Net Zero Energy Feasibility Study: Summary Report

Overview

This 22-page summary, dated January 30, 2015, condenses a feasibility study that Maclay Architects prepared for Efficiency Vermont with energy modeler Energy Balance, cost estimator JAMorrissey, and builder Huntington Homes. It asks a blunt question for developers and owners: once you finance the extra cost, does a net-zero-ready or net-zero building cost more or less to own than one built to the 2015 Vermont energy code? The team modeled six building types (single-family, duplex, quadplex, open office, closed office, and a 27,000-square-foot office/light-manufacturing building) and then scaled the results to a proposed 300,000-square-foot community in Hinesburg, Vermont.

Key Findings

• Net-zero-ready versions used 57% to 74% less energy than code versions, with EUIs of 17 to 25 kBtu per square foot per year versus 49 to 67 for code, thanks to R-40 walls, R-60 roofs, R-5 windows, tight air sealing, and cold-climate heat pumps.
• The efficiency upgrades added $13 to $16 per square foot (10% to 12% of cost) for homes and $9 to $17 per square foot (6% to 13%) for commercial buildings; rooftop PV at $3 per watt made them net zero.
• Financed at 4% over 30 years, net-zero homes cost less to own from year one with no incentives, and saved $39,000 to $59,000 per unit over the loan term.
• Net-zero-ready offices also beat code from year one; code buildings' operating costs were more than double those of the net-zero-ready versions.
• The office/manufacturing building was the exception. Its large, tall envelope pushed the upgrade cost to $17 per square foot, and it needed an Efficiency Vermont incentive of about $1 per square foot, the 30% federal solar credit, and SBA-rate financing to come out ahead of code.
• Choosing an open office over a closed plan saved about $24 per square foot, which by itself more than paid for the net-zero upgrades.
• Across the full community, net-zero-ready construction cut annual energy use from 18 million to 5.6 million kBtu and reduced the PV needed for net zero from 5.8 MW to 2.3 MW; commercial owners would save $3.3 million over 20 years and residents $3 million over 30.

Why It Matters for Daylighting

The office/manufacturing model is the one most relevant to industrial owners, and it is where daylighting shows up explicitly: the net-zero-ready design gave the manufacturing floor skylights equal to about 3% of floor area with automatic daylight controls, double the 1.5% minimum the 2015 draft code required. That is consistent with the study's finding that lighting, not heating, becomes the largest electric load once the envelope is tight, so prismatic skylights and daylight-responsive controls are among the cheapest remaining kilowatt-hours in a high-performance warehouse or plant. The report's candor about the manufacturing building's harder economics is also useful; it shows why utility incentives and reduced lighting loads matter more for big-volume buildings than for offices.

The study's tie to the Vermont code also mirrors the national trend: the IECC and ASHRAE 90.1 now require toplighting and daylight controls in large single-story spaces, so the code baseline itself is moving toward skylights.

About the Source

Efficiency Vermont is the statewide energy efficiency utility, and Maclay Architects of Waitsfield, Vermont, led by William Maclay, is a nationally recognized net-zero design practice. The summary report was issued January 30, 2015, and runs 22 pages; a full report with the energy models, cost takeoffs, and financial appendix accompanies it. Both documents are posted as white papers on Efficiency Vermont's website.