Reducing the impacts of weather variability on long-term building energy performance by adopting energy-efficient measures and systems: a case study

Abstract

This case study uses whole-building simulation software to investigate the ability of alternative sets of energy conservation measures to limit the sensitivity in energy use and heating, ventilation, and air-conditioning (HVAC) peak electricity demands by residential buildings due to weather variability. Four alternative building designs are considered: a net-zero energy design based on the National Institute of Standards and Technology (NIST) net-zero energy residential test facility (NZERTF), a comparable, yet less efficient design built according to the 2015 International Energy Conservation Code (IECC), and two low-energy designs at varying levels of energy-efficiency. The findings from this study reveal which measures best ensure robust annual energy performance and occupant comfort by low- and net-zero energy homes given weather variability, as well as how much resulting energy performances vary across the sets of conservation measures considered in this work.

Keywords:

• low-energy
• net-zero energy
• weather variability
• sensitivity analysis
• whole-building simulation
• EnergyPlus

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. Certain trade names and company products are mentioned in the text in order to adequately specify the technical procedures and equipment used. In no case does such identification imply recommendation or endorsement by the NIST, nor does it imply that the products are necessarily the best available for the purpose.

2. Kneifel et al. (2015) found that the results of their validated (post-demonstration) NZERTF simulation model and that of the measured performance matched closely. Annual electricity consumption fell within 4% of the measured consumption, while simulated production fell within 3% of measured energy production.

3. The capacity factor is held constant at 1.0 for all simulations to allow for isolation of the impacts of weather variability. The optimal capacity factor could vary across HVAC systems depending on the characteristics of each system and whether you focus on thermal comfort, energy performance, or some combination of the two.

4. Use of 2 × 6 – 24 in. (5.1× 15.2 – 61.0 cm) centres reduced the amount of lumber needed for construction (board-feet) from 5% to 10%, and provides 60% more cavity insulation.

5. At the basement/foundation wall, two insulation types are used on the exterior of the concrete foundation wall. The first being a 2 in. (5.08 cm) foil-faced polyisocyanurate insulation, which adds a thermal resistance of R-10 (R_SI-1.76). The second is a 2 in. (5.08 cm) XPS slotted rigid insulation adding a thermal resistance of R-12 (R_SI-2.11).

6. The basement floor includes 2 in. (5.08 cm) XPS rigid foam slab insulation beneath the concrete slab, resulting in a measured thermal resistance of R-10 (R_SI-1.76) for the foundation floor.

7. For the MCC and MCC + Envelope simulation models, “Fans” refers only to the electricity used to power the HVAC system fans. In the case of the MCC + Systems and NZERTF simulation models, where building system equipment is more energy-efficient, the “Fans” end-use category captures electricity used to power the HVAC fans and the DHW Heat Pump fan.

8. HVAC system fans for all designs cycle with system compressors.

9. This result was found to be consistent with a study conducted by Ng and Payne (2016) which found that the additional fan energy required for the continuous operation of the HRV system at the NIST NZERTF was offset by the reduced annual energy usage of the efficient air-to-air heat pump compared with ventilating with no heat recovery.