Sunspaces in a Land of Fog and Moss . . . . . . . . . . . . . . . . . . . . . . 2

Oregon Sunspace Redesign / Build . . . . . . . . . . . . . . . . . . . . . . . . 6

Thermal Batteries for Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Hybrid Ventilation in a Chicago Academic Center . . . . . . . . . . . . 12

Passive Cooling in Everett Community College Offices . . . . . . 14

Night Cooling of Mass in the Vernonia K-12 School . . . . . . . . . . 16

3-D Thermal Bridging in Wall Assemblies . . . . . . . . . . . . . . . . . . . 16

Natural Ventilation in the Lillis Business Complex . . . . . . . . . . . 17

Teaching: Passive Heating and Cooling Design . . . . . . . . . . . . . . 18

Relevant Funding Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

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Passive Heating & Cooling Design for the 21st CenturyPassive solar heating, shading, evaporative cooling, natural ventilation, and effective use of thermal mass offer durable, climate-responsive, socially-in-clusive pathways to thermal comfort and thermal architectural delight. Pas-sive heating and cooling guidelines have changed little in decades, however, despite new insights into solar radiation transmission, fluid mechanics, ma-terials science, and climate modeling, as well as more powerful and efficient field instruments and vastly improved computational tools. With energy con-sumption an inescapable reality of architectural practice, and with passive strategies offering the lowest embodied-energy solutions, educators and researchers must bring passive heating and cooling design into sync with current energy science. This is the goal of my work.

Pyranometer deployed in a sunspace Alexandra Rempel, Ph.D., M.Arch., 2013

Cont

ents

2

Sunspaces in a Land of Fog and Moss

What would it take for passive solar heating to perform well in the cloudy, rainy winters of Eugene, Oregon? With a West Coast Marine climate (Köp-pen Cfb) and high latitude, the Pacific Northwest’s overcast skies disguise a solar resource unexpect-edly well-matched to its mild winters and long, cool springs. Yet passive solar heating is rarely practiced here, despite widespread enthusiasm for low-energy building design.

Field work. To investigate Eugene’s passive solar po-tential, four sunspaces were instrumented January through June 2011, measuring indoor and outdoor air temperature, humidity, mass surface temperatures, surface heat flux, mean radiant temperatures, and in-cident solar radiation. The Gates and Shaw sunspac-es were similar, with massive floors and moderate shading, while the Page and Cashman spaces were highly shaded and the latter had little effective mass.

Modeling. Each sunspace was then modeled in EnergyPlus, a simulation tool well-suited to passive heating and cooling. Models were validated by com-parison to measured field data, showing the ability to predict about 90% of the variability in these mea-surements.

Sunspace air temperatures (above left) remained many degrees warmer than outside air temperatures throughout the study, particularly in the higher-mass Gates and Shaw sunspaces. Air warmth was greatest during afternoons, as expected, and in-creased through the season except for March, which was anom-alously cool and rainy in 2011.

Mass surface temperatures (above right) in the higher-mass spaces showed even greater warmth, with nighttime tempera-tures frequently 15-17°F higher than outside conditions during January, April, and May. Surface heat flux measurements quan-tified heat returned from the mass to the space during these

Figure 3. Figure 4.

