Passive House and Passive Solar: A Comparison of Two Approaches to Low Energy Heating

14 May 2012

World Renewable Energy Forum

The Built Environment

Matt Hogan & Alison Kwok

University of Oregon

hogan2@uoregon.edu | akwok@uoregon.edu

Passive Solar

“south-facing glass... for solar collection, and thermal

mass for heat absorption, storage and distribution.”

- Ed Mazria

Balcomb House, 1979

Source: nmsea.org

Passive House

“Superinsulation proponents sought to create a simpler

solution with small window areas, large quantities of

insulation, and simple geometries.”

- Alex Wilson, Building Green, Inc.

Saskatchewan Conservation House, 1977

Source: greenbuidlingadvisor.com

Two Approaches Compared

Passive House Passive Solar

Superinsulated Well-insulated

Airtight Not necessarily airtight

Small glazing area Large south glazing area

No significant thermal mass Significant thermal mass

Heat recovery ventilator HRV optional

Compact shape Elongated east-west axis

Constant temperature (68°F) Daily temperature swings

The Learning House

Research Questions

1. Can a passive solar house in Eugene, Oregon maintain an

average indoor temperature of 68°F (20°C) during the winter

design week while using less energy than a Passive House of

an identical program, living area, and volume?

Research Questions

1. Can a passive solar house in Eugene, Oregon maintain an

average indoor temperature of 68°F (20°C) during the winter

design week while using less energy than a Passive House of

an identical program, living area, and volume?

2. Can the indoor temperature swings of the passive solar house

during the winter design week be kept to less than 10°F

above and below 68°F (20°C)?

Methodology

1. Model Learning House in PHPP

Methodology

1. Model Learning House in PHPP

2. Model Learning House in DesignBuilder

Methodology

1. Model Learning House in PHPP

2. Model Learning House in DesignBuilder

3. Redesign Learning House for passive solar

Methodology

1. Model Learning House in PHPP

2. Model Learning House in DesignBuilder

3. Redesign Learning House for passive solar

4. Model passive solar house in DesignBuilder

Methodology

1. Model Learning House in PHPP

2. Model Learning House in DesignBuilder

3. Redesign Learning House for passive solar

4. Model passive solar house in DesignBuilder

5. Compare results of DesignBuilder simulations

Methodology

Variables

- Area of south facing glass

- Thermal mass

- Indoor temperature

Methodology

Variables

- Area of south facing glass

- Thermal mass

- Indoor temperature

Constants

- Assembly R-values

- Backup electric resistance heat

Passive House Model

Annual site electricity use:

10.9 kBtu/ft2yr

Annual CO2 Emissions:

6336.30 lbs

Redesign Learning House for Passive Solar

Area of south glass:

9% of floor area

Solar Savings Fraction: 32%

No significant thermal mass

Passive House

Redesign Learning House for Passive Solar

Area of south glass:

9% of floor area

Solar Savings Fraction: 32%

No significant thermal mass

Area of south glass:

19% of floor area

Solar Savings Fraction: 50%

Mass to glass ratio: 3.7

Passive House

Passive Solar

Area of Thermal Mass

Passive Solar Model

Annual site electricity use:

9.8 kBtu/ft2yr

Annual CO2 Emissions:

5739.97 lbs

Results Compared

Performance Data Passive House Passive Solar

Annual Electricity

Demand (site)

10.9 kBtu/ft2 yr 9.8 kBtu/ft2 yr

Annual CO2

Emissions

6336.30 lbs 5739.97 lbs

Annual Electric

Lighting Demand

4589.04 kBtu/yr 4498.99 kBtu/yr

Annual Heating

from Solar Gains

6645.37 kBtu/yr 9835.51 kBtu/yr