Adaptive Comfort

The Adaptive Comfort Standard of ASHRAE

Adaptive Comfort Zone graph

You need to know what range of temperature you are likely to find comfortable when you are planning a house or its heating and cooling. This graph is a guide to the temperature range for comfort.

The graph explains itself. People are comfortable at rather higher temperatures in places, or at times of year, when the climate is warmer. They are comfortable at lower temperatures if the climate is cooler.
For any month in any place, you must simply look up the mean temperature for that month. Then 90% of all people will feel comfortable at temperatures in the five-degree range between the magenta line and the green line. At temperatures in the seven-degree range between the red and blue lines, 80% of people will feel comfortable.

Generally, using the local mean temperatures for January and July will give enough information for your planning. Sydney provides an example:

Because the Sydney mean temperature in the coldest month, July, is 13°, 80% of people will remain comfortable if a house gets no colder than 18°.

Because the Sydney mean temperature in the hottest month, January, is 23°, 80% of people will remain comfortable if a house gets no hotter than 29°.

The adaptive comfort zone shown on the graph was proposed by Richard de Dear and Gail Schiller Brager (2001).
This adaptive comfort zone has been incorporated in the de facto international standard: ANSI/ASHRAE Standard 55-2004, Section 5.3,, as summarised here. 

By this innovation, the American Society of Heating, Refrigeration, and Air-conditioning Engineers (ASHRAE) recognised publicly that full climate control of buildings at one “ideal” temperature and humidity may not be the way of the future.

I have used this Adaptive Comfort Standard in many of my posts, notably the one showing how my house maintained a temperature almost completely within the Comfort Zone through a whole year.

This material, with its graph, was posted originally to a “weatherzone” forum more than seven years ago. Unfortunately, the photo-hosting website “Photobucket” has now withdrawn the image from public use. This post is to make it available again.

Managing my low-energy house: I. Features needing no attention

Photo of sunlit house interior

July sun heats the house

This post, and the companion post “II. Features needing attention” were posted originally to a forum of the Alternative Technology Association (See Note below.)

My low-energy house at Manilla, NSW, maintains year-round comfort in a climate of daily and seasonal extremes. In the climate classification of the Building Code of Australia, it is in Zone 4: “Hot dry summer, cool winter”, along with Tamworth, Mildura and Kalgoorlie.
This house differs from most houses in relying on the design of the house to achieve comfort, with hardly any energy needed for heaters or coolers.
There is little artificial control: the “home automation system” consists only of timers set twice a year. Some of the comfort features call for daily action in certain seasons. However, these simple daily chores could have been avoided by small changes in the design. [See “Note added 2016” below.]

The success of the house in maintaining comfort in all seasons is shown by scatter-plots of daily indoor and outdoor maximum and minimum temperatures over a period of three years.

I. Features needing no attention

Heat transfer to and from the heat bank

The mass of concrete, bricks and rubble under the concrete floor slab is edge-insulated with foam to a depth of half a metre to prevent heat leaking sideways to and from the surrounding soil and subsoil. This 150 tonne edge-insulated under-floor mass is a “heat bank” which absorbs and yields heat so slowly that it holds the same temperature (at 750 mm depth) within a degree for weeks at a time.
Double-brick walls (17 tonnes) inside the house, and the floor slab itself (28 tonnes), are also parts of the heat bank. Their exposed surfaces (See photo.) absorb heat from sunshine (and yield heat to cool flows of air) so as to spread heat (or coolness) around the rooms. Within each day they conduct heat to and from the rooms of the house, and from room to room. They then conduct heat slowly to and from the under-floor mass.
In the absence of the house, the under-floor mass would have the same temperature as the subsoil of the area. A thermometer at 750 mm in the subsoil near the house shows a 14.6° yearly temperature range, from 12.9° to 27.5°. Even an ordinary light-weight, poorly-insulated house built on a concrete slab on the ground here would be made more comfortable by these stable subsoil temperatures. Midsummer and midwinter temperatures in such a house (next door) are plotted here and here.
It is clear that temperatures in that conventional house vary much less than outdoor temperatures, and remain close to that of the subsoil. The heat bank under my solar-passive house has an even more stable temperature than that of the surrounding subsoil. (There is a graph showing one year of heat bank and subsoil temperatures here.)


Thermal insulation reduces the flow of heat in and out of the house. With sufficient insulation, the heat of the day is replaced by the cool of night before the house becomes too warm. Insulation improves comfort permanently. Continue reading

Geoff’s solar-passive house at Manilla

View of solar-passive house

Geoff’s solar-passive house

A second high-mass solar-passive house was built in 2009 at Manilla, within 300 metres of mine.
My friend Geoff designed his house and used the same builder that I did. Sadly, after five comfortable years in his house, Geoff has passed away. Thanks to his daughter, I can show you the features of the house.
Thermometers, and power bills show that its performance is similar to mine. That is to say, it is very successful!

In Manilla’s climate of daily and seasonal temperature extremes, Geoff rarely needed to use his low-powered reverse-cycle air conditioner.

Plan of solar-passive house

Strafford Street solar-passive house: plan



Length, East-West:     18.28 m
Width, North-South:    9.45 m
Ceiling height:               2.70 m


Room area, Living/Kit/Bed 1/Study:      115.9 m^2
Room area, Bed 2:                                    13.8 m^2
Room area, Bed 3:                                    14.1 m^2
Room area, Bathroom:                              8.6 m^2
Room area, Laundry/Darkroom:               7.7 m^2
Area of walls:                                             12.7 m^2
Total House Area (without patio):       172.8 m^2

Exterior walls

North wall: double brick
East, west, and south walls: 90 mm stud, including 9.61 m reverse brick veneer
Cladding of stud walls: custom orb (horizontal)
Cladding of gable ends: plain roofing panels with 50 mm foam

Interior walls

Single brick:    17.16 m
Stud wall:        11.66 m

Windows (and two glass doors)

All double-glazed 3/6/3 in uPVC frames
(North-facing window area is 16% of the floor area of the house.)
North-facing:           27.00 m^2 (76%)
East-facing:               3.84 m^2 (11%)
South-facing:            4.50 m^2 (13%)
West-facing:             0.00 m^2 (0%)
Total:                      35.34 m^2 (100%) Continue reading