Figure 4.a) Gates

0-6a 17 11 16 15 14 10 6 9 9 8

6a-noon 16 10 14 12 10 9 6 8 7 6

noon-6p 17 10 19 16 12 9 6 10 9 7

6p-mid 17 12 17 15 12 10 7 10 8 7

b) Shaw0-6a 14 9 15 13 13 8 5 8 7 7

6a-noon 13 9 12 9 8 7 5 6 5 4

noon-6p 12 9 15 10 8 7 5 8 6 4

6p-mid 14 10 15 12 11 8 6 8 7 6

c) Page0-6a 15 12 15 13 15 9 7 8 7 8

6a-noon 14 10 11 7 7 8 6 6 4 4

noon-6p 13 10 12 5 9 7 6 7 3 5

6p-mid 15 11 15 10 12 8 6 8 5 7

d) Cashman0-6a 11 7 8 7 8 6 4 4 4 4

6a-noon 10 7 6 3 1 6 4 3 2 1

noon-6p 10 7 7 4 1 5 4 4 2 0

6p-mid 12 8 8 7 6 6 4 4 4 3

e) Outside0-6a 35 42 41 45 52 2 6 5 7 11

6a-noon 39 46 48 52 60 4 8 9 11 16

noon-6p 44 49 53 58 67 7 9 12 14 19

6p-mid 38 44 45 49 56 3 7 7 9 13

Feb Mar Apr May Jun

a) Gates0-6a 10 12 8 11 11 10 5 7 4 6 6 6

6a-noon 10 12 8 11 10 9 5 7 5 6 5 5

noon-6p 11 14 12 17 13 13 6 8 7 9 7 7

6p-mid 11 12 9 13 11 10 6 7 5 7 6 5

b) Shaw0-6a 6 7 4 8 8 8 4 4 2 4 4 5

6a-noon 8 9 8 9 9 8 4 5 5 5 5 4

noon-6p 13 13 14 19 14 13 7 7 8 10 8 7

6p-mid 7 8 6 11 10 9 4 4 3 6 5 5

c) Page0-6a 8 15 11 13 12 11 4 8 6 7 7 6

6a-noon 7 14 12 11 7 6 4 8 7 6 4 3

noon-6p 8 14 14 11 7 9 4 8 8 6 4 5

6p-mid 9 15 12 14 11 10 5 8 7 8 6 6

d) Cashman0-6a 9 9 7 7 7 5 5 5 4 4 4 3

6a-noon 8 8 7 8 5 4 4 5 4 4 3 2

noon-6p 8 10 8 10 7 5 5 6 5 5 4 3

6p-mid 9 10 8 8 7 5 5 6 5 4 4 3

e) Outside0-6a 38 35 42 41 45 52 3 2 6 5 7 11

6a-noon 40 39 46 48 52 60 4 4 8 9 11 16

noon-6p 47 44 49 53 58 67 8 7 9 12 14 19

6p-mid 41 38 44 45 49 56 5 3 7 7 9 13

Jan Feb Mar Apr May Jun

Figure 4.a) Gates

0-6a 17 11 16 15 14 10 6 9 9 8

6a-noon 16 10 14 12 10 9 6 8 7 6

noon-6p 17 10 19 16 12 9 6 10 9 7

6p-mid 17 12 17 15 12 10 7 10 8 7

b) Shaw0-6a 14 9 15 13 13 8 5 8 7 7

6a-noon 13 9 12 9 8 7 5 6 5 4

noon-6p 12 9 15 10 8 7 5 8 6 4

6p-mid 14 10 15 12 11 8 6 8 7 6

c) Page0-6a 15 12 15 13 15 9 7 8 7 8

6a-noon 14 10 11 7 7 8 6 6 4 4

noon-6p 13 10 12 5 9 7 6 7 3 5

6p-mid 15 11 15 10 12 8 6 8 5 7

d) Cashman0-6a 11 7 8 7 8 6 4 4 4 4

6a-noon 10 7 6 3 1 6 4 3 2 1

noon-6p 10 7 7 4 1 5 4 4 2 0

6p-mid 12 8 8 7 6 6 4 4 4 3

e) Outside0-6a 35 42 41 45 52 2 6 5 7 11

6a-noon 39 46 48 52 60 4 8 9 11 16

noon-6p 44 49 53 58 67 7 9 12 14 19

6p-mid 38 44 45 49 56 3 7 7 9 13

Feb Mar Apr May Jun

a) Gates0-6a 10 12 8 11 11 10 5 7 4 6 6 6

6a-noon 10 12 8 11 10 9 5 7 5 6 5 5

noon-6p 11 14 12 17 13 13 6 8 7 9 7 7

6p-mid 11 12 9 13 11 10 6 7 5 7 6 5

b) Shaw0-6a 6 7 4 8 8 8 4 4 2 4 4 5

6a-noon 8 9 8 9 9 8 4 5 5 5 5 4

noon-6p 13 13 14 19 14 13 7 7 8 10 8 7

6p-mid 7 8 6 11 10 9 4 4 3 6 5 5

c) Page0-6a 8 15 11 13 12 11 4 8 6 7 7 6

6a-noon 7 14 12 11 7 6 4 8 7 6 4 3

noon-6p 8 14 14 11 7 9 4 8 8 6 4 5

6p-mid 9 15 12 14 11 10 5 8 7 8 6 6

d) Cashman0-6a 9 9 7 7 7 5 5 5 4 4 4 3

6a-noon 8 8 7 8 5 4 4 5 4 4 3 2

noon-6p 8 10 8 10 7 5 5 6 5 5 4 3

6p-mid 9 10 8 8 7 5 5 6 5 4 4 3

e) Outside0-6a 38 35 42 41 45 52 3 2 6 5 7 11

6a-noon 40 39 46 48 52 60 4 4 8 9 11 16

noon-6p 47 44 49 53 58 67 8 7 9 12 14 19

6p-mid 41 38 44 45 49 56 5 3 7 7 9 13

Jan Feb Mar Apr May Jun

Interpretation of passive solar field data with EnergyPlus models: Un-conventional wisdom from four sunspaces in Eugene, Oregon. Building and Environment 2013, 60:158-172.

Air Temperatures (°F and °C) Mass Temperatures

Figure 3. Figure 4.

