Cooler rooms,
lower bills
Energy proposal · November 2026
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The bill
LKR
237,207
October
29 days · 6,380 kWh
1 kWh saved
= LKR 37
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The year
kWh per day
89
Jan
89
Feb
257
Mar
2 new ACs
289
Apr
236
May
214
Jun
207
Jul
178
Aug
235
Sep
220
Oct
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+25% tariff
El Niño 2027
Strong to very strong
NOAA outlook, October 2026: lasting into early 2027
WMO: higher chance that 2027 becomes the warmest year on record
Sri Lanka, past El Niño years: tend to be drier in the wet and intermediate zones, warmer in the Yala season
Results differ by region. One Dry Zone study found the opposite.
NOAA October 2026 outlook · WMO · Sri Lanka studies · forecasts and past patterns, not measurements at Mira
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Where it goes
12
air
conditioners
Probably more
than half of
the bill
Not measured yet
Dorm units: mostly old
Extra units added for hot rooms
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Sun and building
8 h
of sun a day on the SW side in January
about 5 h in July
Noon sun 61–73° high: the roof gets the most
Calculated for Mirissa · trees and neighbours not counted
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The roof heats
the room
+4
°C
Yoga room · thermal camera · surface temperatures
Ceiling 39 °C
Wall 35 °C
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Heat with nowhere to go
Breakout stairwell · no exit for hot air
Thermal camera · surface temperatures
Outdoor unit 55 °C
Walls 45 °C
Ceiling 47 °C
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The yoga room
One room, two classes
Two ACs on for every class
Big SW windows · no fans, no fresh air
Yoga room
Thermal camera: windows and ceiling
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What was seen
1
Doors open, AC on
2
AC on, room empty
3
ACs left on
4
Hot roof
5
Afternoon sun on glass
6
Trapped hot air at the outdoor unit
7
Old ACs, no smart control
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Two ways to
cut the bill
Keep heat out
Roof · windows · divider · outdoor unit
By quote
Use the AC less
Habits · door closers · timers · controls
Priced
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Roof
Cool roof: up to 14 °C cooler surface, about half less roof heat
Zingre et al. 2015 · Singapore · model tested on two apartments
Solar panels as shade: about 60% less peak roof heat by day
Dominguez et al. 2011 · San Diego · field measurement
Next: check the roof · quote · thermal camera before and after
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Roof: three options
By quote
Reflective roof paint
Shade mesh on poles
Solar panels on a frame: shade and power
Example photos · not Mira
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Reflective roof paint
Measured at Mira · small study
Ceiling below: 34 °C instead of 40 °C
Part of the roof painted with simple white wall paint. Felt with bare feet, and measured with a thermal camera.
Roof: painted part
Roof: thermal camera
Ceiling under painted part
Ceiling under unpainted part
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Windows
SW
glass
Solar film outside: about 44% less sun heat through the glass
Yin et al. 2012 · Shanghai · calibrated simulation
Clear film keeps the view
Or: outside sun screens, down when the room is empty
By quote
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Yoga divider
Open: one big room
Closed: one AC instead of two for a reformer class
Saving: depends on the class timetable
Example: folding glass divider
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The outdoor unit breathes its own hot air
An AC works harder when the air at its outdoor unit is hot
1 · Log the air at the unit for one day · free
2 · Only if it is hot: move the unit or add an extract fan
3 · Quote
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Free actions
Setpoint about 25 °C, checked with thermometers
Clean filters every 2–4 weeks
AC off while cleaning, doors closed
LKR 5,000–12,000 / month
Estimate
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Door closers
21×
More outside air with the door open than closed
Same AC, same setpoint: the room stayed 5 °C warmer
Lee 2019 · measured in a shop with AC, Japan
First 7 closers: Dorm 1, Dorm 2, coworking
