |
Airing | 0.5 L/smenv2 | By opening windows [23]. |
Parameters | Best-Case Scenario | Worst-Case Scenario |
---|---|---|
Building envelope | ||
P2. Form factor (nr. of floors) | 0.39 (8 floors, 47 apartments, 82 occupants, 2807 m2 heated floor area, and an average U-value of 0.35 W/m2K.) | 0.52 (3 floors, 17 apartments, 30 occupants, 1167 m2 heated floor area, and an average U-value of 0.29 W/m2K.) |
P3. Window to floor area ratio (%) | 10 (the recommended minimum in BBR [22].) | 20 |
P4. Average U-value (W/m2K) | 0.20 | 0.40 (maximum allowed in BBR [22].) |
P5. Envelope air leakage @ 50 Pa a (L/smenv2) | 0.3 (required in the Swedish passive house criteria [44].) | 0.9 |
Technical installations | ||
P6. Heating system b | HP (with a COP factor of 5 for heating and 3 for domestic hot water.) | PB (with an efficiency of 80%, the average of 11 pellet boilers used in Sweden [73].) |
P7. Ventilation heat recovery efficiency a (%) | 90 | 70 (recommended minimum in BBR [22].) |
P8. Specific fan power a (kW/(m3/s)) | 1.5 | 2.5) |
Building operation | ||
P9. Indoor temperature a (°C) | 21 | 23 |
P10. Ventilation rate a (L/sm2) | 0.25 (representing a lower ventilation need e.g., due to demand control). | 0.45 (representing a higher ventilation need e.g., due to air contaminants.) |
P11. Supply to exhaust air rate ratio a,c | - | 1.05 (supply air rate 105% of exhaust air rate.) |
User behavior | ||
P12. Energy use for household appliances a,d (W/m2) | 4.4 | 2.4 |
P13. Energy use for domestic hot water a (kWh/m2 year) | 20 | 30 |
P14. Number of occupants a,d | 60 | 20 |
P15. Airing a (L/smenv2) | 0.25 | 0.75 |
Category of Issues | Issues | Number of Respondents | |
---|---|---|---|
1st rank within Each Category | 1st Rank Overall | ||
Requirements on specific purchased energy | Tough requirements on purchased energy requirements and possible fines are risky, since it is not possible to control all factors that influence building’s energy performance. | 8 | 5 |
To ensure compliance with the energy efficiency requirements, a substantial safety margin is required due to the various factors that may cause uncertainty. | 4 | 1 | |
Uncertainties and responsibility | Purchased energy is significantly affected by the users’ behavior | 4 | 6 |
Fixing the liability/responsibility is ambiguous in situations when the energy requirement is not met | 3 | 4 | |
Operating times, ventilation, and indoor temperatures as well as envelope air leakage and airing are factors that have a major impact on the purchased energy. | 3 | 5 | |
Verification method | With improper follow-up, competition in procurement can be distorted when accounting for the promised performance and the one stickler for the rules may find it difficult to win projects against unscrupulous competitors. | 8 | 6 |
It is problematic to do the follow-up during the first years when the building is not dried out properly and control of the installations have not been optimized. | 5 | 3 | |
Parameters influencing the purchased energy | The heating source and heating system efficiency affects the amount of purchased energy (heat pumps and solar panels are favored). | 6 | 5 |
Hot water usage is increasing with more people/m2, despite better installations. | 4 | 3 |
Parameters | Reference | Variations | Indicators | ||||
---|---|---|---|---|---|---|---|
I3. | I4. | I5. | I6. | I7. | |||
Average U-Value | SHLWDT | L | Specific Net Energy | Specific Purchased Energy | |||
(W/m2K) | (W/m2K) | (kWh/°C) | (kWh/m2) | (kWh/m2) | |||