Figure 4.a) Gates

0-6a 17 11 16 15 14 10 6 9 9 8

6a-noon 16 10 14 12 10 9 6 8 7 6

noon-6p 17 10 19 16 12 9 6 10 9 7

6p-mid 17 12 17 15 12 10 7 10 8 7

b) Shaw0-6a 14 9 15 13 13 8 5 8 7 7

6a-noon 13 9 12 9 8 7 5 6 5 4

noon-6p 12 9 15 10 8 7 5 8 6 4

6p-mid 14 10 15 12 11 8 6 8 7 6

c) Page0-6a 15 12 15 13 15 9 7 8 7 8

6a-noon 14 10 11 7 7 8 6 6 4 4

noon-6p 13 10 12 5 9 7 6 7 3 5

6p-mid 15 11 15 10 12 8 6 8 5 7

d) Cashman0-6a 11 7 8 7 8 6 4 4 4 4

6a-noon 10 7 6 3 1 6 4 3 2 1

noon-6p 10 7 7 4 1 5 4 4 2 0

6p-mid 12 8 8 7 6 6 4 4 4 3

e) Outside0-6a 35 42 41 45 52 2 6 5 7 11

6a-noon 39 46 48 52 60 4 8 9 11 16

noon-6p 44 49 53 58 67 7 9 12 14 19

6p-mid 38 44 45 49 56 3 7 7 9 13

Feb Mar Apr May Jun

a) Gates0-6a 10 12 8 11 11 10 5 7 4 6 6 6

6a-noon 10 12 8 11 10 9 5 7 5 6 5 5

noon-6p 11 14 12 17 13 13 6 8 7 9 7 7

6p-mid 11 12 9 13 11 10 6 7 5 7 6 5

b) Shaw0-6a 6 7 4 8 8 8 4 4 2 4 4 5

6a-noon 8 9 8 9 9 8 4 5 5 5 5 4

noon-6p 13 13 14 19 14 13 7 7 8 10 8 7

6p-mid 7 8 6 11 10 9 4 4 3 6 5 5

c) Page0-6a 8 15 11 13 12 11 4 8 6 7 7 6

6a-noon 7 14 12 11 7 6 4 8 7 6 4 3

noon-6p 8 14 14 11 7 9 4 8 8 6 4 5

6p-mid 9 15 12 14 11 10 5 8 7 8 6 6

d) Cashman0-6a 9 9 7 7 7 5 5 5 4 4 4 3

6a-noon 8 8 7 8 5 4 4 5 4 4 3 2

noon-6p 8 10 8 10 7 5 5 6 5 5 4 3

6p-mid 9 10 8 8 7 5 5 6 5 4 4 3

e) Outside0-6a 38 35 42 41 45 52 3 2 6 5 7 11

6a-noon 40 39 46 48 52 60 4 4 8 9 11 16

noon-6p 47 44 49 53 58 67 8 7 9 12 14 19

6p-mid 41 38 44 45 49 56 5 3 7 7 9 13

Jan Feb Mar Apr May Jun

Figure 4.a) Gates

0-6a 17 11 16 15 14 10 6 9 9 8

6a-noon 16 10 14 12 10 9 6 8 7 6

noon-6p 17 10 19 16 12 9 6 10 9 7

6p-mid 17 12 17 15 12 10 7 10 8 7

b) Shaw0-6a 14 9 15 13 13 8 5 8 7 7

6a-noon 13 9 12 9 8 7 5 6 5 4

noon-6p 12 9 15 10 8 7 5 8 6 4

6p-mid 14 10 15 12 11 8 6 8 7 6

c) Page0-6a 15 12 15 13 15 9 7 8 7 8

6a-noon 14 10 11 7 7 8 6 6 4 4

noon-6p 13 10 12 5 9 7 6 7 3 5

6p-mid 15 11 15 10 12 8 6 8 5 7

d) Cashman0-6a 11 7 8 7 8 6 4 4 4 4

6a-noon 10 7 6 3 1 6 4 3 2 1

noon-6p 10 7 7 4 1 5 4 4 2 0

6p-mid 12 8 8 7 6 6 4 4 4 3

e) Outside0-6a 35 42 41 45 52 2 6 5 7 11

6a-noon 39 46 48 52 60 4 8 9 11 16

noon-6p 44 49 53 58 67 7 9 12 14 19

6p-mid 38 44 45 49 56 3 7 7 9 13

Feb Mar Apr May Jun

a) Gates0-6a 10 12 8 11 11 10 5 7 4 6 6 6

6a-noon 10 12 8 11 10 9 5 7 5 6 5 5

noon-6p 11 14 12 17 13 13 6 8 7 9 7 7

6p-mid 11 12 9 13 11 10 6 7 5 7 6 5

b) Shaw0-6a 6 7 4 8 8 8 4 4 2 4 4 5

6a-noon 8 9 8 9 9 8 4 5 5 5 5 4

noon-6p 13 13 14 19 14 13 7 7 8 10 8 7

6p-mid 7 8 6 11 10 9 4 4 3 6 5 5

c) Page0-6a 8 15 11 13 12 11 4 8 6 7 7 6

6a-noon 7 14 12 11 7 6 4 8 7 6 4 3

noon-6p 8 14 14 11 7 9 4 8 8 6 4 5

6p-mid 9 15 12 14 11 10 5 8 7 8 6 6

d) Cashman0-6a 9 9 7 7 7 5 5 5 4 4 4 3

6a-noon 8 8 7 8 5 4 4 5 4 4 3 2

noon-6p 8 10 8 10 7 5 5 6 5 5 4 3

6p-mid 9 10 8 8 7 5 5 6 5 4 4 3

e) Outside0-6a 38 35 42 41 45 52 3 2 6 5 7 11

6a-noon 40 39 46 48 52 60 4 4 8 9 11 16

noon-6p 47 44 49 53 58 67 8 7 9 12 14 19

6p-mid 41 38 44 45 49 56 5 3 7 7 9 13

Jan Feb Mar Apr May Jun

hours, confirming that the mass was active in solar per-formance but also, as shown below, losing substantial heat to underlying soil.

Models (below) showed close correspondence to mea-sured air temperatures, mass surface temperatures, and heat fluxes, predicting 80-95% of the variability in the data and allowing them to be used to gain further in-sight into heat gain and loss pathways. Please see publi-cation for further details.

Agreement between Measured and Modeled Air TemperaturesFigure 7.

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Tem

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Fig 7

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4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21

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b) Shaw

Fig 7

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4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21

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c) Page

Fig 7

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4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21

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d) Cashman

Fig 7

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Figure 7.

Tem

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Temperature (°C

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a) Gates

Fig 7

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4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21

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Fig 7

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Fig 7

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Fig 7

Figure 2.

0 15’ 30’ 60’

a) Gates

a) Shaw

c) Page

d) Cashman

b)

Alexandra Rempel, Ph.D., M.Arch., 2013

Suns

pace

s

4

Un-Conventional Wisdom. The vener-able work of Balcomb and colleagues still guides passive solar design educa-tion, cited by Sun Wind & Light, Heat-ing, Cooling, & Lighting, Mechanical and Electrical Engineering for Buildings, and numerous others. In the Pacific Northwest, however, these ideas need substantial revision.

1. Pacific Northwest passive solar heat-ing potential is far greater than indi-cated by Balcomb’s Solar Savings Frac-tions, which discount gains through cloudy skies and tilted glazing.

2. Wide deviations from southerly orientation are acceptable, since much of the solar resource originates from above and tree shading can be severe.

3. Roof glazing is essential since most winter solar energy enters from above and since passive cooling is effective in summer conditions.

4. Vertical glazing must be site-specif-ic. On a shady site, it may even be op-tional, contributing primarily to views.

5. Thermal mass must be isolated from wet ground, by insulation or possibly drainage, to avoid losing a substantial fraction of solar gains.Please see publication for further details.

Fig. 10

Gain (kWh): 450

Gain (kWh): 460

Gain (kWh): 245

Gain (kWh): 205

Jan Feb Mar Apr May June

1030 1040

b) S

haw

Floor

c) P

age

d) C

ashm

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Glazed Roof

Gla

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Infilt-ration

250 255 315

Opa

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Wal

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a) G

ates

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550 650 980

325 400 550 600 580

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550 540 760Solar Heat Gain Paths. Most solar energy entered through tilted roof glazing (orange sectors, left), even in spaces with southeast orientation, countering conventional wisdom that only vertical glazing (blue sectors) should be used to take advantage of low winter sun angles and avoid summer over-heating. Indeed, the widely-cited sizing tables of Balcomb et al. limit consideration of tilted glazing to its “projected verti-cal area”, greatly diminishing its predicted importance.

Since overcast skies are brightest at the top of the sky dome, however, and tall trees are ubiquitous in the North-west, the greatest solar resource was found to exist over-head in this climate. (This also greatly diminished orienta-tion dependence.) Because the Balcomb method neglects these factors, it vastly underpredicted tilted-glazing solar gain for these spaces, estimating only 35-52% of the total in normal months, for example, for the Gates space (below).

