Going Beyond Code: Monitoring Disaggregated Energy and Modeling Detached Houses in Hawai‘i
2. Materials and Methods
2.1. Monitoring Methods
2.2. IECC 2015 Energy Model Methods
2.3. Parametric Energy Simulation and Optimization Methods
3. Results and Discussion
3.1. Energy and Thermal Performance of Monitored Houses
3.2. Parametric Energy Simulation and Optimization Results
- Increasing the nominal R-value of the wall insulation from R-2.3 m2-K/W (R-13 h-ft2-°F/Btu) to R-2.6 m2-K/W (R-15 h-ft2-°F/Btu) showed an energy savings value of 0.2%. During a conversation with the builder, we agreed that the modest energy cost savings do not justify the increased cost of additional insulation.
- Incrementally changing the ceiling insulation from nominal R-5.3 m2-K/W (R-30 h-ft2-°F/Btu) up to R-10.6 m2-K/W (R-60 h-ft2-°F/Btu) showed almost zero energy savings and is not included in the figure or optimization.
- Changing the exterior wall absorptivity from 0.75 (a medium-dark-colored fiber-cement finish) to 0.30 (a light-colored vinyl finish) reduces the annual energy use by 3.5%. During a conversation with the builder, we confirmed that light-colored exterior walls are cheap to implement.
- Changing the roof material from asphalt medium-colored shingles with an absorptivity of 0.75 to a white metal roof with an absorptivity of 0.30 reduces the annual energy by 2.8%. The builder later responded that light-colored shingles are not used because they get soiled by red dirt and algae, and the modest energy savings would not warrant the additional cost of a metal roof.
- Extending the eaves from 0.6 to 0.9 m reduces the annual energy by 1.6%. During a conversation with the builder, an increased overhang depth was determined to be infeasible for their developments due to encroachment on the required setback from the property line.
- Adding a double-sided foil radiant barrier in the roof reduces the annual energy consumption by 1.4%. During a conversation with the builder, it was ascertained that the main barrier to implementation is installing the radiant barrier across multiple roof trusses.
- Reducing the ratio of the window area to the conditioned floor area from 15% to 9% shows an annual energy savings of 2.8%, due to a reduction in cooling. Developers would not likely reduce the window area due to an undesirable reduction in occupants’ daylight and views. These options were not included in the optimization.
- Changing the window U-values from 2.8 W/m2-K (0.5 Btu/h-ft2-°F) to 2.3 W/m2-K (0.4 Btu/h-ft2-°F) or 1.7 W/m2-K (0.3 Btu/h-ft2-°F) increased the annual energy consumption by 0.1% and 0.3%, respectively. The better-insulated windows trapped heat inside and slightly increased the cooling energy in the evening, especially during the cooler months.
- Adding window overhangs of 0.6 to 0.9 m to all windows decreased the annual energy use by 0.5% and 1.1%, respectively (not shown in the figures; not included in the optimization).
- Upgrading from 75% to 100% high-efficacy electric lighting shows an estimated 0.3% annual energy savings. Although the savings are modest, the measure is recommended because there is little to no increased initial cost. The 75% efficiency was not included in the optimization.
- Increasing the HVAC system efficiency from SEER 14 to SEER 16, SEER 18, SEER 21, and SEER 24.5 results in estimated annual energy savings of 7.6%, 11.9%, 16.9%, and 28.6%, respectively. During a conversation with the builders (in late 2018), we learned that their houses built in 2019–2020 will likely have an SEER 20 rating, representing a notable improvement over the existing or minimally code-compliant cooling systems. The builders appreciated quantitative estimates of energy savings with more efficient air-conditioning systems, which helped them prioritize purchases to meet their goal to reduce energy costs for the homeowner. This energy efficiency measure has a high likelihood of being implemented because the builder controls the selection of the air-conditioning SEER rating (which is a marketable feature), unlike some of the energy-saving measures that rely on occupant behavior.
- The addition of an energy recovery ventilator (ERV; total recovery efficiency of 0.48) or heat recovery ventilator (HRV; total recovery efficiency 0.20 (Personal communication, Kosol Kiatreungwattana, senior engineer, NREL, Golden, CO, e-mail, 30 May 2019 and )) increased the annual energy consumption by 1.8% and 3.2%, respectively, mainly due to an increased ventilation fan energy. In other words, the amount of recovered cooling energy was less than the ERV or HRV fan energy. The cooling and cooling/fan energy decreased slightly with the ERV and increased slightly with the HRV. Both were set to use the ASHRAE 62.2 2013 ventilation rate (same as the IECC 2015 benchmark). These were not included in the optimization.