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Smart remotes
Sends the AC’s own remote signal on a timetable · works with old ACs · normal remote still works
Coworking
business hours only
Breakout
off overnight
Yoga 1 and 2
on 15 min before class, off 5 min before the end
First 3 weeks: staff note which ACs run in empty rooms
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Three steps
FIX
FIX
MEASURE
stop or continue
FIX
MEASURE
CONTROL
stop or continue
stop or continue
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Step 1 · Fix
LKR
46,000
Rough estimate · at cost, no markup
7 door closers
4 smart remotes
Free actions
Saves
LKR 10,000–22,000 / month
Estimate
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Step 2 · Measure
+ LKR
114,000
160,000 including Fix
Rough estimate · at cost
Power meters, door sensors, thermometers in 2 dorms
Nothing is switched
Saves: nothing
by itself
Gives: the real
numbers
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Step 3 · Control
+ LKR
60,000
220,000 including Fix and Measure
Rough estimate · at cost
AC off when a door/window stays open
AC off after 20 min in an empty room (daytime only)
Remote stays in the room · staff can override
Adds
LKR 2,000–5,000 / month
Estimate
Tested with the rule on and off in random 2-day blocks
Optional: +LKR 26,000 for two untreated comparison rooms
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Price
Rough estimate · at cost
Minimal
46,000
46,000
Measure
46,000
+114,000
160,000
Control
46,000
+114,000
+60,000
220,000
LKR
Minimal
Measure · includes Minimal
Control · includes Measure
Equipment
46,000
160,000
220,000
Setup + installation (flat)
50,000
100,000
120,000
Total
96,000
260,000
340,000
Saves per month
10,000–22,000
10,000–22,000
12,500–27,000
Payback (months), all savings
4–9
12–25
13–27
Payback, paid items only
9–19
25–52
22–47
Equipment: rough estimates, rounded, passed through at cost. No markup, no commission. Final amount = actual receipts. Savings: low to high case. Building options (roof, film, divider, outdoor unit) not included: by quote. Excludes ongoing support.
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The timetable runs the AC
Example day
Classes · via Bookwhen API
Yoga
Reformer
Yoga
Yoga room · AC 1
AC on
AC on
AC on
Yoga room · AC 2
AC on
AC on
06:00
08:00
10:00
12:00
14:00
16:00
18:00
20:00
On 15 minutes before class, off when it ends
A reformer class needs one AC, not two. Rooms work the same way, from the bookings in Cloudbeds: check-in cools the room, check-out switches it off.
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Guests cool their own room
Running at The Stables
1
From the beach, one tap starts 10 minutes of turbo cooling
2
Back in time: it stays on. Nobody back: it switches off
3
Door or window open: the AC stops, and the page says what to close
The Stables · stay page, sent on WhatsApp at check-in · no app, no login
1
2
3
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Each room, live
Running at The Stables
AC: on or off, set and room temperature
Doors and windows: open or closed
Checked in: from the bookings
Occupied: someone is in the room
AC power: live, in watts
Bookings and the building on one screen
The Stables · room 6 · building dashboard
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Every kWh is labelled
Running at The Stables
The Stables · AC energy per room, 14 days · guest rooms, vacant rooms, maintenance and mould runs
An AC running in an empty room shows up as waste
The system knows who is checked in. Housekeeping cooling a room with the doors open counts as vacant, not as guest use.
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Messages to the guests in the house
The system knows who is staying, so each message reaches only the guests it concerns.
Running at The Stables
AC turned off
Which door or window is open, and what to do
Surf check at dawn
Worth getting up? From the hotel's own weather station
Power cut tomorrow
From the power company's calendar: charge your devices
Poya tomorrow
No alcohol sold. Sent the day before
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Passport check-in
Same system, beyond energy
Running at The Stables
Not priced for Mira
1
Before arrival: a WhatsApp link lets guests scan their own passport
2
Not done yet? Reception scans it on the phone at the desk
3
Either way the form fills itself in (read from MRZ).