Heat Loss Paths. Slab-on-grade floors created significant heat loss pathways in the two spaces (Gates and Shaw) that used them as thermal mass; infiltration and single glazing accounted for most of the remainder. The slab heat loss was unexpected, as it conflicted directly with design guides that advocate only perimeter insulation for slab-on-grade floors unless they contain radiant heating tubes. In wet envi-ronments with fine-grained soils, however, moisture can be wicked far underneath buildings, and soil moisture greatly increases soil thermal conductivity; this apparently caused the patterns found.

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Figure 8.

kWh

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Heat Loss Pathways as Proportions of Total Solar Gainone filled box = 5% of the total

Alexandra Rempel, Ph.D., M.Arch., 2013

Suns

pace

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Figure 8.Roof Solar Gain

Window Solar Gain

% of 2011 actual solar gain predicted

Gates Shaw Page CashmanBalcomb Methoda percentage of 2011 model values

January 35b 38 68 45February 42 37 70 43

March 63 43 104 67April 52 31 93 60May 51 34 107 66

EnergyPlus / TMY3c

January 93 94 92 92February 89 93 91 91

March 121 122 125 126April 98 97 98 100May 101 104 102 102

a According to Passive Solar Heating Analysis [22]; Appendix B.b Text style indicates each value’s relationship to the 2011 model-predicted

value: plain = lower, bold boxed = ±20%, italics underlined: higher. c Sunspace models simulated with typical, rather than 2011, weather data.

Table 3. Contrasting Predictions of Roof Solar GainConventional Method Underestimates Roof Solar Gain

35b

42635251

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Oregon Sunspace Redesign / Build

Redesign. In light of results from the ini-tial field study (above), builder Ken Gates dismantled his sunspace, excavated, and added gravel and R-10 insulation beneath a new concrete slab. The new slab held ~30% more mass, as well, in accord with model results suggesting that the space could store more heat. It did not provide as much mass as suggested by conventional mass sizing tables, however.

Methods. To evaluate the redesign per-formance and to gain insight into climate-responsive priorities for thermal mass, monitoring resumed from January-June 2012 with added emphasis on surface heat flux measurements. The similar Shaw space was monitored simultaneously for compari-son, and models were again validated with field data before further interpretation.

Results. Mass surface temperatures were substantially warmer after the redesign (upper panels), particularly near the center where solar access was greatest, reflecting a reduction in heat loss by about 75% (mid-dle panels). For the heating-season month of April, this diminished slab heat loss from about 150 kWh, or 20% of the total gain, to about 38 kWh, or about 5% (lower panels).

kWhOriginal mid‐6a  66 69 74 70 86 79

6a‐noon  28 22 17 9 7 7

noon‐6p  15 9 10 4 4 5

6p‐mid  63 69 74 68 70 68

Redesign mid‐6a  74 92 101 109 133 117

6a‐noon  29 28 24 17 14 13

noon‐6p  18 16 20 16 26 22

6p‐mid  77 97 109 118 135 120

High Mass mid‐6a  84 93 100 98 119 108

6a‐noon  35 30 24 14 12 12

noon‐6p  15 9 10 3 2 2

6p‐mid  75 84 89 83 86 81

High Water mid‐6a  87 105 112 117 148 132

6a‐noon  37 37 29 20 19 19

noon‐6p  14 10 10 4 3 4

6p‐mid  73 90 95 95 104 97

Jan Feb Mar Apr May June

New Priorities for Thermal Mass. The Gates redesign held much less thermal mass than recommended by Sun Wind & Light, Heat-ing, Cooling, & Lighting, and Mechanical and Electrical Equipment for Buildings, suggesting that more mass should have been add-ed. The field-validated Gates model was therefore used to sim-ulate a “high mass” option, using the textbook consensus on concrete mass, and a “high water” option, using the consensus water mass. The three redesign options returned comparable total heat to the spaces, all greater than the original (left).

However, the actual redesign showed consistently warmer surface and operative temperatures during occupied evening hours (upper graph), and as a result, much greater heat flux to the space when people were actually using it (lower graph).

This work therefore supported the priority of separating mass from wet soil, suggested by the initial field study (above), and added a new one, explored below: tailoring thermal mass to the program at hand. Please see the publication for further details.

Oregon sunspace redesign/build: New priorities for thermal mass. American Solar Energy Society National Conference, April 2013.Revising thermal mass design rules for the Pacific Northwest. Building and Environment (submitted August 2013).

Thermal Mass Slab-on-Grade Surface Temperatures and Heat LossGates sunspace model, validated with 2011 and 2012 field data, showing April 2012 averages

Original Redesign

April 17 17.7 18.1 18.0 18 23 23.2 23.8 23.6 23

17 18.0 18.3 18.2 18 23 23.7 24.1 24.1 24

18 18.7 18.7 18.5 18 23 24.6 24.6 24.4 24

19 19.4 19.0 18.7 18 24 25.4 24.9 24.6 24

18 18.6 18.4 18.3 18 23 24.3 24.0 23.9 24

0.1 0.15 0.16 0.18 0.1 0.03 0.04 0.04 0.04 0.04

0.2 0.16 0.17 0.19 0.2 0.04 0.04 0.04 0.04 0.04

0.2 0.17 0.17 0.18 0.2 0.04 0.04 0.04 0.05 0.04

0.2 0.19 0.18 0.18 0.2 0.05 0.05 0.04 0.05 0.04

0.2 0.18 0.18 0.19 0.1 0.04 0.04 0.04 0.05 0.04

1 3.4 5.1 4.4 1 0.3 0.8 1.2 1.1 0.3

3 9.8 13.9 12.5 3 0.8 2.4 3.3 3.0 0.8

3 9.4 12.6 10.8 3 0.8 2.4 3.2 2.8 0.8

4 10.8 13.4 11.3 3 0.9 2.6 3.3 2.8 0.8

1 4.3 5.4 4.8 1 0.3 1.0 1.3 1.2 0.3

Tempe

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Heat Return to Sunspaces by Thermal Mass Redesign + ModelsMonthly kWh; High Mass, High Water show design guide recommendations

Mass Temperatures and Heat Fluxes of Redesign + ModelsRedesign returns heat earlier, during occupied hours

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Thermal Batteries for Buildings Thickness. Increasing mass thick-ness, shown for exposed mass walls characteristically delayed heat de-livery, as expected (right); design guides often recommend increasing the thickness of a thermal mass ele-ment for this exact purpose.

