Of course, a “comfortable temperature” is subjective. A worker in a warehouse might find the temperature too hot for the strenuous job he or she may have, while another worker in an office may find it too cold. There are, however, steps you can take to ensure that your building’s temperature is the most comfortable for everyone.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) defines thermal comfort as “the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation.” But as anyone who’s been in a busy warehouse or an auditorium can attest, humans are heat engines. As the number of people increases, so too does the heat.
ASHRAE Standard 55 “specifies conditions for acceptable thermal environments and is intended for use in design, operation, and commissioning of buildings and other occupied spaces.” Given the fact that thermal comfort relies not only on technical factors but subjective ones as well, it’s a challenging task. But with the right tools, you can ensure everyone in the building is as close to comfortable as possible.
Figuring out what a “comfortable” temperature is for everyone inside your building depends upon several factors. Air circulation, the mean radiant temperature, clothes workers wear, and other factors contribute to it, and while it's not a complete solution, it does aid in minimizing discomfort.
According to some studies, the ideal temperature for human comfort and productivity is somewhere between 68°F to 77°F (20°C to 25°C). If the temperature in a building exceeds that range, productivity and comfort are negatively affected. Therefore, maintaining a comfortable temperature will produce better productivity and have significant financial impacts.
There are six main elements of thermal comfort:
Mean radiant temperature:
The mean radiant temperature is more than how much warming or cooling you get from the air, it’s also how much warming or cooling you get from the exchange of radiant heat from all the objects in a given space, like metal tables, warm walls, or floors heated by a sunny window, and even heat from computer banks.
Indoor air temperature:
Indoor air temperature and mean radiant temperature are different things. Indoor air temperature is, simply put, the temperature of the air in a room. It’s how much the air in a room warms or cools your body.
If you’re wearing a heavy coat in a warm building, you’ll feel hotter. If you’re wearing shorts and a t-shirt in a cold building, you’ll feel colder. Each person experiences temperature differently, so finding the temperature that everyone likes can be challenging. Ideally, workers will dress in a way that makes them able to control their own temperature by putting on layers or taking some off, but still, creating a space that makes that as easy as possible is necessary.
A person’s metabolic rate:
Everyone has a different metabolism. It’s a complex chemical process that your body uses to function normally, and includes breaking down food for energy, building and repairing your body, and regulating temperature. When you exercise, your body produces more heat; but yours might produce more or less than someone else’s. But your internal body heat and your metabolism play a major role in the perception of thermal comfort.
Humidity is the amount of moisture in the air. It affects the perceived temperature. Since we sweat to cool down, a dry heat feels cooler than a humid heat. Our sweat evaporates more quickly off the skin in dry air, cooling our bodies down in the process. It is generally agreed that a humidity level between 30% and 55% is recommended for a comfortable temperature. Humidity affects more than temperature. It can create health issues. When the humidity is too low, particles that can include allergens and viruses tend to float in the air longer. High humidity, on the other hand, promotes the growth of bacteria and mold. Neither extreme is good for people.
Anyone who has ever owned a fan or stood in a steady breeze can attest to the fact that air speed has a lot to do with how warm or cold you feel. The movement of air across your skin can help cool you down on a hot day by pulling your body heat away from you faster. However, it can also make a room feel drafty and cold when air speeds are too high, or the weather is cooler. Maintaining proper air movement in a building is critical and ASHRAE recommends an average air speed of 40 FPM or less for most spaces (unless the indoor temperature is high).
A handful of secondary factors also affect thermal comfort:
It becomes harder for our body to regulate its temperature as we age. Once an older person is cold, it can be harder to warm up and once they are warm, it can take longer to cool down.
Thermal adaptability is a pretty amazing quirk of the human body. Not just humans, in fact, but mammals in general. Depending on your genes, you may be more or less likely to deal well with heat or cold, but it’s largely out of your control.