External conditions | |||||||
P1. Climate data | Umeå1961-1990 | Umeå2000-2009 | ±0% | ±0% | −0.94% | −1.6% | −1.6% |
Building envelope | |||||||
P2. Form factor (no. of | 0.47 | 0.39 | +13% | −16% | +84% | −4.9% | −4.85% |
floors) | 0.52 | −6.6% | +1.3% | −21% | +3.1% | +3.1% | |
P3. Window to floor | 16.3 | 10 | −19% | −9.2% | −16% | −10% | −10% |
area ratio (%) | 20 | +11% | +8.0% | +9.9% | +5.7% | +5.7% | |
P4. Average U-value | 0.31 | 0.2 | −34% | −25% | −25% | −22% | −22% |
(W/m2K) | 0.4 | +32% | +22% | +25% | +24% | +24% | |
P5. Envelope air leakage @ 50 Pa | 0.6 | 0.3 | ±0% | −5.9% | −0.75% | −1.8% | −1.8% |
(L/smenv2) | 0.9 | ±0% | +6.0% | +0.71% | +1.8% | +1.8% | |
Technical installations | |||||||
P6. Heating system | DH | HP | ±0% | ±0% | −80% | ±0% | −67% |
DH + S | ±0% | ±0% | +0.64% | ±0% | −15% | ||
NGB | ±0% | ±0% | +9.9% | ±0% | +6.5% | ||
PB | ±0% | ±0% | +25% | ±0% | +22% | ||
P7. Ventilation heat recovery efficiency (%) | 80 | 90 | ±0% | −8.0% | −8.8% | −7.4% | −7.4% |
70 | ±0% | +8.0% | +9.1% | +7.6% | +7.6% | ||
P8. Specific fan power | 2 | 1.5 | ±0% | ±0% | −0.12% | −2.4% | −2.4% |
(kW/(m3/s)) | 2.5 | ±0% | ±0% | +0.084% | +2.4% | +2.4% | |
Building operation | |||||||
P9. Indoor temperature | 22 | 21 | ±0% | −2.4% | ±0% | −4.7% | −4.7% |
(°C) | 23 | ±0% | +2.4% | ±0% | +4.9% | +4.9% | |
P10. Ventilation rate | 0.35 | 0.25 | ±0% | −4.6% | −6.4% | −7.3% | −7.3% |
(L/sm2) | 0.45 | ±0% | +4.6% | +6.5% | +7.3% | +7.23% | |
P11. Supply to exhaust | 1 | 0.95 | ±0% | −5.3% | −0.42% | −0.49% | −0.49% |
air rate ratio | 1.05 | ±0% | +1.9% | +5.2% | +3.4% | +3.4% | |
User behavior | |||||||
P12. Energy for household appliances | 3.42 | 4.4 | ±0% | ±0% | ±0% | −5.7% | −5.7% |
(W/m2) | 2.4 | ±0% | ±0% | ±0% | +6.0% | +6.0% | |
P13. Energy for domestic hot water | 25 | 20 | ±0% | ±0% | ±0% | −8.1% | −8.1% |
(kWh/m2) | 30 | ±0% | ±0% | ±0% | +7.7% | +7.7% | |
P14. Number of | 40 | 60 | ±0% | ±0% | −0.19% | −1.1% | −1.1% |
occupants | 20 | ±0% | ±0% | +0.30% | +5.4% | +5.4% | |
P15. Airing (L/sm2) | 0.5 | 0.25 | ±0% | ±0% | −0.60% | −1.5% | −1.5% |
0.75 | ±0% | ±0% | +0.60% | +1.5% | +1.5% |
Studied Indicators | Preferred by the Building Practitioners | Less Dependent of Building Operation and User Behavior Compared to the Specific Purchased Energy (I7) | Less Dependent of the Technical Installations Compared to the Specific Purchased Energy (I7) |
---|---|---|---|
For calculation based evaluations | |||
U-values for different building parts (I2) | X | X a | X b |
Average U-value (I3) | X | X ac | X b |
SHLWDT (I4) | X | X c | X c |
L (I5) | - | X c | X c,d |
Specific net energy (I6) | - | - | X c |
Specific purchased energy (I7) | - | - | - |
For measurement based evaluations | |||
Envelope air leakage (I1) | X | X a | X b |
L (I5) | - | X c | X c,d |
Specific net energy (I6) | - | - | X c |
Specific purchased energy (I7) | - | - | - |
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Allard, I.; Olofsson, T.; Nair, G. Energy Performance Indicators in the Swedish Building Procurement Process. Sustainability 2017, 9, 1877. https://doi.org/10.3390/su9101877
Allard I, Olofsson T, Nair G. Energy Performance Indicators in the Swedish Building Procurement Process. Sustainability. 2017; 9(10):1877. https://doi.org/10.3390/su9101877
Chicago/Turabian StyleAllard, Ingrid, Thomas Olofsson, and Gireesh Nair. 2017. "Energy Performance Indicators in the Swedish Building Procurement Process" Sustainability 9, no. 10: 1877. https://doi.org/10.3390/su9101877