Increased thickness also, however, substantially diminished the mag-nitude of the heat delivered, to the point that the thickest walls per-formed net cooling functions (e.g. 24-in adobe). This feature is notably absent from design guides but is readily predictable from mass ther-mal properties.

Thermal diffusivity. Granite is denser and more thermally conductive than concrete, but has a lower specific heat capacity. To choose between two different materials (apart from cost), their relative “thermal diffusiv-ities” are useful, which express the rates at which they equilibrate ther-mally with an environment. Granite, with the highest value, exchanges substantially more heat with the interior space than concrete as a re-sult. Together, these show that both material and thickness may be inten-tionally matched to the timing and intensity of a space’s heating need.

Design Intent. Passive solar design guides usually ex-press one of two design intents: (1) minimizing diurnal temperature swings and/or (2) maximizing heat delivery on an aggregated monthly basis. These may easily miss the most important goal, however, of delivering heat (or coolth) when it is most needed. Given the diversity of thermal behavior among materials, it seems plausible to match material, configuration, and size to an architec-tural program more specifically than is typically discussed. Program-responsive heat delivery patterns might include, for example, evening heating, afternoon heating, all-night heating, and cooling (right).

Method. To determine whether such programmatic ap-plication of thermal mass might be feasible, EnergyPlus models were used to simulate performance of exposed wall, Trombe wall, direct-gain, and sunspace configura-tions (below) with varying materials and thicknesses.

Rocks, clays, water, and salts: Highly durable, infinitely recharge-able, eminently controllable thermal batteries for buildings. Special Issue: Geoscience of the Built Environment. Geosciences 2013, 3: 63-101.

Ideal patterns for solar heat gain and delivery to indoor spacesThermal mass wall sections; yellow = solar gain, blue = delivery

Effects of Material and Thickness on Heat Return from Thermal Mass Walls

8(a) Exposed mass wall (b) Trombe wall (c) Direct-gain space (d) Sunspace(a) Exposed mass wall (b) Trombe wall (c) Direct-gain space (d) Sunspace(a) Exposed mass wall (b) Trombe wall (c) Direct-gain space (d) Sunspace(a) Exposed mass wall (b) Trombe wall (c) Direct-gain space (d) Sunspace

a) Exposed mass wall b) Trombe wall c) Direct gain space d) Sunspace Alexandra Rempel, Ph.D., M.Arch., 2013Alexandra Rempel, Ph.D., M.Arch., 2013

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Internal Convection. Water is widely acknowledged as a good thermal mass material in the de-sign literature, but the extraordi-nary potential of internal convec-tion to sustain heat delivery over hours seems underappreciated.

In a Trombe wall configuration, for example (upper panel), models showed that water could combine a strong afternoon heat pulse with lower, all-night heat delivery (4-in), while the thickest walls (12-in) fully absorbed pulses of heat gain and delivered heat at a constant rate to the interior all night.

The explanation for this behavior is straightforward: heat transfer is limited in part by the surface tem-peratures of the entities involved, so the ability of warm water to rise, leaving the solar collection surface, and be replaced by cooler water facilitates its solar heat gain. Similarly, the falling of cool water on the interior surface and replace-ment by warmer bulk water facili-tates sustained heat delivery.

Thermal Batteries for Buildings

Heat Loss to Soil. Previous work suggested that heat loss to ground can be high when soils are moist and fine-grained. Moreover, the standard TMY3 weather files use an incorrect default value for soil thermal diffusivity (α). As a result, potential heat loss to ground is hid-den from designers not just by design guides,

stating perimeter insulation is sufficient, but by climate files and energy models as well. Correction of values to those in the soil sci-ence literature (above) shows that thermal mass needs minimal separation from low-diffu-sivity soils, but that it should be well-protected from moderate-to-high diffusivity soils.

Latent Heat. Water’s heat-delivery con-stancy is rivaled only by phase-change materials (PCMs), hydrated salts that absorb heat as they melt and release it as they solidify. The “latent heats of fusion” of these materials are quite large, and the phase change itself occurs at a near-con-

stant temperature, avoiding the diminish-ing returns that occur during solar uptake as a solid mass heats up. As a result, PCMs are effective at fractions of the thickness of concrete and water, as shown by the 4-in panel of calcium chloride and 2-in panel of zinc nitrate salts below.

Internal Mass. Mass con-tained fully within a space loses virtually no heat to underlying soil, making it a good choice in direct-gain and sunspaces with persis-tently wet soils. In the form of water drums, it also offers the warmest possible night-time indoor temperatures for plants (below left).

Thermal Mass for People and Plants. This work shows that thermal mass materials, configuration, and size can indeed be matched to spe-cific design intents. Adobe, brick, granite, concrete, wa-ter, PCMs, and other materi-als each have their thermal niches, and once chosen, their thicknesses, volumes, and separation from soil can be calculated to optimize the timing and amplitude of heat delivery for the pro-gram at hand. This provides a program-responsive, climate-responsive, and material-spe-cific alternative to one-size-fits-all mass-to-glass ratios.

Please see the publication for further details.

Evenness of Heat Delivery by Water Trombe Walls

Evenness of Heat Delivery by Thin PCM Trombe Walls

Slab-on-Grade Heat Loss over Typical Soil Typesα = soil thermal diffusivities reported in soil science literature

Internal Mass: Complete Protection from Ground Heat Loss

10 Alexandra Rempel, Ph.D., M.Arch., 2013Alexandra Rempel, Ph.D., M.Arch., 2013

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Hybrid Ventilation in the Harm A. Weber Academic Center at Judson College

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Center-In, Edge-Out. The Weber Academic Center near Chicago, Illinois (Alan Short & Assoc., UK) consists of a “block” of studios and library connected to a “bowtie” of offices to the south. In the block (above), ventilation air was taken in actively at ground level (a) and drawn through a plenum into a central lightwell (photo). Air was then to flow upward passively, entering occupied space through floor-level vents and exiting through wall-edge vents leading to terminal stacks (a).