When taken together, each of these factors can help you build a roadmap of sorts to a building with proper thermal comfort. So now that you have a firm grasp on the elements that contribute to thermal comfort, let’s look at five measures you can take to ensure that you’re providing thermal comfort in a building.
1. Ensure good air control
Establishing a comfortable and safe environment in your building starts with using dampers, louvers, and gravity ventilators. All direct air where it needs to go and are part of a typical HVAC system. Louvers and gravity ventilators maintain the passage of air into and out of your building, all without letting rain, snow, or other unwanted elements in. Dampers, including life safety dampers, ensure a safe and comfortable environment by directing airflow to different parts of the building as needed by current conditions.
Air movement products are crucial components in providing thermal comfort. Supply and exhaust fans move air into and out of buildings, minimizing contaminants and controlling temperature to maintain a safe environment. Circulators, including high volume low speed (HVLS) fans, also assist with thermal comfort by providing a cooling breeze in the summer or addressing an issue known as stratification in the winter. Stratification is the formation of thermal layers when heat enters a space. Hot air rises and cool air sinks, creating layers of warmer air near the ceiling. An HVLS fan circulates and mixes the air, creating an even temperature throughout the space, something very effective in large areas, like warehouses. A high-quality HVLS fan can gently move enough air so that the temperature difference between the ceiling and floor is relatively small. Since thermostats are generally located nearer to the floor than the ceiling, this gentle air movement goes a long way toward providing thermal comfort.
Kitchens needs good ventilation. Without them, your cooking area can be smoky, hot, and generally uncomfortable, which is both unhealthy and bad for productivity. Kitchen hoods, hood fans, utility distribution systems, make-up air units, and fire suppression systems are all part of a proper kitchen ventilation system.
Units that heat, cool, and dehumidify air are extraordinarily important when it comes to thermal comfort and energy savings. Units that condition air can include make-up air units, air handlers, energy recovery devices, and dedicated outdoor air systems (DOAS).
You need to have easy control of the thermal comfort in your building, and to do so, you need high-quality controls that enable you to adjust the quality of the indoor air, the temperature, the humidity, the airflow, and the air pressure with the push of a button or the turn of a dial.
You can be reasonably certain the thermal comfort level will be just about perfect for most workers if you incorporate these measures. However, there are a few things in addition to mechanical equipment and environment that affect the indoor temperature.
First, and perhaps most importantly, is leakage. A perfectly designed HVAC system will be rendered ineffective if every door and window is open in a building. Air leakage will negatively impact the performance of your HVAC system. Air entering the building through leaky windows or under drafty doors will affect the desired temperature.
Another consideration is that workers will likely want to have some control over their own thermal comfort. Accessible thermostats or airflow controls can help, but since everyone has a different level of comfort, it’s not a perfect science. Having the correct equipment in place, however, goes a long way to getting as close to perfect as possible and creating a space where people are in control of the temperature of their surroundings, which will also encourage comfort and productivity.
Of course, maintaining a precise temperature in a large indoor area using a single thermostat, can be challenging. Someone operating a forklift near a fan may think the air speed is too high, someone loading crates directly beneath a conditioning unit may feel too cold, and someone in an office next to a window may be more affected by the temperature outdoors. In order to achieve a higher level of control over the temperatures in a building, the space can be split into a number of thermal zones according to job type. Thermostats should be at least 3.3 feet from a source of heat or cold to ensure that the reading is accurate.
The best equipment in the world won’t continue working as well as it should if it’s not properly maintained. To maintain a good thermal environment, proper maintenance is key. But remember, no matter what kind of building it is, all share the same basic ventilation needs. Whether it’s a warehouse, a restaurant, a school, a hospital, or an office, the people inside each require and expect fresh air, a comfortable temperature, and quiet equipment. It’s not always going to be the same equipment that’s needed but designing for maintaining thermal comfort and by using the proper equipment is more than a way to keep people comfortable — it’s also a way to increase performance and profitability.