Thermal Comfort

BUILDINGS & THERMAL COMFORT

What are the qualities that
assure we are comfortable
in our homes?

Designers & Builders of FUTURE FRIENDLY HOMES • Certified Passive House Consultants


The ability to provide
thermal comfort is one of
the most important
functions of a building

not too hot, not too cold…



…which we might think of as our third “skin”.


Optimal thermal comfort requires the heat loss of the
human body to be in BALANCE with its heat production.
This is similar to the relationship between an activity
(exercising, skiing...) and clothes - our second skin.

Heat
Production

Heat Loss



The conditions that maintain this
thermal balance in a building are:

o  air temperature
o  the temperature of the surrounding
surfaces ( the ”mean radiant temperature")
o  air speed and turbulence
o  humidity of the air



When we adjust a thermostat we are setting a
goal for a comfortable air temperature



How that temperature actually feels depends
on drafts and air currents in the room



and the temperatures* of the wall, window,
ceiling, and floor surfaces in the room

* this condition is called the
“mean radiant temperature”



and the level of humidity at that temperature


This chart illustrates the summer and winter comfort zones
relative to temperature and humidity

In cold weather we are more comfortable “wetter”
In hot weather we prefer it “drier”


To feel good, a range of combinations create a comfort field in which:

•  the air is not too humid
•  air speeds remain within established limits
•  the difference between radiant and
air temperature remains small
•  the difference of the radiant temperature in different directions
(between your body and adjacent surfaces) remains small
•  room air temperature between head and feet is small
•  the perceived temperature varies less than 1.5°F within the
living area
•  the air is clean


Maintaining this comfort field is the domain
of these two important building systems:

o  BUILDING ENVELOPE
which includes the walls, floors, and roof or ceilings
that enclose the building, and any penetrations of
that enclosure for doors, windows, chimneys, vents,
etc. plus the accumulated air leakage created by
gaps in the structure

o  MECHANICAL SYSTEMS
that provide supplemental heating, sometimes
cooling, and any controlled ventilation.


Shortcomings in the building envelope often require us to
tolerate conditions outside the comfort field.

Buildings that are leaky, drafty, and
minimally insulated, with average
windows, variation in temperature
between ceiling and floor, and cold
surrounding surfaces are likely to be
experienced as uncomfortable

… this is typical of MOST buildings!


We seek control over these conditions thru the use
of mechanical systems like boilers and furnaces.

… that stuff in the basement that keeps us warm


… with the turn of a dial

though fuel costs may prompt other strategies


To overcome our discomfort
we may rely (at a cost) on
additional fans, heaters,
humidifiers, etc. to establish
a local comfort zone

… or just wear more clothes


By making integrated improvements to the building envelope and
mechanical systems we can provide a more dependable comfort field.

This is an illustration
of Passive House
strategies


These are the strategies and effects that we rely on
to create the conditions that assure thermal comfort
STRATEGIES EFFECT
Maximize insulation levels Retard the transfer of heat (including
losses to ground)
Eliminate thermal bridges Retard the transfer of heat (thru solid
materials)
Dramatically reduce air leaks Retard the transfer of heat and
moisture (thru air leakage)
Install Net Gain Windows Gain more energy than is lost thru glass
Orient the building to capture solar Maximize ability to gain energy without
energy and shade to prevent the risk of overheating
overheating
Use natural ventilation to cool Reduce the need for mechanical cooling
Use heat recovery ventilation Assure a constant and controlled rate
of fresh air while recovering energy



NET GAIN WINDOWS
These improvements allow us to acquire greater control
over each of the factors that determine comfort.

The effect, while scientifically quantifiable,
is ultimately valued for its quality:

We can be considerably and consistently
more comfortable in our homes.



MAKE
SENSE


Thermal Comfort

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