Methods. To investigate the system’s performance, air temperature sensors were placed vertically along the lightwell (a, above), through-out Level 3 (b), and in a transect extending across Level 4 (c) for one August week, and flow bubbles, infrared (IR) photography, and ane-mometers were used to document airflow paths.

Solar Gain. Although the lightwell was shaded internally, it warmed substantially each day, with afternoon peaks of ~83°F (right). Heat radi-ated outward from this central point (IR photos), creating a noticeable thermal gradient across Levels 3 and 4 (right) and causing the studios and library to exceed thermal comfort limits for most occupied hours.

Volume 3, Number 1 61

well within the comfort zone. Conditions on Lev-els 3 and 4 changed little compared to the noon set, however, suggesting that mechanical cooling had in-creased, but was not noticeably affecting conditions above Level 2.

An alternative means of viewing thermal comfort, developed by Victor Olgyay (18), shows the effect of airspeed explicitly and therefore enables prediction of airspeeds necessary to provide thermal comfort; this “bioclimatic” visualization is considered es-pecially useful for design and evaluation of passive cooling strategies (4). When dry-bulb temperatures and relative humidities from 8/23, 12:00 noon (for which operative temperature was plotted in Figure 4b) are plotted on a bioclimatic chart (4), it becomes clear that positions on Levels 2, 3, and 4 could have been brought into the bioclimatic comfort zone with slight decreases in relative humidity combined with increases in ambient airspeed: a decrease in dry-bulb temperature would not have been necessary, though it would have served as an effective alternative (Fig-ure 5).

A second alternative, known as the adaptive model of human thermal comfort, is often used to establish comfort criteria in unconditioned build-ings and is also incorporated into ASHRAE 55-2004. This approach, which defi nes the acceptable range of indoor temperatures on the basis of mean monthly outdoor temperatures, was considered by the designers but ultimately discarded in favor of the conventional standard (20).

Hypothesis 1 was therefore proven false: the HAWAC was, in fact, not operated to keep Levels 3

and 4 within the ASHRAE 55-2004 comfort zone during the study. Deviations from the zone were caused by high humidity rather than high tempera-ture, however, and bioclimatic evaluation indicates that airspeeds were also lower than ideal. Consis-tent with these observations, commentary overheard from occupants referred primarily to air stillness and stuffi ness, rather than heat. Increased potential for comfort might therefore be achieved with least energy by approaching humidity and/or airspeed values first, perhaps by making greater use of the lightwell airfl ow pathway, considered further below, or individually-operable fans.

AIRFLOW ISOLATION WITHIN THE BLOCKGiven the unique emphasis on center-in, edge-out airfl ow paths within the block, as well as the con-ditioned, cool, dry status of the bowtie during the study, it was expected that airfl ow paths within the block would be nearly isolated from the bowtie. At the same time, it was expected that airfl ow from the lightwell, through the block, to the stack apertures would proceed as described (10, 11, 20). To investi-gate these hypotheses, all apertures found between Levels 3 and 4, the bowtie, the lightwell, and perim-eter stacks were examined with fl utter-strip apparati, anemometers, and infrared thermography on mul-tiple occasions each day.

Level 3 (Library) PerimeterThe library on Levels 2 and 3 is served by 23 pe-rimeter stacks embedded within thick walls. Those

Figure 3. Positions of Hobo dataloggers projected in section (a) and in plan on Levels 3 (b) and 4 (c).

a) b) c)

JGB_V3N1_a05_ahmann.indd 61 3/5/08 4:03:35 PM

Airflow Paths. The bowtie was air-condi-tioned, and its air was meant to be kept separate from the hybrid-ventilated, mini-mally cooled block by interior doors.

Warm block occupants, however, soon discovered that cooling was available by propping these doors open (blue arrows, right). These doors were later restored to the intended closed positions with signs (below), but air short-circuits persisted: transfer grilles in common walls admitted cool air at high speed (photo 3, left), as did large gaps around interior doors. The lightwell discharged hot air through its unsealed door as well (top IR photo, right diagram).

Importance of Field Work. These results illustrated the perils of combining day-lighting and cooling intents into a single element and assuming that connected buildings can act independently (see Lil-lis, below). More importantly, however, they show the value of straightforward, methodical field work in revealing specific reasons that high-performance buildings fail to perform as intended.

Hybrid Ventilation in the Harm A. Weber Academic Center: A Late-Summer Case Study. Journal of Green Building 2008, 3:56-73.

Temperature Transect: Lightwell Heating of Level 4

LightwellPlacement of Temperature Sensors

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IR: Lightwell Air Leak

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cool air (a/c)ambient-temperature airwarm air

12 Interior Doors to Bowtie Alexandra Rempel, Ph.D., M.Arch., 2013Alexandra Rempel, Ph.D., M.Arch., 2013

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Airflow Pathways: Single-Sided Natural Ventilation through Stacked Awning Windows (EnergyPlus)

Cross Ventilation Study Area: Offices and Atrium

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Passive Cooling of Everett, WA Community College Offices

Would single-sided natural ven-tilation with restricted awning windows (section) be sufficient to cool faculty offices (above) during the warm dry summers of Everett, Washington? Or would cross ventila-tion be necessary, possibly at night?

To answer these questions, an airflow network was created with EnergyPlus to simulate bulk airflow between nodes in offices, outdoors, and in the atrium under typical weather conditions. Preliminary modeling showed that stacked aw-ning windows allowed greater ex-change than side-by-side windows, allowing air to enter below and exit above (right).

Cooling Challenge. While outdoor air temperatures were ideal for natu-ral ventilation cooling, reaching the necessary air exchange was not possible with daytime single-sided ventilation alone for any of the test offices (left). At the same time, faculty desired complete acoustic separa-tion from the atrium, limiting cross-ventilation options. Night ventilation, thermal mass, and ceiling fans were therefore explored in detail.

Solutions. Ultimately, in collaboration with the architects, automatic vents were developed to allow nighttime cooling of limited thermal mass by cross-ventilation through the atrium; in combination with daytime single-sided ventilation and ceiling fans, this system predicted accept-able comfort in all but a few August hours (below left, and below).

