Domes Community Analysis
Prepared for Josh Redman — Baggins End Innovative Housing, UC Davis
210+
Days of improved comfort
per dome, per year
$989
Community savings per year
14 domes — summer + winter combined
YEAR-ROUND
Summer exhaust • Winter supply
Zero grid cost — 100% solar powered
The Thermal Mass Advantage
One System, Two Seasons
The same dome geometry that traps heat in summer becomes a free thermal
battery in winter. SolMod simply reverses airflow direction.
Summer — Exhaust Mode
↑
Problem: Dome traps heat — indoor 10–19°F above outdoor
Solution: Solar fan pulls hot air out through apex
Result: Peak indoor reduced 3–5°F, compound cycle broken with battery
Winter — Supply Mode
↓
Advantage: Same thermal mass STORES warm air
Solution: Solar fan pushes warm daytime air in
Result: 124 fewer heater hours, $56/dome saved per winter
The Problem
The Domes Trap Heat
Dome geometry creates a solar collector effect. Indoor temperatures run
10–19°F above outdoor — even on mild days. The curved shell
concentrates heat at the apex with nowhere for it to escape.
82°F
Average indoor temp when all 3 residents activated cooling
Outdoor was only 67°F. The dome added 15°F through passive solar gain alone.
11°F
Overnight recovery gap
Even when outdoor drops to 56°F at night, dome interiors only cool to 68°F. Each hot day compounds on the previous — the thermal mass never fully resets.
Thermal Analysis
Why It Gets Worse Each Day
Over 5 consecutive warm days in June 2014, Dome 10's overnight low rose 7°F.
The thermal mass absorbed more heat each day than it could release overnight.
Jun 5–10, 2014 — Dome 10 (no HVAC installed).
The indoor minimum temperature (blue solid line) climbed from 68°F to 75°F
over the event. Meanwhile, outdoor overnight lows remained around 56°F. The dome
was accumulating heat faster than it could shed it — a compound heat cycle.
Occupant Impact
When Residents Reach Their Breaking Point
Three domes had cooling systems during the 2014 SWARM monitoring period.
Their activation data reveals dramatically different heat tolerance levels.
Most Heat-Sensitive
75.8°
Dome 14 — Heat Pump
Thermostat-controlled. This resident needed cooling most of the summer.
630 activations
Moderate Tolerance
79.4°
Dome 13 — Ground-Source
Manual activation. Moderate tolerance but still needed relief on warm days.
86 activations
Most Heat-Tolerant
86.9°
Dome 15 — Window PTAC
Manual PTAC. Only activated when heat became unbearable — last-resort behavior.
37 activations
On 16 days, all three residents activated cooling simultaneously —
conditions had become unbearable for everyone. Outdoor temperature on those days
averaged only 67°F. This proves the problem is compound heat accumulation,
not extreme outdoor conditions.
Current Systems
Current Cooling Systems Don't Work
Even the best-performing system only achieved 5.7°F of cooling. On 100°F+ days,
indoor temperatures still exceeded 80°F with AC running.
Dome 14's heat pump was the most effective at −5.7°F, but at $0.22 per degree-day
it was also the most expensive overall ($36.99/summer). Dome 13's ground-source system
was cheapest per degree-day ($0.19) but only achieved −3.5°F of cooling —
documented as the worst thermal performance experiment on campus.
The Solution
SolMod Breaks the Heat Cycle
Instead of fighting heat with more energy, SolMod targets the root cause —
trapped hot air at the dome apex. Zero operating cost. Zero grid connection.
How It Works
1
Solar DC fan mounted at dome apex — directly where heat concentrates
2
Exhaust mode pulls trapped hot air out through the top of the dome
3
Targets the root cause: thermal trapping, not outdoor temperature
✓
Zero operating cost — solar powered, no grid connection required
Impact Projection
↓
Estimated 3–5°F reduction in indoor-outdoor temperature delta
↓
Reduces peak indoor from 91°F to 86–88°F
+
Extends comfortable days by approximately 40–50 per year
✓
Eliminates approximately 12 AC days per dome per summer entirely
The Real Value
Why a Battery Changes Everything
The battery is not for storing solar energy. It is for running the exhaust fan
overnight when outdoor temperatures are lowest — breaking the compound heat cycle entirely.
Without Battery
Daytime Only
Fan runs during peak heat (10am–6pm)
Indoor peak reduced by 3–5°F
Does NOT address overnight heat retention
Compound heat cycle still builds over consecutive days
Effective for single hot days. Insufficient for the multi-day heat events
that cause the worst comfort crises.
With Battery
24-Hour Ventilation
Fan runs overnight when outdoor is coolest (56–66°F)
Leverages cool night air to flush dome thermal mass
Overnight gap reduced from 11°F to ~3–5°F
Breaks the compound heat cycle — each day starts fresh
The dome cools fully overnight. Multi-day heat events no longer compound.
This is the primary value proposition of the battery.
Projected impact on the Jun 5–10 compound heat event.
Without a battery (red dashed), the overnight low climbs each day as heat accumulates.
With a battery running overnight exhaust (green solid), the dome fully cools each night
and each day starts near the outdoor low.
Year-Round Value — Winter Heating Offset
SolMod Works In Winter Too
The same thermal mass that traps heat in summer STORES free heat in winter.
SolMod reverses airflow — pushing warm daytime outdoor air INTO the dome.
How Supply Mode Works
1
Supply mode: SolMod reverses airflow — pushes warm daytime outdoor air INTO the dome
2
Davis daytime temps exceed 60°F for 12–56% of winter hours depending on month
3
Thermal mass absorbs and stores this warmth into evening
4
Residents run space heaters fewer hours — or not at all
Per-dome kWh offset by month. March and November provide the greatest
benefit due to warmer daytime temperatures and longer useful solar hours. Data from
PTAC model analysis of Davis winter temperature profiles.
124
Fewer space heater hours per dome per winter
$55.64
Savings per dome per winter
Financial Analysis
Annual Savings — Summer + Winter Combined
SolMod delivers value year-round. Summer exhaust reduces cooling demand,
winter supply mode offsets space heater usage. Combined, the system pays
for itself faster than any single-season analysis suggests.
|
Summer (Exhaust) |
Winter (Supply) |
Annual Total |
| Comfort days improved |
60+ days |
150 days |
210+ days |
| Energy offset |
Reduces AC runtime |
185 kWh heater offset |
185+ kWh |
| Cost saved |
$15–367 (depends on AC type) |
$55.64 |
$70–423 |
| Scenario |
Per Summer |
Per Winter |
Annual |
Key insight: The "do nothing" scenario has a hidden cost.
Resident complaints, turnover, and potential heat-related health liability
are real expenses that don't appear on a utility bill. The Domes have a
waiting list — but only if they're livable in summer.
Historical Pattern
Heat Events by Year
Using CIMIS Station 6 weather data, we identify months where compound heat
conditions are likely: monthly average > 63°F AND monthly max > 85°F.
This is not an occasional problem — it is a seasonal certainty.
Every year has 4–6 months of compound heat risk.
The pattern is consistent across a decade of data. Dome residents face this
thermal stress annually. SolMod addresses it permanently.
