Temperature is one of the key determinants in how we experience indoor climate

But what is temperature?

It is the quantification of the degree or intensity of hotness or coldness in a person, object or space. Simply put, it is the measure of the intensity using a thermometer calibrated with a scale, such as Celsius, Fahrenheit, etc. It is not heat.

Air molecules move faster and possess more energy when the temperature is higher. The energy passes from high energy molecules to low energy molecules when the molecules collide with each other. When we cool a room, we remove heat.

Scales of measurement

We use different scales to measure and communicate temperature. Science usually employs the Kelvin scale, an absolute temperature scale with a theoretical absolute zero, 0° K. At this point, atomic and molecular movement and vibration cease. All particles are at their lowest level of energy at 0° K.

Otherwise, depending on where you live, you use either Celsius, also called centigrade, or Fahrenheit.

About temperature

For most people, room temperature is the thermometer reading in the room. But for most scientific and industrial applications, controlled specific temperatures are common. Sometimes, though, people do describe temperatures in relation to humidity.

• Dry-bulb temperature (DBT), measured using a standard thermometer, is the type of temperature we usually talk about.

• Wet-bulb temperature (WBT) is the ambient temperature measured when the bulb of a thermometer is wrapped in a wet cloth. As the water in the cloth evaporates, heat dissipates from the thermometer, lowering temperature. WBT is relative to the DBT and humidity. The wet-bulb temperature is the lowest possible temperature achievable under current ambient conditions by the evaporation of water only. If you apply this to the evaporation of your sweat, you can begin to see the significance of this.

• Operative temperature on the other hand, quantifies the level of environmental thermal comfort, incorporating the exchange of convective and radiative heat between the occupant and indoor space.

   

Understanding the building science

Interior building heat has several sources, including people’s bodies, electrical appliances, such as lighting, computers, refrigerators and freezers. Solar gain is another source, warming building interiors via windows, exterior walls, roofs, etc.

If it is warmer outdoors than indoors, heat will tend to move toward the interior of the building through the envelope. Likewise, if it is warmer inside the building, heat will attempt to move outwards through the building envelope. This is thermal conduction and it involves the spontaneous movement of heat from a hotter to a colder body.

Besides conduction, infiltration is another means of heat movement. Often called air leakage, it is the unintentional or accidental passage, of outdoor air into a building.

Another is exfiltration, which describes the intentional or unintentional movement of indoor air through the envelope to the outdoors.

A mechanical ventilation system is capable of moving large volumes of air throughout the building, providing or extracting heat and coolness, meeting specific seasonal or personal requirements.

Good thermal indoor climate is subjective

If we’re going to use the opinions of a building’s occupants as the basis for determining what is an optimal thermal indoor climate, we have to remember such input is highly subjective. Rightfully so. But we’ll need to identify the types of activities performed, clothing worn, metabolism and much more.

Anyone who has been in a sauna, has noticed how dousing the heater with water has added significant humidity to the air, changing how they perceive the temperature. And those who have braved a winter storm with howling winds know the windchill factor accurately describes how we feel temperature, not the thermometer alone.

We all know how sitting near a window with a cold window pane or cold adjacent surfaces or being near an infrared or masonry heater can affect us. These are examples of radiating surfaces.

Further complicating matters is the fact that we are sensitive to differences in temperature between the different members of our bodies, for example, cold feet, etc.

Do indoor thermal comfort guidelines exist?

According to ISO 7730, requirements may be formulated and put into effect that apply to indoor thermal climate. Depending on local/individual requirements and which activity levels and clothing factors are integrated into the requirements, this usually results in requirements for operative temperatures within 20-24° C in winter and 23-26° C in summer.