Reception checks and taps Verify
The SLTDA guest register, complete and ready for inspection
Passport read on the phone, not uploaded for reading · check digits verified · images deleted after a year · personal data hidden in this screenshot
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What is known,
what is not
Know
Don’t know yet
The bill
The tariff
Hot roof and stairwell (measured)
What was seen on site (sun, open doors, AC on in vain)
How much goes to AC
How long ACs run idle
How much each fix saves here
Measured results are reported,
whatever they are
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The tariff
36
LKR / kWh · tariff (General Purpose)
18
LKR / kWh · Hotel tariff
Eligibility decided by EDL and SLTDA
The plan is calculated at 36
Ask EDL and SLTDA in writing: tariff and solar scheme
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Next steps
Short visit: doors and AC labels
3 weeks: read the meter daily, change nothing
Free actions + Fix
Before vs after
Decide the next step
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In parallel
Building quotes
Tariff and solar scheme: ask EDL and SLTDA in writing
Bills, 2026
Month
Days
kWh
kWh / day
LKR
Jan
31
2,769
89
98,201
Feb
31
2,768
89
98,166
Mar
27
6,948
257
243,930
Apr
33
9,529
289
343,575
May
31
7,305
236
271,419
Jun
30
6,414
214
238,466
Jul
29
5,993
207
222,921
Aug
31
5,514
178
205,235
Sep
32
7,535
235
279,856
Oct
29
6,380
220
237,210
Total
304
61,155
201
2,238,980
EDL bills, month of the bill. LKR = month’s charge incl. levy (October total due 237,207 after a −3 adjustment). Tariff LKR 34 / kWh until March, 36 from April.
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Green on the roof
Real plants: bare roof 57 °C, under the garden 27 °C
Wong et al. 2003 · Singapore · field measurement
Roof must carry the weight · needs water
Artificial grass: no cooling, gets hotter than real grass
Devitt et al. 2008 · Las Vegas · field measurement
Example photos · not Mira
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Solar: rough numbers
Estimate
About a fifth to a quarter of the bill
Option
Roof
Saves LKR / month
Cost LKR
Payback
10 kWp, no battery
about 70 m²
43,000–48,000
1.8–2.8M
3–5 years
15 kWp, no battery
about 100 m²
52,000–71,000
2.7–4.2M
3–7 years
15 kWp + 15 kWh battery
about 100 m²
62,000–68,000
4.1–7.0M
5–10 years
If all power must be sold to the grid (Net Plus)
10 kWp
27,000–30,000 / month
5–9 years
15 kWp
34,000–37,000 / month
6–10 years
Battery
no gain
Battery adds little: daytime use takes most of the power.
Which scheme applies: to ask EDL in writing.
Yield 1,576 kWh per kWp per year (Global Solar Atlas) · PUCSL feed-in tariffs Aug 2026 · installer prices 2026, quotes needed
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Sources
1. Roof, cool roof: Zingre K.T., Wan M.P. et al. (2015). Modeling of cool roof heat transfer in tropical climate. Renewable Energy 75, 210–223. Model validated on two apartments in Singapore.
2. Roof, solar panels: Dominguez A., Kleissl J., Luvall J.C. (2011). Effects of solar photovoltaic panels on roof heat transfer. Solar Energy 85(9). doi:10.1016/j.solener.2011.06.010. Field measurement, San Diego, USA.
3. Windows, solar film: Yin R., Xu P., Shen P. (2012). Case study: energy savings from solar window film in two commercial buildings in Shanghai. Energy and Buildings 45, 132–140. Calibrated simulation.
4. Door closers: Lee S. (2019). Study on energy loss through door open while air conditioner running in commercial store. IOP Conf. Series: Materials Science and Engineering 609, 032069. doi:10.1088/1757-899X/609/3/032069. Measured in one shop, Japan.
5. Green roof: Wong N.H., Chen Y., Ong C.L., Sia A. (2003). Investigation of thermal benefits of rooftop garden in the tropical environment. Building and Environment 38(2), 261–270. doi:10.1016/S0360-1323(02)00066-5. Field measurement, Singapore.
6. Artificial grass: Devitt D.A., Young M.H., Baghzouz M., Bird B.M. (2008). Surface temperature, heat loading and spectral reflectance of artificial turfgrass. Journal of Turfgrass and Sports Surface Science 83, 63–82. Field measurement, Las Vegas, USA.
7. Tariff: PUCSL electricity tariff schedule, effective 11 May 2026.
8. Bills: EDL bills, January to October 2026. Thermal images: StillCurrent thermal camera, Mira, October 2026.
9. Solar yield: Global Solar Atlas (World Bank / Solargis), PV output for 5.948° N, 80.456° E: 1,576 kWh per kWp per year, accessed 5 November 2026.
10. Solar export rates: PUCSL, Decision on Feed-in Tariffs effective 25 August 2026 (valid to 24 February 2027). Net Plus for new connections: Ministry of Energy, reported by pv magazine, 22 September 2026.
11. Solar prices: Sri Lankan installer price lists, 2026. Estimates until quotes exist.
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