Passive Ventilation in Large Buildings. As this building, the Weber Cen-ter, and the Lillis Business Complex (p.17) show, passive ventilation is quite feasible in large buildings. However, it seems to be explored rarely, apparently because of perceived uncertainty in outcomes. Good model-ing tools, however, combined with rigorous field work, can remedy this.

Natural Ventilation in Everett Community College Offices. Prepared for SRG Architecture, April 2009. Report available upon request.

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Natural Ventilation in Everett Community College Offices. Prepared for SRG Architecture, April 2009. Report available upon request.

Alexandra Rempel, Ph.D., M.Arch., 2013Alexandra Rempel, Ph.D., M.Arch., 2013

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Vernonia School District / BOORA Architects

SOLARC ARCHITECTURE AND ENGINEERING7

Thermal Comfort in Passively-Cooled Zones

4.1 Passively Cooled SpacesSouthwest Classroom, Level 2. The west-wing classrooms on the upper level, with southern exposure, present the greatest cooling challenge among the building spaces due to intermittently high occupancy, solar gain through skylights and windows, and minimal losses through the well-insulated envelope. Nevertheless, model-predicted in-door operative temperatures remained well within the ASHRAE 55-2004 adaptive comfort range, with credit taken for elevated air speed (ceiling fan operation), even on the hottest September days (Fig. 3).

Computer Laboratory. Although this space has a northern exposure, high internal loads cause it to experience some warm hours. As for the other classroom, though, these remain within the adaptive comfort range.

Administration, Level 2. Offices have the highest sustained internal loads in the building, causing the skylit up-per administration area to be an area of concern. Here, too, operative temperatures remained within the adaptive comfort range.

Science Laboratory. The second-floor laboratory, with scientific equipment loads and intermittent high occu-pancy, had the fourth-greatest cooling load and was therefore included in the test zones; however, its operative temperatures remained in the comfort range even without the elevated air speed credit.

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Fig. 3 (above and following pages). Indoor operative and slab temperatures during the 48-hour test period, compared to outdoor dry-bulb and wet-bulb temperatures. The September comfort zone denotes the September adaptive comfort threshold (66-78.80F) with the addition of the 5.40F allowance for elevated air speed.

DRAFT

Thermal Comfort in Passively-Cooled Zones (LEED IAQ Credit 7.1). Prepared for BOORA Architects, June 2011. Report available upon request.

Design-Day Adaptive Comfort from Night Cooling of Thermal Mass + Operable Windows. Academic-year design day; orange limits show adaptive comfort zone.

To achieve low-energy cooling for LEED Platinum and Net-Zero performance goals, the design team devel-oped a scheme in which evaporatively-cooled water was pumped through tubes in concrete slabs at night, creating cool mass to take up the following day’s heat gains. Teachers controlled operable windows and ceil-ing fans each day, qualifying classrooms for adaptive comfort standards. EnergyPlus modeling was used to understand interac-tions between mechanical and passive systems and to evaluate resulting thermal comfort on the warmest academic-year days.

Final Wall Assembly: Steel cladding over horizontal Z-girts + XPS Insulation over verti-cal steel studs + batt insulation

Final Wall Performance: Temperatures from inside (red, 68°F) to outside (blue, 14°F); composite U=0.052 Btu/h SF °F.

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Night Cooling of Mass in the Vernonia K-12 School

Natural Ventilation in the Lillis Business Complex, Univ. of Oregon

3D Thermal Bridging in Walls Architects intended air from classrooms and offices to flow to the central atrium, up, and out through roof vents. Anemometers and flow bubbles showed, however, that air instead flowed rapidly (≥25 fpm) outward from the atrium through corridors and out through open windows, par-ticularly those of connected buildings (above). Fire doors (circled) were found open at all times. To determine wheth-er they were counteracting atrium stack formation, airflows were monitored from atrium bridges with all fire doors closed (left). Flow bubbles showed progressively greater buoyancy over time from blue (time 0) to green (t=30’), yel-low (t=1h), orange (t=1.5h), and red (t=2h), supporting this hypothesis and showing the value of field work in revealing passive system performance under occupied conditions.

Stack Restoration Experiment. One warm evening, atrium fire doors were closed and air buoyancy was monitored with flow bubbles from the atrium bridges over time. Arrows show bubble paths and clouds show areas of bubble congregation.

Three-dimensional heat transfer is too computation-ally intensive to be included in whole-building energy simulators, which require users to account for thermal bridging in wall layers. To find composite heat trans-fer coefficients for complex assemblies, accounting for studs, cladding supports, and fasteners, numerical methods are required. Here, the finite element solver AnTherm was used to optimize opaque envelope op-tions for a LEED-Platinum college building.

Wall Assembly 3D Thermal Modeling for the Lane Communi-ty College Downtown Campus. Prepared for SRG Architects, January 2011. Report available upon request.

Natural Ventilation Design Intent: Air from corridors is intended to flow into the central atrium, up, and out through rooftop vents (SRG Architecture).

Stack Effect Ventilation in the Lillis Business Complex Atrium. ARCH 597: Building Case Studies (W. Grondzik), June 2006. Available upon request.

Alexandra Rempel, Ph.D., M.Arch., 2013Alexandra Rempel, Ph.D., M.Arch., 2013

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Solar Site Surveying Overhang Shade Analysis Solar Pathfinder DView: Hourly Sky Cover Recent Publicity

Passive Heating and Cooling Design: SUS 4043. Boston Architectural College. Materials available upon request.

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Teaching

Evidence-based. Teaching architecture students not only conceptual schematic design, but also design development skills, for passive heating and cooling is essential. When clients and consultants question the ability of a passive system to work, the architect must be able to provide solid site, climatic, and thermal evidence for making decisions.

Climate-responsive. Most current textbooks and design guides base the critical sizing and positioning of glass and mass on tables and calculations developed in sunny dry cli-mates; these fail to work in numerous other climates. With strong climate analysis skills, however, architects can esti-mate optimal parameters for passive systems quite well.

