thermal comfort

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

BUILDINGS & THERMAL COMFORT

What are the qualities that assure we are comfortable

in our homes?

not too hot, not too cold…

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

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

Heat Production

Heat Loss

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.

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

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 energy and shade to prevent overheating

Maximize ability to gain energy without the risk of 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

These are the strategies and effects that we rely on to create the conditions that assure thermal comfort

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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