- regulate internal body temperature despite extreme outside fluctuations of temperature and humidity, and
- how this model relates to energy efficient strategies to regulate heat and humidity in healthcare buildings.
Our bodies require a narrow internal temperature range for survival, making thermoregulation an essential capability. When challenged by environmental conditions outside of this range, voluntary choices and involuntary physiological responses controlled by the Autonomic Nervous System (ANS) maintain temperature homeostasis using the least amount of energy. Our bodies’ response to non-ideal external thermal conditions can be divided into two processes:
- cooling or losing heat
- warming through increased heat production or decreased heat loss
We transfer heat through four processes:
- Convection – heat transfer through air currents
- Conduction – allowing our bodies to be in direct contact with cool or warm surfaces
- Vaporization – the evaporation of moisture from the surface of our skin or through breathing
- Radiation – allowing sun rays to heat our skin
The ANS assists thermoregulation primarily through two mechanisms.
- The first is by using skin hairs to create a layer of air insulation. In the cold, small ANS-controlled arrector pili muscles attached to hair shafts contract, making hairs stand up, creating “goose bumps,” and slowing the movement of air across the skin and decreasing convective heat loss. In warm conditions, these muscles relax so hair follicles lie flat and air flows across the skin.
- The second important ANS response to maintain core body temperature is varying the diameter of blood vessels near the surface of the skin. In a hot environment, skin vessels dilate and redirect warm core blood into superficial vessels where cooling by convection and conduction occurs. Conversely, in cold environments, constriction of superficial vessels decreases blood flow to the skin so the core stays warm.
When the outside temperature is above the optimal core body temperature, sweating is the only physiological way to lose heat. An ANS process triggers perspiration: glands under the skin secrete water with dissolved ions onto the surface of the skin. When this sweat dries, heat is lost through evaporative cooling. Sometimes we choose to make behavioral adaptations on hot days, for example moving to the shade during the day or avoiding physical exertion until after the sun goes down.
We can also increase heat production when exposed to a cold environment. Most body heat is generated by internal metabolism in organs, however, humans can also generate heat by voluntarily contracting skeletal muscles with movement, or involuntarily through shivering.
Another way to maintain the core body temperature by decreasing convective heat loss is to decrease the body surface area relative to overall body volume. This occurs when we huddle up or wrap our arms around our torso on a cold day. This adaptation also can be seen in body shapes of populations living in extreme climates. Cold climate populations tend to be more insulated, storing fat as energy for metabolism; whereas, warm climate populations may have elongated limbs to facilitate heat dissipation.
Let Human Physiology Guide Hospital Thermoregulation
A critical difference between our bodies and buildings is that we voluntarily and involuntarily seek comfort. The physiological interpretation of comfort is the achievement of thermal equilibrium within the desired body temperature with the minimum amount of bodily regulation and energy expenditure. When comfortable, heat production equals heat loss with minimal action necessary, i.e. when we are comfortable, our bodies operate at maximum efficiency. If a building has to work excessively hard to maintain thermal equilibrium, it is usually expressed in the energy bill, or perhaps by the person who pays this bill!
Hospital thermoregulation can be controlled by similar mechanisms to maintain comfort. An intelligent hospital infrastructure with building automation can detect and alert the appropriate hospital staff of any energy/heating/cooling inefficiencies in order to maintain thermoregulation, while also reducing energy consumption, associated emissions, and hefty energy bills. The tremendous advantage of this approach lies in its ability to conserve energy use with great precision. For example, when building environment monitors are put in areas where temperature and humidity are critical, hospital staff can ensure safe and comfortable conditions and address issues before a cascade of problems occur, which could result in further energy waste or even patient harm.
The chart below shares some of the strategies used by humans, traditional buildings, and intelligent buildings to maintain thermoregulation.
Does your facility use other strategies for optimizing hospital building comfort, thereby decreasing energy use and creating a safe and inhabitable environment for patients and staff? Share your best practices in the comment section below.