Model-savvy. Long-term performance analysis is greatly fa-cilitated by models if good site work has been performed. Passive heating and cooling are not usually taught to me-chanical engineers or building energy consultants, howev-er, and their typical modeling software cannot simulate the hours-long patterns of mass-based systems. The architect must therefore understand the modeling tools available.

1. History and Context

Thermal comfort ∙ Vernacular and contemporary case studies ∙ Direct-gain, indirect-gain, and isolated gain solar configurations ∙ Cross and stack ventilation ∙ Introduc-tion to term project ∙ Term project site selection

2. Climate; Solar and Wind Resources

Graphing direct and diffuse solar radiation on sun path diagrams ∙ Cloud scattering of solar radiation ∙ Graphing heating and cooling degree-days ∙ Buoyancy ∙ Wind roses ∙ Microclimates ∙ Estimating solar glazing angle and tilt

3. EnergyPlus Why model? ∙ Program setup ∙ Opening, viewing, and ed-iting input files ∙ Viewing variables in xEsoView ∙ Export-ing results in *.csv files ∙ Term project program selection

4. Solar Site Surveying

Magnetic declination ∙ Tree shapes & identification ∙ Measuring tree & building height with inclinometers ∙ Drawing shading masks ∙ Modifying optimal solar glazing angle and tilt ∙ Urban tree canopy debate

5. Windows, Shading, and Movable Insulation

Solar spectrum ∙ Window glass composition ∙ Visible and IR transmission ∙ Emissivity and coatings ∙ Multi-glazed windows ∙ Choosing solar glass ∙ Sizing solar glazing by hand ∙ Scheduling shading and movable insulation ∙ Modeling windows in WINDOW 6 for EnergyPlus

6. Thermal Mass

Heat capacity ∙ Thermal conductivity and diffusivity ∙ Convection ∙ Radiation ∙ Adobe, concrete, stone, water, PCMs ∙ Matching material to program ∙ Conceptual sizing ∙ Ground heat transfer ∙ Internal mass ∙ Modeling

7. Natural Ventilation

Airflow and thermal comfort ∙ Evaporative cooling ∙ Site wind paths ∙ Cross ventilation aperture positioning and sizing ∙ Stack ventilation aperture positioning and sizing ∙ Wind site survey ∙ Indoor ventilation survey ∙ Modeling

8. Synthesis Presentation and quantitative performance evaluation of the term-project site and passively conditioned space

Field-validated. Instruments for measuring dry-bulb, wet-bulb, surface, and soil temperatures; air speed and direction; incident solar radiation, il-lumination, and relative humidity are durable and inexpensive, and their value in building students’ intuition for outdoor microclimates and indoor passive system performance is enormous. They are also essential for model validation.

Ready to go. Fortunately, we can equip students with a full set of tools for passive design using a combination of field measurements, climate data, and appropriate modeling tools. The course outline at left describes a course I’ve developed for the Boston Architectural College’s Sustainable Design Institute, described further in a recent In-habitat article (far left; http://inhabitat.com/learn-the-core-concepts-of-passive-design/).Course Outline: Passive Heating and Cooling Design, Boston Arch. College 2013

Wind Rose

Alexandra Rempel, Ph.D., M.Arch., 2013Alexandra Rempel, Ph.D., M.Arch., 2013

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Relevant Funding ProgramsPassive building design work is fundable through sustainability, building envelope, and greenhouse-focused agriculture programs at the federal level. A number of the most promising are listed below. In addition, this work is eligible for funding through the Northwest Energy Efficiency Alliance, covering Montana in addition to Oregon, Washington, and Idaho, as well as state Department of Energy initiatives. Please see my curriculum vitae for a summary of past research funding.

National Science FoundationContact: Bruce Hamilton, Engineering Directorate

1. Sustainable Energy Pathways (SEP). Awards: Up to $2M, 3 years. Topics include: Energy Harvesting & Conversion from Renewable Resources; Sustainable Energy Storage Solutions; Critical Elements & Materials for Sustainable Energy; Nature-Inspired Processes for Sustainable Energy Solutions; Reduc-ing Carbon Intensity from Energy Conversion & Use. Annual; FY2014 announcement planned in June 2013.

2. Environmental Sustainability. Topic 3: Green Engineering. Re-search to advance the sustainability of ... green buildings ... taking a systems or holistic approach to green buildings. In-novations in green engineering techniques to support sustain-able construction projects. Proposals due January 15, 2014.

3. Science in Energy and Environmental Design (SEED). Topics focus on low-energy building design. Annual, but topics vary; FY2014 announcement date pending.

U.S. Department of EnergyContact: Greg Stark, National Renewable Energy Laboratory

4. Energy Savings through Improved Mechanical Systems and Building Envelope Technologies. Topic 1: Energy Saving Heat-ing, Ventilation and Air Conditioning (HVAC) systems, Subtopic 1.2: Alternative Space-Heating Systems. Awards: $10K-$1.5M, 3 years. Annual.

5. Building Technologies Innovations Program. Awards: $250K- $750K, ≤2 years. All building energy topics are eligible for sub-

mission. All proposed technologies or approaches must have the potential to reduce building energy consumption, energy costs, or GHG emissions. Annual.

U.S. Department of AgricultureContact: Bradley Rein, USDA

6. Sustainable Development: Sustainable Agriculture Research and Education Program (SARE). Awards: $60K-$150K; Re-gional; Renewable. Goal: Promote good stewardship of the nation’s natural resources by providing site specific and profitable sustainable farming and ranching methods that ... conserve soil, water, energy, and natural resources. Annual; FY2014 announcement planned April 15, 2013.

7. Agricultural & Food Research Initiative (AFRI): Agricultural and Natural Resources Science for Climate Variability and Change. Goal Area 1. Adaptation: Maximize resiliency and re-duce the impact of climate variability and change on the sus-tainability and productivity of agricultural ecosystems under changing climates by providing producers and decision-mak-ers with new and sustainable management methods and tech-nologies. Annual; FY2014 announcement planned October 13, 2013.

Northwest Energy Efficiency AllianceContact: John Jennings, Charles Stephens

8. Emerging Energy-Efficient Technologies. Projects must pro-mote energy savings in the Northwest and face clear market barriers. Awards: $1-50K. Rolling submissions.

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