Conflicts of Interest
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|House ID#||Total Floor Area (m2)||Living Area (m2)||Bed-rooms||Stories||Year Built||Occupancy||PV||Dates Monitored|
|1||196.6||148.9||4||2||2015||6 a, c||No||23 June 2017–9 February 2018|
|2||203.4||155.7||5||2||2010||6 a, d||No||28 June 2017–27 June 2018|
|3||201.3||153.7||4||2||2010||8 a, c||No f||29 June 2017–28 June 2018|
|4||201.3||153.7||4||2||2009||2 a, e||Yes||28 June 2017–27 June 2018|
|5||196.6||148.9||4||2||2009||2 b, d||Yes||15 September 2017–14 September 2018|
|6||225.4||148.9||4||2||2009||3 a, c||Yes||28 June 2017–27 June 2018|
|7||189.5||141.9||3||1||2009||3 b, c||Yes||15 September 2017–14 September 2018|
|Component||IECC 2015 Minimum Model Inputs|
|Exterior wall||Gypsum board 12.7 mm (0.5”)|
|Wood studs 38 mm × 89 mm (nominal 2” × 4”) spaced 40.6 cm (16”) on center, fiberglass batt R-2.3 m2-K/W (R-13 h-ft2-°F/Btu), oriented strand board, fiber cement finish, medium-dark color 0.04 m2-K/W (R-0.2 h-ft2-°F/Btu) absorptivity 0.75|
|Unfinished attic||Fiberglass batt at ceiling R-5.3 m2-K/W (R-30 h-ft2-°F/Btu) vented, specific leakage area = 0.0051|
|Roof||Asphalt shingle, medium color, absorptivity 0.75, |
No radiant barrier
|Ceiling||Gypsum board 12.7 mm (0.5”)|
|Foundation/floors||Uninsulated concrete slab 10.2 cm (4”), wood floors, no carpet|
|Window areas||15% of conditioned floor area, 25.0 m2 (278 ft2)|
|Windows||Double pane, non-metal frame, U = 2.8 W/m2-K (0.5 Btu/h-ft2-°F), SHGC = 0.25, No window overhangs|
|Interior shading multiplier||Summer = 0.87, Winter = 0.87|
|Doors/door area||Wood U-Value = 2.84 W/m2-K (0.50 Btu/h-°F-ft2), 3.72 m2 (40 ft2)|
|Eaves||Roof eave length 0.6 m (2 ft)|
|Air leakage||5 ACH50|
|Mechanical ventilation||ASHRAE 62.2 2013 standard, exhaust 41.1 L/s (87.1 cfm), fan power 13.1 W|
No energy recovery ventilator or heat recovery ventilator
|Central AC, cooling set-point, ducts||SEER 14, set-point 23.9°C (75°F), ducts in unconditioned attic, insulation R-0.3 m2-K/W (R-1.7 h-ft2-°F/Btu), leakage 1.9 l/s (4 cfm) per 30.48 m (100 ft) at 25 Pa|
|Ceiling fan||1.7 Standard efficiency ceiling fans, US national average number of fans|
|Lighting||75% high efficacy electric lighting|
|Water heater||Solar: collection area 5.95 m2 (64 ft2), electric resistance backup: energy factor 0.99, cycling derate = 0|
|Water distribution||R-0.53 m2-K/W (R-3 h-ft2-°F/Btu), trunk branch, copper|
|Appliances||Standard efficiency refrigerator with a side freezer and ice dispenser, 718 kWh/year, standard electric stove, standard clothes washer, standard electric clothes dryer, no dishwasher|
|Plug loads||National average energy use|
|House ID#||Whole House Electricity Use||Site Energy Use Intensity |
Based on Total Floor Area
|Site Energy Use Intensity |
Based on Living Area
|AC air handling unit||573||1063||1211||1081||918||1069||706|
|Plug loads and lights||4153||2845||3747||2375||3479||4523||4065|
|PV production||0||0||0 b||5422||5262||4066||6851 c|
|House ID#||Temperature (°C)|
|Relative Humidity (%)|
|Neighborhood||Year of |
|Age of |
|EUIs Based on Living Area|
|Kanehili, Kapolei||2017–2018||7–9 a||7||142–156||77.3||24.5|
|IECC 2015 Minimum Baseline Model Component||Least-Cost-Optimized|
|HVAC efficiency SEER 14||Variable speed HVAC SEER 24.5||Variable speed HVAC SEER 24.5|
|No ceiling fans. Cooling set-point 23.9 °C (75°F)||Five premium efficiency fans with occupancy sensorsIncrease the cooling set-point from 23.9 °C (75 °F) to 26.1 °C (79 °F)||Five premium efficiency fans with occupancy sensors|
Increase the cooling set-point from 23.9 °C (75°F) to 26.1 °C (79 °F)
|Appliances: standard efficiency||Appliances: energy efficient, except stove is standard electric||Appliances: energy efficient including induction stove|
|Exterior finish: medium color with absorptivity of 0.75||Exterior finish vinyl light color with absorptivity of 0.30||Exterior finish vinyl light color with absorptivity of 0.30|
|Eaves 0.6 m||Same as IECC 2015||Eaves 0.9 m|
|No radiant barrier||A double-sided foil radiant barrier||A double-sided foil radiant barrier|
|Roof material: medium color asphalt shingle with absorptivity of 0.75||Same as IECC 2015||White metal roof with absorptivity of 0.30|
|75% high efficiency lighting||100% LED lighting||100% LED lighting|
|Window U-value 0.5||Window U-value 0.4||Same as IECC 2015|
|End Use||IECC 2015 Minimum Model||Least-Cost-Optimized Model||Energy-Optimized|
|Annual Energy (kWh/year)||EUI (kWh/m2/year)||Annual Energy (kWh/year)||EUI (kWh/m2/year)||Annual Energy (kWh/year)||EUI (kWh/m2/year)|
|AC air handling unit||1779||167||155|
|Total energy use||12,770||6957||6749|
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Meguro, W.; Peppard, E.; Meder, S.; Maskrey, J.; Josephson, R. Going Beyond Code: Monitoring Disaggregated Energy and Modeling Detached Houses in Hawai‘i. Buildings 2020, 10, 120. https://doi.org/10.3390/buildings10070120
Meguro W, Peppard E, Meder S, Maskrey J, Josephson R. Going Beyond Code: Monitoring Disaggregated Energy and Modeling Detached Houses in Hawai‘i. Buildings. 2020; 10(7):120. https://doi.org/10.3390/buildings10070120Chicago/Turabian Style
Meguro, Wendy, Eileen Peppard, Stephen Meder, James Maskrey, and Riley Josephson. 2020. "Going Beyond Code: Monitoring Disaggregated Energy and Modeling Detached Houses in Hawai‘i" Buildings 10, no. 7: 120. https://doi.org/10.3390/buildings10070120